Rat brain tumor models in experimental neuro-oncology: the C6, 9L, T9, RG2, F98, BT4C, RT-2 and CNS-1 gliomas

Gene therapy-mediated reprogramming tumor infiltrating T cells using IL-2 and inhibiting NF-κB signaling improves the efficacy of immunotherapy in a brain cancer model

Immune-mediated gene therapy using adenovirus expressing Flt3 ligand and thymidine kinase followed by ganciclovir administration (Flt3/TK) effectively elicits tumor regression in preclinical glioma models. Herein, we assessed new strategies to optimize Flt3L/TK therapeutic efficacy in a refractory RG2 orthotopic glioblastoma model. Specifically, we aimed to optimize the therapeutic efficacy of Flt3L/TK treatment in the RG2 model by overexpressing the following genes within the brain tumor microenvironment: 1) a TK mutant with enhanced cytotoxicity (SR39 mutant TK), 2) Flt3L-IgG fusion protein that has a longer half-life, 3) CD40L to stimulate DC maturation, 4) T helper cell type 1 polarizing dendritic cell cytokines interleukin-12 or C-X-C motif ligand 10 chemokine (CXCL)-10, 5) C-C motif ligand 2 chemokine (CCL2) or C-C motif ligand 3 chemokine (CCL3) to enhance dendritic cell recruitment into the tumor microenvironment, 6) T helper cell type 1 cytokines interferon-γ or interleukin-2 to enhance effector T-cell functions, and 7) IκBα or p65RHD (nuclear factor kappa-B [NF-κB] inhibitors) to suppress the function of Foxp3+ Tregs and enhanced effector T-cell functions. Anti-tumor immunity and tumor specific effector T-cell functions were assessed by cytotoxic T lymphocyte assay and intracellular IFN-γ staining. Our data showed that overexpression of interferon-γ or interleukin-2, or inhibition of the nuclear factor kappa-B within the tumor microenvironment, enhanced cytotoxic T lymphocyte-mediated immune responses and successfully extended the median survival of rats bearing intracranial RG2 when combined with Flt3L/TK. These findings indicate that enhancement of T-cell functions constitutes a critical therapeutic target to overcome immune evasion and enhance therapeutic efficacy for brain cancer. In addition, our study provides novel targets to be used in combination with immune-therapeutic strategies for glioblastoma, which are currently being tested in the clinic.

Cryo-image analysis of tumor cell migration, invasion, and dispersal in a mouse xenograft model of human glioblastoma multiforme

PURPOSE

The goals of this study were to create cryo-imaging methods to quantify characteristics (size, dispersal, and blood vessel density) of mouse orthotopic models of glioblastoma multiforme (GBM) and to enable studies of tumor biology, targeted imaging agents, and theranostic nanoparticles.

PROCEDURES

Green fluorescent protein-labeled, human glioma LN-229 cells were implanted into mouse brain. At 20-38 days, cryo-imaging gave whole brain, 4-GB, 3D microscopic images of bright field anatomy, including vasculature, and fluorescent tumor. Image analysis/visualization methods were developed.

RESULTS

Vessel visualization and segmentation methods successfully enabled analyses. The main tumor mass volume, the number of dispersed clusters, the number of cells/cluster, and the percent dispersed volume all increase with age of the tumor. Histograms of dispersal distance give a mean and median of 63 and 56 μm, respectively, averaged over all brains. Dispersal distance tends to increase with age of the tumors. Dispersal tends to occur along blood vessels. Blood vessel density did not appear to increase in and around the tumor with this cell line.

CONCLUSION

Cryo-imaging and software allow, for the first time, 3D, whole brain, microscopic characterization of a tumor from a particular cell line. LN-229 exhibits considerable dispersal along blood vessels, a characteristic of human tumors that limits treatment success.

Growth properties of SF188/V+ human glioma in rats in vivo observed by magnetic resonance imaging

SF188/V+ is a highly vascular human glioma model that is based on transfection of vascular endothelial growth factor (VEGF) cDNA into SF188/V- cells. This study aims to assess its growth and vascularity properties in vivo in a rat model. Thirty-two adult rats were inoculated with SF188/V+ tumor cells, and, for comparison, five were inoculated with SF188/V- tumor cells. Several conventional magnetic resonance imaging (MRI) sequences were acquired, and several quantitative structural (T(2) and T(1)), functional [isotropic apparent diffusion coefficient (ADC) and blood flow], and molecular [protein and peptide-based amide proton transfer (APT)] MRI parameters were mapped on a 4.7 T animal scanner. In rats inoculated with SF188/V+ tumor cells, conventional T(2)-weighted images showed a highly heterogeneous tumor mass, and post-contrast T(1)-weighted images showed a heterogeneous, strong enhancement of the mass. There were moderate increases in T(2), T(1), and ADC, and large increases in blood flow and APT in the tumor, compared to contralateral brain tissue. Microscopic examination revealed prominent vascularity and hemorrhage in the VEGF-secreting xenografts as compared to controls, and immunohistochemical staining confirmed increased expression of VEGF in tumor xenografts. Our results indicate that the SF188/V+ glioma model exhibits some MRI and histopathology features that closely resemble human glioblastoma.

Rat multipotent mesenchymal stromal cells lack long-distance tropism to 3 different rat glioma models

BACKGROUND

Viral gene therapy of malignant brain tumors has been restricted by the limited vector distribution within the tumors. Multipotent mesenchymal stromal cells (MSCs) and other precursor cells have shown tropism for gliomas, and these cells are currently being explored as potential vehicles for gene delivery in glioma gene therapy.

OBJECTIVE

To investigate MSC migration in detail after intratumoral and extratumoral implantation through syngeneic and orthotopic glioma models.

METHODS

Adult rat bone marrow-derived MSCs were transduced to express enhanced green fluorescent protein and implanted either directly into or at a distance from rat gliomas.

RESULTS

We found no evidence of long-distance MSC migration through the intact striatum toward syngeneic D74(RG2), N32, and N29 gliomas in the ipsilateral hemisphere or across the corpus callosum to gliomas located in the contralateral hemisphere. After intratumoral injection, MSCs migrated extensively, specifically within N32 gliomas. The MSCs did not proliferate within tumors, suggesting a low risk of malignant transformation of in vivo grafted cell vectors. Using a model for surgical glioma resection, we found that intratumorally grafted MSCs migrate efficiently within glioma remnants after partial surgical resection.

CONCLUSION

The findings point to limitations for the use of MSCs as vectors in glioma gene therapy, although intratumoral MSC implantation provides a dense and tumor-specific vector distribution.

Gene therapy for brain tumors: basic developments and clinical implementation

Glioblastoma multiforme (GBM) is the most common and deadliest of adult primary brain tumors. Due to its invasive nature and sensitive location, complete resection remains virtually impossible. The resistance of GBM against chemotherapy and radiotherapy necessitate the development of novel therapies. Gene therapy is proposed for the treatment of brain tumors and has demonstrated pre-clinical efficacy in animal models. Here we review the various experimental therapies that have been developed for GBM including both cytotoxic and immune stimulatory approaches. We also review the combined conditional cytotoxic immune stimulatory therapy that our lab has developed which is dependent on the adenovirus mediated expression of the conditional cytotoxic gene, Herpes Simplex Type 1 Thymidine Kinase (TK) and the powerful DC growth factor Fms-like tyrosine kinase 3 ligand (Flt3L). Combined delivery of these vectors elicits tumor cell death and an anti-tumor adaptive immune response that requires TLR2 activation. The implications of our studies indicate that the combined cytotoxic and immunotherapeutic strategies are effective strategies to combat deadly brain tumors and warrant their implementation in human Phase I clinical trials for GBM.

The cell death of C6 astrocytoma cells induced by oridonin and its mechanism

Many studies have shown that oridonin, a compound purified from Rabdosia rubescens, was able to suppress proliferation and induce apoptosis in many cell types. In this study, In order to investigate the proliferation suppression and apoptosis-inducing effect of oridonin on Rat C6 astrocytoma cells, we treated C6 cells with different concentrations of oridonin for various time intervals. Oridonin concentration-time viability curve were used to test the effect of oridonin on the C6 cells. The distribution of cell cycle and percentage of apoptosis cells was analyzed by flow cytometry. The protein expression of Bax, Bcl-2, and caspase-3 in the C6 cells was detected by western blot analysis. The results of viability curve demonstrated that oridonin induced suppression of proliferation in a concentration- and time-dependent manner. Hochest 33258 staining and flow cytometry revealed that oridonin induced apoptosis and arrested the entry into G2/M phase of C6 cells. According to the results of Western blot, oridonin down-regulated Bcl-2, up-regulated Bax protein, and activated caspase-3 in the oridonin-treated C6 cells. All together, our results suggested that oridonin can cause the suppression of proliferation in C6 astrocytoma cells and the cell death induced by oridonin might be associated with mitochondria- mediated apoptosis by activating caspase-3.

