Conaway C C, Jiao D, Chung F L
Division of Carcinogenesis and Molecular Epidemiology, American Health Foundation, Valhalla, New York 10595, USA.
Carcinogenesis. 1996 Nov;17(11):2423-7. doi: 10.1093/carcin/17.11.2423.
A series of arylalkyl and alkyl isothiocyanates, and their glutathione, cysteine, and N-acetylcysteine conjugates were used to study their inhibitory activity toward the dealkylation of ethoxyresorufin (EROD), pentoxyresorufin (PROD), and methoxyresorufin (MROD) in liver microsomes obtained from the 3-methylcholanthrene or phenobarbital-treated rats. These reactions are predominantly mediated by cytochrome P450 (P450) isozymes 1A1 and 1A2, 2B1 and 1A2, respectively. All isothiocyanates inhibited PROD more readily than EROD. Increases in the alkyl chain length of arylalkyl isothiocyanates to C6 resulted in an increased inhibitory potency in these assays; at longer alkyl chain lengths (C8-C10) the inhibitory potency declined. The IC50s for phenethyl isothiocyanate (PEITC) were 47, 46 and 1.8 microM for EROD, MROD and PROD, respectively. Substitution of an additional phenyl group on PEITC also increased the inhibitory potency; the IC50s for 1,2-diphenylethyl isothiocyanate (1,2-DPEITC) and 2,2-diphenylethyl isothiocyanate (2,2-DPEITC) were 0.9 and 0.26 microM for EROD, and 0.045 and 0.13 microM for PROD, respectively. The relative inhibitory potency of PEITC and its conjugates was N-acetylcysteine-PEITC (PEITC-NAC) < glutathione-PEITC (PEITC-GSH) < cysteine-PEITC (PEITC-CYS) < PEITC. The observations that the parent isothiocyanates were more potent inhibitors than the conjugates suggest that dissociation of the conjugate is required for activity. Naturally occurring alkyl isothiocyanates, sulforaphane (SFO) and allyl isothiocyanate (AITC), were very weak inhibitors in the assays. These results suggest the potential of isothiocyanates as structural probes for studying P450 isozymes. In addition, the inhibitory activity of isothiocyanates for PROD correlated with the previously demonstrated tumor inhibitory potency in (4-methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) induced A/J mouse lung tumor bioassays, which supports earlier findings that P450 2B1 is one of the major isozymes involved in NNK activation and that inhibition of this isozyme is an important mechanism for the chemopreventive activity of isothiocyanates.
一系列芳基烷基和烷基异硫氰酸酯及其谷胱甘肽、半胱氨酸和N - 乙酰半胱氨酸共轭物被用于研究它们对从3 - 甲基胆蒽或苯巴比妥处理的大鼠获得的肝微粒体中乙氧基试卤灵（EROD）、戊氧基试卤灵（PROD）和甲氧基试卤灵（MROD）脱烷基化的抑制活性。这些反应分别主要由细胞色素P450（P450）同工酶1A1和1A2、2B1和1A2介导。所有异硫氰酸酯对PROD的抑制作用比对EROD更明显。芳基烷基异硫氰酸酯的烷基链长度增加到C6会导致这些测定中的抑制效力增加；在更长的烷基链长度（C8 - C10）时，抑制效力下降。苯乙基异硫氰酸酯（PEITC）对EROD、MROD和PROD的IC50分别为47、46和1.8微摩尔。在PEITC上额外取代一个苯基也会增加抑制效力；1,2 - 二苯乙基异硫氰酸酯（1,2 - DPEITC）和2,2 - 二苯乙基异硫氰酸酯（2,2 - DPEITC）对EROD的IC50分别为0.9和0.26微摩尔，对PROD的IC50分别为0.045和0.13微摩尔。PEITC及其共轭物的相对抑制效力为N - 乙酰半胱氨酸 - PEITC（PEITC - NAC）＜谷胱甘肽 - PEITC（PEITC - GSH）＜半胱氨酸 - PEITC（PEITC - CYS）＜PEITC。母体异硫氰酸酯比共轭物是更强效的抑制剂这一观察结果表明，共轭物的解离是活性所必需的。天然存在的烷基异硫氰酸酯，萝卜硫素（SFO）和烯丙基异硫氰酸酯（AITC），在这些测定中是非常弱的抑制剂。这些结果表明异硫氰酸酯作为研究P450同工酶的结构探针的潜力。此外，异硫氰酸酯对PROD的抑制活性与先前在（4 - 甲基亚硝胺基）-1 - （3 - 吡啶基）-1 - 丁酮（NNK）诱导的A/J小鼠肺癌生物测定中证明的肿瘤抑制效力相关，这支持了早期的发现，即P450 2B1是参与NNK活化的主要同工酶之一，并且抑制这种同工酶是异硫氰酸酯化学预防活性的重要机制。
