A simian virus 40 large T-antigen segment containing amino acids 1 to 127 and expressed under the control of the rat elastase-1 promoter produces pancreatic acinar carcinomas in transgenic mice

Altered glycosylation in cancer: A promising target for biomarkers and therapeutics

Glycosylation is a well-regulated cell and microenvironment specific post-translational modification. Several glycosyltransferases and glycosidases orchestrate the addition of defined glycan structures on the proteins and lipids. Recent advances and systemic approaches in glycomics have significantly contributed to a better understanding of instrumental roles of glycans in health and diseases. Emerging research evidence recognized aberrantly glycosylated proteins as the modulators of the malignant phenotype of cancer cells. The Cancer Genome Atlas has identified alterations in the expressions of glycosylation-specific genes that are correlated with cancer progression. However, the mechanistic basis remains poorly explored. Recent researches have shown that specific changes in the glycan structures are associated with 'stemness' and epithelial-to-mesenchymal transition of cancer cells. Moreover, epigenetic changes in the glycosylation pattern make the tumor cells capable of escaping immunosurveillance mechanisms. The deciphering roles of glycans in cancer emphasize that glycans can serve as a source for the development of novel clinical biomarkers. The ability of glycans in intervening various stages of tumor progression and the biosynthetic pathways involved in glycan structures constitute a promising target for cancer therapy. Advances in the knowledge of innovative strategies for identifying the mechanisms of glycan-binding proteins are hoped to hold great potential in cancer therapy. This review discusses the fundamental role of glycans in regulating tumorigenesis and tumor progression and provides insights into the influence of glycans in the current tactics of targeted therapies in the clinical setting.

Heterogeneous Effects of Calorie Content and Nutritional Components Underlie Dietary Influence on Pancreatic Cancer Susceptibility

Pancreatic cancer is a rare but fatal form of cancer, the fourth highest in absolute mortality. Known risk factors include obesity, diet, and type 2 diabetes; however, the low incidence rate and interconnection of these factors confound the isolation of individual effects. Here, we use epidemiological analysis of prospective human cohorts and parallel tracking of pancreatic cancer in mice to dissect the effects of obesity, diet, and diabetes on pancreatic cancer. Through longitudinal monitoring and multi-omics analysis in mice, we found distinct effects of protein, sugar, and fat dietary components, with dietary sugars increasing Mad2l1 expression and tumor proliferation. Using epidemiological approaches in humans, we find that dietary sugars give a MAD2L1 genotype-dependent increased susceptibility to pancreatic cancer. The translation of these results to a clinical setting could aid in the identification of the at-risk population for screening and potentially harness dietary modification as a therapeutic measure.

Animal Models: Challenges and Opportunities to Determine Optimal Experimental Models of Pancreatitis and Pancreatic Cancer

At the 2018 PancreasFest meeting, experts participating in basic research met to discuss the plethora of available animal models for studying exocrine pancreatic disease. In particular, the discussion focused on the challenges currently facing the field and potential solutions. That meeting culminated in this review, which describes the advantages and limitations of both common and infrequently used models of exocrine pancreatic disease, namely, pancreatitis and exocrine pancreatic cancer. The objective is to provide a comprehensive description of the available models but also to provide investigators with guidance in the application of these models to investigate both environmental and genetic contributions to exocrine pancreatic disease. The content covers both nongenic and genetically engineered models across multiple species (large and small). Recommendations for choosing the appropriate model as well as how to conduct and present results are provided.

NOD mice, susceptible to pancreatic autoimmunity, demonstrate delayed growth of pancreatic cancer

Pancreatic cancer is a high mortality form of cancer, with a median survival only six months. There are multiple associated risk factors associated, most importantly type 2 diabetes, obesity, pancreatitis and smoking. The relative rarity of the disease, however, has made it difficult to dissect causative risk factors, especially with related risk factors. A major unanswered question with important therapeutic implications is the effect of immunological responses on pancreatic cancer formation, with data from other cancers suggesting the potential for local immunological responses to either increase cancer development or increase cancer elimination. Due to the rarity and late diagnosis of pancreatic cancer direct epidemiological evidence is lacking, thus necessitating a reliance on animal models. Here we investigated the relationship between pancreatic autoimmunity and cancer by backcrossing the well characterised Ela1-Tag transgenic model of pancreatic cancer onto the pancreatic autoimmune susceptible NOD mouse strain. Through longitudinal magnetic resonance imaging we found that the NOD genetic background delayed the onset of pancreatic tumours and substantially slowed the growth rate of tumours after development. These results suggest that elevated autoimmune surveillance of the pancreas limits tumour formation and growth, identifying pancreatic cancer as a promising target for immune checkpoint blockade therapies that unleash latent autoimmunity.

