Biopharmconsortium Blog

Source: Narayanese. http://bit.ly/oi10H1

On July 29, 2011, Merck announced that It was shutting down the San Francisco research laboratory that it had acquired as part of its $1.1 billion acquisition of therapeutic RNAi specialist company Sirna Therapeutics. This announcement was covered in a July 29, 2011 article in Xconomy, and in a news brief in the 4 August issue of Nature and a linked Nature news blog article.

According to the Xconomy article, the shutdown will include the loss of around 50 jobs. Around ten people are being offered transfers to other Merck facilities in nearby Palo Alto CA and on the East Coast.

The Merck facility shutdown continues the exit or retrenchment from therapeutic RNAi research at other Big Pharma companies. The Biopharmconsortium Blog has covered these moves at Roche and Pfizer.

As we discussed in the Roche article, Novartis had also decided to end its 5-year partnership with therapeutic RNAi specialty company Alnylam In September 2010. However, Novartis acquired technology and exclusive development rights for RNAi therapeutics against 31 targets for in-house use as the result of its partnership with Alnylam.  Alnylam is entitled to receive milestone payments for any RNAi therapeutic products that Novartis develops based on these targets. Thus Novartis is still involved in RNAi therapeutics, despite the termination of the Alnylam partnership.

Moreover, according to the Nature news blog, Ian McConnell of Merck’s Scientific Affairs, R&D and Licensing and Partnerships said that Merck will continue to have over 100 scientists working on RNA-based therapeutics, and that it continues to invest significantly in the field. Closing the San Francisco lab represents an effort to trim the budget by eliminating the cost of maintaining a separate RNAi facility.

In our previous blog articles on Big Pharma RNAi therapeutics retrenchment, and in our October 2010 book -length report, RNAi Therapeutics: Second-Generation Candidates Build Momentum, we discussed the strategic issues that are involved in undertaking (or in retrenching from) R&D programs in RNAi therapeutics, and in investing in that area. The therapeutic RNAi (and microRNA) field represents an early-stage area of science and technology. The field may be technologically premature, as was the monoclonal antibody (MAb) drug field in the 1980s.

Big Pharma originally got into RNAi therapeutics in order to help fill weak pipelines, and with the hope of staking out a commanding position in the RNAi field once it became successful. However, with the short-term pressure at Big Pharma companies to cut expenses and programs, Big Pharmas have been losing the needed patience to continue with a technologically premature field like RNAi therapeutics.

In the June 2011 issue of Molecular Therapy, there is an editorial by Arthur Krieg, M.D. (former Chief Scientific Officer of the now-closed Pfizer Oligonucleotide Therapeutics Unit, and now Entrepreneur in Residence at Atlas Venture, Cambridge, MA), entitled “Is RNAi dead?” As discussed in the editorial, the move of Big Pharma away from RNAi, according to some observers, signals the death of the therapeutic RNAi platform. Dr. Krieg outlines an alternative view.

According to Dr. Krieg, Big Pharmas got into RNAi therapeutics with the hope of enabling the rapid development of targeted drugs without the long time lags and uncertainties of small molecule drugs and biologics. In theory, if a research team has a good target, it could rationally design a lead RNAi drug specific for the target and ready for human clinical trials within 15 months. And researchers would not have to worry about “undruggability” of targets. However, there have been several unforeseen hurdles to the development of RNAi drugs, the most formidable of which is the issue of drug delivery. Although certain high-profile publications suggested that the challenge of RNAi drug delivery could be easily overcome, this proved not to be the case in practice.

However, Dr. Krieg believes that the progress in RNAi delivery in recent years has been “nothing short of spectacular”. In 2008, the best RNAi delivery systems for a liver target might have an IC50 (i.e., the RNAi dose required for 50% inhibition of target expression) of 1–3 mg/kg, but in 2010/2011, the IC50 has been reduced to about 1% of this value, which is an improvement of two logs. Dr. Krieg also says that there have also been significant advances in reducing off-target and other undesired systemic effects of RNAi therapeutics in animal models in recent years.

Nevertheless, the advances in RNAi delivery and safety are moving too slowly for Big Pharma’s current short-term mindset. According to Dr. Krieg, if companies are not able to take an RNAi drug into clinical development this year, then the next time there is an R&D portfolio review, investments in “high-risk” technology platforms such as RNAi are likely to be cut. As we have discussed in this blog, and as is well-known to most of you, every Big Pharma company has been cutting R&D and shedding poorly productive and high-risk programs. The focus at many Big Pharmas is on fast, sure returns. High-risk or premature technologies that have not yet yielded any marketed drugs, such as RNAi (and for example, stem cells/regenerative medicine) is not likely to offer such returns.

Dr. Krieg also notes that in the case of another once-premature technology, monoclonal antibody (MAb) drugs, it took several waves of technology development to advance from repeated clinical failure to one of the most successful classes of drugs today. In our view, MAb technology is the classic case (in the life sciences, anyway) of how researchers and companies can take such a premature technology up the technology curve by developing enabling technologies. We discussed this case in our September 28, 2009 blog article, and its applicability to RNAi and stem cells in our July 13, 2009 blog article. As discussed in these articles, and as noted by Dr. Krieg, it was not Big Pharmas, but biotech companies “on the cutting edge” (together with academic labs) that advanced the therapeutic MAb field. Big Pharmas later bought into the MAb field, typically by large acquisitions. This is especially exemplified by the acquisition of MAb drug leader Genentech by Roche.

With respect to RNAi, as mentioned above, at least Merck and Novartis among the Big Pharmas are continuing with in-house RNAi therapeutics programs. And such biotechs as Alnylam, Silence Therapeutics, Quark Phamaceuticals, Dicerna, and Santaris have RNAi and/or microRNA-based drug candidates in clinical trials, often partnered with Big Pharma companies (such as Pfizer) that have cut or reduced their own RNAi drug programs. Therefore, there are companies that are working on advancing RNAi therapeutics up the technology curve. As Dr. Krieg says in his editorial, success in such programs will be expected to lead to Big Pharma reinvestment in RNAi/microRNA therapeutics, just as in the case of MAb drugs.

Vemurafenib

On August 17, 2011 the FDA announced that it had approved the oral targeted therapy vemurafenib (Daiichi Sankyo/Plexxikon/Roche’s Zelboraf; also known as PLX4032) for first-line treatment of metastatic and unresectable melanomas. The drug is indicated for use in patients whose tumors carry the BRAFV600E) mutation. Approximately 50% of melanoma patients have tumors that carry this mutation.

Vemurafenib  was approved together with a test called the cobas 4800 BRAF V600 Mutation Test (Roche Molecular Diagnostics). This is a companion diagnostic designed to determine if a patient’s melanoma cells carry the BRAF(V600E) mutation and thus patients can benefit from therapy with the drug.

Vemurafenib and the companion BRAF(V600E) diagnostic test were approved earlier than scheduled. They had been reviewed under the FDA’s priority review program that provides for an expedited six-month review of drugs that may offer major advances in treatment or that provide a treatment when no adequate therapy exists. The original goal PDUFA (Prescription Drug User Fee Act) review dates for vemurafenib and the companion diagnostic were October 28, 2011 and November 12, 2011, respectively.