Comparison of spheroids formed by rat glioma stem cells and neural stem cells reveals differences in glucose metabolism and promising therapeutic applications

Cancer stem cells (CSCs) are thought to be partially responsible for cancer resistance to current therapies and tumor recurrence. Dichloroacetate (DCA), a compound capable of shifting metabolism from glycolysis to glucose oxidation, via an inhibition of pyruvate dehydrogenase kinase was used. We show that DCA is able to shift the pyruvate metabolism in rat glioma CSCs but has no effect in rat neural stem cells. DCA forces CSCs into oxidative phosphorylation but does not trigger the production of reactive oxygen species and consecutive anti-cancer apoptosis. However, DCA, associated with etoposide or irradiation, induced a Bax-dependent apoptosis in CSCs in vitro and decreased their proliferation in vivo. The former phenomenon is related to DCA-induced Foxo3 and p53 expression, resulting in the overexpression of BH3-only proteins (Bad, Noxa, and Puma), which in turn facilitates Bax-dependent apoptosis. Our results demonstrate that a small drug available for clinical studies potentiates the induction of apoptosis in glioma CSCs.

An Algorithm for the Preclinical Screening of Anticancer Drugs Effective against Brain Tumors

The anticancer drugs screening program is a long and expensive process. It is estimated that only 5% of drugs entering clinical trials are approved by the FDA. Moreover, many of the drugs that enter clinical trials are often of limited use in clinical practice, and most cancers remain untreatable. Brain tumors are particularly difficult to treat due to the presence of the blood brain barrier that limits the penetration of anticancer drugs. Additionally the isolation from most brain tumors of putative cancer stem cells and novel models of cancer stem cell biology suggest that anticancer drugs should be delivered for prolonged time and at higher concentrations to deplete any potential tumorigenic cell. In this paper, current concepts of cancer stem cell biology and novel concepts of anticancer drugs screening are integrated to develop a seven-steps algorithm as a guideline for the preclinical evaluation of active compounds for the treatment of brain tumors. The flexibility of the algorithm allows the inclusion of alternative studies to exhaustively investigate anticancer drugs and creates multiple opportunities where decisions to engage or not in early clinical trials can be made providing a useful tool for translational research in neurooncology.

Imaging, autoradiography, and biodistribution of (188)Re-labeled PEGylated nanoliposome in orthotopic glioma bearing rat model

The (188)Re-labeled pegylated nanoliposome (abbreviated as (188)Re-Liposome) was prepared and evaluated for its potential as a theragnostic agent for glioma. (188)Re-BMEDA complex was loaded into the pegylated liposome core with pH 5.5 ammonium sulfate gradient to produce (188)Re-Liposome. Orthotopic Fischer344/F98 glioma tumor-bearing rats were prepared and intravenously injected with (188)Re-Liposome. Biodistribution, pharmacokinetic study, autoradiography (ARG), histopathology, and nano-SPECT/CT imaging were conducted for the animal model. The result showed that (188)Re-Liposome accumulated in the brain tumor of the animal model from 0.28%±0.09% injected dose (ID)/g (n=3) at 1 hour to a maximum of 1.95%±0.35% ID/g (n=3) at 24 hours postinjection. The tumor-to-normal brain uptake ratio (T/N ratio) increased from 3.5 at 1 hour to 32.5 at 24 hours. Both ARG and histopathological images clearly showed corresponding tumor regions with high T/N ratios. Nano-SPECT/CT detected a very clear tumor image from 4 hours till 48 hours. This study reveals the potential of (188)Re-Liposome as a theragnostic agent for brain glioma.

Analysis of the growth dynamics of angiogenesis-dependent and -independent experimental glioblastomas by multimodal small-animal PET and MRI

The hypothesis of this study was that distinct experimental glioblastoma phenotypes resembling human disease can be noninvasively distinguished at various disease stages by imaging in vivo.

METHODS

Cultured spheroids from 2 human glioblastomas were implanted into the brains of nude rats. Glioblastoma growth dynamics were followed by PET using (18)F-FDG, (11)C-methyl-l-methionine ((11)C-MET), and 3'-deoxy-3'-(18)F-fluorothymidine ((18)F-FLT) and by MRI at 3-6 wk after implantation. For image validation, parameters were coregistered with immunohistochemical analysis.

RESULTS

Two tumor phenotypes (angiogenic and infiltrative) were obtained. The angiogenic phenotype showed high uptake of (11)C-MET and (18)F-FLT and relatively low uptake of (18)F-FDG. (11)C-MET was an early indicator of vessel remodeling and tumor proliferation. (18)F-FLT uptake correlated to positive Ki67 staining at 6 wk. T1- and T2-weighted MR images displayed clear tumor delineation with strong gadolinium enhancement at 6 wk. The infiltrative phenotype did not accumulate (11)C-MET and (18)F-FLT and impaired the (18)F-FDG uptake. In contrast, the Ki67 index showed a high proliferation rate. The extent of the infiltrative tumors could be observed by MRI but with low contrast.

CONCLUSION

For angiogenic glioblastomas, noninvasive assessment of tumor activity corresponds well to immunohistochemical markers, and (11)C-MET was more sensitive than (18)F-FLT at detecting early tumor development. In contrast, infiltrative glioblastoma growth in the absence of blood-brain barrier breakdown is difficult to noninvasively follow by existing imaging techniques, and a negative (18)F-FLT PET result does not exclude the presence of proliferating glioma tissue. The angiogenic model may serve as an advanced system to study imaging-guided antiangiogenic and antiproliferative therapies.

In vivo models of primary brain tumors: pitfalls and perspectives

Animal modeling for primary brain tumors has undergone constant development over the last 60 years, and significant improvements have been made recently with the establishment of highly invasive glioblastoma models. In this review we discuss the advantages and pitfalls of model development, focusing on chemically induced models, various xenogeneic grafts of human cell lines, including stem cell–like cell lines and biopsy spheroids. We then discuss the development of numerous genetically engineered models available to study mechanisms of tumor initiation and progression. At present it is clear that none of the current animal models fully reflects human gliomas. Yet, the various model systems have provided important insight into specific mechanisms of tumor development. In particular, it is anticipated that a combined comprehensive knowledge of the various models currently available will provide important new knowledge on target identification and the validation and development of new therapeutic strategies.

Induction of selective blood-tumor barrier permeability and macromolecular transport by a biostable kinin B1 receptor agonist in a glioma rat model

Treatment of malignant glioma with chemotherapy is limited mostly because of delivery impediment related to the blood-brain tumor barrier (BTB). B1 receptors (B1R), inducible prototypical G-protein coupled receptors (GPCR) can regulate permeability of vessels including possibly that of brain tumors. Here, we determine the extent of BTB permeability induced by the natural and synthetic peptide B1R agonists, LysdesArg⁹BK (LDBK) and SarLys[dPhe⁸]desArg⁹BK (NG29), in syngeneic F98 glioma-implanted Fischer rats. Ten days after tumor inoculation, we detected the presence of B1R on tumor cells and associated vasculature. NG29 infusion increased brain distribution volume and uptake profiles of paramagnetic probes (Magnevist and Gadomer) at tumoral sites (T₁-weighted imaging). These effects were blocked by B1R antagonist and non-selective cyclooxygenase inhibitors, but not by B2R antagonist and non-selective nitric oxide synthase inhibitors. Consistent with MRI data, systemic co-administration of NG29 improved brain tumor delivery of Carboplatin chemotherapy (ICP-Mass spectrometry). We also detected elevated B1R expression in clinical samples of high-grade glioma. Our results documented a novel GPCR-signaling mechanism for promoting transient BTB disruption, involving activation of B1R and ensuing production of COX metabolites. They also underlined the potential value of synthetic biostable B1R agonists as selective BTB modulators for local delivery of different sized-therapeutics at (peri)tumoral sites.

Efficacy of vincristine administered via convection-enhanced delivery in a rodent brainstem tumor model documented by bioluminescence imaging

PURPOSE

Brain stem gliomas account for 20% of childhood brain tumors. Presently, there is no effective treatment for these tumors, and the prognosis remains poor. One reason for this is that chemotherapeutic drugs cannot cross the blood-brain barrier. In this study, we used a rodent brainstem tumor model, monitored both qualitatively and quantitatively, to examine the effectiveness of vincristine (VCR) administered via convection-enhanced delivery (CED).

