EFFECT OF MELPHALAN AND HYPERTHERMIA ON P34(CDC2) KINASE-ACTIVITY IN HUMAN-MELANOMA CELLS

We previously reported that combined treatment with melphalan and mild hyperthermia (1 h at 42 degrees C) caused a synergistic cytotoxic eff ect in JR8 melanoma cells, paralleled by a stabilisation of melphalan- induced G(2)-phase cell block. In this study, we investigated the effe ct of melphalan and hyperthermia on proteins that regulate G(2)-M tran sition. Neither hyperthermia nor melphalan at a concentration of 2.5 m u g ml(-1), which had no antiproliferative effect at 37 degrees C, int erfered with cyclin B-1 expression or p34(cdc2) kinase activity. At a concentration of 8.5 mu g ml(-1), which reduced cell growth by 50% at 37 degrees C, melphalan inhibited p34(cdc2) kinase activity as a conse quence of an increased tyrosine phosphorylation of the protein. A simi lar inhibitory effect on p34(cdc2) kinase was obtained when the lowest melphalan concentration (2.5 mu g ml(-1)) was used under hyperthermic conditions. Our results indicate that thermal enhancement of melphala n cytotoxicity could be mediated at least in part by an inhibition of p34(cdc2) kinase activity, which prevents cell progression into mitosi s.