New approaches for modelling cancer mechanisms in the mouse

Emerging In Vitro and In Vivo Models: Hope for the Better Understanding of Cancer Progression and Treatment

Various cancer models have been developed to aid the understanding of the underlying mechanisms of tumor development and evaluate the effectiveness of various anticancer drugs in preclinical studies. These models accurately reproduce the critical stages of tumor initiation and development to mimic the tumor microenvironment better. Using these models for target validation, tumor response evaluation, resistance modeling, and toxicity comprehension can significantly enhance the drug development process. Herein, various in vivo or animal models are presented, typically consisting of several mice and in vitro models ranging in complexity from transwell models to spheroids and CRISPR-Cas9 technologies. While in vitro models have been used for decades and dominate the early stages of drug development, they are still limited primary to simplistic tests based on testing on a single cell type cultivated in Petri dishes. Recent advancements in developing new cancer therapies necessitate the generation of complicated animal models that accurately mimic the tumor's complexity and microenvironment. Mice make effective tumor models as they are affordable, have a short reproductive cycle, exhibit rapid tumor growth, and are simple to manipulate genetically. Human cancer mouse models are crucial to understanding the neoplastic process and basic and clinical research improvements. The following review summarizes different in vitro and in vivo metastasis models, their advantages and disadvantages, and their ability to serve as a model for cancer research.

Preclinical tumor mouse models for studying esophageal cancer

Preclinical models are extensively employed in cancer research because they can be manipulated in terms of their environment, genome, molecular biology, organ systems, and physical activity to mimic human behavior and conditions. The progress made in in vivo cancer research has resulted in significant advancements, enabling the creation of spontaneous, metastatic, and humanized mouse models. Most recently, the remarkable and extensive developments in genetic engineering, particularly the utilization of CRISPR/Cas9, transposable elements, epigenome modifications, and liquid biopsies, have further facilitated the design and development of numerous mouse models for studying cancer. In this review, we have elucidated the production and usage of current mouse models, such as xenografts, chemical-induced models, and genetically engineered mouse models (GEMMs), for studying esophageal cancer. Additionally, we have briefly discussed various gene-editing tools that could potentially be employed in the future to create mouse models specifically for esophageal cancer research.

Curcumin arrests G-quadruplex in the nuclear hyper-sensitive III1 element of c-MYC oncogene leading to apoptosis in metastatic breast cancer cells

c-MYC is deregulated in triple negative breast cancer (TNBC) pointing to be a promising biomarker for breast cancer treatment. Precise level of MYC expression is important in the control of cellular growth and proliferation. Designing of c-MYC-targeted antidotes to restore its basal level of cellular expression holds an optimistic approach towards anti-cancer treatment. MYC transcription is dominantly controlled by Nuclear Hypersensitive Element III-1 (NHE_III1) upstream of the promoter region possessing G-Quadruplex silencer element (Pu-27). We have investigated the selective binding-interaction profile of a natural phytophenolic compound Curcumin with native MYC G-quadruplex by conducting an array of biophysical experiments and in silico based Molecular Docking and Molecular Dynamic (MDs) simulation studies. Curcumin possesses immense anti-cancerous properties. We have observed significantly increased stability of MYC-G Quadruplex and thermodynamic spontaneity of Curcumin-MYC GQ binding with negative ΔG value. Transcription of MYC is tightly regulated by a complex mechanism involving promoters, enhancers and multiple transcription factors. We have used Curcumin as a model drug to understand the innate mechanism of controlling deregulated MYC back to its basal expression level. We have checked MYC-expression at transcriptional and translational level and proceeded for Chromatin Immuno-Precipitation assay (ChIP) to study the occupancy level of SP1, Heterogeneous nuclear ribonucleoprotein K (hnRNPK), Nucleoside Diphosphate Kinase 2 (NM23-H2) and Nucleolin at NHE_III1 upon Curcumin treatment of MDA-MB-231 cells. We have concluded that Curcumin binding tends to drive the equilibrium towards stable G-quadruplex formation repressing MYC back to its threshold-level. On retrospection of the synergistic effect of upregulated c-MYC and BCL-2 in cancer, we have also reported a new pathway [MYC-E2F-1-BCL-2-axis] through which Curcumin trigger apoptosis in cancer cells.Communicated by Ramaswamy H. Sarma.

