Melanomas acquire resistance to B-RAF(V600E) inhibition by RTK or N-RAS upregulation

Ramin Nazarian, Hubing Shi, Qi Wang, Xiangju Kong, Richard C. Koya, Hane Lee, Zugen Chen, Mi Kyung Lee, Narsis Attar, Hooman Sazegar, Thinle Chodon, Stanley F. Nelson, Grant McArthur, Jeffrey A. Sosman, Antoni Ribas, Roger S. Lo

Research output: Contribution to journalArticlepeer-review

1584 Scopus citations

Abstract

Activating B-RAF(V600E) (also known as BRAF) kinase mutations occur in ∼7% of human malignancies and ∼60% of melanomas. Early clinical experience with a novel class I RAF-selective inhibitor, PLX4032, demonstrated an unprecedented 80% anti-tumour response rate among patients with B-RAF(V600E)-positive melanomas, but acquired drug resistance frequently develops after initial responses. Hypotheses for mechanisms of acquired resistance to B-RAF inhibition include secondary mutations in B-RAF(V600E), MAPK reactivation, and activation of alternative survival pathways. Here we show that acquired resistance to PLX4032 develops by mutually exclusive PDGFRÎ 2 (also known as PDGFRB) upregulation or N-RAS (also known as NRAS) mutations but not through secondary mutations in B-RAF(V600E). We used PLX4032-resistant sub-lines artificially derived from B-RAF(V600E)-positive melanoma cell lines and validated key findings in PLX4032-resistant tumours and tumour-matched, short-term cultures from clinical trial patients. Induction of PDGFRÎ 2 RNA, protein and tyrosine phosphorylation emerged as a dominant feature of acquired PLX4032 resistance in a subset of melanoma sub-lines, patient-derived biopsies and short-term cultures. PDGFRÎ 2-upregulated tumour cells have low activated RAS levels and, when treated with PLX4032, do not reactivate the MAPK pathway significantly. In another subset, high levels of activated N-RAS resulting from mutations lead to significant MAPK pathway reactivation upon PLX4032 treatment. Knockdown of PDGFRÎ 2 or N-RAS reduced growth of the respective PLX4032-resistant subsets. Overexpression of PDGFRÎ 2 or N-RAS(Q61K) conferred PLX4032 resistance to PLX4032-sensitive parental cell lines. Importantly, MAPK reactivation predicts MEK inhibitor sensitivity. Thus, melanomas escape B-RAF(V600E) targeting not through secondary B-RAF(V600E) mutations but via receptor tyrosine kinase (RTK)-mediated activation of alternative survival pathway(s) or activated RAS-mediated reactivation of the MAPK pathway, suggesting additional therapeutic strategies.

Original languageEnglish (US)
Pages (from-to)973-977
Number of pages5
JournalNature
Volume468
Issue number7326
DOIs
StatePublished - Dec 16 2010

ASJC Scopus subject areas

  • General

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