A phase II trial of rosiglitazone in patients with thyroglobulin-positive and radioiodine-negative differentiated thyroid cancer

Peroxisome proliferator-activated receptors: Key regulators of tumor progression and growth

One of the main causes of death on the globe is cancer. Peroxisome-proliferator-activated receptors (PPARs) are nuclear hormone receptors, including PPARα, PPARδ and PPARγ, which are important in regulating cancer cell proliferation, survival, apoptosis, and tumor growth. Activation of PPARs by endogenous or synthetic compounds regulates tumor progression in various tissues. Although each PPAR isotype suppresses or promotes tumor development depending on the specific tissues or ligands, the mechanism is still unclear. PPARs are receiving interest as possible therapeutic targets for a number of disorders. Numerous clinical studies are being conducted on PPARs as possible therapeutic targets for cancer. Therefore, this review will focus on the existing and future uses of PPARs agonists and antagonists in treating malignancies. PubMed, Science Direct, and Scopus databases were searched regarding the effect of PPARs on various types of cancers until the end of May 2023. The results of the review articles showed the therapeutic influence of PPARs on a wide range of cancer on in vitro, in vivo and clinical studies. However, further experimental and clinical studies are needed to be conducted on the influence of PPARs on various cancers.

Peroxisome proliferator-activated receptors as therapeutic target for cancer

Peroxisome proliferator-activated receptors (PPARs) are transcription factors belonging to the nuclear receptor family. There are three subtypes of PPARs, including PPAR-α, PPAR-β/δ and PPAR-γ. They are expressed in different tissues and act by regulating the expression of target genes in the form of binding to ligands. Various subtypes of PPAR have been shown to have significant roles in a wide range of biological processes including lipid metabolism, body energy homeostasis, cell proliferation and differentiation, bone formation, tissue repair and remodelling. Recent studies have found that PPARs are closely related to tumours. They are involved in cancer cell growth, angiogenesis and tumour immune response, and are essential components in tumour progression and metastasis. As such, they have become a target for cancer therapy research. In this review, we discussed the current state of knowledge on the involvement of PPARs in cancer, including their role in tumourigenesis, the impact of PPARs in tumour microenvironment and the potential of using PPARs combinational therapy to treat cancer by targeting essential signal pathways, or as adjuvants to boost the effects of current chemo and immunotherapies. Our review highlights the complexity of PPARs in cancer and the need for a better understanding of the mechanism in order to design effective cancer therapies.

Drug repositioning in thyroid cancer treatment: the intriguing case of anti-diabetic drugs

Cancer represents the main cause of death worldwide. Thyroid cancer (TC) shows an overall good rate of survival, however there is a percentage of patients that do not respond or are refractory to common therapies. Thus new therapeutics strategies are required. In the past decade, drug repositioning become very important in the field of cancer therapy. This approach shows several advantages including the saving of: i) time, ii) costs, iii) de novo studies regarding the safety (just characterized) of a drug. Regarding TC, few studies considered the potential repositioning of drugs. On the other hand, certain anti-diabetic drugs, were the focus of interesting studies on TC therapy, in view of the fact that they exhibited potential anti-tumor effects. Among these anti-diabetic compounds, not all were judjed as appropriate for repositioning, in view of well documented side effects. However, just to give few examples biguanides, DPP-4-inhibitors and Thiazolidinediones were found to exert strong anti-cancer effects in TC. Indeed, their effects spaced from induction of citotoxicity and inhibition of metastatic spread, to induction of de-differentiation of TC cells and modulation of TC microenvironment. Thus, the multifacial anti-cancer effect of these compounds would make the basis also for combinatory strategies. The present review is aimed at discuss data from studies regarding the anti-cancer effects of several anti-diabetic drugs recently showed in TC in view of their potential repositioning. Specific examples of anti-diabetic repositionable drugs for TC treatment will also be provided.

Radioiodine therapy in advanced differentiated thyroid cancer: Resistance and overcoming strategy

Thyroid cancer is the most prevalent endocrine tumor and its incidence is fast-growing worldwide in recent years. Differentiated thyroid cancer (DTC) is the most common pathological subtype which is typically curable with surgery and Radioactive iodine (RAI) therapy (approximately 85%). Radioactive iodine is the first-line treatment for patients with metastatic Papillary Thyroid Cancer (PTC). However, 60% of patients with aggressive metastasis DTC developed resistance to RAI treatment and had a poor overall prognosis. The molecular mechanisms of RAI resistance include gene mutation and fusion, failure to transport RAI into the DTC cells, and interference with the tumor microenvironment (TME). However, it is unclear whether the above are the main drivers of the inability of patients with DTC to benefit from iodine therapy. With the development of new biological technologies, strategies that bolster RAI function include TKI-targeted therapy, DTC cell redifferentiation, and improved drug delivery via extracellular vesicles (EVs) have emerged. Despite some promising data and early success, overall survival was not prolonged in the majority of patients, and the disease continued to progress. It is still necessary to understand the genetic landscape and signaling pathways leading to iodine resistance and enhance the effectiveness and safety of the RAI sensitization approach. This review will summarize the mechanisms of RAI resistance, predictive biomarkers of RAI resistance, and the current RAI sensitization strategies.

Cardiovascular protective effects of PPARγ agonists in hypothyroid rats: protection against oxidative stress

Hypothyroidism disturbs redox homeostasis and takes part in cardiovascular system dysfunction. Considering antioxidant and cardio-protective effects of PPAR-γ agonists including pioglitazone (POG) and rosiglitazone (RSG), the present study was aimed to determine the effect of POG or RSG on oxidants and antioxidants indexes in the heart and aorta tissues of Propylthiouracil (PTU)-induced hypothyroid rats.

MATERIALS AND METHODS

The animals were divided into six groups: (1) Control; (2) propylthiouracil (PTU), (3) PTU-POG 10, (4) PTU-POG 20, (5) PTU-RSG 2, and (6) PTU-RSG 4. Hypothyroidism was induced in rats by giving 0.05% propylthiouracil (PTU) in drinking water for 42 days. The rats of PTU-POG 10 and PTU-POG 20 groups received 10 and 20 mg/kg POG, respectively, besides PTU, and the rats of PTU-RSG 2 and PTU-RSG 4 groups received 2 and 4 mg/kg RSG, respectively, besides PTU. The animals were sacrificed, and the serum of the rats was collected to measure thyroxine level. The heart and aorta tissues were also removed for the measurement of biochemical oxidative stress markers.

