Characterization of in vitro and in vivo metabolism of AG-024322, a novel cyclin-dependent kinase (CDK)

Uncontrolled cell proliferation is the hall mark of many cancers, and is typically manifested by a deregulation of the cell-division cycle. CDKs play critical roles in regulating cell cycle, apoptosis and cell differentiation. AG-024322 is a multitargeted CDK inhibitor that has been shown to induce cancer cell apoptosis and demonstrate significant antitumor activity in human tumor xenograft models. This compound is under clinical development as an intravenous anticancer agent. AG-024322 exhibited moderate to high systemic clearance across preclinical species. In vitro metabolism in human liver microsomes and hepatocytes demonstrates that glucuronidation and oxidation represent the major metabolic pathways of AG-024322. The experiments of chemical inhibition and microsomes containing individual CYP or UGT isoforms revealed that CYP3A and UGT1A1 appear to predominantly mediate AG-024322 oxidation and glucuronidation, respectively. Formation kinetics of the two pathways in human liver microsomes suggested that the glucuronidation activity of AG-024322 was approximately 3-fold higher as compared to CYP-mediated oxidation, contributing approximately 37% and 13% of the total clearance, respectively, based on the projected human clearance. UGT1A1 is a polymorphic isoform involved in glucuronidation of bilirubin. It is of concern if glucuronidation via UGT1A1 plays a major role in the elimination of AG-024322 in humans as competitive inhibition of UGT1A1 has been associated with toxicity (Gilbert and Crigler-Najjar syndromes). Therefore, this information was used to influence the clinical study design to only include subjects having constitutive expression of UGT1A1 in the first human study, thereby decreasing the potential risk of toxicity to patients.