METHODS

C6 rat glioblastoma cells, transduced with an oncoretroviral plasmid containing a luciferase coding sequence, were inoculated into Fischer 344 rat brainstems. Tumor growth was monitored by bioluminescence intensity (BLI), and tumor volume was calculated from serial histopathologic sections. Therapeutic efficacy of VCR delivered via CED was assessed. Intravenous (I.V.) and intraperitoneal (I.P.) drug administration were used as a comparison for CED efficacy.

RESULTS

BLI monitoring revealed progressive tumor growth in inoculated rats. Symptoms caused by tumor burden were evident 16-18 days after inoculation. BLI correlated quantitatively with tumor volume (r(2) = 0.9413), established by histopathological analysis of tumor growth within the pons. VCR administered through CED was more effective than I.V. or I.P. administration in reducing tumor size and increasing survival times. TUNEL assay results suggest that VCR induced glioblastoma cell apoptosis.

CONCLUSIONS

VCR administered by CED was effective in reducing tumors and prolonging survival time.

In vivo characterization of several rodent glioma models by 1H MRS

The assessment of metabolites by (1)H MRS can provide information regarding glioma growth, and may be able to distinguish between different glioma models. Rat C6, 9 L/LacZ, F98 and RG2, and mouse GL261, cells were intracerebrally implanted into the respective rodents, and human U87 MG cells were implanted into athymic rats. Ethyl-nitrosourea induction was also used. Glioma metabolites [e.g. total choline (tCho), total creatine (tCr), N-acetylaspartate (NAA), lactate (Lac), glutamine (Gln), glutamate (Glu), aspartate (Asp), guanosine (Gua), mobile lipids and macromolecules (MMs)] were assessed from (1)H MRS using point-resolved spectroscopy (PRESS) [TE = 24 ms; TR = 2500 ms; variable pulse power and optimized relaxation delay (VAPOR) water suppression; 27-μL and 8-μL voxels in rats and mice, respectively] at 7 T. Alterations in metabolites (Totally Automatic Robust Quantitation in NMR, TARQUIN) in tumors were characterized by increases in lipids (Lip1.3: 8.8-54.5 mM for C6 and GL261) and decreases in NAA (1.3-2.0 mM for RG2, GL261 and C6) and tCr (0.8-4.0 mM for F98, RG2, GL261 and C6) in some models. F98, RG2, GL261 and C6 models all showed significantly decreased (p < 0.05) tCr, and RG2, GL261 and C6 models all exhibited significantly decreased (p < 0.05) NAA. The RG2 model showed significantly decreased (p < 0.05) Gln and Glu, the C6 model significantly decreased (p < 0.05) Asp, and the F98 and U87 models significantly decreased (p < 0.05) Gua, compared with controls. The GL261 model showed the greatest alterations in metabolites. (1)H MRS was able to differentiate the metabolic profiles in many of the seven rodent glioma models assessed. These models are considered to resemble certain characteristics of human glioblastomas, and this study may be helpful in selecting appropriate models.

Lithocholic bile acid selectively kills neuroblastoma cells, while sparing normal neuronal cells

Aging is one of the major risk factors of cancer. The onset of cancer can be postponed by pharmacological and dietary anti-aging interventions. We recently found in yeast cellular models of aging that lithocholic acid (LCA) extends longevity. Here we show that, at concentrations that are not cytotoxic to primary cultures of human neurons, LCA kills the neuroblastoma (NB) cell lines BE(2)-m17, SK-n-SH, SK-n-MCIXC and Lan-1. In BE(2)-m17, SK-n-SH and SK-n-MCIXC cells, the LCA anti-tumor effect is due to apoptotic cell death. In contrast, the LCA-triggered death of Lan-1 cells is not caused by apoptosis. While low concentrations of LCA sensitize BE(2)-m17 and SK-n-MCIXC cells to hydrogen peroxide-induced apoptotic cell death controlled by mitochondria, these LCA concentrations make primary cultures of human neurons resistant to such a form of cell death. LCA kills BE(2)-m17 and SK-n-MCIXC cell lines by triggering not only the intrinsic (mitochondrial) apoptotic cell death pathway driven by mitochondrial outer membrane permeabilization and initiator caspase-9 activation, but also the extrinsic (death receptor) pathway of apoptosis involving activation of the initiator caspase-8. Based on these data, we propose a mechanism underlying a potent and selective anti-tumor effect of LCA in cultured human NB cells. Moreover, our finding that LCA kills cultured human breast cancer and rat glioma cells implies that it has a broad anti-tumor effect on cancer cells derived from different tissues and organisms.

The translocator protein ligand [¹⁸F]DPA-714 images glioma and activated microglia in vivo

PURPOSE

In recent years there has been an increase in the development of radioligands targeting the 18-kDa translocator protein (TSPO). TSPO expression is well documented in activated microglia and serves as a biomarker for imaging neuroinflammation. In addition, TSPO has also been reported to be overexpressed in a number of cancer cell lines and human tumours including glioma. Here we investigated the use of [(18)F]DPA-714, a new TSPO positron emission tomography (PET) radioligand to image glioma in vivo.

METHODS

We studied the uptake of [(18)F]DPA-714 in three different rat strains implanted with 9L rat glioma cells: Fischer (F), Wistar (W) and Sprague Dawley (SD) rats. Dynamic [(18)F]DPA-714 PET imaging, kinetic modelling of PET data and in vivo displacement studies using unlabelled DPA-714 and PK11195 were performed. Validation of TSPO expression in 9L glioma cell lines and intracranial 9L gliomas were investigated using Western blotting and immunohistochemistry of brain tissue sections.

RESULTS

All rats showed significant [(18)F]DPA-714 PET accumulation at the site of 9L tumour implantation compared to the contralateral brain hemisphere with a difference in uptake among the three strains (F > W > SD). The radiotracer showed high specificity for TSPO as demonstrated by the significant reduction of [(18)F]DPA-714 binding in the tumour after administration of unlabelled DPA-714 or PK11195. TSPO expression was confirmed by Western blotting in 9L cells in vitro and by immunohistochemistry ex vivo.

CONCLUSION

The TSPO radioligand [(18)F]DPA-714 can be used for PET imaging of intracranial 9L glioma in different rat strains. This preclinical study demonstrates the feasibility of employing [(18)F]DPA-714 as an alternative radiotracer to image human glioma.

Exposure to N-ethyl-N-nitrosourea in adult mice alters structural and functional integrity of neurogenic sites

Background

Previous studies have shown that prenatal exposure to the mutagen N-ethyl-N-nitrosourea (ENU), a N-nitroso compound (NOC) found in the environment, disrupts developmental neurogenesis and alters memory formation. Previously, we showed that postnatal ENU treatment induced lasting deficits in proliferation of neural progenitors in the subventricular zone (SVZ), the main neurogenic region in the adult mouse brain. The present study is aimed to examine, in mice exposed to ENU, both the structural features of adult neurogenic sites, incorporating the dentate gyrus (DG), and the behavioral performance in tasks sensitive to manipulations of adult neurogenesis.

Methodology/Principal Findings

2-month old mice received 5 doses of ENU and were sacrificed 45 days after treatment. Then, an ultrastructural analysis of the SVZ and DG was performed to determine cellular composition in these regions, confirming a significant alteration. After bromodeoxyuridine injections, an S-phase exogenous marker, the immunohistochemical analysis revealed a deficit in proliferation and a decreased recruitment of newly generated cells in neurogenic areas of ENU-treated animals. Behavioral effects were also detected after ENU-exposure, observing impairment in odor discrimination task (habituation-dishabituation test) and a deficit in spatial memory (Barnes maze performance), two functions primarily related to the SVZ and the DG regions, respectively.

Conclusions/Significance

The results demonstrate that postnatal exposure to ENU produces severe disruption of adult neurogenesis in the SVZ and DG, as well as strong behavioral impairments. These findings highlight the potential risk of environmental NOC-exposure for the development of neural and behavioral deficits.

Rodent Glioma Models: Intracranial Stereotactic Allografts and Xenografts

Modeling human disease in small animals has been fundamental in advancing our scientific knowledge and for the development of novel therapeutic strategies. In the case of brain cancer, implantable tumor models, both intracranial and also in the periphery, have been widely used and extensively characterized. These models can be used to better understand certain aspects of tumor biology such as growth, neovascularization, response to potential therapies, and interaction with the immune system. Brain tumors from patients as well as rodents have been cultured in vitro, in an attempt to establish permanent cell lines. Human glioma tumors have also been maintained by serial passage in the flanks of immune-deficient animals, as it has been shown that it is not feasible to continuously passage them in culture. In this chapter, we describe various gliomas that have been isolated from mice, rats, and humans and subsequently used as syngeneic or xenograft tumor models in vivo. The majority of the models that we present in this chapter arose either spontaneously or by administration of chemical carcinogens. We compare and contrast the histopathological, genetic, and invasive features of the tumor lines as well as identify novel treatment modalities that have been developed. Finally, we present the procedures for intracranial implantation of tumor cells in rodents using stereotactic surgical techniques. The use of this technique enables the generation of large numbers of animals harboring intracranial tumors with relative ease and the survival of tumor-bearing animals is highly reproducible. These characteristics make the use of these in vivo models very attractive when aiming to develop and test the effectiveness of novel anticancer therapies.

