Oxygen dependence of the photosensitizing effect of hematoporphyrin derivative in NHIK 3025 cells.

Cells of the established line NHIK 3025 were incubated with hematoporphyrin derivative and exposed to light at different concentrations of oxygen. The efficiency of photoinactivation of the sensitized cells decreased with decreasing oxygen concentration. No photoinactivation was observed when the atmosphere above the medium overlying the cells was pure N2 gas. With 1% O2 in the atmosphere, the quantum yield of photoinactivation was reduced by 50% compared to the yield in air-saturated medium. It is hardly possible to inactivate cells in anoxic regions of a tumor by means of porphyrin sensitized photochemotherapy. In spite of this, the therapy seems to be efficient in several cases. Thus, it seems that anoxic tumor cells are inactivated in secondary reactions, probably due to breakdown of the circulatory system in the tumor.