Impact of combined mTOR and MEK inhibition in uveal melanoma is driven by tumor genotype

PLoS One. 2012;7(7):e40439. doi: 10.1371/journal.pone.0040439. Epub 2012 Jul 10.

Abstract

Uveal melanomas possess activation of the mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT/mammalian Target of Rapamycin (mTOR) pathways. MAPK activation occurs via somatic mutations in the heterotrimeric G protein subunits GNAQ and GNA11 for over 70% of tumors and less frequently via V600E BRAF mutations. In this report, we describe the impact of dual pathway inhibition upon uveal melanoma cell lines with the MEK inhibitor selumetinib (AZD6244/ARRY-142886) and the ATP-competitive mTOR kinase inhibitor AZD8055. While synergistic reductions in cell viability were observed with AZD8055/selumetinib in both BRAF and GNAQ mutant cell lines, apoptosis was preferentially induced in BRAF mutant cells only. In vitro apoptosis assay results were predictive of in vivo drug efficacy as tumor regressions were observed only in a BRAF mutant xenograft model, but not GNAQ mutant model. We went on to discover that GNAQ promotes relative resistance to AZD8055/selumetinib-induced apoptosis in GNAQ mutant cells. For BRAF mutant cells, both AKT and 4E-BP1 phosphorylation were modulated by the combination; however, decreasing AKT phosphorylation alone was not sufficient and decreasing 4E-BP1 phosphorylation was not required for apoptosis. Instead, cooperative mTOR complex 2 (mTORC2) and MEK inhibition resulting in downregulation of the pro-survival protein MCL-1 was found to be critical for combination-induced apoptosis. These results suggest that the clinical efficacy of combined MEK and mTOR kinase inhibition will be determined by tumor genotype, and that BRAF mutant malignancies will be particularly susceptible to this strategy.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Adaptor Proteins, Signal Transducing / metabolism
  • Animals
  • Apoptosis / drug effects
  • Benzimidazoles / pharmacology
  • Benzimidazoles / therapeutic use
  • Cell Line, Tumor
  • Cell Survival / drug effects
  • Drug Resistance, Neoplasm / drug effects
  • Drug Synergism
  • GTP-Binding Protein alpha Subunits / genetics
  • GTP-Binding Protein alpha Subunits, Gq-G11
  • Genotype
  • Humans
  • Mechanistic Target of Rapamycin Complex 2
  • Melanoma / drug therapy*
  • Melanoma / enzymology
  • Melanoma / genetics*
  • Mice
  • Mitogen-Activated Protein Kinase Kinases / antagonists & inhibitors*
  • Mitogen-Activated Protein Kinase Kinases / metabolism
  • Models, Biological
  • Morpholines / pharmacology
  • Morpholines / therapeutic use
  • Multiprotein Complexes / metabolism
  • Mutation / genetics
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Phosphoproteins / metabolism
  • Phosphorylation / drug effects
  • Protein Kinase Inhibitors / pharmacology*
  • Protein Kinase Inhibitors / therapeutic use*
  • Proto-Oncogene Proteins B-raf / genetics
  • Proto-Oncogene Proteins c-akt / metabolism
  • Proto-Oncogene Proteins c-bcl-2 / metabolism
  • Receptor, IGF Type 1 / metabolism
  • TOR Serine-Threonine Kinases / antagonists & inhibitors*
  • TOR Serine-Threonine Kinases / metabolism
  • Uveal Neoplasms / drug therapy*
  • Uveal Neoplasms / enzymology
  • Uveal Neoplasms / genetics*
  • Xenograft Model Antitumor Assays

Substances

  • AZD 6244
  • Adaptor Proteins, Signal Transducing
  • Benzimidazoles
  • EIF4EBP1 protein, human
  • GNAQ protein, human
  • GTP-Binding Protein alpha Subunits
  • Mcl1 protein, mouse
  • Morpholines
  • Multiprotein Complexes
  • Myeloid Cell Leukemia Sequence 1 Protein
  • Phosphoproteins
  • Protein Kinase Inhibitors
  • Proto-Oncogene Proteins c-bcl-2
  • (5-(2,4-bis((3S)-3-methylmorpholin-4-yl)pyrido(2,3-d)pyrimidin-7-yl)-2-methoxyphenyl)methanol
  • TOR Serine-Threonine Kinases
  • Receptor, IGF Type 1
  • BRAF protein, human
  • Mechanistic Target of Rapamycin Complex 2
  • Proto-Oncogene Proteins B-raf
  • Proto-Oncogene Proteins c-akt
  • Mitogen-Activated Protein Kinase Kinases
  • GTP-Binding Protein alpha Subunits, Gq-G11

Supplementary concepts

  • Uveal melanoma