Design,Synthesis And Biological Evaluation Of Reversible Peptidomimetic Proteasome Inhibitors

Malignant tumors have become one of the major public problems that seriously threaten human health,and it is imminent to develop targeted therapeutic drugs with strong specificity and less toxic and side effects.Accumulated studies have shown that most of the proteins related to life activities such as cell growth,reproduction and apoptosis are regulated by the proteasome.In addition,due to abnormal proliferation of tumor cells,the rapid protein turnover can be achieved through the powerful degradation function of the proteasome,which is essential for the proliferation of tumor cell.When the function of proteasomal degradation is inhibited,the protein levels involved in regulating related signaling pathways are dysregulated,leading to cell cycle disorders and apoptosis.Therefore,proteasome inhibitors are an effective means for treating malignant tumors.At present,three proteasome inhibitors have been approved for marketing and many inhibitors have entered clinical research.Proteasome inhibitors can be divided into covalent and non-covalent ones according to their binding modes to the target.Since most of the covalent binding is irreversible,it often generates severe toxic and side effects.Non-covalent proteasome inhibitors have attracted more and more attention due to their kinetic advantages.In this paper,a non-covalent proteasome inhibitor A19 in the previous study was employed as the lead compound,whose poor activity in vivo was analyzed through metabolic experiments.32 peptidomimetic compounds were designed using metabolism guided optimization strategy.The proteasome inhibitory activities showed that 18 compounds with(R)-1,2,3,4-tetrahydronaphthalene-1-yl group at the carboxyl terminus displayed potent proteasome inhibitory activities and 12 compounds with IC50 values less than 10 n M.Besides,these analogues also displayed potent proliferation inhibitory activities against multiple myeloma cells and acute leukemia cells,which was consistent with the proteasome inhibitory activities In order to verify that compounds with potent inhibitory activities also affect the accumulation of ubiquitinated proteins,selected compounds 1-114,1-115 and 1-125 were further tested through western blotting.The results showed that the accumulation effects of three compounds were obvious,which were even stronger than the positive control.To further validate the feasibility of the metabolism guided optimization strategy,mouse whole blood stability evaluation was performed on the three compounds.Compared with the lead compound A19,the blood half-lives of the three compounds were increased,and the compound 1-115 with the longest half-life revealed a 9-fold improvement in blood stability.Based on the above biological evaluations,compounds 1-115 and 1-125 were selected for testing the proteasome inhibitory activities in blood cells of normal mice.The results revealed that both compounds displayed superior activities with inhibitory rates of about 50% 1 h after administration.The above experimental results indicated that compound 1-115 is a potential proteasome inhibitor for further exploration.Since there are no non-covalent proteasome inhibitors on the market,as an important supplement for the development of new proteasome inhibitors in the future,we designed a series of reversible covalent peptidomimetics constructed with β-lactam ring as proteasome inhibitors.Structure activity relationship studies were performed through exploring influencies of various β-lactam rings and peptide skeletons.21 molecules containing β-lactam rings were designed and synthesized.Proteasome inhibitory activities of these compounds showed that only five molecules with R configuration β-lactam rings at the carboxyl terminus displayed moderate to potent proteasome inhibitory activities.Selected compounds with good proteasome inhibitory activities were tested for their cytotoxicities against hematological malignancy cell lines.However,the proliferation inhibitory activities were not consistent with the proteasome inhibitory activities.It is speculated that the physicochemical properties of the compounds are too poor,resulting in weak tumor cell proliferation inhibitory activities.Further optimizations are required in the future research.