A Phase I Dose-Escalation Study of LY3405105, a Covalent Inhibitor of Cyclin-Dependent Kinase 7, Administered to Patients With Advanced Solid Tumors

Background: This study aimed to evaluate the safety, pharmacokinetics (PKs), and preliminary activity of LY3405105, a covalent inhibitor of cyclin-dependent kinase 7 (CDK7), in patients with advanced solid tumors.

Materials and methods: LY3405105 monotherapy was given once daily (QD; part A1) or thrice weekly (TIW; part A2) starting at 1 and 2 mg orally, respectively, and escalated per a Bayesian design in adult patients. The primary endpoint was safety, and secondary endpoints included PKs and antitumor activity.

Results: Fifty-four patients were enrolled: 43 in part A1 and 11 in part A2. Seven patients had dose-limiting toxicities, all in part A1 (45 mg: n = 3; 35 mg: n = 3; 25 mg: n = 1). Thirty-five patients (64.8%) reported at least one treatment-related adverse event (TRAE). TRAEs (≥10%) were diarrhea, nausea, fatigue, vomiting, abdominal pain, anemia, asthenia, and decreased platelet count. QD dosing showed sustained exposure with less peak-trough fluctuation compared to TIW dosing. Median time to maximum concentration was 1-2 hours and half-life was 15-19 hours. CDK7-target occupancy in skin and peripheral blood on day 15 was dose-dependent and reached near maximal occupancy of 75% at ≥15 mg QD. The maximum tolerated dose (MTD) was 20 mg QD. Twelve patients in part A1 (27.9%) and 5 patients in part A2 (45.5%) had a best overall response of stable disease. No complete response or partial response was observed.

Conclusion: The MTD of LY3405105 monotherapy was 20 mg QD. The most common toxicities were gastrointestinal adverse events, myelosuppression, fatigue, and asthenia. Limited clinical activity was observed in this phase I trial, and there are no plans for further development.

Clinicaltrials.gov identifier: NCT03770494.