GENOTOXICITY OF DNA-DIRECTED ANTINEOPLASTIC AGENTS

DNA损伤剂构成了一个重要的类别， 药物，其中大多数是体外系统的诱变剂。 极有 这些物质的致突变特性可能有助于 化疗的一些副作用，如 肿瘤耐药性的获得， 长期存活者的第二种癌症。 的最终目标 拟议的研究是通过以下方式了解机制： 药物诱导的DNA损伤最终会导致 涉及恶性肿瘤和耐药性的遗传改变。 这种理解将有助于选择和 开发潜在的较少的致突变性和致癌性药物。 为了实现这一目标，一个更直接的目标是 确定某些药物产生的突变类型 在模型系统中，以及识别初始DNA损伤 对这些突变负责。 博莱霉素致突变和 已经在原核生物中详细检查了新制癌素。 系统的基础上的λ噬菌体cI基因。 拟议实验 包括酶修复和其他体外修饰， 药物损伤的DNA被设计来测试两个替代假设 这些研究表明（i）一种特定的氧化类型 脱嘌呤/脱嘧啶位点，即，那些伴随着密切 互补链中的相对断裂，主要是 负责碱基取代诱变，和（ii） 在氧化的醛中的醛部分的次级反应 脱嘌呤/脱嘧啶位点起关键作用。 其他研究 将致力于确定是否有类似的突变 机制发生在哺乳动物细胞中复制的穿梭载体中 以及博来霉素是否特异性诱导c-Ha- ras-1癌基因第12位密码子突变， 原核系统的特异性。 氮芥还 在λ cI基因中具有强烈的诱变性，以及类似的方法 将用于确定突变特异性并鉴定 致突变DNA损伤，在两个E.大肠杆菌和哺乳动物模型。 最后，药物诱导缺失机制的研究 突变将从博来霉素的克隆和测序开始开始， 诱导CHO细胞中aprt基因的缺失。

DNA-damaging agents constitute an important class of antineoplastic drugs, most of which are mutagenic in vitro systems. It is highly likely that the mutagenic properties of these agents contribute substantially to some of the adverse effects of chemotherapy, such as acquisition of drug resistance in tumors, and development of second cancers in long-term survivors. The ultimate objective of the proposed research is an understanding of the mechanisms by which specific forms of drug-induced DNA damage eventually lead to genetic alterations involved in malignancy and drug resistance. Such an understanding would be useful in the selection and development of potentially less mutagenic and carcinogenic drugs. In pursuit of this objective, a more immediate goal is the determination of the types of mutations produced by certain drugs in model systems, and identification of the initial DNA lesions responsible for those mutations. Mutagenesis by bleomycin and neocarzinostatin has been examined in detail in a prokaryotic system based on the cI gene of lambda phage. Proposed experiments involving enzymatic repair and other in vitro modifications of drug-damaged DNA are designed to test two alternative hypotheses suggested by these studies (i) that a specific class of oxidized apurinic/apyrimidinic sites, i.e., those accompanied by closely opposed breaks in the complementary strand, are primarily responsible for base substitution mutagenesis and (ii) that secondary reactions of the aldehyde moiety in the oxidized apurinic/apyrimidinic sites play a critical role. Other studies will be directed toward determining whether similar mutational mechanisms occur in shuttle vectors replicated in mammalian cells and whether bleomycin specifically induces activation of the c-Ha- ras-1 oncogene at codon 12, as predicted from its mutational specificity in the prokaryotic system. Nitrogen mustard also strongly mutagenic in the lambda cI gene, and similar approaches will be employed to determine mutational specificity and identify mutagenic DNA lesions, in both E. coli and mammalian models. Finally, studies on the mechanisms of drug-induced deletion mutations will begin with the cloning and sequencing of bleomycin- induced deletions in the aprt gene in CHO cells.