GENOTOXICITY OF DNA-DIRECTED ANTINEOPLASTIC AGENTS

DNA损伤剂是一类重要的抗肿瘤药物 药物，其中大部分是体外诱变系统。它是高度的 很可能这些制剂的诱变特性有助于 对化疗的一些不良影响，如 随着肿瘤中耐药的获得和肿瘤的发展 长期存活者的第二种癌症。的最终目标是 拟议的研究是对这些机制的一种理解 哪些特定形式的药物诱导的DNA损伤最终会导致 与恶性肿瘤和耐药性有关的基因改变。 这样的理解将有助于选择和 潜在较低诱变性和致癌性药物的开发。 为了实现这一目标，一个更直接的目标是 某些药物产生的突变类型的测定 在模型系统中，并鉴定最初的DNA损伤 对这些突变负有责任。博莱霉素和平阳霉素的诱变作用 新卡西诺抑素已在一种原核生物中被详细检测 基于Lambda噬菌体Ci基因的表达系统。建议的实验 涉及酶修复和其他体外修饰 被药物破坏的DNA被设计用来检验两种替代假说 这些研究表明：(I)特定的一类物质被氧化 无嘌呤/脱嘧啶部位，即那些与 互补链中的相对断裂，主要是 负责碱基替换诱变和(Ii) 氧化产物中醛部分的二次反应 脱嘌呤/脱嘧啶部位起着至关重要的作用。其他研究 将被用于确定类似的突变是否 机制发生在哺乳动物细胞中复制的穿梭载体中 以及博莱霉素是否特异性地诱导c-Ha- Ras-1癌基因第12位密码子突变预测 原核系统中的特异性。氮芥末也 在lambda Ci基因中具有强烈的突变性，以及类似的方法 将被用来确定突变特异性和识别 突变DNA损伤，在大肠杆菌和哺乳动物模型中都是如此。 最后，对药物诱导缺失的机制进行了研究 突变将从博莱霉素的克隆和测序开始。 诱导中国仓鼠卵巢细胞aprt基因缺失。

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.