Pamiparib, an investigational PARP inhibitor, in patients with metastatic castration-resistant prostate cancer (mCRPC) and a circulating tumor cell (CTC) homologous recombination deficiency (HRD) phenotype or BRCA defects: A trial in progress.

Abstract

TPS5086 Background: Men with mCRPC who have a BRCA1/2 mutation ( BRCA1/2mut) or mutations in other genes resulting in HRD have a poor prognosis. A novel liquid biopsy test (EPIC Sciences) identifies CTCs with an HRD phenotype. Preliminary studies showed that these men may respond to treatment with a PARP inhibitor. Pamiparib, an investigational PARP1/2 inhibitor, has shown brain penetration and potent PARP–DNA complex trapping in nonclinical studies. In early phase clinical studies (NCT02361723; NCT03333915), pamiparib was generally well tolerated and showed preliminary antitumor activity; 60 mg orally twice daily (BID) was established as the recommended investigational dose. Methods: This open-label, global, phase 2 study (NCT03712930) evaluates the antitumor activity and safety/tolerability of pamiparib in mCRPC patients (pts) with CTC-HRD, assessed by the CTC-HRD assay, or deleterious germline/somatic mutations in BRCA1/2. Patients must have progressed on/after ≥1 androgen receptor-targeted therapy, received ≥1 taxane-based therapy, and have prostate-specific antigen (PSA) progression per PCWG3 criteria. Four cohorts of pts will receive pamiparib 60 mg BID in 28-day cycles. Cohort 1 will include ~50 pts with CTC-HRD+ +/- BRCA1/2mut mCRPC with measurable metastatic disease; Cohort 2 will include ~30 pts with CTC-HRD+ +/- BRCA1/2mut mCRPC with bone-only disease; Cohorts 3 & 4 will include ~20 pts with CTC-HRD-/unk + BRCA1/2mut mCRPC with measurable metastatic disease (Cohort 3), or bone-only disease (Cohort 4). Disease status will be assessed every 8 wks for 24 wks, then every 12 wks; PSA levels will be tested every 4 wks. Co-primary endpoints are radiographic ORR assessed by IRC (pts with measurable disease) and confirmed PSA response rate per PCWG3 criteria (pts +/- measurable disease). Secondary endpoints include ORR, time to PSA response/progression, duration of PSA response, time to symptomatic skeletal event, radiographic progression-free survival, overall survival, and safety. As of 05 December 2018, this study is actively enrolling. Clinical trial information: NCT03712930.

Mechanisms of resistance to PARP inhibitors - an evolving challenge in oncology

“…Although veliparib is the least potent of the PARPi currently in use, there are multiple combination trials in progress such as the S1416 study (NCT02595905) [14] . Pamiparib is another PARPi under investigation in a number of clinical trials [15][16][17] .…”

Quo Vadis Advanced Prostate Cancer Therapy? Novel Treatment Perspectives and Possible Future Directions

“…In connection to prostate cancer, several other clinical studies investigating the effects of PARPi such as niraparib (phase III, NCT03748641) [99], talazoparib [100] have recently been terminated or are still ongoing (phase III, NCT03395197) [101], veliparib (phase II, NCT01576172, terminated 2020) [102], pamiparib (phase II, NCT03712930, terminated 2020) [103,104] or rucaparib (phase I, NCT03572478) [105]. In these clinical studies, PARPi are usually co-administered with other, commonly used, drugs such as abiraterone acetate, prednisone, enzalutamide, and nivolumab [106][107][108].…”