title: The mibefradil derivative NNC55-0396, a specific T-type calcium channel antagonist, exhibits less CYP3A4 inhibition than mibefradil.
abstract: A novel mibefradil derivative, NNC55-0396, designed to be hydrolysis-resistant, was shown to be a selective T-type Ca(2+) channel inhibitor without L-type Ca(2+) channel efficacy. However, its effects on cytochromes P450 (P450s) have not previously been examined. We investigated the inhibitory effects of NNC55-0396 toward seven major recombinant human P450s--CYP3A4, CYP2D6, CYP1A2, CYP2C9, CYP2C8, CYPC19, and CYP2E1--and compared its effects with those of mibefradil and its hydrolyzed metabolite, Ro40-5966. Our results show that CYP3A4 and CYP2D6 are the two P450s most affected by mibefradil, Ro40-5966, and NNC55-0396. Mibefradil (IC(50) = 33 +/- 3 nM, K(i) = 23 +/- 0.5 nM) and Ro40-5966 (IC(50) = 30 +/- 7.8 nM, K(i) = 21 +/- 2.8 nM) have a 9- to 10-fold greater inhibitory activity toward recombinant CYP3A4 benzyloxy-4-trifluoromethylcoumarin-O-debenzylation activity than NNC55-0396 (IC(50) = 300 +/- 30 nM, K(i) = 210 +/- 6 nM). More dramatically, mibefradil (IC(50) = 566 +/- 71 nM, K(i) = 202 +/- 39 nM) shows 19-fold higher inhibition of CYP3A-associated testosterone 6beta-hydroxylase activity in human liver microsomes compared with NNC55-0396 (IC(50) = 11 +/- 1.1 microM, K(i) = 3.9 +/- 0.4 microM). Loss of testosterone 6beta-hydroxylase activity by recombinant CYP3A4 was shown to be time- and concentration-dependent with both compounds. However, NNC55-0396 (K(I) = 3.87 microM, K(inact) = 0.061/min) is a much less potent mechanism-based inhibitor than mibefradil (K(I) = 83 nM, K(inact) = 0.048/min). In contrast, NNC55-0396 (IC(50) = 29 +/- 1.2 nM, K(i) = 2.8 +/- 0.3 nM) and Ro40-5966 (IC(50) = 46 +/- 11 nM, K(i) = 4.5 +/- 0.02 nM) have a 3- to 4-fold greater inhibitory activity toward recombinant CYP2D6 than mibefradil (IC(50) = 129 +/- 21 nM, K(i) = 12.7 +/- 0.9 nM). Our results suggest that NNC55-0396 could be a more favorable T-type Ca(2+) antagonist than its parent compound, mibefradil, which was withdrawn from the market because of strong inhibition of CYP3A4.
authors.affiliation: Departmental of Pathology and Laboratory Medicine, University of California at Los Angeles, 650 Charles Young Drive, Los Angeles, CA 90095, USA.
authors.forename: Peter H
authors.initials: PH
authors.lastname: Bui
authors.forename: Arnulfo
authors.initials: A
authors.lastname: Quesada
authors.forename: Adrian
authors.initials: A
authors.lastname: Handforth
authors.forename: Oliver
authors.initials: O
authors.lastname: Hankinson
mesh_terms: D002121:Calcium Channel Blockers / Q000494:pharmacology*; D020747:Calcium Channels, T-Type / Q000187:drug effects*; D051544:Cytochrome P-450 CYP3A; D065692:Cytochrome P-450 CYP3A Inhibitors; D006801:Humans; D006868:Hydrolysis; D020748:Mibefradil / Q000737:chemistry* / Q000494:pharmacology; D008862:Microsomes, Liver / Q000187:drug effects / Q000201:enzymology; D011994:Recombinant Proteins / Q000037:antagonists & inhibitors
chemical_list: D002121:Calcium Channel Blockers; D020747:Calcium Channels, T-Type; D065692:Cytochrome P-450 CYP3A Inhibitors; D011994:Recombinant Proteins; D020748:Mibefradil; D051544:Cytochrome P-450 CYP3A; C510163:CYP3A4 protein, human