Dihydroartemisinin Sensitizes Esophageal Squamous Cell Carcinoma to Cisplatin by Inhibiting Sonic Hedgehog Signaling

Background: Platinum-based regimens have been routinely used in the clinical treatment of patients with esophageal squamous cell carcinoma (ESCC). However, administration of these drugs is frequently accompanied by drug resistance. Revealing the underlying mechanisms of the drug resistance and developing agents that enhance the sensitivity to platinum may provide new therapeutic strategies for the patients. Methods: Immunohistochemistry, western blotting, RT-PCR, flow cytometry and immunofluorescence microscopy were used to detect the expression of Shh pathway members and cancer stem cell(CSC) biomarkers in ESCC specimens and cell lines. Functional assays, including MTT, tumorsphere formation assay, RTCA and an in vivo tumour growth assay, were conducted to assess the effect of Dihydroartemisinin (DHA) on the proliferation and renewal ability of ESCC cells. HPLC was used to examine the concention of cisplatin in ESCC cells.Results: We found that the poor outcome of ESCC patients receiving platinum-based regimens was associated with co-expression of Shh and Sox2. The sensitivity of ESCC cell lines to cisplatin was related to their activity of Shh signaling. Manipulating of Shh expression markedly changed the sensitivity of ESCC cells to platinum. Continuous treatment with cisplatin resulted in the activation of Shh signaling and enhanced cancer stem cell-like phenotypes in ESCC cells. DHA, a classic antimalarial drug, was identified as a novel inhibitor of Shh pathway. Treatment with DHA attenuated the cisplatin-induced activation of the Shh pathway in ESCC cells and synergized the inhibitory effect of cisplatin on proliferation, sphere and colony formation of ALDH-positive ESCC cells in vitro and growth of ESCC cell-derived xenograft tumors in vivo. Conclusion: These results demonstrate that the Shh pathway is an important player in cisplatin-resistant ESCC and DHA acts as a promising therapeutic agent to sensitize ESCC to cisplatin treatment.