Intratumoral and s.c. injection of inactivated hemagglutinating virus of Japan envelope (GEN0101) in metastatic castration‐resistant prostate cancer

Inactivated hemagglutinating virus of Japan envelope (HVJ‐E) has an antitumor effect and tumor immunity. We undertook an open‐label, phase I, dose‐escalation study in patients with castration‐resistant prostate cancer (CRPC) to determine the safety and efficacy of intratumoral and s.c. injection of HVJ‐E (GEN0101). Patients with CRPC, who were resistant to or unable to receive standard of care, were included. GEN0101 was injected directly into the prostate and s.c. in two 28‐day treatment cycles. The primary end‐points were to evaluate the safety and tolerability of GEN0101 and determine its recommended dose. The secondary end‐points were to analyze the antitumor effect and tumor immunity. Three patients received 30 000 mNAU GEN0101 and 6 received 60 000 mNAU. There was no dose‐limiting toxicity, and the recommended dose of GEN0101 was defined as 60 000 mNAU. Radiographically, 1 patient had stable disease and 2 had progressive disease in the low‐dose group, whereas 5 patients had stable disease and 1 had progressive disease in the high‐dose group. Three patients in the high‐dose group showed reduction in lymph node metastasis. Prostate‐specific antigen increase rates in the high‐dose group were suppressed more than those in the low‐dose group. Natural killer cell activity was enhanced in 2 patients of the low‐dose group and in 5 patients in the high‐dose group. In conclusion, intratumoral and s.c. injections of GEN0101 were well‐tolerated and feasible to use. The study is registered with the UMIN Clinical Trials Registry (no. UMIN000017092).