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

Abstract

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 þ /H þ exchanger (NHE), which is involved in the homeostasis of intracellular pH (pH i ), are increased in doxorubicin-resistant (HT29-dx) human colon carcinoma cells in comparison with doxorubicin-sensitive HT29 cells. The pH i was significantly higher in HT29-dx cells, which accumulated less doxorubicin than HT29 cells. The NHE inhibitor 5-(Nethyl-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 1 /H1 ionophore mimicking NHE activation, and phorbol 12-myristate 13-acetate (PMA), which stimulates NHE, significantly increased the pH i 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.

Role of pHi, and proton transporters in oncogene-driven neoplastic transformation

“…These compounds no longer inhibited the ENaC and the Na þ /Ca þ exchanger and became much more selective towards NHE1. Inhibitors of this series have been shown effective in retarding tumour development in mice [12] or in rendering chemiotherapy more effective [78,79]. Besides amiloride, the only compounds with NHE1 inhibitory activity that have undergone clinical trials are cariporide and eniporide, however these trials were not in the field of cancer but for ischaemic-reperfusion injury.…”

Dietary Anthocyanins: Impact on Colorectal Cancer and Mechanisms of Action

“…Multidrug resistant 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 fact, the activity and expression of NHE are increased in doxorubicin-resistant (HT29-dx) human colon carcinoma cells in comparison with doxorubicin-sensitive HT29 cells (Miraglia et al, 2005). On the other hand, it was demonstrated that activation of the NHE-1 and the resulting cellular alkalinization play a key role in oncogenic transformation (Reshkin et al, 2000).…”

Targeting Tumor Microenvironments for Cancer Prevention and Therapy

“…Treatment with NHE1 inhibitors sensitized the paclitaxel-induced apoptosis of human breast cancer cells (Reshkin et al, 2003). Moreover, increased activity of NHE was observed in doxorubicinresistant human colon cancer cells and the treatment with the NHE inhibitor 5-(N-ethyl-Nisopropyl)-amiloride (EIPA) sensitized the resistant cells to doxorubicin (Miraglia et al, 2005). Inhibition of NHEs has also been shown to reduce the proliferation and VEGF production of leukemia cells (He et al, 2007;Turturro et al, 2007).…”