RESULTS

Hypothyroidism was induced by PTU administration, which was indicated by lower serum thyroxine levels. Hypothyroidism also was accompanied by a decrease of catalase (CAT), superoxide dismutase (SOD) activities, and thiol concentration in the heart and aorta tissues while increased level of malondialdehyde (MDA). Interestingly, administration of POG or RSG dramatically reduced oxidative damage in the heart and aorta, as reflected by a decrease in MDA and increased activities of SOD, CAT, and thiol content.

CONCLUSION

The results of this study showed that administration of POG or RSG decreased oxidative damage in the heart and aorta tissues induced by hypothyroidism in rats.

Brain‑derived neurotrophic factor and nitric oxide contribute to protective effects of rosiglitazone on learning and memory in hypothyroid rats

The effects of the well‑known peroxisome proliferator‑activated receptor gamma (PPAR-γ) agonist rosiglitazone (Rosi) on brain‑derived neurotrophic factor (BDNF), nitric oxide (NO), and learning and memory were investigated in hypothyroid rats. Hypothyroidism was induced in immature Wistar rats by administration of propylthiouracil in drinking water. Rats were divided into four groups: control, hypothyroid, and hypothyroid treated with Rosi at doses of 2 mg/kg or 4 mg/kg. Memory was then assessed by the Morris water maze (MWM) and passive avoidance (PA) tests. Following anesthetization, brain samples were collected for biochemical measurements. Hypothyroidism increased the escape latency and traveled path in the learning trials of the MWM and decreased the time spent and the distance traveled in the target quadrant on the probe day. Hypothyroidism also impaired the avoidance behavior of rats in the PA test. Rosi improved the performance of rats in both MWM and PA tasks. Hypothyroidism also decreased hippocampal BDNF levels, increased NO metabolites, and induced oxidative damage in the brain. Treatment of hypothyroid rats with both doses of Rosi increased BDNF levels and decreased NO metabolites and malondialdehyde concentrations. In addition, thiol content and superoxide dismutase and catalase activities were increased in the brain regions of hypothyroid rats receiving Rosi. The administration of 4 mg/kg Rosi also significantly increased serum thyroxin levels. The results of the present study showed that BDNF and NO play a role in the protective effects of Rosi against learning and memory impairment in hypothyroid rats.

Molecular mechanisms of radioactive iodine refractoriness in differentiated thyroid cancer: Impaired sodium iodide symporter (NIS) expression owing to altered signaling pathway activity and intracellular localization of NIS

The advanced, metastatic differentiated thyroid cancers (DTCs) have a poor prognosis mainly owing to radioactive iodine (RAI) refractoriness caused by decreased expression of sodium iodide symporter (NIS), diminished targeting of NIS to the cell membrane, or both, thereby decreasing the efficacy of RAI therapy. Genetic aberrations (such as BRAF, RAS, and RET/PTC rearrangements) have been reported to be prominently responsible for the onset, progression, and dedifferentiation of DTCs, mainly through the activation of mitogen-activated protein kinase (MAPK) and phosphoinositide 3-kinase (PI3K)/AKT signaling pathways. Eventually, these alterations result in a lack of NIS and disabling of RAI uptake, leading to the development of resistance to RAI therapy. Over the past decade, promising approaches with various targets have been reported to restore NIS expression and RAI uptake in preclinical studies. In this review, we summarized comprehensive molecular mechanisms underlying the dedifferentiation in RAI-refractory DTCs and reviews strategies for restoring RAI avidity by tackling the mechanisms.

DHA/EPA-Enriched Phosphatidylcholine Suppresses Tumor Growth and Metastasis via Activating Peroxisome Proliferator-Activated Receptor γ in Lewis Lung Cancer Mice

In the present study, the antitumor effects of docosahexaenoic acid-phosphatidylcholine (DHA-PC) and eicosapentanoic acid-phosphatidylcholine (EPA-PC) in Lewis lung cancer mice were investigated. As observed, DHA-PC and EPA-PC obviously inhibited the transplanted tumor growth and the positive expression of Ki67. The metastatic nodules and hematoxylin and eosin (HE) staining of the lung indicated that DHA-PC and EPA-PC suppressed lung metastasis. PPARγ has a key role in cell survival, which may be a target for cancer therapy. Further mechanism research indicated that DHA-PC and EPA-PC significantly enhanced the levels of PPARγ and subsequently downregulated the NF-κB pathway. DHA-PC and EPA-PC accelerate cancer cell apoptosis by decreasing NF-κB-mediated antiapoptotic factors Bcl-2 and Bcl-XL, thereby inhibiting tumor growth. In addition, DHA-PC and EPA-PC significantly decreased the levels of NF-κB-mediated matrix metallopeptidase 9 (MMP9) and heparanase (HPA), which block the extracellular matrix (ECM) degradation, thereby suppressing lung metastasis. These findings suggested that DHA-PC and EPA-PC could be used as food supplements and/or functional ingredients for cancer patients.

Advancements in the treatment of differentiated thyroid cancer

Derived from follicular epithelial cells, differentiated thyroid cancer (DTC) accounts for the majority of thyroid malignancies. The threefold increase in DTC incidence over the last three decades has been largely attributed to advancements in detection of papillary thyroid microcarcinomas. Efforts to address the issue of overtreatment have notably included the reclassification of encapsulated follicular variant papillary thyroid cancers (EFVPTC) to non-invasive follicular thyroid neoplasm with papillary-like nuclear features (NIFTP). In the last 5 years, the overall management approach for this relatively indolent cancer has become less aggressive. Although surgery and radioiodine ablation remain the mainstay of DTC therapy, the role of active surveillance is being explored. Furthermore, the most recent American Thyroid Association (ATA) guidelines offer flexibility between lobectomy and total thyroidectomy for thyroid nodules between 1 cm and 4 cm in the absence of extrathyroidal extension or nodal disease. As our understanding of the natural history and molecular underpinnings of DTC evolves, so might our approach to managing low-risk patients, obviating the need for invasive intervention. Simultaneously, advances in interventional and systemic therapies have greatly expanded treatment options for high-risk surgical candidates and patients with widespread disease, and continue to be areas of active investigation. Continued research efforts are essential to improve our ability to offer effective individualized therapy to patients at all disease stages and to reduce the incidence of recurrent and progressive disease.

