Multimodality imaging of abnormal vascular perfusion and morphology in preclinical 9L gliosarcoma model

Imaging Hallmarks of Sarcoma Progression Via X-ray Computed Tomography: Beholding the Flower of Evil

Simple Summary

Sarcomas represent the largest group of rare solid tumors that arise from mesenchymal stem cells and are a leading cause of cancer death in individuals younger than 20 years of age. There is an immediate need for the development of an algorithm for the early accurate diagnosis of sarcomas due to the high rate of diagnostic inaccuracy, which reaches up to 30%. X-ray computed tomography is a non-invasive imaging technique used to obtain detailed internal images of the human or animal body in clinical practice and preclinical studies. We summarized the main imaging features of soft tissue and bone sarcomas, and noted the development of new molecular markers to reach tumor type-specific imaging. Also, we demonstrated the possibility of the use X-ray computed microtomography for non-destructive 3D visualization of sarcoma progression in preclinical studies. Finding correlations between X-ray computed tomography modalities and the results of the histopathological specimen examination may significantly increase the accuracy of diagnostics, which leads to the initiation of appropriate management in a timely manner and, consequently, to improved outcomes.

Abstract

Sarcomas are a leading cause of cancer death in individuals younger than 20 years of age and represent the largest group of rare solid tumors. To date, more than 100 morphological subtypes of sarcomas have been described, among which epidemiology, clinical features, management, and prognosis differ significantly. Delays and errors in the diagnosis of sarcomas limit the number of effective therapeutic modalities and catastrophically worsen the prognosis. Therefore, the development of an algorithm for the early accurate diagnosis of sarcomas seems to be as important as the development of novel therapeutic advances. This literature review aims to summarize the results of recent investigations regarding the imaging of sarcoma progression based on the use of X-ray computed tomography (CT) in preclinical studies and in current clinical practice through the lens of cancer hallmarks. We attempted to summarize the main CT imaging features of soft-tissue and bone sarcomas. We noted the development of new molecular markers with high specificity to antibodies and chemokines, which are expressed in particular sarcoma subtypes to reach tumor type-specific imaging. We demonstrate the possibility of the use of X-ray computed microtomography (micro-CT) for non-destructive 3D visualization of solid tumors by increasing the visibility of soft tissues with X-ray scattering agents. Based on the results of recent studies, we hypothesize that micro-CT enables the visualization of neovascularization and stroma formation in sarcomas at high-resolution in vivo and ex vivo, including the novel techniques of whole-block and whole-tissue imaging. Finding correlations between CT, PET/CT, and micro-CT imaging features, the results of the histopathological specimen examination and clinical outcomes may significantly increase the accuracy of soft-tissue and bone tumor diagnostics, which leads to the initiation of appropriate histotype-specific management in a timely manner and, consequently, to improved outcomes.

Differentiation of Brain Tumor Microvasculature From Normal Vessels Using Optical Coherence Angiography

BACKGROUND AND OBJECTIVES

Despite rapid advances and discoveries in medical imaging, monitoring therapeutic efficacy for malignant gliomas and monitoring tumor vasculature remains problematic. The purpose of this study is to utilize optical coherence angiography for vasculature characterization inside and surrounding brain tumors in a murine xenograft brain tumor model. Features included in our analysis include fractional blood volume, vessel tortuosity, diameter, orientation, and directionality.

STUDY DESIGN/MATERIALS AND METHODS

In this study, five tumorous mice models at 4 weeks of age were imaged. Human glioblastoma cells were injected into the brain and allowed to grow for 4 weeks and then imaged using optical coherence tomography.

RESULTS

Results suggest that blood vessels outside the tumor contain a greater fractional blood volume as compared with vessels inside the tumor. Vessels inside the tumor are more tortuous as compared with those outside the tumor. Results indicate that vessels near the tumor margin are directed inward towards the tumor while normal vessels show a more random orientation.

CONCLUSION

Quantification of vascular microenvironments in brain gliomas can provide functional vascular parameters to aid various diagnostic and therapeutic studies. © 2021 Wiley Periodicals LLC.

