Biopharmconsortium Blog

Expert commentary from Haberman Associates biotechnology and pharmaceutical consulting.

Posts filed under: Animal Models

Chemokine receptor inhibitors for prevention of cancer metastasis

CXCR-1 N-terminal peptide bound to IL-8

CXCR-1 N-terminal peptide bound to IL-8

In our October 31, 2013 blog article, we discussed recent structural studies of the chemokine receptors CCR5 and CXCR4. We discussed the implications of these studies for the treatment of HIV/AIDS, especially using the CCR5 inhibitor maraviroc (Pfizer’s Selzentry/Celsentri). As discussed in the article, researchers are utilizing the structural studies of CCR5 and CXCR4 to develop improved HIV entry inhibitors that target these chemokine receptors.

Meanwhile, other researchers have been studying the role of chemokine receptors in cancer biology, and the potential use of chemokine receptor antagonists in cancer treatment.

CCR5 antagonists as potential treatments for metastatic breast cancer

One group of researchers, led by Richard G. Pestell, M.D., Ph.D. (Thomas Jefferson University, Philadelphia, PA) has been studying expression of CCR5 and its ligand CCL5 (also known as RANTES) and their role in breast cancer biology and pathogenesis. Their report of this study was published in the August 1, 2012 issue of Cancer Research.

These researchers first studied the combined expression of CCL5 and CCR5 in various subtypes of breast cancer, by analyzing a microarray database of over 2,000 human breast cancer samples. (The database was compiled from 27 independent studies). They found that CCL5/CCR5 expression was preferentially expressed in the basal and HER-2 positive subpopulations of human breast cancer.

Because of the high level of unmet medical need in treatment of basal breast cancer, the authors chose to focus their study on this breast cancer subtype. As the researchers point out, patients with basal breast cancer have increased risk of metastasis and low survival rates. Basal tumors in most cases do not express either androgen receptors, estrogen receptors (ERs), or HER-2. They thus cannot be treated with such standard receptor-targeting breast cancer therapeutics as tamoxifen, aromatase inhibitors, or trastuzumab. The only treatment options are cytotoxic chemotherapy, radiation, and/or surgery. However, these treatments typically results in early relapse and metastasis.

The basal breast cancer subpopulation shows a high degree of overlap with triple-negative (TN) breast cancer. We discussed TN breast cancer, and research aimed at defining subtypes and driver signaling pathways, in our August 2, 2011 article on this blog. In that article, we noted that TN breast cancers include two basal-like subtypes, at least according to one study. Other researchers found that 71% of TN breast cancers are of basal-like subtype, and that 77% of basal-like tumors are TN. A good part of the problem is that there is no accepted definition of basal-like breast cancers, and how best to define such tumors is controversial. However, both the TN and the basal subpopulations are very difficult to treat and have poor prognoses. It is thus crucial to find novel treatment strategies for these subpopulations of breast cancer.

Dr. Pestell and his colleagues therefore investigated the role of CCL5/CCR5 signaling in three human basal breast cancer cell lines that express CCR5. They found that CCL5 promoted intracellular calcium (Ca2+) signaling in these cells. The researchers then determined the effects of CCL5/CCR5 signaling in promoting in vitro cell invasion in a 3-dimensional invasion assay. For this assay, the researchers assessed the ability of cells to move from the bottom well of a Transwell chamber, across a membrane and through a collagen plug, in response to CCL5 as a chemoattractant. The researchers found that CCR5-positive cells, but not CCR5-negative cells, showed CCL5-dependent invasion.

The researchers then studied the ability of CCR5 inhibitors to block calcium signaling and in vitro invasion. The agents that they investigated were maraviroc and vicriviroc. Maraviroc (Pfizer’s Selzentry/Celsentri) is the marketed HIV-1 entry inhibitor that we discussed in our October 31, 2013 articleVicriviroc is an experimental HIV-1 inhibitor originally developed by Schering-Plough. Schering-Plough was acquired by Merck in 2009. Merck discontinued development of vicriviroc because the drug failed to meet primary efficacy endpoints in late stage trials.

Pestell et al. found that maraviroc and vicriviroc inhibited calcium responses by 65% and 90%, respectively in one of their CCR5-positive basal cell breast cancer lines, and gave similar results in another cell line. The researchers then found that  in two different CCR5-positive basal breast cancer cell lines, both maraviroc and vicriviroc inhibited in vitro invasion.

The researchers then studied the effect of maraviroc in blocking in vivo metastasis of a CCR5-positive basal cell breast cancer line, which had been genetically labeled with a fluorescent marker to facilitate noninvasive visualization by in vivo bioluminescence imaging (BLI). They used a standard in vivo lung metastasis assay, in which cells were injected into the tail veins of immunodeficient mice, and mice were treated by oral administration with either maraviroc or vehicle. The researchers then looked for lung metastases. They found that maraviroc-treated mice showed a significant reduction in both the number and the size of lung metastases, as compared to vehicle-treated mice.

In both in vitro and in vivo studies, the researchers showed that maraviroc did not affect cell viability or proliferation. In mice with established lung metastases, maraviroc did not affect tumor growth. Maraviroc inhibits only metastasis and homing of CCR5-positive basal cell breast cancer cells, but not their viability or proliferation.

As the result of their study, the researchers propose that CCR5 antagonists such as maraviroc and vicriviroc may be useful as adjuvant antimetastatic therapies for breast basal tumors with CCR5 overexpression.  They may also be useful as adjuvant antimetastatic treatments for other tumor types where CCR5 promotes metastasis, such as prostate and gastric cancer.

As usual, it must be emphasized that although this study is promising, it is only a preclinical proof-of-principle study in mice, which must be confirmed by human clinical trials.

In an October 25, 2013 Reuters news story, it was revealed that Citi analysts believe that Merck will take vicriviroc into the clinic  in cancer patients in 2014. Citi said that it expected vicriviroc to be tested in combination with “a Merck cancer immunotherapy” across multiple cancer types, including melanoma, colorectal, breast, prostate and liver cancer. (We discussed Merck’s promising cancer immunotherapy agent lambrolizumab/MK-3475 in our June 25, 2013 blog article. But the Merck agent to be tested together with vicriviroc was not disclosed in the Reuters news story.)

Despite this news story, Merck said that it had not disclosed any plans for clinical trials of vicriviroc in cancer.

The CXCR1 antagonist reparixin as a potential treatment for breast cancer

In our In April 2012 book-length report, “Advances in the Discovery of Protein-Protein Interaction Modulators” (published by Informa’s Scrip Insights), we discussed the case of the allosteric chemokine receptor antagonist reparixin (formerly known as repertaxin). Reparixin has been under developed by Dompé Farmaceutici (Milan, Italy). This agent targets both CXCR1 and CXCR2, which are receptors for interleukin-8 (IL-8). IL-8 is a well-known proinflammatory chemokine that is a major mediator of inflammation. As we discussed in our report, reparixin had been in Phase 2 development for the prevention of primary graft dysfunction after lung and kidney transplantation. However, it failed in clinical trials.

Meanwhile, researchers at the University of Michigan (led by Max S. Wicha, M.D., the Director of the University of Michigan Comprehensive Cancer Center) and at the Institut National de la Santé et de la Recherche Médicale (INSERM) in France were working to define a breast cancer stem cell signature using gene expression profiling. They found that CXCR1 was among the genes almost exclusively expressed in breast cancer stem cells, as compared with its expression in the bulk tumor.

IL-8 promoted invasion by the cancer stem cells, as demonstrated in an in vitro invasion assay. The CXCR1-positive, IL-8 sensitive cancer stem cell population was also found to give rise to many more metastases in mice than non-stem cell breast tumor cells isolate from the same cell line. This suggested the hypothesis that a CXCR1 inhibitor such as reparixin might be used as an anti-stem cell, antimetastatic agent in the treatment of breast cancer.

Dr. Wicha and his colleagues then studied the effects of blockade of CXCR1 by either reparixin or a CXCR1-specific blocking antibody on  bulk tumor and cancer stem cells in two breast cancer cell lines. The researchers found in in vitro studies that treatment with either of these two CXCR1 antagonists selectively depleted the cell lines of cancer stem cells (which represented 2% of the tumor cell population in both cell lines).

This depletion was followed by the induction of massive apoptosis of the bulk, non-stem tumor cells. This was mediated via a bystander effect, in which CXCR1-inhibited stem cells produce the soluble death mediator FASL (FAS ligand). FASL binds to FAS receptors on the bulk tumor cells, and induces an apoptotic pathway in these cells that results in their death.

In in vivo breast cancer xenograft models, the researchers treated tumor-bearing mice with either the cytotoxic agent docetaxel, reparixin, or a combination of both agents. Docetaxel treatment–with or without reparixin–resulted in a significant inhibition of tumor growth, while reparixin alone gave only a modest reduction in tumor growth. However, treatment with docetaxel alone gave no reduction (or an increase) in the percentage of stem cells in the tumors, while reparixin–either alone or in combination with docetaxel–gave a 75% reduction in the percentage of cancer stem cells. Moreover, in in vivo metastasis studies in mice, reparixin treatment gave a major reduction in systemic metastases. These results suggest that reparixin may be useful in eliminating breast cancer stem cells and in inhibiting metastasis and thus preventing recurrence of cancer in patients treated with chemotherapy.

As we discussed in our 2012 report, Dr. Wicha’s research on reperixin might represent an opportunity for Dompé to repurpose reperixin for cancer treatment. Since the publication of the 2012 report, Dompé has been carrying out a Phase 2 pilot study of reparixin in patients diagnosed with early, operable breast cancer, prior to their treatment via surgery. The goal of this study is to investigate if cancer stem cells decrease in two early breast cancer subgroups (estrogen receptor-positive and/or progesterone receptor positive/HER-2-negative, and estrogen receptor negative/progesterone receptor negative/HER-2-negative). The goal is to compare any differences between the two subgroups in order to better identify a target population.

Dompé has thus begun the process of clinical evaluation of reparixin for the new indication–treatment of breast cancer in order to inhibit metastasis and prevent recurrence.

Conclusions

Researchers have found promising evidence that at least two chemokine/chemokine receptor combinations may be involved in cancer stem cell biology and thus in the processes of metastasis and cancer recurrence. In at least one case–and perhaps both–companies are in the early stages of developing small-molecule chemokine receptor antagonists for inhibiting breast cancer metastasis and recurrence. Such a strategy might be applicable to other types of cancer as well.

As discussed by Wicha et al., in immune and inflammatory processes, chemokines serve to facilitate the homing and migration of immune cells. In the case of cancer, chemokines may act as “stemokines”, by facilitating the homing of cancer stem cells in the process of metastasis. Other chemokines and their receptors than those discussed in this article may be involved in other types of cancer, and may carry out similar “stemokine” functions.

Since around 90% of cancer deaths are due to metastasis, and since effective treatments for metastatic cancers are few, this is a potentially important area of cancer research and drug development.

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As the producers of this blog, and as consultants to the biotechnology and pharmaceutical industry, Haberman Associates would like to hear from you. If you are in a biotech or pharmaceutical company, and would like a 15-20-minute, no-obligation telephone discussion of issues raised by this or other blog articles, or of other issues that are important to  your company,  please contact us by phone or e-mail. We also welcome your comments on this or any other article on this blog.

Does inflammation in the brain cause aging?