Clinical and Translational Challenges in Thyroid Cancer

Thyroid cancer is the most common endocrine malignancy and it accounts for 1% of all newly diagnosed tumors. Approximately 10% of patients with differentiated thyroid carcinomas (DTC) and 30% with medullary thyroid carcinoma (MTC) could not be cured with locoregional treatment and could develop metastatic disease. In addition, one of the most aggressive solid tumors can arise from the thyroid gland, the anaplastic thyroid carcinoma, with a median overall survival of less than 6 months. Currently, only four drugs are approved for the treatment of DTC and MTC and several unmet needs are focusing the scientific discussions, including the resistant setting, the off-target side effects that may reduce the efficacy and the molecular knowledge-based combinations. In this review, we aimed to discuss the current molecular landscape and treatment of thyroid cancers, and the ongoing clinical and translational research lines focusing on new drugs and drug combinations to improve the inhibition of driver mutations, such as BRAF and RET, and how systemic therapies that improved outcomes of other cancer types, like immunotherapy and peptide receptor radionuclide therapy, may play a role in the future management of advanced thyroid cancers.

Targeting Novel Sodium Iodide Symporter Interactors ADP-Ribosylation Factor 4 and Valosin-Containing Protein Enhances Radioiodine Uptake

The sodium iodide symporter (NIS) is required for iodide uptake, which facilitates thyroid hormone biosynthesis. NIS has been exploited for over 75 years in ablative radioiodine (RAI) treatment of thyroid cancer, where its ability to transport radioisotopes depends on its localization to the plasma membrane. The advent of NIS-based in vivo imaging and theranostic strategies in other malignancies and disease modalities has recently increased the clinical importance of NIS. However, NIS trafficking remains ill-defined. Here, we used tandem mass spectrometry followed by coimmunoprecipitation and proximity ligation assays to identify and validate two key nodes-ADP-ribosylation factor 4 (ARF4) and valosin-containing protein (VCP)-controlling NIS trafficking. Using cell-surface biotinylation assays and highly inclined and laminated optical sheet microscopy, we demonstrated that ARF4 enhanced NIS vesicular trafficking from the Golgi to the plasma membrane, whereas VCP-a principal component of endoplasmic reticulum (ER)-associated degradation-governed NIS proteolysis. Gene expression analysis indicated VCP expression was particularly induced in aggressive thyroid cancers and in patients who had poorer outcomes following RAI treatment. Two repurposed FDA-approved VCP inhibitors abrogated VCP-mediated repression of NIS function, resulting in significantly increased NIS at the cell-surface and markedly increased RAI uptake in mouse and human thyroid models. Collectively, these discoveries delineate NIS trafficking and highlight the new possibility of systemically enhancing RAI therapy in patients using FDA-approved drugs. SIGNIFICANCE: These findings show that ARF4 and VCP are involved in NIS trafficking to the plasma membrane and highlight the possible therapeutic role of VCP inhibitors in enhancing radioiodine effectiveness in radioiodine-refractory thyroid cancer.

New insights into molecular mechanisms of rosiglitazone in monotherapy or combination therapy against cancers

Rosiglitazone (ROSI), a member of thiazolidinediones (TZDs) which act as high-affinity agonists of the nuclear receptor peroxisome-proliferator-activated receptor-γ (PPARγ), is clinically used as an antidiabetic drug which could attenuate the insulin resistance associated with obesity, hypertension, and impaired glucose tolerance in humans. However, recent studies reported that ROSI had significant anticancer effects on various human malignant tumor cells. Mounting evidence indicated that ROSI could exert anticancer effects through PPARγ-dependent or PPARγ-independent ways. In this review, we summarized the PPARγ-dependent antitumor activities of ROSI, which included apoptosis induction, inhibition of cell proliferation and cancer metastasis, reversion of multidrug resistance, reduction of immune suppression, autophagy induction, and antiangiogenesis; and the PPARγ-independent antitumor activities of ROSI, which included inhibition of nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB) pathway, inhibition of prostaglandin E2 (PGE₂), increasing MAPK phosphatase 1 (MKP-1) expression and regulation of other apoptosis-related cell factors. In addition, we discussed the anti-cancer application of ROSI by monotherapy or combination therapy with present chemotherapeutic drugs in vitro and in vivo. Moreover, we reviewed the phase I cancer clinical trials related to ROSI combined with chemotherapeutics and phase II trials about the anti-cancer effects of ROSI monotherapy and the radiotherapy sensitivity of ROSI.

Novel targeted therapies and immunotherapy for advanced thyroid cancers

Thyroid cancer is a frequently encountered endocrine malignancy. Despite the favorable prognosis of this disease, 15–20% of differentiated thyroid cancer (DTC) cases and most anaplastic types, remain resistant to standard treatment options, including radioactive iodine (RAI). In addition, around 30% of medullary thyroid cancer (MTC) cases show resistance after surgery. The evolving understanding of disease-specific molecular therapeutic targets has led to the approval of two targeted therapies (Sorafenib and Lenvatinib) for RAI refractory DTC and another two drugs (Vandetanib and Cabozantinib) for MTC. These advanced therapies exert their effects by blocking the MAPK pathway, which has been widely correlated to different types of thyroid cancers. While these drugs remain reserved for thyroid cancer patients who failed all treatment options, their ability to improve patients’ overall survival remain hindered by their low efficacy and other molecular factors. Among these factors is the tumor’s ability to activate parallel proliferative signaling pathways other than the cascades blocked by these drugs, along with overexpression of some tyrosine kinase receptors (TKR). These facts urge the search for novel different treatment strategies for advanced thyroid cases beyond these drugs. Furthermore, the growing knowledge of the dynamic immune system interaction with tumor microenvironment has revolutionized the cancer immune therapy field. In this review, we aim to discuss the molecular escape mechanisms of thyroid tumors from these drugs. We also highlight novel therapeutic options targeting other pathways than MAPK, including PI3K pathway, ALK translocations and HER2/3 receptors and their clinical impact. We also aim to discuss the usage of targeted therapy in restoring thyroid tumor sensitivity to RAI, and finally turn to extensively discuss the role of immunotherapy as a potential alternative treatment option for advanced thyroid diseases.

Treatment and surveillance of advanced, metastatic iodine-resistant differentiated thyroid cancer

PURPOSE OF REVIEW

This review will focus on the management and treatment of metastatic thyroid cancer that is radioactive iodine refractory and review the new drugs and their mechanism of actions as well as their adverse events.

RECENT FINDINGS

Until recently, there were no efficacious therapeutic modalities for these patients. With advancement in knowledge and research of the molecular aberrations and oncogenic mutations in thyroid cancer as well as further understanding the role of angiogenesis in tumor growth molecular pathogenesis, novel targeted therapies are available for these patients. Some of these drugs have successfully prolonged progression free survival and are now Food and Drug Administration approved. Additional agents are approved for the treatment of other types of cancers and are currently under investigation for differentiated thyroid cancer treatment.

