Toxic effects of 8-methoxypsoralen on lymphocyte division.

Cultured human leucocytes have been used to examine the toxicity and phototoxicity of 8-methoxy psoralen (8-MOP). It has been shown that 8-MOP depresses cell turnover at concentrations of 10(-10) M or above. In black light (UVA), 8-MOP inhibition begins at concentrations of 10(-14) M. Patients treated for psoriasis with 8-MOP show concentrations of 10(-6)-10(-7) M. The inhibition of cell turnover observed with the present technique is at this concentration 40% for 8-MOP alone and 70% for 8-MOP and black light. These results can be related to the micronuclei and chromosome abnormalities seen in dividing cells.