Seidel A, Soballa V J, Raab G, Frank H, Greim H, Grimmer G, Jacob J, Doehmer J
Institut für Toxikologie, Johannes Gutenberg-Universität Mainz, Obere Zahlbacher Str. 67, D-55131 Mainz, Germany.
Environ Toxicol Pharmacol. 1998 May;5(3):179-96. doi: 10.1016/s1382-6689(97)10073-4.
Regio- and stereoselective metabolism mediated by cytochrome P450 (CYP) and metabolite-dependent cytotoxicity of benzo[c]phenanthrene (B[c]Ph) and its trans-3,4-dihydrodiol, the metabolic precursor of the carcinogenic fjord-region B[c]Ph-3,4-dihydrodiol 1,2-epoxides (B[c]PhDE), were investigated with V79 Chinese hamster cells genetically engineered for three rat and six human CYP isoforms. The order of the capabilities of the CYP isoforms to metabolize B[c]Ph was as follows: h1A1>r1A1>r1A2>h1B1>h1A2>r2B1>>h2E1>h2A6>h3A4. Regardless of the species, all individual CYP isoforms preferentially catalyzed the oxidation of B[c]Ph at the 5,6-position (K-region) except human CYP1A1 and human CYP1A2, which oxidized both the 5,6- and the 3,4-position with similar efficiency. While human CYP1A1, rat CYP1A1 and rat CYP1A2 formed almost exclusively the (-)-B[c]Ph-3R,4R-dihydrodiol, human CYP1A2 produced both the (-)-3R,4R- and the (+)-3S,4S-dihydrodiol enantiomers in a ratio of 2:1. Stereoselective activation of B[c]Ph, the (±)-B[c]Ph-3,4-dihydrodiol and its (-)-3R,4R-enantiomer to the fjord-region (-)-anti-B[c]PhDE occurred upon incubation with rat CYP1A1 and rat CYP1A2 as indicated by the formation of two stereoisomeric tetraols, the hydrolysis products of the labile anti-B[c]PhDE. The formation of tetraols in the culture medium was accompanied by a concentration-dependent increase in cytotoxicity indicating that this effect was mediated by the fjord-region (-)-anti-B[c]PhDE formed as reactive intermediate. All human and rat CYP-expressing V79 cell lines investigated did not show any significant capacity to metabolize the (+)-3S,4S-dihydrodiol. The present study indicates that the human CYP isoforms 1A1 and 1B1 have complementary catalytic properties to activate B[c]Ph to its fjord-region B[c]PhDE, whereas other human isoforms play a minor role. Activation of B[c]Ph by human CYP1A1 and 1B1 is less efficient than by rat CYP1A1 or rat CYP1A2, but proceeds with similar stereoselectivity via the (-)-3R,4R-dihydrodiol to the strong carcinogen (-)-anti-B[c]PhDE with (R,S,S,R)-configuration.
利用经基因工程改造表达三种大鼠和六种人类细胞色素P450（CYP）同工型的V79中国仓鼠细胞，研究了苯并[c]菲（B[c]Ph）及其反式-3,4-二氢二醇（致癌性峡湾区B[c]Ph-3,4-二氢二醇1,2-环氧化物（B[c]PhDE）的代谢前体）的区域和立体选择性代谢以及代谢物依赖性细胞毒性。CYP同工型代谢B[c]Ph的能力顺序如下：h1A1>r1A1>r1A2>h1B1>h1A2>r2B1>>h2E1>h2A6>h3A4。无论物种如何，除人类CYP1A1和人类CYP1A2外，所有单个CYP同工型均优先催化B[c]Ph在5,6位（K区域）的氧化，而人类CYP1A1和人类CYP1A2以相似的效率氧化5,6位和3,4位。虽然人类CYP1A1、大鼠CYP1A1和大鼠CYP1A2几乎只形成（-）-B[c]Ph-3R,4R-二氢二醇，但人类CYP1A2产生（-）-3R,4R-和（+）-3S,4S-二氢二醇对映体，比例为2:1。与大鼠CYP1A1和大鼠CYP1A2孵育后，B[c]Ph、（±）-B[c]Ph-3,4-二氢二醇及其（-）-3R,4R-对映体立体选择性激活为峡湾区（-）-反式-B[c]PhDE，这通过两种立体异构四醇（不稳定的反式-B[c]PhDE的水解产物）的形成得以表明。培养基中四醇的形成伴随着细胞毒性的浓度依赖性增加，表明这种效应是由作为反应中间体形成的峡湾区（-）-反式-B[c]PhDE介导的。所有研究的表达人类和大鼠CYP的V79细胞系均未显示出代谢（+）-3S,4S-二氢二醇的任何显著能力。本研究表明，人类CYP同工型1A1和1B1具有互补的催化特性，可将B[c]Ph激活为其峡湾区B[c]PhDE，而其他人类同工型作用较小。人类CYP1A1和1B1对B[c]Ph的激活效率低于大鼠CYP1A1或大鼠CYP1A2，但通过（-）-3R,4R-二氢二醇以相似的立体选择性生成具有（R,S,S,R）构型的强致癌物（-）-反式-B[c]PhDE。
