Medullary Thyroid Carcinoma Cell Line Research Articles

DLK1 Is Associated with Stemness Phenotype in Medullary Thyroid Carcinoma Cell Lines

Medullary thyroid carcinoma (MTC) is a rare and aggressive tumor, often requiring systemic treatment in advanced or metastatic stages, where drug resistance presents a significant challenge. Given the role of cancer stem cells (CSCs) in cancer recurrence and drug resistance, we aimed to identify CSC subpopulations within two MTC cell lines harboring pathogenic variants in the two most common MEN2-associated codons. We analyzed 15 stemness-associated markers, along with well-established thyroid stem cell markers (CD133, CD44, and ALDH1), a novel candidate (DLK1), and multidrug resistance proteins (MRP1 and MRP3). The ability to efflux the fluorescent dye Hoechst 3342 and form spheroids, representing CSC behavior, was also assessed. MZ-CRC-1 cells (p.M918T) displayed higher expressions of canonical markers, DLK1, and MRP proteins than TT cells (p.C634W). MZ-CRC-1 cells also formed more spheroids and showed less dye accumulation (p < 0.0001). Finally, we observed that DLK1+ cells (those expressing DLK1) in both cell lines exhibited significantly higher levels of stemness markers compared to DLK1− cells (those lacking DLK1 expression). These findings underscore DLK1’s role in enhancing the stemness phenotype, providing valuable insights into MTC progression and resistance and suggesting potential therapeutic implications.

Combination Antitumor Activation of Anlotinib with Radiofrequency Ablation in Human Medullary Thyroid Carcinoma.

Currently, Medullary Thyroid Carcinoma (MTC) is considered a kind of rare neuroendocrine tumor, and molecular-targeted drugs have previously been used for MTC treatment. However, the prognosis of MTC patients is still not significant. In the present work, we aimed to explore the antitumor activity of the molecularly targeted drug anlotinib in combination with radiofrequency ablation on MTC. The targets of anlotinib were clearly expressed in MTC tissue specimens, and the expression level of these factors was much higher in MTC clinical specimens than in nontumor tissues. At the same time, anlotinib or Radiofrequency Ablation (RFA) showed clear antitumor activity against the MTC cell line TT (TT cells) and the tumor tissue it formed. Anlotinib, in combination with RFA, significantly increased the antitumor activity of RFA. These results indicated that the combination of anlotinib with radiofrequency ablation could be a promising therapeutic strategy for MTC treatment.

Targeting the p90RSK/MDM2/p53 Pathway Is Effective in Blocking Tumors with Oncogenic Up-Regulation of the MAPK Pathway Such as Melanoma and Lung Cancer

In most human tumors, the MAPK pathway is constitutively activated. Since p90RSK is downstream of MAPK, it is often hyperactive and capable of phosphorylating oncogenic substrates. We have previously shown that p90RSK phosphorylates MDM2 at S166, promoting p53 degradation in follicular thyroid carcinomas. Thus, the inhibition of p90RSK restores p53 expression, which in turn inhibits cell proliferation and promotes apoptosis. In the present study, we demonstrated that the p90RSK/MDM2/p53 pathway proved to be an excellent target in the therapy of tumors with MAPK hyperactivation. For this purpose, we selected p53wt melanoma, lung and medullary thyroid carcinoma cell lines with high activation of p90RSK. In these cell lines, we demonstrated that the p90RSK/MDM2/p53 pathway is implicated in the regulation of the cell cycle and apoptosis through p53-dependent transcriptional control of p21 and Bcl-2. Furthermore, with an immunohistochemical evaluation of primary melanomas and lung tumors, which exhibit highly activated p90RSK compared to corresponding normal tissue, we demonstrated that MDM2 stabilization was associated with p90RSK phosphorylation. The results indicate that p90RSK is able to control the proliferative rate and induction of apoptosis through the regulation of p53wt levels by stabilizing MDM2 in selected tumors with constitutively activated MAPKs, making p90RSK a new attractive target for anticancer therapy.

In Vitro Effects of Boric Acid on Cell Cycle, Apoptosis, and miRNAs in Medullary Thyroid Cancer Cells.

