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Photodynamic Toxicity of Polycyclic Aromatic Hydrocarbons in Tissue Culture

( National Cancer Institute, National Institutes of Health, U. S. Public Health Service, Department of Health, Education and Welfare Bethesda, Maryland)

Cells grown in culture were exposed to benzo[a]pyrene and related polycyclic aromatic hydrocarbons dissolved in serum, following which procedure they were irradiated with long-wave ultraviolet light. The sequence of biological responses resulting from this photodynamic effect on the cells was dependent upon the total energy absorbed by the hydrocarbons incorporated in the cells.

The most sensitive response was that of temporary interference with mitotic processes in cells in mitosis or in interphase at the time of irradiation. Cells in the resting stage were not adversely affected. A moderate grade of the response produced gradual cell damage characterized by membrane retraction, blebbing and vacuolization of the cytoplasm, pyknosis of the nucleus, and ultimate cell death within a day or two. An extreme degree of the response resulted in an instant death of the cell with a swelling and reticulation of the cytoplasm.

Irradiation with conventional light and fluorescent lamps for a short time was also capable of inducing responses, provided sufficient benzo[a]pyrene was incorporated into the cells. Continuous exposure in the dark of FL and HeLa cells containing benzo[a]pyrene and other related hydrocarbons did not result in a significant adverse effect even after a week's exposure at the highest concentrations. In contrast, M-5¹ cells, after exposure to 5µg/ml of benzo[a]pyrene, showed no effect for 3 days, following which there was disarrangement of the growth pattern.

No significant quantitative or qualitative difference in the photodynamic activities of several carcinogenic and noncarcinogenic polycyclic hydrocarbons could be observed when the effect was compared on the basis of assumed energy absorption.

¹ Human embryonic skin, diploid serial culture.

^* Present address: Department of Pathology, Osaka University, Osaka, Japan.

Received 3/ 2/64.