Abstract CT158: BrUOG360: A phase Ib/II study of copanlisib combined with rucaparib in patients with metastatic castration-resistant prostate cancer (mCRPC)

Abstract

Abstract Background: Molecular alterations in genes regulating homologous recombination (HR) confer sensitivity of mCRPC to poly ADP-ribose polymerase inhibitors (PARPi). Increased activation of thePI3K-AKT-mTOR pathway in mCRPC contributes to tumor progression and represents an important therapeutic target. Preclinical studies have shown that PI3K inhibitors (PI3Ki) impair HR and sensitize cancer cells to PARPi even in the absence of HR gene mutations. We hypothesize that dual PI3K and PARP inhibition may improve clinical outcomes of mCRPC. We describe preliminary results of a phase Ib/II study investigating safety of the combination of copanlisib (pan-class I PI3Ki) and rucaparib (PARP-1, -2 and -3 inhibitor). Methods: Enrollment criteria included progressive mCRPC, prior androgen inhibitors (abiraterone, enzalutamide, and/or apalutamide); prior taxane chemotherapy was allowed. HR defects (HRD) was not required for the phase Ib but was an inclusion criterion for the Phase II component of the trial. The phase I followed a standard 3+3 escalation design. Dose level (DL) 1 consisted of rucaparib 400 mg PO BID continuously and copanlisib 45 mg IV days 1, 8 and 15 every 28 days; in DL -1 the copanlisib was reduced to 45 mg days 1 and 15 only. Adverse events (AE) were graded by CTCAE v5.0. The primary aim of the phase I was to establish the MTD and the recommended phase II dose (RP2D) of copanlisib in combination with rucaparib. Results: Thirteen patients were enrolled with a median age of 64 (55-78) and a median baseline PSA of 11.7 ng/mL (0.015-1939.2). Nine patients (69%) received prior chemotherapy (docetaxel [6], cabazitaxel [3]). Seven patients had HRD (54%) BRCA1 (1), BRCA2 (4), CDK12 (1), and FANCA (1). Treatment-related AEs included grade 2 (G2) leukopenia (46%), G2/G3 anemia (31%), G2/G3 rash (31%). Two dose-limiting toxicities (DLTs) were observed in 5 patients treated in DL 1: G3 rash and G3 AST/ALT elevation attributed to both drugs. Six patients were treated at DL -1 without DLTs; this was identified as the RP2D. Two additional patients have been treated at this dose in Phase II of the study. By RECIST 1.1 criteria, one patient (8%) achieved a partial response (BRCA1 mutation) and three (23%) achieved stable disease resulting in a clinical benefit rate of 30.7%. Median duration of treatment was 12 weeks. One patient harboring a PALB2 VUS mutation remained on treatment for 21.7 months. Of 13 evaluable patients, there were 2 confirmed PSA responses (15%) (one patient without an HRD and one with a BRCA1 mutation). Conclusions: The combination of rucaparib and copanlisib is well tolerated. The RP2D was rucaparib 400mg BID with copanlisib 45mg (D1, D15; 28-day cycle) with signal of efficacy in patients with and without HRD. Clinical trial information: NCT04253262. Citation Format: Matthew J. Hadfield, Andre De Souza, Dragan Golijanin, Roxanne Wood, Adam Olszewski, Sheldon L. Holder, Wafik S. El-Deiry, Rahul Aggarwal, 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 2023; Part 2 (Clinical Trials and Late-Breaking Research); 2023 Apr 14-19; Orlando, FL. Philadelphia (PA): AACR; Cancer Res 2023;83(8_Suppl):Abstract nr CT158.