Orthotopic Growth of Human Glioma Cells Quantitatively and Qualitatively Influences Radiation-Induced Changes in Gene Expression

Speeding up Glioblastoma Cancer Research: Highlighting the Zebrafish Xenograft Model

Glioblastoma multiforme (GBM) is a very aggressive and lethal primary brain cancer in adults. The multifaceted nature of GBM pathogenesis, rising from complex interactions between cells and the tumor microenvironment (TME), has posed great treatment challenges. Despite significant scientific efforts, the prognosis for GBM remains very poor, even after intensive treatment with surgery, radiation, and chemotherapy. Efficient GBM management still requires the invention of innovative treatment strategies. There is a strong necessity to complete cancer in vitro studies and in vivo studies to properly evaluate the mechanisms of tumor progression within the complex TME. In recent years, the animal models used to study GBM tumors have evolved, achieving highly invasive GBM models able to provide key information on the molecular mechanisms of GBM onset. At present, the most commonly used animal models in GBM research are represented by mammalian models, such as mouse and canine ones. However, the latter present several limitations, such as high cost and time-consuming management, making them inappropriate for large-scale anticancer drug evaluation. In recent years, the zebrafish (Danio rerio) model has emerged as a valuable tool for studying GBM. It has shown great promise in preclinical studies due to numerous advantages, such as its small size, its ability to generate a large cohort of genetically identical offspring, and its rapid development, permitting more time- and cost-effective management and high-throughput drug screening when compared to mammalian models. Moreover, due to its transparent nature in early developmental stages and genetic and anatomical similarities with humans, it allows for translatable brain cancer research and related genetic screening and drug discovery. For this reason, the aim of the present review is to highlight the potential of relevant transgenic and xenograft zebrafish models and to compare them to the traditionally used animal models in GBM research.

The Molecular and Cellular Strategies of Glioblastoma and Non-Small-Cell Lung Cancer Cells Conferring Radioresistance

Ionizing radiation (IR) has been shown to play a crucial role in the treatment of glioblastoma (GBM; grade IV) and non-small-cell lung cancer (NSCLC). Nevertheless, recent studies have indicated that radiotherapy can offer only palliation owing to the radioresistance of GBM and NSCLC. Therefore, delineating the major radioresistance mechanisms may provide novel therapeutic approaches to sensitize these diseases to IR and improve patient outcomes. This review provides insights into the molecular and cellular mechanisms underlying GBM and NSCLC radioresistance, where it sheds light on the role played by cancer stem cells (CSCs), as well as discusses comprehensively how the cellular dormancy/non-proliferating state and polyploidy impact on their survival and relapse post-IR exposure.

A Novel Mice Model for Studying the Efficacy and IRAEs of Anti-CTLA4 Targeted Immunotherapy

Background

Patient-derived orthotopic xenograft (PDOX) is a popular animal model for translational cancer research. Immunotherapy is a promising therapy against glioblastoma (GBM). However, the PDOX model is limited to evaluating immune-related events. Our study aims to establish GBM humanized PDOX (HPDOX) mice models to study the mechanism of anti-CTLA4 immunotherapy and immune-related adverse events (IRAEs).

Methods

HPDOX models were established by culturing GBM tissues and intracranially implanting them in NSG mice. Meanwhile, peripheral blood mononuclear cells (PBMCs) were separated from peripheral blood and of GBM patients and administrated in corresponding mice. The population of CD45+, CD3+, CD4+, CD8+, and regulatory T (Treg) cells was estimated in the peripheral blood or tumor.

Results

T cells derived from GBM patients were detected in HPDOX mice models. The application of anti-CTLA4 antibodies (ipilimumab and tremelimumab) significantly inhibited the growth of GBM xenografts in mice. Moreover, residual patient T cells were detected in the tumor microenvironment and peripheral blood of HPDOX mice and were significantly elevated by ipilimumab and tremelimumab. Additionally, Treg cells were decreased in mice with IRAEs. Lastly, the proportion of CD4+/CD8+ T cells dramatically increased after the administration of ipilimumab. And the degree of IRAEs may be related to CD56+ expression in HPDOX.

Conclusions

Our study established HPDOX mice models for investigating the mechanism and IRAEs of immunotherapies in GBM, which would offer a promising platform for evaluating the efficacy and IRAEs of novel therapies and exploring personalized therapeutic strategies.

Contemporary Mouse Models in Glioma Research

Despite advances in understanding of the molecular pathogenesis of glioma, outcomes remain dismal. Developing successful treatments for glioma requires faithful in vivo disease modeling and rigorous preclinical testing. Murine models, including xenograft, syngeneic, and genetically engineered models, are used to study glioma-genesis, identify methods of tumor progression, and test novel treatment strategies. Since the discovery of highly recurrent isocitrate dehydrogenase (IDH) mutations in lower-grade gliomas, there is increasing emphasis on effective modeling of IDH mutant brain tumors. Improvements in preclinical models that capture the phenotypic and molecular heterogeneity of gliomas are critical for the development of effective new therapies. Herein, we explore the current status, advancements, and challenges with contemporary murine glioma models.

Gene Expression Profiles Induced by High-dose Ionizing Radiation in MDA-MB-231 Triple-negative Breast Cancer Cell Line

BACKGROUND/AIM

Radiation therapy (RT) represents a therapeutic option in breast cancer (BC). Even if a great number of BC patients receive RT, not all of them report benefits, due to radioresistance that gets activated through several factors, such as the hormone receptor status. Herein, we analyzed the gene expression profiles (GEP) induced by RT in triple-negative BC (TNBC) MDA-MB-231, to study signalling networks involved in radioresistance.

