Two major problems that limit the success of cancer therapy are the dose limiting normal tissue toxicities and the development of cancer cells that are resistant to the therapeutic agents. Furthermore, patients who develop resistance to one such agent often exhibit cross- resistance to other agents that are structurally and mechanistically dissimilar. It has been shown that many key anticancer agents produce reactive oxygen radicals. In addition, cells that develop resistance to an oxygen-radical-generating agent also exhibit cross-resistance to other oxygen-radical-generating agents that are structurally unrelated. PI hypothesizes that much of the normal tissue damage associated with cancer therapy is attributed to the production of oxygen radicals and that protection against oxygen radicals may account for the development of cancer cells that are resistant to many therapeutic agents. The goal of the proposed research project is to investigate the role of antioxidant enzyme manganese superoxide dismutase (MnSOD) in the development of resistance in cancer and toxicity to normal tissue during cancer therapy. Specifically, the investigators will determine whether increased MnSOD activity will lead to resistance in cancer cells and/or protection of normal tissue from the toxicity of adriamycin (ADR), tumor necrosis factor (TNF) and (-radiation, three structurally unrelated therapeutic agents known to generate oxygen radicals. The investigation will be undertaken in four phases. First, the endogenous level of MnSOD in tumor cells will be modulated by transfection of sense and antisense MnSOD genes. The incorporation, expression, and localization of the transfected genes and their products will be monitored at all levels from the gene to active protein. The effect of MnSOD transfection on cell growth, respiration, and expression of other cellular proteins will be monitored. Second, the effect of ADR, TNF and (-radiation on cell kill, macromolecule synthesis, lipid peroxidation, and mitochondrial function will be examined in the parental tumor cells and tumor cells with modulated levels of MnSOD in vitro. Third, the effect of ADR, TNF and (-radiation on heart tissue in normal and transgenic mice expressing a range of elevated levels of human MnSOD will be examined by histological and biochemical methods. The effect of ADR, TNF and (- radiation on the livers of transgenic mice, which do not express human MnSOD will be used as a negative control. Finally, cancer cells with modulated levels of MnSOD will be transplanted into both control and transgenic mice, and the effect of ADR, TNF and (-radiation in both cancer cells and heart tissue of cancer-bearing mice will be assessed by the same methods. The results from this study may contribute significantly to the understanding of cancer cell resistance and defense of normal tissue against the toxic effects of oxygen radicals generated by therapeutic agents. It is possible that new concepts of cancer therapy such as the development of specific measures to induce MnSOD in normal tissue or block the induction of MnSOD in tumor cells may lead to improvement of cancer treatment.
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