Design,Synthesis,and Biological Evaluation Of Amidobenzimidazole Derivatives As Stimulator Of Interferon Genes(STING)Receptor Agonists

Stimulator of interferon genes(STING)is an endoplasmic reticulum-localized adaptor protein that is also known as MITA,MPYS,ERIS and TMEM173.Natural cyclic dinucleotides(CDNs)can bind and activate STING,which then triggering the STING-TBK1-IRF3 signaling pathway to regulate the innate immunity.Studies have revealed that the activation of STING can up-regulate the innate immunity,and then inhibiting the growth and metastasis of tumor.Therefore,STING agonists have garnered much attention for tumor immunotherapy.Currently,there are few scaffolds of STING agonists and efforts are mainly focused on the development of modified CDNs.However,modified CDNs have strong polarity and poor membrane permeability.Amidobenzimidazole compounds can activate STING and induce the secretion of I-IFN,which elicit antitumor activity.In this paper,the receptor-based and ligand-based rational drug design strategies were used to design,synthesize and evaluate amidobenzimidazole STING agonists.By analyzing the binding modes of CDN and amidobenzimidazole compounds with STING protein,it was found that the hydrogen bonds formed respectively by Ser241,Ser162,Thr263 and the ligand as well as the π-π interaction formed by Tyr167 and the ligand are key interactions for binding to protein.Four modification sites R1,R2,R3 and R4 were chosen based on the interactions between four key amino acid residues and the amidobenzimidazole ligand.Diverse and multi-round structural modification methods were adopted to improve STING agonistic activity of compounds.Herein,five series of 52 target compounds were designed and synthesized,all of which were characterized by 1HNMR,13CNMR and high resolution mass spectrometry(HMS).The STING agonistic activity of all compounds were evaluated in vitro,and the structure-activity relationships were summarized.Subsequently,the representative compounds 80(Wj0263,EC50=1.24μM),90(Wj0252,EC50=0.287μM)and93(Wj0260,EC50=1.14μM)showedhigh potency for binding to STING in vitro.In vitro STING signaling pathway studies have shown that 80,90 and 93 induced higher protein levels and mRNA levels of IFN-β,CXCL10 and IL-6 than 2’,3’-cGAMP.What’s more,90 markedly induced the phosphorylation of STING and activated the STING-TBK1-IRF3 signaling pathway.In vivo PK/PD studies of 90 showed that treatment with 0.15 mg/kg compound 90 resulted in significant tumor growth inhibition as measured by tumor weight and tumor volume,and 90 possessed good pharmacokinetic characteristics,which endowed it promising the lead compound.