Membrane Lysis in Chinese Hamster Ovary Cells Treated With Hematoporphyrin Derivative Plus Light

Chinese hamster ovary cells in exponential growth were incubated with various concentrations of hematoporphyrin derivative (HpD). Cellular porphyrin content was determined after 2 h incubation at 37°C using [ 3 H]‐hematoporphyrin derivative. Photoactivation of cell‐bound HpD by red light resulted in a family of survival curves with terminal slopes proportional to cellular HpD concentration. The degree of cellular lysis, assayed 1 h after illumination using a chromium‐51 labeling technique, was also found to be related to cellular HpD concentration. The amount of 51Cr released increased with post‐irradiation incubation to a level parallel to cell lethality as measured by colony formation. These data suggest that lysis of the cell membrane may be largely responsible for cellular inactivation following HpD photoirradiation.