Oxygen Dependency of Photocytotoxicity With Haematoporphyrin Derivative

Exposure of Raji cells to haematoporphyrin derivative (HPD) and red light caused marked cytotoxicity. This was completely inhibited under anaerobic conditions. By using sodium dithionite in aqueous solutions, precise and graded oxygen concentrations could be achieved. Cytotoxicity was directly proportional to the oxygen concentration of the medium until a maximum was reached at a pO2 of 90 mm Hg. Sodium dithionite did not affect the viability of test cells and did not alter the chromatographic profile of HPD. Dithionite did not interfere with the uptake of HPD by cells. Dependency of phototoxicity upon aerobic conditions suggests that the cytotoxic agent is derived from oxygen and is consistent with the hypothesis that singlet oxygen and/or oxygen‐derived free radicals play an important role in photochemotherapy with HPD.