Abstract
4565 Background A prior phase 2 study of allogeneic prostate carcinoma cell lines (PC-3 and LNCaP) genetically modified to secrete GM-CSF in 34 metastatic HRPC patients (pts) yielded a median survival of 26 months (Proc ASCO, Vol. 21:183a, 2002). The vaccine was re-engineered to secrete higher levels of GM-CSF, and this GVAX prostate cancer vaccine has been evaluated in a study designed to optimize the dose for phase 3 trials. Methods 80 metastatic HRPC pts were treated for 24 weeks in a dose-escalation trial. Doses (in millions of cells) included 200 monthly (low), 200 bi-weekly (medium), and 500 prime/300 boost bi-weekly (high). Vaccine specific antigenic protein antibodies were measured by Western blot of vaccine lysates against pts sera collected at baseline, Wk 12 and Wk 24. Type I Carboxy-terminal telopeptide (ICTP), a biologic marker useful for monitoring osteoclast activity in metastatic prostate cancer, was assayed at the same time points. PSA was collected at each treatment visit. Results 80 pts enrolled and completed treatment, and have been followed for a median of 5.4 months with no dose-limiting toxicities observed. 6/19 (32%) of pts in the high dose group showed PSA declines following repeat vaccinations. In addition, stable or decreasing ICTP levels occurred in 34/55 (62%) pts tested including all dose groups. The proportion of pts generating an antibody response to at least one cell line at Wk 12 increased with dose, with 87% of pts demonstrating an immune response in the high dose group compared with 72% and 40% in the medium and low dose groups (p=0.001, Kendall's Tau-b). Conclusions GVAX prostate cancer vaccine demonstrates immunogenicity and clinical activity in metastatic HRPC pts which appears to be dose-dependent. Stable or decreasing ICTP levels suggest osteoclast inhibition. Phase 3 trials are planned with the high dose that generated PSA declines and the optimal immunologic response rate. Author Disclosure Employment or Leadership Consultant or Advisory Stock Ownership Honoraria Research Funding Expert Testimony Other Remuneration Cell Genesys Cell Genesys Mentor; Oncura
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