Transgenic Mouse Models in Cancer Research

The use of existing mouse models in cancer research is of utmost importance as they aim to explore the casual link between candidate cancer genes and carcinogenesis as well as to provide models to develop and test new therapies. However, faster progress in translating mouse cancer model research into the clinic has been hampered due to the limitations of these models to better reflect the complexities of human tumors. Traditionally, immunocompetent and immunodeficient mice with syngeneic and xenografted tumors transplanted subcutaneously or orthotopically have been used. These models are still being widely employed for many different types of studies, in part due to their widespread availability and low cost. Other types of mouse models used in cancer research comprise transgenic mice in which oncogenes can be constitutively or conditionally expressed and tumor-suppressor genes silenced using conventional methods, such as retroviral infection, microinjection of DNA constructs, and the so-called "gene-targeted transgene" approach. These traditional transgenic models have been very important in studies of carcinogenesis and tumor pathogenesis, as well as in studies evaluating the development of resistance to therapy. Recently, the clustered regularly interspaced short palindromic repeats (CRISPR)-based genome editing approach has revolutionized the field of mouse cancer models and has had a profound and rapid impact on the development of more effective systems to study human cancers. The CRISPR/Cas9-based transgenic models have the capacity to engineer a wide spectrum of mutations found in human cancers and provide solutions to problems that were previously unsolvable. Recently, humanized mouse xenograft models that accept patient-derived xenografts and CD34+ cells were developed to better mimic tumor heterogeneity, the tumor microenvironment, and cross-talk between the tumor and stromal/immune cells. These features make them extremely valuable models for the evaluation of investigational cancer therapies, specifically new immunotherapies. Taken together, improvements in both the CRISPR/Cas9 system producing more valid mouse models and in the humanized mouse xenograft models resembling complex interactions between the tumor and its environment might represent one of the successful pathways to precise individualized cancer therapy, leading to improved cancer patient survival and quality of life.

Osmolality/salinity-responsive enhancers (OSREs) control induction of osmoprotective genes in euryhaline fish

Fish respond to salinity stress by transcriptional induction of many genes, but the mechanism of their osmotic regulation is unknown. We developed a reporter assay using cells derived from the brain of the tilapia Oreochromis mossambicus (OmB cells) to identify osmolality/salinity-responsive enhancers (OSREs) in the genes of Omossambicus Genomic DNA comprising the regulatory regions of two strongly salinity-induced genes, inositol monophosphatase 1 (IMPA1.1) and myo-inositol phosphate synthase (MIPS), was isolated and analyzed with dual luciferase enhancer trap reporter assays. We identified five sequences (two in IMPA1.1 and three in MIPS) that share a common consensus element (DDKGGAAWWDWWYDNRB), which we named "OSRE1." Additional OSREs that were less effective in conferring salinity-induced trans-activation and do not match the OSRE1 consensus also were identified in both MIPS and IMPA1.1 Although OSRE1 shares homology with the mammalian osmotic-response element/tonicity-responsive enhancer (ORE/TonE) enhancer, the latter is insufficient to confer osmotic induction in fish. Like other enhancers, OSRE1 trans-activates genes independent of orientation. We conclude that OSRE1 is a cis-regulatory element (CRE) that enhances the hyperosmotic induction of osmoregulated genes in fish. Our study also shows that tailored reporter assays developed for OmB cells facilitate the identification of CREs in fish genomes. Knowledge of the OSRE1 motif allows affinity-purification of the corresponding transcription factor and computational approaches for enhancer screening of fish genomes. Moreover, our study enables targeted inactivation of OSRE1 enhancers, a method superior to gene knockout for functional characterization because it confines impairment of gene function to a specific context (salinity stress) and eliminates pitfalls of constitutive gene knockouts (embryonic lethality, developmental compensation).

Wnt-signalling pathways and microRNAs network in carcinogenesis: experimental and bioinformatics approaches

Over the past few years, microRNAs (miRNAs) have not only emerged as integral regulators of gene expression at the post-transcriptional level but also respond to signalling molecules to affect cell function(s). miRNAs crosstalk with a variety of the key cellular signalling networks such as Wnt, transforming growth factor-β and Notch, control stem cell activity in maintaining tissue homeostasis, while if dysregulated contributes to the initiation and progression of cancer. Herein, we overview the molecular mechanism(s) underlying the crosstalk between Wnt-signalling components (canonical and non-canonical) and miRNAs, as well as changes in the miRNA/Wnt-signalling components observed in the different forms of cancer. Furthermore, the fundamental understanding of miRNA-mediated regulation of Wnt-signalling pathway and vice versa has been significantly improved by high-throughput genomics and bioinformatics technologies. Whilst, these approaches have identified a number of specific miRNA(s) that function as oncogenes or tumour suppressors, additional analyses will be necessary to fully unravel the links among conserved cellular signalling pathways and miRNAs and their potential associated components in cancer, thereby creating therapeutic avenues against tumours. Hence, we also discuss the current challenges associated with Wnt-signalling/miRNAs complex and the analysis using the biomedical experimental and bioinformatics approaches.

