The American Society of Clinical Oncology (ASCO) held its 2012 Annual Meeting on June 1-5, 2012. Arguably the highlight of the meeting was the June 2, 2012 presentation by Bristol-Myers Squibb (BMS) on its Phase 1 immunotherapeutic, anti-PD-1 (BMS-936558). The results of this study were also published ahead of print on June 2, in the online version of the New England Journal of Medicine. Nature published a “News in Focus” article on the same subject by Nature staff writer Erika Check Hayden in its 6 June issue.
BMS acquired its anti-PD-1 MAb product BMS-936558 (MDX-1106) via its 2009 acquisition of Medarex. This is the same way in which BMS acquired its now-marketed immunotherapy, ipilimumab (Yervoy), which was approved by the FDA in March 2011. Both BMS-936558 and ipilimumab are monoclonal antibodies (MAbs). Ono Pharmaceuticals has been a partner in the development of anti-PD-1 MAb since its original collaboration with Medarex; Ono retains the right to exclusively develop and market the agent (which is also designated as ONO-4538) in Japan, Korea and Taiwan.
PD-1 (“programmed cell death-1”) is a receptor on the surface of activated T lymphocytes of the immune system. PD-1 is a member of the CD28/CTLA4 family of T cell regulators. Like CTLA4, the target of ipilimumab, PD-1 is a negative regulator of T-cell receptor signals. When a protein on the surface of some tumor cells, known as PD-1 ligand (PD-L1), binds to PD-1 on T cells that recognize antigens on these tumors cells, this results in the blockage of the ability of the T cells to carry out an anti-tumor immune response. Anti-PD-1 MAb binds to PD-1 on T cells, thus preventing PD-L1 on tumor cells from binding to the PD-1 and initiating an inhibitory signal. Anti-tumor T cells are then free to initiate immune responses against the tumor cells. This mechanism of action is completely analogous to that of ipilimumab, which binds to CTLA4 and thus prevents negative signaling from that molecule.
Phase 1 clinical study of Medarex/BMS’s anti-PD-1
The Phase 1 clinical study was carried out by a multi-institution team of investigators, led by Suzanne L. Topalian, M.D. (Johns Hopkins University School of Medicine, Baltimore, MD.) The researchers enrolled patients with advanced melanoma, non-small-cell lung cancer (NSCLC), prostate cancer, renal cell cancer (RCC), or colorectal cancer. Patients received anti-PD-1 at a dose between 0.1 and 10.0 milligrams per kilogram of body weight every two weeks. Tumor response was determined after each 8-week treatment cycle. Patients received up to 12 cycles of treatment until either unacceptable adverse events, disease progression or a complete response occurred. A total of 296 patients received treatment through February 24, 2012.
Among the 236 patients in whom tumor responses could be evaluated, objective responses were observed in patients with NSCLC, melanoma, or RCC. Cumulative response rates (among patients treated with all doses of anti-PD-1) were 18% among patients with NSCLC, 28% among patients with melanoma, and 27% among patients with RCC. These responses were durable–20 of 31 responses lasted 1 year or more in patients with 1 year or more of follow-up. Anti–PD-1 produced objective responses in approximately one in four to one in five patients with NSCLC, melanoma, or RCC.
In addition to patients with objective responses, other patients treated with anti-PD-1 exhibited stable disease lasting 24 weeks or more–5 patients (7%) with NSCLC, 6 patients (6%) with melanoma, and 9 patients (27%) with RCC.
Significant drug-related adverse effects were seen in 11% of the patients, including three deaths due to pulmonary toxicity. In most cases, adverse effects were reversible, and the observed adverse-event profile does not appear to preclude the use of the drug. A maximum tolerated dose was not reached in this study.
The exciting finding of this study is that anti-PD-1 produced durable responses not only in melanoma and RCC (the two types of cancer that are deemed to be “immunogenic”), but also in NSCLC, a much more common cancer that kills more people per year than any other cancer. Moreover, response rates with anti-PD-1 were much higher that those achieved with the other recently approved immunotherapeutics. In the Phase 3 clinical trial of ipilimumab that led to its approval, this drug gave response rates of 11% in melanoma patients. The other recently approved immunotherapeutic, the prostate cancer-specific dendritic cell vaccine Sipuleucel-T (Dendreon’s Provenge, APC8015), gives very low response rates and no complete responses. According to Antoni Ribas (Jonsson Comprehensive Cancer Center, University of California, Los Angeles CA) as quoted Ms. Hayden’s Nature “News in Focus” review, if an immunotherapy “breaks the 10% ceiling” as did anti-PD-1, it becomes “even more important and clinically relevant”.
Despite the exciting efficacy results with anti-PD-1, and despite the fact that it was deemed that the adverse-event profile did not appear to preclude the use of the drug, researchers would still like to get away from the serious adverse effects (including three deaths) seen with anti-PD-1. As with other immunotherapeutics (e.g., ipilimumab), researchers hypothesize that anti-PD-1’s serious adverse effects were due to autoimmune responses.
Phase 1 clinical study of Medarex/BMS’ anti-PD-L1
A potential way of achieving similar efficacy to anti-PD-1 with an improved safety profile is provided by another Phase 1 immunotherapeutic, anti-PD-L1. Anti-PD-L1 MAb drugs are being developed by Medarex/BMS, Roche/Genentech, and other companies. As mentioned earlier, PD-L1 is the binding partner of PD-1 that is expressed on some tumor cells. As quoted in the Nature “News in Focus” review, Ira Mellman (vice-president of research oncology at Genentech), believes that anti-PD-L1 might have fewer adverse effects than anti-PD-1. That is because anti-PD-L1 would target tumor cells while leaving T cells free to participate in immune networks that work to prevent autoimmune reactions.
