Development and characterization of six new human papillary thyroid carcinoma cell lines

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

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

Establishment and Characterization of Amitrole-Induced Mouse Thyroid Adenomatous Nodule-Derived Cell Lines

Background: Thyroid cancer cell lines have been of great value for the study of thyroid cancer. However, the availability of benign thyroid adenoma cell lines is limited. Methods: Cell lines were established from thyroid adenomatous nodules that developed in mice treated with the goitrogen amitrole. Expression of epithelial, mesenchymal, and thyroid markers of these established cell lines was determined, and the effect of lentivirus-transduced overexpression of NKX2-1, a master regulator of thyroid development, on the thyroid marker expression was examined. Signal transduction and cell proliferation were evaluated after treatment with insulin-like growth factor-I (IGF-I) and the selective IGF-I receptor (IGF-IR) inhibitor NVP-ADW742. Xenograft studies were performed to examine tumorigenicity of the cells in mice. Whole-genome sequencing (WGS) was used to comprehensively determine the genetic mutations in the established two cell lines. Results: Five mouse thyroid adenomatous nodules-derived cell lines named CAT (cells from amitrole-treated thyroids) were established. Among these, two cell lines, CAT458/458s (CAT458s: a subline of CAT458) and CAT459, were found to be positive for epithelial markers and negative for a mesenchymal marker. NKX2-1-positive CAT459 cells showed higher messenger RNA (mRNA) expression of some thyroid differentiation markers than NKX2-1-negative CAT458s cells, and NKX2-1 overexpression increased and/or induced their expression. IGF-I signaling was transduced in thyrotropin receptor (Tshr)-negative CAT458s and 459 cells, and NVP-ADW742 suppressed their proliferation. No tumors developed in mice after subcutaneous injection of CAT458s or 459 cells. The WGS analysis revealed the presence of missense mutations in the tumor suppressor genes such as Polk (encoding DNA polymerase kappa) and Tgfb1 (encoding transforming growth factor beta 1), while no mutations were found in the prominent thyroid cancer-related genes Braf, Trp53 (encoding p53), and Tert (encoding telomerase reverse transcriptase). Conclusions: Two mouse thyroid adenomatous nodule-derived cell lines with different thyroid differentiation marker expression were established. NKX2-1 induced partial differentiation of these cell lines. They lacked tumorigenicity and prominent gene mutations involved in thyroid cancer development, while missense mutations were found in some tumor suppressors as revealed by WGS. The CAT458s and 459 provide a new tool to further clarify the process of thyroid multistep carcinogenesis and differentiation.

5hmC Immunohistochemistry: A Predictor of TERT Promoter Mutational Status in Follicular Thyroid Carcinoma?

Telomerase reverse transcriptase (TERT) gene aberrancies correlate to adverse prognosis in follicular thyroid carcinoma (FTC). As loss of 5-hydroxymethylcytosine (5hmC) has been associated with TERT promoter mutations in papillary thyroid carcinoma, this study sought to analyze the levels of 5hmC in a cohort of follicular thyroid tumors with available TERT data. A total of 29 tumors (26 FTCs, 2 follicular thyroid tumors of uncertain malignant potential, and 1 oncocytic thyroid carcinoma) with known TERT promoter mutational status and TERT gene expression were assessed for 5hmC immunoreactivity using two antibodies (clones RM236 and 4D9.) Slides were analyzed using a semiquantitative scoring system. Of the 10 tumor cases with aberrant TERT, only 1 scored negative with both antibodies (1/10; 10%), whereas the remaining 9 cases (9/10; 90%) exhibited some positivity for at least one antibody. Of the 19 TERT wild-type tumors, no case was scored negative using RM236, and 2 cases (2/19; 11%) using 4D9. The differences between TERT promoter mutated and wild-type groups were non-significant. The sensitivity and specificity for 5hmC immunohistochemistry (IHC) to detect mutated cases were 10% and 100% (RM236) and 20% and 89% (4D9). Therefore, 5hmC IHC is not a sensitive marker for detecting TERT promoter mutations in follicular thyroid tumors.

