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

Targeted Therapy for Anaplastic Thyroid Carcinoma: Advances and Management

Anaplastic thyroid carcinoma (ATC) is a rare and highly fatal cancer with the worst prognosis of all thyroid carcinoma (TC) histological subtypes and no standard treatment. In recent years, the explosion of investigations on ATC-targeted agents has provided a new treatment strategy for this malignant condition, and a review of these studies is warranted. We conducted a comprehensive literature search for ATC-targeted drug studies and compiled a summary of their efficacy and adverse effects (AEs) to provide new insights. Multiple clinical trials have demonstrated the efficacy and safety of dabrafenib in combination with trametinib for the treatment of ATC, but vemurafenib and NTRK inhibitors showed limited clinical responses. We found that the previously valued therapeutic effect of lenvatinib may be unsatisfactory; combining tyrosine kinase (TK) inhibitors (TKIs) with other agents results in a higher rate of clinical benefit. In addition, specific medications, including RET inhibitors, mTOR inhibitors, CDK4/6 inhibitors, and Combretastatin A4-phosphate (CA4P), offer tremendous therapeutic potential. The AEs reported for all agents are relatively numerous but largely manageable clinically. More clinical trials are expected to further confirm the effectiveness and safety of these targeted drugs for ATC.

Epidermal growth factor receptor activation confers resistance to lenvatinib in thyroid cancer cells

Thyroid cancer is the most common endocrine malignancy. A multitargeted tyrosine kinase inhibitor, lenvatinib, has been used for the treatment of advanced thyroid cancer. To elucidate the mechanism of resistance to lenvatinib in thyroid cancer cells, we established lenvatinib‐resistant sublines and analyzed the molecular mechanisms of resistance. Two thyroid cancer cell lines (TPC‐1 and FRO) were used, and resistant sublines for lenvatinib (TPC‐1/LR, FRO/LR) were established. In TPC‐1/LR, the phosphorylation of epidermal growth factor receptor (EGFR), extracellular signal‐regulated kinase (ERK), and Akt was enhanced whereas in FRO/LR, the phosphorylation of EGFR and downstream signal transduction molecules was not enhanced. The addition of epidermal growth factor decreased sensitivity to lenvatinib in TPC‐1 and FRO. The combination of EGFR inhibitors lapatinib and lenvatinib significantly inhibited the growth of TPC‐1/LR in both in vitro and mouse xenograft models. Short‐term exposure to lenvatinib enhanced the phosphorylation of EGFR in six thyroid cancer cell lines regardless of their histological origin or driver gene mutations; however, phosphorylation of ERK was enhanced in all cells except TPC‐1. A synergistic growth‐inhibitory effect was observed in three thyroid cancer cell lines, including intrinsically lenvatinib‐resistant cells. The results indicate that signal transduction via the EGFR pathway may be involved in the development of lenvatinib resistance in thyroid cancer cells. The inhibition of the EGFR pathway simultaneously by an EGFR inhibitor may have therapeutic potential for overcoming lenvatinib resistance in thyroid cancer.

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.

Longitudinal assessment of B-RAF V595E levels in the peripheral cell-free tumor DNA of a 10-year-old spayed female Korean Jindo dog with unresectable metastatic urethral transitional cell carcinoma for monitoring the treatment response to a RAF inhibitor (sorafenib)

Transitional cell carcinoma (TCC) is the most common malignant tumor of the canine urinary tract. In this case study, a dog with metastatic urethral TCC was treated with sorafenib. The tumor expression levels of receptor tyrosine kinase genes, including VEGFR-1, VEGFR-2, PDGFR-α, PDGFR-β, ALK, EGFR, ErbB2, and B-RAF, were analyzed. VEGFR was overexpressed in tumor tissues compared to the normal tissues. Considering the high frequency of B-RAF mutation in canine urological tumors, the B-RAF gene was examined, and the B-RAF V595E mutation was detected in the tumor tissue. Therefore, the antitumor effect of sorafenib, a multi-tyrosine kinase inhibitor, on unresectable metastatic urethral TCC characterized by B-RAF V595E was evaluated and circulating cell-free tumor DNA (ctDNA) was assessed for monitoring the treatment response. After the initiation of oral sorafenib therapy (4 mg/kg/day escalated to 10 mg/kg/day), the dysuria was alleviated gradually, and the patient remained stable for 3 months. During that treatment period, the patient showed various levels of changes associated with B-RAF V595E mutation in ctDNA as evident from longitudinal plasma samples after initiation of sorafenib therapy. The findings of this study suggest that ctDNA may serve as a useful non-invasive tool for monitoring the treatment response to anticancer drugs.