Establishment of a murine pancreatic cancer pain model and microarray analysis of pain‑associated genes in the spinal cord dorsal horn

There is emerging evidence on the mechanisms of pancreatic cancer pain. Following the establishment of an orthotropic transplantation model of pancreatic cancer, microarray analysis was performed to identify changes in the expression levels of pain-associated genes in the spinal cord. A mouse model of pancreatic cancer-induced pain was established by implanting SW 1990 cells into the pancreases of female BALB/c-nu mice. The survival rate and body weight were measured following orthotropic transplantation. Gross anatomical techniques and hematoxylin and eosin staining were used to analyze the pancreatic tumor tissue. Multiple behavioral tests were also performed to assess pain-associated responses. Additionally, using samples from mice with or without observable pain, microarray analysis was performed to determine the gene expression profiles in the spinal cord dorsal horn. The survival rate of mice with pancreatic cancer was high during the initial 3 weeks post-surgery, although the body weight decreased progressively. Gross anatomical techniques demonstrated that the tumor size increased significantly following the surgery, and this result was confirmed by solid tumor masses in the pancreatic tissues of the mouse model. Observable pain behavioral responses were also examined in the pancreatic cancer model by measuring the mechanical threshold of the abdominal skin, hunching behavior and visceromotor responses. The profiles of 10 pain specific-associated genes in the spinal cord dorsal horn that accurately reflect the molecular pathological progression of disease were also identified. In conclusion, the present study has developed a novel animal model of pancreatic cancer pain in BALB/c-nu mice that resembles human pancreatic cancer pain, and the expression of pain-associated genes in the spinal cord dorsal horn has been profiled. The results of the present study may further the understanding of the molecular mechanisms that mediate pancreatic cancer pain.

No Functional Role for microRNA-342 in a Mouse Model of Pancreatic Acinar Carcinoma

The intronic microRNA (miR)-342 has been proposed as a potent tumor-suppressor gene. miR-342 is found to be downregulated or epigenetically silenced in multiple different tumor sites, and this loss of expression permits the upregulation of several key oncogenic pathways. In several different cell lines, lower miR-342 expression results in enhanced proliferation and metastasis potential, both in vitro and in xenogenic transplant conditions. Here, we sought to determine the function of miR-342 in an in vivo spontaneous cancer model, using the Ela1-TAg transgenic model of pancreatic acinar carcinoma. Through longitudinal magnetic resonance imaging monitoring of Ela1-TAg transgenic mice, either wild-type or knockout for miR-342, we found no role for miR-342 in the development, growth rate, or pathogenicity of pancreatic acinar carcinoma. These results indicate the importance of assessing miR function in the complex physiology of in vivo model systems and indicate that further functional testing of miR-342 is required before concluding it is a bona fide tumor-suppressor-miR.

miR-29a-deficiency does not modify the course of murine pancreatic acinar carcinoma

The development of cancers involves the complex dysregulation of multiple cellular processes. With key functions in simultaneous regulation of multiple pathways, microRNA (miR) are thought to have important roles in the oncogenic formation process. miR-29a is among the most abundantly expressed miR in the pancreas. Together with altered expression in pancreatic cancer cell lines and biopsies, and known oncogenic functions in leukemia, this expression data has identified miR-29a as a key candidate for miR involvement in pancreatic cancer biology. Here we used miR-29a-deficient mice and the TAg model of pancreatic acinar carcinoma to functionally test the role of miR-29a in vivo. We found no impact of miR-29a loss on the development or growth of pancreatic tumours, nor on the survival of tumour-bearing mice. These results suggest that, despite differential expression, miR-29a is oncogenically neutral in the pancreatic acinar carcinoma context. If these results are extended to other models of pancreatic cancer, they would reduce the attractiveness of miR-29a as a potential therapeutic target in pancreatic cancer.

No Effect of Dietary Aspartame or Stevia on Pancreatic Acinar Carcinoma Development, Growth, or Induced Mortality in a Murine Model

Pancreatic cancer has an extremely poor prognosis, largely due to a poor record for early detection. Known risk factors for pancreatic cancer include obesity, diet, and diabetes, implicating glucose consumption and regulation as a key player. The role of artificial sweeteners may therefore be pertinent to disease kinetics. The oncogenic impact of artificial sweeteners is a highly controversial area. Aspartame, one of the most studied food additives, is widely recognized as being generally safe, although there are still specific areas where research is incomplete due to study limitations. Stevia, by contrast, has been the subject of relatively few studies, and the potential health benefits are based on extrapolation rather than direct testing. Here, we used longitudinal tracking of pancreatic acinar carcinoma development, growth, and lethality in a sensitized mouse model. Despite exposure to aspartame and stevia from the in utero stage onward, we found no disease modification activity, in either direction. These results contribute to the data on aspartame and stevia safety, while also reducing confidence in several of the purported health benefits.

Methods to Study Metastasis in Genetically Modified Mice

Metastasis is often modeled by xenotransplantation of cell lines in immunodeficient mice. A wealth of information about tumor cell behavior in the new environment is obtained from these efforts. Yet by design, this approach is "tumor-centric," as it focuses on cell-autonomous determinants of human tumor dissemination in mouse tissues, in effect using the animal body as a sophisticated "Petri dish" providing nutrients and support for tumor growth. Transgenic or gene knockout mouse models of cancer allow the study of tumor spread as a systemic disease and offer a complimentary approach for studying the natural history of cancer. This introduction is aimed at describing the overall methodological approach to studying metastasis in genetically modified mice, with a particular focus on using animals with regulated expression of potent human oncogenes in the breast.