The Biopharmconsortium Blog has been following the veurafenib story since March 2010. See this January 23, 2011 article, and the links to earlier articles that it contains.

There are now two drugs approved for the treatment of advanced melanoma in 2011 that demonstrate an improvement in progression-free and overall survival, when before there were none. The other drug, the immunomodulator ipilimumab (Medarex/Bristol-Myers Squibb’s [BMS's] Yervoy), was discussed in a March 30, 2011 article on our blog.

The FDA granted early approval for vemurafenib on the basis of the results of the pivotal Phase 3 trial known as BRIM-3. In a previous article on this blog, we discussed a report of an interim analysis of this trial in January 2011. The results of the trial were published in the June 30, 2011 issue of the New England Journal of Medicine. Earlier Phase 1 and 2 clinical trails of the drug had show response rates of over 50% in advanced melanoma patients whose tumors bore the BRAF(V600E) mutation.

In the BRIM-3 trial, researchers compared vemrafenib to dacarbazine (the previous standard of care) in 675 patients with previously untreated metastatic melanoma that had the BRAF(V600E) mutation. Patients were randomized to receive either vemurafenib or dacarbazine. Co-primary end points were rates of overall and progression-free survival. Secondary end points included the response rate, response duration, and safety.

Patients receiving vemurafenib had a 74% reduction in the risk for progression (or death), compared with patients receiving dacarbazine. Mean progression-free survival was 5.3 months in the vemurafenib group, compared with 1.6 months in the dacarbazine group. At 6 months, estimated overall survival was 84% in the vemurafenib group and 64% in the dacarbazine group. The median survival of patients receiving vemurafenib has not been reached, while the median survival for those who received dacarbazine was 8 months.

Response rates were 48% for vemurafenib and 5% for dacarbazine. Common adverse effects in patients receiving vemurafenib were joint pain, rash, hair loss, fatigue, nausea, and skin sensitivity to the sun. Approximately 26% of patients developed cutaneous squamous cell carcinoma, which was managed with surgery. Patients treated with vemurafenib should avoid sun exposure.

FDA approval of the cobas 4800 BRAF V600 mutation test was also based on data from the BRIM-3 trial. Patient tumor samples were tested with the diagnostic in order to select patients for the trial.

The complete response rate seen with vemurafenib has been only 0.9%. The great majority of patients experience tumor regrowth due to drug resistance. As we have discussed in previous article on this blog (for example, our January 23, 2011 article), researchers are hard at work developing combination therapies designed to overcome this resistance. As discussed in our June 8, 2011 blog article, research aimed at developing such combination therapies was extensively discussed at the 2011 ASCO meeting. We have also outlined strategies for overcoming vemurafenib resistance via design of multitargeted combination therapies in our June 2011 book-length report, Multitargeted Therapies: Promiscuous Drugs and Combination Therapies.

2011 has brought good news to patients who have or may develop late-stage melanoma, their families and friends, and to physicians who treat these patients. When previously there had been no FDA approved therapies that can produce improved survival in patients with this deadly disease, now there are two. We hope that research aimed at designing combination therapies to overcome drug resistance will result in even greater ability to control this disease, and that new therapies for still intractable forms of cancer will emerge in the next several years.

Two recent research reports may point the way to developing more effective, personalized therapies for two deadly women’s cancers for which their are currently few treatment options–triple-negative breast cancer and ovarian cancer. The approach followed in both reports is to use gene expression analysis to stratify each of the two diseases into subtypes. Researchers can then use gene expression and order aspects of the biology of each subtype to design subtype-specific targeted therapies, whether single drugs or drug combinations. If the drugs (whether approved or experimental) already exist, they can be tested in clinical trials, stratified by subtype. If no appropriate drugs exist, researchers can discover the drugs based on subtype-appropriate drug targets.

Triple-negative (TN) breast cancer refers to breast cancers that are negative for expression of estrogen receptor (ER), progesterone receptor (PR), and HER2. [HER2 is the target of trastuzumab (Roche/Genentech's Herceptin) and lapatinib (GlaxoSmithKline's Tykerb/Tyverb)]. Lacking all three receptors, it cannot be treated with standard receptor-targeting breast cancer therapeutics (e.g., tamoxifen, aromatase inhibitors, trastuzumab) but must be treated with cytotoxic chemotherapy. TN breast cancer is generally more aggressive than other types of breast cancer, and even treatment with aggressive chemotherapy regimens typically results in early relapse and metastasis.

TN breast cancers constitute approximately 25 percent of breast cancers. They are diagnosed most often in younger women, those who have recently given birth, women with BRCA1 mutations, and African-American and Hispanic women.

There is a Triple Negative Breast Cancer Foundation, which was founded in 2006 in honor of a mother in her mid-thirties who died of the disease.

Ovarian cancer, the ninth most common cancer in women, caused nearly 14,000 deaths in the U.S. in 2010. In its earliest stages, its symptoms are usually very subtle and mimic other, less serious diseases. As a result, it is usually detected at later stages in which treatment is more difficult and gives poorer outcomes. The 2001 five-year survival rate was 47%, up from 38% in the mid-1970s. This compared to an overall survival rate for cancer of 68% in 2001, up from 50% in the mid-1970s.

Treatment usually involves surgery and chemotherapy, and sometimes radiotherapy. Surgery (preferably by a gynecological oncologist) may be sufficient for earlier-stage tumors that are well-differentiated and confined to the ovary. In this early-stage disease (which represents about 19% of women presenting with ovarian cancer), the five-year survival rate is 92.7%. However, about 75% of women presenting with ovarian cancer already have stage III or stage IV disease, in which the cancer has spread beyond the ovaries. Then the prognosis is much poorer, and the vast majority of patients will have a recurrence.

The triple-negative breast cancer study

The TN breast cancer study was carried out by researchers at the Vanderbilt-Ingram Cancer Center (Vanderbilt University, Nashville, TN), and published in the 1 July 2011 issue of the Journal of Clinical Investigation. In this study, the researchers analyzed gene expression profiles from 21 publicly available breast cancer data sets, and identified  587 cases of TN breast cancer (by non-expression of mRNAs that encode ER, PR, and HER2). Using cluster analysis, they identified six TN breast cancer subtypes:

• two basal-like subtypes (BL1 and BL2),
• an immunomodulatory (IM) subtype (i.e., expressing genes involved in immune cell processes)
• a mesenchymal (M) subtype
• a mesenchymal stem–like (MSL) subtype
• a luminal androgen receptor (LAR) subtype.

Using gene expression analysis, the researchers identified TN breast cancer model cell lines that were representative of each of these subtypes. On the basis of their analysis, the researchers predicted “driver” signaling pathways, and targeted them pharmacologically as a proof-of-principle that analysis of gene expression signatures of cancer subtypes can inform selection of therapies.

