In BRAF(V600)-mutant tumours, most mechanisms of resistance to drugs that target the BRAF and/or MEK kinases rely on reactivation of the RAS–RAF–MEK–ERK mitogen-activated protein kinase (MAPK) signal transduction pathway, on activation of the alternative, PI(3)K–AKT–mTOR, pathway (which is ERK independent) or on modulation of the caspase-dependent apoptotic cascade1,2,3. All three pathways converge to regulate the formation of the eIF4F eukaryotic translation initiation complex, which binds to the 7-methylguanylate cap (m7G) at the 5′ end of messenger RNA, thereby modulating the translation of specific mRNAs4,5. Here we show that the persistent formation of the eIF4F complex, comprising the eIF4E cap-binding protein, the eIF4G scaffolding protein and the eIF4A RNA helicase, is associated with resistance to anti-BRAF, anti-MEK and anti-BRAF plus anti-MEK drug combinations in BRAF(V600)-mutant melanoma, colon and thyroid cancer cell lines. Resistance to treatment and maintenance of eIF4F complex formation is associated with one of three mechanisms: reactivation of MAPK signalling, persistent ERK-independent phosphorylation of the inhibitory eIF4E-binding protein 4EBP1 or increased pro-apoptotic BCL-2-modifying factor (BMF)-dependent degradation of eIF4G. The development of an in situ method to detect the eIF4E–eIF4G interactions shows that eIF4F complex formation is decreased in tumours that respond to anti-BRAF therapy and increased in resistant metastases compared to tumours before treatment. Strikingly, inhibiting the eIF4F complex, either by blocking the eIF4E–eIF4G interaction or by targeting eIF4A, synergizes with inhibiting BRAF(V600) to kill the cancer cells. eIF4F not only appears to be an indicator of both innate and acquired resistance but also is a promising therapeutic target. Combinations of drugs targeting BRAF (and/or MEK) and eIF4F may overcome most of the resistance mechanisms arising in BRAF(V600)-mutant cancers.
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Microarray data have been deposited in the ArrayExpress database under accession number E-MTAB-2607.
The authors thank J. Tanaka for providing hippuristanol. We thank the following Gustave Roussy platforms: Imaging and Cytometry Platform IRCIV (S. Salome-Desmoulez), Module de Développement en Pathologie, SIRIC SOCRATE (J. Adam), Translational Research Laboratory and Biobank (M. Breckler and L. Lacroix), Plateforme d’évaluation Préclinique (P. Gonin and K. Ser-le Roux), Genomic Core Facility (N. Pata-Merci) and Bioinformatic Core Facility (G. Meurice). We also thank V. Camara-Clayette for help with 35S experiments, S. Roy for patient data collection and L. Saint Ange for text editing. C.R. and S.V.’s team was supported by Institut National du CAncer (INCA), Association pour la Recherche sur le Cancer (ARC) and Ligue contre le Cancer via an Integrated Research Action Program Melanoma (PAIR Melanome), Cancéropôle Ile de France and Ensemble Contre le Mélanome. L.D. was supported by the Association pour la Recherche sur le Cancer (ARC). We also thank the ARC and AAREC Filia Research for fellowships to N.R. and C.B. O.H. was supported by the Wenner-Gren Foundation and the Swedish Society of Medicine.
Extended data figures
Determination of half-maximum inhibitory concentration (IC50) for the indicated compounds and mutational screening in each of the melanoma cell lines used in this study.
List of genes encoding mRNAs that are translationnally regulated by vemurafenib.
Lists of genes transcriptionally regulated by vemurafenib with a >2 fold change (FC) in either A375 (tab 1) or Mel624 (tab 2).
Patient profile table.
Mutational screening in the tumours of the 7 patients.
List of ON-TARGETplus siRNA sequences provided from ThermoScientific used in Extended Data Fig. 8.
Oligonucleotides used for qPCR experiments.
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