BRAFV600E Papillary Thyroid Carcinoma Research Articles

Mcl-1 mediates intrinsic resistance to RAF inhibitors in mutant BRAF papillary thyroid carcinoma

Papillary thyroid carcinoma (PTC) is the most frequent form of thyroid cancer. PTC commonly presents with mutations of the serine/threonine kinase BRAF (BRAFV600E), which drive ERK1/2 pathway activation to support growth and suppress apoptosis. PTC patients often undergo surgical resection; however, since the average age of PTC patients is under 50, adverse effects associated with prolonged maintenance therapy following total thyroidectomy are a concern. The development of mutant-selective BRAF inhibitors (BRAFi), like vemurafenib, has been efficacious in patients with metastatic melanoma, but the response rate is low for mutant BRAF PTC patients. Here, we assay the therapeutic response of BRAFi in a panel of human PTC cell lines and freshly biopsied patient samples. We observed heterogeneous responses to BRAFi, and multi-omic comparisons between susceptible and resistant mutant BRAF PTC revealed overrepresented stress response pathways and the absence of compensatory RTK activation – features that may underpin innate resistance. Importantly, resistant cell lines and patient samples had increased hallmarks of failed apoptosis; a cellular state defined by sublethal caspase activation and DNA damage. Further analysis suggests that the failed apoptotic phenotypes may have features of “minority mitochondrial outer membrane permeabilization (MOMP)” – a stress-related response characterized by fragmented and porous mitochondria known to contribute to cancer aggressiveness. We found that cells presenting with minority MOMP-like phenotypes are dependent on the apoptotic regulator, Mcl-1, as treatment with the Mcl-1 inhibitor, AZD5991, potently induced cell death in resistant cells. Furthermore, PI3K/AKT inhibitors sensitized resistant cells to BRAFi; an effect that was at least in part associated with reduced Mcl-1 levels. Together, these data implicate minority MOMP as a mechanism associated with intrinsic drug resistance and underscore the benefits of targeting Mcl-1 in mutant BRAF PTC.

Identification of R-Spondin Gene Signature Predictive of Metastatic Progression in BRAFV600E-Positive Papillary Thyroid Cancer.

Papillary thyroid carcinoma (PTC) is the most common malignancy of the thyroid gland and early stages are curable. However, a subset of PTCs shows an unusually aggressive phenotype with extensive lymph node metastasis and higher incidence of locoregional recurrence. In this study, we investigated a large cohort of PTC cases with an unusual aggressive phenotype using a high-throughput RNA sequencing (RNA-Seq) to identify differentially regulated genes associated with metastatic PTC. All metastatic PTC with mutated BRAF (V600E) but not BRAF wild-type expressed an up-regulation of R-Spondin Protein 4 (RSPO4) concomitant with an upregulation of genes involved in focal adhesion and cell-extracellular matrix signaling. Further immunohistochemistry validation confirmed the upregulation of these target genes in metastatic PTC cases. Preclinical studies using established PTC cell lines support that RSPO4 overexpression is associated with BRAF V600E mutation and is a critical upstream event that promote activation of kinases of focal adhesion signaling known to drive cancer cell locomotion and invasion. This finding opens up the potential of co-targeting B-Raf, RSPO and focal adhesion proteins as a pharmacological approach for aggressive BRAF V600E PTC.

Imbalance in DNA repair machinery is associated with BRAFV600E mutation and tumor aggressiveness in papillary thyroid carcinoma.

The involvement of alterations in MLH1, an essential mismatch repair component, in BRAFV600E mutated papillary thyroid carcinoma (PTC) has been suggested to be associated with features of tumor aggressiveness. Thirty-two PTC and surrounding normal thyroid tissues were evaluated for 11 representative DNA repair genes expression. BRAFV600E mutational status assessment and clinicopathological correlations were evaluated for their gene and protein expression. BRAFV600E PTC is associated with lower levels of XPD and MLH1 gene expression. Decrease in MLH1 and XPD mRNA levels in BRAFV600E PTC (but not their protein products) are associated with predictors of poor patient outcomes. Considering the complete subset of patients, MGMT and XRCC2 genes were shown down and upregulated, respectively, in PTC tissues. Low expression of MGMT gene and weak XRCC2 protein expression were correlated with characteristics of tumor aggressiveness. These results suggest that an imbalance in DNA repair gene expression in PTC is associated with aggressive clinicopathological features and BRAFV600E mutation.

