3'-deoxy-3'-[18F]fluorothymidine positron emission tomography is a sensitive method for imaging the response of BRAF-dependent tumors to MEK inhibition.
Activating mutations of BRAF occur in approximately 7% of all human tumors and in the majority of melanomas. These tumors are very sensitive to pharmacologic inhibition of mitogen-activated protein kinase/extracellular signal-regulated kinase kinase (MEK), which causes loss of D-cyclin expression, hypophosphorylation of Rb, and G(1) arrest. Growth arrest is followed by differentiation or senescence and, in a subset of BRAF mutant tumors, by apoptosis. The former effects result in so-called "stable disease" and, in patients with cancer, can be difficult to distinguish from indolent tumor growth. The profound G(1) arrest induced by MEK inhibition in BRAF mutant tumors is associated with a marked decline in thymidine uptake and is therefore potentially detectable in vivo by noninvasive 3'-deoxy-3'-[(18)F]fluorothymidine ([(18)F]FLT) positron emission tomography (PET) imaging. In SKMEL-28 tumor xenografts, MEK inhibition completely inhibited tumor growth and induced differentiation with only modest tumor regression. MEK inhibition also resulted in a rapid decline in the [(18)F]FLT signal in V600E BRAF mutant SKMEL-28 xenografts but not in BRAF wild-type BT-474 xenografts. The data suggest that [(18)F]FLT PET can effectively image induction of G(1) arrest by MEK inhibitors in mutant BRAF tumors and may be a useful noninvasive method for assessing the early biological response to this class of drugs.
Department of Medicine, Memorial Sloan-Kettering Cancer Center, New York, New York 10021, USA.
David B
DB
Solit
Elmer
E
Santos
Christine A
CA
Pratilas
Jose
J
Lobo
Maxim
M
Moroz
Shangde
S
Cai
Ronald
R
Blasberg
Judith
J
Sebolt-Leopold
Steven
S
Larson
Neal
N
Rosen
D000818:Animals; D001549:Benzamides / Q000494:pharmacology*; D015153:Blotting, Western; D015224:Dideoxynucleosides / Q000378:metabolism; D004159:Diphenylamine / Q000031:analogs & derivatives* / Q000494:pharmacology; D019008:Drug Resistance, Neoplasm; D005260:Female; D016193:G1 Phase / Q000187:drug effects / Q000502:physiology; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D008545:Melanoma / Q000000981:diagnostic imaging* / Q000188:drug therapy / Q000378:metabolism*; D051379:Mice; D008819:Mice, Nude; D049268:Positron-Emission Tomography; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics* / Q000378:metabolism; D019275:Radiopharmaceuticals / Q000493:pharmacokinetics; D014407:Tumor Cells, Cultured; D023041:Xenograft Model Antitumor Assays
D001549:Benzamides; D015224:Dideoxynucleosides; D019275:Radiopharmaceuticals; C506614:mirdametinib; D004159:Diphenylamine; C482120:Braf protein, mouse; D048493:Proto-Oncogene Proteins B-raf; D048369:MAP Kinase Kinase 1; C482127:Map2k1 protein, mouse