Characterization and analysis of human chordoma cell lines

A chronicle review of new techniques that facilitate the understanding and development of optimal individualized therapeutic strategies for chordoma

Chordoma is a rare malignant bone tumor that mainly occurs in the sacrum and the clivus/skull base. Surgical resection is the treatment of choice for chordoma, but the local recurrence rate is high with unsatisfactory prognosis. Compared with other common tumors, there is not much research and individualized treatment for chordoma, partly due to the rarity of the disease and the lack of appropriate disease models, which delay the discovery of therapeutic strategies. Recent advances in modern techniques have enabled gaining a better understanding of a number of rare diseases, including chordoma. Since the beginning of the 21st century, various chordoma cell lines and animal models have been reported, which have partially revealed the intrinsic mechanisms of tumor initiation and progression with the use of next-generation sequencing (NGS) techniques. In this study, we performed a systematic overview of the chordoma models and related sequencing studies in a chronological manner, from the first patient-derived chordoma cell line (U-CH1) to diverse preclinical models such as the patient-derived organoid-based xenograft (PDX) and patient-derived organoid (PDO) models. The use of modern sequencing techniques has discovered mutations and expression signatures that are considered potential treatment targets, such as the expression of Brachyury and overactivated receptor tyrosine kinases (RTKs). Moreover, computational and bioinformatics techniques have made drug repositioning/repurposing and individualized high-throughput drug screening available. These advantages facilitate the research and development of comprehensive and personalized treatment strategies for indicated patients and will dramatically improve their prognoses in the near feature.

Personalized chordoma organoids for drug discovery studies

Chordomas are rare tumors of notochordal origin, most commonly arising in the sacrum or skull base. Chordomas are considered insensitive to conventional chemotherapy, and their rarity complicates running timely and adequately powered trials to identify effective treatments. Therefore, there is a need for discovery of novel therapeutic approaches. Patient-derived organoids can accelerate drug discovery and development studies and predict patient responses to therapy. In this proof-of-concept study, we successfully established organoids from seven chordoma tumor samples obtained from five patients presenting with tumors in different sites and stages of disease. The organoids recapitulated features of the original parent tumors and inter- as well as intrapatient heterogeneity. High-throughput screenings performed on the organoids highlighted targeted agents such as PI3K/mTOR, EGFR, and JAK2/STAT3 inhibitors among the most effective molecules. Pathway analysis underscored how the NF-κB and IGF-1R pathways are sensitive to perturbations and potential targets to pursue for combination therapy of chordoma.

Targeted delivery of cancer drug paclitaxel to chordomas tumor cells via an RNA nanoparticle harboring an EGFR aptamer

Paclitaxel has been extensively used in clinics for cancer treatment. However, its limited solubility in aqueous solution and high occurrence of side effects have also been widely reported. In this study, we constructed a biocompatible RNA nanoparticle delivery system (3WJ-EGFR_apt) that includes 3WJ (3-way junction) nanoparticle with a size of 4.85 ± 0.59 nm as a backbone and an EGFR (epidermal growth factor receptor) aptamer for specific targeting to chordomas cells, which owns the encapsulation ability of drug paclitaxel (PTX) for cancer therapy. Confocal microscopy and flow cytometry results confirmed 3WJ-EGFR_apt nanoparticle exhibited excellent specific targeting to chordomas cell U-CH2 which is an EGFR(+) cell line; while the 3WJ nanoparticle lose the targeted ability. Both of the two nanoparticles own no sensitivity to lung cancer cell H520 which is an EGFR(-) cell line. Moreover, the 3WJ-EGFR_apt nanoparticle encapsulated drug PTX could enhance the inhibition efficiency of chordomas tumor cells U-CH2 as compared to free PTX alone. This work demonstrates that RNA-3WJ constructed with a targeting aptamer provides a compromising targeted drug delivery ability on chordomas cells for therapeutics.

