Signaling pathways in follicular cell-derived thyroid carcinomas (review)

Management of radioiodine refractory differentiated thyroid cancer: the Latin American perspective

Radioiodine (RAI) refractory differentiated thyroid cancer is an uncommon and challenging situation that requires a multidisciplinary approach to therapeutic strategies. The definition of RAI-refractoriness is usually a clear situation in specialized centers. However, the right moment for initiation of multikinase inhibitors (MKI), the time and availability for genomic testing, and the possibility of prescribing MKI and selective kinase inhibitors differ worldwide.Latin America (LA) refers to the territories of the world that stretch across two regions: North America (including Central America and the Caribbean) and South America, containing 8.5% of the world's population. In this manuscript, we critically review the current standard approach recommended for patients with RAI refractory differentiated thyroid cancer, emphasizing the challenges faced in LA. To achieve this objective, the Latin American Thyroid Society (LATS) convened a panel of experts from Brazil, Argentina, Chile, and Colombia. Access to MKI compounds continues to be a challenge in all LA countries. This is true not only for MKI but also for the new selective tyrosine kinase inhibitor, which will also require genomic testing, that is not widely available. Thus, as precision medicine advances, significant disparities will be made more evident, and despite efforts to improve coverage and reimbursement, molecular-based precision medicine remains inaccessible to most of the LA population. Efforts should be undertaken to alleviate the discrepancies between the current state-of-the-art care for RAI-refractory differentiated thyroid cancer and the present situation in Latin America.

Dual targeting of MAPK and PI3K pathways unlocks redifferentiation of Braf-mutated thyroid cancer organoids

Thyroid cancer is the most common endocrine malignancy and several genetic events have been described to promote the development of thyroid carcinogenesis. Besides the effects of specific mutations on thyroid cancer development, the molecular mechanisms controlling tumorigenesis, tumor behavior, and drug resistance are still largely unknown. Cancer organoids have been proposed as a powerful tool to study aspects related to tumor development and progression and appear promising to test individual responses to therapies. Here, using mESC-derived thyroid organoids, we developed a BrafV637E-inducible model able to recapitulate the features of papillary thyroid cancer in vitro. Overexpression of the murine BrafV637E mutation, equivalent to BrafV600E in humans, rapidly triggers to MAPK activation, cell dedifferentiation, and disruption of follicular organization. BrafV637E-expressing organoids show a transcriptomic signature for p53, focal adhesion, ECM-receptor interactions, EMT, and inflammatory signaling pathways. Finally, PTC-like thyroid organoids were used for drug screening assays. The combination of MAPK and PI3K inhibitors reversed BrafV637E oncogene-promoted cell dedifferentiation while restoring thyroid follicle organization and function in vitro. Our results demonstrate that pluripotent stem cells-derived thyroid cancer organoids can mimic tumor development and features while providing an efficient tool for testing novel targeted therapies.

Uncovering Actions of Type 3 Deiodinase in the Metabolic Dysfunction-Associated Fatty Liver Disease (MAFLD)

Metabolic dysfunction-associated fatty liver disease (MAFLD) has gained worldwide attention as a public health problem. Nonetheless, lack of enough mechanistic knowledge restrains effective treatments. It is known that thyroid hormone triiodothyronine (T3) regulates hepatic lipid metabolism, and mitochondrial function. Liver dysfunction of type 3 deiodinase (D3) contributes to MAFLD, but its role is not fully understood. Objective: To evaluate the role of D3 in the progression of MAFLD in an animal model. Methodology: Male/adult Sprague Dawley rats (n = 20) were allocated to a control group (2.93 kcal/g) and high-fat diet group (4.3 kcal/g). Euthanasia took place on the 28th week. D3 activity and expression, Uncoupling Protein 2 (UCP2) and type 1 deiodinase (D1) expression, oxidative stress status, mitochondrial, Krebs cycle and endoplasmic reticulum homeostasis in liver tissue were measured. Results: We observed an increase in D3 activity/expression (p < 0.001) related to increased thiobarbituric acid reactive substances (TBARS) and carbonyls and diminished reduced glutathione (GSH) in the MAFLD group (p < 0.05). There was a D3-dependent decrease in UCP2 expression (p = 0.01), mitochondrial capacity, respiratory activity with increased endoplasmic reticulum stress in the MAFLD group (p < 0.001). Surprisingly, in an environment with lower T3 levels due to high D3 activity, we observed an augmented alpha-ketoglutarate dehydrogenase (KGDH) and glutamate dehydrogenase (GDH) enzymes activity (p < 0.05). Conclusion: Induced D3, triggered by changes in the REDOX state, decreases T3 availability and hepatic mitochondrial capacity. The Krebs cycle enzymes were altered as well as endoplasmic reticulum stress. Taken together, these results shed new light on the role of D3 metabolism in MAFLD.