MATERIALS AND METHODS

GEP of MDA-MB-231 BC cells treated with a high dose of radiation, went through cDNA microarray analysis. In addition, to examine the cellular effects induced by RT, analyses of morphology and clonogenic evaluation were also conducted.

RESULTS

A descriptive report of GEP and pathways induced by IR is reported from our microarray data. Moreover, the MDA-MB-231 Radioresistent Cell Fraction (RCF) selected, included specific molecules able to drive radioresistance.

CONCLUSION

In summary, our data highlight, the RT response of TNBC MDA-MB-231 cell line at a transcriptional level, in terms of activating radioresistance in these cells, as a model of late-stage BC.

Intra-Tumoral Metabolic Zonation and Resultant Phenotypic Diversification Are Dictated by Blood Vessel Proximity

Differential exposure of tumor cells to blood-borne and angiocrine factors results in diverse metabolic microenvironments conducive for non-genetic tumor cell diversification. Here, we harnessed a methodology for retrospective sorting of fully functional, stroma-free cancer cells solely on the basis of their relative distance from blood vessels (BVs) to unveil the whole spectrum of genes, metabolites, and biological traits impacted by BV proximity. In both grafted mouse tumors and natural human glioblastoma (GBM), mTOR activity was confined to few cell layers from the nearest perfused vessel. Cancer cells within this perivascular tier are distinguished by intense anabolic metabolism and defy the Warburg principle through exercising extensive oxidative phosphorylation. Functional traits acquired by perivascular cancer cells, namely, enhanced tumorigenicity, superior migratory or invasive capabilities, and, unexpectedly, exceptional chemo- and radioresistance, are all mTOR dependent. Taken together, the study revealed a previously unappreciated graded metabolic zonation directly impacting the acquisition of multiple aggressive tumor traits.

Inhibition of TAZ contributes radiation-induced senescence and growth arrest in glioma cells

Glioblastoma (GBM) is the most aggressive brain tumor and resistant to current available therapeutics, such as radiation. To improve the clinical efficacy, it is important to understand the cellular mechanisms underlying tumor responses to radiation. Here, we investigated long-term cellular responses of human GBM cells to ionizing radiation. Comparing to the initial response within 12 hours, gene expression modulation at 7 days after radiation is markedly different. While genes related to cell cycle arrest and DNA damage responses are mostly modulated at the initial stage; immune-related genes are specifically affected as the long-term effect. This later response is associated with increased cellular senescence and inhibition of transcriptional coactivator with PDZ-binding motif (TAZ). Mechanistically, TAZ inhibition does not depend on the canonical Hippo pathway, but relies on enhanced degradation mediated by the β-catenin destruction complex in the Wnt pathway. We further showed that depletion of TAZ by RNAi promotes radiation-induced senescence and growth arrest. Pharmacological activation of the β-catenin destruction complex is able to promote radiation-induced TAZ inhibition and growth arrest in these tumor cells. The correlation between senescence and reduced expression of TAZ as well as β-catenin also occurs in human gliomas treated by radiation. Collectively, these findings suggested that inhibition of TAZ is involved in radiation-induced senescence and might benefit GBM radiotherapy.

How to Modulate Tumor Hypoxia for Preclinical In Vivo Imaging Research

Tumor hypoxia is related with tumor aggressiveness, chemo- and radiotherapy resistance, and thus a poor clinical outcome. Therefore, over the past decades, every effort has been made to develop strategies to battle the negative prognostic influence of tumor hypoxia. For appropriate patient selection and follow-up, noninvasive imaging biomarkers such as positron emission tomography (PET) radiolabeled ligands are unprecedentedly needed. Importantly, before being able to implement these new therapies and potential biomarkers into the clinical setting, preclinical in vivo validation in adequate animal models is indispensable. In this review, we provide an overview of the different attempts that have been made to create differential hypoxic in vivo cancer models with a particular focus on their applicability in PET imaging studies.

Next-Generation in vivo Modeling of Human Cancers

Animal models of human cancers played a major role in our current understanding of tumor biology. In pre-clinical oncology, animal models empowered drug target and biomarker discovery and validation. In turn, this resulted in improved care for cancer patients. In the quest for understanding and treating a diverse spectrum of cancer types, technological breakthroughs in genetic engineering and single cell "omics" offer tremendous potential to enhance the informative value of pre-clinical models. Here, I review the state-of-the-art in modeling human cancers with focus on animal models for human malignant gliomas. The review highlights the use of glioma models in dissecting mechanisms of tumor initiation, in the retrospective identification of tumor cell-of-origin, in understanding tumor heterogeneity and in testing the potential of immuno-oncology. I build on the deep review of glioma models as a basis for a more general discussion of the potential ways in which transformative technologies may shape the next-generation of pre-clinical models. I argue that refining animal models along the proposed lines will benefit the success rate of translation for pre-clinical research in oncology.

Radiation-Induced Gene Expression Changes in High and Low Grade Breast Cancer Cell Types

BACKGROUND

There is extensive scientific evidence that radiation therapy (RT) is a crucial treatment, either alone or in combination with other treatment modalities, for many types of cancer, including breast cancer (BC). BC is a heterogeneous disease at both clinical and molecular levels, presenting distinct subtypes linked to the hormone receptor (HR) status and associated with different clinical outcomes. The aim of this study was to assess the molecular changes induced by high doses of ionizing radiation (IR) on immortalized and primary BC cell lines grouped according to Human epidermal growth factor receptor (HER2), estrogen, and progesterone receptors, to study how HR status influences the radiation response. Our genomic approach using in vitro and ex-vivo models (e.g., primary cells) is a necessary first step for a translational study to describe the common driven radio-resistance features associated with HR status. This information will eventually allow clinicians to prescribe more personalized total doses or associated targeted therapies for specific tumor subtypes, thus enhancing cancer radio-sensitivity.