O-(2-[18F]-Fluoroethyl)-L-Tyrosine (FET) in Neurooncology: A Review of Experimental Results

In recent years, PET using radiolabelled amino acids has gained considerable interest as an additional tool besides MRI to improve the diagnosis of cerebral gliomas and brain metastases. A very successful tracer in this field is O-(2-[18F]fluoroethyl)-L-tyrosine (FET) which in recent years has replaced short-lived tracers such as [11C]-methyl-L-methionine in many neuro-oncological centers in Western Europe. FET can be produced with high efficiency and distributed in a satellite concept like 2- [18F]fluoro-2-deoxy-D-glucose. Many clinical studies have demonstrated that FET PET provides important diagnostic information regarding the delineation of cerebral gliomas for therapy planning, an improved differentiation of tumor recurrence from treatment-related changes and sensitive treatment monitoring. In parallel, a considerable number of experimental studies have investigated the uptake mechanisms of FET on the cellular level and the behavior of the tracer in various benign lesions in order to clarify the specificity of FET uptake for tumor tissue. Further studies have explored the effects of treatment related tissue alterations on tracer uptake such as surgery, radiation and drug therapy. Finally, the role of blood-brain barrier integrity for FET uptake which presents an important aspect for PET tracers targeting neoplastic lesions in the brain has been investigated in several studies. Based on a literature research regarding experimental FET studies and corresponding clinical applications this article summarizes the knowledge on the uptake behavior of FET, which has been collected in more than 30 experimental studies during the last two decades and discusses the role of these results in the clinical context.

Glucocorticoid-mediated effects on angiogenesis in solid tumors

Angiogenesis is essential in tumor development to maintain the oxygen and nutrient supply. Glucocorticoids have shown both direct and indirect angiostatic properties in various types of solid cancers. In most of the reported cases glucocorticoid-mediated actions involved suppression of multiple pro-angiogenic factors expression by cancer cells. The anti-angiogenic properties of glucocorticoids correlated with diminished tumor vasculature and reduced tumor growth in multiple in vivo studies. However, when glucocorticoid treatment is considered, possible adverse events should be taken into account. Additional research is needed to further test the use of these steroidal drugs in cancer therapy.

Applications and development of permeability imaging in ischemic stroke

Brain permeability imaging techniques are specific for the assessment of blood-brain barrier integrity. The present review article primarily focuses on the application of permeability imaging in cases of ischemic stroke. The permeability maps may be used to predict future hemorrhagic transformation in patients following acute ischemic stroke, that have been treated with tissue plasminogen activator (tPA) or recanalization therapy. The permeability imaging would help make the clinical decision to administer tPA following acute ischemic stroke or not, which is not only due to the current 3-4.5 h time window. Additionally, permeability imaging may also be used to evaluate the collateral circulation in the perfusion and permeability of the ischemic area of the brain.

Influence of blood-brain barrier permeability on O-(2-18F-fluoroethyl)-L-tyrosine uptake in rat gliomas

PURPOSE

O-(2-¹⁸F-fluoroethyl)-L-tyrosine (¹⁸F-FET) is an established tracer for the diagnosis of brain tumors with PET. This study investigates the influence of blood-brain barrier (BBB) permeability on ¹⁸F-FET uptake in two rat glioma models and one human xenograft model.

METHODS

F98 glioma, 9L gliosarcoma or human U87 glioblastoma cells were implanted into the striatum of 56 Fischer or RNU rats. Thereafter, animals were divided into a control group and a group receiving injections of the glucocorticoid dexamethasone (Dex). After 12-13 days of tumor growth animals received injection of Evans blue dye (EBD) to visualize BBB disturbance and underwent ¹⁸F-FET PET followed by autoradiography. Time activity curves, standardized uptake values (SUV) and Tumor-to-brain ratios (TBR) of ¹⁸F-FET uptake [18-61 min post injection (p.i.)] were evaluated using a volume-of-Interest (VOI) analysis. BBB disturbance was quantitatively evaluated by EBD fluorescence. The membrane gaps of blood vessel endothelial tight junctions were measured using electron microscopy to visualize ultrastructural BBB alterations in one untreated and one Dex treated F98 glioma. Data were analyzed by two-way ANOVAs.

