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

PURPOSE

To investigate the mechanism of methylene blue-induced radiosensitization in Escherichia coli cells.

MATERIALS AND METHODS

Bacteriophage lambda15 was irradiated with X-rays in the presence or absence of methylene blue (MB) and infected into bacteria with different repair capabilities preincubated with or without MB. The survival 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 sucrose gradients. An in vitro repair system of pBR322 plasmid DNA irradiated with 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 tumours, it will be of interest to investigate its effects on the repair of irradiated human cells.