Molecular signatures specific to particular tumor types are required to design treatments for resistant tumors.,However, it remains unclear whether tumors and corresponding cell lines used for drug development share such signatures.,We developed similarity core analysis (SCA), a universal and unsupervised computational framework for extracting core molecular features common to tumors and cell lines.,We applied SCA to mRNA/miRNA expression data from various sources, comparing melanoma cell lines and metastases.,The signature obtained was associated with phenotypic characteristics in vitro, and the core genes CAPN3 and TRIM63 were implicated in melanoma cell migration/invasion.,About 90% of the melanoma signature genes belong to an intrinsic network of transcription factors governing neural development (TFAP2A, DLX2, ALX1, MITF, PAX3, SOX10, LEF1, and GAS7) and miRNAs (211-5p, 221-3p, and 10a-5p).,The SCA signature effectively discriminated between two subpopulations of melanoma patients differing in overall survival, and classified MEKi/BRAFi-resistant and -sensitive melanoma cell lines.,Cancer cell lines are at the forefront of drug discovery but are often limited in representing the tumor of origin due to the artificial culture conditions.,Rambow et al. develop a computational approach for identifying tumor cell lineage expression cores.,These core genes reveal relevant molecular dependencies linking aggressiveness, patient survival, and drug sensitivity.
Activated RAS promotes dimerization of members of the RAF kinase family1-3.,ATP-competitive RAF inhibitors activate ERK signaling4-7 by transactivating RAF dimers4.,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 tumor-specific inhibition of ERK signaling results in a broad therapeutic index and RAF inhibitors have remarkable clinical activity in patients with melanomas that harbor mutant BRAF(V600E)8.,However, resistance invariably develops.,Here, we identify a novel resistance mechanism.,We find that a subset of cells resistant to vemurafenib (PLX4032, RG7204) express a 61kd variant form of BRAF(V600E) that lacks exons 4-8, a region that encompasses the RAS-binding domain. p61BRAF(V600E) exhibits 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 signaling 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 tumors of six of 19 patients with acquired resistance to vemurafenib.,These data support the model that inhibition of ERK signaling 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.