Methionine enkephalin (MENK) inhibits human gastric cancer through regulating tumor associated macrophages (TAMs) and PI3K/AKT/mTOR signaling pathway inside cancer cells.

This study was to explore the effect and mechanisms of anti- human gastric cancer by MENK in vitro and in vivo. The results showed in MENK-treated xenograft tissue, the percentage of M2-type macrophages decreased while M1-type macrophages increased. MENK increased the expression of M1-related cytokine TNF-α and attenuated the expression of M2-related cytokine IL-10 expression. MENK upregulated the expression of opioid receptor (OGFr), while it inhibited HGC27 and SGC7901 cells through blocking PI3K/AKT/mTOR signal pathway in vitro and in vivo. These effects of MENK could be cancelled when OGFr was knockdown. This indicates that binding to OGFr by MENK appears to be essential for the anti- GC cells. Therefore, it is concluded that MENK might skew macrophage toward M2 phenotype from M1 phenotype within tumor and induce cells apoptosis though blocking OGFr/PI3K/AKT/mTOR signaling pathway.