Radiation-induced sensitizing effect of folic acid (vitamin B11) and its synergistic action to mitomycin C: in vitro experiments and radiolysis.

Folic acid (FA; vitamin B11) is found to exhibit very strong cytostatic effects upon gamma-irradiation in neutral media. This effect depends on the FA concentration, pH of the media, and on the presence of air. The largest cytostatic efficiency of FA was observed in an air-free environment (pH 7.4), where deltaD37 = -90 for 10(-4) mol/dm3 FA and deltaD37 = -160 for 10(-3) mol/dm3 FA was found. FA also acts as a very efficient electron donor and is therefore able, in air-free neutral media, to enhance the efficiency of 7.5 x 10(-7) mol/dm3 mitomycin C (MMC) from deltaD37 = -80 up to deltaD37 = -200 in the presence of 5 x 10(-5) mol/dm3 FA, respectively. This synergistic effect offers a new pathway for more efficient radiation therapy by joint implementation of MMC and FA. Additionally, FA radiolysis was studied in the absence and presence of air as well as in media saturated with N20 (conversion of e(aq)- into OH). As a result of these investigations, various products were detected: ammonia, aldehydes, and a mixture of carboxylic acids, in addition to some not yet identified compounds. Their individual yields could not be identified at present.