Combined Inhibition Of Proteasome And BET Or CRM1 Proteins As A Potential Therapy For Colorectal Cancer

Purpose:1.BET inhibitors(BETi)are promising epigenetic agents for the treatment of various cancers through suppression of oncogenic transcription factors including c-myc.However,resistance to BETi is common in colorectal cancer(CRC),which can be a critical obstacle for successful translation.In this study,we evaluated the mechanisms underlying resistance to the BETi and proposed effective combination strategy for the treatment of CRC.2.Proteasome inhibitors such as Bortezomib had significant therapeutic effects in multiple myeloma and lymphoma,but not solid tumors.The purpose of this study is to investigate the underlying mechanisms and explore strategies that may enhance the anti-tumor action of proteasome inhibitors on colorectal cancer.Methods:1.We investigated the effect of BETi on CRC proliferation,apoptosis,angiogenesis and c-myc expression.After screened for various combined drugs and gene expression profiles,we further tested the ability of inhibitors targeting the NF-?B pathway to enhance synergistic effect and explored its molecular mechanism.2.Nuclear export of ubiquitinated proteins was assessed by immunofluorescence and subcellular fractionation.The actions of p53 and CRM1 were analyzed by immunoblotting,si RNAs,and specific inhibitors.Results:1.Although BETi impair proliferation and angiogenesis in CRC,a subset of cell lines was distinctly resistant to BETi.Blockade of the NF-?B pathway with Bortezomib rendered resistant cells more sensitive to BETi by repression of c-myc and in turn inducing GADD45 expression.2.Proteasome inhibition induced marked nuclear export of ubiquitinated proteins,including tumor suppressor p53.Blockage of nuclear export by inhibiting CRM1 with KPT330 and specific si RNA enhanced synergistically the cytotoxic action of Bortezomib on p53^+/+colon cancer cells,which was accompanied by expression of p53 target genes and was diminished significantly by p53 knockdown.Conclusion:1.Our findings provide a rationale for combined inhibition of BET proteins and NF-?B pathway as a potential therapy for CRC.2.Nuclear export of p53is a major mediator for the synergistic anti-tumor action of Bortezomib and KPT330.Inhibition of nuclear export is a novel strategy for using proteasome inhibitor in the treatment of colon cancer harboring functional p53.