Dose-effects of 8-methoxypsoralen and long wave UV-light in 3T3 cells: evaluation of phototoxic index.

3T3 cells were cultured until confluency and treated with various doses of 8-methoxypsoralen followed by long wave UV light irradiation. The inhibition of 3H-thymidine incorporation was dose-dependent for both, psoralen and light. A phototoxic index (PTI) was established demonstrating that a constant correlation between psoralen and UVA light exists for the photoinactivation in living cells.