Modulation of Therapeutic Response

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In the interest of improving cancer treatment, considerable attention has been placed on the modification of radiation damage. The interaction of a variety of chemotherapy and/or molecularly targeted agents with radiation is under study to determine if tumors can be made more sensitive or normal tissues more resistant to radiation treatment. The central aim is to identify approaches that will result in a net therapeutic gain, thus improving cancer treatment with radiation. One goal of the project is to define and better understand those aspects of tumor physiology, including cellular and molecular processes and the influence of the tumor microenvironment on treatment response. The ability to enhance the response of the tumor to radiation, without enhancing normal tissue within a given treatment field is desirable. We have recently shown that a molecularly targeted Chk-1 inhibitor provides significant radiosensitization in p53 mutated human tumor cell lines. Normal human fibroblasts (p53 wild type) are not radiosensitized by this agent suggesting differential tumor sensitization. This agent also provides considerable radiation enhancement in vivo (using xenografts) with very little to no normal tissue toxicity. While this agent abrogates the normal radiation-induced delay in G2 of the cell cycle, inhibition of repair of radiation damage appears to be the major mechanism of radiosensitization. We are also evaluating a CK2 inhibitor, which provides impressive radiosensitization when administered post-radiation exposure. Preliminary studies indicate that p53 WT cells are radiosensitized to a greater extent that p53 mutated cell lines. The major focus for the potential application of the CK2 inhibitor is head and neck cancer. Finally, we are evaluating a Jak2/Stat3 inhibitor in human lung cancer cell lines. Preliminary studies have demonstrated radiosensitization of the cell lines and mechanistic studies are ongoing. With respect to normal tissue response to radiation, we have identified a novel 5-membered ring nitroxide (23c) as a potent protector against radiation-induced lethality in mice and studies are planned to determine if protection can be observed in selected normal tissues in mice, particularly the brain since the nitroxide penetrates the blood brain barrier. Lastly, we have shown that the nitroxide, Tempol protects against radiation-induced oral mucositis (both systemic and topically applied). Oral mucositis is a common toxicity associated with the chemoradiation (cisplatin combined with fractionated radiation) treatment of head and neck cancers. Tempol also protects against chemoradiation-induced mucositis yet did not alter chemoradiation with respect to tumor regrowth delay, providing sufficient pre-clinical data to introduce Tempol into human radiation oncology clinical trials.