Phase I study of glasdegib (PF‐04449913), an oral smoothened inhibitor, in Japanese patients with select hematologic malignancies

The hedgehog signaling pathway regulates multiple morphogenetic processes during embryogenesis. Aberrant activation of the hedgehog pathway signal transduction in adult tissues is associated with the pathogenesis of hematologic malignancies and solid tumors. We report findings from an open‐label, multicenter phase I trial of the selective, small‐molecule hedgehog signaling inhibitor glasdegib (PF‐04449913) in Japanese patients with select advanced hematologic malignancies. Glasdegib was administered as once‐daily oral doses (25, 50 and 100 mg) in 28‐day cycles after a lead‐in dose on Day −5. The primary objectives were to determine first‐cycle dose‐limiting toxicities, safety, vital signs and laboratory test abnormalities. Secondary objectives included evaluation of pharmacokinetics, pharmacodynamics and preliminary evidence of clinical activity of glasdegib. No dose‐limiting toxicities were noted in the 13 patients in the present study. All patients experienced at least one treatment‐emergent, all‐causality adverse event. The most frequent treatment‐related adverse events (observed in ≥3 patients) were dysgeusia (n = 9), muscle spasms (n = 5), alopecia, decreased appetite (n = 4 each), and increased blood creatinine phosphokinase, constipation and diarrhea (n = 3 each). Two deaths occurred during the study and were deemed not to be treatment‐related due to disease progression. Glasdegib demonstrated dose‐proportional pharmacokinetics, marked downregulation of the glioma‐associated transcriptional regulator GLI1 expression in normal skin, and evidence of preliminary clinical activity, although data are limited. Glasdegib was safe and well tolerated across the dose levels tested. It is confirmed that the 100‐mg dose is safe and tolerable in Japanese patients, and this dose level will be examined in the future clinical trial.