SUMMARY

Differentiated thyroid cancer (papillary and follicular) is the most common endocrine malignancy. It is generally known to have an excellent prognosis and patients are usually cured with the conventional primary treatments including surgery, radioactive iodine, and thyroid stimulating hormone suppression. A minor proportion of patients do not fully recover mainly because they develop radioactive iodine-resistant disease. These patients have few treatment options, which we aimed to describe here.

Signaling Pathways in Thyroid Cancer

The morbidity of thyroid cancer is increasing gradually year by year, showing an increasing tendency in nationality, sex, age, tumor size, and tumor staging. The changes of thyroid cell genes, signaling pathways, and related molecular dysfunction promote the occurrence, development, invasion, and metastasis of thyroid cancer. Surgical operation, radioiodine, and endocrinotherapy models can achieve a better prognosis for most patients with thyroid cancer. Although targeted therapeutic drugs bring possible therapeutic opportunities for refractory thyroid cancer, there is a great gap between their predictive value and their actual efficacy. Currently, there is still no completely effective drug for the treatment. Based on the signaling pathways, the "reclaim therapy" for residual tumor and systemic intervention aims to increase anticancer ability and to encourage new directions and thoughts in the treatment of refractory thyroid cancer.

Redifferentiation of Radioiodine Refractory Differentiated Thyroid Cancer for Reapplication of I-131 Therapy

Although most differentiated thyroid cancers show excellent prognosis, treating radioiodine refractory differentiated thyroid cancer (RR-DTC) is challenging. Various therapies, including chemotherapy, radiotherapy, and targeted therapy, have been applied for RR-DTC but show limited effectiveness. Redifferentiation followed by radioiodine therapy is a promising alternative therapy for RR-DTC. Retinoic acids, histone deacetylase inhibitors, and peroxisome proliferator-activated receptor-gamma agonists are classically used as redifferentiation agents, and recent targeted molecules are also used for this purpose. Appropriate selection of redifferentiation agents for each patient, using current knowledge about genetic and biological characteristics of thyroid cancer, might increase the efficacy of redifferentiation treatment. In this review, we will discuss the mechanisms of these redifferentiation agents, results of recent clinical trials, and promising preclinical results.

Protective Effect of PPARγ Agonists on Cerebellar Tissues Oxidative Damage in Hypothyroid Rats

The aim of the current study was to investigate the effects of peroxisome proliferator-activated receptor gamma (PPARγ) agonists on cerebellar tissues oxidative damage in hypothyroid rats. The animals included seven groups: group I (control), the animals received drinking water; group II, the animals received 0.05% propylthiouracil (PTU) in drinking water; besides PTU, the animals in groups III, IV, V, VI, and VII, were injected with 20 mg/kg vitamin E (Vit E), 10 or 20 mg/kg pioglitazone, and 2 or 4 mg/kg rosiglitazone, respectively. The animals were deeply anesthetized and the cerebellar tissues were removed for biochemical measurements. PTU administration reduced thiol content, superoxide dismutase (SOD), and catalase (CAT) activities in the cerebellar tissues while increasing malondialdehyde (MDA) and nitric oxide (NO) metabolites. Vit E, pioglitazone, and rosiglitazone increased thiol, SOD, and CAT in the cerebellar tissues while reducing MDA and NO metabolites. The results of present study showed that, similar to Vit E, both rosiglitazone and pioglitazone as PPARγ agonists exerted protective effects against cerebellar tissues oxidative damage in hypothyroid rats.

Commonalities in the Association between PPARG and Vitamin D Related with Obesity and Carcinogenesis

The PPAR nuclear receptor family has acquired great relevance in the last decade, which is formed by three different isoforms (PPARα, PPARβ/δ, and PPAR ϒ). Those nuclear receptors are members of the steroid receptor superfamily which take part in essential metabolic and life-sustaining actions. Specifically, PPARG has been implicated in the regulation of processes concerning metabolism, inflammation, atherosclerosis, cell differentiation, and proliferation. Thus, a considerable amount of literature has emerged in the last ten years linking PPARG signalling with metabolic conditions such as obesity and diabetes, cardiovascular disease, and, more recently, cancer. This review paper, at crossroads of basic sciences, preclinical, and clinical data, intends to analyse the last research concerning PPARG signalling in obesity and cancer. Afterwards, possible links between four interrelated actors will be established: PPARG, the vitamin D/VDR system, obesity, and cancer, opening up the door to further investigation and new hypothesis in this fascinating area of research.

Chemotherapy and chemoprevention by thiazolidinediones

Thiazolidinediones (TZDs) are synthetic ligands of Peroxisome-Proliferator-Activated Receptor gamma (PPARγ). Troglitazone, rosiglitazone, and pioglitazone have been approved for treatment of diabetes mellitus type II. All three compounds, together with the first TZD ciglitazone, also showed an antitumor effect in preclinical studies and a beneficial effect in some clinical trials. This review summarizes hypotheses on the role of PPARγ in tumors, on cellular targets of TZDs, antitumor effects of monotherapy and of TZDs in combination with other compounds, with a focus on their role in the treatment of differentiated thyroid carcinoma. The results of chemopreventive effects of TZDs are also considered. Existing data suggest that the action of TZDs is highly complex and that actions do not correlate with cellular PPARγ expression status. Effects are cell-, species-, and compound-specific and concentration-dependent. Data from human trials suggest the efficacy of TZDs as monotherapy in prostate cancer and glioma and as chemopreventive agent in colon, lung, and breast cancer. TZDs in combination with other therapies might increase antitumor effects in thyroid cancer, soft tissue sarcoma, and melanoma.