Aberrant CDK9 expression within chordoma tissues and the therapeutic potential of a selective CDK9 inhibitor LDC000067

Objectives: Chordomas are slow-growing malignancies that commonly affect vital neurological structures. These neoplasms are highly resistant to current chemotherapeutic regimens and often recur after surgical intervention. Therefore, there is an urgent need to identify molecular targets and more robust drugs to improve chordoma patient outcomes. It is well accepted that cyclin-dependent protein kinase 9 (CDK9) has tumorigenic roles in various cancers; however, the expression and significance of CDK9 in chordoma remains unknown. Methods: Expression of CDK9 in chordoma cell lines and tumor tissues was examined by Western blot and immunohistochemistry (IHC). The correlation between CDK9 expression in patient tissues and clinical prognosis was analyzed. The functional roles of CDK9 in chordoma were investigated after the addition of small interfering RNA (siRNA) and CDK9 inhibitor (LDC000067). Cell growth and proliferation were assessed with MTT and clonogenic assays. The effect of CDK9 inhibition on chordoma cells was further evaluated with a three-dimensional (3D) cell culture model which mimics the in vivo environment. Results: CDK9 was expressed in both chordoma cell lines and chordoma tissues. High- expression of CDK9 correlated with recurrence and poor outcomes for chordoma patients. CDK9 silencing with siRNA decreased growth and proliferation of chordoma cells and lowered levels of Mcl-1 and RNA polymerase II (RNAP II) phosphorylation. Pharmacological inhibition of CDK9 with the small molecular inhibitor LDC000067 reduced cell growth, supported apoptosis, suppressed cell colony formation in a clonogenic assay, and decreased spheroid growth in 3D culture. Conclusion: We demonstrate that CDK9 expression in chordoma correlates with patient outcome, and, when inhibited, chordoma cell growth and proliferation significantly decreases. Taken together, these results support CDK9 as an emerging potential target in chordoma therapy.

Knockdown of cytokeratin 8 overcomes chemoresistance of chordoma cells by aggravating endoplasmic reticulum stress through PERK/eIF2α arm of unfolded protein response and blocking autophagy

Chordoma is a malignant primary osseous spinal tumor with pronounced chemoresistance. However, the mechanisms of how chordoma cells develop chemoresistance are still not fully understood. Cytokeratin 8 (KRT8) is a molecular marker of notochordal cells, from which chordoma cells were believed to be originated. In this study, we showed that either doxorubicin or irinotecan promoted KRT8 expression in both CM319 and UCH1 cell lines, accompanied by an increased unfolded protein response and autophagy activity. Then, siRNA-mediated knockdown of KRT8 chemosensitized chordoma cells in vitro. Mechanistic studies showed that knockdown of KRT8 followed by chemotherapy aggravated endoplasmic reticulum stress through PERK/eIF2α arm of unfolded protein response and blocked late-stage autophagy. Moreover, suppression of the PERK/eIF2α arm of unfolded protein response using PERK inhibitor GSK2606414 partially rescued the apoptotic chordoma cells but did not reverse the blockage of the autophagy flux. Finally, tumor xenograft model further confirmed the chemosensitizing effects of siKRT8. This study represents the first systematic investigation into the role of KRT8 in chemoresistance of chordoma and our results highlight a possible strategy of targeting KRT8 to overcome chordoma chemoresistance.

A historical recount of chordoma

Chordoma, a rare bone tumor that occurs along the spine, has led scientists on a fascinating journey of discoveries. In this historical vignette, the authors track these discoveries in diagnosis and treatment, noting events and clinicians that played pivotal roles in our current understanding of chordoma. The study of chordoma begins in 1846 when Rudolf Virchow first observed its occurrence on a dorsum sellae; he coined the term “chordomata” 11 years later. The chordoma’s origin was greatly disputed by members of the scientific community. Eventually, Müller’s notochord hypothesis was accepted 36 years after its proposal. Chordomas were considered benign and slow growing until the early 1900s, when reported autopsy cases drew attention to their possible malignant nature. Between 1864 and 1919, the first-ever symptomatic descriptions of various forms of chordoma were reported, with the subsequent characterization of chordoma histology and the establishment of classification criteria shortly thereafter. The authors discuss the critical historical steps in diagnosis and treatment, as well as pioneering operations and treatment modalities, noting the physicians and cases responsible for advancing our understanding of chordoma.

