A multicenter, randomized, controlled phase II study: Efficacy and safety of PSMA-targeted radioligand therapy I-131-1095 (1095) plus enzalutamide (enza) in 18F-DCFPyL PSMA scan avid, metastatic castration-resistant prostate cancer (mCRPC) patients post-abiraterone (abi) progression (ARROW).

Abstract

TPS187 Background: PSMA is a transmembrane glycoprotein overexpressed in prostate cancer (PC) and further upregulated in castrate resistant disease. 1095 is a novel PSMA-targeted small molecule radioligand therapeutic that binds to the extracellular domain of PSMA selectively with high affinity, internalized, and delivers a targeted lethal radiation dose to PC cells. 18F-DCFPyL is a novel PSMA-targeted PET imaging agent that has shown robust diagnostic performance for detecting recurrent and metastatic PC. In the ARROW study, pts must demonstrate 18F-DCFPyL avidity prior to 1095 treatment. Methods: ARROW is an open-label, randomized (2:1) trial of enza plus 1095 or enza alone in pts with progressive mCRPC who previously received abi. ~120 pts (80: 1095 + enza; 40: enza alone) will be treated at multiple sites in the US and Canada. Eligible male pts must have metastatic disease documented by bone scan or soft tissue lesions measurable per RECIST 1.1 on CT/MRI, be PSMA-avid as determined by 18F-DCFPyL PET/CT, have evidence of biochemical or radiographic progression on abi, and be ineligible for or refuse to receive chemotherapy. Pts will receive enza (prescribed per approved labeling) with or without 1095 (100 mCi dose, followed by up to 3 additional doses administered at least 8 weeks apart, as determined by dosimetry evaluation and occurrence of dose-limiting events). The primary objective is to determine the efficacy of 1095 plus enza compared to enza alone, based on PSA response (confirmed PSA decline ≥50%) rate according to Prostate Cancer Clinical Trials Working Group 3 (PCWG3) criteria. Additional objectives include objective response rate based on PCWG3-modified RECIST 1.1, progression-free survival (PFS) defined as the first occurrence of radiographic progression (PCWG3-modified RECIST 1.1), unequivocal clinical progression, or death from any cause, duration of response, overall survival, and the safety and tolerability of 1095 radioligand therapy. Due to the COVID-19 pandemic, enrollment was halted in April 2020 but is reopening in October 2020. Clinical trial information: NCT03939689.