Simple radiosensitizing of hypoxic tumor tissues by N2O/Br− mixture

Abstract

The radiosensitization model of hypoxic tumor tissues based on the N2O/Br− mixture is described. The well-documented radiolysis of water in the presence of N2O and Br− ions at a low concentration supports this model. An aqueous solution saturated with N2O gas during the radiolysis generates OH radicals in a large extent. In N2O/Br− media at pH<9, Br2 is formed. Br2 hydrolyzes in an aqueous solution to form a very reactive hypobromous (HOBr) acid. Such process is described by the following chemical reaction:H2O+Br-+N2O+ionizing radiation(IR)→HOBr+N2+OH-.In vivo formed HOBr as a long-lived product with a high biological activity induces the hypoxic tumor cell damage via many unique mechanisms. A local application or inhalation of an N2O–O2 mixture before or during the radiotherapy to enhance the saturation of tissues with N2O is a key prerequisite. Since the extracellular concentration of Br− ions is very low (0.02–0.05mM), an oral or local application of NaBr should be used to shift the extracellular concentration of Br− ions to the mM region.