EFFECTS OF OLOMOUCINE, A SELECTIVE INHIBITOR OF CYCLIN-DEPENDENT KINASES, ON CELL-CYCLE PROGRESSION IN HUMAN CANCER CELL-LINES

We have studied the effects of olomoucine, a selective inhibitor of cd k2, cdc2 and MAP kinase, on the rate of proliferation and the cell cyc le progression in human cancer cells in culture. Olomoucine inhibited the growth of the KB 3-1, MDA-MB-231 and Evsa-T cell lines in a concen tration-dependent manner, with EC50 values of 45, 75 and 85 mu M, resp ectively. Incubation of exponentially growing KB 3-1 cells in the pres ence of olomoucine led to an increased proportion of cells in G(1) pha se after 24 h or more of incubation. Olomoucine failed to rapidly affe ct the phosphorylation of the Rb tumor-supressor gene product. However , [H-3]thymidine incorporation into the cell DNA was rapidly inhibited . We show that this inhibition is due, at least in part, to the diminu tion of thymidine entry into the cells. Suprisingly, all these cell li nes, when synchronized at the G(1)/S interface and relaxed in the pres ence of olomoucine, progressed unhindered through the S phase. Under t hese conditions, the G(2) phase transit was markedly retarded but not prevented. Insufficient permeability of the cell membrane to olomoucin e may explain the low activity of the drug.