Medullary thyroid cancer (MTC) is a highly aggressive and chemotherapy-resistant cancer originating from the thyroid's parafollicular C cells. Due to its resistance to conventional treatments, alternative therapies such as boric acid have been explored. Boric acid, a boron-based compound, has shown anticarcinogenic effects, positioning it as a potential treatment option for MTC. TT medullary thyroid carcinoma cell line (TT cells) and human thyroid fibroblast (HThF cells) were utilized for the cell culture experiments. Cell viability was assessed using the 2,3-bis(2-methoxy-4-nitro-5-sulfophenyl)-2H-tetrazolium-5-carboxanilide (XTT) assay. Total RNA was extracted using Trizol reagent for gene expression and microRNA (miRNA) analysis via reverse transcription-polymerase chain reaction (RT-PCR). The extent of apoptosis induced by boric acid was determined using the terminal deoxynucleotidyl transferase dUTP nick end labeling (TUNEL) assay. Colony formation assays were conducted to evaluate the impact of boric acid on the colony-forming ability of MTC cells. At 48h, 50% inhibitory concentration (IC50) of boric acid was found to be 35μM. Treatment with boric acid resulted in significant modulation of apoptosis-related genes and miRNAs, including increased expression of phorbol-12-myristate-13-acetate-induced protein 1(NOXA), apoptotic protease activating factor 1 (APAF-1), Bcl-2-associated X protein (Bax), caspase-3, and caspase-9. In contrast, the expression of B cell lymphoma 2 (Bcl2), B cell lymphoma- extra-large (Bcl-xl), and microRNA-21 (miR-21), which are linked to the aggressiveness of MTC, was significantly reduced. The TUNEL assay indicated a 14% apoptosis rate, and there was a 67.9% reduction in colony formation, as shown by the colony formation assay. Our study suggests that boric acid may have anticancer activity in MTC by modulating apoptotic pathways. These findings suggest that boric acid could be a potential therapeutic agent for MTC and possibly for other malignancies with similar pathogenic mechanisms.

Abstract 4665: USP18 promotes anlotinib resistance in medullary thyroid carcinoma by stabilizing aurora B kinase

Abstract Targeted therapy resistance is the main cause of disease progression in advanced medullary thyroid carcinoma (MTC). However, the key molecules and mechanisms remain unclear. We previously performed a genome-wide in vitro screen of Anlotinib resistance-related genes in human MTC cell line TT using CRISPR-dCas9-SAM system and identified ubiquitin-specific protease 18 (USP18) as a key molecule mediating Anlotinib resistance in MTC. However, its downstream mechanism needs further clarification. Based on the high-throughput DNA sequencing results of the control group and the Anlotinib screening group, a group of key genes related to Anlotinib resistance in MTC was screened through the MAGeCK algorithm and the enrichment ratio of sgRNA in the Anlotinib screening group. Among them, USP18 ranked first in the enrichment results. Analysis of the correlation between the expression level of USP18 in MTC patient specimens and survival revealed that patients with high USP18 expression in tumor cells had poorer prognosis. Overexpression of USP18 in MTC tumor cells significantly promoted the growth of subcutaneous xenograft tumors in NOD/SCID mice treated with Anlotinib. In vitro cell experiments also showed that overexpression of USP18 promoted the proliferation of MTC tumor cells and significantly inhibited the proportion of cell apoptosis after Anlotinib treatment. Further research found that USP18, as a deubiquitinating enzyme that can specifically remove ISG15-like ubiquitin-like proteins from substrate proteins, can improve the kinase stability of Aurora B by removing ISG15-like ubiquitin modification and promote MTC tumor cell proliferation through the activation of PI3K-Akt signaling regulated by Aurora B kinase. Application of Aurora B kinase inhibitor in Anlotinib-resistant MTC cell lines significantly inhibited tumor cell proliferation, and Aurora B kinase inhibitor significantly increased the proportion of cell apoptosis in MTC tumor cells overexpressing USP18. In the subcutaneous xenograft tumor model of MTC in NOD/SCID mice, the growth of xenograft tumors in the Anlotinib combined with Aurora B kinase inhibitor treatment group was also significantly inhibited. In summary, overexpressed USP18 can activate PI3K-Akt signaling and promote tumor cell proliferation by increasing the stability of Aurora B kinase, ultimately leading to the formation of Anlotinib resistance in MTC patients. Combined use of Aurora B kinase inhibitor is a potentially effective combined treatment strategy for Anlotinib-resistant MTC patients. Citation Format: Xuan Qin, Xing Wan, Dapeng Li, Yimeng Liu, Xianhui Ruan, Fangkun Luan, Kejia Xu, Jia Li, Rong Xiang, Yongjun Piao, Yi Shi, Xiangqian Zheng. USP18 promotes anlotinib resistance in medullary thyroid carcinoma by stabilizing aurora B kinase [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 4665.