Hypothalamic nuclei on one side of the hypothalamus, in 3-D. Source: Was a bee. http://bit.ly/13o91HU

Hypothalamic nuclei on one side of the hypothalamus, in 3-D. Source: Was a bee. http://bit.ly/13o91HU

The Biopharmconsortium Blog has been following novel developments in anti-aging medicine and biology for several years. Much of the interest in this field has centered around sirtuins and potential drugs that modulate these protein deacetylase enzymes. Recently–on May 29, 2013–we published our latest blog article on sirtuins.

However, we have long been aware that studies in the biology of aging reveal that lifespan is controlled by sets of complex, interacting pathways. Sirtuins represent only one control point in these pathways, which might not be the most important one.

Now comes a research article in the 9 May 2013 issue of Nature, on the role of inflammatory pathways in the hypothalamus of the brain in the control of systemic aging. This article (Zhang et al.) was authored by Dongsheng Cai, M.D., Ph.D. of the Albert Einstein College of Medicine (Bronx, NY) and his colleagues. The same issue of Nature contains a News and Views mini-review of Zhang et al., authored by Dana Gabuzda, M.D. and Bruce A. Yankner, M.D., Ph.D. (Harvard Medical School).

The role of the neuroendocrine system–and other tissues–in the regulation of lifespan

The News and Views review begins with the statement that classic studies of aging-related pathways in Caenorhabditis elegans by such pioneering researchers as Cynthia Kenyon and Leonard Guarente, as well as later studies in Drosophila suggested that genetic changes that affect the function of nutrient-sensing and environmental-stress-sensing neurons can regulate aging of the entire organism.

In our May 11, 2010 Biopharmconsortium Blog article that reviewed the aging field, we focused on biochemical pathways that may affect lifespan, not the specific tissues in which they act. That article included a link to a 25 March 2010 review in Nature by Dr. Kenyon, entitled “The genetics of ageing”. As we said in our article, that review “discussed the panoply of aging-related pathways in worms, flies, and mice, especially the insulin/insulin-like growth factor-1 (IGF-1) and TOR pathways, as well as several other biomolecules and biological processes”. However, Dr. Kenyon’s article, and several of the references she cites, also deal with the tissues in which these pathways act.

Numerous leading researchers have found evidence that IGF signaling in the C. elegans nervous system regulates longevity. A 2008 article by Laurent Kappeler (INSERM U893, Hopital Saint-Antoine, Paris, France) and his colleagues referenced in the Kenyon review also found evidence that IGF-1 receptors in the brain control lifespan and growth in mice via a neuroendocrine mechanism.

Nevertheless, there is evidence that the insulin pathway in such tissues as the intestine of C. elegans can also regulate lifespan in a non-cell autonomous manner. These studies indicate that changes in insulin pathway gene expression in one tissue–perhaps with certain tissues (the neuroendocrine system, endoderm, adipose tissue) being especially important–results in coordinated changes in insulin pathway activity among all the relevant tissues of the organism. These studies complicate the determination that the neuroendocrine system is the locus of longevity regulation by the insulin pathway and other aging-related pathways.

The potential role of the hypothalamus in the regulation of mammalian aging

Based on the results of studies of neural regulation of lifespan in C. elegans and Drosophila, Zhang et al. asked whether the hypothalamus may have a fundamental role in the process of aging and in regulation of lifespan. The hypothalamus is a region of the brain that is critically involved in regulating such functions as growth, reproduction and metabolism. An important function of the hypothalamus is to link the nervous system to the endocrine system via the pituitary gland, an endocrine gland that is intimately associated with the hypothalamus, and is the master regulator of the endocrine system. According to the Gabuzda and Yankner News and Views article, the mammalian hypothalamus has similar functions to the nutrient-sensing and environmental-stress-sensing neurons of C. elegans and Drosophila that have been implicated in regulation of aging in those organisms.

Zhang et al. studied the increase in NF-κB (nuclear factor kappa-light-chain-enhancer of activated B cells) in the hypothalamus of mice as a function of aging. NF-κB is a transcriptional regulator that is involved in cellular responses to stress, and in particular mediates inflammatory responses; it has also been implicated as a driver of aging-related gene expression in mice. The researchers found that the numbers of microglia (central nervous system cells that functionally resemble macrophages) in the hypothalamus increased as the mice aged. These microglia exhibited inflammatory function, expressing activated NF-κB and overproducing tumor necrosis factor alpha (TNFα). In turn, secretion of TNF-α (an inflammatory cell-signaling molecule) stimulated NF-κB-mediated signaling in hypothalamic neurons.

Zhang et al. showed–via using genetic models such as specific gene knockouts–that activation of the NF-κB pathway in hypothalamic neurons accelerated the aging process and shortened lifespan. Conversely, inhibiting the NF-κB pathway resulting in delayed aging and increased lifespan. They further showed that activation of neural NF-κB signaling resulted in declines in gonadotropin-releasing hormone (GnRH) levels. Since GnRH stimulates adult neurogenesis in the hypothalamus and hippocampus, decline in GnRH secretion suppressed neurogenesis. Conversely, hypothalamic administration of GnRH reversed aging-associated declines in neurogenesis.

The researchers also treated old mice with GnRH peripherally (i.e., via subcutaneous injection, rather than via hypothalamic administration). Such treatment with GnRH resulted in amelioration of aging-related changes in muscle, skin, and the brain. Notably, GnRH treatment resulted in amelioration of  aging-related cognitive decline. The researchers hypothesize that peripherally-administered GnRH (a neurohormone that is secreted by specific neurons in the hypothalamus) exerts its anti-aging effects via its action on one or more of the GnRH-responsive brain regions that lack a blood–brain barrier, such as the median eminence, subfornical organ and area postrema.

As pointed out by Gabuzda and Yankner in their News and Views article, a 2011 study showed that dendrites of hypothalamic GnRH-producing neurons extend through the blood–brain barrier. These dendrites are able to sense inflammatory and metabolic signals in the blood. Gabuzda and Yankner hypothesize that inflammatory signals in the periphery (which are known to be associated with aging, and such aging-related conditions as insulin resistance, obesity, and cardiovascular disease) may feed back via these dendrites to downregulate GnRH production in the hypothalamus. Such a feedback loop might be analogous to the coordination between peripheral and neural tissues of aging-related pathways seen in C. elegans by Dr. Kenyon and other researchers.

Despite these hypotheses (as pointed out by Zhang et al.), the mechanisms by which GnRH (especially peripherally-administered GnRH) exerts its anti-aging effects are not well-understood, and need further investigation. The researchers conclude, however, that the hypothalamus can integrate NF-κB-directed immunity and the GnRH-driven neuroendocrine system to program development of aging.

With respect to anti-aging therapy, the study of Zhang et al. suggests two potential therapeutic strategies–inhibition of inflammatory microglia in the hypothalamus, and restoration of levels of GnRH. Given the difficulties of specific targeting of microglia in the hypothalamus (across the blood-brain barrier), the second of these alternatives seems to be the more feasible of these strategies.

The GnRH receptor agonist leuprolide as a potential therapy for Alzheimer’s disease

GnRH has a short half-life in the human body, and thus cannot be used as a medication unless it is delivered via infusion pumps. However, the GnRH receptor agonist leuprolide acetate (AbbVie’s Lupron, Sanofi’s Eligard) has been approved by the FDA since 1985. It is available as a slow-release implant (AbbVie’s Lupron Depot) or a formulation delivered via subcutaneous/intramuscular injection. Leuprolide is approved for treatment of prostate cancer, endometriosis, fibroids, and several other conditions. Although leuprolide is the largest-selling GnRH agonist, there are other approved nanopeptide GnRH agonists, such as goserelin (AstraZeneca’s Zoladex) and histrelin (Endo’s Supprelin and Vantas).

As discussed in a 2007 review by Wilson et al., leuprolide acetate has also been under investigation as a therapeutic for Alzheimer’s disease (AD). Studies in mice indicated that leuprolide modulated such markers of AD as amyloid-β (Aβ) and tau phosphorylation, and prevented AD-related cognitive decline. For example, in a 2006 study in a classic mouse model of AD (Tg2576 amyloid precursor protein transgenic mice carrying the Swedish mutation) by Casadesus et al., the researchers demonstrated that leuprolide acetate halted Aβ deposition and improved cognitive performance.

Although Casadesus et al. attributed the efficacy of leuprolide to its suppression of the production of luteinizing hormone, Wilson et al. speculated that it might be possible that leuprolide works directly via GnRH receptors in the brain. Those receptors had only been identified in 2006 by the first author of the review, Andrea Wilson, and her colleagues at the University of Wisconsin. The direct action of leuprolide on GnRH receptors in the brain to ameliorate aging-related cognitive decline–and perhaps AD itself–is consistent with the 2013 findings of Zhang et al.

Development of a leuprolide-based Alzheimer’s disease treatment by Voyager Pharmaceuticals

As discussed in the review of Wilson et al., a Phase 2 clinical trial in women with mild-to-moderate AD receiving acetylcholinesterase inhibitors and implanted subcutaneously with leuprolide acetate showed a stabilization in cognitive decline at 48 weeks. A subsequent study in men (clinical trial number NCT00076440) was documented on ClinicalTrials.gov between 2004 and 2007. However, no results of this trial were ever posted.

The clinical development of a formulation of leuprolide (known as Memryte) as a treatment for AD had been carried our by a small Durham, NC biotech company called Voyager Pharmaceutical Corporation. Memryte was a biodegradable implant filled with leuprolide acetate, designed to treat mild to moderate AD.

After struggling to develop their treatment for nearly a decade, Voyager ran out of money, and stopped its R&D operations in 2007. In 2009, Voyager acquired a new set of investors, and changed its name to Curaxis. In 2010, Curaxis did a reverse stock merger, which enabled it to become a publicly traded company. Also in 2010, Curaxis attracted $25 million from a Connecticut investment firm. Nevertheless, Curaxis noted in its SEC filing that it would need “at least $48 million through 2014” to complete development of Memryte and file a New Drug Application (NDA) with the FDA.

However, Curaxis failed to find the needed funding and/or a partner to complete its development plans. In July 2012, the company filed for bankruptcy.

The failure of Voyager/Curaxis as a company does not necessarily mean that leuprolide may not be a viable treatment for AD. However, as we noted in earlier Biopharmconsortium Blog articles, development of an AD therapy is an enormously long, expensive, and risky proposition, which is beyond the capacity of a small biotech (such as Voyager/Curaxis) unless it attracts a Big Pharma partner. Moreover, treating AD once it reaches the “mild to moderate” stage is unlikely to work.

As we discussed in our April 5, 2013 article, the FDA has been working with industry and academia to develop guidelines for clinical trials of agents to treat the very earliest stages of AD, before the development of extensive irreversible brain damage. If another company endeavors to develop a formulation of leuprolide (or another GnRH pathway activator) for AD, it would probably do best to aim to treat very early-stage disease using the new proposed FDA guidelines.

Conclusions

Why should drug discovery and development researchers and executives be interested in anti-aging research? No pharmaceutical company will be able to run a clinical trial with longevity as an endpoint. However, the hope is that an “anti-aging” drug approved for treatment of one disease of aging will have pleiotropic effects on multiple diseases of aging, and will ultimately be found to increase lifespan or “healthspan” (the length of a person’s life in which he/she is generally healthy and not debilitated by chronic diseases). Numerous pharmaceutical and biotechnology companies have been working on discovery and development of treatments for major aging-related diseases, such as type 2 diabetes and AD. It would be truly spectacular if a new drug for (for example) type 2 diabetes would also be effective against AD.

