Magnetic resonance imaging for the evaluation of a novel metastatic orthotopic model of human neuroblastoma in immunodeficient mice

Low magnification confocal microscopy of tumor angiogenesis

Blood vessels are critical to normal mammalian development, tissue repair, and growth and treatment of cancer. Mouse research models enable mechanistic studies of blood vessels. We detail how to perfuse mice with fluorescent tomato lectin or the lipophilic fluorophore DiI. We provide details on how to image fluorescently labeled blood vessels.

Similarity on neural stem cells and brain tumor stem cells in transgenic brain tumor mouse models

Although it is believed that glioma is derived from brain tumor stem cells, the source and molecular signal pathways of these cells are still unclear. In this study, we used stable doxycycline-inducible transgenic mouse brain tumor models (c-myc⁺/SV40Tag⁺/Tet-on⁺) to explore the malignant trans-formation potential of neural stem cells by observing the differences of neural stem cells and brain tumor stem cells in the tumor models. Results showed that chromosome instability occurred in brain tumor stem cells. The numbers of cytolysosomes and autophagosomes in brain tumor stem cells and induced neural stem cells were lower and the proliferative activity was obviously stronger than that in normal neural stem cells. Normal neural stem cells could differentiate into glial fibrillary acidic protein-positive and microtubule associated protein-2-positive cells, which were also negative for nestin. However, glial fibrillary acidic protein/nestin, microtubule associated protein-2/nestin, and glial fibrillary acidic protein/microtubule associated protein-2 double-positive cells were found in induced neural stem cells and brain tumor stem cells. Results indicate that induced neural stem cells are similar to brain tumor stem cells, and are possibly the source of brain tumor stem cells.

Computed tomography and magnetic resonance imaging

Imaging in Oncology is rapidly moving from the detection and size measurement of a lesion to the quantitative assessment of metabolic processes and cellular and molecular interactions. Increasing insights into cancer as a complex disease with involvement of the tumor stroma in tumor pathobiological processes have made it clear that for successful control of cancer, treatment strategies should not only be directed at the tumor cells but also targeted at the tumor microenvironment. This requires understanding of the complex molecular and cellular interactions in cancer tissue. Recent developments in imaging technology have increased the possibility to image various pathobiological processes in cancer development and response to treatment. For computed tomography (CT) and magnetic resonance imaging (MRI) various improvements in hardware, software, and imaging probes have lifted these modalities from classical anatomical imaging techniques to techniques suitable to image and quantify various physiological processes and molecular and cellular interactions. Next to a more general overview of possible imaging targets in oncology this chapter provides an overview of the various developments in CT and MRI technology and some specific applications.

Adrenal tumor volume in a genetically engineered mouse model of neuroblastoma determined by magnetic resonance imaging

Neuroblastoma is the second most common type of solid tumor in children and is commonly found in the adrenal medulla. Recently, we developed transgenic mice exhibiting tumors bilaterally in the adrenal medulla through the expression of SV40 T-antigen. Since these transgenic mice facilitate the development of new therapeutic approaches for neuroblastoma, non-invasive monitoring methods are required for serial measurement of tumor progression. In this study, we monitored the serial progression of adrenal tumors in transgenic mice by magnetic resonance imaging (MRI) of 9.4 T vertical type, and calculated the tumor volume. The accuracy of the tumor volume determination by MRI was verified by standard volume measurements at autopsy. Adrenal tumors as small as 1.5 mm in diameter were detected and quantitatively measured in the transgenic mice by in vivo MRI without using exogenous contrast agents on T(2)-weighted spin echo images. The tumor sizes by MRI correlated better with tumor weight than the volume by calculation with a caliper. Furthermore, we monitored the change of tumor volume following administration of doxorubicin at weekly intervals. The tumor progression and regression following doxorubicin treatment in the individual mice could be observed by serial MRI. From these findings, non-invasive MRI is likely to be useful for monitoring the response of spontaneous tumors to therapeutic drugs.

A screening platform for glioma growth and invasion using bioluminescence imaging

Object

The study of tumor cell growth and invasion in cancer biology is often limited by the inability to visualize tumor cell behavior in real time in animal models. The authors provide evidence that glioma cells are heterogeneous, with a subset responsible for increased invasiveness. The use of bioluminescence (BL) imaging to investigate dynamic aspects of glioma progression are discussed.

