Short Communication ASSESSMENT OF THE CONTRIBUTIONS OF CYP3A4 AND CYP3A5 IN THE METABOLISM OF THE ANTIPSYCHOTIC AGENT HALOPERIDOL TO ITS POTENTIALLY NEUROTOXIC PYRIDINIUM METABOLITE AND EFFECT OF ANTIDEPRESSANTS ON THE BIOACTIVATION PATHWAY

As a plausible explanation for the large interindividual variability in the pharmacokinetics of the neuroleptic agent haloperidol, the contributions of CYP3A isozymes (CYP3A4 and the polymorphic CYP3A5) predominantly involved in haloperidol bioactivation to the neurotoxic pyridinium species 4-(4-Chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-pyridinium (HPP ) were assessed in human liver microsomes and heterologously expressed enzymes. Based on recent reports on drug-drug interactions between haloperidol and antidepressants including selective serotonin reuptake inhibitors, the inhibitory effects of antidepressants on the CYP3A4/5mediated haloperidol bioactivation were also evaluated. HPP formation followed Michaelis-Menten kinetics in microsomes, recombinant CYP3A4, and CYP3A5 with Km values of 24.4 8.9 M, 18.3 4.9 M, and 200.2 47.6 M, respectively, and Vmax values of 157.6 13.2 pmol/min/mg of protein, 10.4 0.6 pmol/ min/pmol P450, and 5.16 0.6 pmol/min/pmol P450, respectively. The similarity in Km values between human liver microsomal and recombinant CYP3A4 incubations suggests that polymorphic CYP3A5 may not be an important genetic contributor to the interindividual variability in CYP3A-mediated haloperidol clearance pathways. Besides HPP , a novel 4-fluorophenyl-ring-hydroxylated metabolite of haloperidol in microsomes/CYP3A enzymes was also detected. Its formation was consistent with previous reports on the detection of O-sulfate and -glucuronide conjugates of a fluorophenyl ring-hydroxylated metabolite of haloperidol in human urine. Finally, all antidepressants except buspirone inhibited the CYP3A4/5-catalyzed oxidation of haloperidol to HPP in a concentration-dependent manner. Based on the estimated IC50 values for inhibition of HPP formation in microsomes, the antidepressants were ranked in the following order: fluoxetine, nefazodone, norfluoxetine, trazodone, and fluvoxamine. These inhibition results suggest that clinically observed drug-drug interactions between haloperidol and antidepressants may arise via the attenuation of CYP3A4/5-mediated 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-4-piperidinol biotransformation pathways. Although, the neuroleptic agent haloperidol [HP, 4-(4-chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-4-piperidinol] is one of the most widely used antipsychotic drugs, a narrow therapeutic index and a large interindividual and interracial variability in pharmacokinetics results in the requirement of individualized HP dose optimization (Ulrich et al., 1998). The narrow therapeutic index is associated with the frequent occurrence of extrapyramidal side effects including acute dystonic reactions, akathisia, Parkinsonism, and, following chronic treatment, tardive dyskinesias (TD) that are slow to develop and often irreversible (Wright et al., 1998). The persistence of TD in many patients after discontinuation of HP therapy suggests that this condition may be related to a neuronal lesion induced by HP or a reactive metabolite(s) derived from it. HP is extensively metabolized in the liver with only 1% of the administered dose excreted in the urine (Forsman et al., 1977). Major biotransformation pathways of HP in humans have been extensively characterized (see Kudo and Ishizaki, 1999 for a review) and are summarized in Fig. 1. These include 1) glucuronidation of the 3 alcohol moiety (Someya et al., 1992); 2) reduction of the carbonyl group by cytosolic carbonyl reductase, which leads to reduced HP (Eyles and Pond, 1992); 3) reverse oxidation of reduced HP back to HP (Pan et al., 1998); 4) N-dealkylation leading to the formation of 4-(4-chlorophenyl)-4-hydroxypiperidine (CPHP) (Fang et al., 2001); 5) dehydration of 3 alcohol moiety to 4-(4-chlorophenyl)-1-[4-(4fluorophenyl)-4-oxobutyl]-1,2,3,6-tetrahydropyridine (HPTP) (Subramanyam et al., 1991a; Van der Schyf et al., 1994); 6) oxidation of the piperidin-4-ol moiety in HP to the corresponding 4-(4-Chlorophenyl)1-[4-(4-fluorophenyl)-4-oxobutyl]-pyridinium (HPP ) metabolite (Usuki et al., 1996); and 7) oxidation of the piperidin-4-ol moiety in reduced HP to the corresponding 4-(4-Chlorophenyl)-1-[4-(4-fluorophenyl)-4-hydroxybutyl]-pyridinium (RHPP ) metabolite (Eyles et 1 Abbreviations used are: HP, haloperidol; TD, tardive dyskinesias; CPHP, 4-(4-chlorophenyl)-4-hydroxypiperidine; HPTP, 4-(4-Chlorophenyl)-1-[4-(4-fluorophenyl)-4-oxobutyl]-1,2,3,6-tetrahydropyridine; HPP , 4-(4-Chlorophenyl)-1[4-(4-fluorophenyl)-4-oxobutyl]-pyridinium; RHPP , 4-(4-Chlorophenyl)-1-[4-(4fluorophenyl)-4-hydroxybutyl]-pyridinium; MPP , 1-methyl-4-phenylpyridinium; P450, cytochrome P450; DMSO, dimethyl sulfoxide; SSRI, selective serotonin reuptake inhibitor; LC-MS/MS, high performance liquid chromatography-tandem mass spectrometry; HPLC, high performance liquid chromatography; Rt, retention time; CID, collision-induced dissociation; NPP, N-nonyl-4-phenylpyridinium. Address correspondence to: Amit S. Kalgutkar, Pharmacokinetics, Dynamics, and Metabolism Department, Pfizer Global Research and Development, Groton, CT 06340. E-mail: [email protected] 0090-9556/03/3103-243–249$7.00 DRUG METABOLISM AND DISPOSITION Vol. 31, No. 3 Copyright © 2003 by The American Society for Pharmacology and Experimental Therapeutics 882/1042694 DMD 31:243–249, 2003 Printed in U.S.A. 243 at A PE T Jornals on Jne 1, 2017 dm d.aspurnals.org D ow nladed from