RAF inhibitors transactivate RAF dimers and ERK signaling in cells with wild-type BRAF

Program in Molecular Pharmacology and Chemistry and Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York 10065, USA.
Nature (Impact Factor: 41.46). 02/2010; 464(7287):427-30. DOI: 10.1038/nature08902
Source: PubMed

ABSTRACT Tumours with mutant BRAF are dependent on the RAF-MEK-ERK signalling pathway for their growth. We found that ATP-competitive RAF inhibitors inhibit ERK signalling in cells with mutant BRAF, but unexpectedly enhance signalling in cells with wild-type BRAF. Here we demonstrate the mechanistic basis for these findings. We used chemical genetic methods to show that drug-mediated transactivation of RAF dimers is responsible for paradoxical activation of the enzyme by inhibitors. Induction of ERK signalling requires direct binding of the drug to the ATP-binding site of one kinase of the dimer and is dependent on RAS activity. Drug binding to one member of RAF homodimers (CRAF-CRAF) or heterodimers (CRAF-BRAF) inhibits one protomer, but results in transactivation of the drug-free protomer. In BRAF(V600E) tumours, RAS is not activated, thus transactivation is minimal and ERK signalling is inhibited in cells exposed to RAF inhibitors. These results indicate that RAF inhibitors will be effective in tumours in which BRAF is mutated. Furthermore, because RAF inhibitors do not inhibit ERK signalling in other cells, the model predicts that they would have a higher therapeutic index and greater antitumour activity than mitogen-activated protein kinase (MEK) inhibitors, but could also cause toxicity due to MEK/ERK activation. These predictions have been borne out in a recent clinical trial of the RAF inhibitor PLX4032 (refs 4, 5). The model indicates that promotion of RAF dimerization by elevation of wild-type RAF expression or RAS activity could lead to drug resistance in mutant BRAF tumours. In agreement with this prediction, RAF inhibitors do not inhibit ERK signalling in cells that coexpress BRAF(V600E) and mutant RAS.

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Available from: Poulikos I. Poulikakos, Sep 25, 2015
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    • "Moreover, the use of BRAF inhibitors comes with many troubling side effects, including development of keratoaconthomas and invasive squamous cell carcinoma [52] [55]. These proliferations occur in BRAF wild-type cells with mutated RAS and are due to up-regulation of BRAF-CRAF leading to ERK1/2 hyperactivation [32] [63]. This paradoxical ERK1/2 hyperactivation has been shown to lead to the development of RAS-driven squamous cell carcinomas and keratoaconthomas while patients are on vemurafenib and other BRAF inhibitors and, as mentioned above, is thought to be responsible for the inefficacy of BRAF inhibitors in NRAS mutant melanoma [64]. "
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    ABSTRACT: Melanoma is the least common form of skin cancer, but it is responsible for the majority of skin cancer deaths. Traditional therapeutics and immunomodulatory agents have not shown much efficacy against metastatic melanoma. Agents that target the RAS/RAF/MEK/ERK (MAPK) signaling pathway-the BRAF inhibitors vemurafenib and dabrafenib, and the MEK1/2 inhibitor trametinib-have increased survival in patients with metastatic melanoma. Further, the combination of dabrafenib and trametinib has been shown to be superior to single agent therapy for the treatment of metastatic melanoma. However, resistance to these agents develops rapidly. Studies of additional agents and combinations targeting the MAPK, PI3K/AKT/mTOR (PI3K), c-kit, and other signaling pathways are currently underway. Furthermore, studies of phytochemicals have yielded promising results against proliferation, survival, invasion, and metastasis by targeting signaling pathways with established roles in melanomagenesis. The relatively low toxicities of phytochemicals make their adjuvant use an attractive treatment option. The need for improved efficacy of current melanoma treatments calls for further investigation of each of these strategies. In this review, we will discuss synthetic small molecule inhibitors, combined therapies and current progress in the development of phytochemical therapies. Copyright © 2015. Published by Elsevier Ireland Ltd.
    Cancer Letters 01/2015; 359(1). DOI:10.1016/j.canlet.2015.01.016 · 5.62 Impact Factor
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    • "Modèle in vitro, modèle in vivo, tumeurs humaines 16—20 Augmentation de l'expression RAF de type sauvage Modèle in vitro [21] Hyperexpression de la protéine agoniste COT Modèle in vitro, tumeurs humaines [23] Surexpression des récepteurs membranaires PDGFR-␤ et IGF-1R "
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    ABSTRACT: In patients with melanoma positive for the BRAF V600 mutation, clinical response to specific BRAF inhibitors is usually rapid and striking, with significant benefits in terms of progression-free survival and overall survival. However, resistance to treatment almost invariably arises, typically within a median timeframe of 6 months. Indeed, very few patients exhibit long-lasting response to these targeted therapies. It is essential to better understand the mechanisms of resistance to targeted anti-BRAF therapies in order to increase both response rates and the duration of clinical response to treatment. This literature review describes the signaling pathways involving BRAF and presents recent data from clinical trials with these molecules. Furthermore, we aim to describe the main resistance mechanisms linked with targeted anti-BRAF therapies. The keywords (resistance, BRAF, melanoma, targeted therapy, vemurafenib, and dabrafenib) were used to extract relevant articles in the Medline/Pubmed database published before 31 January 2014. Improved knowledge and understanding of the mechanisms of resistance to targeted anti-BRAF therapies should enable the development of new therapeutic strategies in order to overcome such resistance and allow more significant and sustained response rates to be achieved among melanoma patients. Copyright © 2014 Elsevier Masson SAS. All rights reserved.
    Annales de Dermatologie et de Vénéréologie 11/2014; 141(11):671-81. DOI:10.1016/j.annder.2014.06.021 · 0.92 Impact Factor
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    • "However, due to the fact that in BRAF (and NRAS) wild-type melanoma five times more mutations are observed (or needed) it may be speculated that the relative specificity of BRAF/NRAS mutations for the disease is quite high.9 Most of the mutations of BRAF are found in exon 15, at codon 600 (V600).10 In about 75% of the mutations in that area valine is substituted by glutamic acid (V600E). "
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    ABSTRACT: Whereas thin melanomas have an excellent prognosis after sufficient surgical treatment, melanoma disease in advanced stages is still a therapeutic challenge. After decades of frustrating studies, new therapeutic strategies have come up in the past few years. On the one hand, increasing insights into the molecular aberrations in melanoma have led to specific "targeted" therapies to affect only the mutated tumor cells, as in many other types of cancers. Today there are few "targeted" substances which are already approved and successfully used for single or combination therapy, but many others are under development. While on the other hand, nonpersonalized strategy substances have been developed successfully inducing an immunologic tumor response. Both kinds of therapy have been found to result in an improvement not only of the response rate, but also of the overall survival in metastatic disease, which represents a milestone in melanoma therapy. However, using these therapies there is still much to learn regarding the effects, the side effects, and the limitations of these promising substances.
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