76P - STAT3 inhibition reduces self-renewal in gastric cancer and promotes immune activation

Abstract

Background: STAT3 (Signal Transducers and Activators of Transcription- 3) transcription factor participates in inflammation, suppression of anti-tumor immune responses, and also cancer cell proliferation invasion, and even maintenance of embryonic stem cells. In the present study we sought to evaluate the inhibition of STAT3 activation on self-renewal ability and immune modulation in gastric cancer. Methods: Human gastric cancer cell lines (MKN-45 and AGS), as well as patient samples were cultured in low attachment flasks and serum free media supplemented with bFGf, EGF and B27 until gastro-spheres appeared. Following characterization of the gastro-spheres, their effects on T cell response were evaluated by MLR assay as well as T cell culture. Finally the parental cells as well as spheres treated by Sttatic (an inhibitor of STAT3 activation) at IC50 and the self-renewal properties as well as T cell activation and differentiation was evaluated by different in vitro methods. Results: Gastro-Spheroids had higher potential of colony and sphere formation, higher ability of resistance to drugs, increased expression of genes involved in pluripotecy and EMT. So, spheroids were identified as structures enriched for CSCs. They have higher level of activated STAT3 at mRNA and Protein.STAT3 inhibition by Stattic decreased stemness properties including spheroid formation capacity and pluripotency gene expression of gastric cancer. Moreover, gastro-spheres demonstrated potent immunosuppressive effects on T lymphocyte proliferation, VEGF and TGF-β cytokine expression and regulatory T cell differentiation. Furthermore, STAT3 inhibition in cancer cells decreased immunosupression due to cancer cells and Th17/Treg shift towards Th17. Conclusions: The present findings could be useful in therapeutic processes directed at CSCs and give better understanding of tumor cross talk with its niche. However, in vivo investigation of anti-tumor and immunomodulatory effects of STAT3 inhibition is desirable. Legal entity responsible for the study: Royan Institute Ethical Committee Funding: None Disclosure: All authors have declared no conflicts of interest.