Combination Treatment with the BRAFV600E Inhibitor Vemurafenib and the BH3 Mimetic Navitoclax for BRAF-Mutant Thyroid Carcinoma

Thyroid. 2019 Apr;29(4):540-548. doi: 10.1089/thy.2018.0511.

Abstract

Background: Vemurafenib is a selective BRAF inhibitor (BRAFi) that has shown promising activity in BRAFV600E-positive papillary thyroid cancer (PTC). However, adverse events and resistance to a single-agent BRAFi often require discontinuation of the targeted therapy in BRAFV600E-positive PTC. Thus, this study investigated the expression of anti-apoptotic B-cell lymphoma 2 (BCL-2) family members, which are frequently overexpressed in many human cancers to inhibit apoptosis, in PTC harboring the BRAFV600E mutation after BRAFi treatment, and then evaluated the cytotoxic effects of a homology 3 domain (BH3)-mimetic in combination with a BRAFi.

Methods: K1 cells (BRAFV600E-positive human PTC) were treated with various concentrations of vemurafenib to investigate the effect of the BRAFi. In addition, the study analyzed the protein expression profiles of phosphorylated ERK1/2 (p-ERK 1/2) and anti-apoptotic BCL-2 family after vemurafenib treatment and selected the target anti-apoptotic protein. Antitumor effects were measured by cell counting, and effects on apoptosis were determined by terminal deoxynucleotidyl transferase-mediated dUTP nick-end labeling assay and Western blot analysis.

Results: At a concentration of 10 μM, vemurafenib inhibited the growth of K1 cells by 49.4%. Western blot analysis following exposure to 10 μM vemurafenib revealed that p-ERK1/2 gradually decreased over 24 hours, but the expression of B-cell lymphoma-extralarge (BCL-XL) and BCL-2 increased after 12 hours of treatment. Based on this result, the K1 cells were treated with navitoclax (BCL-2/BCL-XL inhibitor) for 24 hours up to a concentration of 4 μM, which resulted in negligible effects on cell survival. However, a combination treatment of 0.5 μM navitoclax with 1 μM vemurafenib resulted in significantly enhanced cell growth inhibition and increased apoptosis.

Conclusions: The results of the present study show that vemurafenib increased the expression of anti-apoptotic proteins of the BCL-2 family. Thus, the combination of vemurafenib with navitoclax may be effective in BRAFV600E-positive PTC treatment.

Keywords: navitoclax; papillary thyroid cancer; proto-oncogene proteins B-raf; thyroid neoplasms; vemurafenib.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Aniline Compounds / pharmacology*
  • Antineoplastic Combined Chemotherapy Protocols / pharmacology*
  • Apoptosis / drug effects
  • Apoptosis Regulatory Proteins / metabolism
  • Biomarkers, Tumor / antagonists & inhibitors*
  • Biomarkers, Tumor / genetics
  • Carcinoma / drug therapy*
  • Carcinoma / enzymology
  • Carcinoma / genetics
  • Carcinoma / pathology
  • Cell Line, Tumor
  • Cell Proliferation / drug effects
  • Drug Synergism
  • Genetic Predisposition to Disease
  • Humans
  • Mutation
  • Proto-Oncogene Mas
  • Proto-Oncogene Proteins B-raf / antagonists & inhibitors*
  • Proto-Oncogene Proteins B-raf / genetics
  • Signal Transduction
  • Sulfonamides / pharmacology*
  • Thyroid Neoplasms / drug therapy*
  • Thyroid Neoplasms / enzymology
  • Thyroid Neoplasms / genetics
  • Thyroid Neoplasms / pathology
  • Vemurafenib / pharmacology*

Substances

  • Aniline Compounds
  • Apoptosis Regulatory Proteins
  • Biomarkers, Tumor
  • MAS1 protein, human
  • Proto-Oncogene Mas
  • Sulfonamides
  • Vemurafenib
  • BRAF protein, human
  • Proto-Oncogene Proteins B-raf
  • navitoclax