Pharmacodynamic characterization of the efficacy signals due to selective BRAF inhibition with PLX4032 in malignant melanoma.
OBJECTIVE
About 65% to 70% of melanomas harbor a mutation in v-raf murine sarcoma viral oncogene homolog B1 (BRAF) that causes the steady-state activation of extracellular signal-regulated kinase (ERK). We sought to investigate the efficacy of PLX4032 (BRAF inhibitor) to identify patterns/predictors of response/resistance and to study the effects of BRAF in melanoma.


METHODS
Well-characterized melanoma cell lines, including several with acquired drug resistance, were exposed to PLX4032. Growth inhibition, phosphosignaling, cell cycle, apoptosis, and gene expression analyses were performed before and after exposure to drug.


RESULTS
Using a growth-adjusted inhibitory concentration of 50% cutoff of 1 microM, 13 of 35 cell lines were sensitive to PLX4032, 16 resistant, and 6 intermediate (37%, 46%, and 17% respectively). PLX4032 caused growth inhibition, G(0)/G(1) arrest, and restored apoptosis in the sensitive cell lines. A BRAF mutation predicted for but did not guarantee a response, whereas a neuroblastoma RAS viral oncogene homolog mutation or wild-type BRAF conferred resistance. Cells with concurrent BRAF mutations and melanocortin 1 receptor germ line variants and/or a more differentiated melanocyte genotype had a preferential response. Acquired PLX4032 resistance reestablishes ERK signaling, promotes a nonmelanocytic genotype, and is associated with an increase in the gene expression of certain metallothioneins and mediators of angiogenesis.


CONCLUSIONS
PLX4032 has robust activity in BRAF mutated melanoma. The preclinical use of this molecule identifies criteria for its proper clinical application, describes patterns of and reasons for response/resistance, and affords insight into the role of a BRAF mutation in melanoma.
Tap
William D
WD
Division of Hematology/Oncology, Department of Medicine, David Geffen School of Medicine, University of California Los Angeles, Los Angeles, CA, USA. wtap@mednet.ucla.edu
Gong
Ke-Wei
KW
Dering
Judy
J
Tseng
Yiou
Y
Ginther
Charles
C
Pauletti
Giovanni
G
Glaspy
John A
JA
Essner
Richard
R
Bollag
Gideon
G
Hirth
Peter
P
Zhang
Chao
C
Slamon
Dennis J
DJ
D017209:Apoptosis / Q000187:drug effects / Q000235:genetics; D054316:Biomarkers, Pharmacological / Q000032:analysis / Q000378:metabolism; D014408:Biomarkers, Tumor / Q000235:genetics / Q000378:metabolism; D002453:Cell Cycle / Q000187:drug effects / Q000235:genetics; D045744:Cell Line, Tumor; D004252:DNA Mutational Analysis; D004353:Drug Evaluation, Preclinical; D019008:Drug Resistance, Neoplasm / Q000187:drug effects* / Q000235:genetics; D015972:Gene Expression Regulation, Neoplastic / Q000187:drug effects; D006801:Humans; D007211:Indoles / Q000493:pharmacokinetics* / Q000494:pharmacology; D008545:Melanoma / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D010766:Phosphorylation / Q000187:drug effects; D047428:Protein Kinase Inhibitors / Q000493:pharmacokinetics / Q000494:pharmacology; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors* / Q000235:genetics / Q000378:metabolism; D015398:Signal Transduction / Q000187:drug effects / Q000235:genetics; D012878:Skin Neoplasms / Q000235:genetics / Q000378:metabolism* / Q000473:pathology; D013379:Substrate Specificity / Q000187:drug effects; D013449:Sulfonamides / Q000493:pharmacokinetics* / Q000494:pharmacology; D016896:Treatment Outcome; D000077484:Vemurafenib
D054316:Biomarkers, Pharmacological; D014408:Biomarkers, Tumor; D007211:Indoles; D047428:Protein Kinase Inhibitors; D013449:Sulfonamides; D000077484:Vemurafenib; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf