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Experimental Therapeutics, Preclinical Pharmacology |
-Independent Mechanism in Breast Cancer-Derived Cell Lines
1 Department of Medicine, Feist-Weiller Cancer Center, 2 Gene Therapy Program, and 3 Department of Molecular and Cellular Physiology, Louisiana State University Health Sciences Center, Shreveport, Louisiana
Purpose: The purpose of this study was to assess whether troglitazone (TRO) would induce cellular acidosis by inhibiting Na+/H+ exchanger (NHE) 1 in breast carcinoma-derived cell lines and, if so, whether cellular acidosis would be associated with a reduction in proliferation.
Experimental Design: Intracellular pH (pHi) and acid extrusion capacity after an exogenous acid load were assayed using (2, 7)-biscarboxyethyl-5(6)-carboxyfluorescein in MCF-7 and MDA-MB-231 cells treated with TRO. Radiolabeled thymidine incorporation was used to assess DNA synthesis. Peroxisome proliferator-activated receptor (PPAR) 
involvement was assessed using an antagonist and PPAR–/– NIH3T3 cells.
Results: TRO induced a prompt (<4 minute) and severe cellular acidosis in both MCF-7 (7.54 ± 0.23 to 6.77 ± 0.06; P < 0.001) and MDA-MB-231 cells (7.38 ± 0.18 to 6.89 ± 0.25; P < 0.05) after 12 minutes, without increasing acid production. Acid extrusion as assessed by the response to an exogenous acid load (NH4Cl pulse) was markedly blunted (MDA-MB-231, P < 0.01) or eliminated (MCF-7, P < 0.001). Chronic exposure to TRO resulted in NHE1 activity reduction (P < 0.05) and a dose-dependent decrease in DNA synthesis (<75% inhibition at 100 µmol/L; P < 0.001 and P < 0.01 for MCF-7 and MDA-MB-231, respectively) associated with a decreased number of viable cells. TRO-mediated inhibition of proliferation was not reversed by the presence of the PPAR inhibitor GW9662 and was demonstrable in PPAR–/– NIH3T3 cells, consistent with a PPAR-independent mechanism.
Conclusions: TRO induces marked cellular acidosis in MCF-7 and MDA-MD-231 cells. Sustained acidosis is consonant with decreased proliferation and growth that is not reversed by a PPAR antagonist. Our results support a NHE-mediated action of TRO that exerts its effect independent of PPAR.
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