Extended ultrastructural characterization of chordoma cells: the link to new therapeutic options

A dynamic actin cytoskeleton is required to prevent constitutive VDAC-dependent MAPK signalling and aberrant lipid homeostasis

The dynamic nature of the actin cytoskeleton is required to coordinate many cellular processes, and a loss of its plasticity has been linked to accelerated cell aging and attenuation of adaptive response mechanisms. Cofilin is an actin-binding protein that controls actin dynamics and has been linked to mitochondrial signaling pathways that control drug resistance and cell death. Here we show that cofilin-driven chronic depolarization of the actin cytoskeleton activates cell wall integrity mitogen-activated protein kinase (MAPK) signalling and disrupts lipid homeostasis in a voltage-dependent anion channel (VDAC)-dependent manner. Expression of the cof1-5 mutation, which reduces the dynamic nature of actin, triggers loss of cell wall integrity, vacuole fragmentation, disruption of lipid homeostasis, lipid droplet (LD) accumulation, and the promotion of cell death. The integrity of the actin cytoskeleton is therefore essential to maintain the fidelity of MAPK signaling, lipid homeostasis, and cell health in S. cerevisiae.

An ultrastructural 3D reconstruction method for observing the arrangement of collagen fibrils and proteoglycans in the human aortic wall under mechanical load

An insight into changes of soft biological tissue ultrastructures under loading conditions is essential to understand their response to mechanical stimuli. Therefore, this study offers an approach to investigate the arrangement of collagen fibrils and proteoglycans (PGs), which are located within the mechanically loaded aortic wall. The human aortic samples were either fixed directly with glutaraldehyde in the load-free state or subjected to a planar biaxial extension test prior to fixation. The aortic ultrastructure was recorded using electron tomography. Collagen fibrils and PGs were segmented using convolutional neural networks, particularly the ESPNet model. The 3D ultrastructural reconstructions revealed a complex organization of collagen fibrils and PGs. In particular, we observed that not all PGs are attached to the collagen fibrils, but some fill the spaces between the fibrils with a clear distance to the collagen. The complex organization cannot be fully captured or can be severely misinterpreted in 2D. The approach developed opens up practical possibilities, including the quantification of the spatial relationship between collagen fibrils and PGs as a function of the mechanical load. Such quantification can also be used to compare tissues under different conditions, e.g., healthy and diseased, to improve or develop new material models. STATEMENT OF SIGNIFICANCE: The developed approach enables the 3D reconstruction of collagen fibrils and proteoglycans as they are embedded in the loaded human aortic wall. This methodological pipeline comprises the knowledge of arterial mechanics, imaging with transmission electron microscopy and electron tomography, segmentation of 3D image data sets with convolutional neural networks and finally offers a unique insight into the ultrastructural changes in the aortic tissue caused by mechanical stimuli.

Tumor Growth Rate as a New Predictor of Progression-Free Survival After Chordoma Surgery

BACKGROUND

Currently, different postoperative predictors of chordoma recurrence have been identified. Tumor growth rate (TGR) is an image-based calculation that provides quantitative information of tumor's volume changing over time and has been shown to predict progression-free survival (PFS) in other tumor types.

OBJECTIVE

To explore the usefulness of TGR as a new preoperative radiological marker for chordoma recurrence.

METHODS

A retrospective single-institution study was carried out including patients reflecting these criteria: confirmed diagnosis of chordoma on pathological analysis, no history of previous radiation, and at least 2 preoperative thin-slice magnetic resonance images available to measure TGR. TGR was calculated for all patients, showing the percentage change in tumor size over 1 mo.

RESULTS

A total of 32 patients were retained for analysis. Patients with a TGR ≥ 10.12%/m had a statistically significantly lower mean PFS (P < .0001). TGR ≥ 10.12%/m (odds ratio = 26, P = .001) was observed more frequently in recurrent chordoma. In a subgroup analysis, we found that the association of Ki-67 labeling index ≥ 6% and TGR ≥ 10.12%/m was correlated with recurrence (P = .0008).

