A phase 1/1b multicenter, open-label, dose escalation and dose expansion study to evaluate the safety, pharmacokinetics, immunogenicity, and antitumor activity of MEDI3726 in patients with metastatic, castration-resistant prostate cancer who have received prior treatment with abiraterone or enzalutamide.

TPS5088 Background: Therapeutic advances have recently been achieved for patients with metastatic, castration-resistant prostate cancer (mCRPC) due to abiraterone acetate (ABI) and enzalutamide (ENZ). However, virtually all patients with mCRPC eventually progress in their disease, and further treatment options are limited. Prostate-specific membrane antigen (PSMA) is highly expressed in nearly all prostate cancers, and its expression is highest in mCRPC. MEDI3726 is an antibody-drug conjugate composed of anti-PSMA antibody derived from J591, site-specifically conjugated to the cytotoxic, DNA cross-linking, pyrrolobenzodiazepine dimer. MEDI3726 has demonstrated potent and specific in vitro and in vivo antitumor activity in human prostate cancer-derived preclinical models with different expression levels of PSMA. Methods: This is a first-in-human, phase 1/1b, multicenter, open-label, dose escalation and dose expansion study in patients who have received prior treatment with ABI or ENZ, with or without prior taxane-based chemotherapy in the mCRPC setting (NCT02991911). The primary objectives are to assess safety and tolerability, describe dose-limiting toxicities, and determine the maximum tolerated dose or maximum administered dose of MEDI3726. The secondary objectives are to evaluate MEDI3726 for its antitumor activity (based on a composite response according to RECIST Version 1.1, a reduction in prostate-specific antigen level of 50% or more compared to baseline, or a conversion in the circulating tumor cell count [defined as a reduction from ≥5 cells/7.5 mL blood to < 5 cells/7.5 mL blood]), safety and tolerability in combination with ENZ, pharmacokinetics alone and in combination with ENZ, and immunogenicity. Recruitment is ongoing for this study, which has an estimated total target enrollment of 224 patients. Clinical trial information: NCT02991911.