HB-302/HB-301 Therapy in Participants With Metastatic Castration-Resistant Prostate Cancer

This is a first-in-human Phase 1/2, multinational, multicenter, open-label study of HB-302/HB-301 alternating 2-vector therapy in participants with metastatic castration-resistant prostate cancer (mCRPC) comprising 2 phases: a Phase 1 Dose Escalation and recommended Phase 2 dose (RP2D) Confirmation, and a Phase 2 Dose Expansion. The Phase 1 Dose Escalation will evaluate HB-302/HB-301 alternating 2-vector therapy for safety and tolerability, preliminary efficacy and immunogenicity, and determination of a safe recommended Phase 2 dose (RP2D). A confirmatory cohort (or cohorts) will inform the determination of the RP2D. The Phase 2 Dose Expansion will assess HB-302/HB-301 alternating 2-vector therapy at the RP2D defined in the Phase 1 part of the study. Study drugs HB-301 and HB-302 are genetically-engineered replicating vectors based on the arenavirus lymphocytic choriomeningitis virus (LCMV) and arenavirus Pichinde virus (PICV), respectively. HB-301 and HB-302 express the same transgenes encoding 2 prostate cancer-associated antigens: prostatic acid phosphatase (PAP) and prostate specific antigen (PSA). HB-302/HB-301 Alternating 2-vector therapy will be administered intravenously every 3 weeks (Q3W) for the first 5 doses and every 6 weeks (Q6W) from the fifth dose and onward. HB-302 is to be administered first followed 3 or 6 weeks later by HB-301. In total, approximately 70 participants aged 18 years and older will be enrolled in this study to receive HB-302/HB-301 alternating 2-vector therapy. About 40 Investigators and study sites in the United States (US) and Europe are expected to participate in this study.