DNA Repair-Mediated BCNU Resistance in CNS Tumors

恶性中枢神经系统(CNS)肿瘤可能是最困难和最令人沮丧的 肿瘤的治疗，在很大程度上是由于这些病变产生和生长的敏感部位。化疗在治疗恶性胶质瘤和髓母细胞瘤中的作用仍在不断发展。氯乙基亚硝脲(CENUS)最初被选择用于治疗中枢神经系统肿瘤，是基于良好的物理化学性质，如亲脂性以及对小鼠体内生长的L1210白血病细胞的活性。然而，尽管恶性胶质瘤对BCNU或CCNU的敏感性中等，但中心仅轻微改变了恶性脑瘤患者的生存。像BCNU这样的cenus在水解后产生高活性的2-氯乙基碳离子，它可以通过乙烯桥双功能烷基化和交联DNA、RNA和蛋白质。抗肿瘤药物 Cenus的活性似乎与DNA链间交联(ICL)的形成成正比。 对包括cenus在内的烷化剂的耐药性是多因素的，在小鼠和人类肿瘤中观察到了不同的机制。这些机制包括用O6-烷基鸟嘌呤-DNA烷基转移酶去除cenus诱导的单加合物，或用谷胱甘肽猝灭单加合物。 然而，CENU诱导的DNA ICL不受AGT去除或谷胱甘肽猝灭的影响。因此，形成DNA ICL的肿瘤细胞对cenus的耐药性一定是由于除AGT-或谷胱甘肽-肿瘤细胞相互作用之外的其他机制所致。这一设想的假设是：DNA ICL的修复是恶性胶质瘤和髓母细胞瘤对氯乙基亚硝脲耐药的主要机制。本建议的具体目的是：1.确定BCNU诱导的DNA ICL修复的分子事件；2.确定在清除BCNU诱导的DNA ICL过程中可操作的DNA修复途径；3.确定BCNU诱导的DNA ICL修复在介导耐药性中的作用。

Malignant central nervous system (CNS) tumors are perhaps the most difficult and frustrating neoplasms to treat, in large part due to the sensitive site in which these lesions arise and grow. The role of chemotherapy in the treatment of both malignant glioma and medulloblastoma continues to evolve. The chloroethylnitrosoureas (CENUs) were originally chosen for treatment of central nervous system tumors on the basis of favorable physiochemical properties such as lipophilicity as well as activity against L1210 leukemia cells growing intracranially in mice. Nevertheless, despite moderate sensitivity of malignant glioma to BCNU or CCNU, the CENUs have only modestly altered survival for patients with malignant brain tumors. CENUs such as BCNU produce highly reactive 2-chloroethyl carbonium ions following hydrolysis which can bifunctionally alkylate and crosslink DNA, RNA and proteins via ethylene bridges. The antitumor activity of CENUs appears to be proportional to DNA interstrand crosslink (ICL) formation. Resistance to alkylating agents including CENUs is multifactorial, with a diverse spectrum of mechanisms observed in murine and human neoplasia. These mechanisms include removal of the initial CENUs-induced mono-adduct by O6-alkylguanine-DNA alkyltransferase or quenching of the mono-adduct by glutathione. However, CENU-induced DNA ICL are not susceptible to either AGT removal or glutathione quenching. Therefore, resistance to CENUs in tumor cells in which DNA ICL are formed must be due to alternative mechanisms other than AGT-or glutathione-tumor cell interactions. The hypothesis of this proposal is that: repair of DNA ICL is a major mechanism of resistance to chloroethylnitrosoureas in malignant glioma and medulloblastoma. The specific aims of this proposal are: 1. Define molecular events mediating repair of BCNU-induced DNA ICL by human cell extracts; 2. Define the DNA repair pathways operational in removal of BCNU-induced DNA ICL; and 3. Define the role of repair of BCNU-induced DNA ICL in mediating resistance.