Moreover, their are also major aging-related conditions, such as sarcopenia (aging-related loss of muscle mass, quality, and strength) that are not normally targets for drug development, but are major causes of disability and death. It would also be amazing if an anti-aging drug aimed at (for example) AD would be effective against sarcopenia as well. Note that Zhang et al. showed that GnRH treatment ameliorated aging-related changes in muscle in their mouse models. (Update: The statement that sarcopenia is “not normally a target for drug development” is no longer true. See our September 4, 2013 article on this blog, “Novartis’ Breakthrough Therapy For A Rare Muscle-Wasting Disease”.)

The study of Zhang et al. constitutes a new approach to anti-aging biology and target and drug discovery. However, aging biology is complex and not well-understood. Researchers will need to study many aspects of aging-related pathways for anyone to be able to discover and develop successful anti-aging drugs. This includes, of course, the sirtuin field, as well as the role of mitochondria in aging related metabolic imbalance, as exemplified by a recent paper in Cell.  As discussed in our other Biopharmconsortium Blog articles on anti-aging biology and medicine, there are many other avenues for investigation as well.

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As the producers of this blog, and as consultants to the biotechnology and pharmaceutical industry, Haberman Associates would like to hear from you. If you are in a biotech or pharmaceutical company, and would like a 15-20-minute, no-obligation telephone discussion of issues raised by this or other blog articles, or of other issues that are important to  your company,  please contact us by phone or e-mail. We also welcome your comments on this or any other article on this blog.

Agios Pharmaceuticals files for an IPO

Agios Nikolaos Orfanos, Thessaloniki, Greece

Agios Nikolaos Orfanos, Thessaloniki, Greece

On June 11, 2013, Agios Pharmaceuticals (Cambridge, MA) filed with the U.S. Securities and Exchange Commission for an Initial Public Offering (IPO). The company plans to raise up to $86 million through this IPO. This news was reported by Fierce Biotech, the Boston Business Journal, and Xconomy, among others.

The Biopharmconsortium Blog has been following Agios since December 31, 2009, and we have posted three additional articles since. Our newest article, posted on December 28, 2012, announced the publication of an article  in the November 19, 2012 issue of Chemical & Engineering News (C&EN) by senior editor Lisa M Jarvis, in which I was quoted. More recently, Agios posted a reprint of that article on its website, which it retitled “Built to Last”. I had used that phrase in my quote in Ms. Jarvis’ article.

Agios specializes in the field of cancer metabolism. The company is working on multiple potential targets, with the goal of dominating that field, using its strong proprietary technology platform. Its financing strategy is aimed at building a company with the potential to endure as an independent firm over a long period of time–hence “built to last”. This contrasts with the recent trend toward “virtual biotech companies”–lean companies with only a very few employees that outsource most of their functions, and that are designed for early acquisition by a Big Pharma or large biotech company. Agios’ ambition to dominate the field of cancer metabolism requires a “built to last” strategy.

As Agios’ CEO David Schenkein said in the C&EN article, “You’re never going to get that with a one-target deal”. In support of that strategy, Agios has raised over a quarter of a billion dollars in funding. This has included two rounds of venture capital funding that raised a total of $111 million, and a partnership with Celgene that brought in a total of $141 million in upfront payments. According to the Fierce Biotech article, Celgene has committed to invest in Agios’ IPO.

As of yet, Agios has no drugs in clinical trials. However, the company has several drug candidates in early development. And according to the Fierce Biotech article, Agios intends to use the proceeds of the IPO to fund its first clinical trials. One of the company’s lead candidates, AG-221, which targets mutant isocitrate dehydrogenase 2 (IDH2), may reach the clinic soon, according to the Fierce Biotech article. Another Agios compound, AG-120, which targets mutant IDH1, is expected to enter the clinic in early 2014.

Recent developments in Agios’ research

The Biopharmconsortium Blog has been reporting on Agios’ research on mutant forms of IDH1 and IDH2, and their roles in human cancer, beginning with our December 31, 2009 article. Briefly, wild-type IDH1 and IDH2 catalyze the NADP+-dependent oxidative decarboxylation of isocitrate to α-ketoglutarate. However, mutant forms of IDH1and IDH2, which are found in certain human cancers, no longer catalyze this reaction, but instead catalyzes the NADPH-dependent reduction of α-ketoglutarate to R(-)-2-hydroxyglutarate (2-HG). The researchers have hypothesized that 2HG is an oncometabolite, and that developing mutant-specific small molecule inhibitors of IDH1 and IDH2 might inhibit the growth or reverse the oncogenic phenotype of cancer cells that carry the mutant enzymes.

As we reported in our December 28, 2012 article, Agios researchers and their collaborators reported a series of compounds that selectively inhibit the mutant form of IDH1. These compounds were found to lower tumor 2-HG in a xenograft model. More recently, on May 3, 2013, Agios researchers and their collaborators published two research reports in the journal Science, and the company also announced the results of these studies in a April 4, 2013 press release. According to that press release, the two reports are the first publications to show the effects of inhibiting mutant IDH1 and IDH2 in patient-derived tumor samples. These results constitute preclinical support for the hypothesis that the two mutant enzymes are driving disease, and that drugs that target the mutant forms of the enzymes can reverse their oncogenic effects.

In the first of these papers (Wang et al.), the researchers reported the development of the small-molecule compound AGI-6780 (a tool compound, not a clinical candidate), which potently and selectively inhibits the tumor-associated mutant IDH2/R140Q. AGI-6780 is an allosteric inhibitor of this mutant enzyme. Treatment with AGI-6780 induced differentiation of two IDH2-bearing tumors in vitro: a TF-1 erythroleukemia genetically engineered to express IDH2, and primary human acute myelogenous leukemia (AML) carrying the IDH2 mutation. These data provide proof-of-principle that inhibitors targeting mutant IDH2/R140Q could have potential applications as a differentiation therapy for AML and other IDH2-driven cancers.

In the second paper (Rohle et al.), Agios researchers and their collaborators focused on a selective mutant IDH1 (R132H-IDH1) inhibitor, AGI-5198 (also a tool compound), which is one of the mutant IDH1 inhibitors that we referred to in our December 28, 2012 article. The researchers studied the effects of AGI-5198 on human glioma cells with endogenous IDH1 mutations. AGI-5198 inhibited, in a dose-dependent manner, the ability of the mutant IDH1 to produce 2-HG. Under conditions of near-complete inhibition of 2-HG production, AGI-5198 induced demethylation of histone H3K9me3 in chromatin, and also induced expression of genes associated with differentiation to glial cells (specifically astrocytes and oligodendrocytes). Blockade with AGI-5198 also impaired the growth of IDH1-mutant—but not IDH1–wild-type—glioma cells. Oral administration of AGI-5198 to mice with established R132H-IDH1 glioma xenografts resulted in impaired growth of the tumors. Treatment of mice with AGI-5198 was well-tolerated, with no signs of toxicity during 3 weeks of daily treatment.

It is possible that Agios’ IDH1/2 inhibitors do not inhibit tumor growth by inducing differentiation, at least in the case of AGI-5198 in glioma. Rohle et al. noted that although high-dose (450 mg/kg) AGI-5198 induced demethylation of histone H3K9me3 and induced gliogenic differentiation markers, a lower dose of AGI-5198 (150 mg/kg) did not. Nevertheless, the lower dose of AGI-5198 resulted in a similar tumor growth inhibition as did the the higher dose. This suggests that in glioma cells, mutant IDH1 regulates cell proliferation and cell differentiation via distinct pathways. These pathways may have different sensitivities to levels of 2-HG, with the differentiation-related pathway requiring increased inhibition of levels of 2-HG than the proliferation-related program.

Is differentiation therapy with IDH1/2 inhibitors sufficient to provide efficacious treatment of AML and/or glioma?

A companion Perspective, authored by Jiyeon Kim and Ralph J. DeBerardinis (Children’s Medical Center Research Institute, University of Texas Southwestern Medical Center, Dallas, TX), was published in the same issue of Science as Wang et al and Rohle et al. Kim and DeBerardinis note that the selective mutant IDH1 and IDH2  inhibitors produced cytostatic rather than cytotoxic effects. Specifically, they induced cancer cell differentiation rather than cell death.

It is possible that inducing a permanent state of differentiation may be sufficient for therapeutic efficacy. However, the survival (in a differentiated, nontumor state) of viable cells still containing potentially oncogenic mutations may eventually give rise to cancer. Therefore, it is important to determine whether the therapeutic effects of these compounds will persist over long periods of time.

In discussing AGI-6780 as a differentiation therapy in hematopoietic malignancies, Wang et al. compared their results to the action of all-trans retinoic acid (ATRA) on acute promyelocytic leukemia (APL). ATRA has be used to treat APL, and it apparently works via relieving a block in differentiation present in these leukemic cells. The use of ATRA in APL has thus been taken as a paradigm of differentiation therapy, and it is used as such a paradigm by Wang et al.

We discussed the case of ATRA treatment of APL in our April 15, 2010 article on this blog. APL patients whose leukemia is due to a PML-RARα translocation in their promyelocytes (who constitute the vast majority of APL patients) initially respond to differentiation therapy with ATRA, but eventually develop resistance to the drug. Combination therapy of ATRA and arsenic trioxide (As 2O 3) cures the majority of patients, rendering a cancer that was once uniformly fatal 90% curable. As discussed in our 2010 article, this was first modeled in transgenic mice, and then applied to human patients. APL patients whose leukemia is due to a PLZF-RARα translocation in their promyelocytes are unresponsive to both ATRA and As 2O 3. However, as discussed in our 2010 article, the corresponding mouse model does respond to a combination of ATRA and a histone deacetylase (HDAC) inhibitor such as sodium phenylbutyrate.

When this combination therapy was tested in one patient in 1998 (presumably the first patient in a clinical trial), she achieved a complete remission. Presumably, clinical trials of newer, approved HDAC inhibitors [e.g., suberoylanilide hydroxamic acid (SAHA), Merck’s Vorinostat] in combination with ATRA could be carried out.  (The SAHA/ATRA combination has been tested in a mouse model of PLZF-RARα APL.)

As in the case of Agios’ AGI-5198, ATRA may work in part via a different mechanism than induction of differentiation in APL. This is despite this case being taken as a paradigm of differentiation therapy. We referred to this briefly in our April 19, 2010 blog post. ATRA appears to produce cancer cell growth arrest at least in part via inducing degradation of the PML-RARα fusion protein. Growth arrest and differentiation appear to be uncoupled in the case of the action of ATRA on PLZF-RARα-bearing cells. [The issue of the uncoupling of RARα transcriptional activation (which induces differentiation) and RARα degradation was investigated further in a study published in April 2013.]

Is it possible–as in the case of ATRA in APL–that Agios’ therapies for targeting mutant forms of IDH1/2 will require combination with another agent to achieve long-term therapeutic efficacy? Only clinical trials can answer this question. However, perhaps it might be possible to design animal models to test this issue, and to use these models to identify agents that may be productively used in combination with the IDH1/2 inhibitors.

Conclusions

Agios IPO comes amidst a boom in biotech IPOs–especially Boston biotech IPOs. In addition to Agios, recent Boston-area IPOs include Epizyme (Cambridge, MA), TetraPhase Pharmaceuticals (Watertown, MA) and Enanta Pharmaceuticals (Watertown, MA). According to a June 14 2013 article in the Boston Business Journal, bluebird bio (Cambridge, MA) is also expected to complete its IPO during the week of June 17, 2013. We discussed bluebird bio in our October 11, 2012 Biopharmconsortium Blog article.