Abstract 5835: Genome-Wide CRISPR gene knockout screens combined with selpercatinib identifies potent combination therapies for RET driven medullary thyroid carcinoma

Abstract Background: Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor driven primarily by activating mutations in the RET proto-oncogene. It accounts for approximately 13% of thyroid cancer-related deaths. Total thyroidectomy is the main treatment option for MTC patients; however, its efficacy is limited due to the high prevalence of metastatic disease at diagnosis. Vandetanib, cabozantinib, and selpercatinib are RET signaling inhibitors (RETi), that have been approved for treating advanced MTC. Despite their effectiveness, many patients relapse or have refractory disease due to eventual resistance to these RETis. Methods: In our study, we employed genome-wide clustered regularly interspaced short palindromic repeats (CRISPR) gene knockout (KO) in MTC cell lines treated with selpercatinib or vehicle to investigate the genetic mechanisms of resistance or sensitivity to RETi. Our overarching goal was to identify potential synergistic or additive drug combinations that may prevent or treat resistant disease. Results: Our research identified key genes and pathways confirming the sensitivity or resistance of MTC cells to RETi. Notably, apoptotic genes along with RAS and mTOR signaling pathways were found to play a significant role in resistance development. Knocking out negative regulators of these pathways (such as NF1 and TSC2) conferred growth advantages to cells treated with RETi. Alternatively, knocking out BCL2, an antiapoptotic protein, led to increased lethality. These findings suggested that targeting RAS, mTOR, or antiapoptotic pathways in conjunction with RETi may be synergistic or have additive activity. To validate the CRISPR screening, we selectively knocked down NF1 in MTC cells and found it led to a nearly two-fold increase in IC50 for selpercatinib. Furthermore, in-vitro and in-vivo testing confirmed significant synergistic activity when using the combination of trametinib, an MEK inhibitor (MEKi; downstream of the RAS pathway), with selpercatinib. Conclusions and Future Directions: We have identified a potent synergistic combination of MEKi with RETi as a novel synergistic drug combination to treat MTC, which may also prevent resistance to RETi. These results will be translated to patients through clinical trials conduced at the NCI. Citation Format: Abdelrahman Rahmy, Arwa Fallatah, David Milewski, Meijie Tian, Young Song, Yong Kim, Hsien-Chao Chou, Xinyu Wen, Chaoyu Wang, Jun Wei, Robert Hawley, John Glod, Javed Khan. Genome-Wide CRISPR gene knockout screens combined with selpercatinib identifies potent combination therapies for RET driven medullary thyroid carcinoma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts); 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84(6_Suppl):Abstract nr 5835.

Preclinical Evaluation of Novel Tyrosine-Kinase Inhibitors in Medullary Thyroid Cancer.

Simple SummaryMedullary thyroid carcinoma (MTC) is a neuroendocrine tumor arising from parafollicular calcitonin-secreting C cells of the thyroid. Most of the patients affected by MTC, especially the familial form, harbor a mutation of the RET proto-oncogene. In patients with advanced disease, medical therapy is represented by two tyrosine-kinase inhibitors: cabozantinib and vandetanib. However, their usage is limited by several adverse events and drug-resistance onset. The aim of this preclinical study was to evaluate the antitumor activity of novel molecules for the therapy of MTC: SU5402, an inhibitor of the fibroblast growth factor receptor type 1 (FGFR-1) and vascular endothelial growth factor receptor (VEGFR)-2; sulfatinib, a multi-target kinase inhibitor selective for FGFR-1 and the VEGFR-1, -2, and -3; SPP86, a RET-specific inhibitor. Our results suggest a potential role in targeting the FGFR and VEGFR signaling pathways as an alternative strategy for resistant tumors and a significative antitumor activity of this new RET-specific inhibitor.Medullary thyroid carcinoma (MTC) is a neuroendocrine tumor arising from parafollicular C cells of the thyroid gland. In this preclinical study, we tested three tyrosine-kinase inhibitors (TKIs): SU5402, a selective inhibitor of fibroblast growth factor receptor (FGFR)-1 and vascular endothelial growth factor receptor (VEGFR)-2; sulfatinib, an inhibitor of FGFR-1 and VEGFR-1, -2, -3; and SPP86, a RET-specific inhibitor. The effects of these compounds were evaluated in vitro in two human MTC cell lines (TT and MZ-CRC-1), and in vivo using xenografts of MTC cells in zebrafish embryos. SU5402, sulfatinib and SPP86 decreased cell viability. Sulfatinib and SPP86 significantly induced apoptosis in both cell lines. Sulfatinib and SPP86 inhibited the migration of TT and MZCRC-1 cells, while SU5402 was able to inhibit migration only in TT cells. In vivo we observed a significant reduction in TT cell-induced angiogenesis in zebrafish embryos after incubation with sulfatinib and SPP86. In conclusion, sulfatinib and SPP86 displayed a relevant antitumor activity both in vitro and in vivo. Moreover, this work suggests the potential utility of targeting FGFR and VEGFR signaling pathways as an alternative therapy for MTC.