BL1 and BL2 subtypes had higher expression of genes involved in the cell cycle and response to DNA damage, and model cell lines preferentially responded to cisplatin. M and MSL subtypes were enriched for expression of genes involved in the epithelial-mesenchymal transition (EMT), and growth factor-related pathways in model cell lines responded to the PI3K/mTOR inhibitor BEZ235 (Novartis, now in Phase 1 and 2 for solid tumors) and to the ABL/SRC inhibitor dasatinib [Bristol-Myers Squibb's Sprycel, currently approved for treatment of chronic myelogenous leukemia (CML) and Philadelphia chromosome-positive acute lymphoblastic leukemia (ALL), and under investigation for treatment of solid tumors). The LAR subtype was characterized by androgen receptor (AR) signaling, and included patients with decreased progression-free survival. LAR model cell lines were uniquely sensitive to the AR antagonist bicalutamide (AstraZeneca's Casodex/Cosudex, currently approved for the treatment of prostate cancer and hirsutism, and under investigation for treatment of androgen receptor-positive, ER negative, PR negative breast cancer).

The researchers plan to use the TN breast cancer subtype-specific model cell lines for further molecular characterization, to identify new components of the “driver” signaling pathways for each subtype. These pathways can be targeted in further drug discovery efforts. The subtype-specific cell lines can also be used in preclinical studies with targeted agents, and in identification of subtype-specific biomarkers that can potentially be used in stratifying TN breast cancer patients so that they might be treated with the best agents for their disease.

The ovarian cancer study

The ovarian cancer study was carried out by the Cancer Genome Atlas Research Network [a consortium of academic researchers jointly funded and managed by the National Cancer Institute (NCI) and the National Human Genome Research Institute (NHGRI)], and published in the 30 June 2011 issue of Nature. In this study, the researchers analyzed mRNA expression, microRNA expression, promoter methylation and DNA copy number in 489 high-grade serous ovarian adenocarcinomas, as well as the DNA sequences of exons from coding genes in 316 of these tumors. Serous adenocarcinoma is the most prevalent form of ovarian cancer, accounting for about 85 percent of all ovarian cancer deaths.

The researchers found that nearly all of the high-grade serous ovarian cancers (HGS-OvCa) studied had mutations in the TP53 gene, which encodes the p53 tumor suppressor protein. On the basis of their gene expression (mRNA) signatures, the researchers divided the population of HGS-OvCa into four subtypes:

• an immunoreactive subtype (i.e., expressing genes involved in immune cell processes)
• a differentiated subtype (high expression of markers of differentiated female reproductive tract epithelia)
• a proliferative subtype (high expression of markers of cell proliferation)
• a mesenchymal subtype (high expression of HOX genes and of markers of mesenchymal-derived cells)

The researchers also determined subtypes on the basis of microRNA expression and promoter methylation. microRNA subtype 1 overlapped the mRNA proliferative subtype and miRNA subtype 2 overlapped the mRNA mesenchymal subtype. Patients with miRNA subtype 1 tumors survived significantly longer that those with tumors of other microRNA subtypes.

Although the researchers found no significant difference in survival between the four transcriptional subtypes, they did identify a 193-gene expression signature that was predictive of overall survival. 108 genes were correlated with poor survival and 85 were correlated with good survival.

The researchers identified cancer-associated pathways in the HGS-OvCA population; this is equivalent to the prediction of “driver” signaling pathways in the TN breast cancer study. They found that 20% of the HGS-OvCA samples had germline or somatic mutations in BRCA1 or BRCA2, and that 11% lost BRCA1 expression through DNA hypermethylation. As we discussed in an earlier article on this blog, BRCA1- or BRCA2-negative tumor cells cannot repair their DNA via homologous recombination. They are dependent on an alternative pathway of DNA repair, which involves the enzyme poly(ADP) ribose polymerase (PARP). These tumors are thus sensitive to a class of drugs known as PARP inhibitors, such as KuDOS/AstraZenaca’s olaparib. There are now six PARP inhibitors, including olaparib, in clinical development.

The researchers found genetic alterations in several other genes involved in homologous recombination. Altogether, defects in homologous recombination may be present in approximately half of HGS-OvCa cases, and these tumors may be sensitive to PARP inhibitors. This provides a rationale for clinical trials of PARP inhibitors in women with ovarian cancers with defects in homologous recombination-related genes.

Olaparib and other PARP inhibitors are in clinical trials in women with advanced with BRCA-1 or -2 mutations and with other defects in homologous recombination. As discussed in the 2011 ASCO meeting, early Phase 2 results indicate that olaparib gives dramatic improvements in progression-free survival in these women. (See this article and this video.) In these studies, in addition to tumors with genetic defects in homologous recombination, olaparib or another PARP inhibitor, Abbott’s ABT-888, appears to give improved progression-free survival in women who have previously been treated with chemotherapy drugs that result in DNA damage. This suggests that oncologists may be able to use a “one-two punch”, consisting of a DNA-damaging drug [such as the alkylating agent temozolomide [Merck's Temodar]) followed by a PARP inhibitor, to treat advanced ovarian cancer.

In addition to BRCA-1 and BRCA-2 mutations and other genetic alterations that result in defects in homologous recombination, the HGS-OvCa population exhibited genetic changes that would result in deregulation of several other cancer related pathways. These pathways included the RB1 (67% of cases), RAS/PI3K (45% of cases), and NOTCH (22% of cases) pathways, as well as the FOXM1 transcription factor network (87% of cases). All of these pathways represent opportunities for target identification and drug discovery. FOXM1 (Forkhead box protein M1) was named the Molecule of the Year for 2010 by the International Society for Molecular and Cell Biology and Biotechnology Protocols and Research (ISMCBBPR) because of “its growing potential as a target for cancer therapies.” FOXM1 overexpression results in destabilization of the cell cycle, which can lead to a malignant phenotype.

The researchers also identified 22 genes that were frequently amplified or overexpressed in HGS-OvCA tumors (other than genes that are involved in homologous recombination). Inhibitors (including approved and experimental compounds) already exist for the products of these genes, and researchers might assess these compounds in HGS-OvCa cases in which target genes are amplified.

Can Verastem develop new therapeutics for triple negative breast cancer?

The private biotechnology company Verastem (Cambridge, MA) focuses on discovery and development of drugs to target cancer stem cells. The company was founded in 2010, and is based on a strategy for screening for compounds that specifically target cancer stem cells. This strategy, published in the journal Cell in 2009, was developed by Drs. Robert Weinberg (MIT Whtehead Institute), Eric Lander (Broad Institute of MIT and Harvard University), and Piyush Gupta (MIT and Broad Institute) and their colleagues. Drs. Weinberg, Lander, and Gupta are on the Scientific Advisory Board of Verastem.

On July 14, 2011, Verstem announced that it had raised $32 million in a Series B financing. Verastem had previously raised $16 million from a group led by former Christoph Westphal’s Longwood Founders Fund. Dr. Westphal (formerly of Sirtris) is now Chairman of Verastem.

Cancer stem cells are best known in acute myeloid leukemia (AML), but their existence in other cancers (especially solid tumors) is controversial. The cancer stem cell hypothesis asserts that a small subpopulations of cells in a leukemia or solid tumor have characteristics that resemble normal adult stem cells, such as self renewal, the ability to give rise to all the cell types found in the leukemia or cancer, and stem cell markers. The hypothesis further asserts that most cancer treatments fail to knock out cancer stem cells, which can repopulate a tumor cell population, resulting in treatment relapses. Cancer stem cell researchers therefore propose developing cancer stem-cell specific therapeutics that can be used to eliminate these cells, which can block these relapses.