CONCLUSION

TGR may be considered as a preoperative radiological indicator of tumor proliferation and seems to preoperatively identify more aggressive tumors with a higher tendency to recur. Our findings suggest that the therapeutic strategy and clinical-radiological follow-up of patients with chordoma can be adapted also according to this new parameter.

Simple method of thawing cryo-stored samples preserves ultrastructural features in electron microscopy

Preservation of ultrastructural features in biological samples for electron microscopy (EM) is a challenging task that is routinely accomplished through chemical fixation or high-pressure freezing coupled to automated freeze substitution (AFS) using specialized devices. However, samples from clinical (e.g. "biobanking" of bulk biopsies) and preclinical (e.g. whole mouse tissues) specimens are often not specifically prepared for ultrastructural analyses but simply immersed in liquid nitrogen before long-term cryo-storage. We demonstrate that ultrastructural features of such samples are insufficiently conserved using AFS and developed a simple, rapid, and effective method for thawing that does not require specific instrumentation. This procedure consists of dry ice-cooled pre-trimming of frozen tissue and aldehyde fixation for 3 h at 37 °C followed by standard embedding steps. Herein investigated tissues comprised human term placentae, clinical lung samples, as well as mouse tissues of different composition (brown adipose tissue, white adipose tissue, cardiac muscle, skeletal muscle, liver). For all these tissues, we compared electron micrographs prepared from cryo-stored material with our method to images derived from directly prepared fresh tissues with standard chemical fixation. Our protocol yielded highly conserved ultrastructural features and tissue-specific details, largely matching the quality of fresh tissue samples. Furthermore, morphometric analysis of lipid droplets and mitochondria in livers of fasted mice demonstrated that statistically valid quantifications can be derived from samples prepared with our method. Overall, we provide a simple and effective protocol for accurate ultrastructural and morphometric analyses of cryo-stored bulk tissue samples.

Long and Very-Long-Chain Ceramides Correlate with A More Aggressive Behavior in Skull Base Chordoma Patients

BACKGROUND

Skull base chordomas are rare tumors arising from notochord. Sphingolipids analysis is a promising approach in molecular oncology, and it has never been applied in chordomas. Our aim is to investigate chordoma behavior and the role of ceramides.

METHODS

Ceramides were extracted and evaluated by liquid chromatography and mass spectrometry in a cohort of patients with a skull base chordoma. Clinical data were also collected and correlated with ceramide levels. Linear regression and correlation analyses were conducted.

RESULTS

Analyzing the association between ceramides level and MIB-1, total ceramides and dihydroceramides showed a strong association (r = 0.7257 and r = 0.6733, respectively) with MIB-1 staining (p = 0.0033 and p = 0.0083, respectively). Among the single ceramide species, Cer C24:1 (r = 0.8814, p ≤ 0.0001), DHCer C24:1 (r = 0.8429, p = 0.0002) and DHCer C18:0 (r = 0.9426, p ≤ 0.0001) showed a significant correlation with MIB-1.

CONCLUSION

Our lipid analysis showed ceramides to be promising tumoral biomarkers in skull base chordomas. Long- and very-long-chain ceramides, such as Cer C24:1 and DHCer C24:1, may be related to a prolonged tumor survival and aggressiveness, and the understanding of their effective biological role will hopefully shed light on the mechanisms of chordoma radio-resistance, tendency to recur, and use of agents targeting ceramide metabolism.