Establishment and characterization of a new patient-derived anaplastic thyroid cancer cell line (C3948), obtained through fine-needle aspiration cytology

PURPOSE

Anaplastic thyroid cancer (ATC) is among the most aggressive and unresectable tumors, presenting a bad prognosis. A better comprehension of the functional and molecular mechanisms behind the aggressiveness of this cancer, as well as new biomarkers for aggressiveness, prognosis, and response to therapy are required. However, owing to their irresectability, ATC tissue is not always accessible. Here we describe the establishment and characterization of a new patient-derived cell line, obtained from an unresectable ATC through fine-needle aspiration cytology (FNAC).

METHODS

The morphology, expression of epithelial and thyroid markers, cytogenetic, mutational and gene expression profiles, doubling time, and drug-resistance profile of the new cell line, designated C3948, were investigated using several methodologies: immunostaining, karyotype analysis, comparative genomic hybridization (CGH), fluorescent in situ hybridization (FISH), next-generation sequencing (NGS), Sanger sequencing, gene expression microarrays, cell counting, and IC₅₀ determination.

RESULTS

Results indicate that C3948 cell line has a histological phenotype representative of original ATC cells and a completely aberrant karyotype with many chromosomal losses and gains; harbors mutated TP53, STK11, and DIS3L2 genes; presents a gene expression profile similar to C643 ATC commercial cell line, but with some unique alterations; has a doubling time similar to C643; and the IC₅₀ profile for paclitaxel, doxorubicin, and cisplatin is similar to C643, although higher for cisplatin.

CONCLUSIONS

These observations are consistent with a typical ATC cell profile, supporting C3948 cell line as a novel preclinical model, and FNAC as a useful approach to better study anaplastic thyroid cancer, including testing of new anticancer therapies.

A novel therapeutic approach for anaplastic thyroid cancer through inhibition of LAT1

A novel therapeutic approach is urgently needed for patients with anaplastic thyroid cancer (ATC) due to its fatal and rapid progress. We recently reported that ATC highly expressed MYC protein and blocking of MYC through its selective inhibitor, JQ1, decreased ATC growth and improved survival in preclinical models. One of the important roles of MYC is regulation of L-neutral amino acid transporter 1 (LAT1) protein and inhibition of LAT1 would provide similar anti-tumor effect. We first identified that while the human ATC expresses LAT1 protein, it is little or not detected in non-cancerous thyroidal tissue, further supporting LAT1 as a good target. Then we evaluated the efficacy of JPH203, a LAT1 inhibitor, against ATC by using the in vitro cell-based studies and in vivo xenograft model bearing human ATC cells. JPH203 markedly inhibited proliferation of three ATC cell lines through suppression of mTOR signals and blocked cell cycle progression from the G0/G1 phase to the S phase. The tumor growth inhibition and decrease in size by JPH203 via inhibition of mTOR signaling and G0/G1 cell cycle associated proteins were further confirmed in xenograft models. These preclinical findings suggest that LAT1 inhibitors are strong candidates to control ATC, for which current treatment options are highly limited.

Sorafenib inhibits vascular endothelial cell proliferation stimulated by anaplastic thyroid cancer cells regardless of BRAF mutation status

Anaplastic thyroid cancer (ATC) is a rare refractory disease, frequently associated with BRAF mutations and aberrant vascular endothelial growth factor (VEGF) secretion. The antitumor effects of sorafenib were evaluated, and its mechanisms of action were investigated. Four human ATC cell lines were used: OCUT‑4, which possesses a BRAF mutation; OCUT‑6 and ACT‑1, which carry NRAS mutations; and OCUT‑2, which possesses mutations in BRAF and PI3KCA. The viability of Sorafenib was evaluated by MTT assay. In order to examine the inhibitory effect of Sorafenib on intracellular signal transduction, expression of mitogen‑activated protein kinase kinase was examined by western blotting. In addition, cell cycle analysis was performed using flow cytometry. The inhibitory effects of sorafenib on the growth of ATC cells and human umbilical vein endothelial cells (HUVECs) stimulated with conditioned media from ATC cells were examined. Sorafenib inhibited the viability of OCUT‑4 more effectively than other ATC cell lines; these effects may have been mediated cytostatically by suppressing mitogen‑activated protein kinase kinase phosphorylation. Conversely, similar suppression was not observed in OCUT‑6 cells, which possess an NRAS mutation. The four cell lines secreted different quantities of VEGF, and the proliferation of HUVECs was differentially stimulated by their conditioned media. Both anti‑VEGF antibody and sorafenib prevented this stimulation of proliferation. In conclusion, sorafenib more effectively inhibited RAF‑generated growth signals in ATC cells compared with signals generated by its upstream gene, RAS. ATC cells stimulated the growth of HUVECs via humoral factors, including VEGF; this effect was clearly inhibited by sorafenib. The present findings highlighted the potential of sorafenib for the treatment of ATC and provided insight into its mechanism of action.

