Furosemide, a blocker of Na(+)/K(+)/2Cl(-) cotransporter (NKCC), is often used as a diuretic to improve edema, ascites, and pleural effusion of patients with cancers. The aim of the present study was to investigate whether an NKCC blocker affects cancer cell growth. If so, we would clarify the mechanism of this action. We found that poorly differentiated gastric adenocarcinoma cells (MKN45) expressed the mRNA of NKCC1 three times higher than moderately differentiated ones (MKN28) and that the NKCC in MKN45 showed higher activity than that in MKN28. A cell proliferation assay indicates that furosemide significantly inhibited cell growth in MKN45 cells, but not in MKN28 cells. Using flow cytometrical analysis, we found that the exposure to furosemide brought MKN45 cells to spend more time at the G(0)/G(1) phase, but not MKN28 cells. Based on these observations, we indicate that furosemide diminishes cell growth by delaying the G(1)-S phase progression in poorly differentiated gastric adenocarcinoma cells, which show high expression and activity of NKCC, but not in moderately differentiated gastric adenocarcinoma cells with low expression and NKCC activity.
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