Dasatinib and Trametinib Promote Anti-Tumor Metabolic Activity

Thyroid cancer is the most common endocrine neoplasm, and despite its overall high survival rate, patients with metastatic disease or tumors that resist radioactive iodine experience a significantly worse prognosis. Helping these patients requires a better understanding of how therapeutics alter cellular function. Here, we describe the change in metabolite profiles after treating thyroid cancer cells with the kinase inhibitors dasatinib and trametinib. We reveal alterations to glycolysis, the TCA cycle, and amino acid levels. We also highlight how these drugs promote short-term accumulation of the tumor-suppressive metabolite 2-oxoglutarate, and demonstrate that it reduces the viability of thyroid cancer cells in vitro. These results show that kinase inhibition profoundly alters the metabolome of cancer cells and highlight the need to better understand how therapeutics reprogram metabolic processes, and ultimately, cancer cell behavior.

Androgen Receptor Activation Induces Senescence in Thyroid Cancer Cells

Thyroid cancer (TC) is the most common endocrine malignancy, with an approximately three-fold higher incidence in women. TCGA data indicate that androgen receptor (AR) RNA is significantly downregulated in PTC. In this study, AR-expressing 8505C (anaplastic TC) (84E7) and K1 (papillary TC) cells experienced an 80% decrease in proliferation over 6 days of exposure to physiological levels of 5α-dihydrotestosterone (DHT). In 84E7, continuous AR activation resulted in G1 growth arrest, accompanied by a flattened, vacuolized cell morphology, with enlargement of the cell and the nuclear area, which is indicative of senescence; this was substantiated by an increase in senescence-associated β-galactosidase activity, total RNA and protein content, and reactive oxygen species. Additionally, the expression of tumor suppressor proteins p16, p21, and p27 was significantly increased. A non-inflammatory senescence-associated secretory profile was induced, significantly decreasing inflammatory cytokines and chemokines such as IL-6, IL-8, TNF, RANTES, and MCP-1; this is consistent with the lower incidence of thyroid inflammation and cancer in men. Migration increased six-fold, which is consistent with the clinical observation of increased lymph node metastasis in men. Proteolytic invasion potential was not significantly altered, which is consistent with unchanged MMP/TIMP expression. Our studies provide evidence that the induction of senescence is a novel function of AR activation in thyroid cancer cells, and may underlie the protective role of AR activation in the decreased incidence of TC in men.

LncRNA HOTAIR impairs the prognosis of papillary thyroid cancer via regulating cellular malignancy and epigenetically suppressing DLX1

PURPOSE

Papillary thyroid cancer (PTC) is the most common endocrine malignancy with a fast-growing incidence in recent decades. HOTAIR as a long non-coding RNA has been shown to be highly expressed in papillary thyroid cancer tissues with only a limited understanding of its functional roles and downstream regulatory mechanisms in papillary thyroid cancer cells.

METHODS

We applied three thyroid cancer cell lines (MDA-T32, MDA-T41 and K1) to investigate the phenotypic influence after gain or loss of HOTAIR. The Cancer Genome Atlas (TCGA) database were utilised to select candidate genes possibly regulated by HOTAIR with validation in the cellular system and immunohistochemical (IHC) staining of PTC tissues.

RESULTS

We observed HOTAIR was highly expressed in MDA-T32 cells but presents significantly decreased levels in MDA-T41 and K1 cells. HOTAIR knockdown in MDA-T32 cells significantly suppressed proliferation, colony formation, migration with cell cycle retardation at G1 phase. On the contrary, HOTAIR overexpression in MDA-T41 cells dramatically enhanced proliferation, colony formation, migration with cell cycle driven toward S and G2/M phases. Similar phenotypic effects were also observed as overexpressing HOTAIR in K1 cells. To explore novel HOTAIR downstream mechanisms, we analyzed TCGA transcriptome in PTC tissues and found DLX1 negatively correlated to HOTAIR, and its lower expression associated with reduced progression free survival. We further validated DLX1 gene was epigenetically suppressed by HOTAIR via performing chromatin immunoprecipitation. Moreover, IHC staining shows a significantly stepwise decrease of DLX1 protein from normal thyroid tissues to stage III PTC tissues.

CONCLUSIONS

Our study pointed out that HOTAIR is a key regulator of cellular malignancy and its epigenetic suppression on DLX1 serves as a novel biomarker to evaluate the PTC disease progression.

Preclinical Models of Follicular Cell-Derived Thyroid Cancer: An Overview from Cancer Cell Lines to Mouse Models

The overall prognosis of thyroid cancer is excellent, but some patients have grossly invasive disease and distant metastases with limited responses to systemic therapies. Thus, relevant preclinical models are needed to investigate thyroid cancer biology and novel treatments. Different preclinical models have recently emerged with advances in thyroid cancer genetics, mouse modeling and new cell lines. Choosing the appropriate model according to the research question is crucial to studying thyroid cancer. This review will discuss the current preclinical models frequently used in thyroid cancer research, from cell lines to mouse models, and future perspectives on patient-derived and humanized preclinical models in this field.

