Cisplatin-induced apoptosis of mesothelioma cells is affected by potassiumion flux modulator amphotericin B and bumetanide

Chemotherapeutic anti-cancer drugs induce cell death by the process of apop tosis, Efflux of potassium ions (K+) is necessary for cell volume reduction during apoptosis and increased inward pumping of K+ thus counteracts apopt osis, Potassium flux modulation could therefore interact with apoptosis and affect the efficiency of cancer chemotherapeutics, We explored if the K+ e fflux stimulator amphotericin B, with or without the Na+, K+, 2Cl(-)-cotran sport (K+ influx) blocker bumetanide, could affect cisplatin- and carboplat in-induced apoptosis and cytotoxicity in the pulmonary mesothelioma cell li ne (P31), Apoptosis was determined by quantifying free nucleosomes and casp ase-3 activity, and cytotoxicity was determined by clone formation and a fl uorometric assay. The pan-caspase enzyme inhibitor Boc-D-FMK was used to fu rther determine the role of caspase activity in K+-flux-modulated cisplatin -/carboplatin-induced apoptosis and cytotoxicity. Amphotericin B (3.2 mu mo l/L) combined with bumetanide(100 mu mol/L) potentiated cisplatin-induced f ree nucleosome and caspase-3 activity, The combination of the K+ modulators did not, however, increase cisplatin cytotoxicity. The caspase inhibitor B oc-D-FMK, but unexpectedly also bumetanide, markedly reduced cisplatin cyto toxicity and annihilated the augmented cytotoxicity of cisplatin in the pre sence of amphotericin B, Carboplatin cytotoxicity was reduced by bumetanide , but not affected by amphotericin B, Carboplatin and carboplatin/bumetanid e cytotoxicity was further reduced by Boc-D-FMK, We conclude that the abili ty of cisplatin, and to a lesser extent carboplatin, to induce apoptosis is indeed influenced by cellular potassium flux modulators. We suggest that K i ionophores such as amphotericin B, and K+ influx blockers such as bumetan ide, alone or in combination, should be further evaluated for their potenti al clinical usefulness in influencing tumor cell apoptosis induced by cispl atin and other cancer chemotherapeutics, (C) 2001 Wiley-Liss. Inc.