Expression of the small T antigen of Lymphotropic Papovavirus is sufficient to transform primary mouse embryo fibroblasts

Polyomaviruses induce cell proliferation and transformation through different oncoproteins encoded within the early region (ER): large T antigen (LT), small T antigen (sT) and, in some cases, additional components. Each virus utilizes different mechanisms to achieve transformation. For instance, the LTs of Simian virus 40 (SV40), BK and/or JC virus can induce transformation; but Merkel Cell Polyomavirus (MCPyV) requires expression of sT. Lymphotropic Papovavirus (LPV) is closely related to Human Polyomavirus 9 (HuPyV9) and, under similar conditions, mice expressing LPV.ER exhibit higher rates of tumor formation than mice expressing SV40.ER. We have investigated the contributions of individual LPV.ER components to cell transformation. In contrast to SV40, LPV.ER transforms mouse embryonic fibroblasts (MEFs), but expression of LPV LT is insufficient to transform MEFs. Furthermore, LPV sT induces immortalization and transformation of MEFs. Thus, in the case of LPV, sT is the main mediator of oncogenesis.

Human glial chimeric mice reveal astrocytic dependence of JC virus infection

Progressive multifocal leukoencephalopathy (PML) is a demyelinating disease triggered by infection with the human gliotropic JC virus (JCV). Due to the human-selective nature of the virus, there are no animal models available to investigate JCV pathogenesis. To address this issue, we developed mice with humanized white matter by engrafting human glial progenitor cells (GPCs) into neonatal immunodeficient and myelin-deficient mice. Intracerebral delivery of JCV resulted in infection and subsequent demyelination of these chimeric mice. Human GPCs and astrocytes were infected more readily than oligodendrocytes, and viral replication was noted primarily in human astrocytes and GPCs rather than oligodendrocytes, which instead expressed early viral T antigens and exhibited apoptotic death. Engraftment of human GPCs in normally myelinated and immunodeficient mice resulted in humanized white matter that was chimeric for human astrocytes and GPCs. JCV effectively propagated in these mice, which indicates that astroglial infection is sufficient for JCV spread. Sequencing revealed progressive mutation of the JCV capsid protein VP1 after infection, suggesting that PML may evolve with active infection. These results indicate that the principal CNS targets for JCV infection are astrocytes and GPCs and that infection is associated with progressive mutation, while demyelination is a secondary occurrence, following T antigen-triggered oligodendroglial apoptosis. More broadly, this study provides a model by which to further assess the biology and treatment of human-specific gliotropic viruses.

Targeted therapy of spontaneous murine pancreatic tumors by polymeric micelles prolongs survival and prevents peritoneal metastasis

Nanoscaled drug-loaded carriers are of particular interest for efficient tumor therapy as numerous studies have shown improved targeting and efficacy. Nevertheless, most of these studies have been performed against allograft and xenograft tumor models, which have altered microenvironment features affecting the accumulation and penetration of nanocarriers. Conversely, the evaluation of nanocarriers on genetically engineered mice, which can gradually develop clinically relevant tumors, permits the validation of their design under normal processes of immunity, angiogenesis, and inflammation. Therefore, considering the poor prognosis of pancreatic cancer, we used the elastase 1-promoted luciferase and Simian virus 40 T and t antigens transgenic mice, which develop spontaneous bioluminescent pancreatic carcinoma, and showed that long circulating micellar nanocarriers, incorporating the parent complex of oxaliplatin, inhibited the tumor growth as a result of their efficient accumulation and penetration in the tumors. The reduction of the photon flux from the endogenous tumor by the micelles correlated with the decrease of serum carbohydrate-associated antigen 19-9 marker. Micelles also reduced the incidence of metastasis and ascites, extending the survival of the transgenic mice.

Large T antigens of polyomaviruses: amazing molecular machines

The large tumor antigen (T antigen) encoded by simian virus 40 is an amazing molecular machine because it orchestrates viral infection by modulating multiple fundamental viral and cellular processes. T antigen is required for viral DNA replication, transcription, and virion assembly. In addition, T antigen targets multiple cellular pathways, including those that regulate cell proliferation, cell death, and the inflammatory response. Ectopic T antigen expression results in the immortalization and transformation of many cell types in culture and T antigen induces neoplasia when expressed in rodents. The analysis of the mechanisms by which T antigen carries out its many functions has proved to be a powerful way of gaining insights into cell biology. The accelerating pace at which new polyomaviruses are being discovered provides a collection of novel T antigens that, like simian virus 40, can be used to discover and study key cellular regulatory systems.