Neutrophils: Critical components in experimental animal models of cancer

Neutrophils have a crucial role in tumor development and metastatic progression. The contribution of neutrophils in tumor development is multifaceted and contradictory. On the one hand, neutrophils prompt tumor inception, promote tumor development by mediating the initial angiogenic switch and facilitate colonization of circulating tumor cells, and on the other hand, have cytotoxic and anti-metastatic capabilities. Our understanding of the role of neutrophils in tumor development has greatly depended on different experimental animal models of cancer. In this review we cover important findings that have been made about neutrophils in experimental animal models of cancer, point to their advantages and limitations, and discuss novel techniques that can be used to expand our knowledge of how neutrophils influence tumor progression.

Animal models of colorectal cancer with liver metastasis

Liver metastasis is a leading cause of death in patients with colorectal cancer. Investigating the mechanisms of liver metastasis and control of disease progression are important strategies for improving survival of these patients. Liver metastasis is a multi-step process and relevant models representing these steps are necessary to understand the mechanism of liver metastasis and establish appropriate treatments. Recently, the development of animal models for use in metastasis research has greatly increased; however, there is still a lack of models that sufficiently represent human cancer. Thus, in order to select an optimal model for of a given study, it is necessary to fully understand the characteristics of each animal model. In this review, we describe the mouse models currently used for colorectal cancer with liver metastasis, their characteristics, and their pros and cons. This may help us specify the mechanism of liver metastasis and provide evidence relevant to clinical applications.

Tamoxifen-Containing Eye Drops Successfully Trigger Cre-Mediated Recombination in the Entire Eye

Embryonic lethality in mice with targeted gene deletion is a major issue that can be circumvented by using Cre-loxP-based animal models. Various inducible Cre systems are available, e.g. such that are activated following tamoxifen treatment, and allow deletion of a specific target gene at any desired time point during the life span of the animal. In this study, we describe the efficiency of topical tamoxifen administration by eye drops using a Cre- reporter mouse strain (R26R). We report that tamoxifen-responsive CAGGCre-ER (TM) mice show a robust Cre- mediated recombination throughout the entire eye.

A non-canonical function of telomerase RNA in the regulation of developmental myelopoiesis in zebrafish

Dyskeratosis congenita (DC) is an inherited disorder with mutations affecting telomerase or telomeric proteins. DC patients usually die of bone marrow failure. Here we show that genetic depletion of the telomerase RNA component (TR) in the zebrafish results in impaired myelopoiesis, despite normal development of haematopoietic stem cells (HSCs). The neutropenia caused by TR depletion is independent of telomere length and telomerase activity. Genetic analysis shows that TR modulates the myeloid-erythroid fate decision by controlling the levels of the master myeloid and erythroid transcription factors spi1 and gata1, respectively. The alteration in spi1 and gata1 levels occurs through stimulation of gcsf and mcsf. Our model of TR deficiency in the zebrafish illuminates the non-canonical roles of TR, and could establish therapeutic targets for DC.

Tnfa signaling through tnfr2 protects skin against oxidative stress-induced inflammation

A new zebrafish model of skin inflammatory disease explains new-onset and worsening psoriasis and lichen planus in patients receiving anti-TNFα therapy.

TNFα overexpression has been associated with several chronic inflammatory diseases, including psoriasis, lichen planus, rheumatoid arthritis, and inflammatory bowel disease. Paradoxically, numerous studies have reported new-onset psoriasis and lichen planus following TNFα antagonist therapy. Here, we show that genetic inhibition of Tnfa and Tnfr2 in zebrafish results in the mobilization of neutrophils to the skin. Using combinations of fluorescent reporter transgenes, fluorescence microscopy, and flow cytometry, we identified the local production of dual oxidase 1 (Duox1)-derived H₂O₂ by Tnfa- and Tnfr2-deficient keratinocytes as a trigger for the activation of the master inflammation transcription factor NF-κB, which then promotes the induction of genes encoding pro-inflammatory molecules. In addition, pharmacological inhibition of Duox1 completely abrogated skin inflammation, placing Duox1-derived H₂O₂ upstream of this positive feedback inflammatory loop. Strikingly, DUOX1 was drastically induced in the skin lesions of psoriasis and lichen planus patients. These results reveal a crucial role for TNFα/TNFR2 axis in the protection of the skin against DUOX1-mediated oxidative stress and could establish new therapeutic targets for skin inflammatory disorders.

