Modeling anaplastic thyroid carcinoma in the mouse

Development of animal models to study aggressive thyroid cancers

The development of mouse models for thyroid cancer has significantly advanced over the years, enhancing our understanding of thyroid tumorigenesis, molecular pathways and treatment responses. The earliest mouse models of thyroid cancer relied on hormone, radiation or chemical carcinogenesis to induce tumors. However, as our understanding of the genetic alterations driving thyroid cancer has expanded, more sophisticated genetic engineering techniques have been employed to create models with thyroid-specific expression of these driver mutations. While driver mutations can initiate tumorigenesis, they are often insufficient to sustain cancer progression and invasion, which significantly limits their usefulness in studying advanced thyroid cancers. Recent studies exploring the genomic landscape of advanced thyroid cancer have identified several cooperating mutations, which are secondary genetic alterations that work alongside driver mutations to promote thyroid tumor progression. Indeed, mice with a combination of oncogenic drivers and common cooperating alterations have been developed, demonstrating that these alterations function in conjunction with the oncogenic driver to promote the progression to advanced thyroid cancer. These models provide important preclinical tools to explore how cooperating alterations influence the response to therapies, particularly those targeting the oncogenic driver. This review will focus on recent publications that broaden the scope of advanced thyroid cancer models by combining thyroid-specific oncogenic driver expression with various cooperating mutations.

Recommendations on Surveillance for Differentiated Thyroid Carcinoma in Children with PTEN Hamartoma Tumor Syndrome

BACKGROUND

PTEN hamartoma tumor syndrome (PHTS) represents a group of syndromes caused by a mutation in the PTEN gene. Children with a germline PTEN mutation have an increased risk of developing differentiated thyroid carcinoma (DTC). Several guidelines have focused on thyroid surveillance in these children, but studies substantiating these recommendations are lacking.

OBJECTIVE

The present study intends to provide the available evidence for a thyroid carcinoma surveillance program in children with PHTS.

METHODS

An extensive literature search was performed to identify all studies on DTC in pediatric PHTS patients. Two pediatric cases are presented to illustrate the pros and cons of thyroid carcinoma surveillance. Recommendations for other patient groups at risk for DTC were evaluated. Consensus within the study team on recommendations for children with PHTS was reached by balancing the incidence and behavior of DTC with the pros and cons of thyroid surveillance, and the different surveillance methods.

RESULTS

In 5 cohort studies the incidence of DTC in childhood ranged from 4 to 12%. In total 57 cases of DTC and/or benign nodular disease in pediatric PHTS patients were identified, of which 27 had proven DTC, with a median age of 12 years (range 4-17). Follicular thyroid carcinoma (FTC) was diagnosed in 52% of the pediatric DTC patients. No evidence was found for a different clinical behavior of DTC in PHTS patients compared to sporadic DTC.

CONCLUSIONS

Children with PHTS are at increased risk for developing DTC, with 4 years being the youngest age reported at presentation and FTC being overrepresented. DTC in pediatric PHTS patients does not seem to be more aggressive than sporadic DTC.

RECOMMENDATIONS

Surveillance for DTC in pediatric PHTS patients seems justified, as early diagnosis may decrease morbidity. Consensus within the study team was reached to recommend surveillance from the age of 10 years onwards, since at that age the incidence of DTC seems to reach 5%. Surveillance for DTC should consist of yearly neck palpation and triennial thyroid ultrasound. Surveillance in children with PHTS should be performed in a center of excellence for pediatric thyroid disease or PHTS.

Plant natural products with anti-thyroid cancer activity

Thyroid cancer is the most frequent endocrine malignancy, with more than 500,000 cases per year worldwide. Differentiated thyroid cancers are the most common forms with best prognosis, while poorly/undifferentiated ones are rare (2% of all thyroid cancer), aggressive, frequently metastasize and have a worse prognosis. For aggressive, metastatic and advanced thyroid cancer novel antitumor molecules are urgently needed and phytochemical products can be a rational and extensive source, since secondary plant metabolites can guarantee the necessary biochemical variability for therapeutic purpose. Among bioactive molecules that present biological activity on thyroid cancer, resveratrol, curcumin, isoflavones, glucosinolates are the most common and used in experimental model. Most of them have been studied both in vitro and in vivo on this cancer, but rarely in clinical trial. This review summarizes phytochemicals, phytotherapeutics and plant derived compounds used in thyroid cancer.

PI3K/mTOR inhibition potentiates and extends palbociclib activity in anaplastic thyroid cancer

Anaplastic thyroid carcinoma (ATC) is the most aggressive form of thyroid cancer. Despite its low incidence, it accounts for a disproportionate number of thyroid cancer-related deaths, because of its resistance to current therapeutic approaches. Novel actionable targets are urgently needed to prolong patient survival and increase their quality of life. Loss and mutation of the RB1 tumor suppressor are rare events in ATC, which suggests that therapies directed at inhibiting the cyclin D/CDK4 complexes, responsible for RB phosphorylation and inactivation, might be effective in this tumor type. In fact, we found that the CDK4/6 inhibitor, palbociclib, strongly inhibits proliferation in all the RB1 wild type ATC cell lines tested. Efficacy was also observed in vivo, in a xenograft model. However, ATC cells rapidly developed resistance to palbociclib. Resistance was associated with increased levels of cyclin D1 and D3. To counter cyclin D overexpression, we tested the effect of combining palbociclib with the PI3K/mTOR dual inhibitor, omipalisib. Combined treatment synergistically reduced cell proliferation, even in cell lines that do not carry PI3K-activating mutations. More importantly, low-dose combination was dramatically effective in inhibiting tumor growth in a xenograft model. Thus, combined PI3K/mTOR and CDK4/6 inhibition is a highly promising novel approach for the treatment of aggressive, therapy-resistant thyroid cancer.

