Altered pH gradient at the plasma membrane of osteosarcoma cells is a key mechanism of drug resistance

Sofia Avnet, Silvia Lemma, Margherita Cortini, Paola Pellegrini, Francesca Perut, Nicoletta Zini, Katsuyuki Kusuzaki, Tokuhiro Chano, Giulia Grisendi, Massimo Dominici, Angelo De Milito, Nicola Baldini

Research output: Contribution to journalArticlepeer-review

Abstract

Current therapy of osteosarcoma (OS), the most common primary bone malignancy, is based on a combination of surgery and chemotherapy. Multidrug resistance mediated by P-glycoprotein (P-gp) overexpression has been previously associated with treatment failure and progression of OS, although other mechanisms may also play a role. We considered the typical acidic extracellular pH (pHe) of sarcomas, and found that doxorubicin (DXR) cytotoxicity is reduced in P-gp negative OS cells cultured at pHe 6.5 compared to standard 7.4. Short-time (24-48 hours) exposure to low pHe significantly increased the number and acidity of lysosomes, and the combination of DXR with omeprazole, a proton pump inhibitor targeting lysosomal acidity, significantly enhanced DXR cytotoxicity. In OS xenografts, the combination treatment of DXR and omeprazole significantly reduced tumor volume and body weight loss. The impaired toxicity of DXR at low pHe was not associated with increased autophagy or lysosomal acidification, but rather, as shown by SNARF staining, with a reversal of the pH gradient at the plasma membrane (ΔpHcm), eventually leading to a reduced DXR intracellular accumulation. Finally, the reversal of ΔpHcm in OS cells promoted resistance not only to DXR, but also to cisplatin and methotrexate, and, to a lesser extent, to vincristine. Altogether, our findings show that, in OS cells, shortterm acidosis induces resistance to different chemotherapeutic drugs by a reversal of ΔpHcm, suggesting that buffer therapies or regimens including proton pump inhibitors in combination to low concentrations of conventional anticancer agents may offer novel solutions to overcome drug resistance.

Original languageEnglish
Pages (from-to)63408-63423
Number of pages16
JournalOncotarget
Volume7
Issue number39
DOIs
Publication statusPublished - 2016

Keywords

  • Doxorubicin
  • Drug resistance
  • Osteosarcoma
  • Plasma membrane pH gradient
  • Tumor microenvironment

ASJC Scopus subject areas

  • Oncology

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