Discovery of Pharmaceutical Composition for Prevention and Treatment in Patient-Derived Metastatic Medullary Thyroid Carcinoma Model.

Medullary thyroid carcinoma (MTC) is a well-known neuroendocrine carcinoma, derived from C cells of the thyroid gland. Additionally, MTC is an uncommon aggressive carcinoma that metastasizes to lymph nodes, bones, lungs and liver. For MTC, the 10-year general survival ratio of patients with localized disease is about 95%, whereas that of patients with local phase disorder is around 75%. Only 20% of patients with distant metastasis to lung at diagnosis survive 10 years, which is notably lower than survival for well-differentiated thyroid carcinoma (WDTC). The management of MTC with distant metastasis to lung could be re-surgery or chemotherapy. In this research, we planned to assess the in vitro and in vivo combinational anticancer effect of a novel combination of low-dose cisplatin and sorafenib in patient-derived MTC. The patient-derived MTC cell lines YUMC-M1, M2, and M3 were isolated and treated with a combination of cisplatin and sorafenib or either agent alone. Cisplatin and sorafenib acted in combination to forward tumor restraint compared with each agent administered alone at a low dose. Therefore, a combination of cisplatin and sorafenib could be a new therapeutic approach for MTC.

CRISPR/Cas9 RET Gene Knockout in Medullary Thyroid Carcinoma Cell-lines: Optimization and Validation.

Medullary Thyroid Cancer (MTC) is a very aggressive type of thyroid carcinoma. Mutation in RET proto-oncogene is demonstrated in MTC development. We aimed to knock-out of RET-oncogene using CRISPR/Cas9 genome editing method in MTC cell-lines. This research was conducted in Shahid Beheshti University of Medical Sciences, Tehran, Iran during 2019-2020. Four different sgRNAs were designed to target exons one, two, and four of RET-oncogene in TT and MZ-CRC-1 cell-lines using bioinformatics tools, then the CRISPR/Cas9 constructs was made. About 72-hours after cell transfection, T7EI method and DNA sequencing were used to confirm the knock-out of RET-oncogene. Expression of RET, Calcitonin genes and RET protein were evaluated by Real-time PCR and ELISA, respectively. The results of T7E1, and DNA sequencing of transfected cells confirmed RET gene knock-out by CRISPR/Cas9. There was a significant decrease in RET gene expression and RET protein in transfected TT and MZ cells compared to controls. The rate of cell apoptosis in transfected cells was significantly increased. Calcitonin gene expression was also significantly reduced in transfected cells. p-RET, p-PI3K, p-AKT, p-MEK, p-ERK protein levels were significantly reduced in TT and MZ transfected cells. For the first time, knock-out of RET gene was performed and confirmed using CRISPR/Cas9. Inhibition of this gene leads to inhibition of the tyrosine kinase RET signal transduction pathway. Therefore, it can be one of the most effective and specific therapeutic goals in the field of Personalized Medicine in the treatment of diseases caused by over activity of RET molecular pathway.

Abstract 2426: Effects of MEN2 mutations on RET receptor localization and function

Abstract Multiple Endocrine Neoplasia type 2 (MEN2) is a cancer syndrome characterized by medullary thyroid carcinoma (MTC) and adrenal tumors. MEN2 is caused by activating point mutations of the REarranged during Transfection (RET) receptor tyrosine kinase, a protein essential for normal cell proliferation, migration, and differentiation in multiple tissues. MEN2 RET mutations can result in constitutive receptor dimerization (MEN2A) or in loss of receptor autoinhibition (MEN2B), which are associated with distinct disease courses and oncogenic potential. However, the specific cellular mechanisms contributing to these differences have not been well characterized. We have previously shown that RET maturation, cell surface localization and trafficking through the endolysosomal system modulate RET signaling and contribute to regulation of normal RET functions. Here, we have explored the contributions of these processes to MEN2A and MEN2B RET mutant activity. In preliminary studies using immunofluorescence (IF) microscopy and MTC cell lines endogenously expressing MEN2A (2ARET) or MEN2B (2BRET) RET mutant forms, we showed that RET mutants do not accumulate in pre-membrane compartments (ER, Golgi) at significant levels. Both 2ARET and 2BRET mutant receptors matured and reached the cell membrane efficiently. Using IF and cell surface protein labeling methods, we demonstrated that wildtype RET, 2ARET and 2BRET forms had differential patterns of plasma membrane distribution in the absence of ligand stimulation. Further, constitutive stimulation of wildtype RET receptors could not recapitulate the pattern observed for MEN2 RET mutants. We showed that, in the absence of ligand, 2ARET and 2BRET, but not wildtype RET, were constitutively phosphorylated, activated downstream signaling pathways and could localize to multiple endosomal compartments. We also showed different extents of protein turnover in 2ARET and 2BRET, which is important for sustained signals and suggests distinct endosomal sorting mechanisms for these receptors. Together, our data indicate that constitutive activation of MEN2 RET mutant receptors is not the only mechanism contributing to aberrant RET function in MEN2. Our results suggest that receptor localization at the membrane and trafficking through endosomal compartments is mutation-specific and may modulate RET signals that contribute to its roles in MEN2 oncogenicity. Citation Format: Eduardo Reyes-Alvarez, Brandy D. Hyndman, Lois M. Mulligan. Effects of MEN2 mutations on RET receptor localization and function [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 2426.

