Genetic alterations and their relationship in the phosphatidylinositol 3-kinase/Akt pathway in thyroid cancer

Do antidiabetic medications play a specific role in differentiated thyroid cancer compared to other cancer types?

The risk for differentiated thyroid cancer, like for many other types of cancer, is increased in obese individuals and people with intermediate hyperglycaemia. The incidence of all cancers, with the exception of thyroid cancer, is also increased in type 2 diabetes mellitus patients. The review compares the prevalence of thyroid carcinoma and other cancers in obese, people with intermediate hyperglycaemia and patients with diabetes and summarizes mode of action and anti-tumourigenic effect of common antidiabetic medications. The over-expression of dipeptidyl peptidase IV in the tumours, not seen in the other cancer types, is suggested as a potential reason for the unique situation in thyroid cancer.

The Akt inhibitor MK2206 synergizes, but perifosine antagonizes, the BRAF(V600E) inhibitor PLX4032 and the MEK1/2 inhibitor AZD6244 in the inhibition of thyroid cancer cells

PURPOSE

The purpose of the study was to explore optimal combinations of currently actively developed drugs for dually targeting the Ras → Raf → MAPK kinase (MEK) → MAPK/ERK (MAPK) and the phosphatidylinositol 3-kinase/Akt pathways as effective treatments for thyroid cancer.

EXPERIMENTAL DESIGN

We tested the combinations of the Akt inhibitors MK2206 or perifosine with the BRAF(V600E) inhibitor PLX4032 or the MEK1/2 inhibitor AZD6244 in thyroid cancer cells harboring both the BRAF(V600E) and PIK3CA mutations.

RESULTS

We found that MK2206 could potently, when used alone, and synergistically, when combined with either PLX4032 or AZD6244, inhibit thyroid cancer cell growth with all the combination index values lower than 1. Perifosine could potently inhibit thyroid cancer cell growth when used alone, but a strong antagonism occurred between this drug and PLX4032 or AZD6244 in the inhibition of thyroid cancer cell growth with all combination index values higher than 1. Combinations of MK2206 with PLX4032 or AZD6244 dramatically enhanced G1 cell cycle arrest induced by each drug alone. However, G2 cell cycle arrest uniquely induced by perifosine alone and G1 cell cycle arrest induced by PLX4032 or AZD6244 were both reversed by combination treatments, providing a mechanism for their antagonism. All these drugs could correspondingly inhibit the MAPK and phosphatidylinositol 3-kinase/Akt signalings, confirming their expected target effects.

CONCLUSIONS

We demonstrated, unexpectedly, opposite outcomes of MK2206 and perifosine in their combinational treatments with BRAF(V600E)/MEK inhibitors in thyroid cancer cells. The data may help appropriate selection of these prominent drugs for clinical trials of combination therapies for thyroid cancer.

Highly frequent PIK3CA amplification is associated with poor prognosis in gastric cancer

Background

The phosphoinositide 3-kinase (PI3K)/Akt pathway plays a fundamental role in cell proliferation and survival in human tumorigenesis, including gastric cancer. PIK3CA mutations and amplification are two major causes of overactivation of this pathway in human cancers. However, until this work, there was no sound investigation on the association of PIK3CA mutations and amplification with clinical outcome in gastric cancer, particularly the latter.

Methods

Using direct sequencing and real-time quantitative PCR, we examined PIK3CA mutations and amplification, and their association with clinicopathological characteristics and clinical outcome of gastric cancer patients.

Results

PIK3CA mutations and amplification were found in 8/113 (7.1%) and 88/131 (67%) gastric cancer patients, respectively. PIK3CA amplification was closely associated with increased phosphorylated Akt (p-Akt) level. No relationship was found between PIK3CA mutations and clinicopathological characteristics and clinical outcome in gastric cancer. PIK3CA amplification was significantly positively associated with cancer-related death. Importantly, Kaplan-Meier survival curves revealed that the patients with PIK3CA amplification had significantly shorter survival times than the patients without PIK3CA amplification.

Conclusions

Our data showed that PIK3CA mutations were not common, but its amplification was very common in gastric cancer and may be a major mechanism in activating the PI3K/Akt pathway in gastric cancer. Importantly, Kaplan-Meier survival curves revealed that PIK3CA amplification was significantly positively associated with poor survival of gastric cancer patients. Collectively, the PI3K/Akt signaling pathway may be an effective therapeutic target in gastric cancer.

Quantitative assessment of gene methylation and their impact on clinical outcome in gastric cancer

BACKGROUND

Promoter methylation is an alternative mechanism of gene silencing in human tumorigenesis. Although a number of methylated genes have been found in gastric cancer, useful methylation markers for early diagnosis and prognostic evaluation of this cancer remain largely unknown.

METHODS

Using quantitative methylation-specific PCR (Q-MSP), we examined promoter methylation of 6 genes, including CALCA, DAPK1, RARbeta, RASSF1A, TIMP3, and PAX6, and explored their association with clinical outcome in gastric cancer.

RESULTS

We found that most of the genes investigated in the present study had significantly higher methylation level in tumor tissues than normal gastric tissues, including CALCA, RARbeta, RASSF1A, TIMP3, and PAX6. With more focus on specificity compared to sensitivity, all genes were hypermethylated in gastric cancer, ranging from 12.8% to 36.9%. Methylation of TIMP3 and PAX6 was strongly associated with differentiation and lymph node metastasis, respectively. Importantly, most of gene methylation, except for DAPK1, was closely associated with poor survival in gastric cancer.

CONCLUSION

We found that a panel of genes was specifically methylated in gastric cancer, and demonstrated the effect of promoter methylation of some genes on clinical outcome in gastric cancer, indicating these methylated genes may be useful biomarkers for prognostic evaluation in this cancer.

The BRAF(V600E) causes widespread alterations in gene methylation in the genome of melanoma cells

Although BRAF(V600E) is well known to play an important role in the tumorigenesis of melanoma, its molecular mechanism, particularly the epigenetic aspect, has been incompletely understood. Here, we investigated the role of BRAF(V600E) signaling in altering gene methylation in the genome of melanoma cells using a methylated CpG island amplification/CpG island microarray system and searched for genes coupled to the BRAF(V600E) signaling through methylation aberrations. The results indicated that a wide range of genes with broad functions were linked to BRAF(V600E) signaling through their hyper- or hypomethylation. Expression of 59 genes hypermethylated upon BRAF knockdown was selectively tested and found to be largely correspondingly underexpressed, suggesting that these genes were naturally hypomethylated, and overexpressed with BRAF(V600E) in melanoma. This BRAF(V600E)-promoted hypomethylation was confirmed on genes selectively examined in primary melanoma tumors. Some of these genes were functionally tested and demonstrated to play a role in melanoma cell proliferation and invasion. As a mechanism of aberrant gene methylation driven by BRAF(V600E), expression of the DNA methyltransferase 1 and histone methyltransferase EZH2 was profoundly affected by BRAF(V600E). We have thus uncovered a previously unrecognized prominent epigenetic mechanism in the tumorigenesis of melanoma driven by BRAF(V600E). Many of the functionally important genes controlled by the BRAF(V600E) signaling through aberrant methylation may prove to be novel therapeutic targets for melanoma.

Molecular study of signaling-pathway genes in experimental rat thyroid carcinoma

INTRODUCTION

A study was conducted on histological patterns and biomolecular changes in Goitrogen-induced experimental rat thyroid tumors. The link between the histological types observed and N-ras, B-raf, and PI3KCA gene mutations widely reported in human thyroid cancers was explored.

