Melanoma

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.

________________________________

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.

On March 1, 2011, Plexxikon, Inc. (Berkeley, CA) announced that it has agreed to be acquired by Daiichi Sankyo, Japan’s third-largest pharmaceutical company, via an all-cash purchase. Under the merger agreement, Daiichi will pay $805 million up-front to purchase Plexxikon. Near-term milestone payments associated with the approval of Plexxikon’s lead drug candidate PLX4032 could total an additional $130 million.

The main driver for the merger is Plexxikon’s lead drug, PLX4032, for the treatment of metastatic melanoma. Plexxikon and its development and commercialization partner Roche/Genentech expect to file for U.S. and European approval of PLX4032 this year; the drug is expected to reach the market in 2012. By acquiring Plexxikon, Daiichi will gain the right to co-promote the drug in the U.S. with Genentech. PLX4032 is a novel oral drug that specifically targets B-Raf kinase carrying the V600E mutation, which is present in the majority of human melanomas.

We have been covering the development of PLX4032 on the Biopharmconsortium Blog. Our most recent article, “Phase 3 trial of targeted anticancer drug PLX4032/RG7204 shows overall survival benefit in melanoma patients”, was posted on January 23, 2011. That article, which discusses the successful Phase 3 trial of PLX4032 (which Roche has designated as RG7204), includes a list of links to our earlier articles. The Phase 3 trial showed that treatment with PLX4032 gave enhanced overall survival as compared with dacarbazine (the standard of care) in previously untreated metastatic melanoma patients carrying the B-Raf(V600E) mutation. Although previous studies showed tumor shrinkage and enhanced progression-free survival (by approximately seven months) in the majority of PLX4032-treated patients as compared to dacarbazine, this is the first report that PLX4032 give enhanced overall survival.

PLX4032 is a personalized medicine, which Plexxikon has planned to pair with a companion diagnostic, developed in partnership with Roche Molecular Diagnostics. The DNA-based companion diagnostic will identify patients whose tumors carry B-Raf(V600E). The companies plan to launch PLX4032 together with the companion diagnostic, so that oncologists can readily identify patients who would benefit from treatment with the drug.

In acquiring Plexxikon, Daiichi also gains a pipeline that includes the kinase inhibitor PLX3397, which is in Phase 1 safety studies, with Phase 2 studies planned in metastatic breast cancer, and PLX-204, an oral PPAR alpha, gamma, and delta partial agonist that is In Phase 2 clinical trials in type 2 diabetes.

Daiichi will also gain Plexxikon’s drug discovery and development technology and strategy. We discussed how Plexxikon used its proprietary scaffold-based drug design technology platform to discover PLX4032, in our March 10, 2010 article on this blog. Daiichi says that it plans to “provide a high degree of independence to the Plexxikon group to support their continuing success,” and to leverage Plexxikon’s technology platform to discover and develop newer drug candidates.

Daiichi’s purchase of Plexxikon is part of a recent trend, in which the leading Japanese pharmaceutical companies have been investing in  oncology R&D in the United States. Two of these investments were large acquisitions. In 2008, Takeda acquired Millennium Pharmaceuticals (Cambridge, MA) for $8.8 billion; Takeda operates its acquisition, renamed Millennium: The Takeda Oncology Company, as a wholly-owned subsidiary. Astellas acquired OSI (Melville, NY) for $4 billion in 2010; OSI also operates as a wholly-owned subsidiary.  Both of the acquired companies boast large-selling drugs–Millennium’s Velcade (bortezomib) and OSI’s Tarceva (erlotinib) (which is partnered with Genentech/Roche).

The Japanese pharmaceutical companies aim to utilize U.S. innovation to compete in the lucrative global oncology market, which analysts project will expand 12 to 15 percent per year, reaching as much as $80 billion by 2012. In contrast, annual sales growth for Japanese pharmaceutical companies is projected to average 1.4 percent from 2009 to 2015. Overseas investments by Japanese companies are also being driven by a strong yen; the yen gained 8 percent gain over the dollar during the past year.

Some analysts believe that Daiichi paid too much for Plexxikon, and that even with the Plexxikon acquisition, Daiichi will not be very competitive in oncology with Takeda and Astellas, each of which acquired much larger U.S. oncology companies. Moreover, Daiichi has other issues to deal with, such as slow sales for its oral antiplatelet agent Effient (Prasugrel) (codeveloped with Lilly, and approved in 2009), which Daiichi hoped would be a blockbuster drug. Moreover, Daiichi’s majority-owned Indian generic drug company Ranbaxy has experienced a fourth-quarter loss due to rising operating expenses.