Psoriasis and lichen planus are chronic, debilitating skin diseases that affect millions of people worldwide. TNFα is a multifunctional cytokine that mediates acute and chronic inflammation. While TNFα antagonist therapy is used for autoimmune or chronic inflammatory diseases, such as inflammatory bowel disease (IBD), numerous studies have reported new-onset psoriasis and lichen planus following such therapy. We have used the unique advantages of the zebrafish embryo to identify a novel phenotype that mirrors this unexplained and paradoxical onset of psoriasis and lichen planus. We found that depletion of Tnfa or its receptor Tnfr2 caused skin inflammation and hyperproliferation of keratinocytes through the activation of a Duox1/H₂O₂/NF-κB positive feedback inflammatory loop. Strikingly, DUOX1 was drastically induced in the skin lesions of psoriasis and lichen planus patients, and pharmacological inhibition of Duox1 abrogated skin inflammation, placing Duox1-derived H₂O₂ upstream of this inflammatory loop. Our results suggest that therapies targeting DUOX1 and H₂O₂ could provide innovative approaches to the management of skin inflammatory disorders.

Gene profiling of canine B-cell lymphoma reveals germinal center and postgerminal center subtypes with different survival times, modeling human DLBCL

Diffuse large B-cell lymphoma (DLBCL) is the most common lymphoma subtype, and fewer than half of patients are cured with standard first-line therapy. To improve therapeutic options, better animal models that accurately mimic human DLBCL (hDLBCL) are needed. Canine DLBCL, one of the most common cancers in veterinary oncology, is morphologically similar to hDLBCL and is treated using similar chemotherapeutic protocols. With genomic technologies, it is now possible to molecularly evaluate dogs as a potential large-animal model for hDLBCL. We evaluated canine B-cell lymphomas (cBCL) using immunohistochemistry (IHC) and gene expression profiling. cBCL expression profiles were similar in many ways to hDLBCLs. For instance, a subset had increased expression of NF-κB pathway genes, mirroring human activated B-cell (ABC)-type DLBCL. Furthermore, immunoglobulin heavy chain ongoing mutation status, which is correlated with ABC/germinal center B-cell cell of origin in hDLBCL, separated cBCL into two groups with statistically different progression-free and overall survival times. In contrast with hDLBCL, cBCL rarely expressed BCL6 and MUM1/IRF4 by IHC. Collectively, these studies identify molecular similarities to hDLBCL that introduce pet dogs as a representative model of hDLBCL for future studies, including therapeutic clinical trials.

The multifaceted effects of omega-3 polyunsaturated Fatty acids on the hallmarks of cancer

Omega-3 polyunsaturated fatty acids, in particular eicosapentaenoic acid, and docosahexaenoic acid have been shown to have multiple beneficial antitumour actions that affect the essential alterations that dictate malignant growth. In this review we explore the putative mechanisms of action of omega-3 polyunsaturated fatty acid in cancer protection in relation to self-sufficiency in growth signals, insensitivity to growth-inhibitory signals, apoptosis, limitless replicative potential, sustained angiogenesis, and tissue invasion, and how these will hopefully translate from bench to bedside.

Rebuilding cancer metastasis in the mouse

Most cancer deaths are due to the systemic dissemination of cancer cells and the formation of secondary tumors (metastasis) in distant organs. Recent years have brought impressive progress in metastasis research, yet we still lack sufficient insights into how cancer cells migrate out of primary tumors and invade into neighboring tissue, intravasate into the blood or the lymphatic circulation, survive in the blood stream, and target specific organs to initiate metastatic outgrowth. While a large number of cellular and animal models of cancer have been crucial in delineating the molecular mechanisms underlying tumor initiation and progression, experimental models that faithfully recapitulate the multiple stages of metastatic disease are still scarce. The advent of sophisticated genetic engineering in mice, in particular the ability to manipulate gene expression in specific tissue and at desired time points at will, have allowed to rebuild the metastatic process in mice. Here, we describe a selection of cellular experimental systems, tumor transplantation mouse models and genetically engineered mouse models that are used for monitoring specific processes involved in metastasis, such as cell migration and invasion, and for investigating the full metastatic process. Such models not only aid in deciphering the pathomechanisms of metastasis, but are also instrumental for the preclinical testing of anti-metastatic therapies and further refinement and generation of improved models.

Cancer biology and genomics: translating discoveries, transforming pathology

Advances in our understanding of cancer biology and discoveries emerging from cancer genomics are being translated into real clinical benefits for patients with cancer. The 2011 Journal of Pathology Annual Review Issue provides a snapshot of recent rapid progress on multiple fronts in the war on cancer or, more precisely, the wars on cancers. Indeed, perhaps the most notable recent shift is reflected by the sharp increase in understanding the biology of multiple specific cancers and using these new insights to inform rationally targeted therapies, with often striking successes. These recent developments, as reviewed in this issue, show how the long-term investments in basic cancer research are finally beginning to bear fruit.