Medical treatment of advanced chordomas

Chordoma is a very rare bone sarcoma that can arise from any site along the spine and from the skull base. En bloc resection is the gold standard for treatment while radiation therapy has been shown to provide both curative and palliative benefit. Unfortunately, local recurrences are common, even after a complete surgical resection, and up to 40% of patients suffer from distant metastases, while salvage treatments are challenging. Patients carrying an advanced disease need a systemic treatment. Unluckily, conventional chordoma are insensitive to cytotoxic chemotherapy that is considered the standard treatment option in patients with metastatic sarcoma. In the last decade, innovative therapies have been introduced, positively impacting disease control and patients' quality of life. In addition, a better understanding of the molecular characteristics of chordoma allowed to detect new potential targets. This review is focused on the pharmacological management of patients affected by an advanced disease, starting with a summary of data available on conventional chemotherapy, then moving to a deeper analysis of available data on molecular agents and immunotherapy, and finally providing an update on ongoing clinical trials and future prospective.

Recent advances in understanding and managing chordomas

Chordomas are rare primary bone tumors arising from embryonic remnants of the notochord. They are slow-growing, locally aggressive, and destructive and typically involve the axial skeleton. Genetic studies have identified several mutations implicated in the pathogenesis of these tumors. Treatment poses a challenge given their insidious progression, degree of local invasion at presentation, and high recurrence rate. They tend to respond poorly to conventional chemotherapy and radiation. This makes radical resection the mainstay of their treatment. Recent advances in targeted chemotherapy and focused particle beam radiation, however, have improved the management and prognosis of these tumors.

Establishment and characterization of a chordoma cell line from the tissue of a patient with dedifferentiated-type chordoma

OBJECTIVE

Chordoma is a rare bone tumor of the axial skeleton believed to originate from the remnants of the embryonic notochord. The available tumor cells are characteristically physaliferous and express brachyury, a transcription factor critical for mesoderm specification. Although chordomas are histologically not malignant, treatments remain challenging because they are resistant to radiation therapy and because wide resection is impossible in most cases. Therefore, a better understanding of the biology of chordomas using established cell lines may lead to the advancement of effective treatment strategies. The authors undertook a study to obtain this insight.

METHODS

Chordoma cells were isolated from the tissue of a patient with dedifferentiated-type chordoma (DTC) that had recurred. Cells were cultured with DMEM/F12 containing 10% fetal bovine serum and antibiotics (penicillin and streptomycin). Cell proliferation rate was measured by MTS assay. Cell-cycle distribution and cell surface expression of proteins were analyzed by fluorescence-activated cell sorting (FACS) analysis. Expression of proteins was analyzed by Western blot and immunocytochemistry. Radiation resistance was measured by clonogenic survival assay. Tumor formation was examined by injection of chordoma cells at hindlimb of nude mice.

RESULTS

The putative (DTC) cells were polygonal and did not have the conventional physaliferous characteristic seen in the U-CH1 cell line. The DTC cells exhibited similar growth rate and cell-cycle distribution, but they exhibited higher clonogenic activity in soft agar than U-CH1 cells. The DTC cells expressed high levels of platelet-derived growth factor receptor–β and a low level of brachyury and cytokeratins; they showed higher expression of stemness-related and epithelial to mesenchymal transition–related proteins than the U-CH1 cells. Intriguingly, FACS analysis revealed that DTC cells exhibited marginal surface expression of CD24 and CD44 and high surface expression of CXCR4 in comparison to U-CH1 cells. In addition, blockade of CXCR4 with its antagonist AMD3100 effectively suppressed the growth of both cell lines. The DTC cells were more resistant to paclitaxel, cisplatin, etoposide, and ionizing radiation than the U-CH1 cells. Injection of DTC cells into the hindlimb region of nude mice resulted in the efficient formation of tumors, and the histology of xenograft tumors was very similar to that of the original patient tumor.

CONCLUSIONS

The use of the established DTC cells along with preestablished cell lines of chordoma may help bring about greater understanding of the mechanisms underlying the chordoma that will lead to therapeutic strategies targeting chordomas.

