Targeting Autophagy To Enhance Paclitaxel Sensitivity In Esophageal Carcinoma

Esophageal cancer is one of the malignancies threatening human health with high incidence and a very low 5-year survival rate with poor outcomes in the developing countries. Chemotherapy has been played indispensable roles while companied with more and more chemoresistance and side effects. Numerous studies have shown that autophagy may play specific role as one of the drug resistance mechanisms through promoting cancer cell survival via self-digestion. Therefore targeting autophagy might be another promising approach of therapeutics in cancer. Paclitaxel(PTX) is widely used for malignant tumors treatment through inducing apoptosis and autophagy. More findings discovered that chemoresistance is still a major hurdle for PTX due to cytoprotective autophagy. In order to investigate whether targeting autophagy could confer the sensitivity of PTX in esophageal carcinoma, chloroquine (CQ) was applied as an autophagy inhibitor to study the esophageal carcinoma cells EC109 co-treated with PTX in vitro and explore the potential molecular mechanisms. Firstly, CQ and PTX were used separately and also combined to treat EC109 cells at different dosages and time points, and the MTT results showed that CQ could contribute to the suppressive effect of PTX on the growth and proliferation of EC109 cells. Meanwhile the migration and invasion abilities of EC109 were significantly inhibited by co-treatment of PTX and CQ comparing with PTX only through scratch test and cell invasion Transwell chamber test, moreover the combination treatment dramatically suppressed the colony formation on soft agar. Further investigation showed that mTOR pathway was activated in CQ or PTX exposure, which resulted in phosphorylated mTOR(p-mTOR) down-regulation, followed by the decline of phosphorylated p70S6K (p-p70S6K) and phosphorylated p-4EBP1, and the autophagy marker LC3I/II conversion and p62 elevated eventually, which indicated that autophagy was mediated in PTX or CQ treatment in EC109 cells. On the other hand, GFP-LC3 was transfected into EC109 cells to observe the LC3 translocation status after CQ or PTX treatment, which usually be regarded as the morphological maker of autophagy, and the results confirmed the findings in Western Blot. Most importantly, the combination treatment of CQ and PTX resulted in synergistic consequences. For further understanding the mTOR pathway was initiated in CQ or PTX mediated autophagy in this study, we used lentiviral shRNA embedding mTOR to knockdown the expression of mTOR first and then studied the signaling pathway changes after CQ and PTX co-treatment, and we found a decrease trend of LC3-II/ I ratio and p62 also compared with the competent mTOR control. From these results, we confirmed that autophagy would benefit the survival of EC109 cells, and our findings demonstrated that targeting of autophagy using CQ could be an effective and potential strategy to improve PTX treatment outcomes in the management of esophageal carcinoma. Citation Format: Jiajing Cai, Yan Cai, Qiang Ma, Jiang Zou, Binfeng He, Fan Chang, Lei Xu, Xiaolan Guo. Targeting autophagy to enhance paclitaxel sensitivity in esophageal carcinoma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3541.