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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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.

 

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.

 

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.

On March 25, 2011, the FDA approved ipilimumab (Medarex/Bristol-Myers Squibb’s [BMS’s] Yervoy) for treatment of unresectable or metastatic melanoma. The drug has been approved for patients with either newly-diagnosed or previously-treated disease.

According to Richard Pazdur, the director of the FDA’s office of oncology drug products, none of the previously-approved treatments for metastatic melanoma, a disease with a poor prognosis, prolonged a patient’s life. “Yervoy is the first therapy approved by the FDA to clearly demonstrate that patients with metastatic melanoma live longer by taking this treatment.”

We discussed ipilimumab briefly in a previous article on this blog. As we stated in that article, the results of a Phase 3 trial of ipilimumab were published in the August 19, 2010 issue of the New England Journal of Medicine.  Ipilimumab is an immunomodulator that blocks cytotoxic T-lymphocyte-associated antigen 4 (CTLA4) to potentate an antitumor T-cell response. The drug is a monoclonal antibody (MAb). In this NEJM article, the researchers reported that ipilimumab treatment–given with or without a gp100 peptide vaccine–showed a median overall survival of 10 months, as compared to 6.4 months in patients receiving gp100 alone. Ipilimumab treatment also gave improved one-year survival compared with gp100 alone–46% versus 25%. Two-year survival was 24% in the ipilimumab group and 14 percent in the gp100 group.

Decision Resources published our report on development of immunomodulators in treatment of cancer in 2007. This report includes a discussion of ipilimumab, and provides further information on its mechanism of action, adverse effects, etc., as well as on other immunomodualtors for treatment of cancer, some of which are now on the market.

BMS plans to report on the results of a later Phase 3 study, which also demonstrated significantly improved survival as compared to a control treatment, at the American Society of Clinical Oncology (ASCO) meeting in Chicago in June.

In its March 25, 2011 press release, BMS said that it had agreed with the FDA to conduct a post-marketing study comparing the safety and efficacy of the 3 mg/kg dose vs. an investigational 10 mg/kg dose in patients with unresectable or metastatic melanoma.

The Full Prescribing Information for ipilimumab will include a boxed warning for immune-mediated adverse effects. Ipilimumab treatment can result in severe or fatal immune-mediated adverse effects, especially enterocolitis, hepatitis, dermatitis, neuropathy, or endocrinopathy. These are usually reversible by discontinuing  ipilimumab therapy and treatment with high-dose steroids. According to the FDA, severe to fatal autoimmune reactions were seen in 12.9% of patients treated with the drug.

As part of the approval of ipilimumab, BMS is collaborating with the FDA to develop a Risk Evaluation and Mitigation Strategy,  to help inform patients and providers about these safety risks. The company  has put in place a system that will enable it to deliver these educational materials to healthcare professionals at the time they order the drug.

Strategic implications for BMS

BMS has hailed the approval of ipilimumab as a victory for its strategic changes over the past several years. The company has been focusing on its pharmaceutical business, selling off such nonpharmaceutical assets as the Mead Johnson Nutrition Company (MJN), and instituting other cost-cutting measures. BMS has at the same time been developing its “String of Pearls” strategy. In this strategy, BMS has been forming a series of acquisitions, alliances and partnerships with biopharmaceutical companies, involving both small molecules and biologics. According to BMS, the String of Pearls strategy has enabled BMS to expand its pipeline by nearly 40 percent. About one-third of BMS’ pipeline drugs are now biologics.

We have discussed the String of Pearls strategy, and two acquisitions that have been part of it, on this blog. These were the acquisition of Medarex (the largest of the “pearls”), and the newest acquisition, ZymoGenetics. It was MAb-therapeutic leader Medarex, now a wholly-owned subsidary of BMS, that initially developed ipilimumab.

BMS faces the expiration of patent protection for its best-selling product,  the anticlotting drug Plavix, in 2012. The introduction of ipilimumab, which several analysts expect to become a blockbuster, should help mitigate the results of the Plavix patient expiration. However, ipilimumab is not likely to fully replace the lost sales due to generic competition with Plavix. Moreover, the approval of one drug–ipilimumab–does not necessarily mean that BMS’ new R&D strategy, based on the String of Pearls acquisitions and partnerships, will yield a rich series of important approved drugs in the next 5-10 years. However, ipilimumab itself is such an important drug, in terms of its path-breaking mechanism of action, its addressing unmet medical need in a fatal disease, and its likely blockbuster status.