Inhibiting MNK kinases promotes macrophage immunosuppressive phenotype to limit CD8+ T cell anti-tumor immunity

To elicit effective anti-tumor responses, CD8+ T cells need to infiltrate tumors and sustain their effector function within the immunosuppressive tumor microenvironment. Here we evaluate the role of MNK kinase activity in regulating CD8+ T cell infiltration and anti-tumor activity in pancreatic and thyroid tumors. We first show that human pancreatic and thyroid tumors with increased MNK kinase activity are associated with decreased infiltration by CD8+ T cells. We then show that while MNK inhibitors increase CD8+ T cells in these tumors, they induce a T cell exhaustion phenotype in the tumor microenvironment. Mechanistically, we show that the exhaustion phenotype is not caused by upregulation of PD-L1 but by tumor-associated macrophages (TAMs) becoming more immunosuppressive following MNK inhibitor treatment. Reversal of CD8+ T cell exhaustion by an anti-PD-1 antibody or TAM depletion synergizes with MNK inhibitors to control tumor growth and prolong animal survival. Importantly, we show in ex vivo human pancreatic tumor slice cultures that MNK inhibitors increase the expression of markers associated with immunosuppressive TAMs. Together, these findings demonstrate a previously unknown role of MNK kinases in modulating a pro-tumoral phenotype in macrophages and identify combination regimens involving MNK inhibitors to enhance anti-tumor immune responses.

Downregulation and Hypermethylation of GABPB1 Is Associated with Aggressive Thyroid Cancer Features

Simple Summary

Promoter mutations of the telomerase reverse transcriptase (TERT) gene have been suggested as an oncogenic event in various cancers, including thyroid cancer (TC). GABPB1 is reported to activate TERT gene expression and has been proposed as a cancer therapeutic target. The aim of this study is to explore the fate of TC cells after disruption of GABPB1 and its role in TC. We found that besides the reported oncogenic role of GABPB1 in activating TERT, it also has tumor-suppressive functions in TC. Therefore, targeting GABPB1 for cancer therapy should be cautious since it may counteract its tumor-suppressive functions.

Abstract

Promoter mutations of the telomerase reverse transcriptase (TERT) gene occur frequently in thyroid carcinoma (TC), including papillary (PTC) and anaplastic subtypes (ATC). Given that the ETS family transcription factors GABPA and GABPB1 activate the mutant TERT promoter and induce TERT expression for telomerase activation, GABPB1 has been proposed as a cancer therapeutic target to inhibit telomerase. Here, we sought to determine the role of GABPB1 in TC pathogenesis. In TC-derived cells carrying the mutated TERT promoter, GABPB1 knockdown led to diminished TERT expression but significantly increased invasive potentials in vitro and metastatic potential in a xenograft zebrafish model and altered expression of markers for epithelial-to-mesenchymal transition. GABPB1 expression was downregulated in aggressive TCs. Low GABPB1 expression correlated with its promoter hypermethylation, which in turn was also associated with shorter disease-free survival. Consistently, DNA methylation inhibitors enhanced GABPB1 expression, as observed upon reduced promoter methylation. Our results suggest that GABPB1 is required for TERT expression and telomerase activation, but itself serves as a tumor suppressor to inhibit TC progression. Furthermore, aberrant DNA methylation leads to GABPB1 silencing, thereby promoting TC aggressiveness. Thus, caution is needed if targeting GABPB1 for cancer therapy is considered.

Novel Anaplastic Thyroid Cancer PDXs and Cell Lines: Expanding Preclinical Models of Genetic Diversity

CONTEXT

Anaplastic thyroid cancer (ATC) is a rare, aggressive, and deadly disease. Robust preclinical thyroid cancer models are needed to adequately develop and study novel therapeutic agents. Patient-derived xenograft (PDX) models may resemble patient tumors by recapitulating key genetic alterations and gene expression patterns, making them excellent preclinical models for drug response evaluation.

OBJECTIVE

We developed distinct ATC PDX models concurrently with cell lines and characterized them in vitro and in vivo.

METHODS

Fresh thyroid tumor from patients with a preoperative diagnosis of ATC was surgically collected and divided for concurrent cell line and PDX model development. Cell lines were created by generating single cells through enzymatic digestion. PDX models were developed following direct subcutaneous implantation of fresh tumor on the flank of immune compromised/athymic mice.

