Differential effects of 5-fluorouracil on human skin melanocytes and malignant melanoma cells in vitro.

We have observed differential effects of the cytotoxicity of 5-fluorouracil (5-FU) on human skin melanocytes and malignant melanoma cells in vitro. In the absence of 5-FU the melanoma cells multiplied much more rapidly than the melanocytes. With a 7-day exposure of 5-FU (1.92 X 10(-5) to 3.84 X 10(-4) M) all the melanoma cells died by 5 W, while even two times longer exposure (a 14-day exposure) of 5-FU the melanocytes survived till 6 W and increased at the lower concentration. In the presence of 5-FU there was a different compensatory increase in [3H] thymidine incorporation between the two cell types. That is, compared with the large increase observed in the incorporation by the melanoma cells, a small increase in the incorporation by the melanocytes was observed. The reason for these differential effects of 5-FU may be the difference in the cell cycle and the post-injury cell renewal of the two cell types.