As with Agios, neither Epizyme, TetraPhase, Enanta, nor bluebird has any revenues from approved and marketed therapeutics. However, unlike Agios, all of these four companies have drug candidates that have reached the clinic. In addition, TetraPhase and Enanta have compounds that have completed Phase 2 clinical trials, and thus have presumably achieved proof-of-concept in humans. Thus the stock of these two companies appear to be lower risk investments than that of Agios, despite Agios’ very compelling scientific and strategic rationale. At least until its compounds achieve proof-of-concept in human studies, investing in Agios is mainly for sophisticated investors who have a high tolerance for risk. ____________________________________________________

As the producers of this blog, and as consultants to the biotechnology and pharmaceutical industry, Haberman Associates would like to hear from you. If you are in a biotech or pharmaceutical company, and would like a 15-20-minute, no-obligation telephone discussion of issues raised by this or other blog articles, or of other issues that are important to  your company,  please contact us by phone or e-mail. We also welcome your comments on this or any other article on this blog.

Identification of a novel Alzheimer’s disease pathway provides potential new avenues for drug discovery

 

Neurofibrillary tangle.

Neurofibrillary tangle.

In August and September of 2012, we published three articles on Alzheimer’s disease on the Biopharmconsortium Blog:

Subsequent to the publication of our articles–on 21 November, 2012–the Wellcome Trust announced the identification of a novel pathway involved in the pathogenesis of Alzheimer’s disease (AD). This research was led by Professor Simon Lovestone and Dr Richard Killick (Kings College, London U.K.), and was published in the online edition of Molecular Psychiatry on 20 November 2012. The Wellcome Trust helped to fund the research.

As we have discussed in earlier articles on this blog, the dominant paradigm among AD researchers and drug developers is that the disease is caused by aberrant metabolism of amyloid-β (Aβ) peptide, resulting in accumulation of neurotoxic Aβ plaques. This paradigm is known as the “amyloid hypothesis”. AD is also associated with neurofibrillary tangles (NFTs) which are intracellular aggregates of hyperphosphorylated tau protein. In contrast to the amyloid hypothesis, some AD researchers have postulated that NFT formation is the true cause of AD. The new research links amyloid toxicity to the formation of NFTs, and identifies potential new drug targets.

The new study is based on the discovery of the role of clusterin–an extracellular chaperone protein–in sporadic (i.e., late-onset, non-familial) AD. The gene for clusterin, CLU, has been identified as a genetic risk factor for sporadic AD via a genome-wide association study published in 2009. Clusterin protein levels are also increased in the brains of transgenic mouse models of AD that express mutant forms of amyloid precursor protein (APP), as well as in the serum of humans with early stage AD.

The researchers first studied the relationship between Aβ and clusterin in mouse neuronal cells in culture. Aβ rapidly increases intracellular concentrations of clusterin in these cells. Aβ-induced increases in clusterin drives transcription of a set of genes that are involved in the induction of tau phosphorylation and of Aβ-mediated neurotoxicity. This pathway is dependent on the action of a protein known as Dickkopf-1 (Dkk1), which is an antagonist of the cell-surface signaling protein wnt. The transcriptional effects of Aβ, clusterin, and Dkk1 are mediated by activation of the wnt-planar cell polarity (PCP) pathway. Among the target genes in the clusterin-induced DKK1-WNT pathway that were identified by the researchers are EGR1 (early growth response-1), KLF10 (Krüppel-like factor-10) and NAB2 (Ngfi-A-binding protein-2)–all of these are transcriptional regulators. These genes are necessary mediators of Aβ-driven neurotoxicity and tau phosphorylation.

The researchers went on to show that transgenic mice that express mutant amyloid display the transcriptional signature of the DKK1-WNT pathway, in an age-dependent manner, as do postmortem human AD and Down syndrome hippocampus. (Most people with Down syndrome who survive into their 40s or 50s suffer from AD.) However, animal models of non-AD tauopathies (non-AD neurodegenerative diseases associated with pathological aggregation of tau, and formation of NFTs, but no amyloid plaques) do not display upregulation of transcription of genes involved in the DKK1-WNT pathway, nor does postmortem brain tissue of humans with these diseases.

The Kings College London researchers concluded that the clusterin-induced DKK1-WNT pathway may be involved in the pathogenesis of AD in humans. They also hypothesize that such strategies as blocking the effect of Aβ on clusterin or blocking the ability of Dkk1 to drive Wnt–PCP signaling might be fruitful avenues for AD drug discovery. According to the Wellcome Trust’s 21 November 2012 press release, Professor Lovestone and his colleagues have shown that they can block the toxic effects of amyloid by inhibiting DKK1-WNT signaling in cultured neuronal cells. Based on these studies, the researchers have begun a drug discovery program, and are at a stage where potential compounds are coming back to them for further testing.

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As the producers of this blog, and as consultants to the biotechnology and pharmaceutical industry, Haberman Associates would like to hear from you. If you are in a biotech or pharmaceutical company, and would like a 15-20-minute, no-obligation telephone discussion of issues raised by this or other blog articles, or an initial one-to-one consultation on an issue that is key to your company’s success, please contact us by phone or e-mail. We also welcome your comments on this or any other article on this blog.

Alzheimer’s disease–where do we go from here?

 

New Alzheimer’s disease model, the CVN mouse

Our August 19, 2012 and our August 28, 2012 articles on this blog focused on the latest developments in Alzheimer’s disease (AD) drug development. To summarize the conclusions of the articles:

  • The results of a new genetic study by DeCode Genetics and its collaborators strongly support the amyloid hypothesis of AD, and especially the hypothesis that reducing the β-cleavage of APP [e.g., by use of an inhibitor of β-secretase (also known as the β-site APP cleaving enzyme 1, or BACE1)] may protect against the disease.
  • Nevertheless, in Phase 3 trials of two anti-amyloid monoclonal antibody (MAb) drugs in patients with mild to moderate AD–Pfizer/Janssen’s bapineuzumab (often called “bapi” for short) and Lilly’s solanezumab–the drugs failed their primary cognitive and functional endpoints.
  • Roche/Genentech, as well as two academic consortia, have begun clinical trials of anti-amyloid MAb drugs in asymptomatic patients with mutations that predispose them to develop AD, or in asymptomatic patients with amyloid accumulation. These studies are based on the hypothesis that the reason for the failure of anti-amyloid MAb drugs in clinical trials has been that the patients being treated had suffered extensive, irreversible brain damage. Treating patients at a much earlier stage of disease with these agents might therefore be expected to be more successful.

Analyses of the data from the Phase 3 studies of both bapi and solanezumab will be presented in scientific meetings in October 2012. An academic research consortium will present its independent analysis of the data from the EXPEDITION studies of solanezumab at the American Neurological Association (ANA) meeting in Boston on October 8, 2012, and at the Clinical Trials on Alzheimer’s Disease (CTAD) meeting in Monte Carlo, Monaco, on October 30, 2012.

According to a September 11, 2012 news article in Drug Discovery & Development, researchers who conducted the Phase 3 trials of bapi found evidence that the drug stabilized amyloid plaque in the brain and may have ameliorated further nerve damage in patients treated with the drug. This finding is among the results to be presented in the October meetings.

Development of BACE1 inhibitors

Strictly speaking, the results of the DeCode Genetics study most strongly support the development of BACE1 inhibitors. In our August 28, 2012 article, we link to a 2010 review that includes a discussion of companies developing BACE1 inhibitors. However, we also note that the development of BACE1 inhibitors has been elusive. This is because of medicinal chemistry considerations. Specifically, it has been difficult to design a specific, high-affinity inhibitor of the BACE1 active site that can cross the blood-brain barrier and which has good drug-like ADME (absorption, distribution, metabolism and excretion) properties. Nevertheless, recently progress has been made in developing such compounds, and several companies are developing BACE1 inhibitors and have entered them into early-stage clinical trials.

Among the companies developing BACE1 inhibitors, as listed in a recent post on Derek Lowe’s In The Pipeline blog are CoMentis/Astellas, Merck, Lilly, and Takeda.

Satori Pharmaceuticals was developing γ-secretase inhibitors, but ran into safety problems

Developing γ-secretase inhibitors has been abandoned by the vast majority of companies, because of the essential role of these enzymes in the Notch pathway and other pathways involved in normal physiology. As a result, development of γ-secretase inhibitors for AD has not progressed beyond the preclinical stage.

Nevertheless, Satori Pharmaceuticals, a Cambridge, MA venture capital-backed biotech company, had been actively involved in developing γ-secretase inhibitors. Satori’s γ-secretase inhibitors were based on a proprietary scaffold derived from a compound isolated from the black cohosh plant (Actaea racemosa). The company utilized modern synthetic and medicinal chemistry to derive compounds based on this scaffold that they believed was suitable for long-term oral therapy for AD in humans. Satori’s lead compound, SPI-1865, was a potent γ-secretase modulator that decreased levels of the amyloidogenic Aβ42 peptide as well as Aβ38, increased levels of Aβ37 and Aβ39, but did not affect Aβ40. Researchers believe that decreasing Aβ42 levels in favor of shorter, less amyloidgenic A-beta forms is beneficial in treatment of AD. SPI-1865 was also selective for Aβ42 lowering over the inhibition of Notch processing, and appeared to be free of any other off-target activities.

In animal models [e.g., wild type mice and rats, and transgenic mice (Tg2576) that overexpress APP and thus have high levels of Aβ peptides] orally-administered SPI-1865 has been found to lower brain Aβ42. SPI-1865 has good brain penetration in these models, and a long half-life that should permit once a day dosing in humans.

SPI-1865 was in the preclinical stage. Satori planned to file an Investigational New Drug (IND) Application with the FDA in late 2012 with the goal of enabling initial human testing to begin in the early part of 2013.

However, in late 2012, a study in monkeys showed that Satori’s lead compound–as well as its backup compounds–disrupted adrenal function. This adverse effect was completely unexpected, and unrelated to the gamma secretase target.  As of May 30, 2013, Satori closed its doors.

Meanwhile, other companies, including Envivo Pharmaceuticals (Watertown, MA), Bristol-Myers Squibb, and Eisai continue with their R&D efforts in gamma secretase modulators for treatment of AD.

A new mouse model for AD

As Derek Lowe says in an August 31, 2012 post on “In the Pipeline” with respect to Lilly’s AD drugs, anti-amyloid MAbs, BACE1 inhibitors, and γ-secretase inhibitors are “some of the best ideas that anyone has for Alzheimer’s therapy”. Given the APP processing pathway as illustrated in the figure at the top of our August 28, 2012 article, these are the “sensible” and “logical” alternatives.

Nevertheless, there is the nagging feeling among many AD researchers that we do not understand the causes of AD, especially sporadic AD, which represents around 95% of all cases of the disease. Sporadic AD occurs in aging individuals who have normal genes for the components of the APP processing pathway. Not only do we not understand the pathobiology of sporadic AD, but we have little understanding of the normal physiological function of APP and of APP processing. Processes that may be involved in the initiation of sporadic AD may include not only those involved in Aβ production, but also those involved in Aβ clearance.

An important tool in understanding the pathobiology of AD, and potentially in developing novel therapies for the disease, would be an animal model that recapitulates the human disease as closely as possible. We published an article on AD mouse models that were designed to more closely recapitulate human AD than the most commonly used models in the September 15, 2004 issue of Genetic Engineering News. However, since the publication of our article, Carol A Colton, Ph.D. (Duke University Medical Center, Durham, NC) and her colleagues have published on their research aimed at producing an even better mouse model, known as the CVN mouse. They published their research in two articles, one in PNAS in 2006 and the other in the Journal of Neuroscience in 2008.

