A phase I and pharmacokinetic study of taladegib, a Smoothened inhibitor, in Japanese patients with advanced solid tumors

Background This phase I dose-escalation study investigated the safety of the Smoothened inhibitor taladegib in Japanese patients with advanced solid tumors. Methods Patients received taladegib orally once daily for 28-day cycles, using a 3 + 3 dose-escalation method. The primary objective was the safety and tolerability of taladegib at doses up to the global recommended dose (400 mg). Secondary objectives included pharmacokinetics, changes in skin glioma-associated oncogene homolog 1 (Gli1) transcript levels, and antitumor activity. Results Nineteen patients received treatment (100 mg: 3; 200 mg: 3; 400 mg: 13). No dose-limiting toxicities (DLTs) were observed at doses of 100 mg or 200 mg; 3 of the 9 patients evaluable for DLTs at the 400 mg dose level experienced DLTs (thrombocytopenia: 1; decreased appetite: 2). The most commonly reported treatment-related adverse events were dysgeusia (13/19, 68.4%), decreased appetite (12/19, 63.2%), nausea (9/19, 47.4%), fatigue (9/19, 47.4%), and vomiting (6/19, 31.6%). The pharmacokinetic profile suggested that exposure to taladegib was higher in Japanese than non-Japanese patients, possibly related to differences in body weight and/or drug formulation. At all dose levels, a high level of inhibition of skin Gli1 transcript levels was observed after 15 and 30 days of exposure to taladegib. Partial response was achieved by 1 patient (basal cell carcinoma of the skin) and stable disease by 4 patients. Conclusions Taladegib doses of 100 mg and 200 mg, but not the global recommended dose of 400 mg, were well tolerated in this population of Japanese patients with advanced solid tumors.