Apoptosis of leukemic cells accompanies reduction in intracellular pH after targeted inhibition of the Na(+)/H(+) exchanger.
The Na(+)/H(+) exchanger isoform 1 (NHE1) is primarily responsible for the regulation of intracellular pH (pH(i)). It is a ubiquitous, amiloride-sensitive, growth factor-activatable exchanger whose role has been implicated in cell-cycle regulation, apoptosis, and neoplasia. Here we demonstrate that leukemic cell lines and peripheral blood from primary patient leukemic samples exhibit a constitutively and statistically higher pH(i) than normal hematopoietic tissue. We then show that a direct correlation exists between pH(i) and cell-cycle status of normal hematopoietic and leukemic cells. Advantage was taken of this relationship by treating leukemic cells with the Na(+)/H(+) exchanger inhibitor, 5-(N, N-hexamethylene)-amiloride (HMA), which decreases the pH(i) and induces apoptosis. By incubating patient leukemic cells in vitro with pharmacologic doses of HMA for up to 5 hours, we show, using flow cytometry and fluorescent ratio imaging microscopy, that when the pH(i) decreases, apoptosis-measured by annexin-V and TUNEL methodologies-rapidly increases so that more than 90% of the leukemic cells are killed. The differential sensitivity exhibited between normal and leukemic cells allows consideration of NHE1 inhibitors as potential antileukemic agents. (Blood. 2000;95:1427-1434)
Rich
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Division of Transplantation Medicine, South Carolina Cancer Center, Palmetto Richland Memorial Hospital, Columbia, SC 29203, USA. ivan.rich@rmh.edu
Worthington-White
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Garden
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Musk
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D000328:Adult; D000584:Amiloride / Q000031:analogs & derivatives* / Q000494:pharmacology; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000187:drug effects / Q000502:physiology*; D006801:Humans; D006863:Hydrogen-Ion Concentration; D020014:K562 Cells; D007938:Leukemia / Q000473:pathology* / Q000503:physiopathology; D008214:Lymphocytes / Q000166:cytology / Q000187:drug effects / Q000276:immunology*; D051379:Mice; D016688:Mice, Inbred NOD; D016513:Mice, SCID; D017923:Sodium-Hydrogen Exchangers / Q000037:antagonists & inhibitors*; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology; D014183:Transplantation, Heterologous; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D017923:Sodium-Hydrogen Exchangers; C057360:5-(N,N-hexamethylene)amiloride; D000584:Amiloride; D013755:Tetradecanoylphorbol Acetate