Recapitulating thyroid cancer histotypes through engineering embryonic stem cells

Thyroid carcinoma (TC) is the most common malignancy of endocrine organs. The cell subpopulation in the lineage hierarchy that serves as cell of origin for the different TC histotypes is unknown. Human embryonic stem cells (hESCs) with appropriate in vitro stimulation undergo sequential differentiation into thyroid progenitor cells (TPCs-day 22), which maturate into thyrocytes (day 30). Here, we create follicular cell-derived TCs of all the different histotypes based on specific genomic alterations delivered by CRISPR-Cas9 in hESC-derived TPCs. Specifically, TPCs harboring BRAF^V600E or NRAS^Q61R mutations generate papillary or follicular TC, respectively, whereas addition of TP53^R248Q generate undifferentiated TCs. Of note, TCs arise by engineering TPCs, whereas mature thyrocytes have a very limited tumorigenic capacity. The same mutations result in teratocarcinomas when delivered in early differentiating hESCs. Tissue Inhibitor of Metalloproteinase 1 (TIMP1)/Matrix metallopeptidase 9 (MMP9)/Cluster of differentiation 44 (CD44) ternary complex, in cooperation with Kisspeptin receptor (KISS1R), is involved in TC initiation and progression. Increasing radioiodine uptake, KISS1R and TIMP1 targeting may represent a therapeutic adjuvant option for undifferentiated TCs.

MAPK Inhibition Requires Active RAC1 Signaling to Effectively Improve Iodide Uptake by Thyroid Follicular Cells

Simple Summary

The Sodium/Iodide Simulator (NIS) is responsible for the uptake of iodide in the thyroid follicular cells. NIS is present in most differentiated thyroid carcinomas (DTC), allowing radioactive iodine (RAI) to be used to destroy malignant cells. However, a significant proportion of DTCs stop picking up iodide and become resistant to RAI therapy. This is mainly due to the symporter no longer being produced or not being placed correctly at the cell’s membrane. This has been associated with mechanisms linked to malignant transformation, namely the overactivation of the so-called MAPK pathway. Thus, several drugs have been developed to inhibit this pathway, attempting to increase NIS levels and iodide uptake. However, MAPK inhibitors have had only partial success in restoring NIS expression. We found that the activity of another protein, the small GTPase RAC1, has an important role in this process, determining the outcome of MAPK inhibitors. Thus, our findings open new opportunities to find effective therapeutic alternatives for DTC resistant to RAI.

Abstract

The Sodium/Iodide Symporter (NIS) is responsible for the active transport of iodide into thyroid follicular cells. Differentiated thyroid carcinomas (DTCs) usually preserve the functional expression of NIS, allowing the use of radioactive iodine (RAI) as the treatment of choice for metastatic disease. However, a significant proportion of patients with advanced forms of TC become refractory to RAI therapy and no effective therapeutic alternatives are available. Impaired iodide uptake is mainly caused by the defective functional expression of NIS, and this has been associated with several pathways linked to malignant transformation. MAPK signaling has emerged as one of the main pathways implicated in thyroid tumorigenesis, and its overactivation has been associated with the downregulation of NIS expression. Thus, several strategies have been developed to target the MAPK pathway attempting to increase iodide uptake in refractory DTC. However, MAPK inhibitors have had only partial success in restoring NIS expression and, in most cases, it remained insufficient to allow effective treatment with RAI. In a previous work, we have shown that the activity of the small GTPase RAC1 has a positive impact on TSH-induced NIS expression and iodide uptake in thyroid cells. RAC1 is a downstream effector of NRAS, but not of BRAF. Therefore, we hypothesized that the positive regulation induced by RAC1 on NIS could be a relevant signaling cue in the mechanism underlying the differential response to MEK inhibitors, observed between NRAS- and BRAF-mutant tumors. In the present study, we found that the recovery of NIS expression induced through MAPK pathway inhibition can be enhanced by potentiating RAC1 activity in thyroid cell systems. The negative impact on NIS expression induced by the MAPK-activating alterations, NRAS Q61R and BRAF V600E, was partially reversed by the presence of the MEK 1/2 inhibitors AZD6244 and CH5126766. Notably, the inhibition of RAC1 signaling partially blocked the positive impact of MEK inhibition on NIS expression in NRAS Q61R cells. Conversely, the presence of active RAC1 considerably improved the rescue of NIS expression in BRAF V600E thyroid cells treated with MEK inhibitors. Overall, our data support an important role for RAC1 signaling in enhancing MAPK inhibition in the context of RAI therapy in DTC, opening new opportunities for therapeutic intervention.

