The long-term objective of this proposal is to take advantage of the relation between NAD metabolism, poly(ADP-Ribose) synthesis and DNA repair to design combination chemotherapy protocols for the treatment of malignant disorders. We have shown that nicotinamide analogs, selected for their ability to inhibit poly(ADP-Ribose) polymerase, block the DNA repair process, potentiate the tumorocidal effects of chemotherapeutic agents and increase the lifespan of animals bearing L1210 leukemia or MOPC-315 myeloma. The goals of the present proposal are to identify new, more effective inhibitors of poly(ADP-Ribose) polymerase and optimize the dose and scheduling of their administration to obtain synergistic interactions with chemotherapeutic agents whose cytotoxic mechanism of action is mediated by induction of DNA damage. These studies will be continued in L1210 leukemia and MOPC-315 myeloma and will be extended to solid tumors including the B16 melanoma, Lewis lung carcinoma, and EMT-6 mammary tumor. We have shown that the nucleoside analogs, Tiazofurin and Selenazole, interfere with maintenance of cellular NAD levels. We will seek to develop sequential blockade protocols in which a nicotinamide analog is used as a direct inhibitor of poly(ADP-Ribose) polymerase and Tiazofurin or Selenazole is used to limit substrate availability. Combinations of these two agents with the DNA damaging agents will be evaluated biochemically for their ability to enhance DNA damage and biologically for their ability to produce synergistic tumor cell killing and enhanced survival. Our studies of the mechanisms of cell killing, following treatment with high dose DNA damaging agents, show a dose dependent activation of poly(ADP-Ribose) synthesis which leads to depletion of NAD and ATP pools and consequent cell death. This bears directly on the organ toxicity experienced in recent clinical studies of high dose chemotherapy with autologous marrow rescue for treatment of refractory malignancies. We will analyze metabolite fluxes following high dose chemotherapy to determine whether this pathway, leading to depletion of energy metabolites, accounts for the fatal organ toxicity. In subsequent studies we will seek to prevent this dose limiting toxicity by treatments designed to amplify and protect cellular pools of pyridine nucleotides and energy metabolites.
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