STAT3 Inhibition as a Therapeutic Strategy for Chordoma

Objective Signal transducer and activator of transcription (STAT) proteins regulate key cellular fate decisions including proliferation and apoptosis. STAT3 overexpression induces tumor growth in multiple neoplasms. STAT3 is constitutively activated in chordoma, a tumor with a high recurrence rate despite maximal surgical and radiation treatment. We hypothesized that a novel small molecule inhibitor of STAT3 (FLLL32) would induce significant cytotoxicity in sacral and clival chordoma cells. Methods Sacral (UCh1) and clival (UM-CHOR-1) chordoma cell lines were grown in culture (the latter derived from primary tumor explants). FLLL32 dosing parameters were optimized using cell viability assays. Antitumor potential of FLLL32 was assessed using clonal proliferation assays. Potential mechanisms underlying observed cytotoxicity were examined using immunofluorescence assays. Results FLLL32 induced significant cytotoxicity in UCh1 and UM-CHOR-1 chordoma cells, essentially eliminating all viable cells, correlating with observed downregulation in activated, phosphorylated STAT3 upon administration of FLLL32. Mechanisms underlying the observed cytotoxicity included increased apoptosis and reduced cellular proliferation through inhibition of mitosis. Conclusion As a monotherapy, FLLL32 induces potent tumor kill in vitro in chordoma cell lines derived from skull base and sacrum. This effect is mediated through inhibition of STAT3 phosphorylation, increased susceptibility to apoptosis, and suppression of cell proliferation.

Expression of programmed cell death ligand 1 (PD-L1) and prevalence of tumor-infiltrating lymphocytes (TILs) in chordoma

Chordomas are primary malignant tumors of the notochord that are resistant to conventional chemotherapy. Expression of programmed cell death ligand 1 (PD-L1), prevalence of tumor-infiltrating lymphocytes (TILs), and their clinical relevance in chordoma remain unknown. We evaluated PD-L1 expression in three chordoma cell lines and nine chordoma tissue samples by western blot. Immunohistochemical staining was performed on a chordoma tissue microarray (TMA) that contained 78 tissue specimens. We also correlated the expression of PD-L1 and TILs with clinical outcomes. PD-L1 protein expression was demonstrated to be induced by IFN-γ in both UCH1 and UCH2 cell lines. Across nine human chordoma tissue samples, PD-L1 protein was differentially expressed. 94.9% of chordoma samples showed positive PD-L1 expression in the TMA. The expression score of PD-L1 for metastatic chordoma tumors was significant higher as compared with non-metastatic chordoma tumors. Expression of PD-L1 protein significantly correlates with the presence of elevated TILs, which correlates with metastasis. In summary, our study showed high levels of PD-L1 are expressed in chordoma, which is correlated with the prevalence of TILs. The current study suggests targeting PD-L1 may be a novel immunotherapeutic strategy for chordoma clinical trials.

MicroRNA-155 expression is independently predictive of outcome in chordoma

Background

Chordoma pathogenesis remains poorly understood. In this study, we aimed to evaluate the relationships between microRNA-155 (miR-155) expression and the clinicopathological features of chordoma patients, and to evaluate the functional role of miR-155 in chordoma.

Methods

The miRNA expression profiles were analyzed using miRNA microarray assays. Regulatory activity of miR-155 was assessed using bioinformatic tools. miR-155 expression levels were validated by reverse transcription-polymerase chain reaction. The relationships between miR-155 expression and the clinicopathological features of chordoma patients were analyzed. Proliferative, migratory and invasive activities were assessed by MTT, wound healing, and Matrigel invasion assays, respectively.

Results

The miRNA microarray assay revealed miR-155 to be highly expressed and biologically active in chordoma. miR-155 expression in chordoma tissues was significantly elevated, and this expression correlated significantly with disease stage (p = 0.036) and the presence of metastasis (p = 0.035). miR-155 expression also correlated significantly with poor outcomes for chordoma patients (hazard ratio, 5.32; p = 0.045). Inhibition of miR-155 expression suppressed proliferation, and the migratory and invasive activities of chordoma cells.