Whether cancer stem cells are involved in the pathobiology of solid tumors or not, the biology of the putative cancer stem cell phenotype can be important in certain subtypes of cancer. Cancer stem cells are characterized by the epithelial-mesenchymal transition (EMT), and in the Cell paper the researchers screened for compounds that specifically targeted breast cancer cells that had been experimentally induced into an EMT, and which as a result exhibited an increased resistance to standard chemotherapy drugs.   They identified the compound salinomycin as a drug that specifically targeted these cells, as well as putative cancer stem cells from patients.

As discussed earlier in this article, TN breast cancer includes two subtypes that have gene expression signatures related to the EMT: the mesenchymal (M) subtype and the mesenchymal stem–like (MSL) subtype. One or both of these subtypes might be sensitive to compounds that specifically target putative breast cancer stem cells. This may be true whether the cancer stem cell hypothesis applies to TN breast cancer or not. Verastem recognizes this, and is thus focusing on TN breast cancer as its first therapeutic target. The Vanderbilt TN breast cancer study suggests that trials of any “cancer stem cell-specific” therapeutics for TN breast cancer should be guided by subtype-specific biomarkers.

Hope for treatment of TN breast cancer and advanced ovarian cancer

Researchers and oncologists have made great strides in increasing the percentage of breast cancers that are treatable or even curable in recent years. For example, prior to the FDA approval of trastuzumab in 1998, HER2 positive breast cancer carried a grim prognosis. But the advent of trastuzumab (and later, lapatinib) has had a major impact on treatment of this once uniformly deadly type of breast cancer.

We hope that the new, personalized medicine-based approach to TN breast cancer and advanced serous ovarian adenocarcinoma will also result in successful new therapeutic strategies for these deadly women’s cancers.

__________________________________________

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.

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. As discussed on the company’s website, FORMA 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.

Huntington's disease. Dr. Steven Finkbeiner. http://bit.ly/q48xdX

In the June 10, 2011 edition of Cell, there is a Leading Edge Preview (short review) and a research Article on a surprising new potential therapeutic strategy for neurodegenerative disease. The Preview is by Peter H Reinhart (Proteostasis Therapeutics, Cambridge MA) and Jeffery W Kelly (Skaggs Institute and Scripps Research Institute, La Jolla CA), and the the Article (Zwilling et al.) is by Paul J Muchowski (Gladstone Institute of Neurological Disease, University of California at San Francisco) and his colleagues. In addition to Dr. Muchowski’s academic collaborators, researchers from the Novartis Institutes for BioMedical Research in Basel, Switzerland participated in that work.

In previous studies, the kynurenine pathway (KP) of tryptophan degradation has been linked to such neurodegenerative diseases as Huntington’s disease (HD) and Alzheimer’s disease (AD). The kynurenine pathway (KP) is the most important pathway for degradation of the amino acid tryptophan in humans. Patients with HD and AD have elevated levels of two metabolites in the KP–quinolinic acid (QUIN) and 3-hydroxykynurenine (3-HK)–in their blood and brains. Studies in rodents have implicated both of these metabolites in pathophysiological processes in the brain. QUIN, which is a selective N-methyl-D-aspartate (NMDA) agonist, has been implicated in excitotoxicity, which is a mechanism by which excessive stimulation of glutamate receptors causes neuronal dysfunction and cell death. (NMDA receptors constitute a major type of glutamate receptor.) 3-HK is a free radical generator that can mediate neuronal cell death. Intrastriatal injection of QUIN in experimental animals duplicated many of the pathological features of HD. Administration of QUIN to other areas of the brain of experimental animals also duplicated features of AD, such as destruction of  basal forebrain cholinergic neurons projecting to the cortex and memory deficits.

In contrast, kynurenic acid (KYNA), which is formed in a side arm of the KP by conversion of kynurenine by the enzyme kynurenine aminotransferase, appears to be neuroprotective. KYNA is an antagonist of ionotropic excitatory amino acid receptors. In particular, KYNA blocks the neuropathological effects of QUIN. Kynurenine aminotransferase is found in the brain, and is thus capable of transforming kynurenine (which is actively transported into the brain by a neutral amino acid transporter) to KYNA in that organ. The concentration of brain KYNA is often decreased in HD and AD.

All of these studies in rodents were done in the 1980s or 1990s. However, no therapies based on that research have yet been advanced into the clinic.

Studies with JM6, a prodrug small-molecule inhibitor of kynurenine 3-monooxygenase, in wild type mice

In the Zwilling et al. study, researchers studied inhibition of  kynurenine 3-monooxygenase (KMO) as a strategy for inducing a more favorable ratio of KYNA to QUIN in vivo. KMO is the enzyme in the KP that converts kynurenine to 3-hydroxykynurenine, which is further converted in three steps to QUIN. KMO is found at high levels in peripheral blood macrophages and other immune cells in the blood. Inhibition of  KMO results in elevation of kynurenine levels in the blood. This kynurenine can then enter the CNS, where it is converted to the neuroprotective metabolite KYNA.

In 1996, researchers at Roche published the synthesis and characterization of a KMO inhibitor, 3,4-dimethoxy-N-[4-(3-nitrophenyl)thiazol-2-yl]benzenesulfonamide, known as Ro 61-8048. Subsequent studies showed that Ro 61-8048 was neuroprotective in rodent models of brain ischemia and cerebral malaria, and in a model of levodopa-induced dyskinesias (movement disorders) in parkinsonian monkeys.

However, Zwilling et al found that Ro 61-8048 was metabolically unstable. They therefore developed an orally bioavailable “slow-release” prodrug of Ro 61-8048, 2-(3,4-dimethoxybenzenesulfonylamino)-4-(3-nitrophenyl)-5-(piperidin-1-yl)methylthiazole (JM6). JM6 was designed to be converted to Ro 61-8048 in the gut. However, when JM6 was administered orally to wild type mice, the researchers found high levels of both JM6 and Ro 61-8048 in the blood. However, neither JM6 nor Ro 61-8048 accumulated to any great extent in the brain, and the brain concentration of both drugs was insufficient to inhibit KMO. Thus neither JM6 nor Ro 61-8048 appeared to cross the blood-brain barrier.

Despite the failure of JM6 and Ro 61-8048 to cross the blood-brain barrier, oral administration of JM6 results in increased brain levels of KYNA. Administration of an inhibitor of kynurenine aminotransferase to the brain inhibits the increase in levels of KYNA in that organ. This is consistent with the hypothesis that Ro 61-8048 inhibition of KMO in the blood results in elevated blood levels of kynurenine, which is transported into the brain. Kynurenine aminotransferase in the brain converts the kynurenine to KYNA. In addition, elevation of KNYA levels in the brain coincides with a decrease in extracellular concentrations of brain glutamate. This is consistent with earlier studies that showed that increases in brain KYNA, via inhibition of presynaptic α7 nicotinic receptors, reduce extracellular brain glutamate levels. Blocking of presynaptic α7 nicotinic receptors results in inhibition of glutamate release from neurons that bear these receptors. Reduction in extracellular brain glutamate levels may be responsible for KYNA’s neuroprotective effects, via reduction of excitotoxicity. However, at high local concentrations of KYNA, this metabolite may also block glutamate receptors directly.