MATERIAL AND METHODS

An analysis was done on paraffin-embedded tumor tissue sections from Wistar rats receiving 1% potassium perchlorate (KClO(4)) added to the ad libitum drinking-water supply over an 18-month period. Three experimental subgroups were formed, each comprising 10 thyroids: subgroup I (control) consisted of thyroids from untreated controls; subgroups II and III (experimental) consisted of thyroids from KClO(4)-treated rats, displaying capsular, vascular, or both invasion but no metastasis (II), or distant metastasis (III). DNA was extracted from paraffin-embedded tissues. To test for the genetic mutations most widely reported in human thyroid cancers, exon 1 of the N-ras gene, exons 9 and 20 of the PI3KCA gene, and exon 15 of the B-raf gene were amplified and sequenced.

RESULTS

All tumors were of the follicular type. None of the 20 experimental rat thyroids displayed the expected gene mutations reported in humans. However, 90% of them contained four new B-raf gene mutations and all were silent and did not cause an amino acid substitution in the protein chain.

CONCLUSIONS

Biomolecular analysis suggested that N-ras, PI3KCA, and B-raf gene mutations may not be involved in thyroid tumor formation using the experimental procedure applied in this study. But the four mutations in B-raf, though without functional repercussions, may be a specific marker for this tumor type.

Expression, localization, and phosphorylation of Akt1 in benign and malignant thyroid lesions

The serine/threonine protein kinase Akt is a key molecule in the phosphatidyl inositol 3-kinase pathway that is often overactivated in human cancers. Three Akt isoforms (Akt1, Akt2, Akt3) have been identified in human cells and they show different distribution and have non-redundant functions. The aim of this study was to determine whether the expression, phosphorylation, and localization of Akt1 isoform in human thyroid malignant lesions are different from those in benign lesions. Nuclear and cytoplasmic fractions were isolated from tissue samples and Western blot method was used to detect Akt1 presence in both cellular fractions. Akt1 expression was also assessed by ELISA method. To estimate Akt1 phosphorylation, kinase was immunoprecipitated from cell lysates and tested with anti-phospho-Akt antibodies. The Akt1 expression in majority of thyroid cancer samples was significantly higher than in benign lesions (p < 0.05). Akt1 both in differentiated cancers (follicular and papillary) and benign lesions was localized mainly in cytoplasmic fraction. In two of three anaplastic cancer samples Akt1 was predominantly localized in nucleus. The ratio of phosphorylated Akt1 to total Akt1 was lower in cancers than in non-neoplastic lesions and adenomas. Thus, although Akt1 seems to be overexpressed in thyroid neoplasms, its high phosphorylation is not characteristic for thyroid cancers.

Gene expression profile of human thyroid cancer in relation to its mutational status

This review describes the gene expression profile changes associated with the presence of different mutations that contribute to thyroid cell carcinogenesis. The results are discussed in the context of thyroid cancer biology and of the implications for disease prognosis, while the diagnostic aspect has been omitted. For papillary thyroid cancer (PTC), the most characteristic gene expression profile is associated with the presence of BRAF mutation. BRAF-associated PTC differ profoundly from RET/PTC or RAS-associated cancers. Simultaneously, they retain many characteristic gene expression features common for all PTCs, induced by the alternative mutations activating MAPK pathway. Although the difference between papillary and follicular thyroid cancer (FTC) is significant at the gene expression profile level, surprisingly, the RAS-related signature of FTC is not well specified. PAX8/peroxisome proliferator-activated receptor γ (PPARγ) rearrangements, which occur in FTC as an alternative to the RAS mutation, are associated with specific changes in gene expression. Furthermore, the difference between well-differentiated thyroid cancers and poorly differentiated and anaplastic thyroid cancers is mainly a reflection of tumor degree of differentiation and may not be attributed to the presence of characteristic mutations.

BRAF(K601E) mutation in a patient with a follicular thyroid carcinoma

BACKGROUND

BRAF mutations, the most common genetic alteration associated with papillary thyroid carcinoma (PTC), have never been associated with follicular thyroid carcinoma (FTC) except for one possible case, which, however, had some cellular features of the follicular variant of PTC. Here, we present a patient with a BRAF mutation within a FTC.

SUMMARY

A 78-year-old man presented with a nodular lesion 8 cm in size in the right thyroid lobe, coexisting with a goiter. Fine-needle aspiration samples were obtained for cytology, immunocytology, and molecular analysis. Immunoblot analysis on thyroid tissues was performed to evaluate the most important tumor activating pathways. Cytology was consistent with "follicular neoplasia" (negative for galectin-3 immunostaining); molecular analysis on the cytology sample detected a K601E mutation in the exon 15 of the BRAF gene. After total thyroidectomy with lymph-node dissection, the diagnosis of FTC was established by histopathological examination. The BRAF(K601E) mutation was confirmed in DNA obtained from different areas of the FTC. In addition, an activating mutation (E545A) in the PKI3CA oncogene was found in the FTC. As expected, immunoblot analysis showed activation of the PI3K/Akt pathway.

CONCLUSION

This article describes what may be the first case of a classical FTC carrying a BRAF mutation. Unlike the most common BRAF mutation seen in PTC carcinoma (BRAF(V600E)), this patient's mutation was a BRAF(K601E) mutation that previously has been associated with some cases of the follicular variant of PTC. The BRAF(K601E) mutation should be included in the spectrum of genetic alterations in FTC.

Thyroid cancer: pathogenesis and targeted therapy

Therapeutic options for advanced, unresectable radioiodine-resistant thyroid cancers have historically been limited. Recent progress in understanding the pathogenesis of the various subtypes of thyroid cancer has led to increased interest in the development of targeted therapies, with potential strategies including angiogenesis inhibition, inhibition of aberrant intracellular signaling in the MAPK and PI3K/AKT/mTOR pathways, radioimmunotherapy, and redifferentiation agents. On the basis of a recent positive phase III clinical trial, the RET, vascular endothelial growth factor receptor (VEGFR), and epidermal growth factor receptor (EGFR) inhibitor vandetanib has received FDA approval as of April 2011 for use in the treatment of advanced medullary thyroid cancer. Several other recent phase II clinical trials in advanced thyroid cancer have demonstrated significant activity, and multiple other promising therapeutic strategies are in earlier phases of clinical development. The recent progress in targeted therapy is already revolutionizing management paradigms for advanced thyroid cancer, and will likely continue to dramatically expand treatment options in the coming years.