Apoferritin/Vandetanib Association Is Long-Term Stable But Does Not Improve Pharmacological Properties of Vandetanib

A tyrosine kinase inhibitor, vandetanib (Van), is an anticancer drug affecting the signaling of VEGFR, EGFR and RET protooncogenes. Van is primarily used for the treatment of advanced or metastatic medullary thyroid cancer; however, its usage is significantly limited by side effects, particularly cardiotoxicity. One approach to minimize them is the encapsulation or binding of Van in- or onto a suitable carrier, allowing targeted delivery to tumor tissue. Herein, we constructed a nanocarrier based on apoferritin associated with Van (ApoVan). Based on the characteristics obtained by analyzing the average size, the surface ζ-potential and the polydispersive index, ApoVan nanoparticles exhibit long-term stability and maintain their morphology. Experiments have shown that ApoVan complex is relatively stable during storage. It was found that Van is gradually released from its ApoVan form into the neutral environment (pH 7.4) as well as into the acidic environment (pH 6.5). The effect of free Van and ApoVan on neuroblastoma and medullary thyroid carcinoma cell lines revealed that both forms were toxic in both used cell lines, and minimal differences between ApoVan and Van were observed. Thus, we assume that Van might not be encapsulated into the cavity of apoferritin, but instead only binds to its surface.

Assessment of AXL and mTOR genes expression in medullary thyroid carcinoma (MTC) cell line in relation with over expression of miR-144 and miR-34a.

The aim of the present study was to investigate the expression of AXL and mTOR genes and their targeting microRNAs (miRNAs) including miR-34a and miR-144 in Medullary Thyroid Carcinoma (MTC) cell line, TT, and determine the effect of these two miRNAs on their target genes to introduce new molecular markers or therapeutics. The expression of miR-34a, miR-144, and their targets genes including AXL and mTOR was evaluated by quantitative Real-time PCR. Luciferase assay was performed to confirm the interaction between miRNAs and their target mRNAs. The expression level of AXL and mTOR was evaluated before and after miRNAs induction in TTcell line compared with Cos7 as control cells. The expression of AXL and mTOR were up-regulated significantly, while miR-34a and miR-144 were down-regulated in TTcell line compared to Cos7. After transduction, the overexpression of miR-34a and 144 caused down-regulation of both genes. Luciferase assay results showed that the mTOR is targeted by miR-34a and miR-144 and the intensity of luciferase decreased in the presence of miRNAs. Based on the results of the present study and since AXL and mTOR genes play a critical role in variety of human cancers, suppression of these genes by their targeting miRNAs, especially miR-34a and miR-144, can be propose as a new strategy for MTC management. However, more studies are needed to approve the hypothesis.

Antineoplastic Activity of an Old Natural Antidiabetic Biguanide on the Human Thyroid Carcinoma Cell Line.