Strong immunoexpression of midkine is associated with multiple lymph node metastases in BRAFV600E papillary thyroid carcinoma.

e17552Background: Midkine is a multifunctional, heparin-binding growth factor that is frequently expressed in patients with malignancies but is undetectable in healthy adults. In various cancers, h...

Long-term vemurafenib treatment drives inhibitor resistance through a spontaneous KRAS G12D mutation in a BRAF V600E papillary thyroid carcinoma model.

The BRAF V600E mutation is commonly observed in papillary thyroid cancer (PTC) and predominantly activates the MAPK pathway. Presence of BRAF V600E predicts increasing risk of recurrence and higher mortality rate, and treatment options for such patients are limited. Vemurafenib, a BRAF V600E inhibitor, is initially effective, but cells inevitably develop alternative mechanisms of pathway activation. Mechanisms of primary resistance have been described in short-term cultures of PTC cells; however, mechanisms of acquired resistance have not. In the present study, we investigated possible adaptive mechanisms of BRAF V600E inhibitor resistance in KTC1 thyroid cancer cells following long-term vemurafenib exposure. We found that a subpopulation of KTC1 cells acquired resistance to vemurafenib following 5 months of treatment with the inhibitor. Resistance coincided with the spontaneous acquisition of a KRAS G12D activating mutation. Increases in activated AKT, ERK1/2, and EGFR were observed in these cells. In addition, the resistant cells were less sensitive to combinations of vemurafenib and MEK1 inhibitor or AKT inhibitor. These results support the KRAS G12D mutation as a genetic mechanism of spontaneously acquired secondary BRAF inhibitor resistance in BRAF V600E thyroid cancer cells.

Strong immunoexpression of midkine is associated with multiple lymph node metastases in BRAFV600E papillary thyroid carcinoma.

Midkine is a multifunctional, heparin-binding growth factor that is frequently expressed in patients with malignancies but is undetectable in healthy adults. In various cancers, high expression of midkine is associated with aggressive clinical behavior and a poor prognosis. In the present study, we investigated the expression of midkine in papillary thyroid carcinoma (PTC) and assessed its association with a BRAFV600E mutation and the clinicopathological parameters. We determined the presence of a BRAFV600E mutation in 79 cases of PTC and examined the effects of the BRAFV600E mutation on midkine expression in primary thyrocytes. In addition, we evaluated the association between midkine expression and various clinicopathological parameters. We found that midkine is more frequently expressed in BRAFV600E PTC (68.3%) than in BRAF wild-type PTC (18.8%). BRAFV600E transduction could up-regulate midkine expression in primary thyrocytes. Moreover, midkine expression was associated with multiple lymph node (≥5) metastases in BRAFV600E PTC. In conclusion, our results suggest that midkine expression could be a clinically useful marker in predicting the presence of multiple lymph node metastases in BRAFV600E PTC.

Thyroid Targeted KrasG12D/Pten−/− Mice and Their Cell Lines: New Tools to Study Thyroid Cancer Biology

ThyroidVol. 21, No. 9 Editorials and CommentaryThyroid Targeted KrasG12D/Pten−/− Mice and Their Cell Lines: New Tools to Study Thyroid Cancer BiologyRebecca E. Schweppe and Bryan R. HaugenRebecca E. SchweppeSearch for more papers by this author and Bryan R. HaugenSearch for more papers by this authorPublished Online:30 Aug 2011https://doi.org/10.1089/thy.2011.2109.edAboutSectionsView articleView Full TextPDF/EPUB ToolsPermissionsDownload CitationsTrack CitationsAdd to favorites Back To Publication ShareShare onFacebookTwitterLinked InRedditEmail View articleFiguresReferencesRelatedDetailsCited byLong-term vemurafenib treatment drives inhibitor resistance through a spontaneous KRAS G12D mutation in a BRAF V600E papillary thyroid carcinoma model26 April 2016 | Oncotarget, Vol. 7, No. 21 Volume 21Issue 9Sep 2011 InformationCopyright 2011, Mary Ann Liebert, Inc.To cite this article:Rebecca E. Schweppe and Bryan R. Haugen.Thyroid Targeted KrasG12D/Pten−/− Mice and Their Cell Lines: New Tools to Study Thyroid Cancer Biology.Thyroid.Sep 2011.941-944.http://doi.org/10.1089/thy.2011.2109.edPublished in Volume: 21 Issue 9: August 30, 2011PDF download