Analysis of Brca1-deficient mouse mammary glands reveals reciprocal regulation of Brca1 and c-kit

Disruption of the breast cancer susceptibility gene Brca1 results in defective lobular-alveolar development in the mammary gland and a predisposition to breast tumourigenesis in humans and in mice. Recent evidence suggests that BRCA1 loss in humans is associated with an expansion of the luminal progenitor cell compartment in the normal breast and tumours with a luminal progenitor-like expression profile. To further investigate the role of BRCA1 in the mammary gland, we examined the consequences of Brca1 loss in mouse mammary epithelial cells in vitro and in vivo. Here, we show that Brca1 loss is associated with defective morphogenesis of SCp2 and HC11 mouse mammary epithelial cell lines and that in the MMTV-Cre Brca1(Co/Co) mouse model of Brca1 loss, there is an accumulation of luminal progenitor (CD61(+)CD29(lo)CD24(+)) cells during pregnancy. By day 1 of lactation, there are marked differences in the expression of 1379 genes, with most significantly altered pathways and networks, including lactation, the immune response and cancer. One of the most differentially expressed genes was the luminal progenitor marker, c-kit. Immunohistochemical analysis revealed that the increase in c-kit levels is associated with an increase in c-kit positivity. Interestingly, an inverse association between Brca1 and c-kit expression was also observed during mammary epithelial differentiation, and small interfering RNA-mediated knockdown of Brca1 resulted in a significant increase in c-kit mRNA levels. We found no evidence that c-kit plays a direct role in regulating differentiation of HC11 cells, suggesting that Brca1-mediated induction of c-kit probably contributes to Brca1-associated tumourigenesis via another cellular process, and that c-kit is likely to be a marker rather than a mediator of defective lobular-alveolar development resulting from Brca1 loss.

Targeting inhibitory pathways in cancer immunotherapy

The clinical success of adaptive transfer of in vitro expanded antigen-specific CD8(+) T cells isolated from patients' tumors has demonstrated that effector cells of the adaptive immune system can effectively eliminate even large tumor masses. Nevertheless, cancer vaccines that aim to expand such CD8(+) T cells in situ have had remarkably little success in spite of numerous attempts. Recent advances in basic immunology have revealed layers of complexity controlling activation and maintenance of adaptive immune responses that are tightly controlled by immunoinhibitory pathways to avoid horror autotoxicus. During tumor progression the activities of negative pathways increase and together with cancer immune evasion tactics presumably prevent induction of an efficacious immune response by cancer vaccines that solely provide more antigen to an already suppressed system. Cancer vaccines may thus need to readjust the imbalance of the cancer patients' immune system by inhibiting immunoinhibitors; such regimens have shown preclinical efficacy and are now entering clinical trials hopefully ending the Kafkaesque futility of cancer vaccines.

CD13 is dispensable for normal hematopoiesis and myeloid cell functions in the mouse

While the myeloid marker CD13 has been implicated in numerous myeloid cell functions, its genetic ablation reveals a nominal contribution of CD13 to these functions.

The robust and consistent expression of the CD13 cell surface marker on very early as well as differentiated myeloid hematopoietic cells has prompted numerous investigations seeking to define roles for CD13 in myeloid cells. To address the function of myeloid CD13 directly, we created a CD13 null mouse and assessed the responses of purified primary macrophages or DCs from WT and CD13 null animals in cell assays and inflammatory disease models, where CD13 has been implicated previously. We find that mice lacking CD13 develop normally with normal hematopoietic profiles except for an increase in thymic but not peripheral T cell numbers. Moreover, in in vitro assays, CD13 appears to be largely dispensable for the aspects of phagocytosis, proliferation, and antigen presentation that we tested, although we observed a slight decrease in actin‐independent erythrocyte uptake. However, in agreement with our published studies, we show that lack of monocytic CD13 completely ablates anti‐CD13‐dependent monocyte adhesion to WT endothelial cells. In vivo assessment of four inflammatory disease models showed that lack of CD13 has little effect on disease onset or progression. Nominal alterations in gene expression levels between CD13 WT and null macrophages argue against compensatory mechanisms. Therefore, although CD13 is highly expressed on myeloid cells and is a reliable marker of the myeloid lineage of normal and leukemic cells, it is not a critical regulator of hematopoietic development, hemostasis, or myeloid cell function.