In the last decades, metformin (Met), an herbal anti-diabetic medicine, has been proposed as an anti-cancer agent. Thyroid cancers are the most common malignancy of the endocrine system. Therefore, the current study was performed to assess the effects of Met on cell proliferation and activation of the Phosphoinositide 3- Kinase (PI3K)/Protein kinase B (AKT)/Forkhead Box O1 (FOXO1) signaling pathway in the Medullary Thyroid Carcinoma (MTC) cells. The effects of Met on the expression of REarranged during Transfection (RET) proto-oncogene were also investigated. MTC cell line (TT) was treated with 0, 2.5, 5, 10, 20, 30, 40, 50, and 60 mM concentrations of Met for 24, 48, and 72h. The viability and apoptosis of the treated cells were measured by the 3-(4,5-Dimethylthiazol- 2-yl)-2,5-diphenyltetrazolium bromide (MTT) and Annexin V- Propidium Iodide (PI) assays. The expression level of PI3K, AKT, FOXO1, and RET genes was investigated by quantitative Real-Time Polymerase Chain Reaction (qRT-PCR), and phosphorylation of their proteins was determined by the Enzyme-Linked Immunosorbent Assay (ELISA). Results showed that Met significantly decreased the viability of the MTC cells. Met also reduced the expression level of PI3K, AKT, and FOXO1 genes (P<0.05), whereas it elevated the expression level of RET proto-oncogene (P<0.05). It seems that the Met has a cytostatic effect on the TT cells. Our results showed that anti-tumoral effects of Met may be cell type-specific, and according to the induction of RET (as a proto-oncogene) and inhibition of FOXO1 (as a tumor suppressor gene), Met could not be an appropriate agent in the treatment of MTC. The antineoplastic activity of Met has been confirmed against several malignancies in "in vitro" and "in vivo" studies. However, its molecular mechanisms in the treatment of different carcinomas particularly in thyroid cancers are not clearly understood and more studies are required to confirm its exact effect on the MTC.

MiR‑592 acts as an oncogene and promotes medullary thyroid cancer tumorigenesis by targeting cyclin‑dependent kinase 8.

Medullary thyroid carcinoma (MTC) is a relatively rare subtype of thyroid cancer, accounting for 5–10% of all cases of thyroid cancer worldwide. Due to the current lack of knowledge regarding the tumorigenesis of MTC, the clinical treatment of MTC remains a challenge. It has been reported that microRNAs (miRNAs) regulate the progression of MTC; however, the regulatory network of miRNAs and the exact underlying mechanisms are not completely understood. In the present study, an miRNA expression profile (GSE40807), consisting of 80 samples, was downloaded and analyzed using Gene Expression Omnibus-2R to identify differentially expressed miRNAs between MTC and normal samples. miR-592 expression levels were significantly increased in MTC tissues and cell lines compared with normal tissues and cell lines. Patients with high miR-592 expression levels exhibited a less favorable prognosis compared with patients with low miR-592 expression. The results suggested that miR-592 overexpression promoted TT and MZ-CRC-1 cell proliferation in vitro. In addition, miR-592 negatively regulated cyclin-dependent kinase 8 (CDK8) via targeted binding in MTC cells. Moreover, co-transfection of CDK8 overexpression plasmid and miR-592 mimic reversed miR-592-mediated MTC cell proliferation. In conclusion, miR-592 may serve as an oncogene in MTC by decreasing the expression of CDK8, indicating that the miR-592/CDK8 axis might serve as a promising therapeutic target for MTC.

Salinomycin and its derivatives as potent RET transcriptional inhibitors for the treatment of medullary thyroid carcinoma (MTC).

Rearranged during transfection kinase (RET) is a validated molecular target in medullary thyroid cancer (MTC), as activating mutations in RET are often associated with the development of MTC. The present study reports the first preclinical characterization of salinomycin and selected analogs as potent RET transcriptional inhibitors. Reverse transcription‐PCR and immunoblotting revealed that salinomycin profoundly decreased RET expression in the TT human MTC cell line by inhibiting RET transcription. Moreover, salinomycin resulted in remarkable anti‐proliferative activity against MTC that is driven by RET (gain of function mutation) by selectively inhibiting the intracellular PI3K/Akt/mTOR signaling pathway. Also, flow cytometry and fluorescence‐activated cell sorting showed that salinomycin induces G1 phase arrest and apoptosis by reducing the expression of retinoblastoma protein, E2F1, cyclin D and CDK4. The structure‐activity relationship of salinomycin was investigated in this study. Some of the salinomycin derivatives showed the ability to reduce RET expression where others fail to alter RET expression. These results suggest that the RET‐suppressing effect of salinomycin may be largely attributed to disruption of the Wnt pathway, presumably through interference with the ternary LRP6‐Frizzled‐Wnt complex. Furthermore, these findings support the further preclinical evaluation of salinomycin and its analogs as a promising new class of therapeutic agents for the improved treatment of MTCSupport or Funding InformationAmerican Cancer Society for their support of this study (grant no. RSGM‐12‐046‐01‐CDD).

