Photodynamic inactivation of cancer cells in vitro. Effect of irradiation temperature and dose fractionation.

Human cancer cells in vitro (NHIK 3025), derived from a carcinoma in situ are inactivated when exposed to visible light in the presence of hematoporphyrin. Irradiation at 4 degrees C results in much more efficient inactivation than irradiation at 37 degrees C. Furthermore, a given total light dose is more efficient when it is fractionated than when it is given in a single exposire. These findings may be taken advantage of in future photochemotherapy of cancer.