title: BRAF V600E disrupts AZD6244-induced abrogation of negative feedback pathways between extracellular signal-regulated kinase and Raf proteins.
abstract: AZD6244 (ARRY 142886) is a potent and selective mitogen-activated protein kinase (MAPK)/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitor currently in early clinical trials. We examined the activity of AZD6244 in a panel of non-small cell lung cancer and a panel of cell lines representing many cancer types using in vitro growth assays. AZD6244 induced G(0)-G(1) cell cycle arrest in sensitive cell lines that primarily included cells containing the BRAF V600E mutation. In these cells, G(0)-G(1) arrest is accompanied by the up-regulation of the cell cycle inhibitors p21(WAF1) and p27(Kip1) and down-regulation of cyclin D1. In the majority of cell lines tested, including those with K-ras or non-V600E BRAF mutations, AZD6244 induced the accumulation of phospho-MEK, an effect not observed in the most sensitive BRAF V600E-containing cells. Accumulation of phospho-MEK in non-V600E-containing cell lines is due to abrogation of negative feedback pathways. BRAF V600E disrupts negative feedback signaling, which results in enhanced baseline phospho-MEK expression. Exogenous expression of BRAF V600E disrupts feedback inhibition but does not sensitize cells to AZD6244. Specific suppression of endogenous BRAF V600E does not confer resistance to AZD6244 but enhances sensitivity to AZD6244. Thus, our findings show that BRAF V600E marks cells with an in vitro requirement for MAPK signaling to support proliferation. These cells are exquisitely sensitive to AZD6244 (IC(50), <100 nmol/L), have high baseline levels of phospho-MEK, and lack feedback inhibition between ERK and Raf. These data suggest an approach to identifying cells that may be sensitive to AZD6244 and other MEK inhibitors.
authors.affiliation: Department of Oncology, Mayo Clinic, Rochester, Minnesota, USA.
authors.forename: Bret B
authors.initials: BB
authors.lastname: Friday
authors.forename: Chunrong
authors.initials: C
authors.lastname: Yu
authors.forename: Grace K
authors.initials: GK
authors.lastname: Dy
authors.forename: Paul D
authors.initials: PD
authors.lastname: Smith
authors.forename: Liang
authors.initials: L
authors.lastname: Wang
authors.forename: Stephen N
authors.initials: SN
authors.lastname: Thibodeau
authors.forename: Alex A
authors.initials: AA
authors.lastname: Adjei
mesh_terms: D001483:Base Sequence; D001562:Benzimidazoles / Q000494:pharmacology*; D045744:Cell Line, Tumor; D050759:Cyclin-Dependent Kinase Inhibitor p21 / Q000378:metabolism; D050760:Cyclin-Dependent Kinase Inhibitor p27; D017931:DNA Primers; D015536:Down-Regulation; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism*; D006801:Humans; D047908:Intracellular Signaling Peptides and Proteins / Q000378:metabolism; D009154:Mutation; D016133:Polymerase Chain Reaction; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics / Q000502:physiology*; D048490:raf Kinases / Q000378:metabolism*
chemical_list: C517975:AZD 6244; D001562:Benzimidazoles; C493956:CDKN1A protein, human; C436291:CDKN1B protein, human; D050759:Cyclin-Dependent Kinase Inhibitor p21; D017931:DNA Primers; D047908:Intracellular Signaling Peptides and Proteins; D050760:Cyclin-Dependent Kinase Inhibitor p27; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D048490:raf Kinases; D048049:Extracellular Signal-Regulated MAP Kinases