MR imaging features of high-grade gliomas in murine models: how they compare with human disease, reflect tumor biology, and play a role in preclinical trials

Murine models are the most commonly used and best investigated among the animal models of HGG. They constitute an important weapon in the development and testing of new anticancer drugs and have long been used in preclinical trials. Neuroimaging methods, particularly MR imaging, offer important advantages for the evaluation of treatment response: shorter and more reliable treatment end points and insight on tumor biology and physiology through the use of functional imaging DWI, PWI, BOLD, and MR spectroscopy. This functional information has been progressively consolidated as a surrogate marker of tumor biology and genetics and may play a pivotal role in the assessment of specifically targeted drugs, both in clinical and preclinical trials. The purpose of this Research Perspectives was to compile, summarize, and critically assess the available information on the neuroimaging features of different murine models of HGGs, and explain how these correlate with human disease and reflect tumor biology.

Annexin A2 promotes glioma cell invasion and tumor progression

Gliomas are highly invasive, lethal brain tumors. Tumor-associated proteases play an important role in glioma progression. Annexin A2 is overexpressed in many cancers and correlates with increased plasmin activity on the tumor cell surface, which mediates degradation of extracellular matrix and promotes neoangiogenesis to facilitate tumor growth. In this study, we used two glioma cell lines, mouse GL261-EGFP and rat C6/LacZ, as well as stable clones transfected with an annexin A2 knockdown construct. We find that the annexin A2 knockdown decreased glioma cell migration in vitro and decreased membrane-bound plasmin activity. In vivo, we injected the glioma cells into the rodent brain and followed glioma progression. Knockdown of annexin A2 in glioma cells decreased tumor size and slowed tumor progression, as evidenced by decreased invasion, angiogenesis, and proliferation, as well as increased apoptosis in the tumor tissue of the annexin A2 knockdown group. Moreover, we report that the levels of expression of annexin A2 in human glioma samples correlate with their degree of malignancy. Together, our findings demonstrate that inhibition of annexin A2 expression in glioma cells could become a new target for glioma therapy.

Novel animal glioma models that separately exhibit two different invasive and angiogenic phenotypes of human glioblastomas

OBJECTIVE

Invasive behaviors of malignant gliomas are fundamental traits and major reasons for treatment failure. Delineation of invasive growth is important in establishing treatment for gliomas and experimental neuro-oncology could benefit from an invasive glioma model. In this study, we established two new cell line-based animal models of invasive glioma.

METHODS

Two cell lines, J3T-1 and J3T-2, were derived from the same parental canine glioma cell line, J3T. These cells were inoculated to establish brain tumors in athymic mice and rats. Pathologic samples of these animal gliomas were examined to analyze invasive patterns in relation to angiogenesis, and were compared with human glioblastoma samples. The molecular profiles of these cell lines were also shown.

RESULTS

Histologically, J3T-1 and J3T-2 tumors exhibited different invasive patterns. J3T-1 cells clustered around newly developed vessels at tumor borders, whereas J3T-2 cells showed diffuse single cell infiltration into surrounding healthy parenchyma. In human malignant glioma samples, both types of invasion were observed concomitantly. Molecular profiles of these cell lines were analyzed by immunocytochemistry and with quantitative reverse transcription polymerase chain reaction. Vascular endothelial growth factor, matrix metalloproteinase-9, hypoxia-inducible factor-1, and platelet-derived growth factor were overexpressed in J3T-1 cells rather than in J3T-2 cells, whereas integrin αvβ3, matrix metalloproteinase-2, nestin, and secreted protein acidic and rich in cysteine were overexpressed in J3T-2 cells rather than in J3T-1 cells.

CONCLUSIONS

These animal models histologically recapitulated two invasive and angiogenic phenotypes, namely angiogenesis-dependent and angiogenesis-independent invasion, also observed in human glioblastoma. These cell lines provided a reproducible in vitro and in vivo system to analyze the mechanisms of invasion and angiogenesis in glioma progression.

Repeated assessment of orthotopic glioma pO(2) by multi-site EPR oximetry: a technique with the potential to guide therapeutic optimization by repeated measurements of oxygen

Tumor hypoxia plays a vital role in therapeutic resistance. Consequently, measurements of tumor pO(2) could be used to optimize the outcome of oxygen-dependent therapies, such as, chemoradiation. However, the potential optimizations are restricted by the lack of methods to repeatedly and quantitatively assess tumor pO(2) during therapies, particularly in gliomas. We describe the procedures for repeated measurements of orthotopic glioma pO(2) by multi-site electron paramagnetic resonance (EPR) oximetry. This oximetry approach provides simultaneous measurements of pO(2) at more than one site in the glioma and contralateral cerebral tissue. The pO(2) of intracerebral 9L, C6, F98 and U251 tumors, as well as contralateral brain, were measured repeatedly for five consecutive days. The 9L glioma was well oxygenated with pO(2) of 27-36 mm Hg, while C6, F98 and U251 glioma were hypoxic with pO(2) of 7-12mm Hg. The potential of multi-site EPR oximetry to assess temporal changes in tissue pO(2) was investigated in rats breathing 100% O(2). A significant increase in F98 tumor and contralateral brain pO(2) was observed on day 1 and day 2, however, glioma oxygenation declined on subsequent days. In conclusion, EPR oximetry provides the capability to repeatedly assess temporal changes in orthotopic glioma pO(2). This information could be used to test and optimize the methods being developed to modulate tumor hypoxia. Furthermore, EPR oximetry could be potentially used to enhance the outcome of chemoradiation by scheduling treatments at times of increase in glioma pO(2).

Split immunity: immune inhibition of rat gliomas by subcutaneous exposure to unmodified live tumor cells

Gliomas that grow uninhibited in the brain almost never metastasize outside the CNS. The rare occurrences of extracranial metastasis are usually associated with a suppressed immune system. This observation raises the possibility that some gliomas might not grow outside the CNS due to an inherent immune response, We report in this study that the highly malignant F98 Fischer rat undifferentiated glioma, which grows aggressively in the brain, spontaneously regresses when injected live s.c. We found that this regression is immune-mediated and that it markedly enhances the survival or cures rats challenged with the same tumor intracranially either before or after the s.c. live-cell treatment. Adoptive transfer experiments showed the effect was immune-mediated and that the CD8 T cell fraction, which exhibited direct tumor cytotoxicity, was more effective than the CD4 T cell fraction in mediating resistance to intracranial challenge of naive rats. Brain tumors from treated rats exhibited enhanced CD3(+)CD8(+)CD4(-) and CD3(+)CD4(+)CD8(-) T cell infiltration and IFN-γ secretion. The results in the F98 glioma were corroborated in the Lewis rat CNS-1 astrocytoma. In both tumor models, s.c. treatment with live cells was significantly better than immunization with irradiated cells. We propose in this study a location-based immunotherapeutic phenomenon we term "split immunity": a tumor that thrives in an immune-privileged site may be inhibited by injecting live, unmodified tumor cells into a site that is not privileged, generating protective immunity that spreads back to the privileged site. Split immunity could explain several long-standing paradoxes regarding the lack of overt extracranial metastasis in patients with primary brain tumors.

Seeing is believing: are cancer stem cells the Loch Ness monster of tumor biology?

Tumors are complex systems with a diversity of cell phenotypes essential to tumor initiation and maintenance. With the heterogeneity present within the neoplastic compartment as its foundation, the cancer stem cell hypothesis posits that a fraction of tumor cells has the capacity to recapitulate the parental tumor upon transplantation. Over the last decade, the cancer stem cell hypothesis has gained support and shown to be relevant in many highly lethal solid tumors. However, the cancer stem cell hypothesis is not without its controversies and critics question the validity of this hypothesis based upon comparisons to normal somatic stem cells. Cancer stem cells may have direct therapeutic relevance due to resistance to current treatment paradigms, suggesting novel multimodal therapies targeting the cancer stem cells may improve patient outcomes. In this review, we will use the most common primary brain tumor, glioblastoma multiforme, as an example to illustrate why studying cancer stem cells holds great promise for more effective therapies to highly lethal tumors. In addition, we will discuss why the abilities of self-renewal and tumor propagation are the critical defining properties of cancer stem cells. Furthermore, we will examine recent progress in defining appropriate cell surface selection markers and mouse models which explore the potential cell(s) or origin for GBMs. What remains clear is that a population of cells is present in many tumors which are resistant to conventional therapies and must be considered in the design of the next generation of cancer treatments.