Update on human polyomaviruses and cancer

Over 50 years of polyomavirus research has produced a wealth of insights into not only general biologic processes in mammalian cells, but also, how conditions can be altered and signaling systems tweaked to produce transformation phenotypes. In the past few years three new members (KIV, WUV, and MCV) have joined two previously known (JCV and BKV) human polyomaviruses. In this review, we present updated information on general virologic features of these polyomaviruses in their natural host, concentrating on the association of MCV with human Merkel cell carcinoma. We further present a discussion on advances made in SV40 as the prototypic model, which has and will continue to inform our understanding about viruses and cancer.

A spontaneous acinar cell carcinoma model for monitoring progression of pancreatic lesions and response to treatment through noninvasive bioluminescence imaging

PURPOSE

We have generated an EL1-luc/TAg transgenic mouse model that develops spontaneous and bioluminescent acinar cell carcinomas. We applied this model to noninvasively monitor tumor development and drug response.

EXPERIMENTAL DESIGN

EL1-luc/TAg transgenic mice of 11 weeks of age were treated with rapamycin (5 mg/kg, i.p.) or vehicle for 6 to 12 weeks. Tumor development was monitored through bioluminescence imaging and necropsy at the study end point.

RESULTS

EL1-luc/TAg transgenic mice showed pancreas-specific bioluminescence signal before tumor progression and produced increasing light emission from the onset of the pancreatic acinar cell carcinomas. The latency of tumor development ranged from 10 to >20 weeks of age in these mice. Progression of the primary acinar cell carcinoma was accompanied by emergence of metastatic lesions in the abdominal organs, including liver and gastrointestinal fat tissues. Rapamycin treatment suppressed tumor development.

CONCLUSIONS

The EL1-luc/TAg mouse provides a noninvasive approach for monitoring spontaneous acinar cell carcinoma development and comprises a convenient tool for the evaluation of novel therapeutics against pancreatic cancers. Tumor growth suppression through inhibition of the mammalian target of rapamycin pathway further validates this model as clinically relevant.

T antigen transgenic mouse models

The study of polyomavirus has benefited immensely from two scientific methodologies, cell culture and in vitro studies on one side and the use of transgenic mice as experimental models on the other. Both approaches allowed us to identify cellular products targeted by the viruses, the consequences of these interactions at the phenotypic and molecular level, and thus the potential roles of the targets within their normal cellular context. In particular, cell culture and in vitro reports suggest a model explaining partially how SV40 large T antigen contributes to oncogenic transformation. In most cases, T antigen induces cell cycle entry by inactivation of the Rb proteins (pRb, p130, and p107), thus activating E2F-dependent transcription and subsequent S-phase entry. Simultaneously, T antigen blocks p53 activity and therefore prevents the ensuing cell-cycle arrest and apoptosis. For the most part, studies of T antigen expression in transgenic mice support this model, but the use of T antigen mutants and their expression in different tissue and cell type settings have expanded our knowledge of the model system and raised important questions regarding tumorigenic mechanisms functioning in vivo.

SV40: Cell transformation and tumorigenesis

The story of SV40-induced tumorigenesis and cellular transformation is intimately entwined with the development of modern molecular biology. Because SV40 and other viruses have small genomes and are relatively easy to manipulate in the laboratory, they offered tractable systems for molecular analysis. Thus, many of the early efforts to understand how eukaryotes replicate their DNA, regulate expression of their genes, and translate mRNA were focused on viral systems. The discovery that SV40 induces tumors in certain laboratory animals and transforms many types of cultured cells offered the first opportunity to explore the molecular basis for cancer. The goal of this article is to highlight some of the experiments that have led to our current view of SV40-induced transformation and to provide some context as to how they contributed to basic research in molecular biology and to our understanding of cancer.

CD8+ T cells targeting a single immunodominant epitope are sufficient for elimination of established SV40 T antigen-induced brain tumors

Immunotherapy of established solid tumors is rarely achieved, and the mechanisms leading to success remain to be elucidated. We previously showed that extended control of advanced-stage autochthonous brain tumors is achieved following adoptive transfer of naive C57BL/6 splenocytes into sublethally irradiated line SV11 mice expressing the SV40 T Ag (T Ag) oncoprotein, and was associated with in vivo priming of CD8(+) T cells (T(CD8)) specific for the dominant epitope IV (T Ag residues 404-411). Using donor lymphocytes derived from mice that are tolerant to epitope IV or a newly characterized transgenic mouse line expressing an epitope IV-specific TCR, we show that epitope IV-specific T(CD8) are a necessary component of the donor pool and that purified naive epitope IV-specific T(CD8) are sufficient to promote complete and rapid regression of established tumors. While transfer of naive TCR-IV cells alone induced some initial tumor regression, increased survival of tumor-bearing mice required prior conditioning of the host with a sublethal dose of gamma irradiation and was associated with complete tumor eradication. Regression of established tumors was associated with rapid accumulation of TCR-IV T cells within the brain following initial priming against the endogenous T Ag in the peripheral lymphoid organs. Additionally, persistence of functional TCR-IV cells in both the brain and peripheral lymphoid organs was associated with long-term tumor-free survival. Finally, we show that production of IFN-gamma, but not perforin or TNF-alpha, by the donor lymphocytes is critical for control of autochthonous brain tumors.

