Research Papers:

P-glycoprotein-mediated chemoresistance is reversed by carbonic anhydrase XII inhibitors

Joanna Kopecka, Gregory M. Rankin, Iris C. Salaroglio, Sally-Ann Poulsen and Chiara Riganti _

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Oncotarget. 2016; 7:85861-85875. https://doi.org/10.18632/oncotarget.13040

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Joanna Kopecka1, Gregory M. Rankin2, Iris C. Salaroglio1, Sally-Ann Poulsen2,*, Chiara Riganti1,*

1Department of Oncology, University of Torino, 10126 Torino, Italy

2Eskitis Institute for Drug Discovery, Griffith University, Brisbane, Nathan, Queensland, 4111, Australia

*These authors contributed equally to this work

Correspondence to:

Sally-Ann Poulsen, email: [email protected]

Chiara Riganti, email: [email protected]

Keywords: carbonic anhydrase XII, P-glycoprotein, doxorubicin, chemoresistance, intracellular pH

Received: August 26, 2016     Accepted: October 28, 2016     Published: November 03, 2016


Carbonic anhydrase XII (CAXII) is a membrane enzyme that maintains pH homeostasis and sustains optimum P-glycoprotein (Pgp) efflux activity in cancer cells. Here, we investigated a panel of eight CAXII inhibitors (compounds 1–8), for their potential to reverse Pgp mediated tumor cell chemoresistance. Inhibitors (5 nM) were screened in human and murine cancer cells (colon, lung, breast, bone) with different expression levels of CAXII and Pgp. We identified three CAXII inhibitors (compounds 1, 2 and 4) that significantly (≥ 2 fold) increased the intracellular retention of the Pgp-substrate and chemotherapeutic doxorubicin, and restored its cytotoxic activity. The inhibitors lowered intracellular pH to indirectly impair Pgp activity. Ca12-knockout assays confirmed that the chemosensitizing property of the compounds was dependent on active CAXII. Furthermore, in a preclinical model of drug-resistant breast tumors compound 1 (1900 ng/kg) restored the efficacy of doxorubicin to the same extent as the direct Pgp inhibitor tariquidar. The expression of carbonic anhydrase IX had no effect on the intracellular doxorubicin accumulation. Our work provides strong evidence that CAXII inhibitors are effective chemosensitizer agents in CAXII-positive and Pgp-positive cancer cells. The use of CAXII inhibitors may represent a turning point in combinatorial chemotherapeutic schemes to treat multidrug-resistant tumors.

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