METHODS

Nontumorigenic (MCF10A) and BC (MCF7 and MDA-MB-231) immortalized cell lines, as well as healthy (HMEC) and BC (BCpc7 and BCpcEMT) primary cultures, were divided into low grade, high grade, and healthy groups according to their HR status. At 24 h post-treatment, the gene expression profiles induced by two doses of IR treatment with 9 and 23 Gy were analyzed by cDNA microarray technology to select and compare the differential gene and pathway expressions among the experimental groups.

RESULTS

We present a descriptive report of the substantial alterations in gene expression levels and pathways after IR treatment in both immortalized and primary cell cultures. Overall, the IR-induced gene expression profiles and pathways appear to be cell-line dependent. The data suggest that some specific gene and pathway signatures seem to be linked to HR status.

CONCLUSIONS

Genomic biomarkers and gene-signatures of specific tumor subtypes, selected according to their HR status and molecular features, could facilitate personalized biological-driven RT treatment planning alone and in combination with targeted therapies.

Etoposide-induced DNA damage affects multiple cellular pathways in addition to DNA damage response

DNA damage response (DDR) coordinates lesion repair and checkpoint activation. DDR is intimately connected with transcription. However, the relationship between DDR and transcription has not been clearly established. We report here RNA-sequencing analyses of MCF7 cells containing double-strand breaks induced by etoposide. While etoposide does not apparently cause global changes in mRNA abundance, it altered some gene expression. At the setting of fold alteration ≥ 2 and false discovery rate (FDR) ≤ 0.001, FDR < 0.05, or p < 0.05, etoposide upregulated 96, 268, or 860 genes and downregulated 41, 133, or 503 genes in MCF7 cells. Among these differentially expressed genes (DEGs), the processes of biogenesis, metabolism, cell motility, signal transduction, and others were affected; the pathways of Ras GTPase activity, RNA binding, cytokine-mediated signaling, kinase regulatory activity, protein binding, and translation were upregulated, and those pathways related to coated vesicle, calmodulin binding, and microtubule-based movement were downregulated. We further identified RABL6, RFTN2, FAS-AS1, and TCEB3CL as new DDR-affected genes in MCF7 and T47D cells. By metabolic labelling using 4-thiouridine, we observed dynamic alterations in the transcription of these genes in etoposide-treated MCF7 and T47D cells. During 0-2 hour etoposide treatment, RABL6 transcription was robustly increased at 0.5 and 1 hour in MCF7 cells and at 2 hours in T47D cells, while FAS-AS1 transcription was dramatically and steadily elevated in both cell lines. Taken together, we demonstrate dynamic alterations in transcription and that these changes affect multiple cellular processes in etoposide-induced DDR.

Orthotopic Patient-Derived Glioblastoma Xenografts in Mice

Patient-derived xenografts (PDX) provide in vivo glioblastoma (GBM) models that recapitulate actual tumors. Orthotopic tumor xenografts within the mouse brain are obtained by injection of GBM stem-like cells derived from fresh surgical specimens. These xenografts reproduce GBM's histologic complexity and hallmark biological behaviors, such as brain invasion, angiogenesis, and resistance to therapy. This method has become essential for analyzing mechanisms of tumorigenesis and testing the therapeutic effect of candidate agents in the preclinical setting. Here, we describe a protocol for establishing orthotopic tumor xenografts in the mouse brain with human GBM cells.

Gene and miRNA expression profiles of mouse Lewis lung carcinoma LLC1 cells following single or fractionated dose irradiation

In clinical practice ionizing radiation (IR) is primarily applied to cancer treatment in the form of fractionated dose (FD) irradiation. Despite this fact, a substantially higher amount of current knowledge in the field of radiobiology comes from in vitro studies based on the cellular response to single dose (SD) irradiation. In addition, intrinsic and acquired resistance to IR remains an issue in clinical practice, leading to radiotherapy treatment failure. Numerous previous studies suggest that an improved understanding of the molecular processes involved in the radiation-induced DNA damage response to FD irradiation could improve the effectiveness of radiotherapy. Therefore, the present study examined the differential expression of genes and microRNA (miRNA) in murine Lewis lung cancer (LLC)1 cells exposed to SD or FD irradiation. The results of the present study indicated that the gene and miRNA expression profiles of LLC1 cells exposed to irradiation were dose delivery type-dependent. Data analysis also revealed that mRNAs may be regulated by miRNAs in a radiation-dependent manner, suggesting that these mRNAs and miRNAs are the potential targets in the cellular response to SD or FD irradiation. However, LLC1 tumors after FD irradiation exhibited no significant changes in the expression of selected genes and miRNAs observed in the irradiated cells in vitro, suggesting that experimental in vitro conditions, particularly the tumor microenvironment, should be considered in detail to promote the development of efficient radiotherapy approaches. Nevertheless, the present study highlights the primary signaling pathways involved in the response of murine cancer cells to irradiation. Data presented in the present study can be applied to improve the outcome and development of radiotherapy in preclinical animal model settings.