Charles River Laboratories (CRL) (Wilmington, MA) now offers the CVN mouse to researchers who might wish to employ it in their AD research. CRL has also recently produced a webinar (with the participation of Dr. Colton) on the CVN mouse, entitled “CVN Mouse: A More Translatable Alzheimer’s Efficacy Model”. You may access this webinar by registering at http://www.criver.com/thesource.

Genome-wide association studies (GWAS) in humans, as well as various functional studies, have implicated variants in genes involved in inflammation and immune responses in susceptibility to late-onset, sporadic AD in humans. The Colton group, noting that commonly-used mouse models of AD recapitulated human disease very poorly, looked for differences between mice and humans in innate immunity. The biggest difference they found was that expression of nitric oxide synthase 2 (NOS2) the inducible form of nitric oxide synthase, is high in mice and low in humans. NOS2 is an enzyme that produces nitric oxide (NO), a highly reactive oxidant that can serve in signal transduction, neurotransmission and in cell killing by macrophages. Microglia, the macrophages of the brain, express NOS2 and NO. The Colton group has been studying the role of microglia and oxidants and antioxidants in microglia that can produce oxidative stress in the brain in normal aging and in AD.

Because of the striking difference in NOS2 expression between mice and humans, the Colton group created a transgenic mouse AD model by crossing mice that  expressed a mutant form of human APP known as APPSwDI (APP Swedish Dutch Iowa) with NOS2 knockout (NOS2 -/-) mice. The APPSwDI transgenic mouse, a well-characterized standard AD mouse model, was chosen because it expresses low levels of APP and high levels of Aβ peptides in the brain. The APPSwDI/NOS2 -/- mouse is the CVN mouse that is available from CRL.

Unlike APPSwDI mice and other standard AD mouse models, the CVN mouse recapitulates many features of human AD as the animals age, including AD-like amyloid pathology (starting at 6 weeks of age, which is early), perivascular deposition of amyloid, AD-like tau pathology (including aggregated hyperphosphoryated tau), AD-like neuronal loss, and reduction in interneuron numbers (including NPY interneurons). Age-related cognitive (learning and memory) loss (as assessed by the radial arm water maze test) was also seen. The researchers also saw increases in immune activation and inflammation (e.g., microglial activation) over the course of the disease; this appeared to be dependent on increases in Aβ and in tau.

The researchers also used the mouse to study changes in immune-related proteins over the course of the disease. Several protein that are encoded by genes that have been associated with sporadic AD via GWAS change over time in this mouse model, including APOE (which has been known to be important in AD for a long time) and BIN1. Other proteins that change over the course of disease include the complement component C1QB, and the centrosomal protein ninein. Immune activation genes such as those that encode IL-1α and TGF-β also show changes over the course of disease in these mice. The Colton group will soon publish their work on changes in these proteins and genes in the CVN mouse in a peer-reviewed journal.

In summary, the CVN mouse more faithfully models AD-like progression than other mouse models that have been used to study AD, including those that have been used in preclinical studies of such failed drug candidates as solanezumab, bapineuzumab, Flurizan (tarenflurbil), and Alzhemed (3-amino-1-propanesulfonic acid). It also allows researchers to study the role of genes and proteins such as those identified in GWAS studies in AD, and especially in sporadic AD. (However since the CVN mouse expresses a mutant form of APP, it can not be used to study all aspects of the pathophysiology of sporadic AD, especially the initiation of the disease process.) The CVN mouse can also be used in drug discovery and preclinical studies.

One example of such drug discovery studies is being carried out by the Colton group. They have recently been studying small APOE mimetic peptides in CVN mice. The subcutaneously administered APOE mimetics were reported to significantly improve behavior, while decreasing the inflammatory cytokine IL-6, as well as decreasing neurofibrillary tangle-like and amyloid plaque-like structures. These improvements are associated with apoE mimetic-mediated increases in protein phosphatase 2A (PP2A) activity. [Decreased PP2A levels in AD may be involved in formation of neurofibrillary tangles (NFTs) which are aggregates of hyperphosphorylated tau; PP2A may also be involved in the production of Aβ peptides. The APOE mimetic are thus potential AD therapeutics.

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As the producers of this blog, and as consultants to the biotechnology and pharmaceutical industry, Haberman Associates would like to hear from you. If you are in a biotech or pharmaceutical company, and would like a 15-20-minute, no-obligation telephone discussion of issues raised by this or other blog articles, or of other issues that are important to  your company, please click here. We also welcome your comments on this or any other article on this blog.

Co-clinical mouse/human trials for cancer continue to advance

 

RAS/BRAF/PI3K pathways. Source: Source BioScience

Two previous articles on this blog have included discussions of the “co-clinical mouse/human trial” strategy for improving mouse models of human cancer, and simultaneously improving human clinical trials of drugs for these cancers. Now comes an article on the use of a co-clinical trial strategy in personalized treatment of non-small cell lung cancer (NSCLC) in the 29 March 2012 issue of Nature. In the same issue of Nature is a News and Views article by Genentech’s Leisa Johnson Ph.D. that provides a minireview of the research article.

As we discussed in our April 15, 2010 article on this blog, the co-clinical trial strategy has been developed by Pier Paolo Pandolfi, MD, PhD (Director, Cancer and Genetics Program, Beth Israel-Deaconess Medical Center Cancer Center and the Dana-Farber/Harvard Cancer Center) and his colleagues.

As discussed in that article, these researchers constructed genetically engineered transgenic mouse strains that have genetic changes that mimic those found in human cancers. These mouse models spontaneous develop cancers that resemble the corresponding human cancers. In Dr. Pandolfi’s  ongoing co-clinical mouse/human trial project, researchers simultaneously treat a genetically engineered mouse model and patients with tumors that exhibit the same set of genetic changes with the same experimental targeted drugs. The goal of this two-year project is to determine to what extent the mouse models are predictive of patient response to therapeutic agents, and of tumor progression and survival. The studies may thus result in validated mouse models that are more predictive of drug efficacy than the currently standard xenograft models.

The human clinical trials being “shadowed” by simultaneous studies in mice included Phase 3 trials of several targeted therapies for lung and prostate cancer. Xenograft models in which tumor tissue from the patients had been transplanted into immunosuppressed mice were also being tested in parallel with the genetically engineered mouse models. This project represents the most rigorous test to date of how well genetically engineered mouse models of cancer can predict clinical outcomes.

Our October 28, 2011 blog article, which is mainly a review of a 29 September 2011 Nature article by Nature writer Heidi Ledford, Ph.D., focuses on ways to fix the clinical trial system. Our article includes a discussion of a co-clinical trial published in January 2011. This trial utilized two genetically-engineered PDGF (platelet-derived growth factor)-driven mouse models of the brain tumor glioblastoma multiforme (GBM), one of which had an intact PTEN gene and the other of which was PTEN deficient. In this trial, researchers tested the Akt inhibitor perifosine (Keryx Biopharmaceuticals, an alkylphospholipid) and the mTOR inhibitor CCI-779 (temsirolimus; Pfizer’s Torisel), both alone and in combination, in vitro and in vivo. The drugs and drug combinations were tested in cultured primary glioma cell cultures derived from the PTEN-null and PTEN-intact mouse PDGF-driven GBM models, and in the animal models themselves.

The studies showed that both in vitro and in vivo, the most effective inhibition of Akt and mTOR activity in both PTEN-intact and PTEN-null cells in animals was achieved by using both inhibitors in combination.  In vivo, the decreased Akt and mTOR signaling seen in mice treated with the combination therapy correlated with decreased tumor cell proliferation and increased cell death; these changes were independent of PTEN status. The co-clinical animal study also suggested new ways of screening GBM patients for inclusion in clinical trials of treatment with perifosine and/or CCI-779.

The new co-clinical trial reported in the March 2012 issue of Nature

The March 2012 Nature report describes research carried out by a large, multi-institution academic consortium, which included Dr. Pandolfi. It focuses on strategies for treatment of patients with non-small-cell lung cancer (NSCLC) with activating mutations in KRAS (Kirsten rat sarcoma viral oncogene homolog). These mutations occur in 20–30% of NSCLC cases, and patients whose tumors carry KRAS driver mutations have a poor prognosis. Moreover, KRAS is a “hard” or “undruggable” target, and no researchers have thus been able to discover inhibitors of oncogenic KRAS.

Because of the intractability of oncogenic KRAS as a target, researchers have been attempting to develop combination therapies for mutant-KRAS tumors (including, for example, colorectal cancers as well as NSCLCs) that address downstream pathways controlled by KRAS. We discussed examples of these strategies in our book-length report Multitargeted Therapies: Promiscuous Drugs and Combination Therapies, published by Cambridge Healthtech Institute/Insight Pharma Reports in 2011. Strategies discussed in that report are based on the finding that KRAS controls signal transduction via two key pathways: the B-Raf-MEK-ERK pathway and the PI3K-Akt pathway. This is illustrated in the figure at the top of this article. As discussed in our 2011 report, researchers are attempting to develop treatments of mutant-KRAS tumors that involve combination therapies with an inhibitor of the mitogen-activated protein kinase (MEK) together with an inhibitor of phosphatidylinositol 3-kinase (PI3K). Researchers are also attempting to develop combination therapies of MEK inhibitors with standard cytotoxic chemotherapies, which if successful will avoid having to use combinations of two expensive targeted therapies.

In the co-clinical trial that is the focus of the 29 March 2012 Nature research report and News and Views commentary, researchers developed a genetically-engineered mouse model to study treatment of mutant-KRAS NSCLCs with either the antimitotic chemotherapy drug docetaxel alone, or docetaxel in combination with the MEK kinase inhibitor selumetinib (AZD6244, AstraZeneca). In the parallel human clinical trial, researchers are also studying treatment of patients with mutant-KRAS NSCLC with docetaxel alone or docetaxel plus selumetinib. (There is no treatment arm in the human clinical trial in which patients are treated with selumetinib alone, since selumetinib monotherapy of NSCLC patients had shown no efficacy in a previous Phase 2 study; this was confirmed in mouse model studies.)

In humans with mutant-KRAS NSCLC, many tumors with mutations in KRAS have concomitant genetic alterations in other genes that may affect response to therapy. Therefore, the co-clinical trial researchers wished to design mouse models with lung tumors with either Kras mutations alone or with mutations in both Kras and another gene that is often concomitantly mutated in mutant-KRAS NSCLCs in humans. The researchers therefore constructed mouse models with cancers bearing the activating Kras(G12D) mutation, either alone or together with an inactivating mutation in either p53 or Lkb1. The researchers achieved this via a conditional mutation system using nasal instillation of specifically genetically-engineered adenoviruses. As result, a small percentage of lung epithelial cells harbored these mutations. It is from these cells that the NSCLC-like tumors arose, analogous to the clonal origin of sporadic lung tumors in humans.

Of the two tumor suppressor genes that are frequently mutated in human mutant-KRAS NSCLCs and that were modeled by the co-clinical trial researchers, p53, often called the “guardian of the genome”, is familiar to most of you. The other gene, Lkb1 [liver kinase B1, also known as serine/threonine kinase 11 (STK11)], was discussed in an earlier article on the Biopharmconsortium Blog, entitled “The great metformin mystery–genomics, diabetes, and cancer.”

