Phase 1 Study of Safety and Preliminary Clinical Activity of JNJ-63898081, a PSMA and CD3 Bispecific Antibody, for Metastatic Castration-Resistant Prostate Cancer

Introduction Cancer immunotherapies have limited efficacy in prostate cancer due to the immunosuppressive prostate microenvironment. Prostate specific membrane antigen (PSMA) expression is prevalent in prostate cancer, preserved during malignant transformation, and increases in response to anti-androgen therapies, making it a commonly targeted tumor associated antigen for prostate cancer. JNJ-63898081 (JNJ-081) is a bispecific antibody targeting PSMA-expressing tumor cells and CD3-expressing T cells, aiming to overcome immunosuppression and promoting antitumor activity. Patients and Methods We conducted a phase 1 dose escalation study of JNJ-081 in patients with metastatic castration-resistance prostate cancer (mCRPC). Eligible patients included those receiving ≥1 prior line treatment with either novel androgen receptor targeted therapy or taxane for mCRPC. Safety, pharmacokinetics, and pharmacodynamics of JNJ-081, and preliminary antitumor response to treatment were evaluated. JNJ-081 was administered initially by intravenous (IV) then by subcutaneous (SC) route. Results Thirty-nine patients in 10 dosing cohorts received JNJ-081 ranging from 0.3 µg/kg to 3.0 µg/kg IV and 3.0 µg/kg to 60 µg/kg SC (with step-up priming used at higher SC doses). All 39 patients experienced ≥1 treatment-emergent AE, and no treatment-related deaths were reported. Dose-limiting toxicities were observed in 4 patients. Cytokine release syndrome (CRS) was observed at higher doses with JNJ-081 IV or SC; however, CRS and infusion-related reaction (IRR) were reduced with SC dosing and step-up priming at higher doses. Treatment doses >30 µg/kg SC led to transient PSA decreases. No radiographic responses were observed. Anti-drug antibody responses were observed in 19 patients receiving JNJ-081 IV or SC. Conclusion JNJ-081 dosing led to transient declines in PSA in patients with mCRPC. CRS and IRR could be partially mitigated by SC dosing, step-up priming, and a combination of both strategies. T cell redirection for prostate cancer is feasible and PSMA is a potential therapeutic target for T cell redirection in prostate cancer.