Randomized phase 2 trial of a PARP inhibitor TSL-1502 in germline BRCA-mutated, HER2-negative locally advanced/metastatic breast cancer

Glucuronide prodrug strategies may enhance target specificity and reduce the toxicity of PARP inhibitors, but no clinical evaluation has been performed. We evaluated TSL-1502, a novel glucuronide prodrug of a PARP inhibitor, in a randomized, open-label, phase 2 study at 28 sites in China (NCT05420779). Eligible patients were women aged 18-75 years with HER2-negative locally advanced or metastatic breast cancer and germline BRCA mutations. Patients were assigned randomly (2:2:1) to receive TSL-1502 at 350 mg or 500 mg once daily or the investigator's choice of chemotherapy (eribulin, capecitabine, or vinorelbine) in 3-week cycles. Sixty-three patients were enrolled between August 18, 2022, and March 5, 2024. According to the Independent Review Committee assessment, the objective response rates were 36.0% (95% CI, 18.0-57.5) in the 350 mg group, 55.6% (95% CI, 35.3-74.5) in the 500 mg group, and 40.0% (95% CI, 12.2-73.8) in the chemotherapy group. The median progression-free survival times were 5.6 (95% CI, 4.0-8.2), 8.8 (95% CI, 5.7-not assessable [NA]), and 9.2 (95% CI, 1.38-NA) months, respectively, and the overall survival times were 17.4 months (95% CI, 9.1-NA), not reached (95% CI, 16.9-NA), and 19.8 months (95% CI, 9.2-NA), respectively. Grade ≥3 treatment-related adverse events occurred in 60.0%, 59.3%, and 80.0% of patients, with anemia most common in the TSL-1502 group and neutropenia most common with chemotherapy. No treatment-related deaths occurred. TSL-1502 at 500 mg showed promising antitumor activity and a manageable safety profile, supporting further clinical development.