Influence of diphosphopyridine nucleotide (DPN) on photodynamic effects of low concentrations of methylene blue in ascites tumor cells.

When four thiazine dyes were added to ascites cell suspensions to yield 10(-4) M final concentration, the order of increasing effectiveness, for both stimulation of aerobic glycolysis in the dark and inhibition of aerobic glycolysis in the presence of added light, was thionine, methylene blue, thionine blue, and new methylene blue. After illumination, inhibition of anaerobic glycolysis occurred in the same respective dye order. Studies in depth of photodynamic effects of methylene blue on Ehrlich ascites cells revealed marked metabolic effects of light and 10(-4) M dye or lower. Diphosphopyridine nucleotide (DPN) with 5 X 10(-6) M methylene blue and light almost completely abolished the Pasteur effect after only 10 minutes' illumination of the dye-cell-coenzyme system. The ability of light, methylene blue, and exogenous DPN to specifically inhibit the Pasteur effect is consistent with the view that DPN can be important to proper functioning of the Pasteur effect mechanism. It is suggested that perfusion with some of the less toxic photosensitive dyes in combination with conventional or lasered light may result in significant selective destruction of tumor cells in vivo.