Omipalisib Inhibits Esophageal Squamous Cell Carcinoma Growth Through PI3K/AKT/mTOR Signaling Pathway Disruption

Background: Esophageal squamous cell carcinoma(ESCC)is a lethal digestive tract malignancy with limited effective interventions.The aberrant activation of phosphoinositide 3-kinase(PI3K)/AKT/mammalian target of rapamycin(mTOR)signaling pathway is associated with the tumorigenesis of ESCC,providing a potential target for its treatment.However,antineoplastic effect of inhibitors of PI3K/AKT/mTOR has remained elusive.In this study,we investigated the therapeutic effects and underlying mechanisms of omipalisib,a dual inhibitor for both PI3 K and mTOR in ESCC cells based on a screen of compound library.Methods: MTT assay was utilized to screen compounds in the library and assess cell viability of ESCC cells exposed to various concentrations of omipalisib.Flow cytometry was used to determine cell cycle distribution and apoptosis occurred in ESCC cells treated with omipalisib.RNA sequencing(RNA-Seq)was performed for global changes in genes expression in ESCC cells treated with omipalisib.Real time PCR was done to detect mRNA expression.Western blot was conducted for protein expression.And xenograft nude mouse model was established to evaluate the effect of omipalisib on tumour growth in vivo.Results: In the pilot screen of 1404 compounds library,69 compounds demonstrated an obvious antineoplastic effect,with the inhibitory rate above 50%.Based on the TCGA and the GTEx database analysis,we found PI3 K and mTOR mRNA expression is significant higher in esophageal tumour tissue than normal esophageal tissue and focused on omipalisib,a dual inhibitor for PI3 K and mTOR of the 69 compounds.We demonstrated that omipalisib markedly inhibited cell proliferation and colony formation in a panel of ESCC cell lines.Mechanistically,omipalisib induced G0/G1 phase arrest and apoptosis.RNA-seq,KEGG and GSEA analyses revealed that the PI3K/AKT/mTOR signaling pathway is the primary target of omipalisib in ESCC cells.Treatment with omipalisib decreased expression of p-AKT,p-4EBP1,p-p70S6 K,p-S6 and p-ERK,therefore disrupting the activation of PI3K/AKT/mTOR and MAPK/ERK signaling pathway and suppressing proliferation of cells.In nude mouse xenograft model,omipalisib significantly suppressed the tumour growth in ESCC tumour bearing mice without obvious side effects.Conclusion: Omipalisib inhibits the proliferation and growth of ESCC by disrupting the PI3K/AKT/mTOR signaling pathway.The present study supports the rationale for omipalisib as a therapeutic approach to ESCC cases and suggests the potential clinical evaluation of the strategy.