Genetically engineered mouse models in cancer research

Mouse models of human cancer have played a vital role in understanding tumorigenesis and answering experimental questions that other systems cannot address. Advances continue to be made that allow better understanding of the mechanisms of tumor development, and therefore the identification of better therapeutic and diagnostic strategies. We review major advances that have been made in modeling cancer in the mouse and specific areas of research that have been explored with mouse models. For example, although there are differences between mice and humans, new models are able to more accurately model sporadic human cancers by specifically controlling timing and location of mutations, even within single cells. As hypotheses are developed in human and cell culture systems, engineered mice provide the most tractable and accurate test of their validity in vivo. For example, largely through the use of these models, the microenvironment has been established to play a critical role in tumorigenesis, since tumor development and the interaction with surrounding stroma can be studied as both evolve. These mouse models have specifically fueled our understanding of cancer initiation, immune system roles, tumor angiogenesis, invasion, and metastasis, and the relevance of molecular diversity observed among human cancers. Currently, these models are being designed to facilitate in vivo imaging to track both primary and metastatic tumor development from much earlier stages than previously possible. Finally, the approaches developed in this field to achieve basic understanding are emerging as effective tools to guide much needed development of treatment strategies, diagnostic strategies, and patient stratification strategies in clinical research.

Modeling glioma growth and invasion in Drosophila melanogaster

Glioblastoma is the most common and most malignant intrinsic human brain tumor, characterized by extensive invasion and proliferation of glial (astrocytic) tumor cells, frequent activation of tyrosine kinase receptor signaling pathways, relative resistance to chemotherapy and radiotherapy, and poor prognosis. Using the Gal4-UAS system, we have produced glioma models in Drosophila by overexpressing homologs of human tyrosine kinase receptors under control of the glia-specific promoter reversed polarity (repo). Glial overexpression of activated epidermal growth factor receptor (EGFR) resulted in enhanced proliferation and migration of larval glial cells with increased numbers in the eye imaginal disc, diffuse tumor-like enlargement of the optic stalk, and marked ectopic invasion of glial cells along the optic nerve. Glial overexpression of the downstream kinase PI3K showed similar pathology. Overexpression of activated pvr (platelet-derived growth factor receptor/vascular endothelial growth factor receptor homolog) led to migration of glial cells along the optic nerve, whereas expression of activated htl (fibroblast growth factor receptor 1 homolog) and INR (insulin receptor) showed markedly elevated numbers of glial cells in the optic stalk. The EGFR/phosphatidylinositol 3-phosphate kinase (PI3K) phenotype was partly reverted by the administration of the EGFR tyrosine kinase inhibitor gefitinib and completely rescued by the PI3K inhibitor wortmannin and the Akt inhibitor triciribine. We suggest that Drosophila models will be useful for deciphering signaling cascades underlying abnormal behavior of glioma cells for genetic screens to reveal interacting genes involved in gliomagenesis and for experimental therapy approaches.

Experimental models of hepatocellular carcinoma

Hepatocellular carcinoma (HCC) is a common and deadly cancer whose pathogenesis is incompletely understood. Comparative genomic studies from human HCC samples have classified HCCs into different molecular subgroups; yet, the unifying feature of this tumor is its propensity to arise upon a background of inflammation and fibrosis. This review seeks to analyze the available experimental models in HCC research and to correlate data from human populations with them in order to consolidate our efforts to date, as it is increasingly clear that different models will be required to mimic different subclasses of the neoplasm. These models will be instrumental in the evaluation of compounds targeting specific molecular pathways in future preclinical studies.

Cancer genetics: mouse models of intestinal cancer

The capacity to model cancer within the mouse has advanced significantly in recent years. Perhaps the most notable technical gains have been in the development of techniques that allow the temporal and spatial control of gene expression, so that it is now possible to regulate target genes in the tissue of choice and at a given time [Maddison and Clarke (2005) J. Pathol. 205, 181-193; Shaw and Clarke (2007) DNA Repair 6, 1403-1412; Marsh and Clarke (2007) Expert Rev. Anticancer Ther. 7, 519-531]. We have used these approaches to study tumorigenesis in the murine intestine. Loss of function of the tumour-suppressor gene Apc (adenomatous polyposis coli) has been associated with the development of both human and murine neoplasia, principally those of the intestinal epithelium. However, as Apc has been implicated in multiple cellular functions, the precise mechanisms underlying these associations remain somewhat unclear. I review here the use of an inducible strategy to co-ordinately delete genes from the adult murine epithelium. This approach has allowed a characterization of the direct consequences of inactivation of gene function. For Apc, these include failure in the differentiation programme, failure to migrate, aberrant proliferation and the aberrant induction of apoptosis. Transcriptome analysis of this model has also identified potential new targets for therapeutic intervention, such as Sparc (secreted protein acidic and rich in cysteine), deficiency of which, we have now shown, suppresses adenoma formation. Finally, we have been able to address how other genes modulate the consequences of Apc loss. Thus we show that there is little effect following loss of cyclin D1, Tcf-1 and p53, but that there are marked differences following loss of either c-Myc or Mbd2. The models therefore allow us to define the earliest events associated with carcinogenesis in the intestine.

