Inhibition of Human Cytochrome P450 Enzymes by 1,2-Dithiole-3-thione, Oltipraz and Its Derivatives, and Sulforaphane

• Published in: Chemical research in toxicology Vol. 13; no. 4; pp. 245 - 252
• Main Authors: Langouët, Sophie, Furge, Laura Lowe, Kerriguy, Nathalie, Nakamura, Katsunori, Guillouzo, André, Guengerich, F. Peter
• Format: Journal Article
• Language: English
• Published: United States American Chemical Society 01.04.2000
• Subjects: 1,2-Dithiole-3-thione; Anticarcinogenic Agents - pharmacology; Cytochrome P-450 CYP1A2 Inhibitors; Cytochrome P-450 Enzyme Inhibitors; cytochrome P450; Humans; Isothiocyanates; oltipraz; Pyrazines - pharmacology; Quinolines - metabolism; Quinolines - toxicity; sulforaphane; Thiocyanates - pharmacology; Thiones - pharmacology; Thiophenes - pharmacology
• ISSN: 0893-228X; 1520-5010
• DOI: 10.1021/tx990189w

Recent studies have demonstrated that two chemoprotective agents, oltipraz (OPZ), a synthetic derivative of the natural compound 1,2-dithiole-3-thione (D3T), and sulforaphane (SF), an isothiocyanate, are not only inducers of glutathione S-transferases but also inhibitors of some major cytochrome P450 enzymes (P450s) involved in xenobiotic metabolism. We examined P450 inhibition by the two compounds and compared two OPZ metabolites (OPZ M3 and M8) and D3T using human P450s expressed in Escherichia coli membranes. OPZ was a more potent inhibitor than D3T or SF, in the following order of inhibition:  P450 1A2 > 3A4 > 1A1 ∼ 1B1 > 2E1. OPZ M3 also inhibited P450s 1A2, 1A1, 1B1, and 3A4 but not more effectively than OPZ. OPZ M8 was not inhibitory. OPZ behaved as a competitive inhibitor of P450 1A2, with a K i of 1.5 μM. Incubation of P450 1A2 with OPZ and NADPH led to a first-order loss of the P450 spectrum, and the loss was not blocked by glutathione. No such time-dependent loss of P450 was seen with P450 1A2 and D3T, P450 1A2 and OPZ M3, P450 1A2 and SF, P450 3A4 and OPZ, P450 3A4 and D3T, P450 2E1 and OPZ, or P450 2E1 and D3T. The time- and concentration-dependent loss of P450 1A2 activity in the presence of OPZ was characterized with a K i of 9 μM and a k inactivation of 0.19 min-1. The activation of 2-amino-3,5-dimethylimidazo[4,5-f]quinoline (MeIQ) in an E. coli lac-based mutagenicity tester system containing functional human P450 1A2 was inhibited by OPZ (IC50 < 1 μM) but not appreciably by 40 μM D3T. Our results indicate that OPZ is a competitive and mechanism-based inhibitor of P450 1A2, and the extent of this inhibition is significantly greater than that of other chemoprotective chemicals with P450 1A2 or other human P450s.