Abstract
Background: Small bowel adenocarcinoma (SBA) is a rare malignant tumor of gastrointestinal tract. Currently, there is no standard treatment approach for late-stage SBA, which lead to poor outcome and prognosis. Rapamycin is an immunosuppressive agent that has been reported to inhibit the proliferation of tumor cells. However, whether rapamycin inhibit the growth of SBA remains to be investigated. Aim: To observe the inhibitory effect of rapamycin on small intestinal adenocarcinoma cells. Methods: Methylthiazolyldiphenyl-tetrazolium bromide assay, colony formation assay, cell cycle analysis, and glycolysis assay were used to observe the phenotypic changes of rapamycin-treated HUTU 80 cells. RNA sequencing and untargeted ultra-high performance liquid chromatography-tandem mass spectrometry (UHPLC-MS/MS) metabolomics were also used to find the potential targets of action of rapamycin in inhibiting HUTU 80 cells proliferation, and validate potential targets by quantitative polymerase chain reaction and western blotting. The construction of a subcutaneous HUTU 80 xenograft in BALB/c nude mice was used to explore the tumor suppression effect of rapamycin. Results: Rapamycin inhibited HUTU 80 cell proliferation in vitro and in vivo. Rapamycin inhibited the migration, invasion, and glycolysis of HUTU 80 cells, and induced cell cycle arrest. RNA sequencing and untargeted UHPLC-MS/MS metabolomic analysis indicated that the mechanism of rapamycin action was linked to the hypoxia-inducible factor (HIF)-1α signaling pathway and the related gluconeogenesis/glycolysis pathways. Subsequent experiments found that rapamycin downregulated the messenger RNA expression of HIF-1α and its downstream target genes, LDHA, PDK1 and VEGF. Additionally, rapamycin inhibited expression of phosphorylated mammalian target of rapamycin (mTOR), phosphorylated-70 kDa ribosomal protein S6 kinase (p70S6k), phosphorylated eukaryotic translation initiation factor 4E-binding protein 1 (4E-BP1) and HIF-1α proteins in vitro and in vivo. Conclusion: Downregulation of mTOR/p70S6k/4E-BP1/HIF-1α signaling pathway activation, leading to decreased glycolysis and cell cycle arrest, may be the pivotal mechanism by which rapamycin inhibits SBA.