RESULTS

Six ATC PDX models and 4 cell lines were developed with distinct genetic profiles. Mutational characterization showed one BRAF/TP53/CDKN2A, one BRAF/CDKN2A, one BRAF/TP53, one TP53 only, one TERT-promoter/HRAS, and one TERT-promoter/KRAS/TP53/NF2/NFE2L2 mutated phenotype. Hematoxylin-eosin staining comparing the PDX models to the original patient surgical specimens show remarkable resemblance, while immunohistochemistry stains for important biomarkers were in full concordance (cytokeratin, TTF-1, PAX8, BRAF). Short tandem repeats DNA fingerprinting analysis of all PDX models and cell lines showed strong concordance with the original tumor. PDX successful establishment rate was 32%.

CONCLUSION

We have developed and characterized 6 novel ATC PDX models with 4 matching cell lines. Each PDX model harbors a distinct genetic profile, making them excellent tools for preclinical therapeutic trials.

A High-throughput Approach to Identify Effective Systemic Agents for the Treatment of Anaplastic Thyroid Carcinoma

BACKGROUND

Despite the use of aggressive multimodality treatment, most anaplastic thyroid carcinoma (ATC) patients die within a year of diagnosis. Although the combination of BRAF and MEK inhibitors has recently been approved for use in BRAF-mutated ATC, they remain effective in a minority of patients who are likely to develop drug resistance. There remains a critical clinical need for effective systemic agents for ATC with a reasonable toxicity profile to allow for rapid translational development.

MATERIAL AND METHODS

Twelve human thyroid cancer cell lines with comprehensive genomic characterization were used in a high-throughput screening (HTS) of 257 compounds to select agents with maximal growth inhibition. Cell proliferation, colony formation, orthotopic thyroid models, and patient-derived xenograft (PDX) models were used to validate the selected agents.

RESULTS

Seventeen compounds were effective, and docetaxel, LBH-589, and pralatrexate were selected for additional in vitro and in vivo analysis as they have been previously approved by the US Food and Drug Administration for other cancers. Significant tumor growth inhibition (TGI) was detected in all tested models treated with LBH-589; pralatrexate demonstrated significant TGI in the orthotopic papillary thyroid carcinoma model and 2 PDX models; and docetaxel demonstrated significant TGI only in the context of mutant TP53.

CONCLUSIONS

HTS identified classes of systemic agents that demonstrate preferential effectiveness against aggressive thyroid cancers, particularly those with mutant TP53. Preclinical validation in both orthotopic and PDX models, which are accurate in vivo models mimicking tumor microenvironment, may support initiation of early-phase clinical trials in non-BRAF mutated or refractory to BRAF/MEK inhibition ATC.

Therapeutic targeting of FOS in mutant TERT cancers through removing TERT suppression of apoptosis via regulating survivin and TRAIL-R2

The telomerase reverse transcriptase (TERT) has long been pursued as a direct therapeutic target in human cancer, which is currently hindered by the lack of effective specific inhibitors of TERT. The FOS/GABPB/(mutant) TERT cascade plays a critical role in the regulation of mutant TERT, in which FOS acts as a transcriptional factor for GABPB to up-regulate the expression of GABPB, which in turn activates mutant but not wild-type TERT promoter, driving TERT-promoted oncogenesis. In the present study, we demonstrated that inhibiting this cascade by targeting FOS using FOS inhibitor T-5224 suppressed mutant TERT cancer cells and tumors by inducing robust cell apoptosis; these did not occur in wild-type TERT cells and tumors. Mechanistically, among 35 apoptotic cascade-related proteins tested, the apoptosis induced in this process specifically involved the transcriptional activation of tumor necrosis factor-related apoptosis-inducing ligand receptor 2 (TRAIL-R2) and inactivation of survivin, two key players in the apoptotic cascade, which normally initiate and suppress the apoptotic cascade, respectively. These findings with suppression of FOS were reproduced by direct knockdown of TERT and prevented by prior knockdown of TRAIL-R2. Further experiments demonstrated that TERT acted as a direct transcriptional factor of survivin, up-regulating its expression. Thus, this study identifies a therapeutic strategy for TERT promoter mutation-driven cancers by targeting FOS in the FOS/GABPB/(mutant) TERT cascade, circumventing the current challenge in pharmacologically directly targeting TERT itself. This study also uncovers a mechanism through which TERT controls cell apoptosis by transcriptionally regulating two key players in the apoptotic cascade.

