Cell Genesys Inc.'s independent data monitoring committee (IDMC) gave the firm the thumbs-up to continue its Phase III clinical trial of its prostate cancer immunotherapeutic GVAX, a nonpatient-specific investigational therapy comprised of tumor cells genetically modified to secrete granulocyte-macrophage colony-stimulating factor, an immune-stimulating cytokine. The multicenter, randomized, controlled Phase III study, known as VITAL-1, is comparing GVAX with Sanofi-Aventis Group's chemotherapy agent Taxotere (docetaxel) plus prednisone in 626 patients with hormone-refractory prostate cancer (HRPC) whose disease has metastasized and are asymptomatic for cancer-related pain.
The primary endpoint of the trial, which was started in 2004 and is being conducted at about 130 sites in North American and Europe, is improvement in survival.
The IDMC's recommendation to continue the study, said CEO Stephen Sherwin, is "an encouraging measure of progress in our Phase III program." The outcome of the preplanned interim analysis, he said Monday during a conference call, was "consistent with our expectations."
In addition, Sherwin said, the interim analysis occurred in the time frame originally estimated, meaning that the firm had to make certain assumptions about the survival in each treatment arm to estimate when it would have enough events in total across the two arms to trigger the analysis. "The timing of the VITAL-1 interim analysis was consistent with such assumptions," he declared.
Positive interim analyses in cancer trials are "quite uncommon," particularly in trials with survival as the prespecified endpoint, Sherwin added. "We believe that this will be even more true for immunotherapies," which have a slower onset of action and tend to have accumulative effects over time compared with cytotoxic chemotherapy drugs, he said.
Sherwin noted that his firm was "entirely blinded" from the results of the IDMC's interim analysis. Cell Genesys will not have access to efficacy data from the Phase III trial until the final analysis is complete, which is expected in the second half of 2009, he said. "We intend to fastidiously preserve the blinding of the trial to ensure the greatest comfort possible on the part of FDA with respect to results of what we consider to be a very important study." Cell Genesys expects to complete enrollment of its second Phase III trial of GVAX in prostate cancer, VITAL-2, by the first half of 2009 with an interim analysis expected in the same period, he said.
VITAL-2 is comparing the safety and efficacy of GVAX immunotherapy in combination with Taxotere with Taxotere chemotherapy and prednisone in patients with HRPC whose disease has metastasized and are symptomatic for cancer-related pain. The primary endpoint of VITAL-2 also is an improvement in survival, Sherwin noted. VITAL-2, initiated in June 2005, plans to enroll about 600 patients at about 90 sites in North America and Europe, he said, adding that Cell Genesys expects to complete enrollment in the first half of 2009. Both VITAL-1 and VITAL-2 are being conducted under special protocol assessments granted by the FDA.
Sherwin also reported to investors and analysts Monday that Cell Genesys completed enrollment of a 16-patient prostate cancer expansion study of GVAX in combination with ipilimumab (MDX-010), a fully human anti-CTLA-4 antibody that is being developed jointly by Princeton, N.J.-based Medarex and New York-based Bristol-Myers Squibb Co. The firms expect to provide an update on that study by midyear, he said.
The companies in June reported that Phase I data of GVAX administered in combination with ipilimumab demonstrated antitumor activity in five patients, including prostate-specific antigen declines of greater than 50 percent that were maintained in four of them for at least six months, with the longest response to date at about 16 months. Cell Genesys also is "continuing to benefit" from its collaboration with Johns Hopkins University examining GVAX in patients with pancreatic cancer and leukemia in multiple clinical trials.
While Sherwin said he is reluctant to "forecast a precise timeline" for a partnering deal with GVAX in prostate cancer, "I think it must be obvious to all that if this transaction is to be completed prior to final Phase III data, that this would have to be the year in which that takes place."
Shares of Cell Genesys (NASDAQ:CEGE) rose 5 cents Monday, to close at $2.11.