Sustained ERK inhibition maximizes responses of BrafV600E thyroid cancers to radioiodine
James Nagarajah, … , Wolfgang A. Weber, James A. Fagin
James Nagarajah, … , Wolfgang A. Weber, James A. Fagin
Published September 26, 2016
Citation Information: J Clin Invest. 2016;126(11):4119-4124. https://doi.org/10.1172/JCI89067.
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Brief Report Oncology

Sustained ERK inhibition maximizes responses of BrafV600E thyroid cancers to radioiodine

Abstract

Radioiodide (RAI) therapy of thyroid cancer exploits the relatively selective ability of thyroid cells to transport and accumulate iodide. Iodide uptake requires expression of critical genes that are involved in various steps of thyroid hormone biosynthesis. ERK signaling, which is markedly increased in thyroid cancer cells driven by oncogenic BRAF, represses the genetic program that enables iodide transport. Here, we determined that a critical threshold for inhibition of MAPK signaling is required to optimally restore expression of thyroid differentiation genes in thyroid cells and in mice with BrafV600E-induced thyroid cancer. Although the MEK inhibitor selumetinib transiently inhibited ERK signaling, which subsequently rebounded, the MEK inhibitor CKI suppressed ERK signaling in a sustained manner by preventing RAF reactivation. A small increase in ERK inhibition markedly increased the expression of thyroid differentiation genes, increased iodide accumulation in cancer cells, and thereby improved responses to RAI therapy. Only a short exposure to the drug was necessary to obtain a maximal response to RAI. These data suggest that potent inhibition of ERK signaling is required to adequately induce iodide uptake and indicate that this is a promising strategy for the treatment of BRAF-mutant thyroid cancer.

Authors

James Nagarajah, Mina Le, Jeffrey A. Knauf, Giuseppe Ferrandino, Cristina Montero-Conde, Nagavarakishore Pillarsetty, Alexander Bolaender, Christopher Irwin, Gnana Prakasam Krishnamoorthy, Mahesh Saqcena, Steven M. Larson, Alan L. Ho, Venkatraman Seshan, Nobuya Ishii, Nancy Carrasco, Neal Rosen, Wolfgang A. Weber, James A. Fagin

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Figure 1

Profound inhibition of MAPK signaling is required to restore differentiated gene expression in thyroid PCCL3-BRAF cells and in murine BrafV600E-induced PTCs.

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Profound inhibition of MAPK signaling is required to restore differentia...
(A) Western blots of PCCL3-BRAF cells treated with dox for 4 days to induce BRAFV600E, and then for 3 days with the indicated concentrations (μM) of PLX4032 or U0126. (B) Graph shows loading-adjusted p-ERK vs. NIS levels from the Western blot. The large green and orange dots indicate the –dox and +dox conditions, respectively. (C and D) Western blots of PTCs from TPO-Cre LSL-BrafV600E mice treated with vehicle, AZD6244 (50 mg/kg twice per day), or CKI (1.5 mg/kg/d) for 3 days. On the fourth day tissues were harvested at the indicated times after dosing while remaining on the same treatment schedule. Vehicle lanes represent mice that never received active compound (they do not represent a time 0). (E) Western blots of TPO-Cre LSL-BrafV600E mouse PTCs (n = 3) treated with the indicated compounds for 4.5 days. Thyroid lobes were collected 2 hours after the final dose. (F and G) Quantitative RT-PCR of MAPK transcriptional output markers (F) or iodine metabolism–related genes (G) in thyroid tissues from mice treated with the indicated doses of AZD6244 (n = 3) or CKI (n = 5) for 4.5 days. Data represent percentage change in β-actin–normalized expression compared with vehicle-treated TPO-Cre LSL-BrafV600E (F) or wild-type mice (G). **P = 0.008, ***P = 0.0003, ****P < 0.0001, Mann-Whitney test. QD, once per day; BID, twice per day; tERK, total ERK.