Development of Novel Follicular Thyroid Cancer Models Which Progress to Poorly Differentiated and Anaplastic Thyroid Cancer

Recent developments in thyroid cancer research have been hindered by a lack of validated in vitro models, allowing for preclinical experimentation and the screening of prospective therapeutics. The goal of this work is to develop and characterize three novel follicular thyroid cancer (FTC) cell lines developed from relevant animal models. These cell lines recapitulate the genetics and histopathological features of FTC, as well as progression to a poorly differentiated state. We demonstrate that these cell lines can be used for a variety of in vitro applications and maintain the potential for in vivo transplantation into immunocompetent hosts. Further, cell lines exhibit differing degrees of dysregulated growth and invasive behavior that may help define mechanisms of pathogenesis underlying the heterogeneity present in the patient population. We believe these novel cell lines will provide powerful tools for investigating the molecular basis of thyroid cancer progression and lead to the development of more personalized diagnostic and treatment strategies.

F-Box protein 4 inhibits progression of papillary thyroid cancer

OBJECTIVE

We aimed to investigate the role of F-Box protein 4 (FBXO4) in the progression of papillary thyroid cancer (PTC) and to reveal the underlying signaling pathways responsible for FBXO4 action in PTC.

METHODS

FBXO4 expression was evaluated in tissues from PTC patients as well as in cell lines. Overexpression of FBXO4 was re-introduced into PTC cell line B-CPAP, followed by analysis of cell migration, invasion, apoptosis and epithelial-mesenchymal transition (EMT) marker profile. An in vivo xenograft tumor mouse model was employed to address the role of FBXO4 in tumorigenesis as well.

RESULTS

Endogenous FBXO4 was downregulated in PTC patient tissues and cell lines. Upon re-introducing its expression, FBXO4 suppressed migration and invasion and induced apoptosis of PTC cells, as well as inhibited EMT. Using a xenograft tumor mouse model, the pro-apoptotic and anti-EMT functions of FBXO4 are also validated in vivo, resulting in considerably slowed tumor growth rate of inoculated FBXO4-expressing PTC cells.

CONCLUSION

Our results therefore propose the potential therapeutic value of FBXO4 in targeted treatments against PTC.

Downregulation of lncRNA ZFAS1 inhibits the hallmarks of thyroid carcinoma via the regulation of miR‑302‑3p on cyclin D1

At present, treatment options for thyroid carcinoma remain limited. The present study aimed to investigate the role of ZFAS1 in various major hallmarks of cancer and the underlying mechanisms in thyroid carcinoma cells. The interactions between long non‑coding RNAs (lncRNAs), microRNAs (miRs) and target genes were predicted by bioinformatics and confirmed by performing dual‑luciferase assays. The mRNA and protein expressions were determined by reverse transcription‑quantitative PCR and western blotting. Cell invasion, migration, and viability were evaluated via Transwell, wound‑healing and Cell Counting Kit‑8 assays, respectively. The results demonstrated that lncRNA ZFAS1 expression was upregulated in thyroid carcinoma tissues, TT and SW579 cells, and was associated with the proliferation of these two cell lines. Notably, downregulation ZFAS1 reduced migration and invasion, and reversed the promotive effects of miR‑302a‑3p inhibitor on the proliferation, migration and invasion of TT and SW579 cells. Moreover, cyclin D1 (CCND1) is targeted by miR‑302a‑3p, and was regulated by ZFAS1. In addition, the downregulation of ZFAS1 not only reversed the promotive effects of miR‑302a‑3p inhibitor on CCND1 expression and the epithelial‑mesenchymal transition (EMT) of TT and SW579 cells, but also targeted and increased the expression of miR‑302a‑3p, and further reduced the expression of CCND1, resulting in suppression of the proliferation, migration, invasion and EMT of thyroid carcinoma cells.