Methods

Glioblastoma multiforme–initiating cells were generated under conditions typically used to sustain neural stem cells. The invasiveness potential was determined using a Matrigel chamber. The presence of an “invasiveness gene signature” that correlated with patient survival outcome was ascertained through microarray gene expression analysis. To measure invasiveness, the authors devised a method focussed on BL imaging and tested it in vitro and in vivo using a zebrafish xenograft model. Bioluminescence imaging signals were verified using known inhibitors of glioma growth: AEE788, N-[(3,5-Difluorophenyl)acetyl]-L-alanyl-2-phenylglycine-1,1-dimethylethyl ester, and compound E.

Results

The authors' data support the idea that glioblastoma multiforme–initiating cells are heterogeneous and possess an invasive subset; BL imaging was used as a readout method to assess this invasive subset. The in vitro data obtained using a known glioma growth inhibitor, AEE788, showed that BL imaging could detect cellular movement and invasion even before overall cell death was detectable on conventional viability assays. Further work using a zebrafish tumor xenograft model supported the efficacy of BL imaging in monitoring changes in tumor load.

Conclusions

The authors used optically transparent zebrafish and high-resolution confocal imaging to track tumor growth in vivo and demonstrate the efficacy of this model for screening antitumor and antiangiogenic compounds. The integration of zebrafish transgenic technology into human cancer biological studies may aid in the development of cancer models targeting specific organs, tissues, or cell types within tumors. Zebrafish could also provide a cost-effective means for the rapid development of therapeutic agents directed at blocking tumor growth and invasion.

In vivo bioluminescence imaging for early detection and monitoring of disease progression in a murine model of neuroblastoma

BACKGROUND

We evaluated the potential of bioluminescence imaging (BLI) for early tumor detection, demonstrating occult sites of disseminated disease and assessing disease progression in a murine model of neuroblastoma.

METHODS

Neuroblastoma cells engineered to express the enzyme firefly luciferase were used to establish localized tumors and disseminated disease in SCID mice. Bioluminescent signal intensity was measured at serial time points, and compared with traditional methods of evaluating tumor growth.

RESULTS

Bioluminescence imaging detected subcutaneous and retroperitoneal tumors weeks before they were palpable or appreciable by ultrasound. Bioluminescent signal intensity at both sites then paralleled tumor growth. After intravenous administration of tumor cells, BLI revealed disseminated disease in the liver, lungs, and bone marrow, again weeks before any gross disease was present. The presence of tumor within these sites at early time points was confirmed by reverse transcriptase-polymerase chain reaction. Finally, BLI permitted a real-time, noninvasive, quantitative method for following response to therapy in a model of minimal residual disease.

CONCLUSION

Bioluminescence imaging detects tumor much earlier than traditional methods. In addition, it can detect, quantify, and follow micrometastasis in real-time during disease progression. This methodology is extremely valuable for studying tumor tissue tropism, mechanisms of metastasis, and response to therapy in murine tumor models.

High-frequency ultrasound detection and follow-up of Wilms' tumor in the mouse

The goal of this study was to validate high-frequency (24 MHz) ultrasound imaging techniques for early detection and follow-up of renal tumors in a murine Wilms' tumor model (n = 26). For 11 mice, maximum tumor dimensions were estimated from images along three orthogonal axes for comparison with posteuthanasia caliper and histologic measurements. Tumor size in the 15 remaining mice was checked biweekly. The mice were then euthanized and histologic study assessed tumor position and nature. Tumors were detected in vivo between 7 to 14 days after injection of tumor-inducing cells. Tumor maximum cross-sectional area varied from 0.07 mm2 to 5.7 mm2 at the time of initial detection. The relative r.m.s. error between ultrasonic and histologic estimations of maximum cross-sectional area was estimated to be 19%. Results demonstrate feasibility of noninvasive ultrasound biomicroscopy early detection and characterization of renal tumor development for longitudinal monitoring of the same animal.