The BRAFV600E mutation analysis and risk stratification in papillary thyroid carcinoma

OBJECTIVE

Although the prognostic role of BRAFV600E mutation in papillary thyroid carcinoma (PTC) is controversial, the American Thyroid Association (ATA) includes the mutational status in their risk stratification system. To evaluate the impact of the BRAFV600E mutation status on PTC risk stratification.

METHODS

PTC patients attending a university-based hospital who had the analysis of the BRAFV600E mutation were included. Persistent disease was defined as the presence of biochemical or structural disease. The performance of the ATA risk stratification system on predicting persistent disease with or without the BRAFV600E mutation status information was evaluated.

RESULTS

Of the 134 patients evaluated, 44 (32.8%) carried BRAFV600E mutation. The median tumor size was 1.7 cm (P25-75 1.0-3.0), 64 (47.8%) patients had lymph node, and 11 (8.2%) distant metastases. According to the ATA risk stratification system, patients were classified as low, intermediate, and high risk in 55 (41%), 59 (44%), and 20 (14%) patients, respectively. The data on BRAFV600E mutation reclassified 12 (8.9%) patients from low to intermediate risk. After a median follow-up of 8.5 years, the prevalence of persistent disease was similar in patients with and without BRAFV600E mutation (P = 0.42). Multivariate analysis failed to demonstrate an association between the BRAFV600E mutation and persistent disease status (RR 0.96; 95%CI 0.47-1.94). Notably, none of the patients reclassified from low to intermediate risk showed persistent disease on follow-up.

CONCLUSION

Inclusion of BRAFV600E mutational status has a limited impact on risk stratification and does not add to the prediction of outcomes in PTC patients.

Associations of urinary phthalate metabolites with risk of papillary thyroid cancer

Some studies have revealed thyrotoxicity of phthalates; however, associations of phthalate exposure with papillary thyroid cancer (PTC) remain unclear. We conducted a pair-matching case-control study of 111 PTC cases and 111 age- and sex-matched non-PTC controls to examine associations between urinary concentrations of phthalate metabolites and PTC. Phthalate metabolites were determined in fasting urine specimens by ultra-performance liquid chromatography - tandem mass spectrometry (UPLC-MS/MS). After adjusting for potential confounders and other phthalate metabolites, the concentrations of the sum of di (2-ethylhexly) phthalate (DEHP) metabolites in urine were positively associated with PTC [odds ratio (OR) = 5.35; 95% confidence interval (CI): 1.61-17.83], suggesting the effect of phthalates exposure on PTC development. The findings require confirmation.

Polymorphism in lncRNA AC016683.6 and its interaction with smoking exposure on the susceptibility of lung cancer

Background

Long non-coding RNAs play pivotal roles in the carcinogenesis of multiple types of cancers. This study is firstly to evaluate influence of rs4848320 and rs1110839 polymorphisms in long non-coding RNA AC016683.6 on the susceptibility of lung cancer.

Methods

The present study was a hospital-based case–control study with 434 lung cancer patients and 593 cancer-free controls. Genotyping of the two SNPs detected by Taqman^® allelic discrimination method.

Results

There were no statistically significant associations between rs4848320 and rs1110839 polymorphisms in AC016683.6 and risk of lung cancer in overall population. However, in the smoking population, rs4848320 and rs1110839 polymorphisms significantly increased the risk of lung cancer in dominant and homozygous models (Rs4848320: P = 0.029; Rs1110839: P = 0.034), respectively. In male population, rs1110839 genetic variant was related to the risk of lung cancer in all genetic models (GG vs. TT: P = 0.008; Dominant model: P = 0.029; Recessive model: P = 0.027) rather than heterozygous model. The crossover analyses provided rs4848320 and rs1110839 risk genotypes carriers combined with smoking exposure 2.218-fold, 1.755-fold increased risk of lung cancer (Rs4848320: P = 0.005; Rs1110839: P = 0.017). Additionally, there were significantly positive multiplicative interaction of rs4848320 polymorphism with smoking status, with adjusted OR of 2.244 (1.162–4.334), but rs1110839 polymorphism did not exist.

