The overall objective of this research is to use metabolic controls to inhibit potentially lethal damage recovery (PLDR) of human tumor cells in vitro. The emphasis is on the role of extracellular PH (PHe) as a modifier of: cellular energy metabolism, rates of synthesis of macromolecules, cell growth and division, and activities of drugs which inhibit repair of radiation-damaged DNA. We have found that PLDR of A549 human lung carcinoma cells is dependent on pHe. In order to elucidate underlying mechanisms, Specific Aim 1 will investigate relationships between PLDR and changes in intracellular pH (pHi), changes in rates of biochemical reactions important for synthesis of macromolecules and production of ATP, and charges in the extent of DNA damage and the rate of its repair. Recent results with the K+/H+ ionophore nigericin suggest that such drugs may be useful for selective radiosensitization and heat sensitization of tumor cells in an acidic environment (pHe 6.5- 6.8). The mechanisms by which ionophores inhibit PLDR and increase heat toxicity will be studied as a function pHe. Optimium effects of the drugs using will be sought using metabolic controls, as well as effects of ionophores on heat radiosensitization. An important objective is to increase radiosensitivity of human tumor cells at clinically relevant radiation doses. Thus treatments which inhibit PLDR when cells are given a dose of 9 Gy will then be tested for their ability to reduce the shoulder of the dose-response curve. We have found that addition of insulin to plateau Phase A549 cells causes inhibition of PLDR.
Specific Aim 2 will continue co investigate the mechanism for this effect. Responses of human tumor cells to insulin, epidermal growth factor, transferrin and insulin-like growth factors will be optimized before mechanistic studies are undertaken. It will be of particular interest to determine limits to which alterations of cellular metabolic states can increase the radiosensitizing activities of drugs such as araA, araC, caffeine and misonidazole. The above studies will use log and plateau phase A549 cells, and occasionally CHO cells as model systems. In order to evaluate the general applicability of successful in vitro protocols, Specific Aim 3 will examine colon carcinoma cells established from human tumors ar several stages of disease progression. The health relatedness of this research is to radiation therapy and to heat treatment of cancer.
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