The MEK1 inhibitor PD98059 sensitizes C8161 melanoma cells to cisplatin-induced apoptosis.

The regulation of apoptosis is believed to be dependent on the balance of the activities of different intracellular signalling systems. Activation of the SAPK/JNK pathway is implied in pro-apoptotic signalling, while activation of the MEK1/ERK pathway may have a viability-promoting effect. We show here that treatment with the MEK1 inhibitor PD98059 sensitizes the human melanoma cell line C8161 to cisplatin-induced apoptosis. In these cells, cisplatin at 40 microM did not elicit significant cell death, whereas massive cell death was seen when cells were pretreated for 20 h with 40 microM PD98059 before the addition of cisplatin. Concomitant addition of PD98059 and cisplatin did not have any sensitizing effect, and PD98059 on its own did not induce apoptosis. However, in three other human melanoma cell lines PD98059 did not potentiate cisplatin-induced apoptosis. Instead, in one of these cell lines (AA), PD98059 protected against cisplatin-induced cytotoxicity. We conclude that blocking of the MEK1/ERK pathway may, in some instances, potentiate the cytotoxic effect of cisplatin on human melanoma cell lines, whereas in other instances it may have a protective effect. Thus it cannot be regarded as a general approach to sensitizing melanoma cells to drug-induced apoptosis.