Active receptor tyrosine kinases, but not Brachyury, are sufficient to trigger chordoma in zebrafish

The aberrant activation of developmental processes triggers diverse cancer types. Chordoma is a rare, aggressive tumor arising from transformed notochord remnants. Several potentially oncogenic factors have been found to be deregulated in chordoma, yet causation remains uncertain. In particular, sustained expression of TBXT – encoding the notochord regulator protein brachyury – is hypothesized as a key driver of chordoma, yet experimental evidence is absent. Here, we employ a zebrafish chordoma model to identify the notochord-transforming potential of implicated genes in vivo. We find that Brachyury, including a form with augmented transcriptional activity, is insufficient to initiate notochord hyperplasia. In contrast, the chordoma-implicated receptor tyrosine kinases (RTKs) EGFR and Kdr/VEGFR2 are sufficient to transform notochord cells. Aberrant activation of RTK/Ras signaling attenuates processes required for notochord differentiation, including the unfolded protein response and endoplasmic reticulum stress pathways. Our results provide the first in vivo evidence against a tumor-initiating potential of Brachyury in the notochord, and imply activated RTK signaling as a possible initiating event in chordoma. Furthermore, our work points at modulating endoplasmic reticulum and protein stress pathways as possible therapeutic avenues against chordoma.

Summary: An injection-based chordoma model in zebrafish shows that the hypothesized chordoma oncogene brachyury is insufficient, whereas EGFR and VEGFR2 are sufficient, to trigger notochord hyperplasia in our model.

Human melanoma brain metastases cell line MUG-Mel1, isolated clones and their detailed characterization

Melanoma is a leading cause of high mortality that frequently spreads to the brain and is associated with deterioration in quality and quantity of life. Treatment opportunities have been restricted until now and new therapy options are urgently required. Our focus was to reveal the potential heterogeneity of melanoma brain metastasis. We succeeded to establish a brain melanoma metastasis cell line, namely MUG-Mel1 and two resulting clones D5 and C8 by morphological variety, differences in lipidome, growth behavior, surface, and stem cell markers. Mutation analysis by next-generation sequencing, copy number profiling, and cytogenetics demonstrated the different genetic profile of MUG-Mel1 and clones. Tumorigenicity was unsuccessfully tested in various mouse systems and finally established in a zebra fish model. As innovative treatment option, with high potential to pass the blood-brain barrier a peptide isolated from lactoferricin was studied in potential toxicity. Brain metastases are a major clinical challenge, therefore the development of relevant in vitro and in vivo models derived from brain melanoma metastases provides valuable information about tumor biology and offers great potential to screen for new innovative therapies.

5-Aminolevulinic acid-based photodynamic therapy of chordoma: In vitro experiments on a human tumor cell line

BACKGROUND

Chordomas are very rare tumors of the skull base and the sacrum. They show infiltrating and destructive growth and are known to be chemo- and radio-resistant. After surgical resection, the recurrence rate is high and overall survival limited. As current adjuvant treatments are ineffective, new treatment concepts are urgently needed. 5-aminolevulinic acid-based photodynamic therapy (5-ALA based PDT) showed promising results for malignant gliomas. However, it is unknown so far, whether chordomas accumulate protoporphyrin IX (PPIX) after application of 5-ALA and whether they are sensitive to subsequent 5-ALA based PDT.

METHODS

The immortalized human chordoma cells U-CH2 were used as in vitro model. After incubation for 4h or 6h with different 5-ALA concentrations, PPIX accumulation was determined by flow cytometry. To assess sensitivity to PDT, chordoma cells were incubated at 30.000cells/well (high cell density) or 15.000cells/well (low cell density) with graded doses of 5-ALA (0-50μg/ml) in 96-well plates and subsequently exposed to laser light of 635nm wavelength (18.75J/cm2). Cell survival was measured 24h after exposure to laser light using the WST-1 assay.

RESULTS

U-CH2 cells dose-dependently accumulated PPIX (ANOVA; p<0.0001). PPIX fluorescence was significantly higher, when cells were incubated with 5-ALA for 6h compared to 4h at higher 5-ALA concentrations (ANOVA/Bonferroni; p≤0.05 for≥30μg/ml 5-ALA). For both cell densities, a 5-ALA dose-dependent decline in viability was observed (ANOVA; p<0.0001). Viability was significantly lower at higher 5-ALA concentrations, when 30.000 cells/wells were treated compared to 15.000cells/well (ANOVA/Bonferroni; p≤0.001 for≥30μg/ml 5-ALA). LD50 was 30.25μg/ml 5-ALA.

