Resistance to selective BRAF inhibition can be mediated by modest upstream pathway activation.
A high percentage of patients with BRAF(V600E) mutant melanomas respond to the selective RAF inhibitor vemurafenib (RG7204, PLX4032) but resistance eventually emerges. To better understand the mechanisms of resistance, we used chronic selection to establish BRAF(V600E) melanoma clones with acquired resistance to vemurafenib. These clones retained the V600E mutation and no second-site mutations were identified in the BRAF coding sequence. Further characterization showed that vemurafenib was not able to inhibit extracellular signal-regulated kinase phosphorylation, suggesting pathway reactivation. Importantly, resistance also correlated with increased levels of RAS-GTP, and sequencing of RAS genes revealed a rare activating mutation in KRAS, resulting in a K117N change in the KRAS protein. Elevated levels of CRAF and phosphorylated AKT were also observed. In addition, combination treatment with vemurafenib and either a MAP/ERK kinase (MEK) inhibitor or an AKT inhibitor synergistically inhibited proliferation of resistant cells. These findings suggest that resistance to BRAF(V600E) inhibition could occur through several mechanisms, including elevated RAS-GTP levels and increased levels of AKT phosphorylation. Together, our data implicate reactivation of the RAS/RAF pathway by upstream signaling activation as a key mechanism of acquired resistance to vemurafenib, in support of clinical studies in which combination therapy with other targeted agents are being strategized to combat resistance.
Discovery Oncology, Hoffmann-La Roche Inc., Nutley, New Jersey, USA. fei.su@roche.com
Fei
F
Su
William D
WD
Bradley
Qiongqing
Q
Wang
Hong
H
Yang
Lizhong
L
Xu
Brian
B
Higgins
Kenneth
K
Kolinsky
Kathryn
K
Packman
Min Jung
MJ
Kim
Kerstin
K
Trunzer
Richard J
RJ
Lee
Kathleen
K
Schostack
Jade
J
Carter
Thomas
T
Albert
Soren
S
Germer
Jim
J
Rosinski
Mitchell
M
Martin
Mary Ellen
ME
Simcox
Brian
B
Lestini
David
D
Heimbrook
Gideon
G
Bollag
D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D000971:Antineoplastic Combined Chemotherapy Protocols / Q000627:therapeutic use*; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm; D005260:Female; D006801:Humans; D048289:Imidazolidines / Q000008:administration & dosage; D007211:Indoles / Q000627:therapeutic use*; D020935:MAP Kinase Signaling System / Q000187:drug effects; D008545:Melanoma / Q000188:drug therapy*; D051379:Mice; D016513:Mice, SCID; D009154:Mutation; D010654:Phenylbutyrates / Q000008:administration & dosage; D010766:Phosphorylation; D011518:Proto-Oncogene Proteins / Q000378:metabolism*; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D019908:Proto-Oncogene Proteins c-raf / Q000378:metabolism; D016283:Proto-Oncogene Proteins p21(ras); D015398:Signal Transduction / Q000187:drug effects; D013449:Sulfonamides / Q000627:therapeutic use*; D014162:Transfection; D000077484:Vemurafenib; D023041:Xenograft Model Antitumor Assays; D018631:ras Proteins / Q000378:metabolism*
C547875:2-(4-(4-(2,3-dihydroxy-propoxy)phenyl)-2,5-dioxo-imidazolidin-1-yl)-N-(2-fluoro-4-iodo-phenyl)-3-phenylbutyramide; D000970:Antineoplastic Agents; D048289:Imidazolidines; D007211:Indoles; C117307:KRAS protein, human; D010654:Phenylbutyrates; D011518:Proto-Oncogene Proteins; D013449:Sulfonamides; D000077484:Vemurafenib; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D051057:Proto-Oncogene Proteins c-akt; D019908:Proto-Oncogene Proteins c-raf; D016283:Proto-Oncogene Proteins p21(ras); D018631:ras Proteins