title: Cytostatic potential of novel agents that inhibit the regulation of intracellular pH.
abstract: Cells within the acidic extracellular environment of solid tumours maintain their intracellular pH (pHi) through the activity of membrane-based ion exchange mechanisms including the Na(+)/H(+) antiport and the Na(+)-dependent Cl(-)/HCO(3)(-) exchanger. Inhibition of these regulatory mechanisms has been proposed as an approach to tumour therapy. Previously available inhibitors of these exchangers were toxic (e.g. 4,4-diisothiocyanstilbene-2,2-disulphonic acid), and/or non-specific (e.g. 5-N-ethyl-N-isopropyl amiloride). Using two human (MCF7, MDA-MB231) and one murine (EMT6) breast cancer cell lines, we evaluated the influence of two new agents, cariporide (an inhibitor of the Na(+)/H(+) antiport) and S3705 (an inhibitor of the Na(+)-dependent Cl(-)/HCO(3)(-) exchanger) on the regulation of intracellular pH (pHi). The cytotoxicity of the two agents was assessed by using clonogenic assays. Our results suggest that cariporide has similar efficacy and potency to 5-N-ethyl-N-isopropyl amiloride for inhibition of Na(+)/H(+) exchange while S3705 is more potent and efficient than 4,4-diisothiocyanstilbene-2,2-disulphonic acid in inhibiting Na+-dependent Cl(-)/HCO3(-) exchange. The agents inhibited the growth of tumour cells when they were incubated at low pHe (7.0-6.8), but were non-toxic to cells grown at doses that inhibited the regulation of pHi. Our results indicate that cariporide and S3705 are selective cytostatic agents under in vitro conditions that reflect the slightly acidic microenvironment found in solid tumours.
authors.affiliation: Department of Medical Biophysics, Princess Margaret Hospital/Ontario Cancer Institute, University of Toronto, Toronto, M5G 2M9, Canada.
authors.forename: P
authors.initials: P
authors.lastname: Wong
authors.forename: H-W
authors.initials: HW
authors.lastname: Kleemann
authors.forename: I F
authors.initials: IF
authors.lastname: Tannock
mesh_terms: D000230:Adenocarcinoma / Q000737:chemistry / Q000473:pathology; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000737:chemistry / Q000473:pathology; D002455:Cell Division / Q000187:drug effects; D027963:Chloride-Bicarbonate Antiporters / Q000037:antagonists & inhibitors*; D015195:Drug Design; D004354:Drug Screening Assays, Antitumor; D006146:Guanidines / Q000494:pharmacology*; D006801:Humans; D006863:Hydrogen-Ion Concentration / Q000187:drug effects*; D007424:Intracellular Fluid / Q000737:chemistry / Q000187:drug effects*; D008325:Mammary Neoplasms, Experimental / Q000737:chemistry / Q000473:pathology; D009363:Neoplasm Proteins / Q000037:antagonists & inhibitors*; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors*; D013450:Sulfones / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000737:chemistry / Q000187:drug effects; D014410:Tumor Stem Cell Assay
chemical_list: D000970:Antineoplastic Agents; D027963:Chloride-Bicarbonate Antiporters; D006146:Guanidines; D009363:Neoplasm Proteins; D017923:Sodium-Hydrogen Exchangers; D013450:Sulfones; D000584:Amiloride; C093373:cariporide; C039614:ethylisopropylamiloride