BRAFV600E Transduction of an SV40-Immortalized Normal Human Thyroid Cell Line Induces Dedifferentiated Thyroid Carcinogenesis in a Mouse Xenograft Model

Background: Despite active studies of the clinical importance of BRAF^V600E, suitable research models to investigate the role of this mutation in the etiopathogenesis of human thyroid cancers are limited. Thus, we generated cell lines by transducing the simian virus (SV)-40 immortalized human thyroid cell line Nthy-ori 3-1 (Nthy) with lentiviral vectors expressing either BRAF^WT (Nthy/WT) or BRAF^V600E. Nthy/WT and Nthy/V600E cells were then xenografted into mice to evaluate the carcinogenic role of BRAF^V600E. Methods: Each cell line was subcutaneously injected into NOD.Cg-Prkdc^scid Il2rg^tm1Wjl/SzJ mice, and a pathological analysis was performed. The effects of the mutation were further verified by using a BRAF^V600E-selective inhibitor (PLX-4032, vemurafenib). The transcriptome was analyzed by RNA sequencing and compared with data from The Cancer Cell Line Encyclopedia and Gene Expression Omnibus. Results: While Nthy/WT was not tumorigenic in vivo, Nthy/V600E formed tumors reaching 2784.343 mm³ in 4 weeks, on average. A pathological analysis indicated that Nthy/V600E tumors were dedifferentiated thyroid cancer. We found metastases in the lung, liver, and relevant lymph nodes. A transcriptomic analysis revealed 5512 differentially expressed genes (DEGs) between the mutant and wild-type cell lines, and more DEGs were shared with anaplastic thyroid cancer than with papillary thyroid cancer. BRAF^V600E activated the cell cycle mainly by regulating G1/S phases. PLX-4032 treatment significantly inhibited tumor growth and metastasis. Conclusions: Our data show that BRAF^V600E plays a pivotal role in the carcinogenic transformation of an SV40-transfected immortalized normal human thyroid cell line. This xenograft model is expected to contribute to studies of the etiopathogenesis and treatment of highly malignant thyroid cancers.

Quercetin Enhances the Anti-Tumor Effects of BET Inhibitors by Suppressing hnRNPA1

Bromodomain and extraterminal domain (BET) proteins, which are important epigenetic readers, are often dysregulated in cancer. While a number of BET inhibitors are currently in early phase clinical trials, BET inhibitors show limited single-agent activity. The purpose of this study is to determine if Quercetin, a naturally occurring polyphenolic flavonoid often found abundant in fruits and vegetables, can enhance the anti-tumor effects of BET inhibitors. The efficacy of the combination was evaluated in vitro and in a xenograft model of pancreatic cancer. Co-treatment with BET inhibitors and Quercetin promoted apoptosis, decreased sphere-forming ability by cancer cells, and decreased cell proliferation. We found that hnRNPA1, a nuclear protein known to control mRNA export and mRNA translation of anti-apoptotic proteins, mediates some anti-tumor effects by Quercetin. Additionally, we show that combining BET inhibitors with Quercetin or hnRNPA1 knockdown decreased the anti-apoptotic protein Survivin. Significantly, Quercetin decreased hnRNPA1 in vivo and enhanced the effects of BET inhibitors at suppressing tumor growth. Together, these results demonstrate that Quercetin enhances the efficacy of BET inhibitors by suppressing hnRNPA1, and identify combination therapy with Quercetin and BET inhibitors for the treatment of cancer patients.

Parthenolide Inhibits the Proliferation of MDA-T32 Papillary Thyroid Carcinoma Cells in Vitro and in Mouse Tumor Xenografts and Activates Autophagy and Apoptosis by Downregulation of the Mammalian Target of Rapamycin (mTOR)/PI3K/AKT Signaling Pathway

Background

This study aimed to examine the effects of the sesquiterpene lactone, parthenolide, on migration, autophagy, and apoptosis of MDA-T32 human papillary thyroid carcinoma cells in vitro and in mouse tumor xenografts.

Material/Methods

Cell proliferation and viability of MDA-T32 human papillary thyroid carcinoma cells were determined by MTT assay, and cell migration was studied using a transwell assay. Fluorescence microscopy using acridine orange (AO) and ethidium bromide (EB) staining evaluated apoptosis. Transmission electron microscopy was used to study the effects of parthenolide on autophagy, and Western blot examined the levels of autophagy-associated proteins, including Bax, Bcl-2, and LC3-ll. Mice (n=10) were injected with 5×10⁶ MDA-T32 cells subcutaneously into the left flank, and xenograft tumors were grown for six weeks. Control untreated mice (n=5) were compared with treated mice (n=5) given parthenolide three times per week.

Results

Parthenolide resulted in a dose-dependent reduction in viability and cell migration of MDA-T32 cells, with a half-maximal inhibitory concentration (IC₅₀) of 12 μM. AO and EB staining showed that parthenolide induced cell apoptosis and electron microscopy identified autophagosomes in MDA-T32 cells. Parthenolide induced increased expression of the autophagocytic proteins, LC3-II and beclin-1, had a dose-dependent inhibitory effect on the mTOR/PI3K/AKT cascade in MDA-T32 cells and inhibited the growth of the mouse xenograft tumors in vivo.

