Competitive Radioprotection and Radiosensitization in Chemical Systems

Abstract

threshold for sensitization occurs at a sensitizer redox potential of approximately -0.3 V vs SCE required to oxidise the DNA radicals. The nitrofurans add to and oxidize DNA target radicals, whereas, for benzoquinone, radiation induced binding to target radicals predominates. Radioprotection may involve either OH-scavenging or H-donation. The action of H-donating species such as cysteamine has been shown to involve competition with sensitizers for the same target free radicals, presumably sugar radicals formed by OH-attack. Steady-state radiolysis allows us to measure the ratios of rate constants for the competing reactions between target radicals and either protectors and sensitizers, or different sensitizers including oxygen. These rate constants have, where possible, been verified by direct experimental measurement using pulse radiolysis. The radiosensitizing effect of the cellular radiosensitizer Diamide is affected in chemical systems by added H-donating species. It appears to act by both an electron affinic mechanism and also by chemically inactivating the H-donating species which would