Retinoic acid receptors: from molecular mechanisms to cancer therapy

Retinoic acid (RA), the major bioactive metabolite of retinol or vitamin A, induces a spectrum of pleiotropic effects in cell growth and differentiation that are relevant for embryonic development and adult physiology. The RA activity is mediated primarily by members of the retinoic acid receptor (RAR) subfamily, namely RARα, RARβ and RARγ, which belong to the nuclear receptor (NR) superfamily of transcription factors. RARs form heterodimers with members of the retinoid X receptor (RXR) subfamily and act as ligand-regulated transcription factors through binding specific RA response elements (RAREs) located in target genes promoters. RARs also have non-genomic effects and activate kinase signaling pathways, which fine-tune the transcription of the RA target genes. The disruption of RA signaling pathways is thought to underlie the etiology of a number of hematological and non-hematological malignancies, including leukemias, skin cancer, head/neck cancer, lung cancer, breast cancer, ovarian cancer, prostate cancer, renal cell carcinoma, pancreatic cancer, liver cancer, glioblastoma and neuroblastoma. Of note, RA and its derivatives (retinoids) are employed as potential chemotherapeutic or chemopreventive agents because of their differentiation, anti-proliferative, pro-apoptotic, and anti-oxidant effects. In humans, retinoids reverse premalignant epithelial lesions, induce the differentiation of myeloid normal and leukemic cells, and prevent lung, liver, and breast cancer. Here, we provide an overview of the biochemical and molecular mechanisms that regulate the RA and retinoid signaling pathways. Moreover, mechanisms through which deregulation of RA signaling pathways ultimately impact on cancer are examined. Finally, the therapeutic effects of retinoids are reported.

Establishment, characterization and comparison of seven authentic anaplastic thyroid cancer cell lines retaining clinical features of the original tumors

BACKGROUND

Anaplastic thyroid cancer (ATC) is thought to often be transformed from pre-existing differentiated thyroid cancer. It is one of the most aggressive malignancies and has a dismal prognosis due to its resistance to multimodal therapies. Basic exploratory studies using authentic ATC cell lines that retain its clinical features are necessary. We investigated the characteristics of seven ATC cell lines newly established at our institute to confirm their possible utility for basic studies.

METHODS

Seven distinct cell lines from six patients were established. Their molecular characteristics and sensitivities to cytotoxic anti-cancer drugs were investigated and compared with each other, and with the clinical features of the original tumors.

RESULTS

All cells showed extensive chromosomal abnormality and Pax8 expression, indicating human thyroid follicular cell origin. Vascular endothelial growth factor was secreted from all cells, suggesting possible candidacy for targeted therapy. Vimentin was expressed, but E-cadherin expression was lost in all cells but OCUT-1C, which showed different features from those of OCUT-1F derived from the same tumor, suggesting a mixture of cancer cell clones with various degrees of differentiation within a single ATC tumor. Cells were likely to show sensitivity for taxanes, indicating the usefulness of taxanes as the first-line chemotherapy. OCUT-2, a cell line with both B-Raf and PI3 KCA mutation, demonstrated the importance of molecular target-oriented therapy.

CONCLUSIONS

Basic studies using authentic ATC cell lines retaining the clinical features of the original tumor are useful models for investigating the mechanism of anaplastic transformation and exploring novel therapeutic strategies.

Advanced radioiodine-refractory differentiated thyroid cancer: the sodium iodide symporter and other emerging therapeutic targets

Approximately 30% of patients with advanced, metastatic differentiated thyroid cancer have radioiodine-refractory disease, based on decreased expression of the sodium iodide symporter SLC5A5 (NIS), diminished membrane targeting of NIS, or both. Patients with radioiodine-refractory disease, therefore, are not amenable to (131)I therapy, which is the initial systemic treatment of choice for non-refractory metastatic thyroid cancer. Patients with radioiodine-refractory cancer have historically had poor outcomes, partly because these cancers often respond poorly to cytotoxic chemotherapy. In the past decade, however, considerable progress has been made in delineating the molecular pathogenesis of radioiodine-refractory thyroid cancer. As a result of the identification of key genetic and epigenetic alterations and dysregulated signalling pathways, multiple biologically targeted drugs, in particular tyrosine-kinase inhibitors, have been evaluated in clinical trials with promising results and have begun to meaningfully impact clinical practice. In this Review, we summarise the current knowledge of the molecular pathogenesis of advanced differentiated thyroid cancer and discuss findings from clinical trials of targeted drugs in patients with radioiodine-refractory disease. Additionally, we focus on the molecular basis of loss of NIS expression, function, or both in refractory disease, and discuss preclinical and clinical data on restoration of radioiodine uptake.

Molecular pathogenesis and targeted therapies in well-differentiated thyroid carcinoma

Four proto-oncogenes commonly associated with well-differentiated thyroid carcinoma, rearranged during transfection (RET)/papillary thyroid cancer, BRAF, RAS, and PAX8/peroxisome proliferator activated receptor-γ, may carry diagnostic and prognostic significance. These oncogenes can be used to improve the diagnosis and management of well-differentiated thyroid carcinoma. Limited therapeutic options are available for patients with metastatic well-differentiated thyroid cancer, necessitating the development of novel therapies. Vascular endothelial growth factor (VEGF)- and RET-directed therapies such as sorafenib, motesanib, and sunitinib have been shown to be the most effective at inducing clinical responses and stabilizing the disease process. Further clinical trials of these therapeutic agents may soon change the management of thyroid cancer.

Energy restriction mimetic agents to target cancer cells: comparison between 2-deoxyglucose and thiazolidinediones

The use of energy restriction mimetic agents (ERMAs) to selectively target cancer cells addicted to glycolysis could be a promising therapeutic approach. Thiazolidinediones (TZDs) are synthetic agonists of the nuclear receptor peroxisome proliferator-activated receptor (PPAR)γ that were developed to treat type II diabetes. These compounds also display anticancer effects which appear mainly to be independent of their PPARγ agonist activity but the molecular mechanisms involved in the anticancer action are not yet well understood. Results obtained on ciglitazone derivatives, mainly in prostate cancer cell models, suggest that these compounds could act as ERMAs. In the present paper, we introduce how compounds like 2-deoxyglucose target the Warburg effect and then we discuss the possibility that the PPARγ-independent effects of various TZD could result from their action as ERMAs.

Comparative serum proteomic analysis identified afamin as a downregulated protein in papillary thyroid carcinoma patients with non-131I-avid lung metastases

BACKGROUND

The loss of 131I uptake ability in metastases from differentiated thyroid carcinoma (DTC) is becoming a major obstacle in radioiodine treatment. However, there is no effective way to screen for 131I uptake ability in metastases. The identification of differentially expressed proteins by serum proteomics may contribute to our understanding of the mechanisms underlying the dedifferentiation of DTC.

MATERIALS AND METHODS

Serum samples were obtained from papillary thyroid carcinoma patients with non-131I-avid lung metastases and 131I-avid lung metastases. Differential protein analysis was performed using two-dimensional gel electrophoresis. Candidate protein spots showing differences in expression between the two groups were identified by means of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry and were validated by western blotting.

RESULTS

We found that afamin is downregulated in the serum of papillary thyroid carcinoma patients with non-131I-avid lung metastases.

