PROSTVAC-VF comprises two recombinant viral vectors, each encoding transgenes for prostate-specific antigen (PSA), and three immune costimulatory molecules (B7.1, ICAM-1, and LFA-3, designated TRICOM). Vaccinia-based vector was used for priming followed by six planned fowlpox-based vector boosts. PROSTVAC-VF treatment was evaluated for safety and for prolongation of progression-free survival (PFS) and overall survival (OS) in a randomized, controlled, and blinded phase II study. In total, 125 patients were randomly assigned in a multicenter trial of vaccination series. Eligible patients had minimally symptomatic castration-resistant metastatic prostate cancer (mCRPC). Patients were allocated (2:1) to PROSTVAC-VF plus granulocyte-macrophage colony-stimulating factor or to control empty vectors plus saline injections. Eighty-two patients received PROSTVAC-VF and 40 received control vectors. Patient characteristics were similar in both groups. The primary end point was PFS, which was similar in the two groups (P = .6). However, at 3 years post study, PROSTVAC-VF patients had a better OS with 25 (30%) of 82 alive versus 7 (17%) of 40 controls, longer median survival by 8.5 months (25.1 v 16.6 months for controls), an estimated hazard ratio of 0.56, and stratified log-rank P = .0061. PROSTVAC-VF immunotherapy was well tolerated and associated with a 44% reduction in the death rate and an 8.5-month improvement in median OS in men with mCRPC. These provocative data provide preliminary evidence of clinically meaningful benefit but need to be confirmed in a larger phase III study.A concurrent multicenter, randomized Phase II trial employing PROSTVAC-VF provided further evidence of enhanced median OS (p = 0.0061) in patients with mCRPC. Thirty-two patients were vaccinated once with recombinant vaccinia containing the transgenes for prostate-specific antigen (PSA) and three costimulatory molecules. Patients received boosters with recombinant fowlpox containing the same four transgenes. Twelve of 32 patients showed declines in serum PSA post-vaccination and 2/12 showed decreases in index lesions. Median OS was 26.6 months (predicted median OS by the Halabi nomogram was 17.4 months). Patients with greater PSA-specific T-cell responses showed a trend (p = 0.055) toward enhanced survival. There was no difference in T-cell responses or survival in cohorts of patients receiving GM-CSF versus no GM-CSF. Patients with a Halabi predicted survival of <18 months (median predicted 12.3 months) had an actual median OS of 14.6 months, while those with a Halabi predicted survival of greater than or equal to 18 months (median predicted survival 20.9 months) will meet or exceed 37.3 months, with 12/15 patients living longer than predicted (p = 0.035). Treg suppressive function was shown to decrease following vaccine in patients surviving longer than predicted, and increase in patients surviving less than predicted. This hypothesis-generating study provides evidence that patients with more indolent mCRPC (Halabi predicted survival of greater than or equal to 18 months) may best benefit from vaccine therapy. In solid tumors such as prostate cancer, novel paradigms are needed to assess therapeutic efficacy. We utilized a method estimating tumor growth and regression rate constants from serial PSA measurements, and assessed its potential in patients with metastatic castration resistant prostate carcinoma (mCRPC). Patients were enrolled in five phase II studies, including an experimental vaccine trial, representing the evolution of therapy in mCRPC. PSA measurements obtained before, and during, therapy were used. Data analysis using a two-phase mathematical equation yielded concomitant PSA growth and regression rate constants. Growth rate constants (g) can be estimated while patients receive therapy and in such patients g is superior to PSA doubling time in predicting OS. Incremental reductions in growth rate constants were recorded in successive trials with a 10-fold slower g in the most recent combination therapy trial relative to single-agent thalidomide more than a decade earlier. Growth rate constants correlated with survival, except in patients receiving vaccine-based therapy where the evidence demonstrates prolonged survival presumably due to immunity developing subsequent to vaccine administration. Incremental reductions in tumor growth rate constants suggest increased efficacy in successive chemotherapy trials. The derived growth rate constant correlates with survival, and may be used to assess efficacy. The PSA-TRICOM vaccine appears to have provided marked benefit not apparent during vaccination, but consistent with subsequent development of a beneficial immune response. If validated as a surrogate for survival, growth rate constants would offer an important new efficacy endpoint for clinical trials. A global Phase III randomized, placebo vector controlled clinical trial is ongoing employing PSA-TRICOM vaccine (PROSTVAC) in patients with mCRPC.A recently completed study in mCRPC demonstrated that when ipilimumab (anti-cytotoxic T lymphocyte-associated antigen 4 (CTLA4) monoclonal antibody) was combined with PSA-TRICOM (PROSTVAC) at escalating doses, the median survival was 34 months, which compares favorably to previous vaccine trials in mCRPC that resulted in median survivals of approximately 26 months. These and other data support the rationale for randomized studies employing immune checkpoint inhibitors in combination with TRICOM-based vaccines.Two of the most widely studied human tumor-associated antigens (TAAs) are CEA and mucin-1 (MUC-1). CEA is overexpressed in a wide range of human carcinomas, including gastrointestinal, breast, lung, pancreatic, medullary thyroid, ovarian, and prostate. MUC-1 is a tumor-associated mucin, which is overexpressed and hypoglycosylated in all human carcinomas as well as in acute myeloid leukemia (AML) and multiple myeloma. Studies have demonstrated that the C-terminus of MUC-1 functions as an oncogene. A study was conducted to obtain preliminary evidence of clinical response in metastatic breast and ovarian cancer patients with PANVAC (rV,rF-CEA-MUC1-TRICOM). Twenty-six patients were enrolled and given monthly vaccinations. These patients were heavily pretreated, with 21 of 26 patients having had three or more prior chemotherapy regimens. Side effects were largely limited to mild injection-site reactions. For the 12 breast cancer patients enrolled, median time to progression was 2.5 months (1-37+) and median OS was 13.7 months. Four patients had stable disease. One patient had a complete response by RECIST (Response Evaluation Criteria on Solid Tumors) and remained on study for over 37 months. Another patient with metastatic disease confined to the mediastinum had a 17% reduction in mediastinal mass and was on study for 10 months. Patients with stable or responding disease had fewer prior therapies and lower tumor marker levels than patients with no evidence of response. Further studies to confirm these results are warranted. A randomized multicenter study has been initiated evaluating docetaxel vs docetaxel plus PANVAC vaccine (rV-, rF-CEA-MUC1-TRICOM) in patients (n=48) with metastatic breast carcinoma. Preliminary findings to date indicate a substantial increase in time to progression in the combination arm vs the docetaxel alone arm.
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