LKB1 (whether in regulation of gluconeogenesis in the liver or in its role as a tumor suppressor) acts by activation of AMPK (AMP-activated kinase, a sensor of intracellular energy status.) In lung cancer (as shown by the same group that performed the 2012 co-clinical trial), LKB1 acts to modulate lung cancer differentiation and metastasis.  Germline mutations in LKB1 are associated with the familial disease Peutz-Jegher syndrome, in which patients develop benign polyps in the gastrointestinal tract. Studying a mouse model of mutant-LKB1 Peutz-Jeger syndrome, Reuben J. Shaw (Howard Hughes Medical Institute, The Salk Institute for Biological Studies, La Jolla, CA, who was prominently mentioned in our “great metformin mystery” article) and his colleagues showed that the LKB1-AMPK pathway downregulates the mTOR pathway–specifically the rapamycin-sensitive mTOR complex 1 (mTORC1) and its downstream effector hypoxia-inducible factor-1α (HIF-1α). HIF-1α expression in turn upregulates the expression of its downstream effectors hexokinase II and glucose transporter 1 (GLUT1), which are involved in cellular utilization of glucose. LKB1-deficient polyps in this mouse model thus show increased expression of hexokinase II and GLUT1, resulting in dramatically increased glucose utilization.

In the new co-clinical trial, genetically-engineered mice that showed established lung tumors [as determined via magnetic resonance imaging (MRI)] were randomized to receive either docetaxel, selumetinib, or a combination of the two drugs. For tumors with only a Kras mutation, treatment with docetaxel alone resulted in a modest rate of response, with 30% of mice showing a partial response. Mice that bore mutant-Kras tumors that also had mutations in either p53 or Lkb1 had much lower rates of response to docetaxel monotherapy (5% and 0%, respectively), and more of these mice showed progressive disease on MRI or died of their disease. Of mice treated with the docetaxel/selumetinib combination, those with single-mutant Kras tumors showed a 92% overall response rate, and those with mutant Kras/p53 tumors showed a 61% overall response rate. However, mice with mutant Kras/Lkb1 cancers showed only a modest response to the docetaxel/selumetinib combination; 33% of mice achieved a partial response. The difference in response rate of mice with Kras/Lkb1 tumors to docetaxel/selumetinib compared to the other two genotypes was found to be statistically significant.

Using the genetically-engineered NSCLC mouse model in biomarker development

In human patients in clinical trials or in treatment for their cancers, performing repeated biopsies to monitor treatment is difficult. The co-clinical trial researchers therefore wished to develop less invasive means of monitoring both co-clinical and clinical trials of docetaxel/selumetinib treatment of NSCLC. They therefore tested the use of positron emission tomography (PET) with 18F-fluoro-2-deoxyglucose (FDG-PET) as an indicator of early response to therapy that could be used in the clinic.  Prior to its radioactive decay (109.8 minute half -life), 18F-FDG is a nonmetabolizable glucose analogue that moves into cells that is preferentially taken up by high-glucose utilizing cells. The researchers found that both Kras/p53 and Kras/Lkb1 tumors showed higher FDG uptake in vivo in the mouse model than did single-mutant Kras tumors. As expected from the earlier study, GLUT1 expression was elevated in Kras/Lkb1 mutant tumors. In human patients, pre-treatment, mutant KRAS/LKB1 tumors also showed a higher FDG uptake that did KRAS tumors negative for LKB1.

Treatment of the mice with docetaxel alone gave no significant changes in FDG uptake in Kras, Kras/p53, or Kras/Lkb1 tumors in vivo. However, within 24 hours of the first dosing of docetaxel/selumetinib, FDG uptake was markedly inhibited in Kras and Kras/p53 tumors. In contrast, treatment of mice with Kras/Lkb1 mutant tumors gave no appreciable decrease in FDG uptake in these tumors. These results show that early changes in tumor metabolism, as assessed by FDG-PET, predict antitumor efficacy of docetaxel/selumetinib treatment.

The FDG-PET study in this mouse model supports the use of this imaging method as a biomarker to monitor the course of treatment in humans.

Cellular signaling in mutant Kras, Kras/p53, and Kras/Lkb1 tumors

The researchers assessed activation of relevant intracellular pathways in tumors in treated and untreated mice with mutant Kras, Kras/p53, and Kras/Lkb1 lung cancers. They performed these studies using two different methods–immunostaining of cancer nodules for phosphorylated ERK, and immunoblotting of tumor lysates. In untreated mice, Kras/Lkb1 tumors show less activation of ERK than do Kras and Kras/p53 tumors, with Kras/p53 tumors showing the greatest amount of activation of the MEK-ERK pathway. Docetaxel had no discernible effect on signaling via the MEK-ERK pathway. Selumetinib alone resulted in decreased ERK activation in Kras and Kras/p53 tumors, but there was still residual activity. The docetaxel/selumetinib combination, however, was more effective in eliminating ERK activation. Pharmacokinetic studies indicated that selumetinib levels were higher in both serum and tumors of mice treated with docetaxel/selumetinib that in those treated with selumetinib alone; this might account for the more potent suppression of MEK-ERK signaling by the combination therapy as compared to selumetinib monotherapy. The researchers studied MEK-ERK activation (as determined by phospho-ERK staining) in  a set of 57 human NSCLC tumors with known RAS, p53 and LKB1 mutation status. As with the tumors in the mouse model, of seven patients whose tumors harbored the KRAS activating mutation, the three patients with concurrent p53 mutations showed higher levels of ERK activation.

The decreased activation of ERK in Kras/Lkb1 tumors suggested that these tumors utilize other pathways to drive their proliferation. On the basis of their prior studies of signal transduction in mutant-Lkb1 lung tumors, the researchers focused on AKT and SRC. Immunoblotting studies showed that Kras/Lkb1 mutant tumors had elevated activation of both AKT and SRC. As one can see from the figure at the top of this article, AKT is a downstream effector of PI3K; since the PI3K/AKT pathway regulates expression of GLUT1 and hexokinase, increased activation of the PI3K/AKT pathway is consistent with the increased uptake of FDG of mutant Kras/Lkb1 tumors. In the figure, SRC (which is not shown) represents one of the major “other effectors” controlled by RAS. These results indicate that concomitant mutation of Lkb1 in mutant-Kras NSCLCs may shift the signaling pathways that drive tumor proliferation from MEK-ERK to PI3K/AKT and/or SRC. This shift would result in primarily resistance of Kras/Lkb1 tumors to treatment with docetaxel/selumetinib.

Long-term benefits of treatment of mice with mutant-Kras and Kras/p53 tumors with docetaxel/selumetinib as opposed to docetaxel monotherapy

The researchers studied long-term treatment of mice with mutant-Kras and Kras/p53 tumors with docetaxel monotherapy versus docetaxel/selumetinib. In mice with mutant-Kras tumors, treatment with docetaxel monotherapy gave stable disease for several weeks, while docetaxel/selumetinib treatment resulted in tumor regression and slower regrowth of tumors. The addition of selumetinib to docetaxel significantly prolonged progression-free survival in these mice. In mice with Kras/p53 tumors, treatment with docetaxel alone resulted in progressive disease, but docetaxel/selumetinib treatment resulted in initial disease regression followed by progression, resulting in prolonged progression-free survival. These results indicate that treatment with combination therapy as opposed to docetaxel alone results in improved progression-free survival, but not cure, in mice with Kras– and Kras/p53-mutant tumors.

The researchers also investigated mechanisms of acquired tumor resistance in mice with mutant-Kras and Kras/p53 tumors, which had been treated long-term with docetaxel/selumetinib. In moribund animals that had received this treatment, all tumor nodules examined showed a recurrence of ERK phosphorylation. This suggested that acquired resistance could be at least in part due to reactivation of MEK–ERK signaling despite ongoing treatment with selumetinib. Evaluation of resistant tumor nodules suggested that more than one mechanism for pathway reactivation was occurring; study of these mechanisms is ongoing.

Conclusions of the new co-clinical study

The results of this co-clinical study predict that docetaxel/selumetinib combination therapy will be more effective than docetaxel monotherapy in several sub-classes of mutant-KRAS NSCLC. This prediction is consistent with the early results of a Phase 2 clinical trial of these two drug combinations in second-line treatment of patients with KRAS-mutant NSCLC.

However, the co-clinical trial also predicts that concurrent mutation of LKB1 in mutant-KRAS  tumors will result in primary resistance to docetaxel/selumetinib combination therapy, perhaps via activation of parallel signaling pathways such as AKT and SRC. Since LKB1 status is not being prospectively assessed in the ongoing human clinical trial, the presence of patients with cancers having concurrent LKB1 mutations may diminish the differences between treatment arms based solely on KRAS status. The results of the co-clinical trial suggests that researchers perform retrospective analysis of p53 and LKB1 status in samples from the concurrent human clinical trial. Future clinical trials should then be designed that involve prospective analysis to ensure sufficient enrollment of patients with all three genotypes to enable sufficiently powered sub-group analyses.

Although the results of the co-clinical trial indicate that patients with mutant KRAS/LBK1 tumors be excluded from trials of docetaxel/selumetinib treatment, the research group that has been conducting the co-clinical trial has also been conducting studies that may lead to treatment strategies for KRAS/LBK1 tumors.

The co-clinical trial also allowed researchers to design and validate biomarker strategies, specifically the potential use of the less-invasive FDG-PET to predict efficacy and to monitor treatment. The co-clinical animal-model study also enabled the discovery of mechanisms of both primary and acquired resistance that might benefit future clinical trials and discovery/development of drugs. (The studies on acquired resistance are in a early stage and are ongoing). Any mechanisms of acquired resistance discovered in co-clinical studies should be confirmed in human clinical trials by examining biopsy samples from patients who relapse on therapy. The ability to assess mechanisms of resistance in preclinical or co-clinical animal studies may enable researchers to design rational drug combination strategies that can be implemented in future clinical studies.

The results of the new co-clinical trial strengthens the contention that co-clinical trials in genetically-engineered mice can provide data that can predict the outcome of parallel human clinical trials. Co-clinical trials can also be used to generate new hypotheses for use in analyzing concurrent human trials, and for design of future clinical studies. Moreover, co-clinical trials can result in the validation of improved animal models for human cancers, which can be used in research and preclinical testing of oncology agents, and in validation of biomarkers for clinical studies in oncology. Given the inadequacy of “standard” xenograft models, which is a major factor in the high attrition rate of pipeline oncology drugs, the availability of validated genetically-engineered animal models may be expected to enable improved oncology drug development.

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As the producers of this blog, and as consultants to the biotechnology and pharmaceutical industry, Haberman Associates would like to hear from you. If you are in a biotech or pharmaceutical company, and would like a 15-20-minute, no-obligation telephone discussion of issues raised by this or other blog articles, or of other issues that are important to  your company, please click here. We also welcome your comments on this or any other article on this blog.

How can we fix the clinical trial system?

 

http://bit.ly/dGrWW3

In recent months, there have been quite a few articles on the need to fix the clinical trial system. Among the most recent articles is the one by Boston-based Nature writer Heidi Ledford, Ph.D. published as a News Feature in the 29 September issue of Nature. In my humble opinion, this is the best article on the subject among those that have been published recently.

The pharmaceutical/biotechnology industry is frustrated with the increasing expense and the low output of the clinical trial system. This low productivity is economically unsustainable. The current clinical trial paradigm is over 50 years old. Back in the 1960s, the norm was to conduct single trials at single sites, each designed to answer a single question.

