title: BH3-only protein silencing contributes to acquired resistance to PLX4720 in human melanoma.
abstract: 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.
authors.affiliation: Department of Cancer Biology and Kimmel Cancer Center, Thomas Jefferson University, Philadelphia, PA 19107, USA.
authors.forename: Y
authors.initials: Y
authors.lastname: Shao
authors.forename: A E
authors.initials: AE
authors.lastname: Aplin
mesh_terms: D048868:Adaptor Proteins, Signal Transducing / Q000235:genetics / Q000378:metabolism; D017209:Apoptosis / Q000187:drug effects; D051017:Apoptosis Regulatory Proteins / Q000235:genetics / Q000378:metabolism; D000072224:Bcl-2-Like Protein 11; D045744:Cell Line, Tumor; D019008:Drug Resistance, Neoplasm / Q000187:drug effects*; D059585:G1 Phase Cell Cycle Checkpoints / Q000187:drug effects; D006655:Histone Deacetylases / Q000737:chemistry / Q000378:metabolism; D006801:Humans; D006877:Hydroxamic Acids / Q000494:pharmacology; D007211:Indoles / Q000633:toxicity*; D008545:Melanoma / Q000378:metabolism / Q000473:pathology; D008565:Membrane Proteins / Q000235:genetics / Q000378:metabolism; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3 / Q000378:metabolism; D011518:Proto-Oncogene Proteins / Q000235:genetics / Q000378:metabolism; D048493:Proto-Oncogene Proteins B-raf / Q000378:metabolism; D019253:Proto-Oncogene Proteins c-bcl-2 / Q000378:metabolism; D059807:S Phase Cell Cycle Checkpoints / Q000187:drug effects; D013449:Sulfonamides / Q000633:toxicity*; D015854:Up-Regulation; D000077484:Vemurafenib; D000077337:Vorinostat
chemical_list: D048868:Adaptor Proteins, Signal Transducing; D051017:Apoptosis Regulatory Proteins; C000606775:BCL2L11 protein, human; C486655:BMF protein, human; D000072224:Bcl-2-Like Protein 11; D006877:Hydroxamic Acids; D007211:Indoles; D008565:Membrane Proteins; D011518:Proto-Oncogene Proteins; D019253:Proto-Oncogene Proteins c-bcl-2; D013449:Sulfonamides; D000077484:Vemurafenib; D000077337:Vorinostat; D048493:Proto-Oncogene Proteins B-raf; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D006655:Histone Deacetylases