RAF inhibitor resistance is mediated by dimerization of aberrantly spliced BRAF(V600E)
Poulikos I Poulikakos, Yogindra Persaud, Manickam Janakiraman, Xiangju Kong, Charles Ng, Gatien Moriceau, Hubing Shi, Mohammad Atefi, Bjoern Titz, May Tal Gabay, Maayan Salton, Kimberly B Dahlman, Madhavi Tadi, Jennifer A Wargo, Keith T Flaherty, Mark C Kelley, Tom Misteli, Paul B Chapman, Jeffrey A Sosman, Thomas G Graeber, Antoni Ribas, Roger S Lo, Neal Rosen, David B Solit, Poulikos I Poulikakos, Yogindra Persaud, Manickam Janakiraman, Xiangju Kong, Charles Ng, Gatien Moriceau, Hubing Shi, Mohammad Atefi, Bjoern Titz, May Tal Gabay, Maayan Salton, Kimberly B Dahlman, Madhavi Tadi, Jennifer A Wargo, Keith T Flaherty, Mark C Kelley, Tom Misteli, Paul B Chapman, Jeffrey A Sosman, Thomas G Graeber, Antoni Ribas, Roger S Lo, Neal Rosen, David B Solit
Abstract
Activated RAS promotes dimerization of members of the RAF kinase family. ATP-competitive RAF inhibitors activate ERK signalling by transactivating RAF dimers. In melanomas with mutant BRAF(V600E), levels of RAS activation are low and these drugs bind to BRAF(V600E) monomers and inhibit their activity. This tumour-specific inhibition of ERK signalling results in a broad therapeutic index and RAF inhibitors have remarkable clinical activity in patients with melanomas that harbour mutant BRAF(V600E). However, resistance invariably develops. Here, we identify a new resistance mechanism. We find that a subset of cells resistant to vemurafenib (PLX4032, RG7204) express a 61-kDa variant form of BRAF(V600E), p61BRAF(V600E), which lacks exons 4-8, a region that encompasses the RAS-binding domain. p61BRAF(V600E) shows enhanced dimerization in cells with low levels of RAS activation, as compared to full-length BRAF(V600E). In cells in which p61BRAF(V600E) is expressed endogenously or ectopically, ERK signalling is resistant to the RAF inhibitor. Moreover, a mutation that abolishes the dimerization of p61BRAF(V600E) restores its sensitivity to vemurafenib. Finally, we identified BRAF(V600E) splicing variants lacking the RAS-binding domain in the tumours of six of nineteen patients with acquired resistance to vemurafenib. These data support the model that inhibition of ERK signalling by RAF inhibitors is dependent on levels of RAS-GTP too low to support RAF dimerization and identify a novel mechanism of acquired resistance in patients: expression of splicing isoforms of BRAF(V600E) that dimerize in a RAS-independent manner.
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References
- Weber CK, Slupsky JR, Kalmes HA, Rapp UR. Active Ras induces heterodimerization of cRaf and BRaf. Cancer Res. 2001;61:3595–3598.
- Rushworth LK, Hindley AD, O’Neill E, Kolch W. Regulation and role of Raf-1/B-Raf heterodimerization. Mol Cell Biol. 2006;26:2262–2272. doi:26/6/2262 [pii] 10.1128/MCB.26.6.2262-2272.2006.
- Wellbrock C, Karasarides M, Marais R. The RAF proteins take centre stage. Nat Rev Mol Cell Biol. 2004;5:875–885. doi:nrm1498 [pii] 10.1038/nrm1498.
- Poulikakos PI, Zhang C, Bollag G, Shokat KM, Rosen N. RAF inhibitors transactivate RAF dimers and ERK signalling in cells with wild-type BRAF. Nature. 2010;464:427–430. doi:10.1038/nature08902.
- Heidorn SJ, et al. Kinase-dead BRAF and oncogenic RAS cooperate to drive tumor progression through CRAF. Cell. 2010;140:209–221. doi:S0092-8674(09)01626-2 [pii] 10.1016/j.cell.2009.12.040.