Nowadays, the norm is the large, multicenter clinical trial, especially for Phase 3 trials. “Multicenter” means that a trial is conducted at multiple sites, often in different countries, and could involve thousands of investigators and staff members. As pointed out in Dr.Ledford’s article, the large trials are mandated by the need in our more risk-adverse world to detect safety issues that occur in only a small percentage of patients, and to obtain good statistics for drugs that confer only a small benefit over the standard of care. However, certain major diseases require large trials of long duration even for drugs that may confer large benefits. For example, because the percentage of patients per year in cardiovascular disease (CVD) trials who experience cardiovascular events is small, these trials must be large and multiyear, in order to see any benefit even for a breakthrough drug.

The advent of personalized medicine–developing drugs and combinations of drugs that are specific for the molecular mechanism behind a patient’s disease–has put additional burdens on the clinical trial system. A disease may be found to be a collection of rare diseases in terms of mechanistic subtypes, each of which affects only a small number of people. This makes patient recruitment difficult.

As stated by Dr.Ledford, “Solving the problem may require fundamental changes to the clinical-trial system to make it faster, cheaper, more adaptable and more in tune with modern molecular medicine.”

Don’t use an “e-commerce” approach to determining drug efficacy!

Other commentators have recently noted the need to make clinical trials “faster, cheaper, and more adaptable.” Several of them have suggested bringing in strategies from other industries, especially e-commerce and social media.

For example, in an editorial published in the 23 September issue of Science, Andrew Grove, the former Chief Executive Officer of Intel, proposes moving towards an “e-trial” system, based on such large-scale e-commerce platforms as that of Amazon.com. Under the proposed e-trial system, the FDA would ensure safety only, not efficacy, and would continue to regulate Phase 1 trials. Once Phase 1 trials have been successfully completed, patients would be able to obtain a new drug through qualified physicians.

Patients’ responses to a drug would be stored in a database, along with their medical histories. There would be measures to protect a patient’s identity, and the database would be accessible to qualified medical researchers as a “commons.” The response of any patient or group of patients to a drug or treatment could then be tracked and compared to those of others in the database who were treated in a different manner or were untreated. These comparisons would provide insights into a drug’s efficacy, and how individuals or subgroups (perhaps defined in part via biomarkers) respond to the drug. This would liberate clinical trials from the “tyranny of the average” that characterize most trials today. As the database grows over time, analysis of the data would also provide information needed for postmarketing studies and comparative effectiveness studies.

Dr. Grove’s proposal is one of several in which the mandate of the FDA (and regulatory agencies in Europe, Japan, etc.) is to regulate safety only (via Phase 1 clinical trials) not efficacy. Efficacy is then determined via some sort of open system, with information gathered and provided to patients and physicians electronically, via systems reminiscent of e-commerce or social media.

We are opposed to removing efficacy from the oversight of the FDA and other regulatory agencies. There are two reasons for this, both of which are illustrated graphically in Box 1 of Dr. Ledford’s article, entitled “the clinical trial cliff”. Approximately half of Phase 2 clinical trials between 2008 and 2010 failed due to inability to demonstrate efficacy. (Around one-third of Phase 2 failures were due to safety, and the remaining failures were mainly due to strategic decisions to terminate a drug.) Among Phase 3 failures between 2007 and 2010, around two-thirds were due to efficacy, and around one-quarter were due to safety. These results indicate that the majority of drugs entered into clinical trials lack efficacy.

The second reason is that many safety problems–especially the rarer safety issues that occur in only a small percentage of patients–are typically not detected in Phase 1, but in Phase 3 and even the postmarking period.

Reduce clinical attrition with new trial designs and improved animal models

Dr. Ledford’s proposals for fixing clinical trials leave regulatory agencies in charge of overseeing both safety and efficacy. They mainly focus on improving clinical trials by reducing “attrition”–i.e., failure of drugs in the clinic, especially in Phase 2 and Phase 3, and on improving patient recruitment. Haberman Associates has produced publications–as well as articles on this blog–during the 2009-2011 period that provide a more in-depth discussion of strategies for reducing attrition than is possible in a 3-page article such as Dr. Ledford’s.

Two of Dr. Ledford’s strategies involve modifications of clinical trial design. Both of these are discussed in Chapter 6 of our book-length Cambridge Healthtech Institute (CHI) Insight Pharma Report, Approaches to Reducing Phase II Attrition. The first is the “Phase 0” trial. This is a type of pre-Phase 1 clinical trial, which uses microdoses of a drug to assess such parameters as pharmacokinetics and target occupancy. As Dr. Ledford suggests, in some cases Phase 0 trials can reduce or eliminate pharmacological testing in animals, and allow researchers to get human data more quickly.

The other trial design strategy mentioned in Dr, Ledford’s article is the use of adaptive clinical trials. This type of trial allows researchers to change the course of a trial in response to trial results. For example, this may mean assigning new patients to specific doses, changing the numbers of patients assigned to each arm of a trial, and changes in hypotheses or endpoints. Monitoring and changing the trial is typically done by an independent data monitoring committee [DMC] so that ideally, double-blind conditions are maintained.

As Dr. Ledford states, adaptive clinical trials may result in shortening the time and cost of the clinical trial process. But, as with Phase 0 microdosing trials, there are many controversies surrounding adaptive clinical trials. Both of these strategies are works in progress.

The other strategy for reducing attrition discussed in Dr. Ledford’s article is to use improved animal models (i.e., animal models designed to more faithfully model human disease) in preclinical studies. We discussed this strategy in Approaches to Reducing Phase II Attrition, and in greater detail in another book-length report, Animal Models for Therapeutic Strategies. I also recently led the workshop “Developing Improved Animal Models in Oncology and CNS Diseases to Increase Drug Discovery and Development Capabilities” at Hanson Wade’s 2011 World Drug Targets Summit.

Several articles on our Biopharmconsortium Blog also focus on improved animal models for predicting efficacy of drug candidates in discovery research and in preclinical studies. Our April 15, 2010 blog post, based on an article in The Scientist, focused on “co-clinical mouse/human trials”. This type of clinical trial was developed by Pier Paolo Pandolfi, MD, PhD (Director, Cancer and Genetics Program, Beth Israel-Deaconess Medical Center Cancer Center and the Dana-Farber/Harvard Cancer Center) and his colleagues.

These trials utilize genetically engineered transgenic mouse strains that have genetic changes that mimic those found in specific human cancers. These mouse models spontaneous develop cancers that resemble the corresponding human cancers. In the co-clinical mouse/human trials, researchers simultaneous treat a genetically engineered mouse model and patients with tumors that exhibit the same set of genetic changes with the same experimental targeted drugs. The goal is to determine to what extent the mouse models are predictive of patient response to therapeutic agents, and of tumor progression and survival. The studies may thus result in validated mouse models that are more predictive of drug efficacy than the currently standard xenograft models.

The new Ledford Nature article discusses co-clinical trials as a means to develop more predictive animal model studies–not only using improved, potentially more predictive animal models, but also treating these animals in similar way (in terms of doses, formulations, schedules of medication, etc.) to the humans in the parallel human clinical trial.

The Ledford article mentions the animal-model portion of a co-clinical trial, which was published in January 2011. This trial utilized two genetically-engineered PDGF (platelet-derived growth factor)-driven mouse models of the brain tumor glioblastoma multiforme (GBM), one of which has an intact PTEN gene and the other of which is PTEN deficient.

Unlike the “standard” mouse xenograft models, these models more closely mimicked the human disease, including growth of tumors within the brain, not subcutaneously. Thus any drug administered to these mice systemically (e.g., intraperitoneally, as was done in this study) had to cross the blood-brain barrier (BBB), as in the case of human clinical trials. This would not be the case with a standard xenograft model, which is one deficiency of these models for brain tumors such as GBM.

GBM is both the most common and the most malignant primary brain tumor in adults. It has a poor prognosis. PDGF-driven GBMs, which results from deregulation of the PDGF receptor (PDGFR) or overexpression of PDGF, account for about 25-30% of human GBMs. These mutations result in the activation of the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTOR) pathway. These tumors may also exhibit mutation or loss of heterozygosity of the tumor suppressor PTEN, which also upregulates the PI3K/Akt/mTOR pathway.

The researchers tested the Akt inhibitor perifosine (Keryx Biopharmaceuticals, an alkylphospholipid) and the mTOR inhibitor CCI-779 (temsirolimus; Pfizer’s Torisel; originally developed by Wyeth prior to the Pfizer merger and approved for treatment of renal cell carcinoma), both alone and in combination, in vitro and in vivo. Specifically, the drugs and drug combinations were tested in cultured primary glioma cell cultures derived from the PTEN-null and PTEN-intact mouse PDGF-driven GBM models, and in the animal models themselves.

The studies showed that both in vitro and in vivo, the most effective inhibition of Akt and mTOR activity in both PTEN-intact and PTEN-null cells or animals was achieved by using both inhibitors in combination.  In vivo, the decreased Akt and mTOR signaling seen in mice treated with the combination therapy correlated with decreased tumor cell proliferation and increased cell death; these changes were independent of PTEN status. The co-clinical animal study also suggested new ways of screening GBM patients for inclusion in clinical trials of treatment with perifosine and/or CCI-779.

According to Dr. Ledford’s Nature article, the National Cancer Institute (NCI) invested $4.2 million in Dr. Pandolfi’s co-clinical trials in prostate and lung cancer in 2009. In addition to the co-clinical trials with genetically-engineered mouse models run by Dr. Pandolfi and others, researchers at the Jackson Laboratory are conducting co-clinical trials with mouse xenograft models that receive tumor cells from patients to be treated in human clinical trials.

Use patient registries in recruitment of patients for clinical trials

In Dr, Ledford’s article, she discusses a crucial factor other than clinical attrition that hinders progress in conducting clinical trials–patient recruitment. According to the article, at least 90% of trials are extended by at least six weeks because of failure to enroll patients on schedule. Only about one-third of the sites involved in a typical multicenter trial manage to enroll the expected number of patients. As a result, clinical trials are longer and more expensive, and some of them are never completed.

Personalized medicine, in which researchers use biomarkers or other criteria to determine what fraction of patients with a particular disease are eligible for a trial (e.g., cancer patients with an activating mutation in a kinase that is the target of the drug to be tested), makes recruitment harder. That is because researchers must screen large numbers of patients to identify the fraction of patients that would be eligible for the trial. So they need to recruit (and screen) a much larger number of patients than in conventional clinical trials with no patient stratification.

Therefore, researchers, “disease organizations”, and patient advocates are devising new strategies to facilitate recruitment of eligible volunteers. Dr. Ledford cites the example of the Alpha-1 Foundation (Miami, Florida), a “disease organization” that focuses on the familial disease alpha-1 antitrypsin deficiency. (This disease renders patients susceptible to lung and liver diseases.) This foundation has  created a registry of patients with alpha-1 antitrypsin deficiency who are willing to be contacted about and to participate in clinical trials.

There are also cancer registries. Dr. Ledford mentions the Total Cancer Care program run by the Moffitt Cancer Center (Tampa, Florida). This program, which involves 18 hospitals, compiles medical history, tissue samples (stored for future analysis) and genetic information about each patient’s tumor. Patients can consent to doctors contacting them about trials. There are other similar programs being developed in the Netherlands and elsewhere. Dr.Ledford mentions the difficulty in negotiating agreements between institutions, and the need for adequate, ultra-secure networks to support registries that connect multiple hospitals and research centers.