Oncolytic virotherapy for anaplastic and poorly differentiated thyroid cancer: a promise or a clinical reality?

Oncolytic viruses (OVs) selectively infect and lyse cancer cells. A direct lytic effect of OVs has been theorized in the initial studies; however, the antineoplastic effect of OVs is also due to the induction of an immune response against cancer cells. Anaplastic thyroid cancer is one of the most aggressive human malignancies with a short survival time of about 6–12 months from the diagnosis. The lack of effective therapies has prompted to investigate the efficacy of OVs in anaplastic thyroid carcinoma. Different OVs have been tested in preclinical studies, either as single agents or in combinatorial treatments. In this review, the results of these studies are summarized and future perspective discussed.

Selective Ablation of Tumor Suppressors in Parafollicular C Cells Elicits Medullary Thyroid Carcinoma

Among the four different types of thyroid cancer, treatment of medullary thyroid carcinoma poses a major challenge because of its propensity of early metastasis. To further investigate the molecular mechanisms of medullary thyroid carcinoma and discover candidates for targeted therapies, we developed a new mouse model of medullary thyroid carcinoma based on our CGRPCreER mouse line. This system enables gene manipulation in parafollicular C cells in the thyroid, the purported cells of origin of medullary thyroid carcinoma. Selective inactivation of tumor suppressors, such as p53, Rb, and Pten, in mature parafollicular C cells via an inducible Cre recombinase from CGRPCreER led to development of murine medullary thyroid carcinoma. Loss of Pten accelerated p53/Rb-induced medullary thyroid carcinoma, indicating interactions between pathways controlled by tumor suppressors. Moreover, labeling differentiated parafollicular C cells by CGRPCreER allows us to follow their fate during malignant transformation to medullary thyroid tumor. Our findings support a model in which mutational events in differentiated parafollicular C cells result in medullary thyroid carcinoma. Through expression analysis including RNA-Seq, we uncovered major signaling pathways and networks that are perturbed following the removal of tumor suppressors. Taken together, these studies not only increase our molecular understanding of medullary thyroid carcinoma but also offer new candidates for designing targeted therapies or other treatment modalities.

Mouse models of thyroid cancer: A 2015 update

Thyroid cancer is the most common endocrine neoplasm, and its rate is rising at an alarming pace. Thus, there is a compelling need to develop in vivo models which will not only enable the confirmation of the oncogenic potential of driver genes, but also point the way towards the development of new therapeutics. Over the past 20 years, techniques for the generation of mouse models of human diseases have progressed substantially, accompanied by parallel advances in the genetics and genomics of human tumors. This convergence has enabled the development of mouse lines carrying mutations in the genes that cause thyroid cancers of all subtypes, including differentiated papillary and follicular thyroid cancers, poorly differentiated/anaplastic cancers, and medullary thyroid cancers. In this review, we will discuss the state of the art of mouse modeling of thyroid cancer, with the eventual goal of providing insight into tumor biology and treatment.

Targeting lipid metabolism for the treatment of anaplastic thyroid carcinoma

INTRODUCTION

Anaplastic thyroid carcinoma (ATC) is the rarest subtype of thyroid cancer; however, it disproportionately accounts for a large percentage of all thyroid cancer-related deaths and is considered one of the most lethal solid tumors in humans, having a median survival of only a few months upon diagnosis. Although a variety of treatment options are available including surgery, radiation and targeted therapies, response rates are low, due in part to the drug-resistant nature of this disease; therefore, new avenues for therapeutic intervention are surely needed. Recent investigation into the metabolic profile of ATC has revealed a tumor-specific dependency for increased de novo lipogenesis, offering new insight into the molecular mechanisms that govern disease initiation and progression.

AREAS COVERED

Herein we summarize known oncogenic signaling pathways and current therapeutic strategies for the treatment of ATC. We further discuss the unique expression pattern of lipid metabolism constituents in this disease. Additionally, the current literature correlating aberrant lipogenesis with carcinogenesis is reviewed, and the implications of targeting this pathway as an innovative approach for treating ATC and other malignancies are discussed. As stearoyl-CoA desaturase (SCD) is the most differentially expressed constituent of lipid metabolism in ATC, an additional focus on this enzyme as a novel therapeutic target is applied.

EXPERT OPINION

This section is used to summarize the current research efforts underway in defining the role of lipid metabolism specifically in thyroid carcinoma. Included is a brief summary of lipid metabolism factors for which inhibitors have been generated and are under current investigation as anti-cancer agents. Finally, research limitations regarding the use of these inhibitors against components of this pathway are discussed.