Cofilin is a mediator of RET-promoted medullary thyroid carcinoma cell migration, invasion and proliferation

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor that originates from parafollicular thyroid C cells and accounts for 5% of thyroid cancers. In inherited cases of MTC, and in about 40% of sporadic cases, activating mutations of the receptor tyrosine kinase proto-oncogene RET are found. Constitutively active RET triggers signaling pathways involved in cell proliferation, survival and motility, but the mechanisms underlying malignant transformation of C-cells have been only partially elucidated.Cofilin is a key regulator of actin cytoskeleton dynamics. A crucial role of cofilin in tumor development, progression, invasion and metastasis has been demonstrated in different human cancers, but no data are available in MTC. Interestingly, RET activation upregulates cofilin gene expression.The aim of this study was to investigate cofilin contribution in invasiveness and growth of MTC cells, and its relevance in the context of mutant RET signaling.We found that cofilin transfection in human MTC cell line TT significantly increased migration (178 ± 44%, p < 0.001), invasion (165 ± 28%, p < 0.01) and proliferation (146 ± 18%, p < 0.001), accompanied by an increase of ERK1/2 phosphorylation (2.23-fold) and cyclin D1 levels (1.43-fold). Accordingly, all these responses were significantly reduced after genetic silencing of cofilin (−55 ± 10% migration, p < 0.001, −41 ± 8% invasion, p < 0.001, −17 ± 3% proliferation, p < 0.001). These results have been confirmed in primary cells cultures obtained from human MTCs.The inhibition of constitutively active RET in TT cells by both the RET pharmacological inhibitor RPI-1 and the transfection of dominant negative RET mutant (RETΔTK) resulted in a reduction of cofilin expression (−37 ± 8%, p < 0.001 and −31 ± 16%, p < 0.01, respectively). Furthermore, RPI-1 inhibitory effects on TT cell migration (−57 ± 13%, p < 0.01), but not on cell proliferation, were completely abolished in cells transfected with cofilin.In conclusion, these data indicate that an unbalanced cofilin expression, induced by oncogenic RET, contributes to promote MTC invasiveness and growth, suggesting the possibility of targeting cofilin pathway for more effective treatment of MTC.

Retroposed copies of RET gene: a somatically acquired event in medullary thyroid carcinoma

BackgroundDifferent pathogenic germline mutations in the RET oncogene are identified in MEN 2, a hereditary syndrome characterized by medullary thyroid carcinoma (MTC) and other endocrine tumors. Although genetic predisposition is recognized, not all RET mutation carriers will develop the disease during their lifetime or, likewise, RET mutation carriers belonging to the same family may present clinical heterogeneity. It has been suggested that a single germline mutation might not be sufficient for development of MEN 2-associated tumors and a somatic bi-allelic alteration might be required. Here we investigated the presence of somatic second hit mutation in the RET gene in MTC.MethodsWe integrated Multiplex Ligation-dependent Probe Amplification (MLPA) and whole exome sequencing (WES) to search for copy number alteration (CNA) in the RET gene in MTC samples and medullary thyroid cell lines (TT and MZ-CR-1). We next found reads spanning exon-exon boundaries on RET, an indicative of retrocopy. We subsequently searched for RET retrocopies in the human reference genome (GRCh37) and in the 1000 Genomes Project data, by looking for reads reporting joined exons in the RET locus or distinct genomic regions. To determine RET retrocopy specificity and recurrence, DNA isolated from sporadic and MEN 2-associated MTC (n = 37), peripheral blood (n = 3) and papillary thyroid carcinomas with RET fusion (n = 10) samples were tested using PCR-sequencing methodology.ResultsThrough MLPA we have found evidence of CNA in the RET gene in MTC samples and MTC cell lines. WES analysis reinforced the presence of the CNA and hinted for a retroposed copy of RET not found in the human reference genome and 1.000 Genomes Project. Extended analysis confirmed the presence of a somatic MTC-related retrocopy of RET in both sporadic and hereditary tumors. We further unveiled a recurrent (28%) novel point mutation (p.G548 V) found exclusively in the retrocopy of RET. The mutation was also found in cDNA of mutated samples, suggesting it might be functional.ConclusionWe here report a somatic specific RET retroposed copy in MTC samples and cell lines. Our results support the idea that generation of retrocopies in somatic cells is likely to contribute to MTC genesis and progression.

Establishment and characterization of a novel cell line of medullary thyroid carcinoma from a dog.

