title: Using cells devoid of RAS proteins as tools for drug discovery.
abstract: Mutational activation of RAS proteins occurs in nearly 30% of all human tumors. To date direct pharmacological inhibition of RAS oncoproteins has not been possible. As a consequence, current strategies are focusing on the development of inhibitors that target those kinases acting downstream of RAS proteins, including those of the RAF/MEK/ERK and PI3K/AKT pathways. Most of these inhibitors have undesired off-target effects that mask the potential therapeutic effect of blocking their targeted kinases. To facilitate the screening of selective inhibitors, we have generated lines of mouse embryonic fibroblasts that lack endogenous Ras proteins. These cells proliferate due to ectopic expression of either Ras oncoproteins that selectively activate the Raf/Mek/Erk pathway such as H-Ras(G12V/D38E) or constitutively active kinases such as B-Raf and Mek1. These cell lines were exposed to inhibitors against the RAF, MEK, and AKT kinases as well as inhibitors of other kinases known to crosstalk with RAS signaling such as JNK and p38. Amongst all compounds tested, only the MEK inhibitors U0126 and PD0325901, showed the expected specificity pattern. Yet, PD0325901, but not U0126, was able to inhibit a cell line lacking Ras proteins that owed its proliferative properties to loss of p53. Thus, suggesting unexpected off-target activities for this compound. The use of cell lines whose proliferative properties exclusively depend on selective targets provide a novel strategy to analyze the specificity of selective inhibitors designed against molecular targets implicated in human cancer.
authors.affiliation: Molecular Oncology Programme, Centro Nacional de Investigaciones Oncológicas (CNIO), Madrid, Spain.
authors.forename: Jelena
authors.initials: J
authors.lastname: Urosevic
authors.forename: Eleanor Y M
authors.initials: EY
authors.lastname: Sum
authors.forename: Victoria
authors.initials: V
authors.lastname: Moneo
authors.forename: Matthias
authors.initials: M
authors.lastname: Drosten
authors.forename: Alma
authors.initials: A
authors.lastname: Dhawahir
authors.forename: Mercedes
authors.initials: M
authors.lastname: Becerra
authors.forename: Amancio
authors.initials: A
authors.lastname: Carnero
authors.forename: Mariano
authors.initials: M
authors.lastname: Barbacid
mesh_terms: D000818:Animals; D001483:Base Sequence; D015153:Blotting, Western; D002460:Cell Line; D049109:Cell Proliferation; D017931:DNA Primers; D055808:Drug Discovery; D006801:Humans; D020935:MAP Kinase Signaling System; D051379:Mice; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D020133:Reverse Transcriptase Polymerase Chain Reaction; D018631:ras Proteins / Q000235:genetics*
chemical_list: D017931:DNA Primers; D047428:Protein Kinase Inhibitors; D018631:ras Proteins