In addition to its acquisition of Plexxikon, Daiichi is also codeveloping (with ArQule, of Woburn MA) ARQ 197, a c-Met kinase inhbitor; this compound is in Phase 3 clinical trials in non-small cell lung cancer (NSCLC). Daiichi also acquired German oncology firm U3 Pharma (Martinsried, Germany) for $235 million in 2008. U3 Pharma (which operates as a wholly-owned subsidiary of Daiichi) is developing MAb-based anticancer therapies. Daiichi also, in 2007, licensed Japanese development and commercialization rights to Amgen’s MAb drug denosumab. Denosumab, marketed as Xgeva, was approved in the U.S. in 2010 for prevention of skeletal-related events in patients with bone metastases of solid tumors.

Will the acquisition of Plexxikon help Daiichi to compete in the worldwide oncology market, with its Japanese rivals and with other pharmaceutical companies? Only time will tell. PLX4032 is an exciting, breakthrough medicine that is likely to be approved in 2012. Moreover, if Daiichi allows Plexxikon the freedom to innovate and invests in its R&D activity, and if it can also harness Plexxikon’s technology platform to discover and develop novel drugs across different therapeutic areas, the Plexxikon acquisition may prove to be a major competitive advantage despite its small size.

________________________________

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.

PLX4032

On January 19, 2011, Plexxikon and Roche announced the results of an interim analysis of a large multicenter Phase 3 clinical study (the BRIM3 trial) of the targeted anticancer drug PLX4032 (which Roche has designated as RG7204). PLX4032 is a kinase inhibitor that is exquisitely specific for B-Raf carrying the V600E mutation [B-Raf(V600E)]. This is the most common somatic mutation found in human melanomas (accounting for approximately 50% of cases of this disease), and is a “driver mutation” that is particularly critical for the malignant phenotype of human metastatic melanomas that carry the mutation.

According to the Plexxikon and Roche press releases, the Phase 3 trial met its prespecified criteria for co-primary endpoints of overall survival and progression-free survival, as compared to a control arm, in which patients were treated with the current standard of care, dacarbazine. The safety profile was consistent with previous clinical studies of the drug.

Based on the results of the interim analysis, patients in the dacarbazine arm of the study will have the option to crossover to receive PLX4032. Moreover, the Expanded Access Program will be opened to previously untreated melanoma patients whose tumors carry the B-Raf(V600E) mutation. As the companies announced in November 2010, as the result of widespread demand from patients, oncologists, and patient advocates, they had been in discussion with global regulatory authorities regarding an Expanded Access Program for PLX4032. In late December 2010, the Expanded Access Program for PLX4032 was initiated. A cofounder of one of the patient advocate organizations pushing for expanded access to PLX4032 prior to its FDA approval, the Abigail Alliance, commented on this issue on our blog in November 2010.

The big news in Plexxikon and Roche’s report on the BRIM3 trial is that treatment with PLX4032 gave enhanced overall survival as companied with dacarbazine in previously untreated metastatic melanoma patients carrying the B-Raf(V600E) mutation. Although previous studies showed tumor shrinkage and enhanced progression-free survival (by approximately seven months) in the majority of PLX4032-treated patients as compared to dacarbazine, this is the first report that PLX4032 give enhanced overall survival. However, the companies did not report the extend of the enhanced overall survival. They plan to present comprehensive data from the BRIM3 trial at a major scientific meeting later this year. We expect that in due course the researchers that have been conducting the trial will publish the results in a peer-reviewed medical journal, as in the case of the published Phase 1 trial.

On November 8, 2010, Plexxikon and Roche reported preliminary results of a parallel open-label Phase 2 trial (designated BRIM2) of PLX4032 in previously treated metastatic melanoma patients whose tumors carried the B-Raf(V600E) mutation. Researchers who had been conducting that trial presented the data at the Seventh Annual International Melanoma Research Congress of the Society for Melanoma Research (SMR) in Sydney, Australia. Consistent with earlier Phase 1 trials, the BRIM2 trial showed that of the 132 patients enrolled, 3 patients had complete responses, and 66 had partial responses (i.e., tumor shrinkage of over 30 percent). The overall response rate was 52 percent, with a median duration of response of 6.8 months. At the time the results were reported, it was too early to gauge overall survival.

