Pantoprazole pretreatment elevates sensitivity to vincristine in drug-resistant oral epidermoid carcinoma in vitro and in vivo

Resistance to chemotherapeutic agents is a major cause of treatment failure in patients with oral cancer. Proton pump inhibitors (PPIs), essentially H+-K+-ATPase inhibitors which are currently used in the treatment of acid related diseases, have demonstrated promising antitumor and chemo-sensitizing efficacy. The main purpose of the present study was to investigate whether pantoprazole (PPZ, one of PPIs) could increase the sensitivity of chemoresistant oral epidermoid carcinoma cells (KB/V) to vincristine (VCR) and elucidate the underlying action mechanism. Results showed that combination treatment of PPZ and VCR synergistically inhibited the proliferation of KB/V cells in vitro and in vivo. Furthermore, administration of PPZ and VCR not only induce apoptosis and G2/M phase arrest in KB/V cells but also suppress the migration and invasion of KB/V cells. The mechanism underlying synergistic anti-tumor effect of PPZ and VCR was related to the inhibition of the function and expression of P-glycoprotein (P-gp) and the down-regulation of EGFR/MAPK and PI3K/Akt/mTOR signaling pathways in KB/V cells. Additionally, we observed that PPZ treatment induced an increase in lysosomal pH and inhibited the activity of lysosomal enzyme acid phosphatase in KB/V cells, which could functionally reduce the sequestration of VCR in lysosomes and sensitized KB/V cells to VCR. In conclusion, our study demonstrated that PPZ could be included in new combined therapy of human oral cancer (especially on VCR-resistant therapy) together with VCR.