Molecular genetics of pancreatic ductal adenocarcinomas and recent implications for translational efforts

Pancreatic ductal adenocarcinoma (ie, pancreatic cancer) is among the most devastating of human malignancies. It is commonly diagnosed at advanced, already metastatic, and, hence, incurable stages. Despite extensive research efforts in recent decades, pancreatic cancer remains resistant to almost all clinically available therapy regimens. Recent advances in our understanding of the underlying pathophysiology and molecular biology have opened up avenues for the development of novel diagnostic and therapeutic strategies, some of which have shown highly promising preclinical results and are currently being translated into clinical application. Here in we present a review of recent literature on the molecular genetics of pancreatic cancer and emphasize clinical implications for the development of novel diagnostic and therapeutic approaches.

Intestinal hyperplasia induced by simian virus 40 large tumor antigen requires E2F2

The simian virus 40 large T antigen contributes to neoplastic transformation, in part, by targeting the Rb family of tumor suppressors. There are three known Rb proteins, pRb, p130, and p107, all of which block the cell cycle by preventing the transcription of genes regulated by the E2F family of transcription factors. T antigen interacts directly with Rb proteins and disrupts Rb-E2F complexes both in vitro and in cultured cells. Consequently, T antigen is thought to inhibit transcriptional repression by the Rb family proteins by disrupting their interaction with E2F proteins, thus allowing E2F-dependent transcription and the expression of cellular genes needed for entry into S phase. This model predicts that active E2F-dependent transcription is required for T-antigen-induced transformation. To test this hypothesis, we have examined the status of Rb-E2F complexes in murine enterocytes. Previous studies have shown that T antigen drives enterocytes into S phase, resulting in intestinal hyperplasia, and that the induction of enterocyte proliferation requires T-antigen binding to Rb proteins. In this paper, we show that normal growth-arrested enterocytes contain p130-E2F4 complexes and that T-antigen expression destroys these complexes, most likely by stimulating p130 degradation. Furthermore, unlike their normal counterparts, enterocytes expressing T antigen contain abundant levels of E2F2 and E2F3a. Concomitantly, T-antigen-induced intestinal proliferation is reduced in mice lacking either E2F2 alone or both E2F2 and E2F3a, but not in mice lacking E2F1. These studies support a model in which T antigen eliminates Rb-E2F repressive complexes so that specific activator E2Fs can drive S-phase entry.

Tumor antigen-based immunotherapy and immunoprevention of cancer

Any approach to the treatment and prevention of cancer must face the daunting reality that each cancer may be as individual as the patient in whom it has evolved. The challenge is also to develop a therapy that would eradicate that which is abnormal while preserving what is normal. For many years, therapies have been sought that could target a specific abnormal cancerous processes, such as rapid division or increased vascular flow, but with only limited success. Unfortunately, these successes have also been accompanied by varying degrees of toxicity and there is currently no standard therapy that can eradicate clinical disease and prevent recurrence while leaving normal tissue unharmed. However, approaches directed towards manipulating tumor-specific immunity hold promise for effective treatment and lasting cure. These approaches are based on the exceptional specificity of the immune system, the potential for long-term protective memory, and the accumulated evidence that affected individuals have spontaneous immune responses against their own tumors.

Endogenous opioids inhibit early-stage pancreatic pain in a mouse model of pancreatic cancer

BACKGROUND & AIMS

The endogenous opioid system is involved in modulating the experience of pain, the response to stress, and the action of analgesic therapies. Recent human imaging studies have shown a significant tonic modulation of visceral pain, raising the question of whether endogenous opioids tonically modulate the pain of visceral cancer.

METHODS

Transgenic mice expressing the first 127 amino acids of simian virus 40 large T antigen, under the control of the rat elastase-1 promoter, that spontaneously develop pancreatic cancer were used to investigate the role of endogenous opioids in the modulation of pancreatic cancer pain. Visceral pain behaviors were assessed as degree of hunching and vocalization.

RESULTS

Although mice with late-stage pancreatic cancer displayed spontaneous, morphine-reversible, visceral pain-related behaviors such as hunching and vocalization, these behaviors were absent in mice with early-stage pancreatic cancer. After systemic administration of the central nervous system (CNS)-penetrant opioid receptor antagonists naloxone or naltrexone, mice with early-stage pancreatic cancer displayed significant visceral pain-related behaviors, whereas systemic administration of the CNS-nonpenetrant opioid antagonist naloxone-methiodide did not induce an increase in visceral pain behaviors.

CONCLUSIONS

Our findings suggest that a CNS opioid-dependent mechanism tonically modulates early and late-stage pancreatic cancer pain. Understanding the mechanisms that mask this pain in early stage disease and drive this pain in late-stage disease may allow improved diagnosis, treatment, and care of patients with pancreatic cancer.