Studies with JM6 in mouse models of Alzheimer’s and Huntington’s disease

After performing these studies in wild type mice, the researchers then tested the effects of JM6 in mouse models of AD and HD. Transgenic J20 mice that express a mutant form of the human amyloid precursor protein (hAPP) develop spatial memory deficits and synaptic loss starting at 4-5 months of age. Oral administration of JM6 starting at 2 months of age gave significant improvement in spatial memory in mice tested at 6 months of age, as compared to untreated J20 APPtg (transgenic APP) mice. JM6 treatment also prevented synaptic loss in J20 APPtg mice. However, JM6 treatment had no effect on beta amyloid (Aβ) plaque load, which was increased in the hippocampus and cortex of JM6-treated and untreated J20 mice. Under the amyloid hypothesis of AD pathogenesis, Aβ plaques are central to the causation of AD.

J20 APPtg mice had lower brain KYNA levels than wild type littermate controls, consistent with findings in AD patients. Treatment of J20 APPtg mice with oral JM6 (over a 120 day period) increased brain and plasma levels of KYNA. KMO activity, and 3-HK and QUIN levels in the brains and QUIN levels in the plasma of J20 APPtg mice treated with JM6 were not significantly different from levels in wild type controls.

The researchers also tested the effects of oral JM6 administration in R6/2 mice, the best characterized mouse model of HD. HD is a trinucleotide repeat disorder in which a cytosine-adenine-guanine (CAG) repeat segment in exon one of the huntingtin gene (HTT) (encoded in the germline of the individual) exceeds a normal range. The HD CAG repeat region encodes 36 or greater repeated glutamines in the polyQ region of the huntingtin protein (Htt); people without the disease have fewer than 36 glutamines. The disease-associated huntingtin protein is neurotoxic.

In the R6/2 mouse model, mice are transgenic for the 5′ end of the human HD gene carrying a large CAG repeat expansion. These mice develop a progressive neurologic disease, including motor deficits, weight loss, and premature death. The researchers started oral JM6 administration at 4 weeks of age, which is an early symptomatic stage in R6/2 mice. JM6 administration had a dramatic dose-dependent effect on survival. JM6 treatment did not affect the weight of the mice, but it did modestly improve performance on an accelerating rotarod (a measure of motor performance). JM6 treatment also prevented synaptic loss and reduced CNS inflammation in R6/2 mice.

JM6 treatment of R6/2 mice did not influence the size or abundance of neuronal inclusion bodies in these mice. These inclusion bodes are related to those seen in HD in humans. Thus in mouse models of both AD and HD, JM6 treatment did not affect the aggregated proteins (Aβ plaques and mutated Htt inclusion bodies, respectively) that are thought to cause the diseases; nevertheless, they ameliorated disease symptoms.

In chronically JM6-treated J20 APPtg (AD model) and R6/2 (HD model) mice, although JM6 and Ro 61-8048 accumulated in plasma, brain levels of these compounds were nil. Thus JM6 treatment of both neurodegenerative disease models resulted in increased brain levels of KYNA and neurodegenerative disease amelioration, despite the inability of JM6 and R0 61-8048 to cross the blood-brain barrier.

JM6 treatment is a surprising therapeutic strategy for neurodegenerative diseases for three reasons.

• JM6 cannot cross the blood-brain barrier, which is almost always a sine qua non of CNS disease therapy.
• JM6 ameliorates disease without affecting the protein aggregates that are usually thought to cause the diseases.
• JM6 ameliorates multiple neurodegenerative diseases.

How might this novel therapeutic strategy be moved into the clinic?

Clinical trials in AD are notoriously long and expensive. Therefore, Drs. Reinhart and Kelly in their Preview suggest that it might be best to first conduct clinical trials in HD, since the cause of HD is much better understood than for AD, and disease progression in placebo controls is better characterized than for AD.

The results of the mouse model studies suggest that JM6 will ameliorate, but not cure, HD and AD. However, since there are no disease-modifying therapies for either disease, demonstrating amelioration of HD comparable to that seen in the mouse models (provided the drug is proven to be safe in humans) will almost certainly gain approval for the drug. However, in the long run JM6 would need to be combined with other disease-modifying drugs to more effectively treat diseases such as HD and AD. Since other drugs  developed for neurodegenerative diseases will almost always act directly in the brain, combining them with JM6, which does not enter the brain, may help maximize the clinical benefit of a combination therapy. It may also aid in minimizing the toxicity of combination therapies (since the two drugs would not interact in the brain).

Lennart Mucke, MD, the director of the Gladstone Institute, suggested that Dr. Muchowski and his colleagues might begin testing JM6 in patients within the next two years.

The ability of JM6/Ro 61-8048 to ameliorate neurodegenerative diseases in animal models also raises questions as to the mechanisms by which it does so, and how these mechanisms might interact with mechanisms thought to be central to the pathobiology of neurodegenerative diseases (e.g., the amyloid and Tau pathways in AD, huntingtin inclusions, inflammatory pathways, apoptotic pathways, etc.). What are the molecular mechanisms downstream from KYNA elevation? Is JM6 treatment prophylactic, or is it efficacious in animals (and in humans) that are already suffering disease symptoms and that have pathogenic protein aggregates?

Research to answer these questions may lead to still newer therapeutic strategies, including potentially more effective combination therapies for neurodegenerative diseases that include JM6.

__________________________________________

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.

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.

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

On June 1, 2011, Cambridge Healthtech Institute’s (CHI’s) Insight Pharma Reports announced the publication of our new book-length report, Multitargeted Therapies: Promiscuous Drugs and Combination Therapies.

In the past 20 years or so, pharmaceutical and biotechnology industry R&D has been increasingly aimed at developing drugs to treat complex diseases such as cancer, cardiovascular disease, type 2 diabetes, and Alzheimer’s disease. However, the one drug-one target-one disease paradigm that has become dominant in the post-genomic era has proven to be inadequate to address complex diseases, which have multiple “causes”, and each of which may be more than one disease. This has been a major cause of clinical failure and the low productivity of the pharmaceutical industry.

Moreover, researchers have found that most of the successful, FDA-approved small-molecule drugs that were developed prior to the year 2000 are promiscuous, i.e., they are single drugs that address multiple targets. In addition, the great majority of kinase inhibitors, one of the most successful drug classes of the early 21st century, are also promiscuous.

The study of small-molecule drug promiscuity has spawned the emerging field of network pharmacology, which can be applied both to study drug promiscuity and to rationally design small-molecule multitargeted drugs. (Researchers can discover or design multitargeted kinase inhibitors without the use of network pharmacology, however.)

Meanwhile, the development of targeted drugs such as kinase inhibitors and monoclonal antibodies has resulted in the need to develop multitargeted combination therapies. This has been especially true in cancer, where disease causation may involve multiple signaling pathways. In particular, the development of resistance to targeted antitumor drugs has spawned the need to develop second-generation treatments, many of which are multitargeted combination therapies.