Conclusions

We have shown miR-155 expression to independently affect prognosis in chordoma. These results collectively indicate that miR-155 expression may serve not only as a prognostic marker, but also as a potential therapeutic target in chordoma.

Investigating microenvironmental regulation of human chordoma cell behaviour

The tumour microenvironment is complex and composed of many different constituents, including matricellular proteins such as connective tissue growth factor (CCN2), and is characterized by gradients in oxygen levels. In various cancers, hypoxia and CCN2 promote stem and progenitor cell properties, and regulate the proliferation, migration and phenotype of cancer cells. Our study was aimed at investigating the effects of hypoxia and CCN2 on chordoma cells, using the human U-CH1 cell line. We demonstrate that under basal conditions, U-CH1 cells express multiple CCN family members including CCN1, CCN2, CCN3 and CCN5. Culture of U-CH1 cells in either hypoxia or in the presence of recombinant CCN2 peptide promoted progenitor cell-like characteristics specific to the notochordal tissue of origin. Specifically, hypoxia induced the most robust increase in progenitor-like characteristics in U-CH1 cells, including increased expression of the notochord-associated markers T, CD24, FOXA1, ACAN and CA12, increased cell growth and tumour-sphere formation, and a decrease in the percentage of vacuolated cells present in the heterogeneous population. Interestingly, the effects of recombinant CCN2 peptide on U-CH1 cells were more pronounced under normoxia than hypoxia, promoting increased expression of CCN1, CCN2, CCN3 and CCN5, the notochord-associated markers SOX5, SOX6, T, CD24, and FOXA1 as well as increased tumour-sphere formation. Overall, this study highlights the importance of multiple factors within the tumour microenvironment and how hypoxia and CCN2 may regulate human chordoma cell behaviour.

Chemotherapy of skull base chordoma tailored on responsiveness of patient-derived tumor cells to rapamycin

Skull base chordomas are challenging tumors due to their deep surgical location and resistance to conventional radiotherapy. Chemotherapy plays a marginal role in the treatment of chordoma resulting from lack of preclinical models due to the difficulty in establishing tumor cell lines and valuable in vivo models. Here, we established a cell line from a recurrent clival chordoma. Cells were cultured for more than 30 passages and the expression of the chordoma cell marker brachyury was monitored using both immunohistochemistry and Western blot. Sensitivity of chordoma cells to the inhibition of specific signaling pathways was assessed through testing of a commercially available small molecule kinase inhibitor library. In vivo tumorigenicity was evaluated by grafting chordoma cells onto immunocompromised mice and established tumor xenografts were treated with rapamycin. Rapamycin was administered to the donor patient and its efficacy was assessed on follow-up neuroimaging. Chordoma cells maintained brachyury expression at late passages and generated xenografts closely mimicking the histology and phenotype of the parental tumor. Rapamycin was identified as an inhibitor of chordoma cell proliferation. Molecular analyses on tumor cells showed activation of the mammalian target of rapamycin signaling pathway and mutation of KRAS gene. Rapamycin was also effective in reducing the growth of chordoma xenografts. On the basis of these results, our patient received rapamycin therapy with about six-fold reduction of the tumor growth rate upon 10-month follow-up neuroimaging. This is the first case of chordoma in whom chemotherapy was tailored on the basis of the sensitivity of patient-derived tumor cells.

Generation of a patient-derived chordoma xenograft and characterization of the phosphoproteome in a recurrent chordoma

OBJECT

The management of patients with locally recurrent or metastatic chordoma is a challenge. Preclinical disease models would greatly accelerate the development of novel therapeutic options for chordoma. The authors sought to establish and characterize a primary xenograft model for chordoma that faithfully recapitulates the molecular features of human chordoma.

METHODS

Chordoma tissue from a recurrent clival tumor was obtained at the time of surgery and implanted subcutaneously into NOD-SCID interleukin-2 receptor gamma (IL-2Rγ) null (NSG) mouse hosts. Successful xenografts were established and passaged in the NSG mice. The recurrent chordoma and the derived human chordoma xenograft were compared by histology, immunohistochemistry, and phospho-specific immunohistochemistry. Based on these results, mice harboring subcutaneous chordoma xenografts were treated with the mTOR inhibitor MLN0128, and tumors were subjected to phosphoproteome profiling using Luminex technology and immunohistochemistry.

