Phase I/II study evaluating the safety and clinical efficacy of temsirolimus and bevacizumab in patients with chemotherapy refractory metastatic castration-resistant prostate cancer

Background Mammalian target of rapamycin (mTOR) pathway and angiogenesis through vascular endothelial growth factor (VEGF) have been shown to play important roles in prostate cancer progression. Preclinical data in prostate cancer has suggested the potential additive effect dual inhibition of VEGF and mTOR pathways. In this phase I/II trial we assessed the safety and efficacy of bevacizumab in combination with temsirolimus for the treatment of men with metastatic castration-resistant prostate cancer (mCRPC). Methods In the phase I portion, eligible patients received temsirolimus (20mg or 25mg IV weekly) in combination with a fixed dose of IV bevacizumab (10mg/kg every 2weeks). The primary endpoint for the phase II portion was objective response measured by either PSA or RECIST criteria. Exploratory endpoints included changes in circulating tumor cells (CTC) and their correlation with PSA response to treatment. Results Twenty-one patients, median age 64 (53-82), with pre-treatment PSA of 205.3 (11.1-1801.0), previously treated with a median of 2 (0-5) lines of therapy for mCRPC received the combination of temsirolimus weekly at 20mg (n=4) or 25mg (n=17) with bevacizumab 10mg/kg every 2 weeks (n=21). Median time to progression was 2.6months (95% CI, 1.2-3.9) and the median best PSA change from baseline to 12weeks was a 32% increase (-40-632%) which met the predefined futility rule and led to early termination of the study. Nine patients (43%) had grade 3 toxicity that included fatigue (24%), anorexia (10%), nausea/vomiting (5%) and lymphopenia (5%). In exploratory analysis, a decrease in CTC levels was observed in 9 out of 11 patients. No association between PSA levels and CTC levels was detected. Conclusions The combination of temsirolimus and bevacizumab showed limited clinical activity in mCRPC patients previously treated with chemotherapy and was associated with significant adverse events (AEs). Transient decrease in CTC levels was independent from PSA response. NCT01083368.