Phase I study of pucotenlimab (HX008), an anti-PD-1 antibody, for patients with advanced solid tumors

Background: Pucotenlimab is a humanized immunoglobulin G4 (IgG4) anti programmed cell death protein 1 (anti-PD-1) monoclonal antibody (mAb) with a S228P hinge mutation and an engineered Fc domain. Preclinical data suggests that pucotenlimab exerts antitumor effects. In this phase I study, which was prospectively registered on www.chinadrugtrials. org.cn (CTR20180125), the safety, maximum tolerated dose, preliminary antitumor activity, pharmacokinetics, and immunogenicity of pucotenlimab were evaluated in patients with advanced solid tumors. Methods: Patients with advanced solid tumors refractory to standard therapies were recruited. In a 3+3 dose escalation study, 13 patients received pucotenlimab intravenously every 3 weeks (03W) until disease progression or unacceptable toxicity occurred at doses of 1 mg/kg, 3 mg/kg, 10 mg/kg, and 200 mg. 17 additional patients were assigned in the expansion period. Results: A total of 30 patients were enrolled. No dose-limiting toxicity was observed. The maximum tolerated dose was not reached. The most common treatment-related adverse events of any grade were proteinuria (40%), fatigue (36.7%), weight loss (26.7%), fever (26.7%), increased aspartate aminotransferase (26.7%), rash (23.3%), and anorexia (20.0%). Partial responses occurred in five patients, with an objective response rate of 16.7%. Pharmacokinetics analysis showed rapid absorption followed by slow terminal elimination, with a mean half-life of 17.1-23.5 days across all dose groups. Conclusions: Pucotenlimab had an acceptable toxicity profile at doses up to 10 mg/kg and the maximum tolerated dose was not reached. Based on the pharmacokinetics, efficacy, and safety profile, 3 mg/kg Q3W or 200 mg Q3W are optimal for further drug development.