RESULTS

SF8894 is a novel chordoma xenograft established from a recurrent clival chordoma that faithfully recapitulates the histopathological, immunohistological, and phosphoproteomic features of the human tumor. The PI3K/Akt/mTOR pathway was activated, as evidenced by diffuse immunopositivity for phospho-epitopes, in the recurrent chordoma and in the established xenograft. Treatment of mice harboring chordoma xenografts with MLN0128 resulted in decreased activity of the PI3K/Akt/mTOR signaling pathway as indicated by decreased phospho-mTOR levels (p = 0.019, n = 3 tumors per group).

CONCLUSIONS

The authors report the establishment of SF8894, a recurrent clival chordoma xenograft that mimics many of the features of the original tumor and that should be a useful preclinical model for recurrent chordoma.

Tissue microarray immunohistochemical detection of brachyury is not a prognostic indicator in chordoma

Brachyury is a marker for notochord-derived tissues and neoplasms, such as chordoma. However, the prognostic relevance of brachyury expression in chordoma is still unknown. The improvement of tissue microarray technology has provided the opportunity to perform analyses of tumor tissues on a large scale in a uniform and consistent manner. This study was designed with the use of tissue microarray to determine the expression of brachyury. Brachyury expression in chordoma tissues from 78 chordoma patients was analyzed by immunohistochemical staining of tissue microarray. The clinicopathologic parameters, including gender, age, location of tumor and metastatic status were evaluated. Fifty-nine of 78 (75.64%) tumors showed nuclear staining for brachyury, and among them, 29 tumors (49.15%) showed 1+ (<30% positive cells) staining, 15 tumors (25.42%) had 2+ (31% to 60% positive cells) staining, and 15 tumors (25.42%) demonstrated 3+ (61% to 100% positive cells) staining. Brachyury nuclear staining was detected more frequently in sacral chordomas than in chordomas of the mobile spine. However, there was no significant relationship between brachyury expression and other clinical variables. By Kaplan-Meier analysis, brachyury expression failed to produce any significant relationship with the overall survival rate. In conclusion, brachyury expression is not a prognostic indicator in chordoma.

Converging paths to progress for skull base chordoma: Review of current therapy and future molecular targets

BACKGROUND

Chordomas of the skull base are rare locally aggressive neoplasms with a predilection for encapsulating critical neurovascular structures, bony destruction and irregular growth patterns, and from which patients succumb to recurrence and treatment failures.

METHODS

A review of the medical literature is performed, using standard search engines and identifying articles related to skull base chordomas, surgery, radiation therapy, chemotherapy, molecular genetics, and prospective trials.

RESULTS

A synthesis of the literature is presented, including sections on pathology, treatment, molecular genetics, challenges, and future directions.

CONCLUSION

Beyond an understanding of the current treatment paradigms for skull base chordomas, the reader gains insight into the collaborative approach applied to orphan diseases, of which chordomas is a prime exemplar.

From notochord formation to hereditary chordoma: the many roles of Brachyury

Chordoma is a rare, but often malignant, bone cancer that preferentially affects the axial skeleton and the skull base. These tumors are both sporadic and hereditary and appear to occur more frequently after the fourth decade of life; however, modern technologies have increased the detection of pediatric chordomas. Chordomas originate from remnants of the notochord, the main embryonic axial structure that precedes the backbone, and share with notochord cells both histological features and the expression of characteristic genes. One such gene is Brachyury, which encodes for a sequence-specific transcription factor. Known for decades as a main regulator of notochord formation, Brachyury has recently gained interest as a biomarker and causative agent of chordoma, and therefore as a promising therapeutic target. Here, we review the main characteristics of chordoma, the molecular markers, and the clinical approaches currently available for the early detection and possible treatment of this cancer. In particular, we report on the current knowledge of the role of Brachyury and of its possible mechanisms of action in both notochord formation and chordoma etiogenesis.