Patient registries that are designed to proactively support recruitment for clinical trials have some resemblance to a “social media” approach to recruitment. However, there is a big difference–the need to secure the privacy of patient records. The current trend in social media (and in some e-commerce platforms) is anti-privacy. This is yet another important reason why a social media or e-commerce approach to clinical trials or other aspects of biotech/pharma R&D is not a suitable model. (To his credit, Dr. Grove mentions the need to maintain patient privacy and confidentiality. But this is not the norm with e-commerce and social media.)

Cutting red tape for faster and cheaper clinical trials

Dr Ledford also mentions ways to deal with more bureaucratic issues that can slow down or block the progress of clinical trials. The NCI is now initiating a data-management system that will standardize data entry across all 2,000 sites that conduct NCI-sponsored trials. This should help reduce costs and cut down on record-keeping errors and omissions.The FDA is also looking into ways to reduce reporting requirements and paperwork. so that investigators can submit summaries of case reports rather than each individual document.

To adapt to the multicenter nature of clinical trials, the US Office for Human Research Protections (Rockville, Maryland), which oversees NIH-funded human studies, has proposed changes to its guidelines that would require designation of a single review board for each project. This may greatly improve the current situation, in which multicenter trials must get approval from each center’s institutional review board. This can take months or even years. Despite the definite advantages of more centralized review, individual research centers may be reluctant to give up their direct oversight of clinical trials.

Something important was not in Dr. Ledford’s article

The space limitations for Dr. Ledford’s “News Feature” article, plus its strict focus on clinical trials per se, did not permit her to include something of crucial importance to reduce clinical attrition. That is utilizing such strategies as biology-driven drug discovery in the research phase of drug development. These strategies are designed to select the best targets and to discover drugs that are more likely to be efficacious in treating a particular group of patients. These research strategies are then coupled with early development strategies that emphasize designing clinical trials aimed at obtaining rapid proof of concept in humans. Such trials typically involve the use (and often the discovery) of biomarkers.

We discussed these issues extensively in our report, Approaches to Reducing Phase II Attrition, as well as in an article published in Genetic Engineering and Biotechnology News (and available on our website) “Overcoming Phase II Attrition Problem“. We also discussed a specific case of the use of this strategy in our October 25, 2010 article on this blog.

Conclusions

Given the low productivity of pharmaceutical R&D, it is tempting to take an envious look at the success of e-commerce and social media, and to attempt to devise strategies that apply methodologies from these industry sectors to the biotech/pharmaceutical industry. We should remember, however, that not so long ago some pharmaceutical executives attempted to apply methodologies from such industries as aerospace, computer hardware, and the auto industry to pharma R&D. Not only did that not work too well for the pharmaceutical industry, but as we all know, the industries that served as a model for these approaches haven’t done very well in recent years either.

In contrast, pharmaceutical and biotechnology companies that have formulated strategies that embrace the uniqueness of biology, such as Novartis and Genentech (the latter now merged with Roche), have done a lot better.

There are other strategies for making clinical trials faster, cheaper, and better that are now under discussion in the biotech/pharma industry and the FDA.  These strategies are based on clinical experience, not e-commerce. We shall discuss them in further blog posts.

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As the producers of this blog, and as consultants to the biotechnology and pharmaceutical industry, Haberman Associates would like to hear from you. If you are in a biotech or pharmaceutical company, and would like a 15-20-minute, no-obligation telephone discussion of issues raised by this or other blog articles, or of other issues that are important to  your company, please click here. We also welcome your comments on this or any other article on this blog.

World Drug Targets Summit, Cambridge MA, July 19-21

 

Hanson Wade’s World Drug Targets Summit took place on July 20-21, 2011, with pre-conference workshops on July 19. The conference was held in the Sheraton Commander Hotel in Harvard Square in Cambridge, MA.

I led the first workshop on the 19th, on “Developing Improved Animal Models in Oncology and CNS Diseases to Increase Drug Discovery and Development Capabilities”. The workshop was well-attended, with good questions and discussion from those in attendance. For a description of the workshop, see our July 5, 2011 blog post. The second workshop, on “Exploiting Kinase Signaling Pathways: Opportunities for Drug Development”, was led by Kamal D Puri and Heather Webb, both of Gilead Sciences (Foster City, CA).

The main conference included speakers from both Big Pharmas (Novartis, UCB Pharma, Merck, Pfizer, AstraZeneca, Boehringer Ingelheim, Bayer Schering Pharma) and such biotech companies as Gilead, Infinity Pharmaceuticals, Merrimack Pharmaceuticals, NeurAxon, and FORMA Therapeutics, as well as a couple of researchers from Harvard Medical School and its teaching hospitals. Attendees who were not speakers included people from these same companies and from other Big Pharmas, as well as from such up-and-coming biotechs as Aileron Therapeutics and Proteostasis Therapeutics (both in Cambridge, MA and both mentioned on our blog), and other companies in the U.S. and in Europe.

In addition to case studies and strategies for identifying and validating drug targets that would be likely to yield safe, efficacious, and commercializable drugs, there was a section on strategies for fostering outsourcing and collaboration in target identification and validation. These included Bayer’s Grants 4 Targets program and Tempero Pharmaceuticals’ collaborative programs. (Tempero is a wholly owned subsidiary of GlaxoSmithKline located in Cambridge, MA.)

One highlight of the Summit was a section on “undruggable” targets (and hard targets known as “high-hanging fruit”); this section occurred at the end of the conference. John Andrews of NeurAxon (Mississauga, Ontario Canada) gave an overview of companies working on “undruggables”, which included not only protein-protein interactions (PPIs), but also what we have called areas of “premature technology” such as RNAi therapeutics and, up until the mid-1990s, monoclonal antibody drugs. (See our blog articles located here, here, and here.) He then presented NeurAxon’s own work on developing a first-in-class neuronal nitric oxide synthase (nNOS) inhibitor for treatment of migraine. nNOS inhibitors represent “high-hanging fruit” because of the difficulty of designing drug-like compounds that are selective for nNOS as opposed to endothelial NOS (eNOS).

At the end of Dr. Andrews’ presentation, I briefly outlined the concept of “premature technologies”, and the development of enabling technologies to overcome technological prematurity. MAb drugs constitute a classic case. I then asked if researchers were developing enabling technologies to make possible the efficient discovery of small-molecule drugs to address PPIs, as opposed to the case-by-case development of such drugs as occurs now. (See this article on our blog for an example.)

The chairman for the day, David Winkler of Infinity Pharmaceuticals, instead of having Dr. Andrews answer the question, moved on to the final speaker of the day, Mark Tebbe of FORMA Therapeutics (Cambridge, MA). Dr. Tebbe discussed FORMA’s technology platforms, which are designed to be enabling technologies for discovery of small-molecule drugs to address PPIs, thus answering my question.

In particular, Dr. Tebbe cited FORMA’s CS-Mapping platform, which enables company researchers to interrogate PPIs in intracellular environments, to define hot spots on the protein surfaces that might constitute targets for small-molecule drugs. (For an example of hot spots that are critical for binding in a PPI in the Wnt signaling pathway, see this research report, which we cited in our PPI blog article.) FORMA combines CS-Mapping technology with its chemistry technologies (e.g., structure guided drug discovery, diversity orientated synthesis) to discover drugs.

As an example of hot spot determination, Dr. Tebbe cited the GTP/GDP biding site of the RAS protein. RAS is a notoriously “undruggable” target that is important in a large percentage of human cancers.

FORMA also has a collaboration with the Leukemia & Lymphoma Society to discover and develop small-molecule compounds that target the interaction between the transcriptional repressor Bcl-6 and the SMRT co-repressor. This interaction is key to signaling pathways that are involved in diffuse large B cell lymphoma, a type of aggressive non-Hodgkin’s lymphoma.

FORMA has several executives and board members with Novartis backgrounds, and Novartis is an investor in FORMA and collaborates with FORMA in the area of small-molecule drugs for PPIs in oncology. As discussed in the blog article mentioned earlier on development of small-molecule drugs to target PPIs, Novartis has also been collaborating with researchers at Harvard teaching hospitals in that area. These collaborations show the interest of Novartis in the PPI area, which many pharmaceutical companies shun because of its difficulty and high risk.

The World Drug Targets Summit was a relatively small conference, but had a high concentration of pharmaceutical and biotechnology company R&D leaders, especially in target identification and validation. This provided excellent opportunities to ask questions of the speakers, and to interact with speakers and other attendees during breaks, and in the “speed networking” session and at the conference’s networking dinner. All and all, it was a good conference.

Update: Workshop on improved animal models for pharma R&D at the World Drug Targets Summit, July 2011

 


The time for the July 2011 World Drug Targets Summit in Cambridge MA is looming closer and closer! Registration for the conference is still open, however.

I will lead a workshop entitled “Developing Improved Animal Models in Oncology and CNS Diseases to Increase Drug Discovery and Development Capabilities” at the Summit on July 19.  A workshop on addressing kinase signaling in drug discovery and development will take place later that day. The main conference follows on July 20-21. I am planning to attend the entire conference.

Our workshop will be a discussion of four case studies involving development of novel animal models in oncology and CNS diseases, aimed at more closely modeling human disease than current models. Drug discovery and development in these therapeutic areas has been severely hampered by animal models that are  poorly predictive of efficacy. This is a major cause of clinical attrition in these areas.

There will be one case study on a zebrafish cancer model, two on mouse cancer models, and one on a mouse CNS disease model. The case studies will include applications of these animal models to understanding disease biology, developing new therapeutic strategies, overcoming resistance to breakthrough targeted cancer therapeutics, and identifying drug candidates and advancing them into the clinic.

The main conference will focus on developing improved target discovery and validation strategies that are capable of meeting the challenges of drug discovery and development in the early 21st century–minimizing drug attrition in the clinic, and delivering commercially differentiated products that address unmet medical needs to the market. Speakers will include target discovery and validation leaders from leading pharmaceutical companies, biotechnology companies, and academic institutions.

Workshop on improved animal models for pharma R&D at the World Drug Targets Summit, July 2011

 

I will lead a workshop entitled “Developing Improved Animal Models in Oncology and CNS Diseases to Increase Drug Discovery and Development Capabilities” at the World Drug Targets Summit in Cambridge MA in July 2011.

Workshops will be held on July 19, and the main conference on July 20-21. I am planning to attend the entire conference.

Our workshop will be a discussion of 2-3 case studies involving development of novel animal models in oncology and CNS diseases, aimed at more closely modeling human disease than current models. Drug discovery and development in these therapeutic areas has been severely hampered by animal models that are  poorly predictive of efficacy. This is a major cause of clinical attrition in these areas.

We shall discuss the implications of these case studies for developing novel therapeutic strategies, target identification and validation, drug discovery, preclinical studies, and reducing clinical attrition. We shall also discuss hurdles to industry adoption of novel animal models developed in academic laboratories.

The main conference will focus on ways of building successful target strategies to minimize drug attrition in the clinic, and specifically how to identify and validate targets that can lead to commercially differentiated products. Speakers will include target discovery and validation leaders from such companies as Pfizer, Merck, NeurAxon, Gilead Sciences, Boehringer Ingelheim, Merrimack Pharmaceuticals, Bayer Schering Pharma AG, FORMA Therapeutics, Roche, Novartis, Tempero Pharmaceuticals, UCB Pharma, Infinity Pharmaceuticals, and from such academic institutions as Harvard Medical School.

The conference agenda and brochure, as well as online registration, are available on the conference website.