A quantitative analysis of the sensory and sympathetic innervation of the mouse pancreas

Pain from pancreatitis or pancreatic cancer can be both chronic and severe although little is known about the mechanisms that generate and maintain this pain. To define the peripheral sensory and sympathetic fibers involved in transmitting and modulating pancreatic pain, immunohistochemistry and confocal microscopy were used to examine the sensory and sympathetic innervation of the head, body and tail of the normal mouse pancreas. Myelinated sensory fibers were labeled with an antibody raised against 200 kD neurofilament H (clone RT97), thinly myelinated and unmyelinated peptidergic sensory fibers were labeled with antibodies raised against calcitonin gene-related peptide (CGRP) and post-ganglionic sympathetic fibers were labeled with an antibody raised against tyrosine hydroxylase (TH). RT97, CGRP, and TH immunoreactive fibers were present in parenchyma of the head, body and tail of the pancreas with the relative density of both RT97 and CGRP expressing fibers being head>body>tail, whereas for TH, a relatively even distribution was observed. In all three regions of the pancreas, RT97 fibers were associated mainly with large blood vessels, the CGRP fibers were associated with the large- and medium-sized blood vessels and the TH were associated with the large- and medium-sized blood vessels as well as capillaries. In addition to this extensive set of sensory and sympathetic nerve fibers that terminate in the pancreas, there were large bundles of en passant nerve fibers in the dorsal region of the pancreas that expressed RT97 or CGRP and were associated with the superior mesenteric plexus. These data suggest the pancreas receives a significant sensory and sympathetic innervation. Understanding the factors and disease states that sensitize and/or directly excite the nerve fibers that terminate in the pancreas as well as those that are en passant may aid in the development of therapies that more effectively modulate the pain that frequently accompanies diseases of the pancreas, such as pancreatitis and pancreatic cancer.

SV40 large T antigen targets multiple cellular pathways to elicit cellular transformation

DNA tumor viruses such as simian virus 40 (SV40) express dominant acting oncoproteins that exert their effects by associating with key cellular targets and altering the signaling pathways they govern. Thus, tumor viruses have proved to be invaluable aids in identifying proteins that participate in tumorigenesis, and in understanding the molecular basis for the transformed phenotype. The roles played by the SV40-encoded 708 amino-acid large T antigen (T antigen), and 174 amino acid small T antigen (t antigen), in transformation have been examined extensively. These studies have firmly established that large T antigen's inhibition of the p53 and Rb-family of tumor suppressors and small T antigen's action on the pp2A phosphatase, are important for SV40-induced transformation. It is not yet clear if the Rb, p53 and pp2A proteins are the only targets through which SV40 transforms cells, or whether additional targets await discovery. Finally, expression of SV40 oncoproteins in transgenic mice results in effects ranging from hyperplasia to invasive carcinoma accompanied by metastasis, depending on the tissue in which they are expressed. Thus, the consequences of SV40 action on these targets depend on the cell type being studied. The identification of additional cellular targets important for transformation, and understanding the molecular basis for the cell type-specific action of the viral T antigens are two important areas through which SV40 will continue to contribute to our understanding of cancer.

Pancreatic cancer pain and its correlation with changes in tumor vasculature, macrophage infiltration, neuronal innervation, body weight and disease progression

To begin to understand the relationship between disease progression and pain in pancreatic cancer, transgenic mice that develop pancreatic cancer due to the expression of the simian virus 40 large T antigen under control of the rat elastase-1 promoter were examined. In these mice precancerous cellular changes were evident at 6 weeks and these included an increase in: microvascular density, macrophages that express nerve growth factor and the density of sensory and sympathetic fibers that innervate the pancreas, with all of these changes increasing with tumor growth. In somatic tissue such as skin, the above changes would be accompanied by significant pain; however, in mice with pancreatic cancer, changes in pain-related behaviors, such as morphine-reversible severe hunching and vocalization only became evident at 16 weeks of age, by which time the pancreatic cancer was highly advanced. These data suggest that in mice as well as humans, there is a stereotypic set of pathological changes that occur as pancreatic cancer develops, and while weight loss generally tracks disease progression, there is a significant lag between disease progression and behaviors indicative of pancreatic cancer pain. Defining the mechanisms that mask this pain in early and mid-stage disease and drive the pain in late-stage disease may aid in earlier diagnosis, survival, and increased quality of life of patients with pancreatic cancer.