Conclusions

Rs4848320 and rs1110839 polymorphisms may be associated with lung cancer susceptibility. Interaction of rs4848320 risk genotypes with smoking exposure may strengthen the risk effect on lung cancer.

Role of thyroid hormones in the neoplastic process: an overview

Thyroid hormones (TH) are critical regulators of several physiological processes, which include development, differentiation and growth in virtually all tissues. In past decades, several studies have shown that changes in TH levels caused by thyroid dysfunction, disruption of deiodinases and/or thyroid hormone receptor (TR) expression in tumor cells, influence cell proliferation, differentiation, survival and invasion in a variety of neoplasms in a cell type-specific manner. The function of THs and TRs in neoplastic cell proliferation involves complex mechanisms that seem to be cell specific, exerting effects via genomic and nongenomic pathways, repressing or stimulating transcription factors, influencing angiogenesis and promoting invasiveness. Taken together, these observations indicate an important role of TH status in the pathogenesis and/or development of human neoplasia. Here, we aim to present an updated and comprehensive picture of the accumulated knowledge and the current understanding of the potential role of TH status on the different hallmarks of the neoplastic process.

Anaplastic Thyroid Carcinoma Treated with Lenvatinib

OBJECTIVE

We report a case of anaplastic thyroid carcinoma (ATC) with local recurrence and distant metastasis that responded very well to treatment with lenvatinib, a new molecular-targeted anticancer drug.

CASE REPORT

A 91-year-old Japanese woman presented with a 5-month history of a painless mass in her left anterior neck. She had a past history of total thyroidectomy and neck dissection for papillary carcinoma of the thyroid. Here she underwent neck dissection, and the histopathological diagnosis was lymph node metastasis of papillary carcinoma with anaplastic transformation. Five months later, a cervical lymph node swelled up again. Computed tomography demonstrated an enhanced mass in the neck and multiple nodules in both lungs. Recurrent ATC with multiple lung metastases was diagnosed, and molecular-targeted therapy with lenvatinib was initiated. The neck tumor reduced in 1 week, and the pulmonary nodules became completely hollow within 1 month. However, we had to discontinue lenvatinib because of severe side effects including high blood pressure, hypocalcemia, and hypoalbuminemia. Soon after discontinuation, the side effects subsided, but the tumor rapidly regrew. The patient died of lymphangiosis carcinomatosa 6 days after discontinuation.

CONCLUSION

Although recent advances in molecular-targeted therapy have provided powerful cancer therapy tools, the negative side of this therapy must be addressed.

15-Deoxy-Δ12,14-prostaglandin J2 inhibits migration of human thyroid carcinoma cells by disrupting focal adhesion complex and adherens junction

Metastasis is frequently observed in human follicular thyroid carcinoma. The present study investigated the peroxisome proliferator-activated receptor γ agonist, 15-deoxy-Δ^12,14-prostaglandin J² (15d-PGJ₂), and its effect on the migration of CGTH W-2 human thyroid carcinoma cells. 15d-PGJ₂ decreased the survival rate of CGTH W-2 cells in a dose-dependent manner. The Transwell migration assay demonstrated that 15d-PGJ₂ reduced the migration rate of CGTH W-2 cells by 35% following treatment with 30 µM 15d-PGJ₂ compared with control cells. The cell adhesion assay indicated that, following 15d-PGJ₂ treatment for 24 h, cell adhesion decreased by 26% compared with the control group. The expression levels of focal adhesion proteins, including integrin β1, phospho-focal adhesion kinase and p-paxillin, were downregulated following treatment with 15d-PGJ₂. Immunostaining revealed that the puncta of vinculin were reduced and the actin stress fiber was disassembled following 15d-PGJ₂ treatment. By contrast, p120-catenin (p120-ctn) and β-catenin levels staining accumulated in the region of the lamellipodium following 15d-PGJ₂ treatment. Membrane fractionation revealed that p120-ctn and N-cadherin were decreased in the cell membrane, but increased in the cytoplasm of 15d-PGJ₂-treated cells. Therefore, 15d-PGJ₂ inhibited human thyroid carcinoma cell migration and this may be due to the impairment of focal adhesion complexes and the accumulation of p120-ctn in the cytoplasm in the region of the lamellipodium.

