CELL-CYCLE DEPENDENT SENSITIVITY OF HUMAN-MELANOMA CELLS TO MELPHALANIS CORRELATED WITH THE ACTIVITY AND CELLULAR CONCENTRATION OF GLUTATHIONE TRANSFERASES

Glutathione transferases (GSTs) are enzymes involved in the resistance of tumor cells to bifunctional alkylating cytostatic drugs. We invest igated the melphalan sensitivity together with activity and cellular c oncentration of GST isoenzymes of human melanoma cell line RPMI 8322 i n different phases of the cell cycle. By centrifugal elutriation three cell fractions containing different proportions of cells in the G(1) phase were isolated. Melphalan sensitivity was estimated by the colony formation assay. The cell fraction with the largest proportion of G(1 ) cells was more sensitive to the drug than the fractions enriched in S and G(2) cells. The GST activity of the cell fractions was measured with 1-chloro-2,4-dinitrobenzene (CDNB) as substrate and the concentra tions of GST P1-1, GST M1-1 and GST A1-1 were quantitated by use of is oenzyme-specific ELISA. The results show that there were less GST acti vity and lower GST P1-1 and A1-1 concentrations in the G(1) cell enric hed fraction, demonstrating a cell cycle dependence of GST expression. Thus, the cell fraction most sensitive to melphalan had the highest p roportion of G(1) cells and displayed the lowest GST activity, suggest ing that the cell cycle dependent sensitivity to melphalan may at leas t partially depend on the expression of GSTs.