The contribution of bone marrow-derived cells to the tumor vasculature in neuroblastoma is matrix metalloproteinase-9 dependent

The contribution of the tumor stroma to cancer progression has been increasingly recognized. We had previously shown that in human neuroblastoma tumors orthotopically implanted in immunodeficient mice, stromal-derived matrix metalloproteinase-9 (MMP-9) contributes to the formation of a mature vasculature by promoting pericyte recruitment along endothelial cells. Here we show that MMP-9 is predominantly expressed by bone marrow-derived CD45-positive leukocytes. Using a series of bone marrow transplantation experiments in MMP-9(+/+) and MMP-9(-/-) mice xenotransplanted with human neuroblastoma tumors, we show that bone marrow-derived MMP-9 is critical for the recruitment of leukocytes from bone marrow into the tumor stroma and for the integration of bone marrow-derived endothelial cells into the tumor vasculature. Expression of MMP-9 by bone marrow-derived cells in the tumor stroma is also critical for the formation of a mature vasculature and coverage of endothelial cells with pericytes. Furthermore, in primary human neuroblastoma tumor specimens of unfavorable histology, we observed a higher level of tumor infiltration with MMP-9 expressing phagocytic cells and a higher degree of coverage of endothelial cells by pericytes when compared with tumor specimens with a favorable histology. Taken together, the data show that in neuroblastoma, MMP-9 plays a critical role in the recruitment of bone marrow-derived cells to the tumor microenvironment where they positively contribute to angiogenesis and tumor progression.

In vivoechographic evidence of tumoral vascularization and microenvironment interactions in metastatic orthotopic human neuroblastoma xenografts

Human neuroblastoma (NB) is the second most frequent solid tumor of childhood and represents a highly heterogeneous disease at clinical and biologic levels. Little progress has been made to improve the poor prognosis of patients with high-stage NB. Tumor progression and metastatic dissemination still represent major obstacles to the successful treatment of advanced stage disease. In order to develop and evaluate new, targeted, therapeutic strategies, fully defined and biologically relevant in vivo models of NB are strongly needed. We have developed an orthotopic model of metastatic human NB in the nude mouse, using 2 well-characterized NB cell lines. Tumor growth, vascular properties and metastatic patterns were investigated using a sensitive and newly developed in vivo echographic technology in addition to immunohistochemistry and PCR analyses. Results show that implantation of low numbers of NB cells directly into the adrenal gland of nude mice resulted in rapid and homogeneous tumor growth without tumor morbidity. Nude mice were shown to rapidly develop highly vascularized adrenal tumors that selectively metastasized to the liver and bone marrow. In addition, the newly formed mouse vessels in orthotopic but not in heterotopic tumors, were found to express the highly angiogenic alphavbeta3 integrin marker, indicating the development of a truly malignant neovasculature in orthotopic conditions only. This observation confirms the impact of the regional microenvironment on tumor biology and suggests the existence of cross-talk with the tumor cells. In conclusion, such model faithfully reproduces the growth, vascular and metastatic patterns as observed in patients. It therefore represents a powerful and biologically relevant tool to improve our understanding of the biology of NB and to develop and assess new antiangiogenic and metastasis-targeted therapies.

Stromal Matrix Metalloproteinase-9 Regulates the Vascular Architecture in Neuroblastoma by Promoting Pericyte Recruitment

