Development of a Nucleotide Exchange Inhibitor That Impairs Ras Oncogenic Signaling

Despite more than three decades of intense effort, no anti-Ras therapies have reached clinical application. Contributing to this failure has been an underestimation of Ras complexity and a dearth of structural information. In this regard, recent studies have revealed the highly dynamic character of the Ras surface and the existence of transient pockets suitable for small-molecule binding, opening up new possibilities for the development of Ras modulators. Herein, a novel Ras inhibitor (compound 12) is described that selectively impairs mutated Ras activity in a reversible manner without significantly affecting wild-type Ras, reduces the Ras–guanosine triphosphate (GTP) levels, inhibits the activation of the mitogen-activated protein kinase (MAPK) pathway, and exhibits remarkable cytotoxic activity in Ras-driven cellular models. The use of molecular dynamics simulations and NMR spectroscopy experiments has enabled the molecular bases responsible for the interactions between compound 12 and Ras protein to be explored. The new Ras inhibitor binds partially to the GTP-binding region and extends into the adjacent hydrophobic pocket delimited by switch II. Hence, Ras inhibitor 12 could represent a new compound for the development of more efficacious drugs to target Ras-driven cancers; a currently unmet clinical need.This work was supported by ExonHit Therapeutics and bygrants from the Spanish Ministerio de EconomíaayCompetitividad (MINECO, SAF2013-48271-R, SAF2014-59716-R, and SAF2016-78792-R) and Comunidad de Madrid (S2010/BMD-2353). We thank the Campus de Excelencia CEI Moncloa fora predoctora lfellowship to N.I.M.-R.,the UCM’sCAI Cytometryand Fluorescence Microscopy for their assistance, and the com-puter resources provided by the Barcelona Supercomputing Center-Centro Nacional de Supercomputació