Synthesis And Optimization Of Small Molecule Inhibitors Targeting STING Proteins

As an important component of the innate immune system,the c GAS-STING signalling pathway initiates a powerful and broad immune response through non-specific recognition of DNA which induces the expression of IFN-βand other pro-inflammatory cytokines to defend against pathogenic invasion and suppress tumours.However,while transient inflammatory signalling is essential for the body to defend itself against exogenous invasion,dysregulation of chronic inflammatory signalling may lead to STING-related autoimmune diseases as well as inflammatory disorders.Small molecule inhibitors targeting STING proteins have been reported to be promising for the treatment of STING-related chronic inflammatory diseases,and the study of novel potent small molecule inhibitors of STING will facilitate the development of drugs for the treatment of autoimmune and inflammatory diseases.In this work,we selected a high-affinity backbone ligand of STING,tetrahydroisoquinolinone-4-carboxylic acid,which has been previously reported,for structural modification.The best compound,compound 18,was found to have an effective concentration of68 n M in the binding assay,but the cellular inhibitory activity of the compounds reported in the article was poor,with the best compound inhibiting the active site of STING in a THP-1 cell model at a concentration of 11μM.Based on this,we hope to continue optimizing this class of structures through systematic optimization of the compounds to obtain the compound with better activity based on the establishment of certain SAR.After four rounds of compound optimisation,we obtained a total of 182 compounds in five series,A(carboxylic acid),B(ester),C(carboxamide),D(extension amide)and E(indene),and combined them with dual luciferase reporter gene experiments for SAR analysis.Among the 46 compounds obtained in the first round of optimisation,we found that the activity was better when the R~2 molecular fragment was a hydrophobic group,and that increasing the length of the R~3 fragment significantly improved the activity of the compounds.Based on this,a second round of optimisation was carried out,focusing on the structural modification of the R~1carboxylic acid group and the R~5 molecular fragment,resulting in 82 compounds.The structural and bioactivity evaluation of these compounds showed that the activity of the hydrophobic group R~5 was significantly better than that of the other groups,and it was tentatively suspected that there might be a hydrophobic interaction with the target protein at R~5.A third round of optimisation was carried out on the basis of the best active compound,A38,obtained in the second round.34compounds were synthesised and evaluated for in vitro cellular activity and it was found that the modification of the R~4 substitution did not favour the binding of the molecule to the protein.The fourth round of optimisation was based on a specific modification of R~1 and was divided into two types to obtain a total of 20 compounds.In one type,the extension of the R~1 part was expected to result in better binding to enhance the in vitro cellular activity,but the activity of 16compounds in this batch was mediocre;in the other type,four indenoisoquinoline structures were synthesized with good activity,further enriching the backbone of STING small molecule inhibitors.In summary,our structural modifications based on the structure of tetrahydroisoquinolinone-4-carboxylic acid reported in the article yielded a total of 182compounds,of which 181 compounds were not previously reported.Among them,compound A38showed the best activity with an in vitro cell half inhibition concentration of 20 n M,which was greatly improved from the orignal compounds as the start of opmization.