No abstract

1 The ability of olanzapine to inhibit the metabolism of marker catalytic activities for the cytochromes P450 CYP3A, CYP2D6, CYP2C9, and CYP2C19 was examined. This inhibitory capability was compared with that obtained with clozapine and known inhibitory compounds for the same cytochromes P450. 2 Olanzapine, clozapine, and ketoconazole were all found to non-competitively inhibit 1'-hydroxy midazolam formation, form selective for CYP3A, yielding K , values of 491, 99 and 0.11 p~, respectively. The 1'-hydroxylation of bufuralol, form selective for CYP2D6, was competitively inhibited by olanzapine (Ki = 89 p~) , clozapine ( K , = 19 p~) , and quinidine (Ki =0.03 p~) . Tolbutamide metabolism to 4-hydroxy tolbutamide, form selective for CYP2C9, was competitively inhibited by clozapine and phenytoin (Ki of 31 p~ and 17 PM, respectively). Olanzapine non-competitively inhibited tolbutamide metabolism with a Ki of 715 p~. The marker catalytic activity for CYP2C19 mediated metabolism, 4'-hydroxy S-mephenytoin formation, was competitively inhibited by clozapine (Ki = 69 p~) and omeprazole (Ki = 4.1 p~). Noncompetitive inhibition of CYP2C19 mediated metabolism was seen with olanzapine with a Ki of 920 p~. 3 The calculated percent inhibition by olanzapine of substrates metabolized by CYP3A, CYP2D6, CYP2C9, and CYP2C19 was modeled assuming a total plasma concentration in the therapeutic range (0.2 p~) . Total olanzapine us unbound olanzapine was used to model the worst case (most conservative) situation. In all cases, the calculated percent inhibition of these cytochromes P450 by olanzapine was <0.3%, suggesting that there would be little in uivo inhibition of the metabolism of substrates of these enzymes when co-administered with olanzapine.

ABSTRACT:Studies were performed to determine the cytochromes P450 (P450) responsible for the biotransformation of (S) Over the last several years, evidence has accumulated that implicates the hyperglycemia-induced activation of protein kinase C (PKC 1 ) as one of the mechanisms responsible for the development and/or progression of chronic complications of diabetes. Hyperglycemia-induced increases in diacylglycerol, a physiological activator of PKC, have been demonstrated in the organs that are susceptible to developing diabetic complications, including the retina, kidney, aorta, and heart (Craven and DeRubertis, 1989;Ayo et al., 1991;Inoguchi et al., 1992;Shiba et al., 1993). In diabetes, hyperglycemia-induced generation of diacylglycerol activates the beta 1 and 2 isoforms of the PKC gene family (Inoguchi et al., 1992;Ishii et al., 1996). (S)-9-((Dimethylamino)methyl)-6,7,10,11-tetrahydro-9H,18H-5,21:12,17-dimethenodibenzo(e,k)pyrrolo(3,4-h)(1,4,13)oxadiaza-cyclohexadecine-18,20(19H)-dione (LY333531) (Engel et al., 2000), is a selective inhibitor of PKC beta. LY333531 and its N-desmethyl metabolite, which is formed in animals and humans, inhibit PKC beta 1 and 2 isoforms with an approximate IC 50 of 5 nM . Therefore, LY333531 may be useful in the treatment of diabetic complications and is currently under clinical development for the treatment of diabetic microvascular complications including retinopathy, macular edema, and peripheral neuropathy.-In vitro methodologies using human liver tissue have been developed to aid in the prediction of possible variation in metabolic clearance in vivo and drug-drug interactions for a new molecular entity. The studies described herein used these in vitro techniques to identify the P450(s) responsible for the formation of the major (and equipotent) metabolite of LY333531, N-desmethyl LY333531. The initial step in the identification of these enzymes was a kinetic analysis of the formation of N-desmethyl LY333531 following incubations of the drug with human liver microsomes. The identification of the enzyme(s) involved in the formation of N-desmethyl LY333531 was then accomplished by correlating the rate of formation of the metabolite with immunoquantified levels and/or the associated formselective catalytic activities for the drug-metabolizing enzymes by a bank of human liver microsomes. The ability of specific cDNAexpressed cytochromes P450 (P450s) to form N-desmethyl LY333531 was used to corroborate the results of the correlation studies. Finally, P450-selective inhibitors were used to examine their effect on the formation of the metabolite in question.To predict interactions that may occur in the clinical setting between LY333531 and coadministered drugs, the ability of the PKC beta inhibitor, LY333531, and its N-desmethyl metabolite to inhibit metabolism mediated by CYP3A, CYP2D6, CYP1A2, and CYP2C9 was examined. Using in vitro metabolism of specific form-selective substrates as probes of metabolism, CYP2D6, CYP2C9, CYP1A2,