Our report covers both discovery and design of small-molecule promiscuous/multitargeted drugs, and of multitargeted combination therapies.

The design of multitargeted combination therapies is one of the hottest areas of cancer R&D today, especially with respect to developing means to overcome resistance to targeted therapies. This area was the focus of many key presentations at the 2011 American Society of Clinical Oncology (ASCO) Annual Meeting, which was held in Chicago on June 3-7. For example, treatment with vemurafenib (PLX4032) of metastatic melanoma patients whose tumors carry the B-Raf(V600E) mutation has produced spectacular overall response rates and increased survival. However, in nearly all cases, the tumors relapse. The latest results with vemurafenib were discussed at ASCO 2011, as well as strategies to overcome resistance to therapy. Our new report also discusses strategies for overcoming vemurafenib resistance, all of which involve design of multitargeted combination therapies.

Another topic discussed at ASCO 2011 was antitumor strategies based on synthetic lethality. We discussed this strategy in an earlier article on this blog, especially with respect to poly(ADP) ribose polymerase (PARP) inhibitors such as KuDOS/AstraZenaca’s olaparib. At a session at the ASCO meeting entitled “PARP Inhibitors, DNA Repair, and Beyond: Theory Meets Reality in the Clinic”, speakers reviewed current progress in developing PARP inhibitors, of which six are now in clinical development.

This session also included a presentation by Michael B. Kastan, MD, PhD (St. Jude Children’s Research Hospital, Memphis TN) on other ways of using the synthetic lethally strategy, for example by targeting kinases involved in DNA repair pathways such as ATM (Ataxia-Telangiectasia Mutated) or Chk1 checkpoint kinase, or even utilizing features of the tumor microenviroment such as hypoxia. Such strategies might be used to design multitargeted combination therapies that specifically target cancer cells with defects in DNA repair and/or in hypoxic solid tumors, and/or to sensitize cancer cells to radiation.

Our new report includes a chapter on using the synthetic lethality strategy to design combination therapies of a cytotoxic drug with a chemosensitizing agent, and to develop therapies for p53-negative cancers. (The key tumor suppressor p53 is deleted, mutated, or inactivated in the majority of human cancers).

Although design of multitargeted combination therapies, as well as discovery and design of kinase inhibitors, are of key importance for current oncology R&D and are also being applied to other diseases, design of single small-molecule multitargeted drugs via network pharmacology is an early-stage, and perhaps a premature, technology. Nevertheless, given the current pharmaceutical company R&D business model that emphasizes outsourcing early-stage R&D, academic research groups and biotechnology companies that are active in this area may be able to forge partnerships with pharmaceutical companies.

For more information on Multitargeted Therapies: Promiscuous Drugs and Combination Therapies, or to order it, see the Insight Pharma Reports website.

Niacin (nicotinic acid)

In our blog post of May 19, 2011, we discussed the late-stage development of two cholesterol ester transfer protein (CETP) inhibitors, designed to raise serum high-density lipoprotein (HDL), or “good cholesterol”. These agents are Merck’s anacetrapib and Roche’s dalcetrapib. The clinical results with these agents have  have reignited enthusiasm for CETP inhibitors in the medical and drug discovery and development community.

Now comes the news that The National Heart Lung and Blood Institute (NHLBI) of the National Institutes of Health (NIH) stopped a large clinical trial of Abbott’s Niaspan, an extended-release formulation of high-dose niacin, because the drug failed to prevent heart attacks and strokes. High-dose niacin is the only drug that is approved for raising HDL. Generic high-dose niacin is usually taken 2-3 times per day, and can cause adverse effects such as skin flushing and itching. Niaspan, as an extended-release formulation of the drug, is taken once a day, and was developed to reduce the extent of these adverse effects. Niaspan is an FDA-approved drug.

Merck has meanwhile been developing its high-dose non-flushing niacin product, Tredaptive/Cordaptive (extended-release niacin/laropiprant). This is a combination product consisting of extended-release high dose niacin plus  laropiprant. Laropiprant is designed to block the ability of prostaglandin D2 to cause skin flushing; niacin-induced skin flushing works via the action of prostaglandin D2 in the skin. In 2008, the FDA rejected Merck’s New Drug Application for Tredaptive/Cordaptive, so the drug remains investigational in the US. However, in 2009 Merck launched Tredaptive in international markets including Mexico, the UK and Germany. The drug is approved in over 45 countries. Merck is also conducting a 25,000-person trial of Tredaptive for reducing the rate of cardiovascular events in patients who are at risk for cardiovascular disease (CVD). Merck intends to file for approval of the drug in the US in 2012, based on the results of this trial if it is positive.

According to an NIH press release, the NHLBI trial, known as AIM-HIGH, involved combination therapy with Niaspan and a statin (simvastatin). Participants selected for the trial had been taking a statin and had well-controlled LDL, but were still at risk for cardiovascular events since they had a history of CVD, as well as low serum HDL and high serum triglycerides. In the treatment arm of the study, participants received a combination of a stain and Niaspan, while those in the control arm received a statin plus placebo.

During the 32 months of the study, subjects in the treatment arm exhibited increased HDL and lower triglyceride levels, as compared to participants in the control arm.  However, combination Niaspan/statin treatment did not reduce cardiovascular events or strokes as compared to statin treatment plus placebo. The NIH therefore stopped the trial 18 months earlier than planned.

In the AIM-HIGH study, subjects had a lower rate of cardiovascular events and strokes than the trial researchers expected. Of the 1,718 people in the treatment arm, 5.8 people per year had cardiovascular events, as opposed to 5.6 cardiovascular events per year among the 1,696 people in the control arm. There was a small increased rate of strokes in patients taking Niaspan, but researchers cautioned that this may have been due to chance. However, the increased rate of strokes, along with the failure to demonstrate efficacy, contributed to the NHLBI’s decision to end the trial early.

As noted by the AIM-HIGH researchers (and mentioned in the NIH press release), the lack of efficacy of high-dose niacin was unexpected, and in striking contrast to the results of previous trials and of observational studies. For example, a 2010 meta-analysis of clinical trials evaluating niacin, alone or in combination with other lipid-lowering drugs (published between 1966 and mid-2008) found significantly positive effects of niacin in preventing cardiovascular events and in reversing or slowing the progression of atherosclerosis. However, the bulk of the studies analyzed had been performed before statin therapy had become the standard of care. As pointed out in a recent article by clinical outcomes researcher Harlan Krumholz, MD (Yale University School of Medicine), it was important to compare Niasapn with a good treatment–in this case, the standard treatment with a statin–rather than comparing it to a poor treatment or to placebo alone.

The results of the AIM-HIGH study may not apply to other patient populations, including higher-risk groups such as patients with acute heart attack or acute coronary syndromes, or in patients who have poorly-controlled LDL despite statin treatment. As a press release from Abbott pointed out, the relevance of the results of AIM-HIGH to patient populations other than the one studied–patients with stable, non-acute, pre-existing cardiovascular disease and very well controlled LDL on simvastatin–is unknown. However, it is not known whether there are any patient populations that might benefit from treatment with Niaspan plus a statin as compared to a statin alone.

