Synergistic Anti-myeloma Effect Of BET Inhibitor OTX015 And Proteasome Inhibitors And Its Mechanism

ObjectiveMultiple myeloma?MM?is an incurable malignant tumor that affects plasma cells of the bone marrow.Proteasome inhibitors have become the frontline agents in the treatment of MM in recent years.Nevertheless,consequent resistance to proteasome inhibitors has been brought to the forefront.Our previous research confirmed that OTX015 had anti-myeloma effect.This study was aiming at exploring the antineoplastic effects of the combination of OTX015 and proteasome inhibitors on myeloma cell line as well as the potential mechanism,to provide a new strategy and theoretical basis to clinicians who seek treatment to proteasome inhibitor resistant MM.Methods1.The combination effects of OTX015 and proteasome inhibitors?Bortezomib,Carfilzomib and Ixazomib?on MM cells?RPMI 8226?were detected with Cell Couting Kit-8.2.MM cells?RPMI 8226?were divided into four groups as following:control,OTX015,proteasome and OTX015+proteasome inhibitor.The relative expressions of c-myc,PSMB5 and PSMB7 were detected by Quantitative Real-time PCR.Meanwhile,the proteins were detected by western blot and the chymotrypsin-like activities of proteasome were detected with Proteasome-Glo^TM Chymotrypsin-Like Cell-Based Assay.3.Links between c-myc and gene PSMB5,PSMB7 were demonstrated by CHIP.Results1.Synergistic effects of OTX015 and proteasome inhibitors were shown to inhibit the growth of myeloma cells within a certain concentration range of each agent?CI<1?.2.Quantitative Real-time PCR manifested significant decline of the relative expressions of c-myc,PSMB5 and PSMB7 in OTX015+proteasome inhibitors groups compared with proteasome inhibitor groups?p<0.05?.The expressions of protein c-myc were downregulated obviously in OTX015+proteasome inhibitors groups and the expressions of proteasome subunits?2 and?5 also decreased slightly.Moreover,OTX015+proteasome inhibitors groups had lower chymotrypsin-like proteasome activities than proteasome inhibitors groups?p<0.05?.3.We demonstrated that protein c-myc binded to the promoter regions of PSMB5and PSMB7 in myeloma cells by CHIP.ConclusionOTX015 and proteasome inhibitors have in vitro synergistic anti-myeloma effect and the mechanism probably is that OTX015 downregulates the transcriptions of proteasome subunits and proteasome generation via inhibiting the expression of c-myc.OTX015inhibits ubiquitin-proteasome system on the level different from proteasome inhibitors and anti-myeloma results achieved ultimately.Therefore,OTX015 is a prospective drug applied to the treatment of MM,and proteasome inhibitors resistance MM in especial.