RESULTS

In Dex treated animals EBD extravasation was significantly reduced in 9L (P < 0.001) and U87 (P = 0.008) models and showed a trend in F98 models (P = 0.053). In contrast, no significant differences of ¹⁸F-FET uptake were observed between Dex treated animals and control group except a decrease of the TBR in the 9L tumor model in PET (P < 0.01). Ultrastructural evaluation of tumor blood vessel endothelia revealed significant reduction of the cleft diameter between endothelial cells after Dex treatment in F98 model (P = 0.010).

CONCLUSION

Despite a considerable reduction of BBB permeability in rat gliomas after Dex treatment, no relevant changes of ¹⁸F-FET uptake were noted in this experimental study. Thus, ¹⁸F-FET uptake in gliomas appears to be widely independent of the permeability of the BBB.

Preoperative prognostic value of dynamic contrast-enhanced MRI-derived contrast transfer coefficient and plasma volume in patients with cerebral gliomas

BACKGROUND AND PURPOSE

The prognostic value of dynamic contrast-enhanced MR imaging-derived plasma volume obtained in tumor and the contrast transfer coefficient has not been well-established in patients with gliomas. We determined whether plasma volume and contrast transfer coefficient in tumor correlated with survival in patients with gliomas in addition to other factors such as age, type of surgery, preoperative Karnofsky score, contrast enhancement, and histopathologic grade.

MATERIALS AND METHODS

This prospective study included 46 patients with a new pathologically confirmed diagnosis of glioma. The contrast transfer coefficient and plasma volume obtained in tumor maps were calculated directly from the signal-intensity curve without T1 measurements, and values were obtained from multiple small ROIs placed within tumors. Survival curve analysis was performed by dichotomizing patients into groups of high and low contrast transfer coefficient and plasma volume. Univariate analysis was performed by using dynamic contrast-enhanced parameters and clinical factors. Factors that were significant on univariate analysis were entered into multivariate analysis.

RESULTS

For all patients with gliomas, survival was worse for groups of patients with high contrast transfer coefficient and plasma volume obtained in tumor (P < .05). In subgroups of high- and low-grade gliomas, survival was worse for groups of patients with high contrast transfer coefficient and plasma volume obtained in tumor (P < .05). Univariate analysis showed that factors associated with lower survival were age older than 50 years, low Karnofsky score, biopsy-only versus resection, marked contrast enhancement versus no/mild enhancement, high contrast transfer coefficient, and high plasma volume obtained in tumor (P < .05). In multivariate analysis, a low Karnofsky score, biopsy versus resection in combination with marked contrast enhancement, and a high contrast transfer coefficient were associated with lower survival rates (P < .05).

CONCLUSIONS

In patients with glioma, those with a high contrast transfer coefficient have lower survival than those with low parameters.

Relative cerebral blood volume from dynamic susceptibility contrast perfusion in the grading of pediatric primary brain tumors

INTRODUCTION

The aim of this study is to evaluate the utility of relative cerebral blood volume (rCBV) data from dynamic susceptibility contrast (DSC) perfusion in grading pediatric primary brain tumors.

METHODS

A retrospective blinded review of 63 pediatric brain tumors with DSC perfusion was performed independently by two neuroradiologists. A diagnosis of low- versus high-grade tumor was obtained from conventional imaging alone. Maximum rCBV (rCBVmax) was measured from manual ROI placement for each reviewer and averaged. Whole-tumor CBV data was obtained from a semi-automated approach. Results from all three analyses were compared to WHO grade.

RESULTS

Based on conventional MRI, the two reviewers had a concordance rate of 81% (k = 0.62). Compared to WHO grade, the concordant cases accurately diagnosed high versus low grade in 82%. A positive correlation was demonstrated between manual rCBVmax and tumor grade (r = 0.30, P = 0.015). ROC analysis of rCBVmax (area under curve 0.65, 0.52-0.77, P = 0.03) gave a low-high threshold of 1.38 with sensitivity of 92% (74-99%), specificity of 40% (24-57%), NPV of 88% (62-98%), and PPV of 50% (35-65%) Using this threshold on 12 discordant tumors between evaluators from conventional imaging yielded correct diagnoses in nine patients. Semi-automated analysis demonstrated statistically significant differences between low- and high-grade tumors for multiple metrics including average rCBV (P = 0.027).