CONCLUSION

Afamin may be a potential serum biomarker for early screening of 131I uptake ability in DTC metastases and could therefore be of value in guiding radioiodine treatment decisions.

Membrane Proteins Involved in Epithelial-Mesenchymal Transition and Tumor Invasion: Studies on TMPRSS4 and TM4SF5

The epithelial-mesenchymal transition (EMT) is one mechanism by which cells with mesenchymal features can be generated and is a fundamental event in morphogenesis. Recently, invasion and metastasis of cancer cells from the primary tumor are now thought to be initiated by the developmental process termed the EMT, whereby epithelial cells lose cell polarity and cell-cell interactions, and gain mesenchymal phenotypes with increased migratory and invasive properties. The EMT is believed to be an important step in metastasis and is implicated in cancer progression, although the influence of the EMT in clinical specimens has been debated. This review presents the recent results of two cell surface proteins, the functions and underlying mechanisms of which have recently begun to be demonstrated, as novel regulators of the molecular networks that induce the EMT and cancer progression.

Dose effect of thiazolidinedione on cancer risk in type 2 diabetes mellitus patients: a six-year population-based cohort study

WHAT IS KNOWN AND OBJECTIVE

Prior studies found that thiazolidinediones (TZDs) might have tumour-suppressor activity mediated through cell-cycle arrest, induction of apoptosis and inhibition of cell invasion. The main objective of this study was to investigate the effects of TZDs on the risk of cancer among patients with type 2 diabetes mellitus (DM).

METHODS

Patients diagnosed with DM between 1 January 1998 and 31 December 2002 were identified from the Longitudinal Health Insurance Database (LHID) within the Taiwan National Health Insurance (NHI) programme. Using Cox regression models, we assessed the association between prescribed TZDs and cancer risk, TZDs' dose effect and the association between TZDs and specific cancer types. Hazard ratios (HR) were adjusted for potential confounders (age, gender, income, Charlson score index, metformin and insulin use).

RESULTS AND DISCUSSION

The adjusted HRs for those prescribed TZD were 0·74 (95% CI 0·43-1·26, P = 0·27), 0·39 (95% CI 0·33-0·45, P < 0·001) and 0·49 (95% CI 0·27-0·89, P = 0·02), respectively, relative to non-DM patients, DM patients prescribed other anti-DM drugs besides TZDs and DM patients not prescribed any anti-DM drugs. In addition, the effects of TZDs were shown to be significantly dose dependent (P for trend < 0·001). The risk of breast, brain, colorectal, ear-nose-throat, kidney, liver, lung, lymphatic, prostate, stomach, and uterus cancer was significantly lower in those prescribed TZDs.

WHAT IS NEW AND CONCLUSIONS

The results showed a decrease in cancer risk in diabetic patients using TZD, and the association was dose dependent.

New therapeutic options for advanced forms of thyroid cancer

INTRODUCTION

While the vast majority of patients with thyroid cancer have an excellent prognosis, those with more aggressive courses experience significant morbidity and mortality. Advanced forms of thyroid cancer are typically refractory to standard therapy. Numerous agents with potential usefulness in the treatment of advanced thyroid cancer have recently come under study.

AREAS COVERED

This article reviews agents identified through a systematic review of the scientific literature as being under investigation for treatment of advanced thyroid cancer. A search of both PubMed and the NCI Clinical Trials website was performed to identify such agents having reached Phase II or III testing. Improved understanding of cancer cell signaling pathways has led to the identification of > 500 kinases as potential therapeutic targets. Additional agents of interest include those that inhibit neoangiogenesis, alter epigenetic factors or stimulate antitumor immune reactions. While presently available agents have shown promise in improving progression-free survival (PFS), complete responses are not seen and significant adverse side effects are encountered.

EXPERT OPINION

The development of numerous new anticancer agents holds the promise of treatment regimens that will extend PFS and ultimately overall survival in patients with advanced thyroid cancer. Anticipated future developments include individualized, multimodal treatment regimens based on specific tumor cell biology and driver mutations.

Soft tissue metastases from differentiated thyroid cancer diagnosed by 18F FDG PET-CT

Distant metastases of differentiated thyroid cancer are unusual; lung and bones are the most frequently affected sites. Soft tissue metastases (STM) are extremely rare. We describe two cases of patients with differentiated thyroid cancer metastasizing to soft tissues. Both patients had widespread metastatic disease; clinically asymptomatic soft tissue metastases were found by 18-Fluordeoxyglucose positron emission tomography/computed tomography (18F FDG PET-CT), and confirmed by cytological and/or histopathological studies. These findings underscore the ability of 18F FDG PET-CT in accurately assessing the extent of the disease, as well as the utility of the method to evaluate regions of the body that are not routinely explored.

Radioiodine therapy in benign thyroid diseases: effects, side effects, and factors affecting therapeutic outcome

Radioiodine ((131)I) therapy of benign thyroid diseases was introduced 70 yr ago, and the patients treated since then are probably numbered in the millions. Fifty to 90% of hyperthyroid patients are cured within 1 yr after (131)I therapy. With longer follow-up, permanent hypothyroidism seems inevitable in Graves' disease, whereas this risk is much lower when treating toxic nodular goiter. The side effect causing most concern is the potential induction of ophthalmopathy in predisposed individuals. The response to (131)I therapy is to some extent related to the radiation dose. However, calculation of an exact thyroid dose is error-prone due to imprecise measurement of the (131)I biokinetics, and the importance of internal dosimetric factors, such as the thyroid follicle size, is probably underestimated. Besides these obstacles, several potential confounders interfere with the efficacy of (131)I therapy, and they may even interact mutually and counteract each other. Numerous studies have evaluated the effect of (131)I therapy, but results have been conflicting due to differences in design, sample size, patient selection, and dose calculation. It seems clear that no single factor reliably predicts the outcome from (131)I therapy. The individual radiosensitivity, still poorly defined and impossible to quantify, may be a major determinant of the outcome from (131)I therapy. Above all, the impact of (131)I therapy relies on the iodine-concentrating ability of the thyroid gland. The thyroid (131)I uptake (or retention) can be stimulated in several ways, including dietary iodine restriction and use of lithium. In particular, recombinant human thyrotropin has gained interest because this compound significantly amplifies the effect of (131)I therapy in patients with nontoxic nodular goiter.