RAC1b overexpression stimulates proliferation and NF-kB-mediated anti-apoptotic signaling in thyroid cancer cells

Overexpression of tumor-associated RAC1b has been recently highlighted as one of the most promising targets for therapeutic intervention in colon, breast, lung and pancreatic cancer. RAC1b is a hyperactive variant of the small GTPase RAC1 and has been recently shown to be overexpressed in a subset of papillary thyroid carcinomas associated with unfavorable outcome. Using the K1 PTC derived cell line as an in vitro model, we observed that both RAC1 and RAC1b were able to induce a significant increase on NF-kB and cyclin D1 reporter activity. A clear p65 nuclear localization was found in cells transfected with RAC1b-WT, confirming NF-kB canonical pathway activation. Consistently, we observed a RAC1b-mediated decrease in IκBα (NF-kB inhibitor) protein levels. Moreover, we show that RAC1b overexpression stimulates G1/S progression and protects thyroid cells against induced apoptosis, the latter through a process involving the NF-kB pathway. Present data support previous findings suggesting an important role for RAC1b in the development of follicular cell-derived thyroid malignancies and point out NF-kB activation as one of the molecular mechanisms associated with the pro-tumorigenic advantage of RAC1b overexpression in thyroid carcinomas.

Promotion of metastasis of thyroid cancer cells via NRP-2-mediated induction

Tumor-node-metastasis is one of the leading causes of morbidity and mortality in thyroid cancer patients. Upregulation of vascular endothelial growth factor-C (VEGF-C) increases the migratory ability of thyroid cancer cells to lymph nodes. Expression of neuropilin-2 (NRP-2), the co-receptor of VEGF-C, has been reported to be correlated with lymph node metastasis in human thyroid cancer. The present study investigated the role of VEGF-C/NRP-2 signaling in the regulation of metastasis of two different types of human thyroid cancer cells. The results indicated that the VEGF-C/NRP-2 axis significantly promoted the metastatic activities of papillary thyroid carcinoma cells through the activation of the mitogen-activated protein kinase (MAPK) kinase (MEK)/extracellular signal-regulated kinase and p38 MAPK signaling cascades. However, neither MEK or p38 MAPK inhibitors produced significant inhibition of the migratory activity and invasiveness regulated by the VEGF-C/NRP-2 axis in follicular thyroid carcinoma cells. Finally, VEGF-C/NRP-2-mediated invasion and migration of thyroid cancer cells required the expression of NRP-2. The present results demonstrate that the promotion of metastasis by VEGF-C is mainly due to the upregulation of NRP-2 in thyroid cancer cells, and this metastatic activity regulated by the VEGF-C/NRP-2 axis provides further insight into the process of tumor metastasis.

Prognostic markers and response to vandetanib therapy in sporadic medullary thyroid cancer patients

OBJECTIVE

Medullary thyroid carcinoma (MTC) occurs sporadically in 75% of patients. Metastatic disease is associated with significantly poorer survival. The aim of this study was to identify prognostic markers for progressive MTC and oncogenic factors associated with response to vandetanib therapy.

DESIGN AND METHODS

Clinical courses of 32 patients with sporadic MTC (n=10 pN0cM0, n=8 pN1cM0, n=14 pN1cM1) were compared with genetic profiles of the patients' primary tumour tissue. Analysis for RET proto-oncogene mutations was performed by Sanger sequencing and next-generation sequencing (NGS). The mRNA expression (mRNA count) of 33 targets was measured by nCounter NanoString analysis.

RESULTS

Somatic RET mutations occurred in 21/32 patients. The RET918 mutation was found in 8/14 pN1cM1 patients. BRAF (P=0.019), FGFR2 (P=0.007), FGFR3 (P=0.044) and VEGFC (P=0.042) mRNA expression was significantly lower in pN1cM0/pN1cM1 compared with pN0cM0 patients, whereas PDGFRA (P=0.026) mRNA expression was significantly higher in pN1cM0/pN1cM1 when compared with pN0cM0 patients. Among the 10/32 vandetanib-treated patients, 5 showed partial response (PR), all harbouring the RET918 mutation. mRNA expression of FLT1 (P=0.039), FLT4 (P=0.025) and VEGFB (P=0.042) was significantly higher in therapy responders.

CONCLUSIONS

In this study, we identified molecular markers in primary tumour tissue of sporadic MTC associated with the development of metastasis (both lymph node and organ metastasis) as well as response to vandetanib therapy.