Radiation-induced translational control of gene expression

Radiation-induced gene expression has long been hypothesized to protect against cell death. Defining this process would provide not only insight into the mechanisms mediating cell survival after radiation exposure, but also a novel source of targets for radiosensitization. However, whereas the radiation-induced gene expression profiles using total cellular mRNA have been generated for cell lines as well as normal tissues, with few exception, the changes in mRNA do not correlate with changes in the corresponding protein. The traditional approach to profiling gene expression, i.e., using total cellular RNA, does not take into account posttranscriptional regulation. In this review, we describe the use of gene expression profiling of polysome-bound RNA to establish that radiation modifies gene expression via translational control. Because changes in polysome-bound mRNA correlate with changes in protein, analysis of the translational profiles provides a unique data set for investigating the mechanisms mediating cellular radioresponse.

Preclinical Data on Efficacy of 10 Drug-Radiation Combinations: Evaluations, Concerns, and Recommendations

BACKGROUND

Clinical testing of new therapeutic interventions requires comprehensive, high-quality preclinical data. Concerns regarding quality of preclinical data have been raised in recent reports. This report examines the data on the interaction of 10 drugs with radiation and provides recommendations for improving the quality, reproducibility, and utility of future studies. The drugs were AZD6244, bortezomib, 17-DMAG, erlotinib, gefitinib, lapatinib, oxaliplatin/Lipoxal, sunitinib (Pfizer, Corporate headquarters, New York, NY), thalidomide, and vorinostat.

METHODS

In vitro and in vivo data were tabulated from 125 published papers, including methods, radiation and drug doses, schedules of administration, assays, measures of interaction, presentation and interpretation of data, dosimetry, and conclusions.

RESULTS

In many instances, the studies contained inadequate or unclear information that would hamper efforts to replicate or intercompare the studies, and that weakened the evidence for designing and conducting clinical trials. The published reports on these drugs showed mixed results on enhancement of radiation response, except for sunitinib, which was ineffective.

CONCLUSIONS

There is a need for improved experimental design, execution, and reporting of preclinical testing of agents that are candidates for clinical use in combination with radiation. A checklist is provided for authors and reviewers to ensure that preclinical studies of drug-radiation combinations meet standards of design, execution, and interpretation, and report necessary information to ensure high quality and reproducibility of studies. Improved design, execution, common measures of enhancement, and consistent interpretation of preclinical studies of drug-radiation interactions will provide rational guidance for prioritizing drugs for clinical radiotherapy trials and for the design of such trials.

Chimeric Mouse model to track the migration of bone marrow derived cells in glioblastoma following anti-angiogenic treatments

Bone marrow derived cells (BMDCs) have been shown to contribute in the tumor development. In vivo animal models to investigate the role of BMDCs in tumor development are poorly explored. We established a novel chimeric mouse model using as low as 5 × 10(6) GFP+ BM cells in athymic nude mice, which resulted in >70% engraftment within 14 d. In addition, chimera was established in NOD-SCID mice, which displayed >70% with in 28 d. Since anti-angiogenic therapies (AAT) were used as an adjuvant against VEGF-VEGFR pathway to normalize blood vessels in glioblastoma (GBM), which resulted into marked hypoxia and recruited BMDCs to the tumor microenvironment (TME). We exploited chimeric mice in athymic nude background to develop orthotopic U251 tumor and tested receptor tyrosine kinase inhibitors and CXCR4 antagonist against GBM. We were able to track GFP+ BMDCs in the tumor brain using highly sensitive multispectral optical imaging instrument. Increased tumor growth associated with the infiltration of GFP+ BMDCs acquiring suppressive myeloid and endothelial phenotypes was seen in TME following treatments. Immunofluorescence study showed GFP+ cells accumulated at the site of VEGF, SDF1 and PDGF expression, and at the periphery of the tumors following treatments. In conclusion, we developed a preclinical chimeric model of GBM and phenotypes of tumor infiltrated BMDCs were investigated in context of AATs. Chimeric mouse model could be used to study detailed cellular and molecular mechanisms of interaction of BMDCs and TME in cancer.

Targeting Hypoxia-Inducible Factor 1α in a New Orthotopic Model of Glioblastoma Recapitulating the Hypoxic Tumor Microenvironment

Tissue hypoxia and necrosis represent pathophysiologic and histologic hallmarks of glioblastoma (GBM). Although hypoxia inducible factor 1α (HIF-1α) plays crucial roles in the malignant phenotypes of GBM, developing HIF-1α-targeted agents has been hampered by the lack of a suitable preclinical model that recapitulates the complex biology of clinical GBM. We present a new GBM model, MGG123, which was established from a recurrent human GBM. Orthotopic xenografting of stem-like MGG123 cells reproducibly generated lethal tumors that were characterized by foci of palisading necrosis, hypervascularity, and robust stem cell marker expression. Perinecrotic neoplastic cells distinctively express HIF-1α and are proliferative in both xenografts and the patient tissue. The xenografts contain scattered hypoxic foci that were consistently greater than 50 μm distant from blood vessels, indicating intratumoral heterogeneity of oxygenation. Hypoxia enhanced HIF-1α expression in cultured MGG123 cells, which was abrogated by the HIF-1α inhibitors digoxin or ouabain. In vivo, treatment of orthotopic MGG123 xenografts with digoxin decreased HIF-1α expression, vascular endothelial growth factor mRNA levels, and CD34-positive vasculature within the tumors, and extended survival of mice bearing the aggressive MGG123 GBM. This preclinical tumor model faithfully recapitulates the GBM-relevant hypoxic microenvironment and stemness and is a suitable platform for studying disease biology and developing hypoxia-targeted agents.

