Acquisition of cisplatin-resistance in malignant mesothelioma cells abrogates Na+,K+,2Cl(-)-cotransport activity and cisplatin-induced early membrane blebbing.

AIMS: Resistance mechanisms are important limiting factors in the treatment of solid malignancies with cis-diamminedichloroplatinum(II) (cisplatin). To gain further understanding of the effects of acquired cisplatin-resistance, we compared a human malignant pleural mesothelioma cell line (p31) to a sub-line (p31res1.2) with acquired cisplatin-resistance.

METHODS AND RESULTS: The role of Na(+),K(+),2Cl(-)-cotransport (NKCC1) activity in cisplatin-induced morphological changes and acquired cisplatin-resistance was investigated in a time-resolved manner. Acquisition of cisplatin-resistance resulted in markedly reduced NKCC1 activity, absence of cisplatin-induced early membrane blebbing, and increased basal caspase-3 activity. At equitoxic cisplatin concentrations, P31res1.2 cells had a faster activation of caspase-3 than P31 cells, but the end-stage cytotoxicity and number of cells with DNA fragmentation was similar. Bumetanide inhibition of NKCC1 activity in P31 cells repressed cisplatin-induced early-phase membrane blebbing but did not increase P31 cell resistance to cisplatin.

CONCLUSIONS: Together, these results suggest that active NKCC1 was necessary for cisplatin-induced early membrane blebbing of P31 cells, but not for cisplatin-resistance. Thus, acquisition of cisplatin-resistance can affect mechanisms that have profound effects on cisplatin-induced morphological changes but are not necessary for the subsequent progression to apoptosis.