First-in-human Phase I/Ib Open-label Dose-escalation Study of GWN323 (anti-GITR) As a Single Agent and in Combination with Spartalizumab (anti-PD-1) in Patients with Advanced Solid Tumors and Lymphomas

Background: GWN323 is an IgG1 monoclonal antibody (mAb) against the glucocorticoid-induced tumor necrosis factor receptor-related protein. This first-in-human, open-label phase I/Ib study aimed to investigate the safety and tolerability and to identify the recommended doses of GWN323 with/without spartalizumab, an anti-programmed cell death receptor-1 agent, for future studies. Pharmacokinetics, preliminary efficacy and efficacy biomarkers were also assessed.

Methods: Patients (aged ≥18 years) with advanced/metastatic solid tumors with Eastern Cooperative Oncology Group performance status of ≤2 were included. GWN323 (10-1500 mg) or GWN323+spartalizumab (GWN323 10-750 mg+spartalizumab 100-300 mg) were administered intravenously at various dose levels and schedules during the dose-escalation phase. Dose-limiting toxicities (DLTs) were assessed during the first 21 days in a single-agent arm and 42 days in a combination arm. Adverse events (AEs) were graded per National Cancer Institute-Common Toxicity Criteria for Adverse Events V.4.03 and efficacy was assessed using Response Evaluation Criteria in Solid Tumors V.1.1.

Results: Overall, 92 patients (single-agent, n=39; combination, n=53) were included. The maximum administered doses (MADs) in the single-agent and combination arms were GWN323 1500 mg every 3 weeks (q3w) and GWN323 750 mg+spartalizumab 300 mg q3w, respectively. No DLTs were observed with single-agent treatment. Three DLTs (6%, all grade ≥3) were noted with combination treatment: blood creatine phosphokinase increase, respiratory failure and small intestinal obstruction. Serious AEs were reported in 30.8% and 34.0%, and drug-related AEs were reported in 82.1% and 77.4% of patients with single-agent and combination treatments, respectively. Disease was stable in 7 patients and progressed in 26 patients with single-agent treatment. In combination arm patients, 1 had complete response (endometrial cancer); 3, partial response (rectal cancer, adenocarcinoma of colon and melanoma); 14, stable disease; and 27, disease progression. GWN323 exhibited a pharmacokinetic profile typical of mAbs with a dose-dependent increase in the pharmacokinetic exposure. Inconsistent decreases in regulatory T cells and increases in CD8+ T cells were observed in the combination arm. Gene expression analyses showed no significant effect of GWN323 on interferon-γ or natural killer-cell signatures.

Conclusions: GWN323, as a single agent and in combination, was well tolerated in patients with relapsed/refractory solid tumors. The MAD was 1500 mg q3w for single-agent and GWN323 750 mg+spartalizumab 300 mg q3w for combination treatments. Minimal single-agent activity and modest clinical benefit were observed with the spartalizumab combination.

Trial Registration Number: NCT02740270.