BH3-only protein silencing contributes to acquired resistance to PLX4720 in human melanoma

Cell Death Differ. 2012 Dec;19(12):2029-39. doi: 10.1038/cdd.2012.94. Epub 2012 Aug 3.


B-RAF is mutated to a constitutively active form in 8% of human cancers including 50% of melanomas. In clinical trials, the RAF inhibitor, PLX4032 (vemurafenib), caused partial or complete responses in 48-81% of mutant B-RAF harboring melanoma patients. However, the average duration of response was 6-7 months before tumor regrowth, indicating the acquisition of resistance to PLX4032. To understand the mechanisms of resistance, we developed mutant B-RAF melanoma cells that displayed resistance to RAF inhibition through continuous culture with PLX4720 (the tool compound for PLX4032). Resistance was associated with a partial reactivation of extracellular signal-regulated kinase 1/2 (ERK1/2) signaling, recovery of G1/S cell-cycle events, and suppression of the pro-apoptotic B-cell leukemia/lymphoma 2 (Bcl-2) homology domain 3 (BH3)-only proteins, Bcl-2-interacting mediator of cell death-extra large (Bim-EL) and Bcl-2 modifying factor (Bmf). Preventing ERK1/2 reactivation with MEK (mitogen-activated protein/extracellular signal-regulated kinase kinase) inhibitors blocked G1-S cell-cycle progression but failed to induce apoptosis or upregulate Bim-EL and Bmf. Treatment with the histone deacetylase (HDAC) inhibitor, suberoylanilide hydroxamic acid, led to de-repression of Bim-EL and enhanced cell death in the presence of PLX4720 or AZD6244 in resistant cells. These data indicate that acquired resistance to PLX4032/4720 likely involves ERK1/2 pathway reactivation as well as ERK1/2-independent silencing of BH3-only proteins. Furthermore, combined treatment of HDAC inhibitors and MEK inhibitors may contribute to overcoming PLX4032 resistance.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Adaptor Proteins, Signal Transducing / genetics
  • Adaptor Proteins, Signal Transducing / metabolism
  • Apoptosis / drug effects
  • Apoptosis Regulatory Proteins / genetics
  • Apoptosis Regulatory Proteins / metabolism
  • Bcl-2-Like Protein 11
  • Cell Line, Tumor
  • Drug Resistance, Neoplasm / drug effects*
  • G1 Phase Cell Cycle Checkpoints / drug effects
  • Histone Deacetylases / chemistry
  • Histone Deacetylases / metabolism
  • Humans
  • Hydroxamic Acids / pharmacology
  • Indoles / toxicity*
  • Melanoma / metabolism
  • Melanoma / pathology
  • Membrane Proteins / genetics
  • Membrane Proteins / metabolism
  • Mitogen-Activated Protein Kinase 1 / metabolism
  • Mitogen-Activated Protein Kinase 3 / metabolism
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism
  • Proto-Oncogene Proteins B-raf / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • S Phase Cell Cycle Checkpoints / drug effects
  • Sulfonamides / toxicity*
  • Up-Regulation
  • Vemurafenib
  • Vorinostat


  • Adaptor Proteins, Signal Transducing
  • Apoptosis Regulatory Proteins
  • BCL2L11 protein, human
  • BMF protein, human
  • Bcl-2-Like Protein 11
  • Hydroxamic Acids
  • Indoles
  • Membrane Proteins
  • Proto-Oncogene Proteins
  • Proto-Oncogene Proteins c-bcl-2
  • Sulfonamides
  • Vemurafenib
  • Vorinostat
  • Proto-Oncogene Proteins B-raf
  • Mitogen-Activated Protein Kinase 1
  • Mitogen-Activated Protein Kinase 3
  • Histone Deacetylases