An overview of the role of cancer stem cells in spine tumors with a special focus on chordoma

Chordoma cancer stem cell subpopulation characterization may guide targeted immunotherapy approaches to reduce disease recurrence

Introduction

Cancer stem cells (CSCs), a group of tumor-initiating and tumor-maintaining cells, may be major players in the treatment resistance and recurrence distinctive of chordoma. Characterizing CSCs is crucial to better targeting this subpopulation.

Methods

Using flow cytometry, six chordoma cell lines were evaluated for CSC composition. In vitro, cell lines were stained for B7H6, HER2, MICA-B, ULBP1, EGFR, and PD-L1 surface markers. Eighteen resected chordomas were stained using a multispectral immunofluorescence (mIF) antibody panel to identify CSCs in vivo. HALO software was used for quantitative CSC density and spatial analysis.

Results

In vitro, chordoma CSCs express more B7H6, MICA-B, and ULBP1, assessed by percent positivity and mean fluorescence intensity (MFI), as compared to non-CSCs in all cell lines. PD- L1 percent positivity is increased by >20% in CSCs compared to non-CSCs in all cell lines except CH22. In vivo, CSCs comprise 1.39% of chordoma cells and most are PD-L1+ (75.18%). A spatial analysis suggests that chordoma CSCs cluster at an average distance of 71.51 mm (SD 73.40 mm) from stroma.

Discussion

To our knowledge, this study is the first to identify individual chordoma CSCs and describe their surface phenotypes using in vitro and in vivo methods. PD-L1 is overexpressed on CSCs in chordoma human cell lines and operative tumor samples. Similarly, potential immunotherapeutic targets on CSCs, including B7H6, MICA-B, ULBP1, EGFR, and HER2 are overexpressed across cell lines. Targeting these markers may have a preferential role in combating CSCs, an aggressive subpopulation likely consequential to chordoma's high recurrence rate.

Single-cell transcriptome reveals cellular hierarchies and guides p-EMT-targeted trial in skull base chordoma

Skull base chordoma (SBC) is a bone cancer with a high recurrence rate, high radioresistance rate, and poorly understood mechanism. Here, we profiled the transcriptomes of 90,691 single cells, revealed the SBC cellular hierarchies, and explored novel treatment targets. We identified a cluster of stem-like SBC cells that tended to be distributed in the inferior part of the tumor. Combining radiated UM-Chor1 RNA-seq data and in vitro validation, we further found that this stem-like cell cluster is marked by cathepsin L (CTSL), a gene involved in the packaging of telomere ends, and may be responsible for radioresistance. Moreover, signatures related to partial epithelial-mesenchymal transition (p-EMT) were found to be significant in malignant cells and were related to the invasion and poor prognosis of SBC. Furthermore, YL-13027, a p-EMT inhibitor that acts through the TGF-β signaling pathway, demonstrated remarkable potency in inhibiting the invasiveness of SBC in preclinical models and was subsequently applied in a phase I clinical trial that enrolled three SBC patients. Encouragingly, YL-13027 attenuated the growth of SBC and achieved stable disease with no serious adverse events, underscoring the clinical potential for the precision treatment of SBC with this therapy. In summary, we conducted the first single-cell RNA sequencing of SBC and identified several targets that could be translated to the treatment of SBC.

Combinatorial Natural Killer Cell-based Immunotherapy Approaches Selectively Target Chordoma Cancer Stem Cells

Chordoma is a rare tumor derived from notochord remnants that has a propensity to recur and metastasize despite conventional multimodal treatment. Cancer stem cells (CSC) are implicated in chordoma's resistant and recurrent behavior; thus strategies that target CSCs are of particular interest. Using in vitro cytotoxicity models, we demonstrated that anti-programmed death-ligand 1 (N-601) and anti-epidermal growth factor receptor (cetuximab) antibodies enhanced lysis of chordoma cells by healthy donor and chordoma patient NK cells through antibody-dependent cellular cytotoxicity (ADCC). Treatment of NK cells with an IL-15 superagonist complex (N-803) increased their cytotoxicity against chordoma cells, which was further enhanced by treatment with N-601 and/or cetuximab. PD-L1-targeted chimeric antigen receptor NK cells (PD-L1 t-haNKs) were also effective against chordoma cells. CSCs were preferentially vulnerable to NK cell killing in the presence of N-601 and N-803. Flow cytometric analysis of a chordoma CSC population showed that CSCs expressed significantly more NK activating ligand B7-H6 and PD-L1 than non-CSCs, thus explaining a potential mechanism of selective targeting. These data suggest that chordoma may be effectively targeted by combinatorial NK cell-mediated immunotherapeutic approaches and that the efficacy of these approaches in chordoma and other CSC-driven tumor types should be investigated further in clinical studies.