Controlled release of doxorubicin from pH-responsive microgels

Stimuli-responsive hydrogels have enormous potential in drug delivery applications. They can be used for site-specific drug delivery due to environmental variables in the body such as pH and temperature. In this study, we have developed pH-responsive microgels for the delivery of doxorubicin (DOX) in order to optimize its anti-tumor activity while minimizing its systemic toxicity. We used a copolymer of oligo(polyethylene glycol) fumarate (OPF) and sodium methacrylate (SMA) to fabricate the pH-responsive microgels. We demonstrated that the microgels were negatively charged, and the amounts of charge on the microgels were correlated with the SMA concentration in their formulation. The resulting microgels exhibited sensitivity to the pH and ionic strength of the surrounding environment. We demonstrated that DOX was efficiently loaded into the microgels and released in a controlled fashion via an ion-exchange mechanism. Our data revealed that the DOX release was influenced by the pH and ionic strength of the solution. Moreover, we designed a phenomenological mathematical model, based on a stretched exponential function, to quantitatively analyze the cumulative release of DOX. We found a linear correlation between the maximum release of DOX calculated from the model and the SMA concentration in the microgel formulation. The anti-tumor activity of the released DOX was assessed using a human chordoma cell line. Our data revealed that OPF-SMA microgels prolonged the cell killing effect of DOX.

Establishment and characterization of a novel chordoma cell line: CH22

Chordoma is a rare primary malignant bone tumor and there exist only a few established human chordoma cell lines. The scarcity of robust chordoma cell lines has limited the ability to study this tumor. In this report, we describe the establishment of a novel chordoma cell line and characterize its in vitro and in vivo behaviors. The tumor tissue was isolated from a patient with recurrent chordoma of the sacrum. After 6 months in culture, the chordoma cell line, referred here as CH22, was established. Microscopic analysis of two-dimensional culture confirmed that the CH22 cells exhibited a typical vacuolated cytoplasm similar to the well-established chordoma cell line U-CH1. Electron microscopy showed cohesive cells with numerous surface filopodia, pockets of glycogen and aggregates of intermediate tonofilaments in cytoplasm. Three-dimensional culture revealed that the CH22 cells could grow and form clusters by day 8. The MTT assays demonstrated that, compared with sensitive osteosarcoma cell lines, CH22 cells were relatively resistant to conventional chemotherapeutic drugs. Western blotting and immunofluorescence analysis confirmed that the CH22 cells expressed brachyury, vimentin, and cytokeratin. Finally, histological analysis of CH22 xenograft tumor tissues demonstrated the appearance of physaliphorous cells and positive staining of brachyury, cytokeratin, and S100. By CT and MRI, imaging xenografts showed the typical appearances seen in human chordomas. These findings suggest that the established novel human chordoma cell line CH22 and its tumorigenecity in SCID nude mice may serve as an important model for studying chordoma cell biology and the development of new therapeutic modalities.

Novel therapeutic targets in chordoma

INTRODUCTION

Chordomas are malignant bone tumors arising from notochordal remnants. They most commonly occur at the sacrum, skull base, and spine. The gold standard treatment for these tumors is a combination of en-bloc resection and radiation therapy.

AREAS COVERED

Recent genomic studies have identified duplication of the gene brachyury as a major susceptibility mutation in familial chordomas. Studies on sporadic chordomas have identified several tumor markers, using microRNAs and Comparative Genome Hybridization. In this article, we highlight current advances in research on the molecular characterization of chordomas.

EXPERT OPINION

Scientific advances have allowed for the identification of numerous tumor markers involved in chordoma pathogenesis. In the future, chordoma cell lines will be produced that silence or over-express these tumor markers. As we increase our understanding of the mechanism of chordoma tumor proliferation, we can expect the development of targeted drug therapies.

