title: MEK-independent survival of B-RAFV600E melanoma cells selected for resistance to apoptosis induced by the RAF inhibitor PLX4720.
abstract: OBJECTIVE
  To examine mechanisms that determine long-term responses of B-RAF(V600E) melanoma cells to B-RAF inhibitors.
  
  
  METHODS
  B-RAF(V600E) melanoma cells were exposed to the B-RAF inhibitor PLX4720 for prolonged periods to select for cells resistant to apoptosis induced by the inhibitor. The resultant cells were analyzed for activation of extracellular signal regulated kinase (ERK), MAP/ERK kinase (MEK), and Akt, and related signals. Their roles in survival of the cells were also examined.
  
  
  RESULTS
  B-RAF(V600E) melanoma cells selected for resistant to PLX4720-induced apoptosis retained the V600E mutation in B-RAF, and proliferated steadily in the presence of the inhibitor, albeit with slow growth rate. These cells displayed high levels of ERK activation, that is, at least in part, independent of the conventional RAF/MEK/ERK pathway, as MEK activation was low and inhibition of MEK did not significantly block activation of ERK. In contrast, extracellular signals appeared involved. This was associated with elevated activation of the phosphoinositide 3-kinase (PI3k)/Akt pathway and could be inhibited by serum starvation and inhibition of PI3k/Akt. Inhibition of MEK did not impact on survival of these cells, whereas serum starvation, inhibition of PI3K/Akt, and inhibition of ERK1/2 reduced their viability.
  
  
  CONCLUSIONS
  These results indicate that sensitivity to induction of apoptosis may be a major determinant of long-term responses of B-RAF(V600E) melanomas to specific inhibitors and suggest that rebound melanoma growth after initial treatment with the inhibitors may not be responsive to MEK inhibitors, but may be susceptible to inhibition of the PI3k/Akt pathway.
authors.affiliation: Immunology and Oncology Unit, Newcastle, New South Wales, Australia.
authors.forename: Chen Chen
authors.initials: CC
authors.lastname: Jiang
authors.forename: Fritz
authors.initials: F
authors.lastname: Lai
authors.forename: Rick F
authors.initials: RF
authors.lastname: Thorne
authors.forename: Fan
authors.initials: F
authors.lastname: Yang
authors.forename: Hao
authors.initials: H
authors.lastname: Liu
authors.forename: Peter
authors.initials: P
authors.lastname: Hersey
authors.forename: Xu Dong
authors.initials: XD
authors.lastname: Zhang
mesh_terms: D000970:Antineoplastic Agents / Q000494:pharmacology*; D017209:Apoptosis / Q000235:genetics*; D002070:Butadienes / Q000494:pharmacology; D045744:Cell Line, Tumor; D002470:Cell Survival / Q000187:drug effects / Q000235:genetics; D002867:Chromones / Q000494:pharmacology; D003470:Culture Media; D019008:Drug Resistance, Neoplasm; D004789:Enzyme Activation; D004791:Enzyme Inhibitors / Q000494:pharmacology; D048049:Extracellular Signal-Regulated MAP Kinases / Q000378:metabolism; D015972:Gene Expression Regulation, Neoplastic; D006801:Humans; D007211:Indoles / Q000494:pharmacology*; D048369:MAP Kinase Kinase 1 / Q000037:antagonists & inhibitors / Q000378:metabolism*; D009025:Morpholines / Q000494:pharmacology; D009570:Nitriles / Q000494:pharmacology; D019869:Phosphatidylinositol 3-Kinases / Q000378:metabolism; D000081082:Phosphoinositide-3 Kinase Inhibitors; D048493:Proto-Oncogene Proteins B-raf / Q000037:antagonists & inhibitors*; D051057:Proto-Oncogene Proteins c-akt / Q000378:metabolism; D015398:Signal Transduction; D013449:Sulfonamides / Q000494:pharmacology*
chemical_list: D000970:Antineoplastic Agents; D002070:Butadienes; D002867:Chromones; D003470:Culture Media; D004791:Enzyme Inhibitors; D048049:Extracellular Signal-Regulated MAP Kinases; D007211:Indoles; D048369:MAP Kinase Kinase 1; D009025:Morpholines; D009570:Nitriles; D019869:Phosphatidylinositol 3-Kinases; D000081082:Phosphoinositide-3 Kinase Inhibitors; D048493:Proto-Oncogene Proteins B-raf; D051057:Proto-Oncogene Proteins c-akt; D013449:Sulfonamides; C528407:PLX 4720; C113580:U 0126; C085911:2-(4-morpholinyl)-8-phenyl-4H-1-benzopyran-4-one; C482119:BRAF protein, human