A Study Of The Mechanism Of Methylseleninic Acid Inhibiting Esophageal Cancer Cell Growth

As a member of trace elements,selenium is indispensible for human health.Several diseases such as Kashin-Beck disease,Keshan disease,and Myxedematous endemic cretinism,are associated with selenium deficiency.Epidemiological and experimental studies have indicated that the serum selenium levels also negatively related with all kinds of tumorigenesis and the supplementary of selenium could reduce the risk of some cancers including esophageal cancer.High dose of selenium manifests cytotoxicity against cancer cells while does not influence the normal cells,which shows the prospect of the anti-tumor application of selenium product.Nowadays,the chemotherapeutical studies of selenium in cancer are still in the pre-clinical stage.Methylseleninic acid(MSA)is a stable direct precursor of methylselenol,which is a key metabolite in the process of selenium metabolism.The cytotoxic efficacy of MSA has been determined in prostate,lung,pancreas,breast cancer and clear cell renal carcinoma,while little is known in esophageal cancer.Our lab has always been focusing on the study of the chemotherapeutical effect of MSA in esophageal squamous cell carcinoma(ESCC).Here,we used ESCC cell lines and animal model to explore the mechanism of the anti-tumor effect of MSA.In KYSE150 and KYSE510 cells.MSA treatment dramatically down-regulated Epidermal Growth Factor Receptor(EGFR)at the protein level but not the mRNA level.With a microRNA-array,we found MSA could up-regulate miR-146a which could directly target EGFR.And miR-146a inhibitor could antagonize MSA-induced decrease of EGFR protein.We also evaluated the inhibitory effect of MSA in vivo.Both tumor numbers,tumor burden and EGFR protein in tumor tissues were decreased upon MSA treatment in 4-nitroquinoline-oxide(4NQO)-induced esophageal tumor mice model.Furthermore,we found MSA treatment inhibited EGFR pathway and then down-regulated the secretion of Interleukin-6(IL-6)in both the supernatant of cancer cells and the serum of the 4NQO-induced mice.To further evaluate the association of IL-6 and the anti-tumor effect of MSA on esophageal cancer,we established the 4NQO-induced esophageal tumor model in IL-6 knock-out mice.The results showed that IL-6 deficiency did not affect esophageal tumorigenesis in mice,but the inhibitory effect of MSA was abolished in IL-6 knock-out mice.Although there are plenty of studies demonstrating the importance of selenium for the immune system at nutritional levels,little is known about the effects of selenium on the immune microenvironment at chemotherapeutical doses in cancer.Here,we found MSA treatment could decrease the infiltration of macrophage and neutrophil by using immunohistochemistry(IHC)technique detecting F4/80 and Ly6G and increase the expression of Granzyme B in the 4NQO-induced mice tumor tissues.In addition,IL-6 deficiency attenuated the effects of MSA in the tumor microenvironment.These data demonstrated that the inhibitory effect of MSA on esophageal cancer was dependent on IL-6.In conclusion,our study demonstrated that MSA could down-regulate EGFR via miR-146a and then inhibit EGFR pathway and decrease the secretion of IL-6 both in vitro and in vivo.In tumor microenvironment,MSA could decrease the infiltration of macrophage and neutrophil and increase the expression of Granzyme B,and the inhibitory effect of MSA on tumor microenvironment was dependent on IL-6.