In Vitro Ciclopirox Glucuronidation in Liver Microsomes from Humans and Various Experimental Animals.

Abstract

Background and objective: Ciclopirox is a widely used antifungal drug, redisposition of which has drawn increasing attentions due to multiple promising activities. The drug undergoes extensive glucuronidation, which acts as a major obstacle in the ongoing novel application and still remains poorly understood. The current study aims to phenotype ciclopirox glucuronidation pathway and as well to decipher the related species differences.

Methods: Ciclopirox glucuronidation was investigated in liver microsomes from humans (HLM) and various experimental animals. Assays with recombinant uridine diphosphate glucuronosyltransferases (UGTs), enzyme kinetic analyses and selective inhibitors were used to determine the role of individual UGTs in ciclopirox glucuronidation.

Results: HLM is highly active in ciclopirox glucuronidation with Michaelis-Menten constant (K_m), maximum velocity (V_max), and intrinsic clearance (CL_int) values of 139 μM, 7.89 nmol/min/mg, and 56 μL/min/mg, respectively. UGT1A9 displays by far the highest activity, whereas several other isoforms (UGT1A6, UGT1A7, and UGT1A8) catalyze formation of traced glucuronides. Further kinetic analysis demonstrates that UGT1A9 has a closed K_m value (167 μM) to HLM. UGT1A9 selective inhibitor (magnolol) can potently inhibit ciclopirox glucuronidation in HLM with the IC₅₀ value of 0.12 μM. The reaction displays remarkable differences across liver microsomes from mice, rats, cynomolgus monkey, minipig, and beagle dog, with the CL_int values in the range of 26-369 μL/min/mg. In addition, ciclopirox glucuronidation activities of experimental animals' liver microsomes were less sensitive to magnolol than that of HLM.

Conclusions: Ciclopirox glucuronidation displays remarkable species differences with UGT1A9 as a dominant contributor in humans. It is suggested that the pharmacological or toxicological effects of ciclopirox may be UGT1A9 and species dependent.