Tissue-specific transgenic, conditional knockout and knock-in mice of genes in the canonical Wnt signaling pathway

The Wnt signaling pathway plays key roles in the development and homeostasis of a number of organs such as the brain, lung, liver, heart, gastrointestinal tract, mammary gland, skin, and bone, as well as of the immune system. Studies on conventional knockout mice of the genes in the Wnt signaling pathway have revealed its essential roles in these tissues; however, most of these knockout mice die during embryogenesis or soon after birth. Through more advanced techniques such as Cre/loxP and tetracycline-inducible systems, a gene of interest can be expressed or inactivated in a tissue-specific and time-controlled manner. Here we review recent papers on the tissue-specific transgenic, conditional knockout and knock-in mice of the genes in the Wnt signaling pathway In addition to such engineered mice, we also list reporter mice that have been generated to determine the activity of the canonical Wnt signaling pathway in mouse tissues.

Assessment of a chemically induced model of lung squamous cell carcinoma in mice by 18F-FDG small-animal PET

BACKGROUND

Small-animal imaging has become a relevant research field in pre-clinical oncology. In particular, metabolic information provided by small-animal positron emission tomography (PET) is very useful to closely monitor tumour growth and assess therapy response in murine models of human disease. There are various murine models for human lung adenocarcinoma, but those for squamous cell lung carcinoma, the most common form of human cancer, are lacking.

AIM

To assess the feasibility of 18F-FDG small-animal PET to monitor tumour growth in a chemically induced model of squamous cell carcinoma of the lung.

MATERIALS AND METHODS

Nineteen NIH Swiss mice were skin painted by N-nitroso-tris-chloroethylurea (NTCU) twice a week, with a 3 day interval, for 8 months and 10 NIH Swiss mice skin painted with NTCU solvent (acetone) were used as controls. 18F-FDG PET was performed under sevofluorane anaesthesia and oxygen supplementation at 2, 4, 6 and 8 months from initial treatment. Images were assessed by visual analysis and semi-quantitatively. When a diffuse distribution of tumour was noted, the mean of the counts/pixel measured at three lung levels, corrected for the effective dose injected and for decay, was used for comparison between mutagen-painted and control mice. Pathological evaluation was carried out from the time of the first positive PET results in a subgroup of the whole population to assess correlation with PET findings. Small animal CT was performed at 8 months in another subgroup.

RESULTS

In both terms of visual analysis and measurement of total lung activity, 18F-FDG PET at 2 and 4 months from initial treatment were comparable in mutagen-painted and controls. At 6 months, PET images showed a faint and diffuse uptake over both lung fields in mutagen-painted mice with multiple focal areas of increased tracer uptake that merged into confluent masses at 8 months and seriously subverting lung architecture on computed tomography. Total lung activity was significantly higher in mutagen-painted versus control mice at 6 (P=0.00000668) and 8 months (P=0.00000043) from initial treatment and paralleled the progressive lung involvement and histological severity.

CONCLUSIONS

18F-FDG PET may be useful in the assessment of this chemically induced murine model of lung squamous cells carcinoma. The total lung activity may be used as a measure of tumour metabolic activity of the tumour-bearing animals and may be useful in new drug testing studies.

Heat shock-inducible Cre/Lox approaches to induce diverse types of tumors and hyperplasia in transgenic zebrafish

RAS family members are among the most frequently mutated oncogenes in human cancers. Given the utility of zebrafish in both chemical and genetic screens, developing RAS-induced cancer models will make large-scale screens possible to understand further the molecular mechanisms underlying malignancy. We developed a heat shock-inducible Cre/Lox-mediated transgenic approach in which activated human kRASG12D can be conditionally induced within transgenic animals by heat shock treatment. Specifically, double transgenic fish Tg(B-actin-LoxP-EGFP-LoxP-kRASG12D; hsp70-Cre) developed four types of tumors and hyperplasia after heat shock of whole zebrafish embryos, including rhabdomyosarcoma, myeloproliferative disorder, intestinal hyperplasia, and malignant peripheral nerve sheath tumor. Using ex vivo heat shock and transplantation of whole kidney marrow cells from double transgenic animals, we were able to generate specifically kRASG12D-induced myeloproliferative disorder in recipient fish. This heat shock-inducible recombination approach allowed for the generation of multiple types of RAS-induced tumors and hyperplasia without characterizing tissue-specific promoters. Moreover, these tumors and hyperplasia closely resemble human diseases at both the morphologic and molecular levels.