Inefficient cross-presentation limits the CD8+ T cell response to a subdominant tumor antigen epitope

CD8(+) T lymphocytes (T(CD8)) responding to subdominant epitopes provide alternate targets for the immunotherapy of cancer, particularly when self-tolerance limits the response to immunodominant epitopes. However, the mechanisms that promote T(CD8) subdominance to tumor Ags remain obscure. We investigated the basis for the lack of priming against a subdominant tumor epitope following immunization of C57BL/6 (B6) mice with SV40 large tumor Ag (T Ag)-transformed cells. Immunization of B6 mice with wild-type T Ag-transformed cells primes T(CD8) specific for three immunodominant T Ag epitopes (epitopes I, II/III, and IV) but fails to induce T(CD8) specific for the subdominant T Ag epitope V. Using adoptively transferred T(CD8) from epitope V-specific TCR transgenic mice and immunization with T Ag-transformed cells, we demonstrate that the subdominant epitope V is weakly cross-presented relative to immunodominant epitopes derived from the same protein Ag. Priming of naive epitope V-specific TCR transgenic T(CD8) in B6 mice required cross-presentation by host APC. However, robust expansion of these T(CD8) required additional direct presentation of the subdominant epitope by T Ag-transformed cells and was only significant following immunization with T Ag-expressing cells lacking the immunodominant epitopes. These results indicate that limited cross-presentation coupled with competition by immunodominant epitope-specific T(CD8) contributes to the subdominant nature of a tumor-specific epitope. This finding has implications for vaccination strategies targeting T(CD8) responses to cancer.

Mouse models expressing human carcinoembryonic antigen (CEA) as a transgene: evaluation of CEA-based cancer vaccines

In recent years, investigators have carried out several studies designed to evaluate whether human tumor-associated antigens might be exploited as targets for active specific immunotherapy, specifically human cancer vaccines. Not too long ago such an approach would have been met with considerable skepticism because the immune system was believed to be a rigid discriminator between self and non-self which, in turn, protected the host from a variety of pathogens. That viewpoint has been challenged in recent years by a series of studies indicating that antigenic determinants of self have not induced absolute host immune tolerance. Moreover, under specific conditions that evoke danger signals, peptides from self-antigen can be processed by the antigen-presenting cellular machinery, loaded onto the major histocompatibility antigen groove to serve as targets for immune intervention. Those findings provide the rationale to investigate a wide range of tumor-associated antigens, including differentiation antigens, oncogenes, and tumor suppressor genes as possible immune-based targets. One of those tumor-associated antigens is the carcinoembryonic antigen (CEA). Described almost 40 years ago, CEA is a M(r) 180-200,000 oncofetal antigen that is one of the more widely studied human tumor-associated antigens. This review will provide: (i) a brief overview of the CEA gene family, (ii) a summary of early preclinical findings on overcoming immune tolerance to CEA, and (iii) the rationale to develop mouse models which spontaneously develop gastrointestinal tumors and express the CEA transgene. Those models have been used extensively in the study of overcoming host immune tolerance to CEA, a self, tumor-associated antigen, and the experimental findings have served as the rationale for the design of early clinical trials to evaluate CEA-based cancer vaccines.

Intestinal dysplasia induced by simian virus 40 T antigen is independent of p53

Transgenic mice expressing simian virus 40 large T antigen in enterocytes develop intestinal hyperplasia that progresses to dysplasia with age. Hyperplasia is dependent on T antigen binding to the retinoblastoma (pRb) family of tumor suppressor proteins. Mice expressing a truncated T antigen that inactivates the pRb-family, but is defective for binding p53, exhibit hyperplasia but do not progress to dysplasia. We hypothesized that the inhibition of the pRb family leads to entry of enterocytes into the cell cycle, resulting in hyperplasia, while inactivation of p53 is required for progression to dysplasia. Therefore, we examined T antigen/p53 complexes from the intestines of transgenic mice. We found that T antigen did not induce p53 stabilization, and we could not detect T antigen/p53 complexes in villus enterocytes. In contrast, T antigen expression led to a large increase in the levels of the cyclin-dependent kinase inhibitor p21. Furthermore, mice in which pRb was inactivated by a truncated T antigen in a p53 null background exhibited intestinal hyperplasia but no progression to dysplasia. These data indicate that loss of p53 function does not play a role in T antigen-induced dysplasia in the intestine. Rather, some unknown function of T antigen is essential for progression beyond hyperplasia.

Tissue plasminogen activator in murine exocrine pancreas cancer: selective expression in ductal tumors and contribution to cancer progression

Tissue plasminogen activator (tPA) is absent from normal human pancreas and is expressed in 95% of human pancreatic adenocarcinomas. We have analyzed the expression of components of the tPA system in murine pancreatic tumors and the role of tPA in neoplastic progression. Transgenic mice expressing T antigen and c-myc under the control of the elastase promoter (Ela1-TAg and Ela1-myc, respectively) were used. tPA was undetectable in normal pancreas, acinar dysplasia, ductal complexes, and in all acinar tumors. By contrast, it was consistently detected in Ela1-myc tumors showing ductal differentiation. Crossing transgenic Ela1-myc with tPA-/- mice had no effect on the proportion of ductal tumors, indicating that tPA is not involved in the acinar-to-ductal transition. Ela1-myc:tPA-/- mice showed an increased survival in comparison to control mice. All ductal tumors, and none of the acinar tumors, overexpressed the tPA receptor annexin A2, suggesting its participation in the effects mediated by tPA. Our findings indicate that murine and human pancreatic ductal tumors share molecular alterations in the tPA system that may play a role in tumor progression.

