HDAC Inhibition Overcomes Acute Resistance to MEK Inhibition in BRAF-Mutant Colorectal Cancer by Downregulation of c-FLIPL.

Abstract

PURPOSE:

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.

EXPERIMENTAL DESIGN:

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: Robbie Carson, Basak Celtikci, Cathy Fenning, Arman Javadi, Nyree Crawford, Lucia Perez Carbonell, Mark Lawler, Daniel B Longley, Patrick G Johnston, Sandra Van Schaeybroeck
• Journal: Clinical cancer research : an official journal of the American Association for Cancer Research (Clin Cancer Res) Vol. 21 Issue 14 Pg. 3230-3240 (Jul 15 2015) ISSN: 1557-3265 [Electronic] United States
• PMID: 25813020 (Publication Type: Journal Article, Research Support, Non-U.S. Gov't)
• Copyright: ©2015 American Association for Cancer Research.

Chemical References

• Antineoplastic Agents
• CASP8 and FADD-Like Apoptosis Regulating Protein
• CFLAR protein, human
• Histone Deacetylase Inhibitors
• RNA, Small Interfering
• BRAF protein, human
• Proto-Oncogene Proteins B-raf
• MAP Kinase Kinase Kinases

Topics

• Animals
• Antineoplastic Agents (pharmacology)
• Blotting, Western
• CASP8 and FADD-Like Apoptosis Regulating Protein (biosynthesis)
• Cell Line, Tumor
• Colorectal Neoplasms (metabolism)
• Down-Regulation
• Drug Resistance, Neoplasm (drug effects)
• Enzyme-Linked Immunosorbent Assay
• Flow Cytometry
• Histone Deacetylase Inhibitors (pharmacology)
• Humans
• MAP Kinase Kinase Kinases
• Mice
• Mice, Inbred BALB C
• Mice, Nude
• Proto-Oncogene Proteins B-raf (genetics)
• RNA, Small Interfering
• Signal Transduction (drug effects)
• Transfection
• Xenograft Model Antitumor Assays