Conclusions

Parthenolide inhibited the growth and migration of MDA-T32 human papillary thyroid carcinoma cells in vitro and mouse tumor xenografts and activated autophagy and apoptosis by downregulation of the mTOR/PI3K/AKT signaling pathway.

Comprehensive Genetic Characterization of Human Thyroid Cancer Cell Lines: A Validated Panel for Preclinical Studies

PURPOSE

Thyroid cancer cell lines are valuable models but have been neglected in pancancer genomic studies. Moreover, their misidentification has been a significant problem. We aim to provide a validated dataset for thyroid cancer researchers.

EXPERIMENTAL DESIGN

We performed next-generation sequencing (NGS) and analyzed the transcriptome of 60 authenticated thyroid cell lines and compared our findings with the known genomic defects in human thyroid cancers.

RESULTS

Unsupervised transcriptomic analysis showed that 94% of thyroid cell lines clustered distinctly from other lineages. Thyroid cancer cell line mutations recapitulate those found in primary tumors (e.g., BRAF, RAS, or gene fusions). Mutations in the TERT promoter (83%) and TP53 (71%) were highly prevalent. There were frequent alterations in PTEN, PIK3CA, and of members of the SWI/SNF chromatin remodeling complex, mismatch repair, cell-cycle checkpoint, and histone methyl- and acetyltransferase functional groups. Copy number alterations (CNA) were more prevalent in cell lines derived from advanced versus differentiated cancers, as reported in primary tumors, although the precise CNAs were only partially recapitulated. Transcriptomic analysis showed that all cell lines were profoundly dedifferentiated, regardless of their derivation, making them good models for advanced disease. However, they maintained the BRAF^V600E versus RAS-dependent consequences on MAPK transcriptional output, which correlated with differential sensitivity to MEK inhibitors. Paired primary tumor-cell line samples showed high concordance of mutations. Complete loss of p53 function in TP53 heterozygous tumors was the most prominent event selected during in vitro immortalization.

CONCLUSIONS

This cell line resource will help inform future preclinical studies exploring tumor-specific dependencies.

Establishment and Characterization of Four Novel Thyroid Cancer Cell Lines and PDX Models Expressing the RET/PTC1 Rearrangement, BRAFV600E, or RASQ61R as Drivers

Cancer cell lines are critical models to study tumor progression and response to therapy. In 2008, we showed that approximately 50% of thyroid cancer cell lines were redundant or not of thyroid cancer origin. We therefore generated new authenticated thyroid cancer cell lines and patient-derived xenograft (PDX) models using in vitro and feeder cell approaches, and characterized these models in vitro and in vivo. We developed four thyroid cancer cell lines, two derived from 2 different patients with papillary thyroid cancer (PTC) pleural effusions, CUTC5, and CUTC48; one derived from a patient with anaplastic thyroid cancer (ATC), CUTC60; and one derived from a patient with follicular thyroid cancer (FTC), CUTC61. One PDX model (CUTC60-PDX) was also developed. Short tandem repeat (STR) genotyping showed that each cell line and PDX is unique and match the original patient tissue. The CUTC5 and CUTC60 cells harbor the BRAF (V600E) mutation, the CUTC48 cell line expresses the RET/PTC1 rearrangement, and the CUTC61 cells have the HRAS (Q61R) mutation. Moderate to high levels of PAX8 and variable levels of NKX2-1 were detected in each cell line and PDX. The CUTC5 and CUTC60 cell lines form tumors in orthotopic and flank xenograft mouse models. IMPLICATIONS: We have developed the second RET/PTC1-expressing PTC-derived cell line in existence, which is a major advance in studying RET signaling. We have further linked all cell lines to the originating patients, providing a set of novel, authenticated thyroid cancer cell lines and PDX models to study advanced thyroid cancer.