Image-Guided Radiotherapy Using a Modified Industrial Micro-CT for Preclinical Applications

Purpose/Objective

Although radiotherapy is a key component of cancer treatment, its implementation into pre-clinical in vivo models with relatively small target volumes is frequently omitted either due to technical complexity or expected side effects hampering long-term observational studies. We here demonstrate how an affordable industrial micro-CT can be converted into a small animal IGRT device at very low costs. We also demonstrate the proof of principle for the case of partial brain irradiation of mice carrying orthotopic glioblastoma implants.

Methods/Materials

A commercially available micro-CT originally designed for non-destructive material analysis was used. It consists of a CNC manipulator, a transmission X-ray tube (10–160 kV) and a flat-panel detector, which was used together with custom-made steel collimators (1–5 mm aperture size). For radiation field characterization, an ionization chamber, water-equivalent slab phantoms and radiochromic films were used. A treatment planning tool was implemented using a C++ application. For proof of principle, NOD/SCID/γc^−/− mice were orthotopically implanted with U87MG high-grade glioma cells and irradiated using the novel setup.

Results

The overall symmetry of the radiation field at 150 kV was 1.04±0.02%. The flatness was 4.99±0.63% and the penumbra widths were between 0.14 mm and 0.51 mm. The full width at half maximum (FWHM) ranged from 1.97 to 9.99 mm depending on the collimator aperture size. The dose depth curve along the central axis followed a typical shape of keV photons. Dose rates measured were 10.7 mGy/s in 1 mm and 7.6 mGy/s in 5 mm depth (5 mm collimator aperture size). Treatment of mice with a single dose of 10 Gy was tolerated well and resulted in central tumor necrosis consistent with therapeutic efficacy.

Conclusion

A conventional industrial micro-CT can be easily modified to allow effective small animal IGRT even of critical target volumes such as the brain.

Altering the response to radiation: sensitizers and protectors

A number of agents are used clinically to enhance the efficacy of radiotherapy today, many of which are cytotoxic chemotherapies. Agents that enhance radiation induced tumor cell killing or protect normal tissues from the deleterious effects of ionizing radiation are collectively termed radiation modifiers. A significant effort in radiobiological research is geared towards describing and testing radiation modifiers with the intent of enhancing the therapeutic effects of radiation while minimizing normal tissue toxicity. In this review, we discuss the characteristics of these agents, the testing required to translate these agents into clinical trials, and highlight some challenges in these efforts.

Contemporary murine models in preclinical astrocytoma drug development

Despite 6 decades of research, only 3 drugs have been approved for astrocytomas, the most common malignant primary brain tumors. However, clinical drug development is accelerating with the transition from empirical, cytotoxic therapy to precision, targeted medicine. Preclinical animal model studies are critical for prioritizing drug candidates for clinical development and, ultimately, for their regulatory approval. For decades, only murine models with established tumor cell lines were available for such studies. However, these poorly represent the genomic and biological properties of human astrocytomas, and their preclinical use fails to accurately predict efficacy in clinical trials. Newer models developed over the last 2 decades, including patient-derived xenografts, genetically engineered mice, and genetically engineered cells purified from human brains, more faithfully phenocopy the genomics and biology of human astrocytomas. Harnessing the unique benefits of these models will be required to identify drug targets, define combination therapies that circumvent inherent and acquired resistance mechanisms, and develop molecular biomarkers predictive of drug response and resistance. With increasing recognition of the molecular heterogeneity of astrocytomas, employing multiple, contemporary models in preclinical drug studies promises to increase the efficiency of drug development for specific, molecularly defined subsets of tumors.

Glioblastoma-associated stromal cells (GASCs) from histologically normal surgical margins have a myofibroblast phenotype and angiogenic properties

Glioblastoma (GB) displays diffusely infiltrative growth patterns. Dispersive cells escape surgical resection and contribute to tumour recurrence within a few centimeters of the resection cavity in 90% of cases. We know that the non-neoplastic stromal compartment, in addition to infiltrative tumour cells, plays an active role in tumour recurrence. We isolated a new stromal cell population from the histologically normal surgical margins of GB by computer-guided stereotaxic biopsies and primary culture. These GB-associated stromal cells (GASCs) share phenotypic and functional properties with the cancer-associated fibroblasts (CAFs) described in the stroma of carcinomas. In particular, GASCs have tumour-promoting effects on glioma cells in vitro and in vivo. Here, we describe a quantitative proteomic analysis, using iTRAQ labelling and mass spectrometry, to compare GASCs with control stromal cells derived from non-GB peripheral brain tissues. A total of 1077 proteins were quantified and 67 proteins were found to differ between GASCs and control stromal cells. Several proteins changed in GASCs are related to a highly motile myofibroblast phenotype, and to wound healing and angiogenesis. The results for several selected proteins were validated by western blotting or flow cytometry. Furthermore, the effect of GASCs on angiogenesis was confirmed using the orthotopic U87MG glioma model. In conclusion, GASCs, isolated from GB histologically normal surgical margins and found mostly near blood vessels, could be a vascular niche constituent establishing a permissive environment, facilitating angiogenesis and possibly colonization of recurrence-initiating cells. We identify various proteins as being expressed in GASCs: some of these proteins may serve as prognostic factors for GB and/or targets for anti-glioma treatment.

Vertebrate animal models of glioma: understanding the mechanisms and developing new therapies

Glioblastoma Multiforme (GBM) is recognized as one of the most deadly cancers characterized by cellular atypia, severe necrosis, and high rate of angiogenesis. In this review, we discuss a diversified group of GBM xenograft models and compare them with the genetically engineered mouse (GEM) model systems. Next, we describe common genetic defects observed in GBM and numerous GEM models that recapitulate these abnormalities. Finally, we focus on the clinical value of other vertebrate animal models such as the canine model by examining their contributions to GBM research.

