A first in man, phase I dose-escalation study of PHA-793887, an inhibitor of multiple cyclin-dependent kinases (CDK2, 1 and 4) reveals unexpected hepatotoxicity in patients with solid tumors

Background: PHA-793887 is an inhibitor of multiple cyclin-dependent kinases (CDK) with activity against CDK2, CDK1 and CDK4. The primary objectives of this first in man study were to determine the dose limiting toxicities (DLTs), maximum tolerated dose (MTD) and recommended phase II dose of PHA-793887. Results: Although toxicity was acceptable at initial dose levels, PHA-793887 was poorly tolerated at doses ≥44 mg/m². The most frequent events across all dose levels were gastrointestinal or nervous system events. DLTs were experienced by two of three patients at the dose level of 66 mg/m², and by three of nine patients at the dose level of 44 mg/m². In all but one patient the DLT was hepatotoxicity; fatal hepatorenal failure was seen in one patient treated at the 44 mg/ m² dose level. There were no objective responses, but disease stabilization was observed in five patients. Over the dose range investigated, pharmacokinetic studies showed that systemic exposure to PHA-793887 increased with the dose and was time-independent. The study terminated after the enrolment of 19 patients due to the severe hepatic toxicity. Patients and Methods: Cohorts of three to six patients were treated at doses of 11, 22, 44 and 66 mg/m² of PHA-793887 administered as 1-hour intravenous infusion on days 1, 8 and 15 in a 4-week cycle. Safety and pharmacokinetics were investigated. Conclusion: PHA-793887 induces severe, dose-related hepatic toxicity, which was not predicted by pre-clinical models and currently precludes its further clinical development.