The results of a Phase 1 clinical study of BMS/Medarex’ anti-PD-L1 (also known as MDX-1105) were also published ahead of print in the online version of the New England Journal of Medicine on June 2, 2012; this was a “companion study” to the Phase 1 study of anti-PD-1. This study was also carried out by a multi-institution team of investigators, led by Julie R. Brahmer, M.D. (Johns Hopkins University School of Medicine, Baltimore, MD.); Dr. Topalian, among other investigators on the anti-PD-1 trial, also participated in the study.
This Phase 1 trial was a dose escalation study that was carried out via a similar protocol to the anti-PD-1 trial discussed earlier. As of February 24, 2012, a total of 207 patients — 75 with NSCLC, 55 with melanoma, 18 with colorectal cancer, 17 with RCC, 17 with ovarian cancer, 14 with pancreatic cancer, 7 with gastric cancer, and 4 with breast cancer — had received anti–PD-L1 antibody, for a median duration of 12 weeks. Among patients with an evaluable response, an objective response (i.e., a complete or partial response) was seen in 17% of patients with melanoma, 12% of patients with RCC, 10% of patients with NSCLC, and 6% of patients with ovarian cancer. Responses lasted for 1 year or more in 8 of 16 patients with at least 1 year of follow-up. Prolonged disease stabilization was seen in 12-41% of patients with advanced cancers, including NSCLC, melanoma, and RCC.
Significant drug-related adverse effects were seen in 9% of patients.
Although the two agents were not compared directly in a randomized trial, the frequency of objective responses for anti–PD-L1 MAb appears to be somewhat lower than that observed for anti–PD-1 MAb in initial Phase 1 trials; the frequency and severity of significant drug-related adverse events also appears to be lower. However, whether these differences will hold up in Phase 2 and 3 clinical trials remains to be determined. The clinically appropriate dose of anti–PD-L1 will also require further definition later studies. Nevertheless, the Phase 1 trial showed that anti-PD-L1 MAb induced durable tumor regression (objective response rate of 6-17%) and prolonged disease stabilization (rate of 12-41% at 24 weeks) in patients with select advanced cancers, including NSCLC, a tumor type that had been deemed to be “non-immunogenic”. This is essentially the same result that was observed for anti-PD-1MAb.
A predictive biomarker for treatment with anti-PD-1?
As with other modes of cancer therapy, it would be very useful to have mechanism-based predictive biomarkers to identify appropriate candidates for treatment with anti-PD-1 or anti-PD-L1 immunotherapy. The findings of the Phase 1 anti-PD-1 study suggest that PD-L1 expression in tumors is a candidate biomarker that warrants further evaluation for use in selecting patients for immunotherapy with anti–PD-1 MAb. The researchers found that 36% of patients with PD-L1–positive tumors achieved an objective response, while no patients with PD-L1–negative tumors achieved such a response. These results suggest that PD-L1 expression on the surface of tumor cells in pre-treatment tumor specimens may be associated with an objective response. However, further studies will be necessary to define the role of PD-L1 as a predictive biomarker of response to anti–PD-1 therapy. Similarly, it appears reasonable that tumor expression of PD-L1 may be a predictive biomarker of response to anti-PD-L1 therapy. However, this hypothesis must also be tested in further clinical studies.
Further studies of anti-PD-1 MAb
Two studies of BMS-936558/MDX-1106 anti–PD-1 MAb, both in advanced/metastatic clear-cell RCC, are now recruiting patients. One trial is a Phase 1 biomarker study involving immunologic and tumor marker correlates of efficacy (progression-free survival and tumor response). The other trial is a Phase 2 efficacy (progression-free survival and tumor response) study; this is a dose ranging study that is designed to determine if a dose response exists. Phase 3 studies of BMS-936558/MDX-1106 anti–PD-1 MAb for the treatment of non–small-cell lung cancer, melanoma, and renal-cell cancer are also being planned.
The exciting results of the studies with BMS’ anti-PD-1 and anti-PD-L1 have only been in Phase 1 studies. Thus caution is advisable in interpreting these results, pending the results of further clinical studies. Nevertheless, these results, together with the recent approval of ipilimumab (Medarex/Bristol-Myers Squibb’s Yervoy) and of Sipuleucel-T (Dendreon’s Provenge), indicate that cancer immunotherapy, a field that not so long ago was regarded as an impractical dream, is very much alive and well. In addition to clinical development and approval of immunotherapeutic agents, exciting basic and drug discovery research in this field is ongoing. This was recognized by the awarding of the 2011 Nobel Prize in Physiology or Medicine for research with profound implications for the development of cancer immunotherapies.
The Biopharmconsortium Blog has been covering new developments in cancer immunotherapy since the spring of 2011. Our earlier articles on this subject (with links) are listed in our December 31, 2011 article, entitled “Read the cancer immunotherapy review in the 22 December 2011 issue of Nature!”
Cancer immunotherapy represents one of several “scientifically premature” or “frontier science” areas discussed in this blog that are providing new opportunities for drug discovery and development–for young entrepreneurial biotech start-ups and for more established biotechnology and pharmaceutical companies. Corporate strategists would do well to explore such areas for potential new R&D programs for their companies.
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