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.
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