CONCLUSION

The human UCH-2 cell line was a very useful in vitro model to study different effects of 5-ALA based PDT. For the first time, it could be shown that human chordoma cells may be destroyed by 5-ALA/PDT.

Targeting the Cohesive Cluster Phenotype in Chordoma via β1 Integrin Increases Ionizing Radiation Efficacy

Chordoma is a rare, radiation-resistant, skull-base and spinal tumor with high local recurrence containing mixed cell-adhesion phenotypes. We characterized DNA damage response (DDR) signaling (γH2AX, pKAP1, pATM) and survival response to ionizing radiation (IR) in human chordoma samples (42 resections, 23 patients) to test if blocking cell adhesion sensitizes U-CH1 tumor cells to IR. U-CH1 cells expressed brachyury, YAP, and laminin adhesion receptors (CD49c, CD49f, CD44), and approximately 15% to 20% of U-CH1 cells featured an α6 integrin-dependent (CD49f) cohesive cluster phenotype, which confers therapeutic resistance and aids metastasis. DDR to IR in U-CH1 cells was compared to normal prostate epithelial (PrEC) and tumor cells (DU145). Flow cytometry showed a dose- and time-dependent increase in γH2AX and pKAP1 expression in all cell lines. However, nearly 50% of U-CH1 cells exhibited nonresponsive phenotype to IR (measured by γH2AX and pKAP1) independent of cell cycle status. Immunofluorescence microscopy verified that only 15% of U-CH1 clustered cells were γH2AX or pKAP1 positive (versus 80% of nonclustered cells) 2 hours following 2-Gy IR. Conversely, both tumor cell lines were uniformly defective in pATM response. HYD1, a synthetic ECM ligand, inhibited DDR through an unresolved γH2AX response. β1 integrin-blocking antibody (AIIB2) decreased cell survival 50% itself and approximately doubled the IR-induced cell kill at all IR doses observed at 2 and 4 weeks posttreatment. These results suggest that a heterogeneity of DDR to IR exists within a chordoma population. Blocking integrin function alone and/or as an adjuvant to IR may eradicate chordomas containing the cohesive cluster phenotype.

Clinical Decision Making: Integrating Advances in the Molecular Understanding of Spine Tumors

STUDY DESIGN

Literature review.

OBJECTIVE

To describe advancements in molecular techniques, biomarkers, technology, and targeted therapeutics and the potential these modalities hold to predict treatment paradigms, clinical outcomes, and/or survival in patients diagnosed with primary spinal column tumors.

SUMMARY OF BACKGROUND DATA

Advances in molecular technologies and techniques have influenced the prevention, diagnosis, and overall management of patients diagnosed with cancer. Assessment of genomic, proteomic alterations, epigenetic, and posttranslational modifications as well as developments in diagnostic modalities and targeted therapeutics, although the best studied in nonspinal metastatic disease, have led to increased understanding of spine oncology that is expected to improve patient outcomes. In this manuscript, the technological advancements that are expected to change the landscape of spinal oncology are discussed with a focus on how these technologies will aid in clinical decision-making for patients diagnosed with primary spinal tumors.

METHODS

A review of the literature was performed focusing on studies that integrated next-generation sequencing, circulating tumor cells/circulating tumor DNA, advances in imaging modalities and/or radiotherapy in the diagnosis and treatment of cancer.

RESULTS

We discuss genetic and epigenetic drivers, aberrations in receptor tyrosine kinase signaling, and emerging therapeutic strategies that include receptor tyrosine kinase inhibitors, immunotherapy strategies, and vaccine-based cancer prevention strategies.

CONCLUSION

The wide range of approaches currently in use and the emerging technologies yet to be fully realized will allow for better development of rationale therapeutics to improve patient outcomes.

LEVEL OF EVIDENCE

N/A.