A Phase I Study of an IDO-1 Inhibitor (LY3381916) as Monotherapy and in Combination With an Anti-PD-L1 Antibody (LY3300054) in Patients With Advanced Cancer.

LY3381916 is an orally available, highly selective, potent inhibitor of indoleamine 2,3-dioxygenase 1. This study explored the safety, tolerability, pharmacokinetics, pharmacodynamics, and antitumor activity of LY3381916 monotherapy and in combination with a programmed death-ligand 1 (PD-L1) inhibitor (LY3300054) in patients with advanced solid tumors. During dose escalation, patients received escalating doses of LY3381916 at 60-600 mg once daily (qd) and 240 mg twice daily in monotherapy (n=21) and in combination with PD-L1 inhibitor at 700 mg every 2 weeks (n=21). A modified toxicity probability interval method was used to guide dose escalation. Dose-limiting toxicities occurred in 3 patients; 1 at LY3381916 240 mg twice daily (alanine aminotransferase/aspartate aminotransferase increase and systemic inflammatory response syndrome) and 2 at LY3381916 240 mg qd in combination with PD-L1 inhibitor (fatigue and immune-related hepatitis). LY3381916, at the recommended phase II dose, 240 mg qd, in combination with PD-L1 inhibitor, produced maximal inhibition of indoleamine 2,3-dioxygenase 1 activity in plasma and tumor tissue, and led to an increase of CD8 T cells in tumor tissue. In the combination dose expansion cohorts, 14 triple-negative breast cancer and 4 non-small cell lung cancer patients were enrolled. Treatment-related liver toxicity (grade ≥2 alanine aminotransferase/aspartate aminotransferase increase or immune-related hepatitis) was the most prominent adverse event in triple-negative breast cancer patients (n=5, 35.7%). Best response was stable disease. These preliminary data suggest an alternative dose level of LY3381916 is needed for the combination with PD-L1 inhibitor. The combination clinical activity was limited in this study.