A novel cell line of canine medullary thyroid carcinoma (MTC) was established from the neck mass, diagnosed histopathologically and immunohistochemically as ectopic MTC. The neoplastic cells arranging trabecular structures were characterized as pleomorphic cells with eosinophilic cytoplasm and nucleus, containing often clear nucleolus. These tumor cells were immuno-positive for calcitonin gene-related protein (CGRP), somatostatin, and chromogranin A. In addition, 8th passaged cultured cells were also immuno-positive for CGRP, somatostatin, and chromogranin A. The cloned tumor cells showed logarithmic cell growth with a doubling time of 33.3h. From the results of DNA sequencing of rearranged during transfection (RET) proto-oncogene, the cloned tumor cells had four single base substitution, including exon 5 codon 82, exon 16 codon 750, exon 17 codon 777, and exon 24 codon 1085, all of which were single nucleotide polymorphism reported in RET gene of dogs. After the xenotransplantation into severe combined immunodeficiency (SCID) mice, the cloned cells showed tumorigenicity potentials. The morphological and immunohistochemical features of the xenotransplanted tumor were almost in conformity with those of the original tumor, including positive immunoreactivity for calcitonin, CGRP, and chromogranin A. To our knowledge, this is the first report of canine MTC cell line, which provides useful in vitro tool for understanding oncogenic mechanism and pathophysiological state of MTC in dogs.

Cofilin is a mediator of RET-promoted medullary thyroid carcinoma cell migration, invasion and proliferation

Abstract Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor that originates from parafollicular thyroid C cells and accounts for 5% of thyroid cancers. In inherited cases of MTC, and in about 40% of sporadic cases, activating mutations of the receptor tyrosine kinase proto-oncogene RET are found. Constitutively active RET triggers signaling pathways involved in cell proliferation, survival and motility, but the mechanisms underlying malignant transformation of C-cells have been only partially elucidated. Cofilin is a key regulator of actin cytoskeleton dynamics. A crucial role of cofilin in tumor development, progression, invasion and metastasis has been demonstrated in different human cancers, but no data are available in MTC. Interestingly, RET activation upregulates cofilin gene expression. The aim of this study was to investigate cofilin contribution in invasiveness and growth of MTC cells, and its relevance in the context of mutant RET signaling. We found that cofilin transfection in human MTC cell line TT significantly increased migration (178 ± 44%, p The inhibition of constitutively active RET in TT cells by both the RET pharmacological inhibitor RPI-1 and the transfection of dominant negative RET mutant (RETΔTK) resulted in a reduction of cofilin expression (−37 ± 8%, p In conclusion, these data indicate that an unbalanced cofilin expression, induced by oncogenic RET, contributes to promote MTC invasiveness and growth, suggesting the possibility of targeting cofilin pathway for more effective treatment of MTC.

SAT-566 Cofilin Is a Mediator of RET-Promoted Medullary Thyroid Carcinoma Cell Migration, Invasion and Proliferation

Medullary thyroid carcinoma (MTC) is a rare neuroendocrine tumor that originates from parafollicular thyroid C cells, accounting for 5% -10% of thyroid cancers. In all inherited cases of MTC, and in about 40% of sporadic cases, activating mutations of the receptor tyrosine kinase proto-oncogene RET are found. Constitutively active RET triggers signaling pathways involved in cell motility, proliferation and survival, but the mechanisms underlying malignant transformation of C-cells have been only partially elucidated. Cofilin is a key regulator of actin cytoskeleton dynamics. A crucial role of cofilin in tumor development, progression, invasion and metastasis has been demonstrated in different human cancers, but no data are available in MTC. Interestingly, RET activation upregulates cofilin gene expression. The aim of this study was to investigate cofilin contribution in invasiveness and growth of MTC cells, and its relevance in the context of mutant RET signaling. We found that cofilin transfection in human MTC cell line TT significantly increased migration (178.5±44%, p<0.001), invasion (194±27%, p<0.05) and proliferation (145.9±18%, p<0.001), accompanied by an increase of ERK1/2 phosphorylation (1.8-fold) and cyclin D1 levels (1.43-fold). Accordingly, all these responses were significantly reduced after genetic silencing of cofilin (-55±10% migration, p<0.001, -40.7±8% invasion, p<0.001, -17±2.6% proliferation, p<0.001). The inhibition of constitutively active RET in TT cells by both the RET pharmacological inhibitor RPI-1 and the transfection of dominant negative RET mutant (RETΔTK) resulted in a reduction of cofilin expression (-30.8±11%, p<0.01 and -31±16%, p<0.01, respectively). Furthermore, RPI-1 inhibitory effects on TT cell migration (-70±18%, p<0.001) and proliferation (-29.4±9% , p<0.01) were completely abolished in cells transfected with cofilin. In conclusion, these data indicate that an unbalanced cofilin expression, induced by oncogenic RET, contributes to promote MTC invasiveness and growth, suggesting the possibility of targeting cofilin pathway for more effective treatment of MTC.