The Biopharmconsortium Blog has been following the PLX4032 story since March 2010. We have published several articles on the drug and on related scientific, clinical trial strategy, and business issues:

https://biopharmconsortium.com/blog/2010/03/02/bringing-targeted-therapy-of-metastatic-melanoma-into-the-clinic-the-crucial-role-of-translational-researchers/

https://biopharmconsortium.com/blog/2010/03/10/plexxikon’s-discovery-of-plx4032-a-selective-targeted-therapeutic-for-metastatic-melanoma/

https://biopharmconsortium.com/blog/2010/08/27/phase-i-trial-of-plx4032-a-selective-therapeutic-for-metastatic-melanoma-published-in-nejm/

https://biopharmconsortium.com/blog/2010/10/13/translational-research-in-cancer-makes-a-big-splash-in-nature-part-1/

https://biopharmconsortium.com/blog/2010/10/25/translational-research-in-cancer-makes-a-big-splash-in-nature-part-2/

The last two articles discuss the novel personalized medicine (or “stratified medicine”) hypothesis-testing clinical trial strategy, which is especially applicable to highly targeted oncology drugs (such as PLX4032) for which the relevant biomarkers are available.

The dramatic results of the Phase 1 trials of PLX4032 (now confirmed by Phase 2 and Phase 3 trials) led some oncologists, as well as patient advocates, to question the ethics of conducting standard controlled Phase 3 trials in which some patients were placed in a dacarbazine arm.  This question might apply to other drugs for cancer and other very serious diseases for which personalized medicine hypothesis-testing clinical trials indicate superior performance as compared to the standard of care. Such cases would at least call for establishment of  Expanded Access Programs for such drugs, on a case-by-case basis.

The clinical trial community, as well as regulatory agencies such as the FDA and the European Medicines Agency, also need to continue to monitor and study the progress of the personalized medicine hypothesis-testing clinical trial strategy. This may led to modifications in clinical trial standards for approval if they deem they are warranted. We can also expect that patient advocates (including M.D. and non-physician advocates), as well as other stakeholders (e.g., third party payers) would be participating in that process.

In parallel with the development of PLX4032, Plexxikon and Roche Molecular Diagnostics are developing a DNA-based companion diagnostic to identify patients whose tumors carry B-Raf(V600E). The companies plan to launch PLX4032 together with the companion diagnostic, so that oncologists can readily identify patients who would benefit from treatment with the drug.

Despite the dramatic results with PLX4032, so far all patients treated with the drug eventually suffer relapses, and die of their disease. This presumably occurs because a fraction of tuner cells develop resistance to PLX4032. Oncologists, especially those who have been involved in the clinical trials of the drug, therefore advocate using PLX4032 as the basis for potentially still more effective treatments, especially combination therapies.

With respect to combination therapies, on January 6, 2011, Plexxikon announced that it had signed an agreement with Genentech (a member of the Roche group) to co-promote PLX4032 (RG7204) in the United States. Plexxikon will also codevelop PLX4032 with Genentech in addition to Roche. Plexxikon and Genentech are planning, beginning in the first quarter of 2011, to begin a Phase 1b clinical trial of a combination therapy of PLX4032 and Exelixis/Genentech’s oral, small-molecule MEK inhibitor RG7420/GDC-0973. MEK is downstream from B-Raf in the signaling pathway by which B-Raf(V600E) acts to produce the malignant phenotype. Researchers studying mechanisms by which PLX4032 resistance occurs have found evidence that suggests that combination therapy with PLX4032 and a MEK inhibitor may overcome resistance that occurs via some mechanisms. More generally, studies of mechanisms of PLX4032 resistance may provide means of developing specific combination therapies for different mechanisms of resistance, and of stratifying patients to determine which particular personalized combination therapy will best treat their disease.

______________________________

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.

Citric acid cycle

The 3 December issue of Science featured a Special Section on metabolism, headed by an introductory article entitled “Metabolism is Not Boring”.

Way back in the 1920s through the 1950s, intermediary metabolism was a hot field of biology. This culminated in the awarding of the Nobel Prize in Physiology or Medicine in 1953 to Hans Krebs “for his discovery of the citric acid cycle” and Fritz Lipmann “for his discovery of co-enzyme A and its importance for intermediary metabolism”.