Prognostic significance of pretreatment plasma D-dimer levels in patients with spinal chordoma: a retrospective cohort study

PURPOSE

Plasma D-dimer levels, a marker of hypercoagulation, have not only been used as an indicator for cascaded reaction in the coagulation process but are also reported to be an underlying biomarker in several types of cancers. This retrospective cohort study was designed to evaluate the prognostic value of preoperative plasma D-dimer level in patients with spinal chordoma.

METHODS

We enrolled 224 patients who underwent surgery for spinal chordoma between 2002 and 2015 at Changzheng Orthopedic Oncology Center. Preoperative clinical parameters were recorded and evaluated by univariate and multivariate Cox regression models. The correlation between preoperative plasma D-dimer levels and survival was assessed using the Kaplan-Meier method.

RESULTS

The optimal cutoff value of pretreatment D-dimer was 840 μg/L determined by X-tile. DFS (disease-free survival) was 64.7% and OS (overall survival) was 75% in the cohort. Multivariate Cox regression model identified D-dimer level as an independent prognostic factor of DFS and OS, as well as treatment history, preoperative Karnofsky Performance Scale, preoperative Frankel score, pathology classification and adjuvant radiotherapy (p < 0.05). In addition, D-dimer level may also be an effective supplement for defining tumor Enneking staging (p < 0.05).

CONCLUSIONS

Higher pretreatment plasma D-dimer level was associated with a poor prognosis in chordoma and could be used as an independent prognostic factor for the survival of the patients with spinal chordoma. With supplementation of D-dimer level, Enneking stage may be more able to accurate stratify individualized risk and determine clinical management. These slides can be retrieved under Electronic Supplementary Material.

Effects of primary and recurrent sacral chordoma on the motor and nociceptive function of hindlimbs in rats: an orthotopic spine model

OBJECTIVE Chordoma is a slow-growing, locally aggressive cancer that is minimally responsive to conventional chemotherapy and radiotherapy and has high local recurrence rates after resection. Currently, there are no rodent models of spinal chordoma. In the present study, the authors sought to develop and characterize an orthotopic model of human chordoma in an immunocompromised rat. METHODS Thirty-four immunocompromised rats were randomly allocated to 4 study groups; 22 of the 34 rats were engrafted in the lumbar spine with human chordoma. The groups were as follows: UCH1 tumor-engrafted (n = 11), JHC7 tumor-engrafted (n = 11), sham surgery (n = 6), and intact control (n = 6) rats. Neurological impairment of rats due to tumor growth was evaluated using open field and locomotion gait analysis; pain response was evaluated using mechanical or thermal paw stimulation. Cone beam CT (CBCT), MRI, and nanoScan PET/CT were performed to evaluate bony changes due to tumor growth. On Day 550, rats were killed and spines were processed for H & E-based histological examination and immunohistochemistry for brachyury, S100β, and cytokeratin. RESULTS The spine tumors displayed typical chordoma morphology, that is, physaliferous cells filled with vacuolated cytoplasm of mucoid matrix. Brachyury immunoreactivity was confirmed by immunostaining, in which samples from tumor-engrafted rats showed a strong nuclear signal. Sclerotic lesions in the vertebral body of rats in the UCH1 and JHC7 groups were observed on CBCT. Tumor growth was confirmed using contrast-enhanced MRI. In UCH1 rats, large tumors were observed growing from the vertebral body. JHC7 chordoma-engrafted rats showed smaller tumors confined to the bone periphery compared with UCH1 chordoma-engrafted rats. Locomotion analysis showed a disruption in the normal gait pattern, with an increase in the step length and duration of the gait in tumor-engrafted rats. The distance traveled and the speed of rats in the open field test was significantly reduced in the UCH1 and JHC7 tumor-engrafted rats compared with controls. Nociceptive response to a mechanical stimulus showed a significant (p < 0.001) increase in the paw withdrawal threshold (mechanical hypalgesia). In contrast, the paw withdrawal response to a thermal stimulus decreased significantly (p < 0.05) in tumor-engrafted rats. CONCLUSIONS The authors developed an orthotopic human chordoma model in rats. Rats were followed for 550 days using imaging techniques, including MRI, CBCT, and nanoScan PET/CT, to evaluate lesion progression and bony integrity. Nociceptive evaluations and locomotion analysis were performed during follow-up. This model reproduces cardinal signs, such as locomotor and sensory deficits, similar to those observed clinically in human patients. To the authors' knowledge, this is the first spine rodent model of human chordoma. Its use and further study will be essential for pathophysiology research and the development of new therapeutic strategies.