EXPERIMENTAL RADIOTHERAPY, CARCINOGENSIS, AND PROTECTORS

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The ultimate goal of this investigation is the characterization of chemopreventive strategies to reduce the risk of genotoxic damage to normal tissues by cancer therapy agents during the treatment of potentially curable neoplastic disease. The experimental models to be used include a C3H mouse system, in which both mutagenesis at the hypoxanthine-guanine phosphoribosyl transferase (hprt) locus and tumor response as a result of radiation and chemotherapy will be investigated, and a number of rodent cell systems in which the chemopreventive effectiveness of selected radioprotector agents will be characterized and contrasted. Both mechanistic and applied issues will be addressed. The three specific aims to be investigated are A) the development of chemoprevention strategies to maintain cytotoxic effectiveness of experimental therapies in mice bearing micro lung tumors, while minimizing the genotoxic risk to normal cells; B) The characterization of chemopreventive effects on the process(es) of spontaneous metastasis formation; and C) the characterization of cellular responses to potential chemopreventive compounds in selected rodent cell systems, to assess the usefulness of measuring intracellular glutathione, glutathione S- transferase, and thiol levels, protein kinase C activity, magnitude of DNA damage and repair, changes in split dose survival and repair, and frequency of mutations at the hprt locus as intermediate biomarkers for chemoprevention. Radioprotector compounds to be studied which possess potential chemopreventive properties include S-2-(3-aminopropylamino)ethyl phosphorothioic acid (WR-2721), 2-((aminopropyl)amino]ethanethiol (WR- 1065) and its disulfide form (WR-33278), N-acetylcysteine (NAC), the prodrug ribose-cysteine (Rib Cys) and captopril. Therapy agents to be used are 60Co and x-ray radiation, cytoxan, and cisplatin. The models for neoplastic disease are four mouse syngeneic tumors, i.e., fibrosarcoma (FSa) fibrosarcoma (NFSA), mammary carcinoma (MCAK), and a lymphoma which can be grown in the lungs or flanks of C3H mice. Techniques to be used include HPLC and monobromobimane fluorescent labeling to assay thiol and disulfide levels, determination of protein kinase C activity by measuring peptide phosphorylation levels corrected for background due to other protein kinases, alkaline elution to measure single-strand breaks in DNA and their associated kinetics of repair, and the hprt mutation assay in T- lymphocytes of mice and in selected cultured cell systems. The hprt mutation system is not proposed to be a predictor of carcinogenesis, but rather is considered to be an excellent marker for assessing genomic damage. This proposal will investigate the efficacy of thiol compounds as chemopreventive agents for use with radiation and chemotherapy.