Preclinical models in radiation oncology

As the incidence of cancer continues to rise, the use of radiotherapy has emerged as a leading treatment modality. Preclinical models in radiation oncology are essential tools for cancer research and therapeutics. Various model systems have been used to test radiation therapy, including in vitro cell culture assays as well as in vivo ectopic and orthotopic xenograft models. This review aims to describe such models, their advantages and disadvantages, particularly as they have been employed in the discovery of molecular targets for tumor radiosensitization. Ultimately, any model system must be judged by its utility in developing more effective cancer therapies, which is in turn dependent on its ability to simulate the biology of tumors as they exist in situ. Although every model has its limitations, each has played a significant role in preclinical testing. Continued advances in preclinical models will allow for the identification and application of targets for radiation in the clinic.

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.

Brain metastases as preventive and therapeutic targets

The incidence of metastasis to the brain is apparently rising in cancer patients and threatens to limit the gains that have been made by new systemic treatments. The brain is considered a 'sanctuary site' as the blood-tumour barrier limits the ability of drugs to enter and kill tumour cells. Translational research examining metastasis to the brain needs to be multi-disciplinary, marrying advanced chemistry, blood-brain barrier pharmacokinetics, neurocognitive testing and radiation biology with metastasis biology, to develop and implement new clinical trial designs. Advances in the chemoprevention of brain metastases, the validation of tumour radiation sensitizers and the amelioration of cognitive deficits caused by whole-brain radiation therapy are discussed.

In vivo profiling of hypoxic gene expression in gliomas using the hypoxia marker EF5 and laser-capture microdissection

Hypoxia is a key determinant of tumor aggressiveness, yet little is known regarding hypoxic global gene regulation in vivo. We used the hypoxia marker EF5 coupled with laser-capture microdissection to isolate RNA from viable hypoxic and normoxic regions of 9L experimental gliomas. Through microarray analysis, we identified several mRNAs (including the HIF targets Vegf, Glut-1, and Hsp27) with increased levels under hypoxia compared with normoxia both in vitro and in vivo. However, we also found striking differences between the global in vitro and in vivo hypoxic mRNA profiles. Intriguingly, the mRNA levels of a substantial number of immunomodulatory and DNA repair proteins including CXCL9, CD3D, and RAD51 were found to be downregulated in hypoxic areas in vivo, consistent with a protumorigenic role of hypoxia in solid tumors. Immunohistochemical staining verified increased HSP27 and decreased RAD51 protein levels in hypoxic versus normoxic tumor regions. Moreover, CD8(+) T cells, which are recruited to tumors upon stimulation by CXCL9 and CXCL10, were largely excluded from viable hypoxic areas in vivo. This is the first study to analyze the influence of hypoxia on mRNA levels in vivo and can be readily adapted to obtain a comprehensive picture of hypoxic regulation of gene expression and its influence on biological functions in solid tumors.

Fractionated radiation therapy can induce a molecular profile for therapeutic targeting

To examine the possibility of using fractionated radiation in a unique way with molecular targeted therapy, gene expression profiles of prostate carcinoma cells treated with 10 Gy radiation administered either as a single dose or as fractions of 2 Gy × 5 and 1 Gy × 10 were examined by microarray analysis. Compared to the single dose, the fractionated irradiation resulted in significant increases in differentially expressed genes in both cell lines, with more robust changes in PC3 cells than in DU145 cells. The differentially expressed genes (>twofold change; P < 0.05) were clustered and their ontological annotations evaluated. In PC3 cells genes regulating immune and stress response, cell cycle and apoptosis were significantly up-regulated by multifractionated radiation compared to single-dose radiation. Ingenuity Pathway Analysis (IPA) of the differentially expressed genes revealed that immune response and cardiovascular genes were in the top functional category in PC3 cells and cell-to-cell signaling in DU145 cells. RT-PCR analysis showed that a flexure point for gene expression occurred at the 6th-8th fraction and AKT inhibitor perifosine produced enhanced cell killing after 1 Gy × 8 fractionated radiation in PC3 and DU145 cells compared to single dose. This study suggests that fractionated radiation may be a uniquely exploitable, non-oncogene-addiction stress pathway for molecular therapeutic targeting.

Location, location, location-makes all the difference for hypoxia in lung tumors

Hypoxia is a clinically important component of the tumor microenvironment because it adversely affects progression, metastasis, response to chemoradiation therapy, and overall patient survival. Here, we describe how different animal tumor models of lung cancer can yield surprisingly different hypoxic profiles.

In vivo bioluminescent imaging of irradiated orthotopic pancreatic cancer xenografts in nonobese diabetic-severe combined immunodeficient mice: a novel method for targeting and assaying efficacy of ionizing radiation

Adenocarcinoma of the pancreas is a lethal malignancy, and better models to study tumor behavior in vivo are needed for the development ofmore effective therapeutics. Ionizing radiation is a treatment modality that is commonly used in the clinical setting, in particular, for locally confined disease; however, good model systems to study the effect of ionizing radiation in orthotopic tumors have not been established. In an attempt to create clinically relevant models for studying treatments directed against pancreatic cancer, we have defined a methodology to measure the effect of varying doses of radiation in established human pancreatic cancer orthotopic xenografts using two different pancreatic cancer cell lines (Panc-1 and BXPC3) infected with a lentiviral vector expressing CMV promoter-driven luciferase to allow bioluminescence imaging of live animals in real time. Quantifiable photon emission from luciferase signaling in vivo correlated well with actual tumor growth. Bioluminescence imaging of the established pancreatic xenografts was used to direct delivery of radiation to the orthotopic tumors and minimize off-target adverse effects. Growth delay was observed with schedules in the range of 7.5 Gy in five fractions to 10 Gy in four fractions, whereas doses 3 Gy or higher produced toxic adverse effects. In conclusion, we describe a model in which the effects of ionizing radiation, alone or in combination with other therapeutics, in orthotopic xenografts, can be studied.