As most of you know, that same year, 1953, Watson and Crick published the structure of DNA, which won them the Nobel Prize in Physiology or Medicine in 1962. This began the great era of molecular biology. As the result of the overwhelming success of molecular biology, the study of intermediary metabolism receded into the background. Answering most questions in leading-edge biology required little or no attention to intermediary metabolism. However, as discussed in the review article by Steven L. McKnight included in the Special Section, metabolism is coming to the forefront of biomedicine again. Research problems that require both consideration of molecular biology and of metabolism now appear as interesting and important challenges.

Considerations of intermediary metabolism have always been important in the study of what are known as metabolic diseases, especially type 2 diabetes and obesity and such related conditions as dyslipidemia. However, as detailed both in the McKnight article and in an article by Arnold J. Levine and Anna M. Puzio-Kuter, the study of intermediary metabolism has now also become important in cancer, with the discovery that alterations in metabolic enzymes can result in the production of “oncometabolites” that support the growth of cancer cells.

In an article on this blog dated December 31, 2009, we discussed research in cancer metabolism that is behind the technology platform of Agios Pharmaceuticals (Cambridge, MA). In that article, we highlighted the discovery that mutations in a metabolic enzyme, cytosolic isocitrate dehydrogenase (IDH1) are a causative factor in a major subset of human brain cancers. The wild-type form of IDH1 catalyzes the NADP+-dependent oxidative decarboxylation of isocitrate to α-ketoglutarate. However, the mutant forms of IDH1 catalyzes the NADPH-dependent reduction of α-ketoglutarate to R(-)-2-hydroxyglutarate (2HG). 2HG appears to be an oncometabolite that is involved in the progression of low-grade gliomas to lethal secondary glioblastomas. Agios researchers and their academic collaborators later implicated mutations in isocitrate dehydrogenase enzymes and the production of the oncometabolite 2HG in the pathogenesis of acute myelogenous leukemia (AML).

Also discussed in our article was the Warburg effect, in which cancer cells carry out aerobic glycolysis (conversion of glucose to lactate, with the production of 2 molecules of ATP even in the presence of oxygen). In contrast, most normal mammalian cells metabolize glucose to CO2 and water via glycolysis coupled to the mitochondrial citric acid cycle, generating 36 molecules of ATP. Agios scientific founder and signal-transduction pioneer Lewis Cantley showed that there is a connection between growth factor-mediated signal transduction and aerobic glycolysis in cancer cells. In particular, Dr. Cantley and his colleagues found that pyruvate kinase M2 (PKM2) is a link between signal transduction and aerobic glycolysis. PKM2 binds to tyrosine-phosphorylated signaling proteins, which results in the diversion of glycolytic metabolites from energy production via mitochondrial oxidative phosphorylation to anabolic processes required for rapid proliferation of cancer cells.

The McKnight and Levine and Puzio-Kuter papers also discuss the Warburg effect in cancer cells, and the role of mutations in several metabolic enzymes that contribute to malignant phenotypes. The McKnight article notes that in addition to dominant mutations in isocitrate dehydrogenates, rare recessive mutations in fumarate hydratase and succinate dehydrogenase are also associated with cancer. Mutations in the genes for these enzymes, coupled with loss of the wild-type allele, result in elevated intracellular levels of fumarate and succinate, respectively. These appear to act as oncometabolites that can induce activation of the hypoxia response pathway, which triggers the induction of aerobic glycolysis (the Warburg effect) and angiogenesis.

The Levine and Puzio-Kuter paper also discusses the role of oncogenes and tumor suppressor genes and their signaling pathways in regulating metabolism and in particular in inducing the Warburg effect. For example, p53 regulation suppresses the Warburg effect and promotes mitochondrial oxidative metabolism. Thus the loss of p53 function seen in most human cancers tends to promote aerobic glycolysis. Other signaling pathways that have been implicated in cancer-associated changes in metabolism include the Akt and mTOR pathways, which are frequently altered by mutations in key genes (e.g., mutations in PTEN and amplifications of such growth factor receptors as Her2 and EGFR) in cancer.  Deregulation of these pathways activates the hypoxia response pathway, thus triggering the Warburg effect.

