title: Inhibitors of intracellular pH regulation induce cisplatin resistance in EMT6 mouse mammary tumor cells.
abstract: Previous results from this laboratory indicated that EMT6 cells treated with inhibitors of the intracellular pH (pHi) regulatory mechanisms were resistant to cisplatin (Laurencot, C.M.; Kennedy, K.A. The effect of low pH on the cytotoxicity of cisplatin in EMT6 mouse mammary tumor cells. Oncol. Res. 7:371-380; 1995.) This inhibitor-induced cisplatin resistance was independent of pH. The purpose of the research presented here was to characterize further cisplatin resistance observed in cells cultured with the Na+/H+ antiport inhibitor 5-(N,N hexamethylene) amiloride (NHMA) and the HCO3-/Cl- exchanger inhibitor 4-acetamido-4'-isothiocyanostilbene-2,2'-disulfonic acid (SITS). Using [195mPt]-DDP, the accumulation of cisplatin into EMT6 mouse mammary tumor cells treated with NHMA and SITS was not changed. Total DNA cross-link formation and DNA-interstrand cross-link formation, however, decreased in NHMA- and SITS-treated cells. Since cisplatin accumulation was unchanged in NHMA- and SITS-treated cells but the amount of DNA cross-links decreased, the intracellular activation of cisplatin appeared to be altered in the cisplatin-resistant cells. Because SITS interferes with chloride transport and chloride has been proposed to be involved in cisplatin activation, cisplatin toxicity in EMT6 cells was evaluated in chloride-deficient medium. EMT6 cells cultured in chloride-deficient medium were less sensitive to cisplatin than cells cultured in chloride-containing medium, but this sensitivity was not altered by NHMA and SITS. Furthermore, the resistance to cisplatin in cells treated with NHMA and SITS was similar in chloride-containing and chloride-deficient medium. These data suggest that the concentration of other ions, in addition to chloride, may be important for cisplatin toxicity.
authors: Department of Pharmacology, George Washington University Medical Center, Washington, DC 20037, USA.
authors: C M
authors: CM
authors: Laurencot
authors: P A
authors: PA
authors: Andrews
authors: K A
authors: KA
authors: Kennedy
mesh_terms: D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid / Q000037:antagonists & inhibitors*; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology; D002945:Cisplatin / Q000378:metabolism / Q000494:pharmacology*; D003432:Cross-Linking Reagents / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D006863:Hydrogen-Ion Concentration; D008325:Mammary Neoplasms, Experimental / Q000188:drug therapy / Q000378:metabolism*; D051379:Mice; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D003432:Cross-Linking Reagents; C057360:5-(N,N-hexamethylene)amiloride; D012856:4-Acetamido-4'-isothiocyanatostilbene-2,2'-disulfonic Acid; D000584:Amiloride; D002945:Cisplatin