Modulation of thyroidal radioiodide uptake by oncological pipeline inhibitors and Apigenin

Targeted radioiodine therapy for thyroid cancer is based on selective stimulation of Na+/I- Symporter (NIS)-mediated radioactive iodide uptake (RAIU) in thyroid cells by thyrotropin. Patients with advanced thyroid cancer do not benefit from radioiodine therapy due to reduced or absent NIS expression. To identify inhibitors that can be readily translated into clinical care, we examined oncological pipeline inhibitors targeting Akt, MEK, PI3K, Hsp90 or BRAF in their ability to increase RAIU in thyroid cells expressing BRAFV600E or RET/PTC3 oncogene. Our data showed that (1) PI3K inhibitor GDC-0941 outperformed other inhibitors in RAIU increase mainly by decreasing iodide efflux rate to a great extent; (2) RAIU increase by all inhibitors was extensively reduced by TGF-β, a cytokine secreted in the invasive fronts of thyroid cancers; (3) RAIU reduction by TGF-β was mainly mediated by NIS reduction and could be reversed by Apigenin, a plant-derived flavonoid; and (4) In the presence of TGF-β, GDC-0941 with Apigenin co-treatment had the highest RAIU level in both BRAFV600E expressing cells and RET/PTC3 expressing cells. Taken together, Apigenin may serve as a dietary supplement along with small molecule inhibitors to improve radioiodine therapeutic efficacy on invasive tumor margins thereby minimizing future metastatic events.

[Intracellular signaling mechanisms in thyroid cancer]

BACKGROUND

Thyroid cancer is the most common malignancy of the endocrine system, the papillary variant accounts for 80-90% of all diagnosed cases. In the development of papillary thyroid cancer, BRAF and RAS genes are mainly affected, resulting in a modification of the system of intracellular signaling proteins known as «protein kinase mitogen-activated» (MAPK) which consist of «modules» of internal signaling proteins (Receptor/Ras/Raf/MEK/ERK) from the cell membrane to the nucleus. In thyroid cancer, these signanling proteins regulate diverse cellular processes such as differentiation, growth, development and apoptosis. MAPK play an important role in the pathogenesis of thyroid cancer as they are used as molecular biomarkers for diagnostic, prognostic and as possible therapeutic molecular targets. Mutations in BRAF gene have been correlated with poor response to treatment with traditional chemotherapy and as an indicator of poor prognosis.

OBJECTIVE

To review the molecular mechanisms involved in intracellular signaling of BRAF and RAS genes in thyroid cancer.

CONCLUSIONS

Molecular therapy research is in progress for this type of cancer as new molecules have been developed in order to inhibit any of the components of the signaling pathway (RET/PTC)/Ras/Raf/MEK/ERK; with special emphasis on the (RET/PTC)/Ras/Raf section, which is a major effector of ERK pathway.

MAPK and SHH pathways modulate type 3 deiodinase expression in papillary thyroid carcinoma

Type 3 deiodinase (DIO3, D3) is reactivated in human neoplasias. Increased D3 levels in papillary thyroid carcinoma (PTC) have been associated with tumor size and metastatic disease. The objective of this study is to investigate the signaling pathways involved in DIO3 upregulation in PTC. Experiments were performed in human PTC cell lines (K1 and TPC-1 cells) or tumor samples. DIO3 mRNA and activity were evaluated by real-time PCR and ion-exchange column chromatography respectively. Western blot analysis was used to determine the levels of D3 protein. DIO3 gene silencing was performed via siRNA transfection. DIO3 mRNA levels and activity were readily detected in K1 (BRAF(V6) (0) (0E)) and, at lower levels, in TPC-1 (RET/PTC1) cells (P<0.007 and P=0.02 respectively). Similarly, DIO3 mRNA levels were higher in PTC samples harboring the BRAF(V600E) mutation as compared with those with RET/PTC1 rearrangement or negative for these mutations (P<0.001). Specific inhibition of BRAF oncogene (PLX4032, 3 μM), MEK (U0126, 10-20 μM) or p38 (SB203580, 10-20 μM) signaling was associated with decreases in DIO3 expression in K1 and TPC-1 cells. Additionally, the blockage of the sonic hedgehog (SHH) pathway by cyclopamine (10  μM) resulted in markedly decreases in DIO3 mRNA levels. Interestingly, siRNA-mediated DIO3 silencing induced decreases on cyclin D1 expression and partial G1 phase cell cycle arrest, thereby downregulating cell proliferation. In conclusion, sustained activation of the MAPK and SHH pathways modulate the levels of DIO3 expression in PTC. Importantly, DIO3 silencing was associated with decreases in cell proliferation, thus suggesting a D3 role in tumor growth and aggressiveness.

