title: Reduction of intracellular pH by inhibitors of natural killer cell activity, nicardipine, methyl 2-(N-benzyl-N-methylamino)ethyl-2,6-dimethyl-4-(2-isopropyl-pyrazolo[1, 5-a]pyridine-3-yl)-1,4-dihydro-pyridine-3,5-dicarboxylate (AHC-52), and 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS).
abstract: Our previous study showed that nicardipine and its structural analog, methyl 2-(N-benzyl-N-methylamino)ethyl-2,6-dimethyl-4-(2-isopropyl-pyrazolo[1,5 -a]pyridine-3-yl)-1,4-dihydro-pyridine-3,5-dicarboxylate (AHC-52), which is devoid of calcium channel blocking activity, were equally effective in inhibiting natural killer (NK) cell activity, perhaps through inhibition of P-glycoprotein. In this study, we confirmed this finding using a human NK-like cell line, YTN, which is highly cytotoxic to JY cells. The YTN cell-mediated cytotoxicity toward JY cells was inhibited by nicardipine and AHC-52 in a concentration-dependent manner, the concentrations required for 50% inhibition being 14 and 7 microM, respectively. We then examined by flow cytometry whether these reagents modulate the intracellular pH (pHi), since P-glycoprotein reportedly plays a role in pHi homeostasis, perhaps by altering chloride translocation. Both reagents reduced pHi at concentrations similar to those required for inhibition of the cytotoxicity. In addition, 4,4'-diisothiocyano-2,2'-disulfonic acid stilbene (DIDS), an inhibitor of anion exchangers, also inhibited NK cell activity, with an IC50 value of 160 microM, and reduced pHi at a similar concentration, although it is not a P-glycoprotein blocker. Thus, the inhibitory activities of nicardipine, AHC-52, and DIDS toward NK cell activity paralleled their lowering activities of pHi, suggesting the possibility that disregulation of pHi is related to inhibition of NK cell activity.
authors.affiliation: Department of Biomolecular Science, Faculty of Science, Toho University, Chiba, Japan.
authors.forename: T
authors.initials: T
authors.lastname: Yamashiro
authors.forename: N
authors.initials: N
authors.lastname: Watanabe
authors.forename: Y
authors.initials: Y
authors.lastname: Kobayashi
mesh_terms: D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid / Q000494:pharmacology*; D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1 / Q000037:antagonists & inhibitors; D003602:Cytotoxicity, Immunologic / Q000187:drug effects*; D004095:Dihydropyridines / Q000494:pharmacology*; D005434:Flow Cytometry; D006801:Humans; D006863:Hydrogen-Ion Concentration; D007694:Killer Cells, Natural / Q000187:drug effects* / Q000276:immunology / Q000378:metabolism; D009529:Nicardipine / Q000494:pharmacology*; D011720:Pyrazoles / Q000494:pharmacology*; D014407:Tumor Cells, Cultured / Q000187:drug effects
chemical_list: D020168:ATP Binding Cassette Transporter, Subfamily B, Member 1; D004095:Dihydropyridines; D011720:Pyrazoles; C059017:AHC 52; D009529:Nicardipine; D017878:4,4'-Diisothiocyanostilbene-2,2'-Disulfonic Acid