Methylene blue inhibits polymerase 1 enzyme and sensitizes Escherichia coli bacteria to X-rays

Purpose: To investigate the mechanism of methylene blue-induced radiosensit ization in Escherichia coli cells. Materials and methods: Bacteriophage lambda 15 was irradiated with X-rays i n the presence or absence of methylene blue (MB) and infected into bacteria wit different repair capabilities preincubated with or without MB. The sur vival of the bacteriophage in each bacterial strain was used to quantify MB -induced radiosensitization. DNA repair in bacteria irradiated with X-rays and incubated with or without MB was examined by alkaline and neutral sucro se gradients. An in vitro repair system of pBR322 plasmid DNA irradiated wi th X-rays was designed to determine the repair enzyme targeted by MB. Conclusions: MB impairs the repair activity of the polymerase 1 enzyme in E . coli cells, sensitizing these bacteria to the lethal effects of ionizing radiation. Since MB accumulates preferentially in some malignant tumors, it will be of interest to investigate its effects on the repair of irradiated human cells.