Inhibition of gap junction transfer sensitizes thyroid cancer cells to anoikis

Resistance to anoikis (matrix deprivation-induced apoptosis) is a critical component of the metastatic cascade. Molecular mechanisms underlying resistance to anoikis have not been reported in thyroid cancer cells. For an in vitro model of anoikis, we cultured follicular, papillary, and anaplastic thyroid cancer cell lines on poly-HEMA-treated low-adherent plates. We also performed immunohistochemical analysis of human cancer cells that had infiltrated blood and/or lymphatic vessels. Matrix deprivation was associated with establishment of contacts between floating thyroid cancer cells and formation of multi-cellular spheroids. This process was associated with activation of gap junctional transfer. Increased expression of the gap junction molecule Connexin43 was found in papillary and anaplastic cancer cells forming spheroids. All non-adherent cancer cells showed a lower proliferation rate compared with adherent cells but were more resistant to serum deprivation. AKT was constitutively activated in cancer cells forming spheroids. Inhibition of gap junctional transfer through Connexin43 silencing, or by treatment with the gap junction disruptor carbenoxolone, resulted in loss of pAKT and induction of apoptosis in a cell-type-specific manner. In human thyroid tissue, cancer cells that had infiltrated blood vessels showed morphological similarity to cancer cells forming spheroids in vitro. Intra-vascular cancer cells demonstrated prominent AKT activation in papillary and follicular cancers. Increased Connexin43 immunoreactivity was observed only in intra-vascular papillary cancer cells. Our data demonstrate that establishment of inter-cellular communication contributes to thyroid cancer cell resistance to anoikis. These findings suggest that disruption of gap junctional transfer could represent a potential therapeutic strategy for prevention of metastases.

Emerging therapeutics for advanced thyroid malignancies: rationale and targeted approaches

INTRODUCTION

Thyroid cancer is an emerging public health concern. In the USA, its incidence has doubled in the past decade, making it the eighth most commonly diagnosed neoplasm in 2010. Despite this alarming increase, most thyroid cancer patients benefit from conventional approaches (surgery, radioiodine, radiotherapy, TSH suppression with levothyroxine) and are often cured. Nevertheless, a minority have aggressive tumors resistant to cytotoxic and other historical therapies; these patients sorely need new treatment options.

AREAS COVERED

Herein the biology and molecular characteristics of the common histological types of thyroid cancer are reviewed to provide context for subsequent discussion of recent developments and emerging therapeutics for advanced thyroid cancers.

EXPERT OPINION

Several kinase inhibitors, especially those targeting VEGFR and/or RET, have already demonstrated promising activity in differentiated and medullary thyroid cancers (DTC, MTC). Although of minimal benefit in DTC and MTC, cytotoxic chemotherapy with anti-microtubule agents and/or anthracyclines in combination with intensity-modulated radiation therapy appears to extend survival for patients with locoregionally confined anaplastic thyroid cancer (ATC), but to have only modest benefit in metastatic ATC. Further discovery and development of novel agents and combinations of agents will be critical to further progress in treating advanced thyroid cancers of all histotypes.

Activation of tumor cell proliferation by thyroid hormone in a mouse model of follicular thyroid carcinoma

Thyroid cancers are the most common malignancy of the endocrine system in humans. To understand the molecular genetic events underlying thyroid carcinogenesis, we have generated a mouse model that spontaneously develops follicular thyroid carcinoma similar to human thyroid cancer (Thrb(PV/PV) mouse). This mutant mouse harbors a dominant-negative mutated thyroid hormone receptor β (denoted PV). The PV mutation was identified in a patient with resistance to thyroid hormone (TH). Thrb(PV/PV) mice exhibit highly elevated serum thyroid-stimulating hormone levels and increased TH. We have previously shown that thyroid-stimulating hormone is required, but not sufficient to induce metastatic follicular thyroid cancer in Thrb(PV/PV) mice. However, whether the elevated TH also contributes to the thyroid carcinogenesis of Thrb(PV/PV) mice was not elucidated. To understand the role of TH in thyroid carcinogenesis, we blocked the production of TH by treating Thrb(PV/PV) mice with propylthiouracil (Thrb(PV/PV)-PTU mice) and compared the development of thyroid cancer in Thrb(PV/PV)-PTU and untreated Thrb(PV/PV) mice. We found that thyroid tumor growth was reduced by ∼42% in Thrb(PV/PV)-PTU mice as compared with Thrb(PV/PV) mice. Analysis by bromodeoxyuridine-nuclear labeling showed decreased incorporation of bromodeoxyuridine in thyroid tumor cells of Thrb(PV/PV)-PTU mice, indicative of decreased tumor cell proliferation. However, cleaved-caspase 3 staining showed no apparent changes in apoptosis of tumor cells in Thrb(PV/PV)-PTU mice. Molecular studies identified a marked attenuation of the PI3K-AKT-β-catenin signaling pathway that led to decreased protein levels of cyclin D2, thereby decreasing tumor cell proliferation in Thrb(PV/PV)-PTU mice. Furthermore, matrix metalloproteinase-2, a downstream target of β-catenin and a key regulator during tumor invasion and metastasis, was also decreased. Thus, the present study uncovers a critical role of TH in promoting the thyroid carcinogenesis of Thrb(PV/PV) mice via membrane signaling events. Importantly, these findings suggest that anti-thyroid drugs could be considered as possible therapeutic agents of thyroid cancer.

Molecular analysis of thyroid tumors

Thyroid cancer is the most common endocrine malignancy, and its incidence is rising in the USA and other countries. Papillary and follicular thyroid carcinomas are the two most common types of thyroid cancer. Non-overlapping genetic alterations, including BRAF and RAS point mutations, and RET/PTC and PAX8/PPARγ rearrangements, are found in more than 70% of papillary and follicular thyroid carcinomas. These represent the most common genetic alterations in thyroid cancer, as well as molecular markers of diagnostic and prognostic significance. The use of these and other emerging molecular markers will likely improve the diagnosis of malignancy in thyroid nodules as well as facilitate more individualized operative and postoperative management. Herein, we provide a brief overview of the common genetic alterations in papillary and follicular thyroid carcinoma and discuss the diagnostic and prognostic significance thereof.

Molecular genetics and diagnosis of thyroid cancer

Thyroid cancer is a common type of endocrine malignancy, and its incidence has been steadily increasing in many regions of the world. Initiation and progression of thyroid cancer involves multiple genetic and epigenetic alterations, of which mutations leading to the activation of the MAPK and PI3K-AKT signaling pathways are crucial. Common mutations found in thyroid cancer are point mutation of the BRAF and RAS genes as well as RET/PTC and PAX8/PPARγ chromosomal rearrangements. The mutational mechanisms seem to be linked to specific etiologic factors. Chromosomal rearrangements have a strong association with exposure to ionizing radiation and possibly with DNA fragility, whereas point mutations probably arise as a result of chemical mutagenesis. A potential role of dietary iodine excess in the generation of BRAF point mutations has also been proposed. Somatic mutations and other molecular alterations have been recognized as helpful diagnostic and prognostic markers for thyroid cancer and are beginning to be introduced into clinical practice, to offer a valuable tool for the management of patients with thyroid nodules.

Pathogenic mechanisms of deregulated microRNA expression in thyroid carcinomas of follicular origin

Thyroid cancer is one of the most common malignancies of the endocrine system with increasing incidence. The vast majority of thyroid carcinomas derive from thyroid hormone producing follicular cells. Carcinomas of follicular origin are classified as follicular (FTCs), papillary (PTCs), partially differentiated (PDTCs) or anaplastic (ATCs) thyroid carcinomas. While FTCs and PTCs can be managed effectively, ATCs are considered one of the most lethal human cancers. Despite the identification of various genetic alterations, pathogenic mechanisms promoting the progression of thyroid carcinomas are still largely elusive. Over the recent years, aberrant microRNA expression was revealed in all as yet analyzed human cancers, including thyroid carcinomas. In view of the rapidly evolving perception that deregulated microRNA expression serves a pivotal role in tumor progression, microRNAs provide powerful tools for the diagnosis of thyroid carcinomas as well as the identification of potential therapeutic targets. Here, we summarize recent findings on microRNA signatures in thyroid carcinomas of follicular origin and discuss how deregulated microRNA expression could promote cancer progression.