- Hatzivassiliou G, et al. RAF inhibitors prime wild-type RAF to activate the MAPK pathway and enhance growth. Nature. 2010;464:431–435. doi:nature08833 [pii] 10.1038/nature08833.
- Joseph EW, et al. The RAF inhibitor PLX4032 inhibits ERK signaling and tumor cell proliferation in a V600E BRAF-selective manner. Proc Natl Acad Sci U S A. 2010;107:14903–14908. doi:1008990107 [pii] 10.1073/pnas.1008990107.
- Flaherty KT, et al. Inhibition of mutated, activated BRAF in metastatic melanoma. N Engl J Med. 2010;363:809–819. doi:10.1056/NEJMoa1002011.
- Solit DB, et al. BRAF mutation predicts sensitivity to MEK inhibition. Nature. 2006;439:358–362. doi:nature04304 [pii] 10.1038/nature04304.
- Whittaker S, et al. Gatekeeper mutations mediate resistance to BRAF-targeted therapies. Sci Transl Med. 2010;2:35ra41. doi:2/35/35ra41 [pii] 10.1126/scitranslmed.3000758.
- Cutler RE, Jr., Stephens RM, Saracino MR, Morrison DK. Autoregulation of the Raf-1 serine/threonine kinase. Proc Natl Acad Sci U S A. 1998;95:9214–9219.
- Rajakulendran T, Sahmi M, Lefrancois M, Sicheri F, Therrien M. A dimerization- dependent mechanism drives RAF catalytic activation. Nature. 2009;461:542–545. doi:nature08314 [pii] 10.1038/nature08314.
- Poulikakos PI, Rosen N. Mutant BRAF melanomas--dependence and resistance. Cancer Cell. 2011;19:11–15. doi:10.1016/j.ccr.2011.01.008.
- McArthur G, et al. Molecular analyses from a phase I trial of vemurafenib to study mechanism of action (MOA) and resistance in repeated biopsies from BRAF mutation-positive metastatic melanoma patients (pts) J Clin Oncol. 2011;29(suppl) abstr 8502.
- Nazarian R, et al. Melanomas acquire resistance to B-RAF(V600E) inhibition by RTK or N-RAS upregulation. Nature. 2010;468:973–977. doi:10.1038/nature09626.
- Johannessen CM, et al. COT drives resistance to RAF inhibition through MAP kinase pathway reactivation. Nature. 2010;468:968–972. doi:10.1038/nature09627.
- Villanueva J, et al. Acquired resistance to BRAF inhibitors mediated by a RAF kinase switch in melanoma can be overcome by cotargeting MEK and IGF-1R/PI3K. Cancer Cell. 2010;18:683–695. doi:S1535-6108(10)00484-8 [pii] 10.1016/j.ccr.2010.11.023.
- Wagle N, et al. Dissecting therapeutic resistance to RAF inhibition in melanoma by tumor genomic profiling. J Clin Oncol. 2011;29:3085–3096. doi:10.1200/JCO.2010.33.2312.
- Luco RF, Allo M, Schor IE, Kornblihtt AR, Misteli T. Epigenetics in alternative pre- mRNA splicing. Cell. 2011;144:16–26. doi:S0092-8674(10)01378-4 [pii] 10.1016/j.cell.2010.11.056.
- Bollag G, et al. Clinical efficacy of a RAF inhibitor needs broad target blockade in BRAF-mutant melanoma. Nature. 2010;467:596–599. doi:nature09454 [pii] 10.1038/nature09454.
- Janakiraman M, et al. Genomic and biological characterization of exon 4 KRAS mutations in human cancer. Cancer Res. 2010;70:5901–5911. doi:0008-5472.CAN-10-0192 [pii] 10.1158/0008-5472.CAN-10-0192.
- Nusse M, Beisker W, Hoffmann C, Tarnok A. Flow cytometric analysis of G1- and G2/M- phase subpopulations in mammalian cell nuclei using side scatter and DNA content measurements. Cytometry. 1990;11:813–821. doi:10.1002/cyto.990110707.
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