Phase 1b study of AVB-500 in combination with paclitaxel or pegylated liposomal doxorubicin platinum-resistant recurrent ovarian cancer

Objective: GAS6 and AXL are expressed in high-grade serous ovarian cancer but not in normal ovarian tissue. AVB-500, a novel high affinity Fc-sAXL fusion protein, binds GAS6 preventing AXL signaling. This Phase 1b study (NCT03639246) evaluated safety, efficacy, and exploratory predictive markers of AVB-500 combined with paclitaxel (PAC) or pegylated liposomal doxorubicin (PLD) in patients with platinum-resistant ovarian cancer (PROC), and used a model informed drug development (MIDD) approach for identification of the recommended phase 2 dose (RP2D). Methods: Eligible patients received AVB-500 at 10, 15, or 20 mg/kg IV q2wk combined with PAC (n = 23) or PLD (n = 30). Patients were treated until progression or unacceptable toxicity. All were followed for survival. Results: No dose limiting toxicities were observed and serum GAS6 was completely suppressed across the three dose levels evaluated. AVB-500 + PAC yielded better clinical activity than AVB-500 + PLD with an ORR of 34.8% (8/23, 2 complete responses) and median DoR, PFS, and OS of 7.0, 3.1, and 10.3 months, respectively. Subgroup analyses showed AVB-500 + PAC patients who had no prior bevacizumab or whose AVB-500 trough levels were >13.8 mg/L exhibited the best clinical response. The ORR and median PFS and OS in patients with these characteristics were ≥50%, ≥7.5 months, and ≥19 months, respectively. Given AVB-500 nor the combination with chemotherapy was expected to cause DLTs, the RP2D of AVB-500 was 15 mg/kg identified using an MIDD approach. Conclusion: AVB-500 was well-tolerated in combination with PAC or PLD and contributed to the clinical activity of PAC in PROC patients. Subgroup analyses identified a population of PROC patients who may benefit the most from AVB-500 treatment, which will be further assessed in an ongoing Phase 3 PROC trial.