Effects of rosiglitazone on radioiodine negative and progressive differentiated thyroid carcinoma as assessed by ¹²⁴I PET/CT imaging

AIM

The aim of this study was to evaluate the redifferentiative and antiproliferative effects of rosiglitazone in patients with progressive differentiated thyroid cancer (DTC) without or with negligible overall radioiodine uptake.

MATERIALS AND METHODS

A total of 9 patients with progressive DTC with either no or only negligible radioiodine accumulation were enrolled in this study. Oral rosiglitazone treatment was applied for 6 months (4 mg per day for 2 weeks followed by 8 mg per day). The compatibility of the medication was initially checked twice weekly and then weekly by laboratory tests and clinical evaluation of side effects. The assessments of alterations in the doses absorbed by the tumor and in lesion sizes over the course of rosiglitazone treatment were performed using serial ¹²⁴I positron emission tomography and computed tomography imaging. The assessment time points were before enrollment and 3 and 6 months posttreatment initiation.

RESULTS

Lesion dosimetry indicated that 5 of 9 patients had an improved lesion absorbed dose per administered activity (LDpA), yielding in radioiodine therapy treatment in 4 patients. One third of the patients (3/9) were unchanged with regard to LDpA, and 1 of 9 had deteriorated LDpA. Volumetric analyses revealed that lesion sizes were regredient in 3 of 9 patients, stable in 4 of 9, and was progressive in 1 of 9. The medication was well-tolerated, and no patient developed clinically important toxicity associated with rosiglitazone treatment. In 2 of 9 of the patients, the medication was terminated after 3 months as a precaution due to progressive heart disease in one patient and bone fracture within a known osteolytic bone lesion in another patient. It is not clear that these complications were caused by rosiglitazone.

CONCLUSION

Rosiglitazone appears to be suitable as off-label therapy in radioiodine-negative and progressive DTC that lacks therapy alternatives. In Europe, rosiglitazone was removed for label use because of reported side effects during diabetes treatment. Further investigations of other available glitazone compounds are necessary.

PPARs: Interference with Warburg' Effect and Clinical Anticancer Trials

The metabolic/cell signaling basis of Warburg's effect ("aerobic glycolysis") and the general metabolic phenotype adopted by cancer cells are first reviewed. Several bypasses are adopted to provide a panoramic integrated view of tumoral metabolism, by attributing a central signaling role to hypoxia-induced factor (HIF-1) in the expression of aerobic glycolysis. The cancer metabolic phenotype also results from alterations of other routes involving ras, myc, p53, and Akt signaling and the propensity of cancer cells to develop signaling aberrances (notably aberrant surface receptor expression) which, when present, offer unique opportunities for therapeutic interventions. The rationale for various emerging strategies for cancer treatment is presented along with mechanisms by which PPAR ligands might interfere directly with tumoral metabolism and promote anticancer activity. Clinical trials using PPAR ligands are reviewed and followed by concluding remarks and perspectives for future studies. A therapeutic need to associate PPAR ligands with other anticancer agents is perhaps an important lesson to be learned from the results of the clinical trials conducted to date.

Pioglitazone therapy in progressive differentiated thyroid carcinoma

AIM

Rosiglitazone achieved promising results in progressive differentiated thyroid carcinoma (DTC) with redifferentiative and antiproliferative effects, but has been taken off the market. Thus we evaluated another glitazone, pioglitazone, expecting similar positive results. PATIENT, MATERIALS, METHODS: Five patients with progressive DTC and no or only negligible iodine uptake were enrolled. Oral pioglitazone treatment was applied for 6 months. The re-differentiative effect was assessed by 124I-NaI PET/CT dosimetry and the anti-proliferative effect by 18F-FDG PET/CT imaging.

RESULTS

A redifferentiative effect of pioglitazone could not be shown. Lesion dosimetry indicated that 3/5 patients had unchanged no lesion absorbed dose per administered activity (LDpA) in any tumour lesion, 2/5 patients had a deterioration of LDpA within some lesions, thus radioiodine therapy was not performed in any patient. Volumetric analysis, using RECIST criteria, revealed progressive disease in 3/5 patients and stable disease in 2/5 patients. Metabolic changes, using EORTC criteria, revealed 3/5 patients with progressive metabolic disease, 1/5 patient with stable metabolic disease and 1/5 patients with partial metabolic response. The medication was well-tolerated, and no patient developed clinically important toxicity associated with the treatment.

CONCLUSION

Pioglitazone revealed some positive effects in radioiodine negative and progressive DTC patients but it did not fulfill the expectations given by the results of rosiglitazone therapy.

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.

Differentiated thyroid cancer: management of patients with radioiodine nonresponsive disease

Differentiated thyroid carcinoma (papillary and follicular) has a favorable prognosis with an 85% 10-year survival. The patients that recur often require surgery and further radioactive iodine to render them disease-free. Five percent of thyroid cancer patients, however, will eventually succumb to their disease. Metastatic thyroid cancer is treated with radioactive iodine if the metastases are radioiodine avid. Cytotoxic chemotherapies for advanced or metastatic noniodine avid thyroid cancers show no prolonged responses and in general have fallen out of favor. Novel targeted therapies have recently been discovered that have given rise to clinical trials for thyroid cancer. Newer aberrations in molecular pathways and oncogenic mutations in thyroid cancer together with the role of angiogenesis in tumor growth have been central to these discoveries. This paper will focus on the management and treatment of metastatic differentiated thyroid cancers that do not take up radioactive iodine.

The role of peroxisome proliferator-activated receptors in carcinogenesis and chemoprevention

Peroxisome proliferator-activated receptors (PPARs) are ligand-activated transcription factors that are involved in regulating glucose and lipid homeostasis, inflammation, proliferation and differentiation. Although all of these functions might contribute to the influence of PPARs in carcinogenesis, there is a distinct need for a review of the literature and additional experimentation to determine the potential for targeting PPARs for cancer therapy and cancer chemoprevention. As PPAR agonists include drugs that are used for the treatment of metabolic diseases, a more complete understanding of the roles of PPARs in cancer will aid in determining any increased cancer risk for patients undergoing therapy with PPAR agonists.