Induction of MNK Kinase-dependent eIF4E Phosphorylation by Inhibitors Targeting BET Proteins Limits Efficacy of BET Inhibitors

BET inhibitors (BETi), which target transcription of key oncogenic genes, are currently being evaluated in early-phase clinical trials. However, because BETis show limited single-agent activity, there is increasing interest in identifying signaling pathways to enhance the efficacy of BETis. Here, we demonstrate increased MNK kinase-dependent eIF4E phosphorylation following treatment with BETis, indicating activation of a prosurvival feedback mechanism in response to BETis. BET PROTACs, which promote degradation of BET proteins, also induced eIF4E phosphorylation in cancer cells. Mechanistically, we show that the effect of BETis on MNK-eIF4E phosphorylation was mediated by p38 MAPKs. We also show that BETis suppressed RacGAP1 to induce Rac signaling-mediated eIF4E phosphorylation. Significantly, MNK inhibitors and MNK1/2 knockdown enhanced the efficacy of BETis in suppressing proliferation of cancer cells in vitro and in a syngeneic mouse model. Together, these results demonstrate a novel prosurvival feedback signaling induced by BETis, providing a mechanistic rationale for combination therapy with BET and MNK inhibitors for synergistic inhibition of cancer cells.

Research ethics dilemmas in thyroid disease

PURPOSE OF REVIEW

Since research ethics dilemmas frequently fall outside the purview of the Institutional Review Board (IRB), we present three unique recent research ethics cases in thyroidology that demonstrate research ethics dilemmas.

RECENT FINDINGS

The cases presented raise questions surrounding epistemic/scientific integrity, publication ethics, and professional, and personal integrity.

SUMMARY

Research ethics dilemmas that fall outside the purview of the IRB are appropriate for a Research Ethics Consultation, a common service in many large academic medical centers.

Methodology, Criteria, and Characterization of Patient-Matched Thyroid Cell Lines and Patient-Derived Tumor Xenografts

OBJECTIVE

To investigate the molecular underpinnings of thyroid cancer, preclinical cell line models are crucial; however, ∼40% of these have been proven to be either duplicates of existing thyroid lines or even nonthyroid-derived lines or are not derived from humans at all. Therefore, we set out to establish procedures and guidelines that should proactively avoid these problems, which facilitated the creation of criteria to make valid preclinical models for thyroid cancer research.

DESIGN

Based on our recommendations, we systematically characterized all new cell lines that we generated by a standardized approach that included (1) determination of human origin, (2) exclusion of lymphoma, (3) DNA fingerprinting and histological comparisons to establish linkage to presumed tissue of origin, (4) examining thyroid differentiation by screening two to three thyroid markers, (5) examination of biological behavior (growth rate, tumorigenicity), and (6) presence of common thyroid cancer genetic changes (TP53, BRAF, PTEN, PIK3CA, RAS, TERT promoter, RET/PTC, PAX8/PPARγ, NF1, and EIF1AX).

RESULTS

We established seven new thyroid cell lines (LAM136, EAM306, SDAR1, SDAR2, JEM493, THJ529, and THJ560) out of 294 primary culture attempts, and 10 patient-derived tumor xenografts (PDTXs; MC-Th-95, MC-Th-374, MC-Th-467, MC-Th-491, MC-Th-493, MC-Th-504, MC-Th-524, MC-Th-529, MC-Th-560, and MC-Th-562) out of 67 attempts. All were successfully validated by our protocols.

CONCLUSIONS

This standardized approach for cell line and PDTX characterization should prevent (or detect) future cross-contamination and ensure that only valid preclinical models are used for thyroid cancer research.

Characterization of thyroid cancer cell lines in murine orthotopic and intracardiac metastasis models

Thyroid cancer incidence has been increasing over time, and it is estimated that ∼1950 advanced thyroid cancer patients will die of their disease in 2015. To combat this disease, an enhanced understanding of thyroid cancer development and progression as well as the development of efficacious, targeted therapies are needed. In vitro and in vivo studies utilizing thyroid cancer cell lines and animal models are critically important to these research efforts. In this report, we detail our studies with a panel of authenticated human anaplastic and papillary thyroid cancer (ATC and PTC) cell lines engineered to express firefly luciferase in two in vivo murine cancer models-an orthotopic thyroid cancer model as well as an intracardiac injection metastasis model. In these models, primary tumor growth in the orthotopic model and the establishment and growth of metastases in the intracardiac injection model are followed in vivo using an IVIS imaging system. In the orthotopic model, the ATC cell lines 8505C and T238 and the PTC cell lines K1/GLAG-66 and BCPAP had take rates >90 % with final tumor volumes ranging 84-214 mm(3) over 4-5 weeks. In the intracardiac model, metastasis establishment was successful in the ATC cell lines HTh74, HTh7, 8505C, THJ-16T, and Cal62 with take rates ≥70 %. Only one of the PTC cell lines tested (BCPAP) was successful in the intracardiac model with a take rate of 30 %. These data will be beneficial to inform the choice of cell line and model system for the design of future thyroid cancer studies.