Extending the Impact of RAC1b Overexpression to Follicular Thyroid Carcinomas

RAC1b is a hyperactive variant of the small GTPase RAC1 known to be a relevant molecular player in different cancers. Previous studies from our group lead to the evidence that its overexpression in papillary thyroid carcinoma (PTC) is associated with an unfavorable prognosis. In the present study, we intended to extend the analysis of RAC1b expression to thyroid follicular neoplasms and to seek for clinical correlations. RAC1b expression levels were determined by RT-qPCR in thyroid follicular tumor samples comprising 23 follicular thyroid carcinomas (FTCs) and 33 follicular thyroid adenomas (FTAs). RAC1b was found to be overexpressed in 33% of carcinomas while no RAC1b overexpression was documented among follicular adenomas. Patients with a diagnosis of FTC were divided into two groups based on longitudinal evolution and final outcome. RAC1b overexpression was significantly associated with both the presence of distant metastases (P = 0.01) and poorer clinical outcome (P = 0.01) suggesting that, similarly to that previously found in PTCs, RAC1b overexpression in FTCs is also associated with worse outcomes. Furthermore, the absence of RAC1b overexpression in follicular adenomas hints its potential as a molecular marker likely to contribute, in conjunction with other putative markers, to the preoperative differential diagnosis of thyroid follicular lesions.

Expression of YY1 in Differentiated Thyroid Cancer

The transcription factor Yin Yang 1 (YY1) has an important regulatory role in tumorigenesis, but its implication in thyroid cancer has not been yet investigated. In the present study, we have analyzed the expression of YY1 in differentiated thyroid cancer and assessed the association of YY1 expression with clinical features. Expression of YY1 was evaluated in human thyroid cancer cell lines, a series of matched normal/tumor thyroid tissues and in a thyroid cancer tissue microarray, using real-time PCR, Western blot, and/or immunohistochemistry. YY1 was overexpressed in thyroid cancer cells, at transcription and protein levels. A significant increase of YY1 mRNA was also observed in tumor thyroid tissues. Moreover, immunohistochemical analysis of the thyroid cancer tissue microarray revealed that both papillary thyroid cancer (PTC) and follicular thyroid cancer (FTC) present increased YY1 protein levels (48 and 19%, respectively). After stratification by the level of YY1 protein, positive YY1 expression identifies 88% of patients with PTC. The association of YY1 expression with clinicopathological features in PTC and FTC showed that YY1 expression was related with age at diagnosis. Our data indicates for the first time overexpression of YY1 in differentiated thyroid cancer, with YY1 being more frequently overexpressed in the PTC subtype.

A mutation screening of oncogenes, tumor suppressor gene TP53 and nuclear encoded mitochondrial complex I genes in oncocytic thyroid tumors

BACKGROUND

Thyroid neoplasias with oncocytic features represent a specific phenotype in non-medullary thyroid cancer, reflecting the unique biological phenomenon of mitochondrial hyperplasia in the cytoplasm. Oncocytic thyroid cells are characterized by a prominent eosinophilia (or oxyphilia) caused by mitochondrial abundance. Although disruptive mutations in the mitochondrial DNA (mtDNA) are the most significant hallmark of such tumors, oncocytomas may be envisioned as heterogeneous neoplasms, characterized by multiple nuclear and mitochondrial gene lesions. We investigated the nuclear mutational profile of oncocytic tumors to pinpoint the mutations that may trigger the early oncogenic hit.

METHODS

Total DNA was extracted from paraffin-embedded tissues from 45 biopsies of oncocytic tumors. High-resolution melting was used for mutation screening of mitochondrial complex I subunits genes. Specific nuclear rearrangements were investigated by RT-PCR (RET/PTC) or on isolated nuclei by interphase FISH (PAX8/PPARγ). Recurrent point mutations were analyzed by direct sequencing.

RESULTS

In our oncocytic tumor samples, we identified rare TP53 mutations. The series of analyzed cases did not include poorly- or undifferentiated thyroid carcinomas, and none of the TP53 mutated cases had significant mitotic activity or high-grade features. Thus, the presence of disruptive TP53 mutations was completely unexpected. In addition, novel mutations in nuclear-encoded complex I genes were identified.

CONCLUSIONS

These findings suggest that nuclear genetic lesions altering the bioenergetics competence of thyroid cells may give rise to an aberrant mitochondria-centered compensatory mechanism and ultimately to the oncocytic phenotype.

Development and characterization of a differentiated thyroid cancer cell line resistant to VEGFR-targeted kinase inhibitors

BACKGROUND

Vascular endothelial growth factor-targeted kinase inhibitors have emerged as highly promising therapies for radioiodine-refractory metastatic differentiated thyroid cancer. Unfortunately, drug resistance uniformly develops, limiting their therapeutic efficacies and thereby constituting a major clinical problem.