Inhibitors of Glioma Growth that Reveal the Tumour to the Immune System

Treated glioblastoma patients survive from 6 to 14 months. In the first part of this review, we describe glioma origins, cancer stem cells and the genomic alterations that generate dysregulated cell division, with enhanced proliferation and diverse response to radiation and chemotherapy. We review the pathways that mediate tumour cell proliferation, neo-angiogenesis, tumor cell invasion, as well as necrotic and apoptotic cell death. Then, we examine the ability of gliomas to evade and suppress the host immune system, exhibited at the levels of antigen recognition and immune activation, limiting the effective signaling between glioma and host immune cells.The second part of the review presents current therapies and their drawbacks. This is followed by a summary of the work of our laboratory during the past 20 years, on oligosaccharide and glycosphingolipid inhibitors of astroblast and astrocytoma division. Neurostatins, the O-acetylated forms of gangliosides GD1b and GT1b naturally present in mammalian brain, are cytostatic for normal astroblasts, but cytotoxic for rat C6 glioma cells and human astrocytoma grades III and IV, with ID50 values ranging from 200 to 450 nM. The inhibitors do not affect neurons or fibroblasts up to concentrations of 4 μM or higher.At least four different neurostatin-activated, cell-mediated antitumoral processes, lead to tumor destruction: (i) inhibition of tumor neovascularization; (ii) activation of microglia; (iii) activation of natural killer (NK) cells; (iv) activation of cytotoxic lymphocytes (CTL). The enhanced antigenicity of neurostatin-treated glioma cells, could be related to their increased expression of connexin 43. Because neurostatins and their analogues show specific activity and no toxicity for normal cells, a clinical trial would be the logical next step.

Novel cryo-imaging of the glioma tumor microenvironment reveals migration and dispersal pathways in vivid three-dimensional detail

Traditional methods of imaging cell migration in the tumor microenvironment include serial sections of xenografts and standard histologic stains. Current molecular imaging techniques suffer from low resolution and difficulty in imaging through the skull. Here we show how computer algorithms can be used to reconstruct images from tissue sections obtained from mouse xenograft models of human glioma and can be rendered into three-dimensional images offering exquisite anatomic detail of tumor cell dispersal. Our findings identify human LN-229 and rodent CNS-1 glioma cells as valid systems to study the highly dispersive nature of glioma tumor cells along blood vessels and white matter tracts in vivo. This novel cryo-imaging technique provides a valuable tool to evaluate therapeutic interventions targeted at limiting tumor cell invasion and dispersal.

Efficacy of interstitial continuous vincristine infusion in a bioluminescent rodent intracranial tumor model

Interstitial chemotherapeutic drug infusion can bypass the blood-brain barrier, and provide high regional drug concentrations without systemic exposure. However, toxicity and efficacy for drugs administered via interstitial continuous (i.c.) infusion have not been characterized. In the current study, vincristine (VIN) was infused into the right frontal lobes of healthy Fisher 344 rats at 30, 45, 60, and 120 μg/ml over a period of 7 days at 1 μl/h, using an Alzet osmotic pump to evaluate toxicity. C6 rat glioblastoma cells transduced with a luciferase gene were inoculated into the right frontal lobe of a second group of rats. VIN was administered to tumor bearing rats via i.c. infusion 7 days later and tumor growth was monitored by bioluminescence intensity (BLI) to assess VIN efficacy, intravenous (i.v.) drug administration was used as a comparison drug delivery method. The results suggested that VIN toxicity is dose-dependent. Efficacy studies showed increased BLI, which correlates with histopathological tumor size, in saline-infused and i.v.-treated tumor-bearing rats. These rats survived an average of 28 ± 0.85 days and 33 ± 1.38 days, respectively. Both groups had large tumors at the time of death. Animals treated with VIN via i.c. infusion survived until day 90, the observation endpoint for this study. This was significantly longer than average survival times in the previous two groups. These results demonstrate that VIN via i.c. infusion is effective in reducing C6 glioblastoma tumors and prolonging rodent survival time compared to i.v. injection and suggest that chemotherapeutic drug administration via i.c. infusion may be a promising strategy for treating malignant brain tumors.

Calcium dependence of purinergic subtype P2Y₁ receptor modulation of C6 glioma cell migration

We have examined activation of purinergic P2Y₁ receptor-dependent Ca²⁺-signaling pathways in mediating C6 glioma cell migration. The administration of 2-methylthioadenosine 5'-diphosphate (2MeSADP), a selective agonist for P2Y₁R, induced marked increases in patterns of glioma migration in both scratch wound and Boyden chamber assays. Antagonism of P2Y₁R with either the broad spectrum purinergic blocker, pyridoxal-phosphate-6-azophenyl-2',4'-disulfonate (PPADS) or the specific P2Y₁R antagonist, 2'-deoxy-N⁶-methyladenosine-3',5'-bisphosphate (MRS2179), significantly inhibited C6 cell migration. Calcium-sensitive spectrofluorometry showed 2MeSADP stimulation of glioma cells caused a biphasic change in intracellular Ca²⁺ ([Ca²⁺]i). The rapid transient phase was unchanged in Ca²⁺-free solution reflecting a [Ca²⁺]i component due to intracellular stores release subsequent to activation of a metabotropic P2Y subtype receptor. The secondary prolonged phase of [Ca²⁺]i was abolished in Ca²⁺-free solution or in glioma cells treated with the store-operated channel (SOC) blocker, SKF96365. Treatment of glioma with either MRS2179 or PPADS significantly attenuated both the rapid and prolonged phases of [Ca²⁺]i. These results suggest critical roles for activation of P2Y₁R in mediating glioma cell mobility and migration with changes in [Ca²⁺]i contributing as a mechanistic link between activated receptor and functional response. Our findings suggest that pharmacological modulation of metabotropic P2Y₁R-dependent signaling pathways may serve as a novel therapeutic procedure to slow glioma progression.

Retinal degeneration induced in adult mice by a single intraperitoneal injection of N-ethyl-N-nitrosourea

Seven-week-old female BALB/c mice received a single intraperitoneal injection of N-ethyl-N-nitrosourea (ENU) (50, 100, 200, 400, or 600 mg/kg), and retinal damage was evaluated after 7 days. Sequential morphological features of the retina and retinal apoptosis, as determined by the TUNEL assay, were analyzed 6, 12, 24, and 72 hr and 7 days after treatment with 600 mg/kg of ENU. Moreover, older mice (25 to 34 weeks of age) received an intraperitoneal injection of 600 mg/kg ENU and were sacrificed 7 days later. All animals were necropsied, and both eyes were examined histopathologically. Two of the 5 mice that received 600 mg/kg ENU died during the experimental period. Histopathologically, all mice that received 600 mg/kg of ENU experienced retinal degeneration characterized by the loss of photoreceptor cells (disappearance of the outer nuclear layer and photoreceptor layer) in both the central and peripheral retina within 7 days. One of 5 mice treated with 400 mg/kg ENU exhibited retinal damage that was restricted to the central retina. Older mice treated with 600 mg/kg ENU exhibited retinal damage that was similar to the retinal damage in younger mice. In the 600 mg/kg ENU-treated mice, TUNEL-positive photoreceptor cells peaked 72 hr after ENU treatment. Retinal thickness and the photoreceptor cell ratio in the central and peripheral retina were significantly decreased, and the retinal damage ratio was significantly increased 7 days after treatment. In conclusion, ENU induces retinal degeneration in adult mice that is characterized by photoreceptor cell apoptosis.

Repeated tumor oximetry to identify therapeutic window during metronomic cyclophosphamide treatment of 9L gliomas

Malignant gliomas are aggressive and angiogenic tumors with high VEGF content. Consequently, approaches such as metronomic chemotherapy, which have an anti-angiogenic effect, are being investigated. However, a lack of an appropriate technique that can facilitate the identification of vascular changes during antiangiogenic treatments has restricted therapeutic optimization. We have investigated the potential of tumor pO2 as a marker to detect vascular changes during metronomic chemotherapy. Electron paramagnetic resonance (EPR) oximetry was used to repeatedly assess tumor pO2 during metronomic cyclophosphamide treatment of subcutaneous 9L tumors. The 9L tumors were hypoxic with a pO2 of 5.6-8 mmHg and a tumor volume of 247-300 mm3 prior to any treatment. Tumor pO2 increased significantly to 19.7 mmHg on day 10 and remained at an elevated level until day 33 during 4 weekly treatments with 140 mg/kg cyclophosphamide. A significant decrease in the tumor volume on days 21-31 occurred in the cyclophosphamide group, while the tumor volume of the control group significantly increased during measurements for two weeks. A significant tumor growth delay was achieved with two weekly treatments of cyclophosphamide plus radiotherapy (4 Gy x 5) as compared to control, cyclophosphamide and radiotherapy alone groups. The results indicate the potential of EPR oximetry to assess tumor pO2 during metronomic chemotherapy. The ability to identify the duration of an increase in tumor pO2, therapeutic window, non-invasively by EPR oximetry could have a significant impact on the optimization of antiangiogenic approaches for the treatment of gliomas. This vital information could also be used to schedule radiotherapy to enhance therapeutic outcome.