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.

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.

Growth arrest by activated BRAF and MEK inhibition in human anaplastic thyroid cancer cells

Anaplastic thyroid cancer (ATC) is a rare malignancy that progresses extremely aggressively and often results in dismal prognosis. We investigated the efficacy of inhibiting the activated RAS/RAF/MEK pathway in ATC cells aiming to clarify the mechanism of effect and resistance. Four human ATC cell lines (ACT-1, OCUT-2, OCUT-4 and OCUT-6) were used. OCUT-4 had a BRAF mutation. OCUT-2 had both BRAF and PI3KCA mutations. ACT-1 and OCUT-6 had wild-type BRAF and NRAS mutations. The effects of dabrafenib, a selective inhibitor of the BRAFV600E kinase, and trametinib, a reversible inhibitor of MEK activity, were investigated. Dabrafenib strongly inhibited the viability in BRAF mutated cells by demonstrating G0/G1-arrest via the downregulation of MEK/ERK phosphorylation. Upregulated phosphorylation of MEK was observed in RAS mutated cells after dabrafenib treatment and caused VEGF upregulation, but was not related to the cellular proliferation. Trametinib inhibited the cellular viability to variable degrees in every cell by downregulating ERK phosphorylation. Dual blockade by both inhibitors demonstrated clear cytostatic effect in all the cells. OCUT-4 showed the weakest sensitivity to trametinib, no additional effect of either inhibitor in combination with the other, and an increase of SNAI1 mRNA expression after treatment with inhibitors, suggesting a mechanism for resistance. Our findings demonstrated the efficacy of a mutation-selective BRAF inhibitor and a MEK inhibitor in human ATC cells in a genetic alteration-specific manner.

Microsatellite instable and microsatellite stable primary endometrial carcinoma cells and their subcutaneous and orthotopic xenografts recapitulate the characteristics of the corresponding primary tumor

OBJECTIVE

Well-characterized, low-passage, primary cell cultures established directly from patient tumors are an important tool for drug screening because these cultures faithfully recapitulate the genomic features of primary tumors. Here, we aimed to establish these cell cultures from primary endometrial carcinomas (ECs) and to develop subcutaneous and orthotopic xenograft models as a model to validate promising treatment options for EC in the in vivo setting.

METHODS

Primary cell cultures of EC tumors were established and validated by analysing histologic and genetic characteristics, telomerase activity, and in vitro and in vivo growth characteristics. Using these primary cell cultures, subcutaneous and orthotopic mouse models were subsequently established.

RESULTS

We established and characterized 7 primary EC cell cultures and corresponding xenograft models of different types of endometrioid tumors. Interestingly, we observed that the chance to successfully establish a primary cell culture seems higher for microsatellite instable than microsatellite stable tumors. For the first time, we also established an orthotopic murine model for EC derived from a primary cell culture. In contrast to EC cell lines, grafted tumor cultures preserved the original tumor structure and mimicked all histologic features. They also established abdominal and distant metastases, reflecting the tumorigenic behavior in the clinical setting. Remarkably, the established cell cultures and xenograft tumors also preserved the genetic characteristics of the primary tumor.

CONCLUSIONS

The established EC cultures reflect the epithelial genetic characteristics of the primary tumor. Therefore, they provide an appropriate model to investigate EC biology and apply high-throughput drug screening experiments. In addition, the established murine xenograft models, in particular the orthotopic model, will be useful to validate promising therapeutic strategies in vivo, as the grafted tumors closely resemble the primary tumors from which they were derived. Microsatellite instable status seems to determine the success rate of establishing primary cell cultures.

