Precancerous lesions upon sporadic activation of beta-catenin in mice

Challenges and Opportunities for the Veterinary Pathologist in Biomedical Research

Animal models have critical roles in biomedical research in promoting understanding of human disease and facilitating development of new therapies and diagnostic techniques to improve human and animal health. In the study of myriad human conditions, each model requires in-depth characterization of its assets and limitations in order for it to be used to greatest advantage. Veterinary pathology expertise is critical in understanding the relevance and translational validity of animal models to conditions under study, assessing morbidity and mortality, and validating outcomes as relevant or not to the study interventions. Clear communication with investigators and education of research personnel on the use and interpretation of pathology endpoints in animal models are critical to the success of any research program. The veterinary pathologist is underutilized in biomedical research due to many factors including misconceptions about high fiscal costs, lack of perceived value, limited recognition of their expertise, and the generally low number of veterinary pathologists currently employed in biomedical research. As members of the multidisciplinary research team, veterinary pathologists have an important role to educate scientists, ensure accurate interpretation of pathology data, maximize rigor, and ensure reproducibility to provide the most reliable data for animal models in biomedical research.

Manipulation of DNA Repair Proficiency in Mouse Models of Colorectal Cancer

Technical and biological innovations have enabled the development of more sophisticated and focused murine models that increasingly recapitulate the complex pathologies of human diseases, in particular cancer. Mouse models provide excellent in vivo systems for deciphering the intricacies of cancer biology within the context of precise experimental settings. They present biologically relevant, adaptable platforms that are amenable to continual improvement and refinement. We discuss how recent advances in our understanding of tumorigenesis and the underlying deficiencies of DNA repair mechanisms that drive it have been informed by using genetically engineered mice to create defined, well-characterized models of human colorectal cancer. In particular, we focus on how mechanisms of DNA repair can be manipulated precisely to create in vivo models whereby the underlying processes of tumorigenesis are accelerated or attenuated, dependent on the composite alleles carried by the mouse model. Such models have evolved to the stage where they now reflect the initiation and progression of sporadic cancers. The review is focused on mouse models of colorectal cancer and how insights from these models have been instrumental in shaping our understanding of the processes and potential therapies for this disease.

Analysis of mouse model pathology: a primer for studying the anatomic pathology of genetically engineered mice

This primer of pathology is intended to introduce investigators to the structure (morphology) of cancer with an emphasis on genetically engineered mouse (GEM) models (GEMMs). We emphasize the necessity of using the entire biological context for the interpretation of anatomic pathology. Because the primary investigator is responsible for almost all of the information and procedures leading up to microscopic examination, they should also be responsible for documentation of experiments so that the microscopic interpretation can be rendered in context of the biology. The steps involved in this process are outlined, discussed, and illustrated. Because GEMMs are unique experimental subjects, some of the more common pitfalls are discussed. Many of these errors can be avoided with attention to detail and continuous quality assurance.

In vivo and in vitro models for the therapeutic targeting of Wnt signaling using a Tet-OΔN89β-catenin system

Although significant progress has been made in understanding the importance of Wnt signaling in the initiation of colorectal cancer, less is known about responses that accompany the reversal of oncogenic Wnt signaling. The aim of this study was to analyze in vivo and in vitro responses to an 'ideal' Wnt pathway inhibitor as a model for the therapeutic targeting of the pathway. A tetracycline-inducible transgenic mouse model expressing truncated β-catenin (ΔN89β-catenin) that exhibited a strong intestinal hyperplasia was analyzed during the removal of oncogenic β-catenin expression both in 3D 'crypt culture' and in vivo. Oncogenic Wnt signaling was rapidly and completely reversed. The strongest inhibition of Wnt target gene expression occurred within 24 h of doxycycline removal at which time the target genes Ascl2, Axin2 and C-myc were downregulated to levels below that in the control intestine. In vitro, the small molecule Wnt inhibitor CCT036477 induced a response within 4 h of treatment. By 7 days following doxycycline withdrawal, gene expression, cell proliferation and tissue morphology were undistinguishable from control animals.In conclusion, these results demonstrate that the reversal of Wnt signaling by inhibitors should ideally be studied within hours of treatment. The reversible system described, involving medium throughput in vitro approaches and rapid in vivo responses, should allow the rapid advance of early stage compounds into efficacy models that are more usually considered later in the drug discovery pipeline.