Targeted treatment of differentiated and medullary thyroid cancer

The incidence of thyroid cancer is increasing, with a concomitant increase in the number of patients with advanced and metastatic disease. Discoveries regarding the pathogenesis of thyroid cancer have led to the recent development of new therapeutic agents that are beginning to appear on the market. Many of these new agents are targeted kinase inhibitors primarily affecting oncogenic kinases (BRAF V600E, RET/PTC) or signaling kinases (VEGFR, PDGFR). Some of these agents report significant partial response rates, while others attain stabilization of disease as their best response. Their impact on survival is unclear. While these agents target similar pathways, a wide variety of differences exist regarding efficacy and side effect profile. Current expert opinion advises that these agents be used only in a specific subset of patients.

Molecular diagnostics of thyroid tumors

CONTEXT

Thyroid cancer is the most common type of endocrine malignancy and its incidence is steadily increasing. Papillary carcinoma and follicular carcinoma are the most common types of thyroid cancer and represent those tumor types for which use of molecular markers for diagnosis and prognostication is of high clinical significance.

OBJECTIVE

To review the most common molecular alterations in thyroid cancer and their diagnostic and prognostic utility.

DATA SOURCES

PubMed (US National Library of Medicine)-available review articles, peer-reviewed original articles, and experience of the author.

CONCLUSIONS

The most common molecular alterations in thyroid cancer include BRAF and RAS point mutations and RET/PTC and PAX8/PPAR γ rearrangements. These nonoverlapping genetic alterations are found in more than 70% of papillary and follicular thyroid carcinomas. These molecular alterations can be detected in surgically resected samples and fine-needle aspiration samples from thyroid nodules and can be of significant diagnostic use. The diagnostic role of BRAF mutations has been studied most extensively, and recent studies also demonstrated a significant diagnostic utility of RAS, RET/PTC, and PAX8/PPAR γ mutations, particularly in thyroid fine-needle aspiration samples with indeterminate cytology. In addition to the diagnostic use, BRAF V600E mutation can also be used for tumor prognostication, as this mutation is associated with higher rate of tumor recurrence and tumor-related mortality. The use of these and other emerging molecular markers is expected to improve significantly the accuracy of cancer diagnosis in thyroid nodules and allow more individualized surgical and postsurgical management of patients with thyroid cancer.

The mTOR protein as a target in thyroid cancer

INTRODUCTION

The mammalian target of rapamycin (mTOR) protein is a downstream effector of the phosphatidilinositol-3 kinase (PI3K)/Akt pathway, which regulates not only cell proliferation and viability, but also iodide uptake in thyroid cells. Genetic alterations in the PI3K/Akt/mTOR pathway are common during thyroid cancer progression, and thus, these proteins are attractive targets for cancer therapy. So far, specific mTOR inhibitors, such as rapamycin analogs, have been developed and studied as anti-cancer agents.

AREAS COVERED

This review discusses evidence that justifies the potential use of mTOR signaling pathway inhibitors as therapeutic agents for thyroid cancer.

EXPERT OPINION

In the near future, mTOR-targeted drugs might represent a new approach for the therapy of thyroid cancer patients; rapamycin analogs have already been developed and are currently being clinically tested. Besides the antiproliferative action of mTOR inhibition, the stimulatory effect on thyroid iodide uptake can also be useful in the treatment of recurrent thyroid cancer. Therefore, if rapamycin analogs are able to increase iodide uptake in thyroid cancer, either alone or in combination with other agents, this will represent a new approach for the treatment of thyroid cancer, which may possibly improve the treatment of patients in which radioiodine therapy is not effective.

Hypoxia-inducible factor in thyroid carcinoma

Intratumoural hypoxia (low oxygen tension) is associated with aggressive disease and poor prognosis. Hypoxia-inducible factor-1 is a transcription factor activated by hypoxia that regulates the expression of genes that promote tumour cell survival, progression, metastasis, and resistance to chemo/radiotherapy. In addition to hypoxia, HIF-1 can be activated by growth factor-signalling pathways such as the mitogen-activated protein kinases- (MAPK-) and phosphatidylinositol-3-OH kinases- (PI3K-) signalling cascades. Mutations in these pathways are common in thyroid carcinoma and lead to enhanced HIF-1 expression and activity. Here, we summarise current data that highlights the potential role of both hypoxia and MAPK/PI3K-induced HIF-1 signalling in thyroid carcinoma progression, metastatic characteristics, and the potential role of HIF-1 in thyroid carcinoma response to radiotherapy. Direct or indirect targeting of HIF-1 using an MAPK or PI3K inhibitor in combination with radiotherapy may be a new potential therapeutic target to improve the therapeutic response of thyroid carcinoma to radiotherapy and reduce metastatic burden.

BRAF mutation-selective inhibition of thyroid cancer cells by the novel MEK inhibitor RDEA119 and genetic-potentiated synergism with the mTOR inhibitor temsirolimus

We examined the therapeutic potential of a novel MEK inhibitor, RDEA119, and its synergism with the mTOR inhibitor, temsirolimus, in thyroid cancer cell lines. RDEA119 potently inhibited the proliferation of the 4 cell lines that harbored BRAF mutation but had no or modest effects on the other 4 cells that harbored wild-type BRAF (IC(50) of 0.034-0.217 μM vs. 1.413-34.120 μM). This inhibitory effect of RDEA119 in selected cell lines OCUT1 (BRAF V600E(+), PIK3CA H1047R(+)) and SW1376 (BRAF V600E(+)) was enhanced by combination with the mTOR inhibitor, temsirolimus. The PTEN-deficient cell FTC133 was highly sensitive to temsirolimus but insensitive to RDEA119, and simultaneous treatment with the latter enhanced the sensitivity of the cell to the former. The KAT18 (wild-type) cell was not sensitive to either drug alone but became sensitive to the combination of the 2 drugs. The drug synergy was confirmed by combination index and isobologram analyses. RDEA119 and temsirolimus also showed synergistic effects on autophagic death of OCUT1 and KAT18 cells selectively tested. Dramatic synergistic effects of the 2 drugs were also seen on the growth of FTC133 xenograft tumors in nude mice. Overall, the effects of the 2 drugs on cell proliferation or autophagic death, either alone or in combination, were more pronounced in cells that harbored genetic alterations in the MAP kinase and PI3K/Akt pathways. Thus, these results demonstrated the important therapeutic potential of the novel MEK inhibitor RDEA119 and its synergism with temsirolimus in thyroid cancer.

Highly frequent promoter methylation and PIK3CA amplification in non-small cell lung cancer (NSCLC)

Background

Lung cancer is the leading cause of cancer-related death worldwide. Genetic and epigenetic alterations have been identified frequently in lung cancer, such as promoter methylation, gene mutations and genomic amplification. However, the interaction between genetic and epigenetic events and their significance in lung tumorigenesis remains poorly understood.

Methods

We determined the promoter methylation of 6 genes and PIK3CA amplification using quantitative methylation-specific PCR (Q-MSP) and real-time quantitative PCR, respectively, and explore the association of promoter methylation with PIK3CA amplification in a large cohort of clinically well-characterized non-small cell lung cancer (NSCLC).

