title: Approach for targeting Ras with small molecules that activate SOS-mediated nucleotide exchange.
abstract: Aberrant activation of the small GTPase Ras by oncogenic mutation or constitutively active upstream receptor tyrosine kinases results in the deregulation of cellular signals governing growth and survival in ∼30% of all human cancers. However, the discovery of potent inhibitors of Ras has been difficult to achieve. Here, we report the identification of small molecules that bind to a unique pocket on the Ras:Son of Sevenless (SOS):Ras complex, increase the rate of SOS-catalyzed nucleotide exchange in vitro, and modulate Ras signaling pathways in cells. X-ray crystallography of Ras:SOS:Ras in complex with these molecules reveals that the compounds bind in a hydrophobic pocket in the CDC25 domain of SOS adjacent to the Switch II region of Ras. The structure-activity relationships exhibited by these compounds can be rationalized on the basis of multiple X-ray cocrystal structures. Mutational analyses confirmed the functional relevance of this binding site and showed it to be essential for compound activity. These molecules increase Ras-GTP levels and disrupt MAPK and PI3K signaling in cells at low micromolar concentrations. These small molecules represent tools to study the acute activation of Ras and highlight a pocket on SOS that may be exploited to modulate Ras signaling.
authors.affiliation: Departments of Biochemistry, Pharmacology, and Chemistry, Vanderbilt University School of Medicine, Nashville, TN 37232.
authors.forename: Michael C
authors.initials: MC
authors.lastname: Burns
authors.forename: Qi
authors.initials: Q
authors.lastname: Sun
authors.forename: R Nathan
authors.initials: RN
authors.lastname: Daniels
authors.forename: DeMarco
authors.initials: D
authors.lastname: Camper
authors.forename: J Phillip
authors.initials: JP
authors.lastname: Kennedy
authors.forename: Jason
authors.initials: J
authors.lastname: Phan
authors.forename: Edward T
authors.initials: ET
authors.lastname: Olejniczak
authors.forename: Taekyu
authors.initials: T
authors.lastname: Lee
authors.forename: Alex G
authors.initials: AG
authors.lastname: Waterson
authors.forename: Olivia W
authors.initials: OW
authors.lastname: Rossanese
authors.forename: Stephen W
authors.initials: SW
authors.lastname: Fesik
mesh_terms: D002853:Chromatography, Liquid; D002855:Chromatography, Thin Layer; D018360:Crystallography, X-Ray; D005454:Fluorescence Polarization; D006367:HeLa Cells; D006801:Humans; D007211:Indoles / Q000378:metabolism*; D008024:Ligands; D009682:Magnetic Resonance Spectroscopy; D013058:Mass Spectrometry; D008958:Models, Molecular; D015394:Molecular Structure; D046912:Multiprotein Complexes / Q000737:chemistry / Q000378:metabolism*; D010880:Piperidines / Q000378:metabolism*; D011487:Protein Conformation; D016283:Proto-Oncogene Proteins p21(ras) / Q000037:antagonists & inhibitors* / Q000737:chemistry; D020837:SOS1 Protein / Q000737:chemistry / Q000378:metabolism*
chemical_list: D007211:Indoles; D008024:Ligands; D046912:Multiprotein Complexes; D010880:Piperidines; D020837:SOS1 Protein; D016283:Proto-Oncogene Proteins p21(ras)