Tumor models for efficacy determination

The first in vivo tumor models were developed in the mid-1960s. These models were mouse leukemia models grown as ascites. The growth pattern was like that of bacteria in vivo and therefore it was possible to apply similar mathematics of growth and response to these tumors as had been worked out for bacteria. Since the development of the murine leukemia models, investigators have devoted a large effort to modeling solid tumors in mice. There are now a variety of models including syngeneic mouse tumors and human tumor xenografts grown as s.c. nodules, syngeneic mouse tumors and human tumor xenografts grown in orthotopic sites, models of disseminated disease, "labeled" tumor models that can be visualized using varied technologies, and transgenic tumor models. Each of these types of models has advantages and disadvantages to the "drug hunter" searching for improved treatments.

Inducible Cre recombinase activity in mouse cerebellar granule cell precursors and inner ear hair cells

A transgenic mouse line expressing the CreER(TM) fusion protein under the control of the Math1 enhancer was generated. Expression of the transgene in the postnatal mouse was restricted to hair cells of the inner ear and granule neurons in the external granule layer of the cerebellum in a temporally regulated manner. Cre activity was virtually nonexistent in uninduced mice; however, treatment of newborn pups with tamoxifen, leading to nuclear translocation of the fusion protein, resulted in efficient recombination at LoxP sites in the appropriate cell types. Up to two thirds of cerebellar granule neurons and 80-90% of cochlear hair cells underwent Cre-specific recombination. This mouse line provides a powerful tool to dissect gene function at early and late stages in development of the cerebellum and inner ear.

Raf kinases: Oncogenesis and drug discovery

Raf kinase signaling has been thoroughly investigated over the last 20 years. A-Raf, B-Raf and C-Raf, the 3 mammalian members of the Raf family, are involved in a variety of cellular processes such as growth, proliferation, survival, differentiation and transformation. The detection of B-RAF mutations in a wide variety of human cancers, the description of wildtype and mutant B-RAF as tumor antigens in melanoma and the promising outcome of clinical trials evaluating the Raf inhibitor Nexavar (Sorafenib, BAY 43-9006) have sparked a broad interest in the scientific community. After a short historical detour and an introduction into Raf kinase signaling, we are going to discuss here recent outcomes of Raf kinase research with respect to tumor formation and give an overview on current efforts to develop anticancer therapies interfering with aberrant Raf kinase signaling.

Sleeping beauty: a novel cancer gene discovery tool

The National Cancer Institute and the National Human Genome Research Institute recently announced a 3-year 100-million-dollar pilot study to use large-scale resequencing of genes in human tumors to identify new cancer genes. The hope is that some of these genes can be used as drug targets for developing better therapeutics for treating cancer. Although this effort will identify new cancer genes, it could be made more efficient by preferentially resequencing genes identified as novel candidate cancer genes in animal models of cancer. Although retroviral insertional mutagenesis has proven to be an effective tool for identifying novel cancer genes in the mouse, these studies are limited by the fact that retroviral mutagenesis primarily induces hematopoietic and mammary cancer, but little else, while the majority of cancers affecting humans are solid tumors. Recently, two groups have shown that sleeping beauty (SB) transposon-based insertional mutagenesis can also identify novel candidate cancer genes in the mouse. Unlike retroviral infection, SB transposition can be controlled to mutagenize any target tissue and thus potentially induce many different kinds of cancer, including solid tumors. SB transposition in animal models of cancer could therefore greatly facilitate the identification of novel human cancer genes and the development of better cancer therapies.

Development of novel cancer chemopreventive agents in Europe--neglected Cinderella or rising phoenix? A critical commentary. ESF Workshop on Cancer Chemoprevention, DKFZ, Heidelberg, September 18-20, 2005

Agents that prevent cancer, delay its onset, or revert premalignant conditions could have dramatic beneficial impacts on human health. Although there is an urgent need to develop cancer chemopreventive agents, researchers in the field suspect that this area of scientific endeavour in Europe leads a Cinderella existence, both in terms of perception of importance and research funding. In order to review current activities in this prevention field and to seek a consensus position, an exploratory workshop was held in September 2005 at the German Cancer Research Center (DKFZ) in Heidelberg, Germany, sponsored mainly by the European Science Foundation (ESF), and also supported by the European Association for Cancer Research (EACR) and the German Cancer Society (DKG). The 35 experts from European countries and the United States of America assessed state-of-the-art cancer chemoprevention research in Europe. The aims that the workshop organizers had pre-defined were: i) assessment of the usefulness of animal models for agent identification; ii) review of ongoing preclinical and clinical work on novel agents; iii) discussion of potential biomarkers predictive for cancer preventive efficacy; and finally iv) the potential role that European pharmaceutical industries could play in furthering chemopreventive agent development. Overall the workshop aimed at raising awareness among European clinical and laboratory researchers of the importance of the development of novel, efficacious and safe cancer preventive agents.