Results

Highly frequent promoter methylation was observed in NSCLC. With 100% diagnostic specificity, excellent sensitivity, ranging from 45.8 to 84.1%, was found for each of the 6 genes. The promoter methylation was associated with histologic type. Methylation of CALCA, CDH1, DAPK1, and EVX2 was more common in squamous cell carcinomas (SCC) compared to adenocarcinomas (ADC). Conversely, there was a trend toward a higher frequency of RASSF1A methylation in ADC than SCC. In addition, PIK3CA amplification was frequently found in NSCLC, and was associated with certain clinicopathologic features, such as smoking history, histologic type and pleural indentation. Importantly, aberrant promoter methylation of certain genes was significantly associated with PIK3CA amplification.

Conclusions

Our data showed highly frequent promoter methylation and PIK3CA amplification in Chinese NSCLC population, and first demonstrated the associations of gene methylation with PIK3CA amplification, suggesting that these epigenetic events may be a consequence of overactivation of PI3K/Akt pathway.

Molecular analysis of thyroid tumors

In the recent years, a large number of molecular alterations in thyroid cancer has been discovered and characterized. Some of these markers may have significant diagnostic utility, can be used for tumor prognostication, and serve as potential therapeutic targets. The diagnostic utility of these markers is of particular importance in thyroid fine-needle aspiration samples. Some molecular markers, such as BRAF, offer help in risk stratification and can be potentially used to optimize surgical and postsurgical management of patients with thyroid cancer. This review discusses major molecular alterations known to occur in thyroid cancer, focusing on those markers that have been extensively characterized, carry clinical significance, and are being introduced into pathology practice.

Recent advances in molecular diagnosis of thyroid cancer

Recent molecular studies have described a number of abnormalities associated with the progression and dedifferentiation of thyroid carcinoma. These distinct molecular events are often associated with specific stages of tumor development. In particular, remarkable advances have occurred in several major biological areas of thyroid cancer, including the molecular alterations for the loss of radioiodine avidity of thyroid cancer, the pathogenic role of the MAP kinase and PI3K/Akt pathways and their related genetic alterations, and the aberrant methylation of functionally important genes in thyroid tumorigenesis and pathogenesis. Recognition of these features is crucial to the management of patients with thyroid cancer. Novel treatments are being designed based on our enhanced understanding of this disease process.

A novel RET inhibitor with potent efficacy against medullary thyroid cancer in vivo

BACKGROUND

Most medullary thyroid carcinomas (MTC) recur or progress despite curative resection. Current targeted therapies show promise but lack durable efficacy and tolerability. The purpose of this study was to build on previous in vitro work and evaluate withaferin A (WA), a novel RET inhibitor, in a metastatic murine model of MTC.

METHODS

A total of 5 million DRO-81-1 human MTC cells injected in the left posterior neck of nu/nu mice generated metastases uniformly to the liver, spleen, and/or lungs. Treatment with WA (8 mg/kg/day, intraperitoneally, for 21 days) was started for neoplasms > 100 mm(3). Endpoints were survival, neoplasm > 15,00 mm(3), decreased body weight, or body score (all measured three times/wk).

RESULTS

All controls (saline; n = 5) died or deteriorated from metastatic disease by 7 weeks postinjection. All treated animals were alive (WA; n = 5), having tumor regression and growth delay without toxicity or weight loss at 6 weeks posttreatment (P < .01). Tumor cells treated with WA demonstrated inhibition of total and phospho-RET levels by Western blot analysis in a dose-dependent manner (almost complete inhibition with treatment of 5 μM WA) as well as potent inhibition of phospho-ERK and phospho-Akt levels.

CONCLUSION

WA is a novel natural-product RET-inhibitor with efficacy in a metastatic murine model of MTC. Further long-term efficacy/toxicity studies are warranted to evaluate this compound for clinical translation.

Mouse models of follicular and papillary thyroid cancer progression

A significant number of well-differentiated thyroid cancers progress or recur, becoming resistant to current therapeutic options. Mouse models recapitulating the genetic and histological features of advanced thyroid cancer have been an invaluable tool to dissect the mechanisms involved in the progression from indolent, well differentiated tumors to aggressive, poorly differentiated carcinomas, and to identify novel therapeutic targets. In this review, we focus on the lessons learned from models of epithelial cell-derived thyroid cancer showing progression from hyperplastic lesions to locally invasive and metastatic carcinomas.

IQGAP1 plays an important role in the invasiveness of thyroid cancer

PURPOSE

This study was designed to explore the role of IQGAP1 in the invasiveness of thyroid cancer and its potential as a novel prognostic marker and therapeutic target in this cancer.

EXPERIMENTAL DESIGN

We examined IQGAP1 copy gain and its relationship with clinicopathologic outcomes of thyroid cancer and investigated its role in cell invasion and molecules involved in the process.

RESULTS

We found IQGAP1 copy number (CN) gain ≥ 3 in 1 of 30 (3%), 24 of 74 (32%), 44 of 107 (41%), 8 of 16 (50%), and 27 of 41 (66%) of benign thyroid tumor, follicular variant papillary thyroid cancer (FVPTC), follicular thyroid cancer (FTC), tall cell papillary thyroid cancer (PTC), and anaplastic thyroid cancer, respectively, in the increasing order of invasiveness of these tumors. A similar tumor distribution trend of CN ≥ 4 was also seen. IQGAP1 copy gain was positively correlated with IQGAP1 protein expression. It was significantly associated with extrathyroidal and vascular invasion of FVPTC and FTC and, remarkably, a 50%-60% rate of multifocality and recurrence of BRAF mutation-positive PTC (P = 0.01 and 0.02, respectively). The siRNA knockdown of IQGAP1 dramatically inhibited thyroid cancer cell invasion and colony formation. Coimmunoprecipitation assay showed direct interaction of IQGAP1 with E-cadherin, a known invasion-suppressing molecule, which was upregulated when IQGAP1 was knocked down. This provided a mechanism for the invasive role of IQGAP1 in thyroid cancer. In contrast, IQGAP3 lacked all these functions.

CONCLUSIONS

IQGAP1, through genetic copy gain, plays an important role in the invasiveness of thyroid cancer and may represent a novel prognostic marker and therapeutic target for this cancer.

Relative quantification of PIK3CA gene expression level in fine-needle aspiration biopsy thyroid specimens collected from patients with papillary thyroid carcinoma and non-toxic goitre by real-time RT-PCR

Background

Recent studies have shown that the phosphatidylinositol 3-kinase (PI3K) signaling pathway is important regulator of many cellular events, including apoptosis, proliferation and motility. PI3K pathway alterations (PIK3CA gene mutations and/or amplification) have been observed in various human tumours. In the majority of diagnosed cases, mutations are localized in one of the three "hot spots" in the gene, responsible for coding catalytic subunit α of class I PI3K (PIK3CA). Mutations and amplification of PIK3CA gene are characteristic for thyroid cancer, as well.

Methods

The aim of our study was to examine a gene expression level of PIK3CA in fine-needle aspiration biopsy (FNAB) thyroid specimens in two types of thyroid lesions, papillary thyroid carcinoma (PTC) and non-toxic goitre (NTG). Following conventional cytological examination, 42 thyroid FNAB specimens, received from patients with PTC (n = 20) and NTG (n = 22), were quantitatively evaluated regarding PIK3CA expression level by real-time PCR in the ABI PRISM^® 7500 Sequence Detection System.

Results

Significantly higher expression level (RQ) of PIK3CA in PTC group has been noted in comparison with NTG group (p < 0.05).