Biometric evidence of diet-induced obesity in Lew/Crl rats

Although Lew/Crl rats are central to a classic model of renal transplantation and may provide a valid system for evaluating the effect of obesity on transplantation outcomes, their response to high-fat diet has not been evaluated sufficiently. The objective of this study was to evaluate biometric and basic metabolic data of Lew/Crl rats fed a 60% kcal, lard-based, very high-fat diet (HFD) compared with those fed a 10% kcal fat control diet (CD). Rats were maintained for 17 wk; body parameters and caloric intake were monitored weekly. Biometric data were collected and calculated before and after euthanasia. Serum was evaluated for liver enzyme activity and total bilirubin, glucose, triglyceride, cholesterol, insulin, leptin, and creatinine concentrations, and urine was evaluated for protein, glucose, specific gravity, and ketones. Tissues were harvested, weighed, and evaluated histologically. Compared with CD rats, HFD rats consumed more calories and weighed more after 3 wk. After 17 wk, HFD rats had significantly increased body weight, girth, volume, epididymal fat pad weight, omental weight, and body fat. In addition, HFD rats had mild elevations in some liver enzymes and a lower serum triglyceride concentration than did CD rats. Histologic assessment and other metabolic markers of disease were not different between the 2 groups. Lew/Crl rats fed a 60% kcal HFD become obese, but they lack significant metabolic abnormalities frequently associated with obesity in other rat strains.

Comparison of intracerebral delivery of carboplatin and photon irradiation with an optimized regimen for boron neutron capture therapy of the F98 rat glioma

In this report we have summarized our studies to optimize the delivery of boronophenylalanine (BPA) and sodium borocaptate (BSH) for boron neutron capture therapy (BNCT) of F98 glioma bearing rats. These results have been compared to a chemoradiotherapeutic approach using the same tumor model. The best survival data from our BNCT studies were obtained using a combination of BPA and sodium borocaptate BSH administered via the internal carotid artery, in combination with blood-brain barrier disruption (BBB-D). This treatment resulted in a mean survival time (MST) of 140 d with a 25% cure rate. The other approach combined intracerebral administration of carboplatin by either convection enhanced delivery (CED) or Alzet pump infusion, followed by external beam photon irradiation. This resulted in MSTs of 83 d and 112 d, respectively, with a cure rate of 40% for the latter. However, a significant problem that must be solved for both BNCT and this new chemoradiotherapeutic approach is how to improve drug uptake and microdistribution within the tumor.

Molecular targeting of glioblastoma: Drug discovery and therapies

Despite advances in treatment for glioblastoma multiforme (GBM), patient prognosis remains poor. Although there is growing evidence that molecular targeting could translate into better survival for GBM, current clinical data show limited impact on survival. Recent progress in GBM genomics implicate several activated pathways and numerous mutated genes. This molecular diversity can partially explain therapeutic resistance and several approaches have been postulated to target molecular changes. Furthermore, most drugs are unable to reach effective concentrations within the tumor owing to elevated intratumoral pressure, restrictive vasculature and other limiting factors. Here, we describe the preclinical and clinical developments in treatment strategies of GBM. We review the current clinical trials for GBM and discuss the challenges and future directions of targeted therapies.

Glial cell lines: an overview

The importance and essential functions of glial cells in the nervous system are now beginning to be understood and appreciated. Glial cell lines have been instrumental in the elucidation of many of these properties. In this Overview, the origin and properties of most of the existing cell lines for the major glial types: oligodendroglia, astroglia, microglia and Schwann cells, are documented. Particular emphasis is given to the culture conditions for each cell line and the degree to which the line can differentiate in vitro and in vivo. The major molecular markers for each glial cell lines are indicated. Finally, methods by which the glial cell lines have been developed are noted and the future directions of glial cell line research are discussed.

Boron neutron capture therapy induces apoptosis of glioma cells through Bcl-2/Bax

BACKGROUND

Boron neutron capture therapy (BNCT) is an alternative treatment modality for patients with glioma. The aim of this study was to determine whether induction of apoptosis contributes to the main therapeutic efficacy of BNCT and to compare the relative biological effect (RBE) of BNCT, γ-ray and reactor neutron irradiation.

METHODS

The neutron beam was obtained from the Xi'an Pulsed Reactor (XAPR) and γ-rays were obtained from [60Co] γ source of the Fourth Military Medical University (FMMU) in China. Human glioma cells (the U87, U251, and SHG44 cell lines) were irradiated by neutron beams at the XAPR or [60Co] γ-rays at the FMMU with different protocols: Group A included control nonirradiated cells; Group B included cells treated with 4 Gy of [60Co] γ-rays; Group C included cells treated with 8 Gy of [60Co] γ-rays; Group D included cells treated with 4 Gy BPA (p-borono-phenylalanine)-BNCT; Group E included cells treated with 8 Gy BPA-BNCT; Group F included cells irradiated in the reactor for the same treatment period as used for Group D; Group G included cells irradiated in the reactor for the same treatment period as used for Group E; Group H included cells irradiated with 4 Gy in the reactor; and Group I included cells irradiated with 8 Gy in the reactor. Cell survival was determined using the 3-(4,5-dimethylthiazol-2-yl-2,5-diphenyltetrazolium (MTT) cytotoxicity assay. The morphology of cells was detected by Hoechst33342 staining and transmission electron microscope (TEM). The apoptosis rate was detected by flow cytometer (FCM). The level of Bcl-2 and Bax protein was measured by western blot analysis.

RESULTS

Proliferation of U87, U251, and SHG44 cells was much more strongly inhibited by BPA-BNCT than by irradiation with [60Co] γ-rays (P < 0.01). Nuclear condensation was determined using both a fluorescence technique and electron microscopy in all cell lines treated with BPA-BNCT. Furthermore, the cellular apoptotic rates in Group D and Group E treated with BPA-BNCT were significantly higher than those in Group B and Group C irradiated by [60Co] γ-rays (P < 0.01). The clonogenicity of glioma cells was reduced by BPA-BNCT compared with cells treated in the reactor (Group F, G, H, I), and with the control cells (P < 0.01). Upon BPA-BNCT treatment, the Bax level increased in glioma cells, whereas Bcl-2 expression decreased.

CONCLUSIONS

Compared with γ-ray and reactor neutron irradiation, a higher RBE can be achieved upon treatment of glioma cells with BNCT. Glioma cell apoptosis induced by BNCT may be related to activation of Bax and downregulation of Bcl-2.

Differential effects of nitric oxide on blood-brain barrier integrity and cerebral blood flow in intracerebral C6 gliomas

Nitric oxide (NO) signaling in tumors and endothelial cells regulates vascular permeability and blood flow and therefore influences tumor uptake and response to therapeutic compounds. As delivery and efficacy of chemotherapy is impaired in CNS neoplasms due to a partially intact blood-brain barrier (BBB), we studied the effects of NO released by the short-acting NO donor disodium 1-[2-(carboxylato)pyrrolidin-1-yl]diazen-1-ium-1,2-diolate methanolate (PROLI/NO) on BBB integrity and blood flow in C6 gliomas using [¹⁴C]-aminoisobutyric acid (AIB) and [¹⁴C]-iodoantipyrine quantitative autoradiography. PROLI/NO selectively increased intratumoral uptake of [¹⁴C]AIB and [¹⁴C]sucrose when given as a 3-minute intracarotid infusion or a 15-minute i.v. infusion (AIB: tumor, K₁ = 68.7 ± 3.2 vs 24.9 ± 0.9 µL g⁻¹ min⁻¹, P < .0001; sucrose, K₁ = 16.9 ± 0.9 vs 11.5 ± 0.9 µL g⁻¹ min⁻¹, P = .0007). This effect was achieved without significant changes in cerebral and tumor blood flow or arterial blood pressure, which indicates that the effect on vascular permeability is independent of changes in vascular tone induced by NO. This effect was mediated by activation of the NO/3',5'-cyclic guanosine monophosphate (cGMP) pathway, as it was blocked by guanylate cyclase inhibition by LY83583 and reproduced by the delivery of 8-bromoguanosine 5'-monophosphate or inhibition of cGMP degradation by the phosphodiesterase inhibitor zaprinast. Inhibition of inducible NO synthase by aminoguanidine or cyclooxygenase inhibition by indometacin or dexamethasone did not reduce the blood-tumor barrier (BTB) response to PROLI/NO. PROLI/NO, and perhaps other NO-donating compounds, can be used to selectively increase BTB permeability in gliomas through the NO/cGMP pathway at doses that do not cause unwanted vasodilatory changes in blood flow and that do not affect the systemic circulation.