The evolution of cancer modeling: the shadow of stem cells

Cancer is a complex and highly dynamic process. Genetically engineered mouse models (GEMs) that develop cancer are essential systems for dissecting the processes that lead to human cancer. These animal models provide a means to determine the causes of malignancy and to develop new treatments, thus representing a resource of immense potential for medical oncology. The sophistication of modeling cancer in mice has increased to the extent that now we can induce, study and manipulate the cancer disease process in a manner that is impossible to perform in human patients. However, all GEMs described so far have diverse shortcomings in mimicking the hierarchical structure of human cancer tissues. In recent years, a more detailed picture of the cellular and molecular mechanisms determining the formation of cancer has emerged. This Commentary addresses new experimental approaches toward a better understanding of carcinogenesis and discusses the impact of new animal models.

The adaptive immune response to sporadic cancer

Most of the current experimental cancer models do not reflect the pathophysiology of real-life cancer. Cancer usually occurs sporadically and is clonal in origin. Between tumor initiation and progression, clinically unapparent pre-malignant cells may persist for years or decades in humans. Recently, mouse models of sporadic cancer have been developed. The mouse germ-line can be engineered with high precision so that defined genes can be switched on and off in the adult organism in a targeted manner. Analysis of the immune response against sporadic tumors requires the knowledge of a tumor antigen. Ideally, a silent oncogene, for which the mice are not tolerant, is stochastically activated in individual cells. This approach offers the opportunity to analyze the adaptive immune response throughout the long process of malignant transformation and most closely resembles cancer in humans. In such a model with the highly immunogenic SV40 large T antigen as a dormant oncogene, we discovered that sporadic cancer is recognized by the adaptive immune system at the pre-malignant stage, concomitant with the induction of tumor antigen-specific tolerance. These results demonstrated that even highly immunogenic sporadic tumors are unable to induce functional cytotoxic T lymphocytes. Based on this model, we conclude that immunosurveillance plays little or no role against sporadic cancer and that tumors must not escape immune recognition or destruction.

'One medicine---one pathology': are veterinary and human pathology prepared?

The American Medical Association and the American Veterinary Medical Association have recently approved resolutions supporting 'One Medicine' or 'One Health' that bridge the two professions. The concept is far from novel. Rudolf Virchow, the Father of Modern Pathology, and Sir William Osler, the Father of Modern Medicine, were outspoken advocates of the concept. The concept in its modern iteration was re-articulated in the 1984 edition of Calvin Schwabe's 'Veterinary Medicine and Human Health.' The veterinary and medical pathology professions are steeped in a rich history of 'One Medicine,' but they have paradoxically parted ways, leaving the discipline of pathology poorly positioned to contribute to contemporary science. The time has come for not only scientists but also all pathologists to recognize the value in comparative pathology, the consequences of ignoring the opportunity and, most importantly, the necessity of preparing future generations to meet the challenge inherent in the renewed momentum for 'One Medicine.' The impending glut of new genetically engineered mice creates an urgent need for prepared investigators and pathologists.

Maximizing mouse cancer models

Animal models of cancer provide an alternative means to determine the causes of and treatments for malignancy, thus representing a resource of immense potential for cancer medicine. The sophistication of modelling cancer in mice has increased to the extent that investigators can both observe and manipulate a complex disease process in a manner impossible to perform in patients. However, owing to limitations in model design and technology development, and the surprising underuse of existing models, only now are we realising the full potential of mouse models of cancer and what new approaches are needed to derive the maximum value for cancer patients from this investment.