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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. Copyright © 2008 S. Karger AG, Basel [ABSTRACT FROM AUTHOR]

Cisplatin treatment efficacy of malignant pleural mesothelioma (MPM) is aggravated by resistance and adverse effects. In P31 MPM cells, cisplatin induces morphological changes and apoptosis. To determine if very early (10 minutes) morphological responses corresponded to apoptosis-induction, cisplatin effects on P31 morphology were examined with phase-contrast microscopy (PCM), scanning electron microscopy (SEM), and flow cytometry (fluorescence-activated cell sorting [FACS]), and compared to apoptosis-induction over time. Increased membrane protrusions were identified with PCM and SEM, but these were not consistent with the induction of apoptosis. The authors concluded that very early morphological changes can be determined with PCM in MPM, but they did not convincingly correspond to apoptosis induction. [ABSTRACT FROM AUTHOR]