Na+/H+ exchanger activity is increased in doxorubicin‐resistant human colon cancer cells and its modulation modifies the sensitivity of the cells to doxorubicin

• Published in: International journal of cancer 2005-07, Vol.115 (6), p.924-929
• Main Authors: Miraglia, Erica, Viarisio, Daniele, Riganti, Chiara, Costamagna, Costanzo, Ghigo, Dario, Bosia, Amalia
• Format: Article
• Language: English
• Subjects: Amiloride - analogs & derivatives; Amiloride - pharmacology; Antineoplastic agents; Biological and medical sciences; colon carcinoma; Colonic Neoplasms - drug therapy; Colonic Neoplasms - metabolism; doxorubicin; Doxorubicin - pharmacology; Drug Resistance, Neoplasm; General aspects; HT29 Cells; Humans; Hydrogen-Ion Concentration; Medical sciences; Monensin - pharmacology; multidrug resistance; Na+/H+ exchanger; Pharmacology. Drug treatments; Sodium-Hydrogen Exchangers - antagonists & inhibitors; Sodium-Hydrogen Exchangers - metabolism; Tetradecanoylphorbol Acetate - pharmacology; Tumors
• ISSN: 0020-7136; 1097-0215
• DOI: 10.1002/ijc.20959

Multidrug resistant (MDR) tumor cells exhibit an altered pH gradient across different cell compartments, which favors a reduced intracellular accumulation of antineoplastic drugs and a decreased therapeutic effect. In our study, we have observed that the activity and expression of Na+/H+ exchanger (NHE), which is involved in the homeostasis of intracellular pH (pHi), are increased in doxorubicin‐resistant (HT29‐dx) human colon carcinoma cells in comparison with doxorubicin‐sensitive HT29 cells. The pHi was significantly higher in HT29‐dx cells, which accumulated less doxorubicin than HT29 cells. The NHE inhibitor 5‐(N‐ethyl‐N‐isopropyl)amiloride (EIPA) significantly reduced the pHi value and increased the intracellular accumulation of doxorubicin in both cell populations: in the presence of EIPA HT29‐dx cells accumulated as much drug as control HT29 cells. On the other hand, monensin, a Na+/H+ ionophore mimicking NHE activation, and phorbol 12‐myristate 13‐acetate (PMA), which stimulates NHE, significantly increased the pHi and decreased the drug accumulation in HT29 cells to values similar to those observed in control HT29‐dx cells. EIPA potentiated the cytotoxic effect of doxorubicin in HT29 cells, and made HT29‐dx cells as sensitive to the cytotoxic effect of the drug as control HT29 cells. Instead, PMA and monensin made HT29 cells as insensitive to doxorubicin as HT29‐dx cells. These results suggest that in MDR cells the higher cytosolic pH is likely to decrease drug accumulation, and that such resistance can be reverted by inhibiting the NHE activity. This result opens the possibility to revert MDR with the clinical use of NHE inhibitors. © 2005 Wiley‐Liss, Inc.