Inhibition Of IRE1-XBP1 Pathway Enhances Cytotoxicity Of Panobinostat In Esophageal Squamous Cancer Cells

Objective: To observe the inhibitory effect of panobinostat alone or in combination with STF083010 on proliferation in esophageal squamous cancer cells(ESCCs).Methods: The growth inhibition of drug on ESCCs was detected by CCK8.The cell cycle was detected by PI single staining.Cell apoptosis was detected by Annexin V / PI double staining.Western blot and Quantitative RT-PCR were used to detect the changes of protein or gene expression levels after drug treatment.Laser confocal observe the effect of drug on ER morphology in ESCC.The anti-tumor effects of panobinostat combined with STF083010 were examined in xenograft nude mice model.Results: The results showed panobinostat could effectively inhibit the growth of Kyse450 and Kyse510 cells were less susceptible to conventional chemotherapy drugs.Panobinostat induced G2/M phase arrest and cell apoptosis with an increase of histone H3 and ?-tubulin acetylation,an up-regulation of cyclin-dependent kinase inhibitor p21 and a reduction of oncogene c-Myc.Meanwhile,panobinostat caused endoplasmic reticulum stress,and activated the IRE1-Xbp1 pathway.The combination of panobinostat and STF083010 could significantly inhibit the proliferation of esophageal cancer cells,and the majority of the combined index(CI)<1.Compared with panobinostat treatment alone,panobinostat combined with STF083010 significantly inhibited pro-survival IRE1-Xbp1 pathway,disrupted the HDAC6-dependent aggresome degradation pathway and increased DDIT3 expression,an apoptosis marker of ER stress,which resulted in downregulation of the ratio of Bcl-x L/Bax,activation caspase cascade,and increasing the PARP cleavage,thereby inducing apoptosis.STF083010 significantly enhanced panobinostat-mediated tumor growth inhibition and tumor cell necrosis in xenograft nude mice model.Conclusion: The IRE1 endonuclease inhibitor STF083010 can promote the effect of growth inhibition induced by panobinostat both in vitro and in vivo,and also can promote cell apoptosis induced by panobinostat in ESCCs.