title: Identification of the MEK1(F129L) activating mutation as a potential mechanism of acquired resistance to MEK inhibition in human cancers carrying the B-RafV600E mutation.
abstract: Although targeting the Ras/Raf/MEK pathway remains a promising anticancer strategy, mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase (MEK) inhibitors in clinical development are likely to be limited in their ability to produce durable clinical responses due to the emergence of acquired drug resistance. To identify potential mechanisms of such resistance, we established MEK inhibitor-resistant clones of human HT-29 colon cancer cells (HT-29R cells) that harbor the B-RafV600E mutation. HT-29R cells were specifically resistant to MEK inhibition in vitro and in vivo, with drug-induced elevation of MEK/ERK and their downstream targets primarily accountable for drug resistance. We identified MEK1(F129L) mutation as a molecular mechanism responsible for MEK/ERK pathway activation. In an isogenic cell system that extended these findings into other cancer cell lines, the MEK1(F129L) mutant exhibited higher intrinsic kinase activity than wild-type MEK1 [MEK1(WT)], leading to potent activation of ERK and downstream targets. The MEK1(F129L) mutation also strengthened binding to c-Raf, suggesting an underlying mechanism of higher intrinsic kinase activity. Notably, the combined use of Raf and MEK inhibitors overcame the observed drug resistance and exhibited greater synergy in HT-29R cells than the drug-sensitive HT-29 parental cells. Overall, our findings suggested that mutations in MEK1 can lead to acquired resistance in patients treated with MEK inhibitors and that a combined inhibition of Raf and MEK may be potentially useful as a strategy to bypass or prevent drug resistance in the clinic.
authors.affiliation: Discovery Oncology, Hoffmann-La Roche Inc., Nutley, New Jersey 07110, USA.
authors.forename: Huisheng
authors.initials: H
authors.lastname: Wang
authors.forename: Sherif
authors.initials: S
authors.lastname: Daouti
authors.forename: Wen-Hui
authors.initials: WH
authors.lastname: Li
authors.forename: Yang
authors.initials: Y
authors.lastname: Wen
authors.forename: Christine
authors.initials: C
authors.lastname: Rizzo
authors.forename: Brian
authors.initials: B
authors.lastname: Higgins
authors.forename: Kathryn
authors.initials: K
authors.lastname: Packman
authors.forename: Neal
authors.initials: N
authors.lastname: Rosen
authors.forename: John F
authors.initials: JF
authors.lastname: Boylan
authors.forename: David
authors.initials: D
authors.lastname: Heimbrook
authors.forename: Huifeng
authors.initials: H
authors.lastname: Niu
mesh_terms: D001483:Base Sequence; D017931:DNA Primers; D019073:HT29 Cells; D006801:Humans; D020128:Inhibitory Concentration 50; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000235:genetics*; D009154:Mutation; D009369:Neoplasms / Q000201:enzymology / Q000235:genetics*; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics*; D023041:Xenograft Model Antitumor Assays
chemical_list: D017931:DNA Primers; D047428:Protein Kinase Inhibitors; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D048369:MAP Kinase Kinase 1; C482125:MAP2K1 protein, human