Effects of PUVA on a human skin epithelial cell line.

An established human epithelial cell line was exposed to photoactivated 8-methoxy psoralen (PUVA) during exponential growth. Effects of PUVA treatment on cell growth were measured by cell kinetic methods (counting of cell numbers, flow cytometric measurements (FCM) of DNA and calculations of labelling indices (LI)). Doses of 8-methoxy psoralen and UVA were comparable to those used in patients. The cell number in PUVA treated cultures remained almost constant, and very few mitoses were seen for 144 h. About 9 h after PUVA, both FCM and LI showed an increase in the fraction of cells in S-phase, reaching a maximum of 85-90% after 24 h. DNA synthesis took place at a low rate in these cells. FCM showed an increasing fraction of polyploid cells after PUVA treatment. The possibility that inhibition of cell proliferation is one of the main effects of PUVA, is discussed.