Chordoma: current concepts, management, and future directions

Chordoma is a rare bone cancer that is aggressive, locally invasive, and has a poor prognosis. Chordomas are thought to arise from transformed remnants of notochord and have a predilection for the axial skeleton, with the most common sites being the sacrum, skull base, and spine. The gold standard treatment for chordomas of the mobile spine and sacrum is en-bloc excision with wide margins and postoperative external-beam radiation therapy. Treatment of clival chordomas is unique from other locations with an enhanced emphasis on preservation of neurological function, typified by a general paradigm of maximally safe cytoreductive surgery and advanced radiation delivery techniques. In this Review, we highlight current standards in diagnosis, clinical management, and molecular characterisation of chordomas, and discuss current research.

Establishment and characterization of a primary human chordoma xenograft model

OBJECT

Chordomas are rare tumors arising from remnants of the notochord. Because of the challenges in achieving a complete resection, the radioresistant nature of these tumors, and the lack of effective chemotherapeutics, the median survival for patients with chordomas is approximately 6 years. Reproducible preclinical model systems that closely mimic the original patient's tumor are essential for the development and evaluation of effective therapeutics. Currently, there are only a few established chordoma cell lines and no primary xenograft model. In this study, the authors aimed to develop a primary chordoma xenograft model.

METHODS

The authors implanted independent tumor samples from 2 patients into athymic nude mice. The resulting xenograft line was characterized by histopathological analysis and immunohistochemical staining. The patient's tumor and serial passages of the xenograft were genomically analyzed using a 660,000 single-nucleotide polymorphism array.

RESULTS

A serially transplantable xenograft was established from one of the 2 patient samples. Histopathological analysis and immunohistochemical staining for S100 protein, epithelial membrane antigen, and cytokeratin AE1/AE3 of the primary patient sample and the xenografts confirmed that the xenografts were identical to the original chordoma obtained from the patient. Immunohistochemical staining and western blot analysis confirmed the presence of brachyury, a recently described marker of chordomas, in the tumor from the patient and each of the xenografts. Genome-wide variation was assessed between the patient's tumor and the xenografts and was found to be more than 99.9% concordant.

CONCLUSIONS

To the best of their knowledge, the authors have established the first primary chordoma xenograft that will provide a useful preclinical model for this disease and a platform for therapeutic development.

Generation of chordoma cell line JHC7 and the identification of Brachyury as a novel molecular target

OBJECT

Chordoma is a malignant bone neoplasm hypothesized to arise from notochordal remnants along the length of the neuraxis. Recent genomic investigation of chordomas has identified T (Brachyury) gene duplication as a major susceptibility mutation in familial chordomas. Brachyury plays a vital role during embryonic development of the notochord and has recently been shown to regulate epithelial-to-mesenchymal transition in epithelial-derived cancers. However, current understanding of the role of this transcription factor in chordoma is limited due to the lack of availability of a fully characterized chordoma cell line expressing Brachyury. Thus, the objective of this study was to establish the first fully characterized primary chordoma cell line expressing gain of the T gene locus that readily recapitulates the original parental tumor phenotype in vitro and in vivo.

METHODS

Using an intraoperatively obtained tumor sample from a 61-year-old woman with primary sacral chordoma, a chordoma cell line (JHC7, or Johns Hopkins Chordoma Line 7) was established. Molecular characterization of the primary tumor and cell line was conducted using standard immunostaining and Western blotting. Chromosomal aberrations and genomic amplification of the T gene in this cell line were determined. Using this cell line, a xenograft model was established and the histopathological analysis of the tumor was performed. Silencing of Brachyury and changes in gene expression were assessed.

RESULTS

The authors report, for the first time, the successful establishment of a chordoma cell line (JHC7) from a patient with pathologically confirmed sacral chordoma. This cell line readily forms tumors in immunodeficient mice that recapitulate the parental tumor phenotype with conserved histological features consistent with the parental tumor. Furthermore, it is demonstrated for the first time that silencing of Brachyury using short hairpin RNA renders the morphology of chordoma cells to a more differentiated-like state and leads to complete growth arrest and senescence with an inability to be passaged serially in vitro.

CONCLUSIONS

This report represents the first xenograft model of a sacral chordoma line described in the literature and the first cell line established with stable Brachyury expression. The authors propose that Brachyury is an attractive therapeutic target in chordoma and that JHC7 will serve as a clinically relevant model for the study of this disease.