The interim Phase I/II efficacy data for BPX-101 (Bellicum Pharmaceuticals, Inc.), a novel dendritic cell vaccine for metastatic castrate resistant prostate cancer (mCRPC), in a Late Breaking poster at the American Association for Cancer Research (AACR) 101st Annual Meeting 2010 held in Washington, D.C. shows systemic and antigen-specific immune responses correlating with clinical response.
Guru Sonpavde, M.D., Principal Investigator at The University of Texas Health Science Center-Houston, presented interim Phase I/II data that suggest a correlation between dose-related variations in levels of inflammatory serum markers and measurable clinical response in patients treated with BPX-101. Correlative PSA declines, suppression of serum IL-6, and antigen-specific immune responses were also reported.
The trial was designed to establish the safety and maximum tolerated dose of BPX-101 in combination with activating agent AP1903, administered every other week for six doses. Exploratory efficacy endpoints include radiological and biochemical assessments of clinical response, and assessments of serum and biopsy samples for systemic and antigenspecific immunological responses.
Interim data from six subjects shows the combination of BPX-101 and AP103 to be safe and well tolerated at low and mid doses of BPX-101, with no unexpected drug-related adverse events reported. Clinical responses were evident within the first 12 weeks of treatment, in both low and mid dose cohorts: ? Four of six subjects had Stable Disease (SD) per RECIST 1.1 at the end of 12 weeks, and three of three who have been on study at least six months remain stable, including one subject who experienced a 20% decline in measurable disease after 12 weeks, improving further to a 25% decline at six months, tracking towards a Partial Response (PR).
Four of six subjects achieved a maximal serum PSA decline of at least 10% from baseline, including the subject tracking towards a PR as reported above, who achieved a maximal serum PSA decline approaching 50%.
Five of six subjects experienced a significant increase in PSA doubling time (PSADT) by 12 weeks, including two subjects with PSA levels below baseline and three subjects with PSADT increases of 80-300%, relative to the pre-treatment PSADT. Four of six subjects achieved declines in serum IL-6, a putative biomarker of metastatic prostate cancer, of 75-99% from baseline.
Systemic immunological responses were determined by assessment of a panel of chemokines and cytokines at each dose and one week after each dose. Clinically responding subjects tended to exhibit dramatic and consistent increases in these serum markers one week after each dose, returning to baseline the following week. Antigen specific immune responses, measured in injection site reaction biopsies taken after three doses, were detected in four of four assessable subjects, including two clear TH1-biased responses.
The apparent dose-response correlation between clinical and immunological responses will be further investigated in six subjects now enrolling in the final, high dose cohort.
Kevin M. Slawin, M.D., President and Chief Medical Officer of Bellicum Pharmaceuticals, the company developing BPX-101, noted, ?We are very excited and encouraged by this early data, which appears to contradict the prevailing belief that while cancer vaccines can prolong overall survival, they do not elicit measurable clinical or biomarker responses in the near term. We look forward to completing our trial later this year and initiating Phase II trials in 2011.?