Sister chromatid exchange frequency in human epidermal cells in culture treated with 8-methoxypsoralen and long-wave UV radiation

The effects of 8-methoxypsoralen with long-wave ultraviolet radiation on the sister chromatid exchange frequency in human epidermal cells in culture was investigated. With a constant amount of radiation the number of exchanges increased in an approximately linear manner with increasing concentrations of 8-methoxypsoralen up to 0.3 micrograms/ml. Above this concentration there were fewer dividing cells and an apparent departure from linearity in the dose-response curve. These results show that 8-methoxypsoralen concentrations equivalent to those found in the serum of patients undergoing photochemotherapy, in conjunction with UVA radiation, cause striking increases in sister chromatid exchange frequency in human epidermal cells in vitro