Peroxisome proliferator-activated receptors and cancer: challenges and opportunities

Peroxisome proliferator-activated receptors (PPARs), members of the nuclear hormone receptor superfamily, function as transcription factors and modulators of gene expression. These actions allow PPARs to regulate a variety of biological processes and to play a significant role in several diseases and conditions. The current literature describes frequently opposing and paradoxical roles for the three PPAR isotypes, PPARα, PPARβ/δ and PPARγ, in cancer. While some studies have implicated PPARs in the promotion and development of cancer, others, in contrast, have presented evidence for a protective role for these receptors against cancer. In some tissues, the expression level of these receptors and/or their activation correlates with a positive outcome against cancer, while, in other tissue types, their expression and activation have the opposite effect. These disparate findings raise the possibility of (i) PPAR receptor-independent effects, including effects on receptors other than PPARs by the utilized ligands; (ii) cancer stage-specific effect; and/or (iii) differences in essential ligand-related pharmacokinetic considerations. In this review, we highlight the latest available studies on the role of the various PPAR isotypes in cancer in several major organs and present challenges as well as promising opportunities in the field.

New treatment modalities in advanced thyroid cancer

BACKGROUND

Thyroid cancer is a heterogeneous disease that is classified into differentiated thyroid carcinoma (DTC), undifferentiated/anaplastic thyroid carcinoma (ATC) and medullary thyroid carcinoma. Results of conventional treatment modalities in advanced thyroid cancer have been disappointing and therefore, new therapies are needed.

METHODS

We searched PubMed, The Cochrane Library, Medline and EMBASE databases and abstracts published in annual proceedings for new treatment modalities in advanced thyroid cancer. We also searched for ongoing trials in www.clinicaltrials.gov.

RESULTS

Six phase I, 17 phase II and 1 phase III trials with tyrosine kinase inhibitors were carried out. We found 2 pilot studies and 11 phase II trials with redifferentiation therapies, mainly in DTC. For antiproliferative approaches, three phase I and four phase II trials were found. Immunomodulatory gene therapy was tested in a pilot study in ATC patients. Two phase II trials were carried out with immunotherapy. One phase I and nine phase II trials were found with radionucleotide therapy in patients with DTC.

CONCLUSION

The developments in the treatment of advanced thyroid cancer are intriguing. Future trials should aim at combinations of targeted agents with or without other treatment modalities, and will hopefully contribute to further improvement of outcomes.

PPARγ Promotes Growth and Invasion of Thyroid Cancer Cells

Undifferentiated (anaplastic) thyroid cancer (ATC) is one of the most aggressive human malignancies and no effective therapy is currently available. We show here that PPARγ levels are elevated in cells derived from ATC. Depletion of PPARγ in HTh74 ATC cells resulted in decreased cell growth, cell cycle arrest and a reduction in pRb and cyclin A and B1 levels. We further showed that both flank and orthotopic thyroid tumors derived from PPARγ-depleted cells grew more slowly than PPARγ-expressing cells. When PPARγ was overexpressed in more differentiated thyroid cancer BCPAP cells which lack PPARγ, there was increased growth and raised pRb and cyclin A and B1 levels. Finally, PPARγ depletion in ATC cells decreased their invasive capacity whereas overexpression in PTC cells increased invasiveness. These data suggest that PPARγ may play a detrimental role in thyroid cancer and that targeting it therapeutically may lead to improved treatment of advanced thyroid cancer.

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.

Alternative medical treatment for radioiodine-refractory thyroid cancers

Thyroid cancer is one of the most rapidly increasing cancers in many countries. Although most thyroid cancers are differentiated cancers and easily treated with radioiodine (RI), a portion of differentiated and undifferentiated cancers is refractory not only to RI therapy, but also to radiotherapy and chemotherapy. Thus, various alternative therapies have been tested in RI-refractory thyroid cancers. These alternative therapies include two major categories: redifferentiation therapy and recent molecular target therapy. Several clinical trials have investigated these therapies. They demonstrated potential effects of the therapies, although the results have been somewhat limited so far. Thus, the future strategy for undifferentiated thyroid cancers will involve individualized, lesion-specific, and combined therapy. In this review, the basic mechanism of each redifferentiation and molecular target therapy is discussed, and results of recent clinical trials using these therapeutic agents are summarized.

PPARgamma and MEK Interactions in Cancer

Peroxisome proliferator-activated receptor-gamma (PPARγ) exerts multiple functions in determination of cell fate, tissue metabolism, and host immunity. Two synthetic PPARγ ligands (rosiglitazone and pioglitazone) were approved for the therapy of type-2 diabetes mellitus and are expected to serve as novel cures for inflammatory diseases and cancer. However, PPARγ and its ligands exhibit a janus-face behaviour as tumor modulators in various systems, resulting in either tumor suppression or tumor promotion. This may be in part due to signaling crosstalk to the mitogen-activated protein kinase (MAPK) cascades. The genomic activity of PPARγ is modulated, in addition to ligand binding, by phosphorylation of a serine residue by MAPKs, such as extracellular signal-regulated protein kinases-1/2 (ERK-1/2), or by nucleocytoplasmic compartmentalization through the ERK activators MAPK kinases-1/2 (MEK-1/2). PPARγ ligands themselves activate the ERK cascade through nongenomic and often PPARγ-independent signaling. In the current review, we discuss the molecular mechanisms and physiological implications of the crosstalk of PPARγ with MEK-ERK signaling and its potential as a novel drug target for cancer therapy in patients.

To Live or to Die: Prosurvival Activity of PPARgamma in Cancers

The role of PPARγ in tumorigenesis is controversial. In this article, we review and analyze literature from the past decade that highlights the potential proneoplastic activity of PPARγ. We discuss the following five aspects of the nuclear hormone receptor and its agonists: (1) relative expression of PPARγ in human tumor versus normal tissues; (2) receptor-dependent proneoplastic effects; (3) impact of PPARγ and its agonists on tumors in animal models; (4) clinical trials of thiazolidinediones (TZDs) in human malignancies; (5) TZDs as chemopreventive agents in epidemiology studies. The focus is placed on the most relevant in vivo animal models and human data. In vitro cell line studies are included only when the effects are shown to be dependent on the PPARγ receptor.

PPAR Ligands for Cancer Chemoprevention

Peroxisome proliferators-activated receptors (PPARs) that are members of the nuclear receptor superfamily have three different isoforms: PPARalpha, PPARdelta, and PPARgamma. PPARs are ligand-activated transcription factors, and they are implicated in tumor progression, differentiation, and apoptosis. Activation of PPAR isoforms lead to both anticarcinogenesis and anti-inflammatory effect. It has so far identified many PPAR ligands including chemical composition and natural occurring. PPAR ligands are reported to activate PPAR signaling and exert cancer prevention and treatment in vitro and/or in vivo studies. Although the effects depend on the isoforms and the types of ligands, biological modulatory activities of PPARs in carcinogenesis and disease progression are attracted for control or combat cancer development. This short review summarizes currently available data on the role of PPAR ligands in carcinogenesis.