CONCLUSIONS

Despite significant positive correlation with tumor grade, rCBV from pediatric brain tumors demonstrates limited specificity, but high NPV in excluding high-grade neoplasms. In selective patients whose conventional imaging is nonspecific, an rCBV threshold may have further diagnostic value.

Dexamethasone alleviates tumor-associated brain damage and angiogenesis

Children and adults with the most aggressive form of brain cancer, malignant gliomas or glioblastoma, often develop cerebral edema as a life-threatening complication. This complication is routinely treated with dexamethasone (DEXA), a steroidal anti-inflammatory drug with pleiotropic action profile. Here we show that dexamethasone reduces murine and rodent glioma tumor growth in a concentration-dependent manner. Low concentrations of DEXA are already capable of inhibiting glioma cell proliferation and at higher levels induce cell death. Further, the expression of the glutamate antiporter xCT (system X_c⁻; SLC7a11) and VEGFA is up-regulated after DEXA treatment indicating early cellular stress responses. However, in human gliomas DEXA exerts differential cytotoxic effects, with some human glioma cells (U251, T98G) resistant to DEXA, a finding corroborated by clinical data of dexamethasone non-responders. Moreover, DEXA-resistant gliomas did not show any xCT alterations, indicating that these gene expressions are associated with DEXA-induced cellular stress. Hence, siRNA-mediated xCT knockdown in glioma cells increased the susceptibility to DEXA. Interestingly, cell viability of primary human astrocytes and primary rodent neurons is not affected by DEXA. We further tested the pharmacological effects of DEXA on brain tissue and showed that DEXA reduces tumor-induced disturbances of the microenvironment such as neuronal cell death and tumor-induced angiogenesis. In conclusion, we demonstrate that DEXA inhibits glioma cell growth in a concentration and species-dependent manner. Further, DEXA executes neuroprotective effects in brains and reduces tumor-induced angiogenesis. Thus, our investigations reveal that DEXA acts pleiotropically and impacts tumor growth, tumor vasculature and tumor-associated brain damage.

Characterization of the 9L gliosarcoma implanted in the Fischer rat: an orthotopic model for a grade IV brain tumor

Among rodent models for brain tumors, the 9L gliosarcoma is one of the most widely used. Our 9L-European Synchrotron Radiation Facility (ESRF) model was developed from cells acquired at the Brookhaven National Laboratory (NY, USA) in 1997 and implanted in the right caudate nucleus of syngeneic Fisher rats. It has been largely used by the user community of the ESRF during the last decade, for imaging, radiotherapy, and chemotherapy, including innovative treatments based on particular irradiation techniques and/or use of new drugs. This work presents a detailed study of its characteristics, assessed by magnetic resonance imaging (MRI), histology, immunohistochemistry, and cytogenetic analysis. The data used for this work were from rats sampled in six experiments carried out over a 3-year period in our lab (total number of rats = 142). The 9L-ESRF tumors were induced by a stereotactic inoculation of 10(4) 9L cells in the right caudate nucleus of the brain. The assessment of vascular parameters was performed by MRI (blood volume fraction and vascular size index) and by immunostaining of vessels (rat endothelial cell antigen-1 and type IV collagen). Immunohistochemistry and regular histology were used to describe features such as tumor cell infiltration, necrosis area, nuclear pleomorphism, cellularity, mitotic characteristics, leukocytic infiltration, proliferation, and inflammation. Moreover, for each of the six experiments, the survival of the animals was assessed and related to the tumor growth observed by MRI or histology. Additionally, the cytogenetic status of the 9L cells used at ESRF lab was investigated by comparative genomics hybridization analysis. Finally, the response of the 9L-ESRF tumor to radiotherapy was estimated by plotting the survival curves after irradiation. The median survival time of 9L-ESRF tumor-bearing rats was highly reproducible (19-20 days). The 9L-ESRF tumors presented a quasi-exponential growth, were highly vascularized with a high cellular density and a high proliferative index, accompanied by signs of inflammatory responses. We also report an infiltrative pattern which is poorly observed on conventional 9 L tumor. The 9L-ESRF cells presented some cytogenetic specificities such as altered regions including CDK4, CDKN2A, CDKN2B, and MDM2 genes. Finally, the lifespan of 9L-ESRF tumor-bearing rats was enhanced up to 28, 35, and 45 days for single doses of 10, 20, and 2 × 20 Gy, respectively. First, this report describes an animal model that is used worldwide. Second, we describe few features typical of our model if compared to other 9L models worldwide. Altogether, the 9L-ESRF tumor model presents characteristics close to the human high-grade gliomas such as high proliferative capability, high vascularization and a high infiltrative pattern. Its response to radiotherapy demonstrates its potential as a tool for innovative radiotherapy protocols.