The results of AIM-HIGH also do not apply to other drugs that are designed to raise levels of serum HDL. Each drug must be tested in the clinic before drawing conclusions about its efficacy and safety. Various drugs may have different effects on human disease biology. Thus, for example, one should not use the results of the AIM-HIGH trial of Niaspan to conclude that the CETP inhibitors anacetrapib and dalcetrapib, discussed in our previous blog post, are not likely to be efficacious.

The 19 May issue of Nature contains a special Insight section on cardiovascular biology. An article in this section, by leading cardiovascular researcher Peter Libby (Brigham and Women’s Hospital, Boston MA, where he is the Chief of the Division of Cardiovascular Medicine) and his colleagues, is entitled “Progress and challenges in translating the biology of atherosclerosis”. That article refers to HDL as a “frustrating next frontier” (beyond lowering LDL with statins) in cardiovascular drug treatment. HDL biology is complex, with HDL promoting efflux of cholesterol from macrophages in atherosclerotic plaques and exerting anti-inflammatory and other beneficial effects, as also discussed in our previous blog post. HDL particles in blood serum are heterogeneous, with some HDL particles having a greater degree of positive effects on atherosclerotic plaque biology than others. As a result, treatments (e.g., drugs, diet) that raise HDL, as determined by standard clinical assays for serum HDL, may not necessarily result in clinical benefit, because of qualitative changes in populations of HDL particles.

In this connection, the 2010 study by Alan Tall and his colleagues, which we discussed in our May 19, 2011 blog article, provides hope for the efficacy of anacetrapib. These researchers showed that although niacin treatment in humans resulted in a moderate increase in the ability of HDL to promote net cholesterol efflux (measured in in vitro assays), anacetrapib treatment caused a more dramatic increase. This was due not only to a higher level of HDL in anacetrapib-treated subjects, but also to enhanced ability of anacetrapib-induced HDL particles to promote cholesterol efflux, especially at high HDL concentrations. Although this study suggests that anacetrapib treatment induces increases in HDL particles that promote beneficial effects on atherosclerotic plaque biology, we must wait for the results of the REVEAL trial (expected in 2014-2016) to determine the efficacy of this drug. Meanwhile, the clinical trial of Roche’s CETP inhibitor dalcetrapib, known as dal-OUTCOMES, is ongoing, with efficacy results expected in 2012-2013.

Steven Nissen, M.D. (chief of cardiovascular medicine at Cleveland Clinic), a veteran HDL researcher who has often been critical of the pharmaceutical industry, was recently interviewed on public television about the AIM-HIGH trial. He said that ever since the introduction of statins in 1987, we have not had a successful new drug class that provides significant clinical benefits by modulating serum lipids. Even when new types of lipid-modulating drugs have given apparently better biochemical results (e.g., LDL lowering or HDL raising), they have not provided clinical benefit in terms of preventing cardiovascular events.

Nevertheless, despite past disappointments with HDL-raising therapies, and despite the results of AIM-HIGH, Dr. Nissen persists in running clinical studies of novel HDL-raising drugs. He is now working on testing Resverlogix’ (Calgary Alberta, Canada) RVX-208, a small-molecule drug related to resveratrol that induces endogenous production of the protein component of HDL, apolipoprotein A1. And, as discussed in our last blog post, Dr. Nissen is enthusiastic about the prospects of Merck’s anacetrapib, although he states that the FDA will require hard clinical avoidance of this drug’s efficacy before approving it.

Statins, despite their leading role in cardiovascular therapy, only reduce the risk of heart attack and stroke by 25% to 35%. Thus there is the need for new classes of drugs, and HDL is–frustrating though it be–the next frontier. Thus researchers persist in discovery and development of HDL-raising drugs, and there are promising new candidates on the horizon.

__________________________________________

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.

Atherosclerosis. From Nephron. http://bit.ly/jL6Zos

In the April 29, 2011 issue of Cell, there is a Leading Edge review entitled “Macrophages in the Pathogenesis of Atherosclerosis”, by Kathryn J. Moore (New York University Medical Center, New York, NY ) and Ira Tabas (Columbia University, New York, NY). This 15-page  review (including 4 pages of references) covers a big subject–the central role of the macrophage in the pathogenesis of atherosclerosis, and of the resulting acute thrombotic vascular disease, including myocardial infarction, stroke, and sudden cardiac death. The review will be helpful to those who wish to update their knowledge of the mechanistic basis of atherothrombotic disease, or to those who want an introduction to the subject.

Included in the review is a discussion of the role of high-density lipoprotein (HDL), or “good cholesterol” in promoting regression of atherosclerotic plaques. HDL, as well as the protein component of HDL, apolipoprotein A1, are key players in the process of cholesterol efflux, or removal of cholesterol from macrophages in atherosclerotic plaques. HDL may also have other beneficial roles, including prevention of subendothelial apolipoprotein B-lipoprotein (apoB-LP) retention (which starts the atherosclerotic process in the first place), decreasing activation of endothelial cells, and reducing LDL oxidation. (ApoB is the protein component of low-density lipoprotein [LDL], or “bad cholesterol”.) In human populations, low HDL is generally recognized as a major cardiovascular risk factor, and high HDL is recognized as being protective.

In its discussion of therapeutic strategies based on our current picture of the mechanistic basis of atherosclerosis, the authors of the review state that the most effective way to treat the condition would be to decrease subendothelial apoB-LP retention by lowering apoB-LPs in the blood via lifestyle changes and drugs. In order to completely prevent atherosclerosis, serum apoB-LPs (i.e., mainly LDL and VLDL [very low-density lipoprotein]) would need to be lowered below the threshold level required for subendothelial apoB-LP retention in the arteries. However, in Western societies (and in other societies that have been rapidly adopting Western lifestyles), initiation of atherosclerotic lesions occurs in the early teens; thus this preventive approach is not currently feasible.

The leading drugs for lowering serum LDL are the statins, such as atorvastatin (Pfizer’s LIpitor, which is the largest-selling statin; Lipitor will go off-patent in November 2011), pravastatin (Bristol-Myers Squibb’s Pravachol, generics), simvastatin (Merck’s Zocor, generics), and rosuvastatin (AstraZeneca’s Crestor). Statins are generally accepted as being effective in decreasing mortality in patients with cardiovascular disease (CVD). These drugs are also widely prescribed for patients with a high risk of developing CVD; i.e., patients with high LDL, type 2 diabetes, and/or other risk factors. However, some researchers question the value of statins in primary prevention in patients without preexisting CVD but at high risk of developing the disease. For example, a 2010 meta-analysis published in the Archives of Internal Medicine did not find evidence that statin therapy was beneficial in primary prevention of all-cause mortality in patients at high risk of developing CVD. Moreover, although statins are highly effective in decreasing cardiovascular events (up to 60%) and cardiovascular deaths in patients with pre-existing CVD, a large percentage of patients with or at high risk of developing CVD, despite statin treatment, still experience cardiovascular events and cardiovascular death. Therefore, researchers and companies would like to develop other, complementary drugs that work via different mechanisms from the statins.

