ENZYMATIC OXIDATION OF DRUGS TO TOXIC AND CARCINOGENIC METABOLITES

主要目标是阐明反应性的结构， 致癌、细胞毒性和致突变的代谢物 多环芳烃和其他化学品的活性 环境化学品。 采取的方法包括：一）研究 用肝微粒体和纯化的 细胞色素P450和环氧化物水解酶，ii）氧化 代谢物，iii）评价的致突变性和致肿瘤性 合成代谢物，iv）阐明 细胞色素P450系统和环氧化物水解酶在调节 这些代谢物的致突变性，v）测定这些代谢物的致突变率， 芳烃氧化物和二醇环氧化物与生物聚合物的反应产物 和模型化合物，以及vi）寻找能够预防 反应性代谢物的致瘤性。 过去一年的工作 集中在两个领域。 （一）K区反应机理研究 芳烃氧化物已经阐明了内在化学物质的作用， 在每个环氧化物碳上的反应性。 构象因素发挥关键作用 在溶剂分解裂解速率和产物测定中的作用 和环氧化物水解酶催化的水解。 我们的研究结果还表明 甲氧基离子亲核进攻的过渡态 K-区域芳烃氧化物（一个模型的攻击水催化 环氧化物水解酶）涉及碳上的部分正电荷， 进行亲核取代。 （二）综合研究 产生了具有生物学意义的寡核苷酸， 二醇环氧加合物。 一种加合物对应于反式打开的 (1R环外氨基菲的（3S，4 R）-二醇环氧化物 将一组脱氧腺苷（dA）掺入到一个九核苷酸中， 包含人K-ras B癌基因的密码子60-62。 一式两份 由该加合寡核苷酸形成，脱氧鸟苷取代 对于修饰的dA相对的互补链中的胸苷， 对熔化温度几乎没有影响。 这一结果表明， 这种碱基对“错配”在由以下原因引起的突变中的可能作用： 二醇环氧化物加合物形成。

The primary goal has been the elucidation of the structures of reactive metabolites responsible for the carcinogenic, cytotoxic and mutagenic activity of drugs, polycyclic aromatic hydrocarbons and other environmental chemicals. The approach taken consists of: i) study of the metabolism of the chemicals with liver microsomes and with purified cytochromes P450 and epoxide hydrolase, ii) synthesis of oxidative metabolites, iii) evaluation of the mutagenicity and tumorigenicity of the synthetic metabolites, iv) elucidation of the roles of the cytochrome P450 system and epoxide hydrolase in modulating the mutagenicity of these metabolites, v) determination of the rates and products of reactions of arene oxides and diol epoxides with biopolymers and model compounds, and vi) search for agents capable of preventing the tumorigenicity of reactive metabolites. Work during the past year has focused in two areas. i) Studies of the reaction mechanisms of K-region arene oxides have elucidated the role of the intrinsic chemical reactivity at each epoxide carbon. Conformational factors play a key role in the determination of rates and products of solvolytic cleavage and epoxide hydrolase-catalyzed hydrolysis. Our results also suggest that the transition state for nucleophilic attack of methoxide ion on the K-region arene oxides (a model for attack of water catalyzed by epoxide hydrolase) involves a partial positive charge on the carbon that undergoes nucleophilic substitution. ii) Synthetic studies have produced biologically significant oligonucleotides containing specific diol epoxide adducts. An adduct corresponding to trans opening of the (1R,2S)-diol (3S,4R)-epoxide of phenanthrene by the exocyclic amino group of deoxyadenosine (dA) was incorporated into a nonanucleotide comprising codons 60-62 of the human K-ras b oncogene. In duplexes formed by this adducted oligonucleotide, substitution of deoxyguanosine for thymidine in the complementary strand opposite the modified dA had almost no effect on the melting temperature. This result suggests a possible role for such base-pair "mismatches" in mutations caused by diol epoxide adduct formation.