Safety and preliminary clinical activity of JNJ-63898081 (JNJ-081), a PSMA and CD3 bispecific antibody, for the treatment of metastatic castrate-resistant prostate cancer (mCRPC).
Authors: Emerson A. Lim, Michael Thomas Schweizer, Kim N. Chi, Rahul Raj Aggarwal, Neeraj Agarwal, James L. Gulley, Edward F. Attiyeh, James Greger, Shujian Wu, Pharavee Jaiprasart, John Loffredo, Nibedita Bandyopadhyay, Hong Xie, Aaron Richard Hansen
Journal: Journal of Clinical Oncology (2022)

279 Background: PSMA expression is increased in response to anti-androgen therapies and is a promising therapeutic target for the treatment of prostate cancer (PCa). JNJ-081 is a bispecific antibody with one arm binding PSMA on cancer cells and the other binding CD3 on T-cells to promote anti-tumor activity. Methods: This Phase 1 Dose Escalation Study evaluated JNJ-081 in mCRPC participants (pts) who progressed after novel androgen targeting therapy (eg, abiraterone, enzalutamide or apalutamide). Prior chemotherapy was permitted. JNJ-081 was administered initially by intravenous (IV) then by subcutaneous (SC) route. Dose escalation followed a continuous reassessment method based on a Bayesian regression model. The primary endpoint to determine the recommended phase 2 dose (RP2D) was based on safety. Pharmacokinetics (PK), pharmacodynamics (PD), immunogenicity, and preliminary anti-tumor activity were also evaluated. Cytokine release syndrome (CRS) was graded by CTCAE V5. Results: As of 10 May 2021, 39 pts were dosed in 10 cohorts ranging from 0.1 µg/kg to 3 µg/kg IV and from 3 µg/kg to 60 µg/kg SC. Premedications included high dose corticosteroids. Step-up priming was implemented at higher SC doses. Most common treatment-emergent AEs were CRS (65%), fatigue (49%) and nausea (43%). 2 pts developed DLTs of Grade (G) 3 or G4 transaminases increased, 1 each at 30 µg/kg SC and priming with 10 µg/kg SC then 55 µg/kg SC, respectively. Both DLTs were in conjunction with or followed an episode of G2 CRS. SC route as well as step-up priming helped mitigate CRS and infusion-related reaction (IRR) during escalation to higher doses: at 3 µg/kg IV, 4 of 5 pts had G2 CRS or IRR; at 30 µg/kg SC, 3 of 4 pts had G2 CRS; priming with 10 µg/kg then 55 µg/kg SC, 4 of 5 pts had G2 CRS. Injection site reactions (G1 or G2) occurred in 24 of 26 pts treated via SC JNJ-081. No treatment related death was reported. Transient PSA decreases were observed at treatment doses greater than 30 µg/kg SC. Two subjects treated with 55 µg/kg had PSA decreases &gt; 50%. No radiographic responses were observed. PK of JNJ-081 was linear over the dose range of 3-60 µg/kg following SC administration. SC bioavailability was approximately 25%. Anti-drug antibodies (ADA) were detected in 2 of 12 subjects treated by IV administration and 14 of 23 pts treated by SC administration. ADA resulted in loss of exposure in some SC pts. Intrapatient dose escalation in 3 pts did not overcome the reduced exposure after ADA seropositivity. Conclusions: JNJ-081 demonstrated transient decreases in PSA in mCRPC patients. Grade 2 CRS was observed at higher doses and was partially mitigated by SC and step-up dosing. ADA resulting in decreased exposure occurred in the majority of pts treated SC. PSMA remains a potential therapeutic target for T-cell redirection for the treatment of PCa. Clinical trial information: NCT03926013.