BRAF V600E Mutation Is Associated with Preferential Sensitivity to Mitogen-Activated Protein Kinase Kinase Inhibition in Thyroid Cancer Cell Lines

Department of Medicine and Human Oncology and Pathogenesis Program, Memorial Sloan-Kettering Cancer Center, 1275 York Avenue, New York, NY 10021, USA.
Journal of Clinical Endocrinology &amp Metabolism (Impact Factor: 6.21). 07/2008; 93(6):2194-201. DOI: 10.1210/jc.2007-2825
Source: PubMed


Mutually exclusive mutations of RET, RAS, or BRAF are present in about 70% of papillary thyroid carcinomas, whereas only the latter two are seen in poorly differentiated and anaplastic cancers. Although the signal output common to these oncoproteins is ERK, a recent report showed that only BRAF mutations consistently predicted responsiveness to MAPK kinase (MEK) inhibitors.
Here we investigated whether sensitivity to MEK inhibition was determined by oncogene status in 13 human thyroid cancer cell lines: four with BRAF mutations, four RAS, one RET/PTC1, and four wild type.
Growth of BRAF (+) cells was inhibited by the MEK antagonist PD0325901 with an IC(50) of less than 5 nm. By contrast, RAS, RET/PTC1, or wild-type cells had IC(50) of 4 nm to greater than 1000 nm. Sensitivity was not predicted by coexisting mutations in PIK3CA or by PTEN status. Similar effects were obtained with the MEK inhibitor AZD6244. PD0325901 induced a sustained G1/S arrest in BRAF (+) but not BRAF (-) lines. PD0325901 was equipotent at inhibiting pERK1/2 after 2 h, regardless of genetic background, but pERK rebounded at 24 h in most lines. MEK inhibitor resistance was associated with partial refractoriness of pERK to further inhibition by the compounds. AZD6244 was more potent at inhibiting growth of NPA (BRAF +) than Cal62 (KRAS +) xenografts.
Thyroid cancers with BRAF mutation are preferentially sensitive to MEK inhibitors, whereas tumors with other MEK-ERK effector pathway gene mutations have variable responses, either because they are only partially dependent on ERK and/or because feedback responses elicit partial refractoriness to MEK inhibition.