Conclusion

These observations may suggest role of PIK3CA alterations in PTC carcinogenesis.

Cross-talk between PI3K and estrogen in the mouse thyroid predisposes to the development of follicular carcinomas with a higher incidence in females

It is well known that thyroid disease is more frequent in women than in men, however the molecular basis for this gender difference is still poorly understood. PI3K activation, through different mechanisms including loss of the PTEN tumor suppressor, is being increasingly recognized as a major player in the development of thyroid neoplastic lesions. Loss of Pten in the mouse thyroid results in a significant increase in the thyrocyte proliferative index, which is more prominent in the female mice. Here we show that 52% of the Pten^−/− female mice, but only 12% of the males, develop follicular adenomas by one year of age. In addition, 50% of female mutants, but only 35% of males older than one year of age develop invasive, and often metastatic, follicular carcinomas. Mutant females have a significantly shorter overall survival compared to male mutants. Hormonal manipulation experiments established a direct role of estrogens in controlling the increased thyrocyte proliferation index in mutant females. Furthermore, while genetic ablation of one Cdkn1b allele accelerated the development of neoplastic lesions, it also abolished the gender differences in survival and reduced the difference in neoplastic lesion development rate, underlining a key role of p27 in mediating estrogen action in the thyroid follicular cells.

These data, based on a clinically relevant model of thyroid follicular carcinoma, provide for the first time in vivo evidence that circulating estrogens are directly responsible for the increased female susceptibility to thyroid disease, at least upon activation of the PI3K pathway, and provide novel insights into the gender differences characterizing thyroid neoplastic disorders.

The evolving field of tyrosine kinase inhibitors in the treatment of endocrine tumors

Activation of tyrosine kinase receptors (TKRs) and their related pathways has been associated with development of endocrine tumors. Compounds that target and inactivate the kinase function of these receptors, tyrosine kinase inhibitors (TKIs), are now being applied to the treatment of endocrine tumors. Recent clinical trials of TKIs in patients with advanced thyroid cancer, islet cell carcinoma, and carcinoid have shown promising preliminary results. Significant reductions in tumor size have been described in medullary and papillary thyroid carcinoma, although no complete responses have been reported. Case reports have described significant tumor volume reductions of malignant pheochromocytomas and paragangliomas. In addition, these compounds showed an initial tumoricidal or apoptotic response followed by long-term static effects on tumor growth. Despite the promising preliminary results, this class of therapeutic agents has a broad spectrum of adverse effects, mediated by inhibition of kinase activities in normal tissues. These adverse effects will have to be balanced with their benefit in clinical use. New strategies will have to be applied in clinical research to achieve optimal benefits. In this review, we will address the genetic alterations of TKRs, the rationale for utilizing TKIs for endocrine tumors, and current information on tumor and patient responses to specific TKIs. We will also discuss the adverse effects related to TKI treatment and the mechanisms involved. Finally, we will summarize the challenges associated with use of this class of compounds and potential solutions.

Genetic alterations in the RAS/RAF/mitogen-activated protein kinase and phosphatidylinositol 3-kinase/Akt signaling pathways in the follicular variant of papillary thyroid carcinoma

BACKGROUND

The follicular variant of papillary thyroid carcinoma (FVPTC) is the second most common histotype among papillary thyroid cancers (PTCs). Although the prognosis of FVPTC is similar to the conventional phenotype, differential diagnostic difficulties may not be uncommon with other follicular thyroid neoplasms, and little is known about their genetic alterations. Defining these alterations may lead to the identification of diagnostic and biologic markers.

METHODS

In this study, the authors evaluated genetic alterations and downstream-activated signals of the Ras/Raf-mitogen-activated protein kinase (MAPK) and phosphatidylinositol 3-kinase (PI3K)/v-akt murine thymoma viral oncogene (Akt) (PI3K/Akt) signaling pathways in 30 FVPTC tissue specimens. Tumors and matched normal thyroid samples were tested for RAS, for the v-raf murine sarcoma viral oncogene (BRAF) substitution of valine (V) for glutamate (E) at codon 600 (the V600E mutation), for phosphatase and tensin homolog (PTEN), for catalytic PI3k p110 subunit alpha (PIK3CA), for AKT, and for the presence of rearranged during transfection (ret) proto-oncogene/PTC (RET-PTC) and paired box-8 (PAX8)/peroxisome proliferator-activated receptor gamma (PPARgamma) fusion protein (PAX8-PPARgamma) rearrangements by direct sequencing and reverse transcriptase-polymerases chain reaction analyses, respectively. Western blot analysis was used to assess the effects of these gene abnormalities on the activation of the 2 pathways.

RESULTS

Genetic alterations were identified in 70% of FVPTCs. Activation of the MAPK and PI3K pathways was observed in 74% and 22% of tumors, respectively. The alterations that were identified in the genes of the 2 pathways were mutually exclusive. Chromosomal RET-PTC and PAX8-PPARgamma rearrangements were observed in 20% and 17% of tumors, respectively. It was noteworthy that some FVPTCs with RET-PTC had the coactivation of both pathways.

CONCLUSIONS

RET-PTC and PAX8-PPARgamma rearrangements and mutations of the neuroblastoma RAS viral oncogene homolog N-RAS at codon 61 were the most common genetic alterations in FVPTCs. Activation of the MAPK pathway was a frequent event in FVPTCs, and the PI3K signaling pathway could be coactivated in RET-PTC tumors. These findings may have important therapeutic implication in patients with FVPTC.

Genetic alterations in the phosphatidylinositol-3 kinase/Akt pathway in thyroid cancer

BACKGROUND

Aberrant activation of the phosphatidylinositol-3 kinase (PI3K)/Akt pathway plays a fundamental role in thyroid tumorigenesis, particularly in follicular thyroid cancer (FTC) and aggressive thyroid cancer, such as anaplastic thyroid cancer (ATC). As the drivers of this process, many genetic alterations activating the PI3K/Akt pathway have been identified in thyroid cancer in recent years.

SUMMARY

This review summarizes the current knowledge on major genetic alterations in the PI3K/Akt pathway. These include PIK3CA mutations and genomic amplification/copy gain, Ras mutations, PTEN mutations, RET/PTC and PPARgamma/Pax8 rearrangements, as well as amplification/copy gain of PIK3CB, PDK1, Akt, and various receptor tyrosine kinase genes. Most of these genetic alterations are particularly common in FTC and many of them are even more common in ATC; they are generally less common in papillary thyroid cancer (PTC), in which the MAP kinase (MAPK) pathway activated by the BRAF mutation instead plays a major role. Methylation and, thus, epigenetic silencing of PTEN, a major negative regulator of the PI3K/Akt pathway, occurs in close association with activating genetic alterations of the PI3K/Akt pathway, constituting a unique self-enhancement mechanism for this pathway. Many of these genetic alterations are mutually exclusive in differentiated thyroid tumors, but with increasing concurrence from benign tumors to FTC to ATC. RET/PTC, Ras, and receptor tyrosine kinase could dually activate the PI3K/Akt and MAPK pathways. Most cases of ATC harbor genetic alterations in these genes or other genetic combinations that can activate both pathways. It is proposed that genetic alterations in the PI3K/Akt pathway promote thyroid cell transformation to FTC and that genetic alterations in the MAPK pathway promote cell transformation to PTC; accumulation of multiple genetic alterations that can activate both pathways promotes thyroid cancer aggressiveness and progression to ATC.

