DNA Damage: Roles in Toxicity and Mutagenicity

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DESCRIPTION (provided by applicant): DNA damage plays a critical role in the cytotoxicity and mutagenicity elicited by carcinogens and many clinically used antineoplastic agents. While mutagenesis and cell death do not necessarily overlap mechanistically, many DNA lesions can induce both biological endpoints. This point is dramatically exposed in the clinical setting where a significant incidence of secondary cancers is attributed to the treatment of patients with antineoplastic agents for their primary cancer. Since DNA remains an extremely attractive target for anticancer agents, it is imperative to identify and eliminate the formation of promutagenic lesions while maintaining those that selectively induce cytotoxicity. Our hypothesis is that the selective formation of N3- methyladenine (3-MeA) lesions presents an approach to kill cells while minimizing mutations associated with secondary cancers. To study this issue, we have synthesized [1-methyl-4-[1-methyl 4-(3-(methoxysulfonyl)- (propanamido)pyrrole-2-carboxamido]pyrrole-2-carboxamido]propane (Me-lex), a methylating dipeptide that selectively affords 3-MeA. The Specific Aims are: (1) To design new minor groove alkylating agents (analogues of Me-lex) with improved activity and bioavailabililty. (2) To understand the cytotoxicity and mutagenicity of specific minor groove DNA lesions induced by the compounds prepared in Aim 1, and to determine the impact of the DNA repair background. (3) To determine the mechanisms responsible for 3- MeA induced stalling of replicative DNA polymerases and translesion synthesis via by-pass polymerases using templates with 3-MeA and a stable analogue of 3-MeA. The effect of DNA sequence on these processes will also be investigated. (4) The cytotoxicity of Me-lex and the analogues synthesized in Aim 1 will be assayed in human glioma cell lines to test the hypothesis that human gliomas resistant to the cytotoxic effects of bis(2-chloroethyl)nitrosourea (BCNU) or temozolomide (TMZ) will not be cross-resistant to Me-lex and its analogs. The effects of stereotactic intratumoral delivery of Me-lex and the analogs on survival of athymic rats with intracerebral human gliomas will be evaluated and compared to similar treatments with BCNU and TMZ. The results of the above aims should provide useful information on the toxicity and tumorigenicity of 3-MeA and related DNA lesions, as well as how tumorigenicity can be avoided to afford improved and safer cancer chemotherapies.