Radiation resistance in glioma cells determined by DNA damage repair activity of Ape1/Ref-1

Since radiation therapy remains a primary treatment modality for gliomas, the radioresistance of glioma cells and targets to modify their radiation tolerance are of significant interest. Human apurinic endonuclease 1 (Ape1, Ref-1, APEX, HAP1, AP endo) is a multifunctional protein involved in base excision repair of DNA and a redox-dependent transcriptional co-activator. This study investigated whether there is a direct relationship between Ape1 and radioresistance in glioma cells, employing the human U87 and U251 cell lines. U87 is intrinsically more radioresistant than U251, which is partly attributable to more cycling U251 cells found in G2/M, the most radiosensitive cell stage, while more U87 cells are found in S and G1, the more radioresistant cell stages. But observed radioresistance is also related to Ape1 activity. U87 has higher levels of Ape1 than does U251, as assessed by Western blot and enzyme activity assays (approximately 1.5-2 fold higher in cycling cells, and approximately 10 fold higher at G2/M). A direct relationship was seen in cells transfected with CMV-Ape1 constructs; there was a dose-dependent relationship between increasing Ape1 overexpression and increasing radioresistance. Conversely, knock down by siRNA or by pharmacological down regulation of Ape1 resulted in decreased radioresistance. The inhibitors lucanthone and CRT004876 were employed, the former a thioxanthene previously under clinical evaluation as a radiosensitizer for brain tumors and the latter a more specific Ape1 inhibitor. These data suggest that Ape1 may be a useful target for modifying radiation tolerance.

Application of carbon-ion beams or gamma-rays on primary tumors does not change the expression profiles of metastatic tumors in an in vivo murine model

PURPOSE

To clarify how carbon-ion radiotherapy (C-ion) on primary tumors affects the characteristics of subsequently arising metastatic tumor cells.

METHODS AND MATERIALS

Mouse squamous cell carcinomas, NR-S1, in synergic C3H/HeMsNrs mice were irradiated with a single dose of 5-50 Gy of C-ion (290 MeV per nucleon, 6-cm spread-out Bragg peak) or gamma-rays ((137)Cs source) as a reference beam. The volume of the primary tumors and the number of metastatic nodules in lung were studied, and histologic analysis and microarray analysis of laser-microdissected tumor cells were also performed.

RESULTS

Including 5 Gy of C-ion and 8 Gy of gamma-rays, which did not inhibit the primary tumor growth, all doses used in this study inhibited lung metastasis significantly. Pathologic findings showed no difference among the metastatic tumor nodules in the nonirradiated, C-ion-irradiated, and gamma-ray-irradiated groups. Clustering analysis of expression profiles among metastatic tumors and primary tumors revealed a single cluster consisting of metastatic tumors different from their original primary tumors, indicating that the expression profiles of the metastatic tumor cells were not affected by the local application of C-ion or gamma-ray radiotherapy.

CONCLUSION

We found no difference in the incidence and histology, and only small differences in expression profile, of distant metastasis between local C-ion and gamma-ray radiotherapy. The application of local radiotherapy per se or the type of radiotherapy applied did not influence the transcriptional changes caused by metastasis in tumor cells.

NS-398, ibuprofen, and cyclooxygenase-2 RNA interference produce significantly different gene expression profiles in prostate cancer cells

Cyclooxygenase-2 (COX-2) plays a significant role in tumor development and progression. Nonsteroidal anti-inflammatory drugs (NSAID) exhibit potent anticancer effects in vitro and in vivo by COX-2-dependent and COX-2-independent mechanisms. In this study, we used microarray analysis to identify the change of expression profile regulated by a COX-2-specific NSAID NS-398 (0.01 and 0.1 mmol/L), a nonspecific NSAID ibuprofen (0.1 and 1.5 mmol/L) and RNA interference (RNAi)-mediated COX-2 inhibition in PC3 prostate cancer cells. A total of 3,362 differentially expressed genes with 2-fold change and P<0.05 were identified. Low concentrations of NSAIDs and COX-2 RNAi altered very few genes (1-3%) compared with the higher concentration of NS-398 (17%) and ibuprofen (80%). Ingenuity Pathway Analysis was used for distributing the differentially expressed genes into biological networks and for evaluation of functional significance. The top 3 networks for both NSAIDs included functional categories of DNA replication, recombination and repair, and gastrointestinal disease. Immunoresponse function was specific to NS-398, and cell cycle and cellular movement were among the top functions for ibuprofen. Ingenuity Pathway Analysis also identified renal and urologic disease as a function specific for ibuprofen. This comprehensive study identified several COX-2-independent targets of NSAIDs, which may help explain the antitumor and radiosensitizing effects of NSAIDs. However, none of these categories were reflected in the identified networks in PC3 cells treated with clinically relevant low concentrations of NS-398 and ibuprofen or with COX-2 RNAi, suggesting the benefit to fingerprinting preclinical drug concentrations to improve their relevance to the clinical setting.

