Radiobiological studies of tumor cell lines established from patients with head and neck cancers who have local recurrences after radiation therapy have implicated radiation resistant and repair proficient cells as a cause of treatment failure. The overall objective of this project is to examine biochemical events that my define the molecular basis for radiation resistance in these cell lines. The enzyme poly(ADP-ribose) polymerase requires DNA for activity, and it is significant that the catalytic activity of this enzyme is directly correlated to the number of strand breaks in DNA, both in vitro and in vivo. Radiation survival studies in the presence of inhibitors of the poly(ADP-ribose) polymerase have demonstrated: 1) radiation sensitization of normal human fibroblasts, and 2) inhibition of potentially lethal radiation damage. Both of these factors seem to relate to clinical radiation resistance. It is our opinion that poly(ADP-ribosylation) modifications of chromatin-associated proteins may function during biological reactions involving DNA strand-breaks, including the repair of damage induced by ionizing radiation. Through collaborative studies with the laboratory of Mark Smulson, we have access to recently isolated complementary DNA (cDNA) corresponding to the human poly(ADP-ribose) polymerase gene. Using standard molecular biology techniques, we propose to comparatively study the roles of poly(ADP-ribose) metabolism in relation to radiation injury in normal human fibroblasts, and in radiation resistant human tumor cell lines of head and neck origin. Transcription of the gene for the polymerase will be studied by northern hybridization of the mRNA in both, exponentially growing cells and in plateau phase cells. In addition, radiation survival studies will be performed on rodent cells induced to hyperexpression of the poly(ADP-ribose) polymerase by stable integration of the cDNA driven by the metallothionein promoter. This will be the first cellular model system to allow experimental control of the levels of this enzyme to assess its role in radiation repair. Such information my be useful in the development of therapeutic strategies in cancer treatment.
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