Convection enhanced delivery of carboranylporphyrins for neutron capture therapy of brain tumors

Boron neutron capture therapy (BNCT) is based on the nuclear capture and fission reactions that occur when non-radioactive 10B is irradiated with low energy thermal neutrons to produce α-particles (10B[n,α] Li). Carboranylporphyrins are a class of substituted porphyrins containing multiple carborane clusters. Three of these compounds, designated H2TBP, H2TCP, and H2DCP, have been evaluated in the present study. The goals were two-fold. First, to determine their biodistribution following intracerebral (i.c.) administration by short term (30 min) convection enhanced delivery (CED) or sustained delivery over 24 h by Alzet™ osmotic pumps to F98 glioma bearing rats. Second, to determine the efficacy of H2TCP and H2TBP as boron delivery agents for BNCT in F98 glioma bearing rats. Tumor boron concentrations immediately after i.c. pump delivery were high and they remained so at 24 h. The corresponding normal brain concentrations were low and the blood and liver concentrations were undetectable. Based on these data, therapy studies were initiated at the Massachusetts Institute of Technology (MIT) Research Reactor (MITR) with H2TCP and H2TBP 24 h after CED or pump delivery. Mean survival times (MST) ± standard deviations of animals that had received H2TCP or H2TBP, followed by BNCT, were of 35 ± 4 and 44 ± 10 days, compared to 23 ± 3 and 27 ± 3 days, respectively, for untreated and irradiated controls. However, since the tumor boron concentrations of the carboranylporphyrins were 3-5× higher than intravenous (i.v.) boronophenylalanine (BPA), we had expected that the MSTs would have been greater. Histopathologic examination of brains of BNCT treated rats revealed that there were large numbers of porphyrin-laden macrophages, as well as extracellular accumulations of porphyrins, indicating that the seemingly high tumor boron concentrations did not represent the true tumor cellular uptake. Nevertheless, our data are the first to show that carboranyl porphyrins can be used as delivery agents for BNCT of an experimental brain tumor. Based on these results, we now are in the process of synthesizing and evaluating carboranylporphyrins that could have enhanced cellular uptake and improved therapeutic efficacy.

Effect of hyperoxygenation on tissue pO2 and its effect on radiotherapeutic efficacy of orthotopic F98 gliomas

PURPOSE

Lack of methods for repeated assessment of tumor pO(2) limits the ability to test and optimize hypoxia-modifying procedures being developed for clinical applications. We report repeated measurements of orthotopic F98 tumor pO(2) and relate this to the effect of carbogen inhalation on tumor growth when combined with hypofractionated radiotherapy.

METHODS AND MATERIALS

Electron paramagnetic resonance (EPR) oximetry was used for repeated measurements of tumor and contralateral brain pO(2) in rats during 30% O(2) and carbogen inhalation for 5 consecutive days. The T(1)-enhanced volumes and diffusion coefficients of the tumors were assessed by magnetic resonance imaging (MRI). The tumors were irradiated with 9.3 Gy x 4 fractions in rats breathing 30% O(2) or carbogen to determine the effect on tumor growth.

RESULTS

The pretreatment F98 tumor pO(2) varied between 8 and 16 mmHg, while the contralateral brain had 41 to 45 mmHg pO(2) during repeated measurements. Carbogen breathing led to a significant increase in tumor and contralateral brain pO(2); however, this effect declined over days. Irradiation of the tumors in rats breathing carbogen resulted in a significant decrease in tumor growth and an increase in the diffusion coefficient measured by MRI.

CONCLUSIONS

The results provide quantitative measurements of the effect of carbogen inhalation on intracerebral tumor pO(2) and its effect on therapeutic outcome. Such direct repeated pO(2) measurements by EPR oximetry can provide temporal information that could be used to improve therapeutic outcome by scheduling doses at times of improved tumor oxygenation. EPR oximetry is currently being tested for clinical applications.

Trans-sodium crocetinate enhancing survival and glioma response on magnetic resonance imaging to radiation and temozolomide

Object

Glioblastoma (GB) tumors typically exhibit regions of hypoxia. Hypoxic areas within the tumor can make tumor cells less sensitive to chemotherapy and radiation therapy. Trans-sodium crocetinate (TSC) has been shown to transiently increase oxygen to hypoxic brain tumors. The authors examined whether this improvement in intratumor oxygenation translates to a therapeutic advantage when delivering standard adjuvant treatment to GBs.

Methods

The authors used C6 glioma cells to create a hypoxic GB model. The C6 glioma cells were stereotactically injected into the rat brain to create a tumor. Fifteen days later, MR imaging was used to confirm the presence of a glioma. The animals were randomly assigned to 1 of 3 groups: 1) temozolomide alone (350 mg/m2/day for 5 days); 2) temozolomide and radiation therapy (8 Gy); or 3) TSC (100 μg/kg for 5 days), temozolomide, and radiation therapy. Animals were followed through survival studies, and tumor response was assessed on serial MR images obtained at 15-day intervals during a 2-month period.

Results

Mean survival (± SEM) of the temozolomide-alone and the temozolomide/radiotherapy groups was 23.2 ± 0.9 and 29.4 ± 4.4 days, respectively. Mean survival in the TSC/temozolomide/radiotherapy group was 39.8 ± 6 days, a statistically significant improvement compared with either of the other groups (p < 0.05).

Although tumor size was statistically equivalent in all groups at the time of treatment initiation, the addition of TSC to temozolomide and radiotherapy resulted in a statistically significant reduction in the MR imaging–documented mean tumor size at 30 days after tumor implantation. The mean tumor size in the TSC/temozolomide/radiotherapy group was 18.9 ± 6.6 mm2 compared with 42.1 ± 2.7 mm2 in the temozolomide-alone group (p = 0.047) and 35.8 ± 5.1 mm2 in the temozolomide/radiation group (p = 0.004).

Conclusions

In a hypoxic GB model, TSC improves the radiological and clinical effectiveness of temozolomide and radiation therapy. Further investigation of this oxygen diffusion enhancer as a radiosensitizer for hypoxic brain tumors seems warranted.

Convection enhanced delivery of carboplatin in combination with radiotherapy for the treatment of brain tumors

The purpose of this study was to further evaluate the therapeutic efficacy of convection enhanced delivery (CED) of carboplatin in combination with radiotherapy for treatment of the F98 rat glioma. Tumor cells were implanted stereotactically into the brains of syngeneic Fischer rats, and 13 or 17 d. later carboplatin (20 μg/10 μl) was administered by either CED over 30 min or by Alzet osmotic pumps (0.5 μg/μl/h for 168 h.) beginning at 7 d after tumor implantation. Rats were irradiated with a 15 Gy fractionated dose (5 Gy × 3) of 6 MV photons to the whole brain beginning on the day after drug administration. Other groups of rats received either carboplatin or X-irradiation alone. The tumor carboplatin concentration following CED of 20 μg in 10 μl was 10.4 μg/g, which was equal to that observed following i.v. administration of 100 mg/kg b.w. Rats bearing small tumors, treated with carboplatin and X-irradiation, had a mean survival time (MST) of 83.4 d following CED and 111.8 d following pump delivery with 40% of the latter surviving >180 d (i.e. cured) compared to 55.2 d for CED and 77.2 d. for pump delivery of carboplatin alone and 31.8 d and 24.2 d, respectively, for X-irradiated and untreated controls. There was no microscopic evidence of residual tumor in the brains of all long-term survivors. Not surprisingly, rats with large tumors had much shorter MSTs. Only modest increases in MSTs were observed in animals that received either oral administration or CED of temozolomide plus X-irradiation (23.2 d and 29.3 d) compared to X-irradiation alone. The present survival data, and those previously reported by us, are among the best ever obtained with the F98 glioma model. Initially, they could provide a platform for a Phase I clinical trial to evaluate the safety and potential therapeutic efficacy of CED of carboplatin in patients with recurrent glioblastomas, and ultimately a Phase II trial of carboplatin in combination with radiation therapy.

