Abstract CT222: BrUOG360: A phase Ib/II study of copanlisib combined with rucaparib in patients with metastatic castration-resistant prostate cancer (mCRPC)

Background: Patients with metastatic prostate cancer invariably progress to a lethal state called metastatic castration-resistant prostate cancer (mCRPC). Approximately 23-28% of patients with mCRPC have molecular alterations in genes associated with homologous recombination (HR) DNA repair mechanisms (e.g., BRCA1/2). These alterations are associated with sensitivity to poly ADP-ribose polymerase inhibitors (PARPi). The responses to PARPi can be short-lived, and several mechanisms of resistance have been described. Preclinical studies demonstrated that PI3K suppression impairs HR and sensitizes cancer cells to PARPi even in the absence of mutations in DNA repair genes. The synergy between olaparib and PI3K inhibition led to marked tumor regression both in vitro and in vivo models of prostate cancer. These preclinical results, coupled with the importance of both the PI3K pathway and DNA damage repair mechanisms in mCRPC, support our hypothesis that dual inhibition of PI3K and PARP might improve clinical outcomes in mCRPC. We describe an ongoing phase Ib/II study aimed to evaluate the safety and determine the maximum tolerated dose (MTD) of the combination of copanlisib (pan-class I PI3K inhibitor) and rucaparib (a PARP-1, -2 and -3 inhibitor) followed by an expansion cohort exploring efficacy among patients with mCRPC. Methods: Phase I, dose-escalation part of the study, aims to establish the MTD and/or recommended phase II dose (RP2D) of copanlisib in combination with rucaparib. Dose escalation will follow a standard 3+3 escalation scheme. Evidence of HR-deficiency is not required to enroll in phase I, but is for phase II. All subjects will be treated with rucaparib (continuous oral administration twice daily) 400mg (dose level I), 500mg (II) or 600mg (III-IV) and intravenous copanlisib (D1, D8, D15; 28-day cycle; dose levels I-III: 45 mg; level IV: 60 mg). Once the RP2D of copanlisib and rucaparib in the phase I part of the study is determined, enrollment will commence into the phase II part of the trial. The primary objective of phase II is to estimate the preliminary efficacy of the combination of copanlisib and rucaparib among subjects with mCRPC carrying mutations in DNA repair genes, as measured by prostate-specific antigen (PSA) response. Up to 20 patients will enroll in the phase II using a Simon9s two-stage design. In the first stage, 14 patients will be accrued. If there are 7 or fewer PSA responses in these 14 patients, the study will be stopped for futility. Otherwise, an additional 6 patients will be accrued. Patients with mCRPC need to have had disease progression during treatment with abiraterone, enzalutamide, and/or apalutamide. Prior therapy with taxanes is allowed. Translational objectives include the correlation of clinical outcomes with HR mutations and PI3K/mTOR pathway gene alterations in the tumor. Genomic analyses will also investigate biomarkers and mechanisms of action of the combination. The clinical trial is recruiting (NCT04253262). Citation Format: Andre De Souza, Rahul Aggarwal, Howard Safran, Dragan Golijanin, Roxanne Wood, Adam Olszewski, Wafik S. El-Deiry, Anthony Mega, Benedito A. Carneiro. BrUOG360: A phase Ib/II study of copanlisib combined with rucaparib in patients with metastatic castration-resistant prostate cancer (mCRPC) [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr CT222.