PI3K-AKT-MTOR Inhibiter Resistance Via Feedback Activation Of STAT3 In Gastric Cancer Cells

Background Gastric cancer is the second leading cause of tumor-ralated death. Gastric cancer remains one of the most common cancer and accounts for nearly 1 million new cases all over the world per year , of which 42% occurred in China. It is the second leading cause of death in urban areas of china. The PI3K/AKT/mTOR signaling pathway is abnormally activated in cancer cells, so a series of inhibitors for this signaling pathway have been developed and entered into clinical trials. The development of targeted therapies has greatly promoted the progress of gastric cancer treatment, However, the drug resistance limited the therapeutic effect of the inhibitors, and the molecular mechanism is unclear.STAT3 feedback activation plays a leading role in the process of drug resistance in cancer cells. Therefore, it is of great significance to study the strategy of combination of these two targets for improving the therapeutic effect of targeted therapy in gastric cancer.Objective To analyze and reveal the feedback activation of STAT3 kinase is an important factor for the resistance of PTEN negative gastric cancer cells to PI3K/AKT/mTOR inhibitors. Elucidate the molecular mechanism of STAT3 kinase feedback activation. To explore the therapeutic strategies of STAT3 kinase and PI3K/AKT/mTOR in the treatment of gastric cancer.Methods A series of gastric cancer cell lines were treated with PI3K/AKT/mTOR inhibitor(LY294002, BEZ235, MK2206, RAD001) alone or combined with STAT3 kinase inhibitor(STATTIC). The phosphorylation level of AKT kinase and STAT3 kinase was detected by Western-blot. Flow cytometry was used to observe the effects of single or combined treatment on cell cycle and apoptosis. A stable HGC27 cell line with low STAT3 expression was established by siRNA, and the corresponding tumor bearing mice model was established. The cell growth was detected by CCK8 assay and plate clone test. Tumor bearing mice model was used to detect the growth rate of HGC27 cells (NC,shSTAT3)with the treatment of BEZ23 5.Results (1) In PTEN negative gastric cancer cells, PI3K/AKT/mTOR signaling pathway inhibitor activates STAT3 kinase activity. (2) Inhibition of STAT3 kinase activity can increase the sensitivity to PI3K/AKT/mTOR inhibitors in gastric cancer cells. (3)Inhibition of PI3K/AKT/mTOR kinase and STAT3 kinase activity could inhibit the growth of gastric cancer cells synergistically. (4) SDF-1/CXCR4 axis is involved in the activation of STAT3 feedback, the feedback activation of STAT3 is related to the secretion of soluble cytokines and genetic background.Conclusions In PTEN negative gastric cancer cells, PI3K/AKT/mTOR inhibitors activate STAT3 kinase activity and are associated with some soluble cytokines. This provides a basis for drug resistance. Inhibition of STAT3 kinase and PI3K/AKT/mTOR kinase activity inhibit the growth of gastric cancer cells synergistically. The results provide guidance for the treatment of patients with PTEN negative gastric cancer.