Selective mechanism-based inactivation of cytochromes P-450 2B1 and P-450 2B6 by a series of xanthates.
Fifteen xanthates with carbon chains of different lengths or substitutions, including the antiviral compound D609 (O-tricyclo[5.2. 1.0(2,6)]dec-9-yl-dithiocarbonate), were tested for their ability to inactivate cytochromes P-450 (P-450s) 2B1 and 2B6. All of the xanthates tested were found to inactivate P-450 2B1 in a time- and concentration-dependent manner. The rates of inactivation at 30 degrees C ranged from 0.22 min-1 to 0.02 min-1. The concentrations required for half-maximal inactivation were between 2.4 and 69 microM. A general trend in the inactivation kinetics could be observed with an increasing chain length of the xanthates. Longer carbon chains resulted in slower rates of inactivation with longer half-times of inactivation and higher partition ratios. For P-450 2B1, the most effective inactivators were xanthates with substitutions of intermediate length. The best inactivator for P-450 2B1 was the C8 xanthate, with an inactivation potency (KI) of 2.4 microM, a rate of inactivation of 0.07 min-1, and a partition ratio of 4. Four xanthates were further examined for their effect on the 7-ethoxy-4-(trifluoromethyl)coumarin activity of P-450 2B6. The C8 xanthate was again the most effective inactivator, with a KI of 1 microM. Although the KI values were generally lower than those found with P-450 2B1, the rates of inactivation for P-450 2B6 with the various xanthates were 3- to 5-fold slower. In addition, the isozyme selectivity of xanthates was tested with P-450s 2E1, 1A1, 3A2, 3A4, 2C9, and 2D6. P-450 2E1 was inactivated by xanthates at concentrations 15- to 100-fold higher than those required to inactivate either P-450 2B1 or 2B6. P-450 1A1 was not inactivated by xanthates. However, all of the xanthates tested were able to inhibit the enzymatic activity of P-450 1A1 to a different extent, depending on the length of the xanthate carbon chain. Virtually no inactivation of P-450s 2D6 or 2C9 was seen, except that C8 and D609 were inhibitory at high concentrations (0.2-0.6 mM). None of the xanthates studied had any effect on the activities of P-450s 3A2 or 3A4.
Yanev
S
S
Department of Drug Toxicology, Institute of Physiology, Bulgarian Academy of Sciences, Sofia, Bulgaria.
Kent
U M
UM
Pandova
B
B
Hollenberg
P F
PF
D000818:Animals; D001189:Aryl Hydrocarbon Hydroxylases; D019362:Cytochrome P-450 CYP2B1 / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D065702:Cytochrome P-450 CYP2B6; D065607:Cytochrome P-450 Enzyme Inhibitors; D003577:Cytochrome P-450 Enzyme System / Q000378:metabolism*; D004789:Enzyme Activation / Q000187:drug effects; D004791:Enzyme Inhibitors / Q000494:pharmacology; D007527:Isoenzymes / Q000037:antagonists & inhibitors / Q000378:metabolism; D007700:Kinetics; D008297:Male; D010089:Oxidoreductases, N-Demethylating / Q000037:antagonists & inhibitors* / Q000378:metabolism*; D051381:Rats; D020318:Rats, Long-Evans; D013871:Thiones / Q000494:pharmacology*
D065607:Cytochrome P-450 Enzyme Inhibitors; D004791:Enzyme Inhibitors; D007527:Isoenzymes; D013871:Thiones; D003577:Cytochrome P-450 Enzyme System; D001189:Aryl Hydrocarbon Hydroxylases; D019362:Cytochrome P-450 CYP2B1; D065702:Cytochrome P-450 CYP2B6; D010089:Oxidoreductases, N-Demethylating