Disruption of pH Dynamics Suppresses Proliferation and Potentiates Doxorubicin Cytotoxicity in Breast Cancer Cells

Abstract

The reverse pH gradient is a major feature associated with cancer cell reprogrammed metabolism. This phenotype is supported by increased activity of pH regulators like ATPases, carbonic anhydrases (CAs), monocarboxylate transporters (MCTs) and sodium–proton exchangers (NHEs) that induce an acidic tumor microenvironment, responsible for the cancer acid-resistant phenotype. In this work, we analyzed the expression of these pH regulators and explored their inhibition in breast cancer cells as a strategy to enhance the sensitivity to chemotherapy. Expression of the different pH regulators was evaluated by immunofluorescence and Western blot in two breast cancer cell lines (MDA-MB-231 and MCF-7) and by immunohistochemistry in human breast cancer tissues. Cell viability, migration and invasion were evaluated upon exposure to the pH regulator inhibitors (PRIs) concanamycin-A, cariporide, acetazolamide and cyano-4-hydroxycinnamate. Additionally, PRIs were combined with doxorubicin to analyze the effect of cell pH dynamic disruption on doxorubicin sensitivity. Both cancer cell lines expressed all pH regulators, except for MCT1 and CAXII, only expressed in MCF-7 cells. There was higher plasma membrane expression of the pH regulators in human breast cancer tissues than in normal breast epithelium. Additionally, pH regulator expression was significantly associated with different molecular subtypes of breast cancer. pH regulator inhibition decreased cancer cell aggressiveness, with a higher effect in MDA-MB-231. A synergistic inhibitory effect was observed when PRIs were combined with doxorubicin in the breast cancer cell line viability. Our results support proton dynamic disruption as a breast cancer antitumor strategy and the use of PRIs to boost the activity of conventional therapy.

New Dual P-Glycoprotein (P-gp) and Human Carbonic Anhydrase XII (hCA XII) Inhibitors as Multidrug Resistance (MDR) Reversers in Cancer Cells

“…By contrast, we focused on the compounds used in the low micromolar range and evaluated their behavior in coadministration with classical chemotherapeutic drugs. Indeed, some hCA XII inhibitors also restored chemotherapeutic drug efficacy by controlling the pHi values, as for instance acetazolamide. , Also, the activity of P-gp is deeply influenced by pHi, being higher at a slightly alkaline pH . These findings are in line with our observation, showing a higher V max , corresponding to a higher catalytic activity, in HT29/DOX and A549/DOX cells that have higher pHi than their sensitive counterpart, caused by the increased expression of hCA XII .…”

Multifunctional Microspheres Dual-Loaded with Doxorubicin and Sodium Bicarbonate Nanoparticles to Introduce Synergistic Trimodal Interventional Therapy

“…Numerous studies have confirmed that the acidic tumor microenvironment is highly correlated with chemotherapy sensitivity. − The acidic tumor microenvironment is maintained by the regulation of pH regulators like ATPases, carbonic anhydrases (CAs), monocarboxylate transporters (MCTs) and sodium–proton exchangers (NHEs), which are responsible for the cancer acid-resistant phenotype . The disruption of the balance of the tumor acidic microenvironment could effectively inhibit the activity of the previously described pH regulators, thereby inhibiting the tumor cell proliferation and increasing the sensitivity of chemotherapy, , which may be the potential mechanism of the synergistic antitumor effect of sodium bicarbonate and doxorubicin.…”

The complex relationship between multiple drug resistance and the tumor pH gradient: a review

“…NHE1 inhibition with cariporide reversed imatinib resistance in BCR-ABL-expressing leukemia cells [ 98 - 100 ] , and NHE1 knockdown sensitized malignant cells to cisplatin-induced apoptosis [ 101 ] . Inhibiting proton extruders, among them NHE1, increased doxorubicin’s cytotoxic effects on breast cancer cell lines [ 102 ] .…”