APPROACH AND METHODS

To study acquired drug resistance and elucidate underlying mechanisms in this setting, BHP2-7 human differentiated thyroid cancer cells were subjected to prolonged continuous in vitro selection with 18 μM pazopanib, a clinically relevant concentration; acquisition of pazopanib resistance was serially assessed, with the resulting resistant cells thereafter subcloned and characterized to assess potential mechanisms of acquired pazopanib resistance.

RESULTS

Stable 2- to 4-fold in vitro pazopanib resistance emerged in response to pazopanib selection associated with similar in vitro growth characteristics but with markedly more aggressive in vivo xenograft growth. Selected cells were cross-resistant to sunitinib and to a lesser extent sorafenib but not to MAPK kinase (MEK1/2) inhibition by GSK1120212. Genotyping demonstrated acquisition of a novel activating KRAS codon 13 GGC to GTT (glycine to valine) mutation, consistent with the observed resistance to upstream vascular endothelial growth factor receptor inhibition yet sensitivity to downstream MAPK kinase (MEK1/2) inhibition.

CONCLUSIONS

Selection of thyroid cancer cells with clinically utilized therapeutics can lead to acquired drug resistance and altered in vivo xenograft behavior that can recapitulate analogous drug resistance observed in patients. This approach has the potential to lead to insights into acquired treatment-related drug resistance in thyroid cancers that can be subjected to subsequent validation in serially collected patient samples and that has the potential to yield preemptive and responsive approaches to dealing with this important clinical problem.

Mechanisms of RET signaling in cancer: current and future implications for targeted therapy

De-regulation of RET signaling by oncogenic mutation, gene rearrangement, overexpression or transcriptional up-regulation is implicated in several human cancers of neuroendocrine and epithelial origin (thyroid, breast, lung). Understanding how RET signaling mechanisms associated with these oncogenic events are deregulated, and their impact in the biological processes driving tumor formation and progression, as well as response to treatment, will be crucial to find and develop better targeted therapeutic strategies. In this review we emphasie the distinct mechanisms of RET signaling in cancer and summarise current knowledge on small molecule inhibitors targeting the tyrosine kinase domain of RET as therapeutic drugs in RET-positive cancers.

Immune response in thyroid cancer: widening the boundaries

The association between thyroid cancer and thyroid inflammation has been repeatedly reported and highly debated in the literature. In fact, both molecular and epidemiological data suggest that these diseases are closely related and this association reinforces that the immune system is important for thyroid cancer progression. Innate immunity is the first line of defensive response. Unlike innate immune responses, adaptive responses are highly specific to the particular antigen that induced them. Both branches of the immune system may interact in antitumor immune response. Major effector cells of the immune system that directly target thyroid cancer cells include dendritic cells, macrophages, polymorphonuclear leukocytes, mast cells, and lymphocytes. A mixture of immune cells may infiltrate thyroid cancer microenvironment and the balance of protumor and antitumor activity of these cells may be associated with prognosis. Herein, we describe some evidences that immune response may be important for thyroid cancer progression and may help us identify more aggressive tumors, sparing the vast majority of patients from costly unnecessary invasive procedures. The future trend in thyroid cancer is an individualized therapy.

The circadian clock in cancer development and therapy

Most aspects of mammalian function display circadian rhythms driven by an endogenous clock. The circadian clock is operated by genes and comprises a central clock in the brain that responds to environmental cues and controls subordinate clocks in peripheral tissues via circadian output pathways. The central and peripheral clocks coordinately generate rhythmic gene expression in a tissue-specific manner in vivo to couple diverse physiological and behavioral processes to periodic changes in the environment. However, with the industrialization of the world, activities that disrupt endogenous homeostasis with external circadian cues have increased. This change in lifestyle has been linked to an increased risk of diseases in all aspects of human health, including cancer. Studies in humans and animal models have revealed that cancer development in vivo is closely associated with the loss of circadian homeostasis in energy balance, immune function, and aging, which are supported by cellular functions important for tumor suppression including cell proliferation, senescence, metabolism, and DNA damage response. The clock controls these cellular functions both locally in cells of peripheral tissues and at the organismal level via extracellular signaling. Thus, the hierarchical mammalian circadian clock provides a unique system to study carcinogenesis as a deregulated physiological process in vivo. The asynchrony between host and malignant tissues in cell proliferation and metabolism also provides new and exciting options for novel anticancer therapies.