Levine and Puzio-Kuter suggest that research aimed at a deeper understanding of how cancer-associated signaling pathways regulate biochemical metabolic pathways and trigger the Warburg effect, and the role of the Warburg effect in the pathogenesis of cancer, may lead to novel drug discovery strategies in oncology.

The Special Section on metabolism also includes an article on autophagy, a process by which cells break down cellular components in order to eliminate damaged biomolecules and organelles or to provide substrates for metabolism in case of starvation. Although autophagy promotes the health of cells and can prevent degenerative diseases, it can also enable cancer cells to survive in nutrient poor tumors.

There is also a review by Jay Keasling on metabolic engineering to produce such substances as natural product drugs, chemicals, and biofuels. Metabolic engineering is a branch of synthetic biology that engineers metabolic pathways to produce such substances, hence the inclusion of this review in the Special Section on metabolism. We have several articles on synthetic biology on this blog, most of which focus on metabolic engineering and its role in drug manufacture and drug discovery.

All in all, the 3 December Special Section on metabolism is worth reading by basic researchers, and by drug discovery and development researchers in biotechnology and pharmaceutical companies. It may broaden your perspectives, and lead to new ideas for R&D or partnering, especially in oncology drug discovery.
___________________________________________________

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.

Resveratrol

In statements to Fierce Biotech and to the Myeloma Beacon, GlaxoSmihtKline (GSK) said that it has stopped all development of its proprietary resveratrol formulation SRT501. Thanks also to the “In the Pipeline” blog for the information on the Myeloma Beacon statement.

As you all may recall, GSK acquired the sirtuin-pathway specialty company Sirtris (Cambridge, MA) for $720 million in June 2008. This gave GSK ownership of Sirtris’ sirtuin modulator drugs, including SRT501. GSK also appointed Christoph Westphal, then CEO of Sirtris, as the Senior Vice President of GSK’s Centre of Excellence in External Drug Discovery (CEEDD), and Michelle Dipp, then vice president of business development at Sirtris, as Vice President and the head of the US CEEDD at GSK.

According to the Fierce Biotech article, the precipitating factor in GSK’s decision to halt development of SRT501 was the result of a Phase 2a study of the drug in advanced multiple myeloma. The company suspended the study after several patients developed kidney failure. GSK said that in its analysis, the company concluded that SRT501 “may only offer minimal efficacy while having a potential to indirectly exacerbate a renal complication common in this patient population.” It then said that the company has “no further plans to develop SRT501.”

Instead, GSK intends to focus on development of Sirtris’ non-resveratrol synthetic selective sirtuin 1 (SIRT1) activators, which in addition to their greater potency, have more favorably drug-like properties. In its statement to the Myeloma Beacon, GSK in particular mentioned SRT2104 and SRT2379 as the focus of its continuing activity. According to the Sirtris website, SRT2104 is in Phase 2 studies in metabolic and cardiovascular disease, and SRT2379 is in Phase 1 studies in healthy volunteers. Neither compound is currently being tested in cancer.

We discussed Sirtris’ SIRT1 activators in the context of the anti-aging biology field, in a February 10, 2010 blog post. In summary, the mechanism of action of reseveratrol and of Sirtris/GSK’s sirtuin activators is unclear. They apparently activate multiple targets, and they may not be direct SIRT1 activators at all. Nevertheless, Sirtris’ studies of these compounds in mice indicate that they have efficacy in treatment of metabolic diseases. The Phase 2 clinical trials in humans are still ongoing.

To complicate matters further, a study published in the journal Diabetes in March 2010 by NIH researcher Jay H. Chung and his colleagues indicates that resveratrol works indirectly, via the energy sensor AMP-activated protein kinase (AMPK), to activate sirtuins. Since activation of AMPK increases fatty acid oxidation and upregulates mitochondrial biogenesis, the effect of resveratrol on AMPK may be more important than its more indirect activation of sirtuins, at least in the case of metabolic diseases.

Thus Sirtris/GSK’s “sirtuin activators” are under a cloud.

However, as we discussed in our blog posts of November 8, 2009 and February 10, 2010, basic research on anti-aging biology has yielded ample material for drug discovery which may eventually lead to novel treatments for metabolic diseases, and perhaps for other conditions such as various cancers. For example, several companies are developing AMPK activator drugs. Thus there are other avenues for harnessing basic research on anti-aging pathways to discover and develop novel drugs for multiple conditions, even if the Sirtris compounds prove to be a dead end.

_______________________________________________________

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.