The integration of quantitative multi-modality imaging data into mathematical models of tumors

Quantitative imaging data obtained from multiple modalities may be integrated into mathematical models of tumor growth and treatment response to achieve additional insights of practical predictive value. We show how this approach can describe the development of tumors that appear realistic in terms of producing proliferating tumor rims and necrotic cores. Two established models (the logistic model with and without the effects of treatment) and one novel model built a priori from available imaging data have been studied. We modify the logistic model to predict the spatial expansion of a tumor driven by tumor cell migration after a voxel's carrying capacity has been reached. Depending on the efficacy of a simulated cytotoxic treatment, we show that the tumor may either continue to expand, or contract. The novel model includes hypoxia as a driver of tumor cell movement. The starting conditions for these models are based on imaging data related to the tumor cell number (as estimated from diffusion-weighted MRI), apoptosis (from 99mTc-Annexin-V SPECT), cell proliferation and hypoxia (from PET). We conclude that integrating multi-modality imaging data into mathematical models of tumor growth is a promising combination that can capture the salient features of tumor growth and treatment response and this indicates the direction for additional research.

Selective tumor blood-brain barrier opening with the kinin B2 receptor agonist [Phe(8)psi(CH(2)NH)Arg(9)]-BK in a F98 glioma rat model: an MRI study

Treatment of malignant glioma with chemotherapy is limited mostly because of delivery impediment related to the blood-brain barrier (BBB). One approach for transporting drugs across the BBB involves the activation of bradykinin-B2 receptors (BK-B2R). Our objective was to pharmacologically characterize the BBB permeability induced by the synthetic biostable BK-B2R analogue [Phe(8)psi(CH(2)NH)Arg(9)]-BK (R523) in F98 glioma-implanted Fischer rats. On day 10 post-inoculation, we detected the presence of B2R in the tumor cells and the peritumoral microvasculature (RT-PCR and immunohistochemistry). We assessed BBB permeability before and after the intracarotid (i.c.) infusion of R523 (0.1ml/min for 5min; 2.5, 10, and 50nmol/kg/min) using non-invasive dynamic contrast-enhanced magnetic resonance imaging (DCE-MRI) with the different sized-contrast agents Gd-DTPA (0.5kDa) and Gadomer (17kDa) (0.25mmol/kg via the caudal vein). T(1)-weighted images were analyzed for the presence or absence of contrast enhancement within and surrounding the tumor area and mathematically processed to yield a contrast agent distribution volume (CADV), which was used as an indicator of vascular permeability. Our results showed that the agonist R523 increased, in a dose-dependent manner, the CADV indexes of Gd-DTPA and Gadomer, with a maximum 2-fold increase in brain uptake of both CA. The increase in CADV induced by R523 (10nmol/kg/min) was prevented by the B2R antagonist HOE140 (20nmol/kg/min, i.c.) and the nitric oxide synthase inhibitor L-NA (5mg/kg, i.v.) but not by the B1R antagonist R892 (20nmol/kg/min, i.c.) or the cyclooxygenase inhibitor Meclofenamate (5mg/kg, i.v.). The BBB permeabilizing effect of R523 (10nmol/kg/min) lasted for <1h and was accompanied by a dose-related fall in arterial blood pressure. We concluded that R523 allows the extravasation of hydrophilic macromolecular agents (17kDa) into tumor tissues by inducing selective tumor BBB permeability via B2R- and NO-dependent mechanisms.

Opening of the blood-brain barrier by low-frequency (28-kHz) ultrasound: a novel pinhole-assisted mechanical scanning device

Disruption of the blood-brain barrier (BBB) may be transiently achieved via high-frequency focused spherical ultrasound in the presence of microbubbles. In this experimental animal study, we sought to determine whether focal reversible opening of the BBB may be achieved using low-frequency (i.e., 20-30 kHz) planar ultrasonic waves. In the presence of microbubbles, we were able to obtain BBB opening using non-focused ultrasound irradiation with a frequency as low as 28 kHz. We also achieved a tight regulation of the ultrasound patterns by using a mechanical scanning device equipped with a pinhole. Histologic examination of the brains supported the feasibility of our system. The areas of BBB disruption obtained with this method were large enough to cover a typical circumscribed cerebral tumor mass. The inherent advantages of our BBB opening method include an improved portability, the possibility to obtain fairly wide areas of BBB opening and a low incidence of hemorrhagic complications. In addition, our system has the potential to reduce the need for image guidance for treating superficial brain lesions.

Efficacy of intracerebral delivery of cisplatin in combination with photon irradiation for treatment of brain tumors

We have evaluated the efficacy of intracerebral (i.c.) convection-enhanced delivery (CED) of cisplatin in combination with photon irradiation for the treatment of F98 glioma-bearing rats. One thousand glioma cells were stereotactically implanted into the brains of Fischer rats and 13 days later cisplatin (6 microg/20 microl) was administered i.c. by CED at a flow rate of 0.5 microl/min. On the following day the animals were irradiated with a single 15 Gy dose of X-rays, administered by a linear accelerator (LINAC) or 78.8 keV synchrotron X-rays at the European Synchrotron Radiation Facility (ESRF). Untreated controls had a mean survival time (MST) + or - standard error of 24 + or - 1 days compared to >59 + or - 13 days for rats that received cisplatin alone with 13% of the latter surviving >200 days. Rats that received cisplatin in combination with either 6 MV (LINAC) or 78.8 keV (synchrotron) X-rays had almost identical MSTs of >75 + or - 18 and >74 + or - 19 days, respectively with 17 and 18% long-term survivors. Microscopic examination of the brains of long-term surviving rats revealed an absence of viable tumor cells and cystic areas at the presumptive site of the tumor. Our data demonstrate that i.c. CED of cisplatin in combination with external X-irradiation significantly enhanced the survival of F98 glioma-bearing rats. This was independent of the X-ray beam energy and probably was not due to the production of Auger electrons as we previously had postulated. Our data provide strong support for the approach of concomitantly administering platinum-based chemotherapy in combination with radiotherapy for the treatment of brain tumors. Since a conventional LINAC can be used as the radiation source, this should significantly broaden the clinical applicability of this approach compared to synchrotron radiotherapy, which could only be carried out at a very small number of specialized facilities.

Fibulin-3 is uniquely upregulated in malignant gliomas and promotes tumor cell motility and invasion

Malignant gliomas are highly invasive tumors with an almost invariably rapid and lethal outcome. Surgery and chemoradiotherapy fail to remove resistant tumor cells that disperse within normal tissue, which are a major cause for disease progression and therapy failure. Infiltration of the neural parenchyma is a distinctive property of malignant gliomas compared with other solid tumors. Thus, glioma cells are thought to produce unique molecular changes that remodel the neural extracellular matrix and form a microenvironment permissive for their motility. Here, we describe the unique expression and proinvasive role of fibulin-3, a mesenchymal matrix protein specifically upregulated in gliomas. Fibulin-3 is downregulated in peripheral tumors and is thought to inhibit tumor growth. However, we found fibulin-3 highly upregulated in gliomas and cultured glioma cells, although the protein was undetectable in normal brain or cultured astrocytes. Overexpression and knockdown experiments revealed that fibulin-3 did not seem to affect glioma cell morphology or proliferation, but enhanced substrate-specific cell adhesion and promoted cell motility and dispersion in organotypic cultures. Moreover, orthotopic implantation of fibulin-3-overexpressing glioma cells resulted in diffuse tumors with increased volume and rostrocaudal extension compared with controls. Tumors and cultured cells overexpressing fibulin-3 also showed elevated expression and activity of matrix metalloproteases, such as MMP-2/MMP-9 and ADAMTS-5. Taken together, our results suggest that fibulin-3 has a unique expression and protumoral role in gliomas, and could be a potential target against tumor progression. Strategies against this glioma-specific matrix component could disrupt invasive mechanisms and restrict the dissemination of these tumors.

Overexpression of Nrp/b (nuclear restrict protein in brain) suppresses the malignant phenotype in the C6/ST1 glioma cell line

Upon searching for glucocorticoid-regulated cDNA sequences associated with the transformed to normal phenotypic reversion of C6/ST1 rat glioma cells, we identified Nrp/b (nuclear restrict protein in brain) as a novel rat gene. Here we report on the identification and functional characterization of the complete sequence encoding the rat NRP/B protein. The cloned cDNA presented a 1767 nucleotides open-reading frame encoding a 589 amino acids residues sequence containing a BTB/POZ (broad complex Tramtrack bric-a-brac/Pox virus and zinc finger) domain in its N-terminal region and kelch motifs in its C-terminal region. Sequence analysis indicates that the rat Nrp/b displays a high level of identity with the equivalent gene orthologs from other organisms. Among rat tissues, Nrp/b expression is more pronounced in brain tissue. We show that overexpression of the Nrp/b cDNA in C6/ST1 cells suppresses anchorage independence in vitro and tumorigenicity in vivo, altering their malignant nature towards a more benign phenotype. Therefore, Nrp/b may be postulated as a novel tumor suppressor gene, with possible relevance for glioblastoma therapy.