Advanced stages of neuroblastoma show increased expression of matrix metalloproteinases MMP-2 and MMP-9, that have been implicated in many steps of tumor progression, suggesting that they play a contributory role. Using pharmacological and genetic approaches, we have examined the role of these MMPs in progression of SK-N-BE (2).10 human neuroblastoma tumors orthotopically xenotransplanted into immunodeficient mice. Mice treated with Prinomastat, a synthetic inhibitor of MMPs, showed an inhibition of tumor cell proliferation in implanted tumors and a prolonged survival (50 versus 39 days in control group, P < 0.035). Treatment with Prinomastat did not affect formation of liver metastases (P = 0.52) but inhibited intravascular colonization by the tumor cells in the lung by 73.8% (P = 0.03) and angiogenesis in both primary tumors and experimental liver metastases. The primary tumors from Prinomastat-treated mice showed a 39.3% reduction in endothelial area detected by PECAM/CD31 staining in tumor sections (P < 0.001), primarily due to the presence of smaller vessels (P = 0.004). MMP-2 is expressed by neuroblastoma tumor cells and stromal cells, whereas MMP-9 is exclusively expressed by stromal cells, particularly vascular cells. To examine the contribution of MMP-9 to tumor angiogenesis, we generated RAG1/MMP-9 double-deficient mice. We observed a significant inhibition of angiogenesis in the immunodeficient RAG1/MMP-9 double-deficient mice orthotopically implanted with tumor cells (P = 0.043) or implanted s.c. with a mixture of tumor cells and Matrigel (P < 0.001). Using an FITC-labeled lectin, we demonstrated an inhibition in the architecture of the tumor vasculature in MMP-9-deficient mice, resulting in fewer and smaller blood vessels. These changes were associated with a 48% decrease in pericytes present along microvessels. Taken together, the data demonstrate that in neuroblastoma, stromally derived MMP-9 contributes to angiogenesis by promoting blood vessel morphogenesis and pericyte recruitment.

In vitro and in vivo effects of easily administered, low-toxic retinoid and phenylacetate compounds on human neuroblastoma cells

We have investigated the effects of the low-toxic retinoid, all-trans retinoyl beta-glucuronide (RAG) alone and in combination with the phenylacetate (PA) derivative 4-chloro-phenylacetate (4-CPA) on the human neuroblastoma cell line, LA-N-5. In vitro studies demonstrated that RAG and 4-CPA treatments alone showed differentiation-inducing activity on LA-N-5 cells, with 4-CPA found to be about three-fold more potent than the PA parent compound in inducing morphologic differentiation and growth inhibition. As previously reported for retinoic acid (RA) and PA, RAG and 4-CPA were significantly more effective in their antiproliferative effects on the cells than either agent alone. Pharmacologic studies of 4-CPA in mice demonstrated that blood plasma levels reached peak concentrations 4 h after bolus administration of the compound and showed slow clearance characteristics with an apparent half-life of 4-8 h. As opposed to PA, 4-CPA was found to be essentially odourless and readily consumed in drinking water, giving rise to steady-state blood plasma levels of 4-CPA in the near mM range. Continuous consumption of 4-CPA in this manner for up to 5 months demonstrated no apparent adverse effects on the mice. Long-term RAG- and/or 4-CPA-treatment of nude mice injected with LA-N-5 cells demonstrated that both compounds alone exhibit potent antitumour activity. Together, RAG plus 4-CPA was the most effective treatment for inhibiting established tumour growth. In contrast, 4-CPA alone was equally as effective as the combination for preventing tumour development. The potent in vivo antitumour effects of 4-CPA could not be accounted for by the known ability of PA compounds to induce expression of the RA nuclear receptor beta (RARbeta) suppressor gene. Taken together, these findings demonstrate the possibility that RAG and/or 4-CPA may serve as effective, less-toxic alternatives to 13-cis RA, which is presently being utilised for nb therapy.

Computerized quantification of tissue vascularization using high-resolution slide scanning of whole tumor sections

Assessment of tissue vascularization using immunohistochemical techniques for microvessel detection has been limited by difficulties in generating reproducible quantitative data. The distinction of individual blood vessels and the selection of microscopic fields to be analyzed remain two factors of subjectivity. In this study, we used imaging analysis software and a high-resolution slide scanner for measurement of CD31-immunostained endothelial area (EA) in whole sections of human neuroblastoma xenograft and murine mammary adenocarcinoma tumors. Imaging analysis software provided objective criteria for analysis of sections of different tumors. The use of the criteria on images of entire tumor section acquired with the slide scanner constituted a rapid method to quantify tumor vascularization. Compared with previously described methods, the "hot spot" and the "random fields" methods, EA measurements obtained with our "whole section scanning" method were more reproducible with 8.6% interobserver disagreement for the "whole section scanning" method vs 42.2% and 39.0% interobserver disagreement for the "hot spot" method and the "random fields," respectively. Microvessel density was also measured with the whole section scanning method and provided additional data on the distribution and the size of the blood vessels. Therefore, this method constitutes a time efficient and reproducible method for quantification of tumor vascularization.