CONCLUSIONS

Genetic alterations are common in the PI3K/Akt pathway in thyroid cancer and play a fundamental role in the tumorigenesis and progression of this cancer. This provides a strong basis for the emerging development of novel genetic-based diagnostic, prognostic, and therapeutic strategies for thyroid cancer.

Genetic Predisposition to Familial Nonmedullary Thyroid Cancer: An Update of Molecular Findings and State-of-the-Art Studies

Familial thyroid cancer has become a well-recognized entity in patients with thyroid cancer originating from follicular cells, that is, nonmedullary thyroid carcinoma. The diagnosis of familial thyroid cancer provides an opportunity for early detection and possible prevention in family members. Understanding the syndromes associated with familial thyroid cancer allows clinicians to evaluate and treat patients for coexisting pathologic conditions. About five percents of patients with well-differentiated thyroid carcinoma have a familial disease. Patients with familial non-medullalry thyroid cancer have more aggressive tumors with increased rates of extrathyroid extension, lymph node metastases, and frequently show the phenomenon of “anticipation” (earlier age at disease onset and increased severity in successive generations). So far, four predisposition loci have been identified in relatively rare extended pedigrees, and association studies have identified multiple predisposing variants for differentiated thyroid cancer. This suggests that there is a high degree of genetic heterogeneity and that the development of this type of tumor is a multifactorial and complex process in which predisposing genetic variants interact with a number of incompletely understood environmental risk factors. Thus, the search for the causative variants is still open and will surely benefit from the new technological approaches that have been developed in recent years.

Mutational and immunohistochemical study of the PI3K/Akt pathway in papillary thyroid carcinoma in Greece

PI3K/Akt signaling pathway plays critical role in many cell processes. There is indication that enhanced activation of PI3K/Akt cascade is implicated in thyroid tumors. Aim of this study was to evaluate the mutational status and expression of PI3K/Akt pathway mediators in papillary thyroid carcinoma in Greece. We evaluated the presence of mutations in PIK3CA (exons 9 and 20), AKT1 (exons 6-11), AKT2 (exons 6-11), AKT3 (exons 5-10), PTEN (exons 3-8), and PDPK1 (exons 4-10) genes in 83 papillary thyroid carcinomas by DNA sequencing. The expression levels of phospho-Akt and insulin-like growth factor I receptor (IGF-IR) were evaluated by immunohistochemistry. PIK3CA mutations were found in three samples. The analysis of AKT1 revealed one silent mutation in exon 9 (G726A) in 16 samples. One specimen carried an AKT3 mutation. One missense mutation was found in one sample in PTEN. No mutations were found in AKT2 and PDPK1. Increased levels of phosphorylated total Akt and IGF-IR were identified in some papillary cancers. Our findings indicate that PI3K/Akt signaling pathway is activated in some papillary tumors. However, mutations in genes coding most mediators of the pathway have not been proven to be the major modus of enhanced activation. These data suggest a potential role for PI3K/Akt-mediated signaling in papillary thyroid tumors.

Signal transduction in the human thyrocyte and its perversion in thyroid tumors

The study of normal signal transduction pathways regulating the proliferation and differentiation of a cell type allows to predict and to understand the perversions of these pathways which lead to tumorigenesis. In the case of the human thyroid cell, three cascades are mostly involved in tumorigenesis: The pathways and genetic events affecting them are described. Caveats in the use of models and the interpretation of results are formulated and the still pending questions are outlined.

The role of the PAX8/PPARgamma fusion oncogene in the pathogenesis of follicular thyroid cancer

When identified at early stages, most well-differentiated thyroid cancers are readily treated and yield excellent outcomes. Follicular thyroid cancer (FTC) however, when diagnosed at a late stage, may be very resistant to treatment, and exhibits 10-year survival rates less than 40%. Despite substantial progress in recent years, we still have limited understanding of the molecular and biological interrelationships between the various subtypes of benign and malignant follicular thyroid neoplasms. In contrast to the wealth of information available regarding papillary thyroid carcinoma (PTC), the triggering mechanisms of FTC development and the major underlying genetic alterations leading to follicular thyroid carcinogenesis remain obscure. Recent studies have focused on a chromosomal translocation, t(2;3) (q13;p25), fusing PAX8, a transcription factor that is essential for normal thyroid gland development, with the peroxisome proliferator-activated receptor gamma (PPARgamma), a member of the steroid/thyroid nuclear receptor family. This chromatin rearrangement results in the expression of a PAX8/PPARgamma fusion protein, designated PPFP, whose incidence is relatively common in FTC and may represent an initiating event in the genesis of FTC. Here we review progress on the studies of PPFP that assess its involvement in FTC tumorigenesis.

The PI3K-Akt-mTOR pathway in initiation and progression of thyroid tumors

The phosphoinositide-3 (OH) kinase (PI3K) signaling cascade is involved in regulating glucose uptake and metabolism, growth, motility, and other essential functions for cell survival. Unregulated activation of this pathway commonly occurs in cancer through a variety of mechanisms, including genetic mutations of kinases and regulatory proteins, epigenetic alterations that alter gene expression and translation, and posttranslational modifications. In thyroid cancer, constitutive activation of PI3K signaling has been shown to play a role in the genetic predisposition for thyroid neoplasia in Cowden's syndrome, and is recognized to be frequently overactivated in sporadic forms of thyroid cancer including those with aggressive clinical behaviors. In this review, the key signaling molecules in the PI3K signaling cascade, the abnormalities known to occur in thyroid cancer, and the potential for therapeutic targeting of PI3K pathway members will be discussed.

Thyroid cancer: current molecular perspectives

The thyroid cancer is a rare oncological entity, representing no more than 1% of all human malignant neoplasms. Recently, it has been demonstrated a sharp increase in incidence of differentiated thyroid carcinoma, equally occurring in both sexes. So far, multiple genetic alterations have been identified in differentiated thyroid carcinoma, leading to investigate the clinical utility of genetic studies. In particular, molecular genetic approaches searching for gene mutations in the material collected by fine needle ago-biopsy may have a particular utility in small nodules and in those specimens with an indeterminate cytology. The expansion of knowledge about genetic mutations occurring in different thyroid tumors has characterized recent years, allowing the identification of a correlation between specific mutations and phenotypic characteristics of thyroid cancers, essential for their prognosis. This review will briefly report on the histological features and the new entity represented by thyroid microcarcinoma and will focus on both environmental and genetic aspects associated with the occurrence of thyroid cancer.