Nestin expression as an independent indicator of poor prognosis for patients with anaplastic thyroid cancer

The protein nestin, a neuronal stem cell marker, has been reported to indicate a poor prognosis in various tumours. Anaplastic thyroid cancer (ATC) is one of the most aggressive malignancies in humans, and its molecular background has not been identified. The present study evaluated the expression of nestin and its significance in ATC. Tissue samples from 23 patients with ATC were subjected to immunohistochemical staining and the staining intensity of nestin in the cytoplasm was evaluated. The expression of nestin in the tumour cytoplasm was confirmed in 6 of the 23 tissue samples (26.1%). Between the nestin-positive group (n=6) and the nestin-negative group (n=17), there were no significant differences in the clinicopathological factors of the patients. However, the nestin-positive group exhibited significantly worse prognoses than the nestin-negative group (median survival time, 86.5 vs. 306 days; P<0.01, log-rank test). The multivariate analysis indicated that nestin expression was a prognostic indicator for the ATC patients (hazard ratio, 5.59; 95% confidence interval, 1.63-19.50; P<0.01), which is independent of the known clinical indicators. Nestin expression has the potential to be an independent indicator of a poor prognosis for patients with ATC.

The antitumor effect of metformin with and without carboplatin on primary endometrioid endometrial carcinoma in vivo

OBJECTIVES

New treatment options for advanced and recurrent endometrial carcinoma (EC) are necessary. Epidemiological studies showed that diabetic patients using metformin have reduced risks of endometrial cancer (EC) incidence. Moreover, pre- and clinical studies demonstrated an antitumor effect by metformin, with and without additional treatments, for different solid malignancies. However, cancer cell-autonomous effects of metformin on EC have not been fully characterized yet. The aim of this study was to investigate the effect of metformin, with or without carboplatin, on patient-derived primary endometrioid EC cells xenografted in nude mice, to assess its ability to reduce or impair growth in already established tumors.

METHODS

Two xenograft models were established by subcutaneous inoculation of primary endometrioid EC cell suspensions. Tumors were allowed to grow and then mice were treated with metformin (250 mg/kg, daily, p.o.), carboplatin (50 mg/kg, 1×/week, i.p.), or the combination of both compounds at the same concentration as single treatment, for three weeks. Effects of metformin treatment on the tumor mass were determined by tumor growth follow-up. Metformin influences on AMPK/mTOR cell signaling were evaluated by investigating AKT, AMPK and S6 phosphorylation levels.

RESULTS

In vivo, metformin did not affect the growth of EC tumors established from patient-derived primary cultures and the phosphorylation of AKT, AMPK and S6. In addition, no enhanced antitumor effect was determined by combining metformin and carboplatin treatments.

CONCLUSIONS

Metformin, at clinically relevant concentrations, did not show effects on the growth of already established tumors. Adding metformin to carboplatin did not have synergistic effects.

Significant cytostatic effect of everolimus on a gefitinib-resistant anaplastic thyroid cancer cell line harboring PI3KCA gene mutation

We previously demonstrated the efficacy of gefitinib, a tyrosine kinase inhibitor of the epidermal growth factor receptor (EGFR), on an anaplastic thyroid cancer (ATC) cell line. We also observed that gefitinib was not effective in regulating cell growth in a different ATC cell line that exhibited an altered EGFR-initiated signal transduction pathway. In the present study, we attempted to regulate the downstream effector of EGFR-Akt-mammalian target of rapamycin (mTOR) pathway by an mTOR inhibitor, everolimus. A total of 8 ATC cell lines were employed, 7 of which were established in our institute. OCUT-2 was known to carry a mutation in the phosphoinositide-3-kinase, catalytic, α polypeptide gene (PI3KCA) and to be gefitinib-resistant, whereas ACT-1 exhibited a remarkable growth arrest by gefitinib. All the cell lines were tested for the cytotoxic effect of everolimus. The mechanisms of cellular toxicity were investigated by EGFR stimulation, cell cycle and concurrent exposure to paclitaxel. In OCUT-2, but not in any of the other cell lines, everolimus achieved a significant growth inhibition (inhibition of 30 and 50% was achieved by concentrations of 0.8 and 5 nM, respectively). The growth in OCUT-2 was inhibited by everolimus, even with concordant EGFR stimulation. This effect was demonstrated by a G2M cell cycle arrest. An additive effect of everolimus onto the cytotoxic effect of paclitaxel was demonstrated at a dose of 1-2 nM. A significant growth inhibitory effect of everolimus on the gefitinib-resistant ATC cell line was demonstrated, suggesting a possible correlation between the efficacy of everolimus and PI3KCA gene mutation and the significance of molecular-targeted therapy in the management of ATC.