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Available from: Neal Rosen, May 11, 2014
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    • "Many genetic alterations have been implicated in thyroid cancer, and the aberrant activation of the Ras-Raf-ERK pathway is most frequent [43]. Inhibition of the MAPK pathway arrests thyroid cancer cells in G1 phase [44]. Therefore, a plausible explanation for our results is that ERK1/2 inhibition increased susceptibility of thyroid cancer cells to other mechanisms of growth inhibition like cell cycle arrest and necrosis, which do not involve caspase activation. "
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    ABSTRACT: Local anesthetics are frequently used in fine-needle aspiration of thyroid lesions and locoregional control of persistent or recurrent thyroid cancer. Recent evidence suggests that local anesthetics have a broad spectrum of effects including inhibition of cell proliferation and induction of apoptosis in neuronal and other types of cells. In this study, we demonstrated that treatment with lidocaine and bupivacaine resulted in decreased cell viability and colony formation of both 8505C and K1 cells in a dose-dependent manner. Lidocaine and bupivacaine induced apoptosis, and necrosis in high concentrations, as determined by flow cytometry. Lidocaine and bupivacaine caused disruption of mitochondrial membrane potential and release of cytochrome c, accompanied by activation of caspase 3 and 7, PARP cleavage, and induction of a higher ratio of Bax/Bcl-2. Based on microarray and pathway analysis, apoptosis is the prominent transcriptional change common to lidocaine and bupivacaine treatment. Furthermore, lidocaine and bupivacaine attenuated extracellular signal-regulated kinase 1/2 (ERK1/2) activity and induced activation of p38 mitogen-activated protein kinase (MAPK) and c-jun N-terminal kinase. Pharmacological inhibitors of MAPK/ERK kinase and p38 MAPK suppressed caspase 3 activation and PARP cleavage. Taken together, our results for the first time demonstrate the cytotoxic effects of local anesthetics on thyroid cancer cells and implicate the MAPK pathways as an important mechanism. Our findings have potential clinical relevance in that the use of local anesthetics may confer previously unrecognized benefits in the management of patients with thyroid cancer.
    PLoS ONE 02/2014; 9(2):e89563. DOI:10.1371/journal.pone.0089563 · 3.23 Impact Factor
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    • "mutation are sensitive to MEK inhibitors (Sebolt-Leopold et al., 1999; Leboeuf et al., 2008; Pratilas et al., 2008; Solit et al., 2006). However, these drugs inhibit ERK signaling in all cells, and toxicity to normal tissue limits their dosing and their therapeutic effects (Kirkwood et al., 2012). "
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    ABSTRACT: BRAF(V600E) drives tumors by dysregulating ERK signaling. In these tumors, we show that high levels of ERK-dependent negative feedback potently suppress ligand-dependent mitogenic signaling and Ras function. BRAF(V600E) activation is Ras independent and it signals as a RAF-inhibitor-sensitive monomer. RAF inhibitors potently inhibit RAF monomers and ERK signaling, causing relief of ERK-dependent feedback, reactivation of ligand-dependent signal transduction, increased Ras-GTP, and generation of RAF-inhibitor-resistant RAF dimers. This results in a rebound in ERK activity and culminates in a new steady state, wherein ERK signaling is elevated compared to its initial nadir after RAF inhibition. In this state, ERK signaling is RAF inhibitor resistant, and MEK inhibitor sensitive, and combined inhibition results in enhancement of ERK pathway inhibition and antitumor activity.
    Cancer cell 11/2012; 22(5):668-82. DOI:10.1016/j.ccr.2012.10.009 · 23.52 Impact Factor
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    • "Both AZD1480 and AZD6244 had a minimal effect on the growth of a RAS- mutant cell line, C643. The insensitivity of RET-activated thyroid cancer cells to MEK inhibition has been previously demonstrated, as opposed to the high sensitivity of thyroid cancer cells expressing BRAFV600E [31]. This resistance might reflect the ability of oncogenic RET to activate alternative signaling pathways, particularly the PI3K/AKT/mTOR pathway [32]. "
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    ABSTRACT: Persistent RET activation is a frequent event in papillary thyroid carcinoma (PTC) and medullary thyroid carcinoma (MTC). In these cancers, RET activates the ERK/MAPK, the PI3K/AKT/mTOR and the JAK/STAT3 pathways. Here, we tested the efficacy of a JAK1/2- inhibitor, AZD1480, in the in vitro and in vivo growth of thyroid cancer cell lines expressing oncogenic RET. Thyroid cancer cell lines harboring RET/PTC1 (TPC-1), RET M918T (MZ-CRC1) and RET C634W (TT) alterations, as well as TPC-1 xenografts, were treated with JAK inhibitor, AZD1480. This inhibitor led to growth inhibition and/or apoptosis of the thyroid cancer cell lines in vitro, as well as to tumor regression of TPC-1 xenografts, where it efficiently blocked STAT3 activation in tumor and stromal cells. This inhibition was associated with decreased proliferation, decreased blood vessel density, coupled with increased necrosis. However, AZD1480 repressed the growth of STAT3- deficient TPC-1 cells in vitro and in vivo, demonstrating that its effects in this cell line were independent of STAT3 in the tumor cells. In all cell lines, the JAK inhibitor reduced phospho-Y1062 RET levels, and mTOR effector phospho-S6, while JAK1/2 downregulation by siRNA did not affect cell growth nor RET and S6 activation. In conclusion, AZD1480 effectively blocks proliferation and tumor growth of activated RET- thyroid cancer cell lines, likely through direct RET inhibition in cancer cells as well as by modulation of the microenvironment (e.g. via JAK/phospho-STAT3 inhibition in endothelial cells). Thus, AZD1480 should be considered as a therapeutic agent for the treatment of RET- activated thyroid cancers.
    PLoS ONE 10/2012; 7(10):e46869. DOI:10.1371/journal.pone.0046869 · 3.23 Impact Factor
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