Exposure-response analysis to inform the optimal dose of veliparib in combination with carboplatin and paclitaxel in BRCA-mutated advanced breast cancer patients.

Purpose: Veliparib, a poly(ADP-ribose)-polymerase (PARP) 1 and 2 enzyme inhibitor, was administered at 120 mg twice daily (BID) for 7 days in a 21-day cycle with carboplatin/paclitaxel in the Phase 2 BROCADE study in patients with BRCA-deficient recurrent or metastatic breast cancer, a dose based on Phase 1 results. Population pharmacokinetic (PK) and exposure-response analyses were undertaken to retrospectively evaluate whether an optimal dose was used in BROCADE.

Methods: A population PK analysis was performed using data from 168 patients in BROCADE along with data from 288 subjects in another 5 studies. The relationship between veliparib exposure and efficacy variables (including progression-free survival [PFS] and objective response rate [ORR]) and safety variables (selected grade 3 or greater hematological adverse events) were analyzed.

Results: Veliparib PK parameters in BROCADE were comparable to the previous studies. Creatinine clearance on veliparib apparent clearance and lean body weight on veliparib apparent volume of distribution were identified as covariates. A trend of better efficacy (PFS and ORR) in the veliparib arm compared to placebo was observed. However, veliparib exposure-efficacy response was relatively flat with higher veliparib exposures not showing better efficacy. No exposure-response relationship was observed in grade 3 or greater hematological toxicities (anemia, neutropenia, leukopenia, and thrombocytopenia).

Conclusions: The exposure-response analysis suggested that intermittent 7-day veliparib 120 mg BID dosing in a 21-day cycle provided additional efficacy without meaningfully impacting the safety and tolerability when co-administered with carboplatin and paclitaxel in patients with BRCA-deficient breast cancer. A higher dose of veliparib is unlikely to provide greater benefit in this combination in patients with BRCA-deficient recurrent or metastatic breast cancer.