Elevated CRAF as a potential mechanism of acquired resistance to BRAF inhibition in melanoma.
Activating BRAF kinase mutations arise in approximately 7% of all human tumors, and preclinical studies have validated the RAF-mitogen-activated protein/extracellular signal-regulated kinase (ERK) kinase-ERK signaling cascade as a potentially important therapeutic target in this setting. Selective RAF kinase inhibitors are currently undergoing clinical development, and based on the experience with other kinase-targeted therapeutics, it is expected that clinical responses to these agents, if observed, will lead to the eventual emergence of drug resistance in most cases. Thus, it is important to establish molecular mechanisms underlying such resistance to develop effective therapeutic strategies to overcome or prevent drug resistance. To anticipate potential mechanisms of acquired resistance to RAF inhibitors during the course of treatment, we established drug-resistant clones from a human melanoma-derived cell line harboring the recurrent V600E activating BRAF mutation, which exhibits exquisite sensitivity to AZ628, a selective RAF kinase inhibitor. We determined that elevated CRAF protein levels account for the acquisition of resistance to AZ628 in these cells, associated with a switch from BRAF to CRAF dependency in tumor cells. We also found that elevated CRAF protein levels may similarly contribute to primary insensitivity to RAF inhibition in a subset of BRAF mutant tumor cells. Interestingly, AZ628-resistant cells demonstrating either primary drug insensitivity or acquired drug resistance exhibit exquisite sensitivity to the HSP90 inhibitor geldanamycin. Geldanamycin effectively promotes the degradation of CRAF, thereby revealing a potential therapeutic strategy to overcome resistance to RAF inhibition in a subset of BRAF mutant tumors.
Center for Molecular Therapeutics, Massachusetts General Hospital Cancer Center, Harvard Medical School, Charlestown, Massachusetts, USA.
Clara
C
Montagut
Sreenath V
SV
Sharma
Toshi
T
Shioda
Ultan
U
McDermott
Matthew
M
Ulman
Lindsey E
LE
Ulkus
Dora
D
Dias-Santagata
Hannah
H
Stubbs
Diana Y
DY
Lee
Anurag
A
Singh
Lisa
L
Drew
Daniel A
DA
Haber
Jeffrey
J
Settleman
D049109:Cell Proliferation / Q000187:drug effects; D019008:Drug Resistance, Neoplasm; D006801:Humans; D017404:In Situ Hybridization, Fluorescence; D048369:MAP Kinase Kinase 1 / Q000378:metabolism; D008545:Melanoma / Q000188:drug therapy* / Q000378:metabolism / Q000473:pathology; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D009154:Mutation / Q000235:genetics; D009369:Neoplasms / Q000188:drug therapy / Q000235:genetics / Q000378:metabolism*; D010766:Phosphorylation / Q000187:drug effects; D016133:Polymerase Chain Reaction; D047428:Protein Kinase Inhibitors / Q000627:therapeutic use*; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism*; D019908:Proto-Oncogene Proteins c-raf / Q000037:antagonists & inhibitors / Q000235:genetics / Q000378:metabolism*; D034741:RNA, Small Interfering / Q000494:pharmacology; D014407:Tumor Cells, Cultured; D015854:Up-Regulation
D047428:Protein Kinase Inhibitors; D034741:RNA, Small Interfering; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D019908:Proto-Oncogene Proteins c-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D048369:MAP Kinase Kinase 1