Another melanoma drug is on the way

The Biopharmconsortium Blog has been following the development of Daichi Sankyo/Plexxikon/Roche’s PLX4032/RG7204 (now designated as vemurafenib) for about a year. We have published several articles on the drug and on related scientific, clinical trial strategy, and business issues. This targeted kinase inhibitor, which is exquisitely specific for the melanoma driver mutation B-Raf(V600E), has been in Phase 3 clinical trials, and its developers filed for U.S. and European approval in May 2011. The drug is expected to reach the market in 2012. As with ipilimumab, Plexxikon and Roche reported that a Phase 3 trial of PLX4032 gave enhanced overall survival as compared with treatment with the standard of care, dacarbazine. The companies also plan to present the results of this trial at the ASCO meeting in June.

Metastatic melanoma patients, who have had few options for treatment, will now have two new, breakthrough drugs that can give them additional months of life, and in some cases longer. However, no treatment now on the horizon will result in long-term survival. In the case of PLX4032, this is due to the development of resistance to the drug. As we discussed previously, researchers are studying mechanisms of PLX4032 resistance, and developing potential combination therapies to overcome it. A clinical trial of at least one combination therapy, in collaboration with Genentech, is planned to begin soon.

A new approach to PLX4032-based combination therapy for melanoma

Meanwhile, another approach to development of an effective combination therapy with PLX4032 comes from an unexpected source.

We had discussed a zebrafish model of melanoma, developed by Leonard Zon’s laboratory at Children’s Hospital/Howard Hughes Medical Institute/Harvard Medical School (Boston, MA), in our 2010 Insight Pharma Report Animal Models for Therapeutic Strategies. In this model, the researchers created transgenic zebrafish strains in which B-Raf(V600E) is expressed under control of the melanocyte-specific mitfa promoter. Wild-type zebrafish expressing B-Raf(V600E) in their melanocytes developed benign nevi, while those with germline mutations in p53 may develop either nevi or melanomas. This suggests these two mutations are necessary, but not sufficient, to cause melanoma. (In humans, nevi may express B-Raf(V600E), which also indicates that it is not sufficient to cause melanoma. And in human melanomas, p53 is either mutated or otherwise rendered inactive.)

Now, in the 24 March issue of Nature, Dr. Zon and his colleagues used this model to study the mechanism of tumorigenesis in melanoma. They found that early-stage embryos of the transgenic zebrafish showed abnormal expansion of neural crest progenitors, and that these progenitors failed to terminally differentiate. (Melanocytes are one of the cell types that develop from the neural crest lineage.) In adult transgenic zebrafish, melanomas develop and are positive for neural crest progenitor markers, and thus appear to retain a neural crest progenitor-like phenotype.

The researchers therefore screened 2,000 compounds to identify those that act as suppressors of neural crest progenitors, without displaying toxicity. The one compound that satisfied these criteria, NSC210627, was similar to brequinar, an inhibitor of dihydroorotate dehydrogenase (DHODH), and NSC210627 also inhibited DHODH in vitro. The researchers therefore tested another more readily-available DHODH inhibitor, leflunomide (Sanofi-Aventis’ Arava). It had the same effects on the zebrafish as NSC210627 and was used for further studies.

Leflunomide treatment resulted in a nearly complete inhibition of neural crest development in zebrafish embryos, and specifically resulted in abrogation of melanocyte development both in zebrafish embryos and in Xenopus (African clawed frog) embryos. The drug’s target, DHODH, catalyzes a step in the synthesis of pyrimidine nucleotides, and thus inhibits transcriptional elongation. The researchers found that leflunomide caused specific defects in the transcriptional elongation of genes necessity for neural crest development in zebrafish. In human melanoma cell lines, leflunomide also inhibited transcriptional elongation in genes necessary for neural crest development and for melanoma growth (e.g, the Myc oncogene, which is required for both processes). Leflunomide (or its active metabolite, A771726) caused inhibition of growth both of human melanoma cell lines in vitro and in vivo in mouse xenograft models, but had little effect on non-melanoma cell lines in vitro. Combined treatment with leflunomide and PLX4032 showed even greater inhibition of growth of human melanoma cells in vitro and in vivo than treatment with either single agent.

Leflunomide is a marketed drug that is approved for treatment of moderate to severe rheumatoid arthritis and psoriatic arthritis. In these diseases, it appears to work via inhibiting the expansion of autoimmune lymphocytes by inhibiting transcriptional elongation in specific genes in these cells. Although leflunomide can have serious adverse effects in a minority of patients (e.g., liver damage), it has a generally favorable safety profile. Dr. Zon and his colleagues suggested that combination therapy of patients whose tumors are positive for B-Raf(V600E) with PLX4032 and leflunomide would be more effective than treatment with either drug alone, and that this combination therapy might help to overcome PLX4032 resistance.

Since leflunomide is already approved by the FDA, and both leflunomide and PLX4032 have been proven to be safe in clinical trials, researchers should be able to readily initiate clinical trials of the combination therapy. Dr. Zon says that  he is now working toward initiation of a clinical trial of the drug combination.

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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.