Tolerability, safety, and preliminary antitumor activity of fuzuloparib in combination with SHR-1316 in patients with relapsed small cell lung cancer: a multicenter, open-label, two-stage, phase Ib trial

BACKGROUND: Second-line treatment options for small cell lung cancer (SCLC) are limited. Preclinical research shows that inhibition of poly (ADP-ribose) polymerase (PARP) could upregulate programmed death-ligand 1 (PD-L1), and thus render cancer cells more sensitive to immune checkpoint inhibitors. This study investigated the tolerability, safety, and preliminary antitumor activity of fuzuloparib (a PARP inhibitor) plus SHR-1316 (a PD-L1 inhibitor) for relapsed SCLC. METHODS: Patients with SCLC who failed previous first-line platinum-based therapy were enrolled in this two-stage phase Ib trial. In stage 1, 2 dose levels were designed: fuzuloparib 100 mg or 150 mg twice daily plus SHR-1316 600 mg every 2 weeks, with 6 patients in each dose level. Based on the tolerability during the first 28-day cycle and the preliminary antitumor activity in stage 1, a recommended phase II dose (RP2D) was determined and introduced in the stage 2 expansion phase. The primary endpoints were safety and RP2D in stage 1 and objective response rate (ORR) in stage 2. RESULTS: A total of 23 patients were enrolled, with 16 receiving fuzuloparib 100 mg plus SHR-1316 and 7 receiving fuzuloparib 150 mg plus SHR-1316. At data cutoff on April 23, 2021, the median follow-up duration was 6.4 months (IQR, 3.0–9.7 months). All patients discontinued study treatment. One patient receiving fuzuloparib 150 mg plus SHR-1316 had clinically significant toxicities, and fuzuloparib 100 mg plus SHR-1316 was considered as the RP2D. In the RP2D cohort, the confirmed ORR was 6.3% (95% CI: 0.2–30.2%), and the disease control rate was 37.5% (95% CI: 15.2–64.6%). The median progression-free survival was 1.4 months (95% CI: 1.3–2.8 months), and the median overall survival was 5.6 months (95% CI: 3.0–16.7 months). Grade ≥3 treatment-related adverse events (TRAE) occurred in 8 patients (34.8%). No treatment-related death occurred, and no patients discontinued treatment due to TRAEs. CONCLUSIONS: Fuzuloparib combined with SHR-1316 failed to improve the outcomes in unselected patients with relapsed SCLC. Future studies with biomarker analysis are warranted to select patients most likely to benefit from this combination treatment. Fuzuloparib 100 and 150 mg plus SHR-1316 were both tolerable with no new signals observed.