HDL raising has long been a key target for pharmaceutical and biotechnology companies in their quest to develop CVD drugs that would be complementary to the statins. In the early-to-mid 2000′s, companies had several candidate drugs, of different types, in development. In an article published by Pharmaceutical Executive in 2006, I was quoted as saying that raising HDL was a big field. However, most of the drugs being developed at that time fell by the wayside, mainly due to failure in the clinic.

A particular focus of pharmaceutical companies has been the development of cholesteryl ester transfer protein (CETP) inhibitors. CETP catalyzes the transfer of cholesteryl esters and triglycerides between LDL/VLDL and HDL, and vice versa. In vivo (in animals and in humans), CETP inhibitor drugs raise HDL and lower LDL.

The leading CETP inhibitor in the early to mid-2000s was Pfizer’s torcetrapib. Pfizer had placed high hopes on torcetrapib, as a potential blockbuster to replace anticipated lost revenues from Lipitor when it went off-patent in 2011. However, in late 2006 Pfizer pulled the drug from Phase 3 trials, after finding that combination therapy with torcetrapib  and atorvastatin gave a 50 percent greater mortality rate that atrovastatin alone. This was not only a huge disappointment for Pfizer and its shareholders, but also cast a pall of gloom over the entire HDL-raising drug field, and especially over CETP inhibitors. Researchers speculated that inhibition of CETP might result in producing a form of HDL that is not cardioprotective, and might even be harmful. There were even calls for pushing the HDL field back to the basic research level, with the need to find just how (and what form of) HDL exerted its cardioprotective effects, in people with elevated HDL due to genetics, lifestyle, or treatment with high-dose niacin (the only drug approved to raise HDL).

However, later studies of torceptrapib found that the toxicity of the compound was not due to an untoward effect of CETP inhibition or HDL raising, but was due to off-target effects of the drug. In animals and in humans, torceptrapib raised serum levels of aldosterone, via release of aldosterone from the adrenals. Aldosterone was responsible for the increase of blood pressure seen in animals and in humans treated with torceptrapib, and aldosterone has proatherogenic effects that go beyond its effects on blood pressure. The hypertensive and aldosterone-raising effects of torceptrapib were independent of its CETP inhibitor activity, and other CETP inhibitors (discussed below) do not raise aldosterone levels or blood pressure.

A March 2011 News and Analysis article in Nature Reviews Drug Discovery reviewed the history of the CETP inhibitor field after the demise of torcetrapib. Although the torcetrapib debacle caused several other companies to exit the CETP inhibitor field, Roche and Merck persisted. Roche has been developing the CETP inhibitor  dalcetrapib, and Merck’s CETP inhibitor is known as anacetrapib.

As mentioned in the Nature Reviews Drug Discovery mini-review, Dr. Alan Tall (Columbia University), working in collaboration with Merck researchers, showed in 2010 that niacin treatment in humans resulted in a 30% increase in HDL, while anacetrapib treatment resulted in a 100% increase in HDL. Niacin treatment in humans resulted in a moderate increase in the ability of HDL to promote net cholesterol efflux (measured in in vitro assays) while anacetrapib treatment caused a more dramatic increase. This was due not only to a higher level of HDL in anacetrapib-treated subjects, but also to enhanced ability of anacetrapib-induced HDL particles to promote cholesterol efflux, especially at high HDL concentrations. HDL from both niacin-treated and anacetrapib-treated subjects also exhibited anti-inflammatory activity. This study should help lay to rest the idea that pharmacological inhibition of CETP might result in abnormal pro-atherogenic HDL, as theorized by some researchers after the clinical failure of torceptrapib.

Currently, Roche’s dalcetrapib is in a 15,600-patient Phase 3 clinical trial known as dal-OUTCOMES; this trial was initiated in 2008, and efficacy results are expected in 2012-2013. As of the time of the Nature Reviews Drug Discovery article, Merck planned to initiate its 30,000-patient REVEAL trial of anacetrapib in April 2011. Efficacy results of REVEAL are anticipated in 2014-2016.

In December 2010, the results of Merck’s moderate-sized (1623 patients with or at high risk for CVD, who were already being treated with a statin) Phase 3 DEFINE trial of anacetrapib were published in the New England Journal of Medicine. The DEFINE trial was designed as a safety study. In this 76-week study, anacetrapib showed no significant differences from placebo in terms of safety, as measured by a pre-specified cardiovascular endpoint (defined as cardiovascular death, myocardial infarction, unstable angina or stroke). These cardiovascular events occurred in 16 anacetrapib-treated patients (2.0 percent) compared with 21 placebo-treated patients (2.6 percent). There were also no significant differences in blood pressure, serum electrolytes, or aldosterone levels between anacetrapib-treated and placebo-treated patients.

Anacetrapib treatment also decreased LDL by 40 percent (from 81 to 45 mg/dl vs. 82 to 77 mg/dl for placebo) and increased HDL by 138 percent (from 40 to 101 mg/dl vs. 40 to 46 mg/dl for placebo). Anacetrapib also had other favorable effects on lipid levels (e.g., 36.4% reduction in lipoprotein(a), and 6.8% reduction in triglycerides, beyond the changes seen with placebo treatment).

Although the DEFINE study was too small to provide definitive results regarding the safety of anacetrapib, it gave a 94% predictive probability that treatment with anacetrapib is not associated with the rate of cardiovascular events seen with torcetrapib. The trial also indicated that anacetrapib treatment does not result in the effects (especially raising of serum aldosterone levels) thought to be responsible for torcetrapib’s toxicity. Moreover, anacetrapib treatment resulted in a dramatic increase in HDL levels (beyond that seen with torcetrapib) in the DEFINE study, and the 2010 study by Dr. Tall and his colleagues indicates that anacetrapib-induced HDL is highly effective in promoting cholesterol efflux.

The results with anacetrapib have reignited enthusiasm for CETP inhibitors in the medical community. Even the often-critical Dr. Steven Nissen (Cleveland Clinic) expressed enthusiasm for anacetrapib. However, despite these promising results, the efficacy of CETP inhibitors, in terms of significantly reducing the rate of cardiovascular events, has not yet been demonstrated. Only large, adequately-powered Phase 3 clinical trials, such as dal-OUTCOMES for Roche’s dalcetrapib and REVEAL for Merck’s anacetrapib, can definitively establish both the efficacy and the safety of these drugs.

The development of CETP inhibitors represents a situation in which the leading drug in the class failed because of off-target effects. However, these off-target effects were not class effects, and targeting CETP in order to raise HDL now seems like a good idea after all. Pfizer ignored warning signs (especially the modest elevation in blood pressure induced by torcetrapib, which did not appear to be very significant) in pursuit of its commercial goals, while Roche and especially Merck pursued a more moderate and science-based approach to development of CETP inhibitors. Other companies stopped development of their CETP inhibitors, thus losing their opportunities in this field. Meanwhile, various companies and academic group have been developing other approaches to HDL raising, such as apolipoprotein A1 mimetics, which are in early stages of development.

Despite its early setbacks, HDL-raising drugs may turn out to be a big field after all.

_____________________________

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.

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.