An orthotopic murine model of sinonasal malignancy

PURPOSE

Malignant sinonasal tumors are clinically challenging due to their proximity to vital structures and their diverse histogenesis and biological behavior. To date, no animal models accurately reflect the clinical behavior of these malignancies. We developed an orthotopic murine model of sinonasal malignancy that reproduces the intracranial extension, bony destruction, and spread along neural fascial planes seen in patients with aggressive sinonasal malignancies of various histologies.

EXPERIMENTAL DESIGN

Human squamous cell carcinoma line (DM14) and adenoid cystic carcinoma line (ACC-3) were implanted in the right maxillary sinus or soft palate in male nude mice. Animals were monitored for tumor growth and survival. Tumor specimens were removed for histopathologic evaluation to assess for intracranial extension, orbital invasion, bony invasion, perineural invasion, and distant metastasis. Statistical analysis was done to calculate P values with the Student's t test for individual tumor volumes. Differences in survival times were assessed using the log-rank test.

RESULTS

Mice with DM14 or ACC-3 implanted in either the maxillary sinus or the soft palate developed large primary tumors. A statistically significant inverse correlation between survival and the number of tumor cells implanted was found. Histopathologic evaluation revealed orbital invasion, intracranial extension, pulmonary metastasis, lymph node metastasis, and perineural invasion.

CONCLUSIONS

We describe the first orthotopic model for sinonasal malignancy. Our model faithfully recapitulates the phenotype and malignant behavior of the aggressive tumor types seen in patients. This model offers an opportunity to identify and specifically target the aberrant molecular mechanisms underlying this heterogeneous group of malignancies.

Radiation-induced gene translation profiles reveal tumor type and cancer-specific components

The microarray analysis of total cellular RNA is a common method used in the evaluation of radiation-induced gene expression. However, profiling the cellular transcriptome does not take into account posttranscriptional processes that affect gene expression. To better define the genes whose expression is influenced by ionizing radiation, we used polysome-bound RNA to generate gene translation profiles for a series of tumor and normal cell lines. Cell lines were exposed to 2 Gy, polysome-bound RNA isolated 6 hours later, and then subjected to microarray analysis. To identify the genes whose translation was affected by radiation, the polysome-bound RNA profiles were compared with their corresponding controls using significance analysis of microarrays (<1% false discovery rate). From the statistically significant genes identified for each cell line, hierarchical clustering was performed by average linkage measurement and Pearson's correlation metric. Ingenuity Pathway Analysis was used for distributing genes into biological networks and for evaluation of functional significance. Radiation-induced gene translation profiles clustered according to tissue of origin; the cell lines corresponding to each tissue type contained a significant number of commonly affected genes. Network analyses suggested that the biological functions associated with the genes whose translation was affected by radiation were tumor type-specific. There was also a set of genes/networks that were unique to tumor or normal cells. These results indicate that radiation-induced gene translation profiles provide a unique data set for the analysis of cellular radioresponse and suggest a framework for identifying and targeting differences in the regulation of tumor and normal cell radiosensitivity.

Differential effects of combined Ad5- delta 24RGD and radiation therapy in in vitro versus in vivo models of malignant glioma

PURPOSE

The integrin-targeted conditionally replicating adenovirus Ad5-delta 24RGD has been shown to possess strong oncolytic activity in experimental tumors and is currently being developed toward phase I clinical evaluation for ovarian cancer and malignant glioma. Previously, we reported that combination therapy of Ad5-delta 24RGD with irradiation led to synergistic antitumor activity in s.c. glioma xenografts. In the current study, the underlying mechanism of action to this synergy was studied and the effects of combined therapy were assessed in an orthotopic glioma model.

EXPERIMENTAL DESIGN AND RESULTS

Sequencing studies in U-87 monolayers showed that delivery of irradiation before Ad5-delta 24RGD infection led to a greater oncolytic effect than simultaneous delivery or infection before irradiation. This effect was not due to enhanced virus production or release. Experiments using a luciferase-encoding vector revealed a small increase in transgene expression in irradiated cells. In tumor spheroids, combination therapy was more effective than Ad5-delta 24RGD or irradiation alone. Staining of spheroid sections showed improved penetration of virus to the core of irradiated spheroids. Mice bearing intracranial tumors received a combination of Ad5-delta 24RGD with 1 x 5 Gy total body irradiation or with 2 x 6 Gy whole brain irradiation. In contrast to the in vitro data and reported results in s.c. tumors, addition of radiotherapy did not significantly enhance the antitumor effect of Ad5-delta 24RGD.

CONCLUSIONS

Combined treatment with Ad5-delta 24RGD and irradiation shows enhanced antitumor activity in vitro and in s.c. tumors, but not in an orthotopic glioma model. These differential results underscore the significance of the selected tumor model in assessing the effects of combination therapies with oncolytic adenoviruses.

Gene expression profile of metastatic human pancreatic cancer cells depends on the organ microenvironment

To determine the influence of the microenvironment on changes in gene expression, we did microarray analysis on three variant lines of a human pancreatic cancer (FG, L3.3, and L3.6pl) with different metastatic potentials. The variant lines were grown in tissue culture in the subcutis (ectopic) or pancreas (orthotopic) of nude mice. Compared with tissue culture, the number of genes of which the expression was affected by the microenvironment was up-regulated in tumors growing in the subcutis and pancreas. In addition, highly metastatic L3.6pl cells growing in the pancreas expressed significantly higher levels of 226 genes than did the L3.3 or FG variant cells. Growth of the variant lines in the subcutis did not yield similar results, indicating that the orthotopic microenvironment significantly influences gene expression in pancreatic cancer cells. These data suggest that investigations of the functional consequence of gene expression require accounting for experimental growth conditions.