Expression of hypoxia-inducible factor 1 alpha in thyroid carcinomas

Hypoxia-inducible factor 1 alpha (HIF-1 alpha) is upregulated by hypoxia and oncogenic signalling in many solid tumours. Its regulation and function in thyroid carcinomas are unknown. We evaluated the regulation of HIF-1 alpha and target gene expression in primary thyroid carcinomas and thyroid carcinoma cell lines (BcPAP, WRO, FTC-133 and 8505c). HIF-1 alpha was not detectable in normal tissue but was expressed in thyroid carcinomas. Dedifferentiated anaplastic tumours (ATCs) exhibited high levels of nuclear HIF-1 alpha staining. The HIF-1 target glucose transporter 1 was expressed to a similar level in all tumour types, whereas carbonic anhydrase-9 was significantly elevated in ATCs. In vitro studies revealed a functionally active HIF-1 alpha pathway in thyroid cells with transcriptional activation observed after graded hypoxia (1% O(2), anoxia) or treatment with a hypoxia mimetic cobalt chloride. High basal and hypoxia-induced expression of HIF-1 alpha in FTC-133 cells that harbour a phosphatase and tensin homologue (PTEN) mutation was reduced by introduction of wild-type PTEN. Similarly, pharmacological inhibition of the phosphoinositide 3-kinase (PI3K) pathway using LY294002 inhibited HIF-1 alpha and HIF-1 alpha targets in all cell lines, including those with B-RAF mutations (BcPAP and 8505c). In contrast, the effects of inhibition of the RAF/MEK/extracellular signal-regulated kinase pathway were restricted by environmental condition and B-RAF mutation status. HIF-1 is functionally expressed in thyroid carcinomas and is regulated not only by hypoxia but also via growth factor signalling pathways and, in particular, the PI3K pathway. Given the strong association of HIF-1 alpha with an aggressive disease phenotype and therapeutic resistance, this pathway may be an attractive target for improved therapy in thyroid carcinomas.

Induction of thyroid gene expression and radioiodine uptake in thyroid cancer cells by targeting major signaling pathways

CONTEXT

Radioiodine ablation is commonly used to treat thyroid cancer, but a major challenge is often the loss of radioiodine avidity of the cancer caused by aberrant silencing of iodide-handling genes.

OBJECTIVES

This study was conducted to test the therapeutic potential of targeting the aberrantly activated MAPK and PI3K/Akt/mTOR pathways and histone deacetylase to restore radioiodine avidity in thyroid cancer cells.

EXPERIMENTAL DESIGN

We tested the effects of specific inhibitors targeting these pathways/molecules that had established clinical applicability, including the MAPK kinase inhibitor RDEA119, mTOR inhibitor temsirolimus, Akt inhibitor perifosine, and histone deacetylase inhibitor SAHA, individually or in combinations, on the expression of iodide-handling genes and radioiodide uptake in a large panel of thyroid cancer cell lines.

RESULTS

The expression of a large number of iodide-handling genes could be restored, particularly the sodium/iodide symporter, TSH receptor, and thyroperoxidase, by treating cells with these inhibitors. The effect was particularly robust and synergistic when combinations of inhibitors containing SAHA were used. Robust expression of sodium/iodide symporter in the cell membrane, which plays the most important role in iodide uptake in thyroid cells, was confirmed by immunofluorescent microscopy. Radioiodide uptake by cells was correspondingly induced under these conditions. Thyroid gene expression and radioiodide uptake could both be further enhanced by TSH.

CONCLUSIONS

Targeting major signaling pathways could restore thyroid gene expression and radioiodide uptake in thyroid cancer cells. Further studies are warranted to test this therapeutic potential in restoring radioiodine avidity of thyroid cancer cells for effective ablation treatment.

Molecular pathogenesis of follicular cell derived thyroid cancers

Thyroid cancers are the most common endocrine malignancy. Radiation exposure, family history of thyroid cancer and some inherited conditions are the most important predisposing factors for the development of thyroid cancer. Three mitogenic signalling pathways have been described in the thyroid cell, which are influenced by various stimulatory and inhibitory hormones, growth factors and neurotransmitters. Various proto-oncogenes and oncogenes like ras, braf, trk, met and RET also play a role in the signal transduction systems. Two theories have been described in thyroid cancer pathogenesis, the foetal cell carcinogenesis theory and the more common, multistep carcinogenesis theory. The multistep carcinogenesis theory is now the accepted model in many human cancers, including thyroid cancer. The early events of tumour formation are the consequence of activation of either various growth factors or the proto-oncogenes like ras, met or ret. This results in the formation of differentiated thyroid cancers like the papillary, follicular or Hurthle cell cancers. The later stages of tumour formation involve further activation of proto-oncogenes and loss or inactivation of tumour suppressor genes like p53. Based on this theory, follicular carcinomas are generated from follicular adenomas and papillary carcinomas from precursor cells generated from thyrocytes. Anaplastic carcinoma may develop from papillary or follicular carcinoma by dedifferentiation. In this review article, we highlight the molecular pathogenesis of thyroid tumours.

A novel HSP90 modulator with selective activity against thyroid cancers in vitro

BACKGROUND

Heat shock protein 90 (HSP90) is a chaperone protein regulating several client proteins involved in thyroid cancer development. The purpose of this study was to mechanistically evaluate a novel, natural product drug with anticancer activity in thyroid cancer cell lines in vitro for future translational applications.

METHODS

A total of 285 natural plant extracts and compounds were evaluated for anticancer activity by MTS assay. Apoptosis and cell cycle arrest were characterized by annexin V-propidium iodide (PI) flow cytometry. HSP90 and client protein modulation, as well as apoptosis confirmation, as demonstrated by Western blot analysis.

RESULTS

Of the 285 compounds and products tested, 45 demonstrated antiproliferative activity in thyroid cancers by MTS assay. BTIMNP_D004 demonstrated the greatest inhibition (IC(50) = 155-2,890 nM in thyroid cancers). Activity was cancer-cell selective compared to fibroblasts, with increased potency over 17-AAG in BCPAP, FTC133, and DRO81-1 cells. D004 modulated cell cycle arrest after 18 hours (G(1)/G(0) --> S and G(2)/M) with 30% FTC133 cells shifted, 22% BCPAP cells shifted, and 15% SW1736 cells shifted versus controls (P < .01, P < .01, and P < .05, respectively). A total of 1 muM D004 induced significant apoptosis, with 76% BCPAP cells gated after 18 hours (annexin V-PI staining vs <3% in controls, P < .01; and 80% FTC133 cells vs 4% controls; P < .01). Western blot analysis demonstrated modulation of HSP90 expression levels, with inhibition of HSF-1, AKT, and caspase-3 expression, and cleavage of PARP in both BCPAP and FTC133 cells.

CONCLUSION

BTIMNP_D004 is a novel natural product drug with anticancer activity against thyroid cancers in vitro, and may act through induction of apoptosis, modulation of cell cycle arrest, and modulation of heat shock chaperone proteins including HSP90. These preliminary in vitro data support future preclinical studies for translational applications.

Molecular diagnostics and predictors in thyroid cancer

BACKGROUND

The accuracy of cancer detection in thyroid nodules by fine-needle aspiration (FNA) cytology and prognostication of thyroid cancer needs further improvement and can benefit from testing for molecular alterations known to occur in thyroid tumors.

SUMMARY

Recent studies have demonstrated the feasibility of mutation detection in clinical FNA samples from thyroid nodules and their contribution to improving the diagnostic accuracy of FNA cytology. It appears that molecular testing is most beneficial for thyroid FNA samples with indeterminate cytology, where it can resolve the diagnosis in a significant number of cases. In addition to BRAF mutation, which has been studied most extensively, detection of RAS, RET/PTC, and PAX8/PPARgamma mutations also contribute substantially to cancer diagnosis. Some of these molecular markers, particularly BRAF, can also be used for tumor prognostication. In clinical setting, molecular testing of thyroid FNA samples and surgically removed tumors should utilize a restricted number of techniques that provide high accuracy and specificity of mutation detection.

CONCLUSION

Testing for cancer-specific mutations in thyroid FNA samples and surgically removed tumor tissues increases diagnostic accuracy of FNA cytology and offers better prognostication of thyroid cancer.