title: HDAC Inhibition Overcomes Acute Resistance to MEK Inhibition in BRAF-Mutant Colorectal Cancer by Downregulation of c-FLIPL.
abstract: OBJECTIVE
  Activating mutations in the BRAF oncogene are found in 8% to 15% of colorectal cancer patients and have been associated with poor survival. In contrast with BRAF-mutant (MT) melanoma, inhibition of the MAPK pathway is ineffective in the majority of BRAFMT colorectal cancer patients. Therefore, identification of novel therapies for BRAFMT colorectal cancer is urgently needed.
  
  
  METHODS
  BRAFMT and wild-type (WT) colorectal cancer models were assessed in vitro and in vivo. Small-molecule inhibitors of MEK1/2, MET, and HDAC were used, overexpression and siRNA approaches were applied, and cell death was assessed by flow cytometry, Western blotting, cell viability, and caspase activity assays.
  
  
  RESULTS
  Increased c-MET-STAT3 signaling was identified as a novel adaptive resistance mechanism to MEK inhibitors (MEKi) in BRAFMT colorectal cancer models in vitro and in vivo. Moreover, MEKi treatment resulted in acute increases in transcription of the endogenous caspase-8 inhibitor c-FLIPL in BRAFMT cells, but not in BRAFWT cells, and inhibition of STAT3 activity abrogated MEKi-induced c-FLIPL expression. In addition, treatment with c-FLIP-specific siRNA or HDAC inhibitors abrogated MEKi-induced upregulation of c-FLIPL expression and resulted in significant increases in MEKi-induced cell death in BRAFMT colorectal cancer cells. Notably, combined HDAC inhibitor/MEKi treatment resulted in dramatically attenuated tumor growth in BRAFMT xenografts.
  
  
  CONCLUSIONS
  Our findings indicate that c-MET/STAT3-dependent upregulation of c-FLIPL expression is an important escape mechanism following MEKi treatment in BRAFMT colorectal cancer. Thus, combinations of MEKi with inhibitors of c-MET or c-FLIP (e.g., HDAC inhibitors) could be potential novel treatment strategies for BRAFMT colorectal cancer.
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Robbie
authors: R
authors: Carson
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Basak
authors: B
authors: Celtikci
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Cathy
authors: C
authors: Fenning
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Arman
authors: A
authors: Javadi
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Nyree
authors: N
authors: Crawford
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Lucia Perez
authors: LP
authors: Carbonell
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Mark
authors: M
authors: Lawler
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Daniel B
authors: DB
authors: Longley
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Patrick G
authors: PG
authors: Johnston
authors: Centre for Cancer Research and Cell Biology, School of Medicine, Dentistry and Biomedical Science, Queen's University Belfast, 97 Lisburn Road, Belfast, BT9 7AE, UK.
authors: Sandra
authors: S
authors: Van Schaeybroeck
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D015153:Blotting, Western; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein / Q000096:biosynthesis*; D045744:Cell Line, Tumor; D015179:Colorectal Neoplasms / Q000378:metabolism*; D015536:Down-Regulation; D019008:Drug Resistance, Neoplasm / Q000187:drug effects; D004797:Enzyme-Linked Immunosorbent Assay; D005434:Flow Cytometry; D056572:Histone Deacetylase Inhibitors / Q000494:pharmacology*; D006801:Humans; D020930:MAP Kinase Kinase Kinases; D051379:Mice; D008807:Mice, Inbred BALB C; D008819:Mice, Nude; D048493:Proto-Oncogene Proteins B-raf / Q000235:genetics; D034741:RNA, Small Interfering; D015398:Signal Transduction / Q000187:drug effects*; D014162:Transfection; D023041:Xenograft Model Antitumor Assays
chemical_list: D000970:Antineoplastic Agents; D053446:CASP8 and FADD-Like Apoptosis Regulating Protein; C506386:CFLAR protein, human; D056572:Histone Deacetylase Inhibitors; D034741:RNA, Small Interfering; C482119:BRAF protein, human; D048493:Proto-Oncogene Proteins B-raf; D020930:MAP Kinase Kinase Kinases