Heidorn SJ, Milagre C, Whittaker S et al.Kinase-dead BRAF and oncogenic RAS cooperate to drive tumor progression through CRAF. Cell 140:209-221

The Institute of Cancer Research, Signal Transduction Team, Section of Cell and Molecular Biology, 237 Fulham Road, London SW3 6JB, UK.
Cell (Impact Factor: 32.24). 01/2010; 140(2):209-21. DOI: 10.1016/j.cell.2009.12.040
Source: PubMed


We describe a mechanism of tumorigenesis mediated by kinase-dead BRAF in the presence of oncogenic RAS. We show that drugs that selectively inhibit BRAF drive RAS-dependent BRAF binding to CRAF, CRAF activation, and MEK–ERK signaling. This does not occur when oncogenic BRAF is inhibited, demonstrating that BRAF inhibition per se does not drive pathway activation; it only occurs when BRAF is inhibited in the presence of oncogenic RAS. Kinase-dead BRAF mimics the effects of the BRAF-selective drugs and kinase-dead Braf and oncogenic Ras cooperate to induce melanoma in mice. Our data reveal another paradigm of BRAF-mediated signaling that promotes tumor progression. They highlight the importance of understanding pathway signaling in clinical practice and of genotyping tumors prior to administering BRAF-selective drugs, to identify patients who are likely to respond and also to identify patients who may experience adverse effects.


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    • "Crystal structures of BRAF in complex with vemurafenib and its analog PLX4720 revealed an asymmetric dimer in which only one of the two ATP sites was effectively occupied by the drug (Bollag et al., 2010, 2012; Tsai et al., 2008). By binding to one RAF subunit and promoting dimer formation, the BRAF selective inhibitors activate the second drug-free partner, by either altering subcellular localization or propagating a conformational change to the drug-free protomer (Heidorn et al., 2010; Poulikakos et al., 2010). Based on the outlined model, we hypothesized that in order to block paradoxical activation, a RAF inhibitor must effectively inhibit not only all RAF isoforms, but also the active RAF homo-and hetero-dimers. "
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    ABSTRACT: LY3009120 is a pan-RAF and RAF dimer inhibitor that inhibits all RAF isoforms and occupies both protomers in RAF dimers. Biochemical and cellular analyses revealed that LY3009120 inhibits ARAF, BRAF, and CRAF isoforms with similar affinity, while vemurafenib or dabrafenib have little or modest CRAF activity compared to their BRAF activities. LY3009120 induces BRAF-CRAF dimerization but inhibits the phosphorylation of downstream MEK and ERK, suggesting that it effectively inhibits the kinase activity of BRAF-CRAF heterodimers. Further analyses demonstrated that LY3009120 also inhibits various forms of RAF dimers including BRAF or CRAF homodimers. Due to these unique properties, LY3009120 demonstrates minimal paradoxical activation, inhibits MEK1/2 phosphorylation, and exhibits anti-tumor activities across multiple models carrying KRAS, NRAS, or BRAF mutation.
    Cancer cell 09/2015; 28(3). DOI:10.1016/j.ccell.2015.08.002 · 23.52 Impact Factor
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    • "In contrast, BGB659, a type II, ATPcompetitive RAF inhibitor (compound 27 from Gould et al., 2011), inhibited ERK signaling driven by p61 BRAF V600E dimers and BRAF V600E monomers at similar doses (Figures 4B and S4D). Its inhibition of ERK signaling is mediated by its binding to BRAF; the T529 BRAF gatekeeper mutation (Heidorn et al., 2010) confers resistance to the drug (Figure S4E). In cells that express either BRAF V600E T529N or p61 BRAF V600E T529N, ERK signaling is resistant to both vemurafenib and BGB659 but not to the MEK inhibitor trametinib. "
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    ABSTRACT: ERK signaling requires RAS-induced RAF dimerization and is limited by feedback. Activated BRAF mutants evade feedback inhibition of RAS by either of two mechanisms. BRAF V600 mutants are activated monomers when RAS activity is low; all other activating BRAF mutants function as constitutive RAS-independent dimers. RAF inhibitors effectively inhibit mutant monomers, but not dimers; their binding to one site in the dimer significantly reduces their affinity for the second. Tumors with non-V600E BRAF mutants are insensitive to these drugs, and increased expression of BRAF V600E dimers causes acquired resistance. A compound that equally inhibits both sites of mutant RAF dimers inhibits tumors driven by either class of mutants or those BRAF V600E tumors with dimer-dependent acquired resistance to monomer-specific inhibitors.
    Cancer cell 09/2015; 28(3). DOI:10.1016/j.ccell.2015.08.001 · 23.52 Impact Factor
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    • "Interestingly , vemurafenib can paradoxically activate the MAPK pathway via heterodimerization of BRAF and CRAF kinases to promote growth in tumors harboring wild-type BRAF or activating RAS mutations. Therefore, vemurafenib monotherapy should not be used in patients with advanced melanoma with wildtype BRAF or RAS mutation (Heidorn et al., 2010; Poulikakos, Zhang, Bollag, & Shokat, 2010; Hatzivassiliou et al., 2010). "
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    ABSTRACT: Somatic point mutations in the BRAF gene have been found in approximately 50% of melanomas. BRAF (V600E), the most common mutation, results in the constitutive activation of BRAF (V600E) kinase, sustaining MAPK signaling and perpetuating cell growth. This groundbreaking discovery led to the clinical development of vemurafenib, a selective BRAF inhibitor. Vemurafenib has been approved for the treatment of patients with BRAF (V600E)-positive unresectable or metastatic melanoma based on survival benefit demonstrated in a randomized phase III study. The current approved dosing schedule of vemurafenib is 960 mg orally twice a day until disease progression or unacceptable toxicity. Vemurafenib is well tolerated, with the most common adverse effects including skin reactions, photosensitivity, headache, and arthralgia. Active research is ongoing to expand the utility of vemurafenib into the adjuvant setting and to circumvent rapid emergence of drug resistance.
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