High-field small animal magnetic resonance oncology studies

This review focuses on the applications of high magnetic field magnetic resonance imaging (MRI) and spectroscopy (MRS) to cancer studies in small animals. High-field MRI can provide information about tumor physiology, the microenvironment, metabolism, vascularity and cellularity. Such studies are invaluable for understanding tumor growth and proliferation, response to treatment and drug development. The MR techniques reviewed here include (1)H, (31)P, chemical exchange saturation transfer imaging and hyperpolarized (13)C MRS as well as diffusion-weighted, blood oxygen level dependent contrast imaging and dynamic contrast-enhanced MRI. These methods have been proven effective in animal studies and are highly relevant to human clinical studies.

Quantification of microvascular cerebral blood flux and late-stage tumor compartmentalization in 9L gliosarcoma using flow enhanced MRI

Measurements of tumor microvasculature are important to obtain an understanding of tumor angiogenesis and for the evaluation of therapies. In this work, we characterize the evolution of the microvascular flux at different stages of tumor growth in the 9L rat brain tumor model. The absolute quantification of cerebral blood flux is achieved with MRI at 7 T using the flow enhanced signal intensity (FENSI) method. FENSI flux maps were obtained between 5 and 14 days after glioma cell inoculation. Based on cerebral blood flux maps, we highlighted two main stages of tumor growth, below and above 3 mm, presenting distinct flux patterns and vascular properties. No significant difference emerged from the group analysis performed on the data collected at an early developmental stage (tumor size < 3 mm) when compared with healthy tissue. At a late developmental stage (tumor size > 3 mm), we observed a significant decrease in the cerebral blood flux inside the gliosarcoma (-33%, p < 0.01) and compartmentalization of the tumor (p < 0.05). FENSI flux maps delineated a low-flux tumor core (58 ± 17 μL/min/cm(2) ) and higher vascularized regions around the tumor periphery (85 ± 21 μL/min/cm(2) ). Histology was performed on 11 animals to finely probe the intratumor heterogeneity and microvessel density, and the results were compared with the information derived from FENSI flux maps. The hyper- and hypoperfused tumor regions revealed with FENSI at the late tumor developmental stage correlated well with the ratios of high and low blood vessel density (R(2) = 0.41) and fractional vascular surface (R(2) = 0.67) observed with fluorescence microscopy [cluster of differentiation 31 (CD31) staining].

Monitoring early tumor response to drug therapy with diffuse optical tomography

Although anti-angiogenic agents have shown promise as cancer therapeutics, their efficacy varies between tumor types and individual patients. Providing patient-specific metrics through rapid noninvasive imaging can help tailor drug treatment by optimizing dosages, timing of drug cycles, and duration of therapy-thereby reducing toxicity and cost and improving patient outcome. Diffuse optical tomography (DOT) is a noninvasive three-dimensional imaging modality that has been shown to capture physiologic changes in tumors through visualization of oxygenated, deoxygenated, and total hemoglobin concentrations, using non-ionizing radiation with near-infrared light. We employed a small animal model to ascertain if tumor response to bevacizumab (BV), an anti-angiogenic agent that targets vascular endothelial growth factor (VEGF), could be detected at early time points using DOT. We detected a significant decrease in total hemoglobin levels as soon as one day after BV treatment in responder xenograft tumors (SK-NEP-1), but not in SK-NEP-1 control tumors or in non-responder control or BV-treated NGP tumors. These results are confirmed by magnetic resonance imaging T2 relaxometry and lectin perfusion studies. Noninvasive DOT imaging may allow for earlier and more effective control of anti-angiogenic therapy.