title: Small molecule binding sites on the Ras:SOS complex can be exploited for inhibition of Ras activation.
abstract: Constitutively active mutant KRas displays a reduced rate of GTP hydrolysis via both intrinsic and GTPase-activating protein-catalyzed mechanisms, resulting in the perpetual activation of Ras pathways. We describe a fragment screening campaign using X-ray crystallography that led to the discovery of three fragment binding sites on the Ras:SOS complex. The identification of tool compounds binding at each of these sites allowed exploration of two new approaches to Ras pathway inhibition by stabilizing or covalently modifying the Ras:SOS complex to prevent the reloading of Ras with GTP. Initially, we identified ligands that bound reversibly to the Ras:SOS complex in two distinct sites, but these compounds were not sufficiently potent inhibitors to validate our stabilization hypothesis. We conclude by demonstrating that covalent modification of Cys118 on Ras leads to a novel mechanism of inhibition of the SOS-mediated interaction between Ras and Raf and is effective at inhibiting the exchange of labeled GDP in both mutant (G12C and G12V) and wild type Ras.
authors.affiliation: AstraZeneca , Alderley Park, Macclesfield, Cheshire, SK10 4TG, United Kingdom.
authors.forename: Jon J G
authors.initials: JJ
authors.lastname: Winter
authors.forename: Malcolm
authors.initials: M
authors.lastname: Anderson
authors.forename: Kevin
authors.initials: K
authors.lastname: Blades
authors.forename: Claire
authors.initials: C
authors.lastname: Brassington
authors.forename: Alexander L
authors.initials: AL
authors.lastname: Breeze
authors.forename: Christine
authors.initials: C
authors.lastname: Chresta
authors.forename: Kevin
authors.initials: K
authors.lastname: Embrey
authors.forename: Gary
authors.initials: G
authors.lastname: Fairley
authors.forename: Paul
authors.initials: P
authors.lastname: Faulder
authors.forename: M Raymond V
authors.initials: MR
authors.lastname: Finlay
authors.forename: Jason G
authors.initials: JG
authors.lastname: Kettle
authors.forename: Thorsten
authors.initials: T
authors.lastname: Nowak
authors.forename: Ross
authors.initials: R
authors.lastname: Overman
authors.forename: S Joe
authors.initials: SJ
authors.lastname: Patel
authors.forename: Paula
authors.initials: P
authors.lastname: Perkins
authors.forename: Loredana
authors.initials: L
authors.lastname: Spadola
authors.forename: Jonathan
authors.initials: J
authors.lastname: Tart
authors.forename: Julie A
authors.initials: JA
authors.lastname: Tucker
authors.forename: Gail
authors.initials: G
authors.lastname: Wrigley
mesh_terms: D001665:Binding Sites; D018360:Crystallography, X-Ray; D006801:Humans; D008958:Models, Molecular; D015394:Molecular Structure; D009154:Mutation / Q000235:genetics; D011485:Protein Binding / Q000187:drug effects; D011487:Protein Conformation; D016283:Proto-Oncogene Proteins p21(ras) / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D020837:SOS1 Protein / Q000737:chemistry / Q000378:metabolism*; D054852:Small Molecule Libraries / Q000737:chemistry / Q000494:pharmacology*
chemical_list: D020837:SOS1 Protein; D054852:Small Molecule Libraries; D016283:Proto-Oncogene Proteins p21(ras)