Troglitazone acts on cellular pH and DNA synthesis through a peroxisome proliferator-activated receptor gamma-independent mechanism in breast cancer-derived cell lines.
OBJECTIVE
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.


METHODS
Intracellular pH (pH(i)) 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) gamma involvement was assessed using an antagonist and PPARgamma(-/-) 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 (NH(4)Cl 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 micromol/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 PPARgamma inhibitor GW9662 and was demonstrable in PPARgamma(-/-) NIH3T3 cells, consistent with a PPARgamma-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 PPARgamma antagonist. Our results support a NHE-mediated action of TRO that exerts its effect independent of PPARgamma.
Turturro
Francesco
F
Department of Medicine, Feist-Weiller Cancer Center, Gene Therapy Program, Louisiana State University Health Sciences Center, Shreveport, Louisiana 71130, USA. fturtu@lsuhsc.edu
Friday
Ellen
E
Fowler
Rocky
R
Surie
Diya
D
Welbourne
Tomas
T
D000138:Acidosis; D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001943:Breast Neoplasms / Q000473:pathology*; D049109:Cell Proliferation; D002839:Chromans / Q000494:pharmacology*; D004247:DNA / Q000096:biosynthesis*; D005260:Female; D005347:Fibroblasts; D006801:Humans; D006863:Hydrogen-Ion Concentration; D051379:Mice; D047495:PPAR gamma / Q000494:pharmacology*; D045162:Thiazolidinediones / Q000494:pharmacology*; D000077288:Troglitazone; D014407:Tumor Cells, Cultured
D000970:Antineoplastic Agents; D002839:Chromans; D047495:PPAR gamma; D045162:Thiazolidinediones; D004247:DNA; D000077288:Troglitazone