Safety and Clinical Activity of a New Anti-PD-L1 Antibody as Monotherapy or Combined with Targeted Therapy in Advanced Solid Tumors: The PACT Phase Ia/Ib Trial.

PURPOSE This phase Ia/Ib PACT study evaluated the safety, pharmacokinetics, pharmacodynamics, and antitumor activity of a new programmed cell death ligand 1 (PD-L1) inhibitor, LY3300054, as monotherapy or in combination with ramucirumab, abemaciclib, or merestinib (a type II MET kinase inhibitor) in patients with advanced, refractory solid tumors (NCT02791334). PATIENTS AND METHODS Patients were enrolled into cohorts of escalating LY3300054 dose (phase Ia) as monotherapy (N = 15) or combined with ramucirumab (N = 10), abemaciclib (N = 24), or merestinib (N = 12). The phase Ib dose expansion enrolled 8 patients with melanoma in the monotherapy arm and 12 patients with pancreatic cancer in the merestinib combination arm. Combination treatments were administered concurrently from day 1 of each cycle. A 14-day lead-in abemaciclib arm was also explored. Primary endpoints were dose-limiting toxicity (DLT) and safety. RESULTS Treatment-related adverse events included fatigue and nausea in the monotherapy arm (13% for each), hypothyroidism (30%) in the ramucirumab arm, diarrhea (54%) in the abemaciclib arm, and nausea (25%) in the merestinib arm. DLTs associated with hepatoxicity were observed in 3 of 4 patients in the abemaciclib lead-in cohorts. No DLTs or grade 3 or 4 hepatoxicity were reported in the concurrent abemaciclib arm. Pharmacokinetic characteristics were comparable with other PD-L1 inhibitors. One patient in each arm experienced a partial response per RECIST v1.1 lasting ≥7 months. CONCLUSIONS LY3300054 was well tolerated without unexpected safety concerns when administered alone or concurrently with ramucirumab, abemaciclib, or merestinib. Lead-in abemaciclib before combining with LY3300054 was not feasible due to hepatotoxicity. Durable clinical benefits were seen in all regimens.