title: Development of inhibitors of heterotrimeric Gαi subunits.
abstract: Heterotrimeric G-proteins are the immediate downstream effectors of G-protein coupled receptors (GPCRs). Endogenous protein guanine nucleotide dissociation inhibitors (GDIs) like AGS3/4 and RGS12/14 function through GPR/Goloco GDI domains. Extensive characterization of GPR domain peptides indicate they function as selective GDIs for Gαi by competing for the GPCR and Gβγ and preventing GDP release. We modified a GPR consensus peptide by testing FGF and TAT leader sequences to make the peptide cell permeable. FGF modification inhibited GDI activity while TAT preserved GDI activity. TAT-GPR suppresses G-protein coupling to the receptor and completely blocked α2-adrenoceptor (α2AR) mediated decreases in cAMP in HEK293 cells at 100nM. We then sought to discover selective small molecule inhibitors for Gαi. Molecular docking was used to identify potential molecules that bind to and stabilize the Gαi-GDP complex by directly interacting with both Gαi and GDP. Gαi-GTP and Gαq-GDP were used as a computational counter screen and Gαq-GDP was used as a biological counter screen. Thirty-seven molecules were tested using nucleotide exchange. STD NMR assays with compound 0990, a quinazoline derivative, showed direct interaction with Gαi. Several compounds showed Gαi specific inhibition and were able to block α2AR mediated regulation of cAMP. In addition to being a pharmacologic tool, GDI inhibition of Gα subunits has the advantage of circumventing the upstream component of GPCR-related signaling in cases of overstimulation by agonists, mutations, polymorphisms, and expression-related defects often seen in disease.
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, SC 29425, United States.
authors.forename: Kathryn M
authors.initials: KM
authors.lastname: Appleton
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, SC 29425, United States.
authors.forename: Kevin J
authors.initials: KJ
authors.lastname: Bigham
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, SC 29425, United States.
authors.forename: Christopher C
authors.initials: CC
authors.lastname: Lindsey
authors.affiliation: Department of Pharmacology, Medical University of South Carolina, Charleston, SC 29425, United States.
authors.forename: Starr
authors.initials: S
authors.lastname: Hazard
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, SC 29425, United States.
authors.forename: Jonel
authors.initials: J
authors.lastname: Lirjoni
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425, United States.
authors.forename: Stuart
authors.initials: S
authors.lastname: Parnham
authors.affiliation: Department of Biochemistry and Molecular Biology, Medical University of South Carolina, Charleston, SC 29425, United States.
authors.forename: Mirko
authors.initials: M
authors.lastname: Hennig
authors.affiliation: Department of Drug Discovery and Biomedical Sciences, Medical University of South Carolina, Charleston, SC 29425, United States. Electronic address: petersy@musc.edu.
authors.forename: Yuri K
authors.initials: YK
authors.lastname: Peterson
mesh_terms: D002478:Cells, Cultured; D004305:Dose-Response Relationship, Drug; D055808:Drug Discovery; D019206:GTP-Binding Protein alpha Subunits, Gi-Go / Q000037:antagonists & inhibitors*; D057809:HEK293 Cells; D006801:Humans; D008958:Models, Molecular; D015394:Molecular Structure; D010455:Peptides / Q000138:chemical synthesis / Q000737:chemistry; D054852:Small Molecule Libraries / Q000737:chemistry / Q000494:pharmacology*; D013329:Structure-Activity Relationship
chemical_list: D010455:Peptides; D054852:Small Molecule Libraries; D019206:GTP-Binding Protein alpha Subunits, Gi-Go
keywords: Docking; Drug discovery; G-protein; GPCR; Guanine nucleotide dissociation inhibitor; NMR; Pertussis toxin; Synthetic chemistry; cAMP