In vivo ligation of CD40 enhances priming against the endogenous tumor antigen and promotes CD8+ T cell effector function in SV40 T antigen transgenic mice

The ability to initiate and sustain CD8(+) T cell responses to tumors in vivo is hindered by the development of peripheral T cell tolerance against tumor-associated Ags. Approaches that counter the onset of T cell tolerance may preserve a pool of potentially tumor-reactive CD8(+) T cells. Administration of agonist Ab to the CD40 molecule, expressed on APCs, can enhance immunization approaches targeting T lymphocytes in an otherwise tolerance-prone environment. In this report, the effects of anti-CD40 administration on priming of naive CD8(+) T cells against an endogenous tumor Ag were investigated. Line 501 mice express the SV40 large T Ag oncoprotein as a transgene from the alpha-amylase promoter, resulting in the development of peripheral CD8(+) T cell tolerance to the H-2-D(b)-restricted immunodominant epitope I of T Ag by 6 mo of age, before the appearance of osteosarcomas. We demonstrate that naive epitope I-specific TCR transgenic (TCR-I) T cells undergo peripheral tolerance following adoptive transfer into 6-mo-old 501 mice. In contrast, administration of agonistic anti-CD40 Ab led to increased expansion of TCR-I T cells in 501 mice, the acquisition of effector function by TCR-I T cells and the establishment of T cell memory. Importantly, this enhanced priming effect of anti-CD40 administration did not require immunization and was effective even if administered after naive TCR-I T cells had encountered the endogenous T Ag. Thus, anti-CD40 administration can block the onset of peripheral tolerance and enhance the recruitment of functionally competent effector T cells toward an endogenous tumor Ag.

Mucins in gastrointestinal cancers

The mucin family has been under study by molecular biologists, biochemists, pathologists and immunologists interested in cancer because of the role these molecules can play in the diagnosis and treatment of cancer. Immense knowledge has been accumulated, but the high speed of progress in the laboratory has not been matched by the progress towards applying this knowledge in the clinic. For example, specific knowledge of cancer-associated changes in the expression and glycosylation of various mucins, which can aid in the diagnosis as well as prognosis of GI cancers, has not yet led to the use of a panel of anti-mucin antibodies as a standard diagnostic tool. Similarly, many more opportunities exist for using mucin-based therapies than are currently being considered in the clinic. This chapter aimed to highlight some of these opportunities and to interest clinician scientists in exploring them in the near future.

Dendritic cell-tumor cell fusion and staphylococcal enterotoxin B treatment in a pancreatic tumor model

BACKGROUND

Surgical resection of pancreatic tumors removes gross disease but not metastases. Adjuvant therapy such as chemotherapy and radiation treatment is of little value in metastatic pancreatic cancer. The hypothesis of this investigation is that specific and effective immunotherapeutic vaccine (dendritic/tumor cell fusion) will activate cytotoxic T lymphocytes (CTLs), leading to the eradication of spontaneous pancreatic cancer.

METHODS

We have developed a double transgenic mouse model (MET) that forms spontaneous pancreatic tumors and expresses the human MUC1 antigen. Seven-week-old MET mice (n = 8) were treated every 3 weeks with the vaccine. In addition, these mice received 50 microg of superantigen staphylococcal enterotoxin B (SEB), a known T cell stimulant, prior to the first vaccination. A second treatment group received SEB alone (n = 8) and controls received no treatment (n = 9). MUC1-specific CTLs were measured by chromium release assay. At 10 weeks of age and at necropsy, MUC1 serum levels were measured using a MUC1-specific ELISA.

RESULTS

Mice were known to harbor microscopic foci of cancer at birth. Survival was enhanced in vaccine as well as SEB-treated mice (75% CI +/- 0.42) compared to controls (11% CI +/- 0.28) and both groups of treated mice exhibited mature CTLs without in vitro stimulation. MUC1 serum levels of the vaccine group were 50% less than that of control (P < 0.04) at 10 weeks. MUC1 serum levels directly correlated with tumor weight at necropsy (r = 0.86).

CONCLUSIONS

This is the first evidence that MUC1-specific CTLs can be stimulated to enhance survival in a spontaneous tumor model.

Simian virus 40 large T antigen and two independent T-antigen segments sensitize cells to apoptosis following genotoxic damage

The simian virus 40 (SV40) large tumor (T) antigen is sufficient to transform cells in cultures and induce tumors in experimental animals. Transformation of primary cells in cultures requires both overcoming growth arrest by stimulating the cell cycle and blocking cell death activities presumably activated by oncogene-mediated hyperproliferation signals. The study presented here examined the ability of specific regions and activities of T antigen to modulate apoptosis in cells treated with the genotoxic agent 5-fluorouracil (5-FU). The results showed that the expression of full-length T antigen rendered rat embryo fibroblasts (REF) sensitive to 5-FU-induced apoptosis. Thus, neither the p53-binding region nor the Bcl-2 homology region of T antigen was sufficient to prevent cell death induced by the DNA-damaging agent. T-antigen-mediated sensitization occurred independently of retinoblastoma protein or p53 and p300 binding. An N-terminal segment containing the first 127 T-antigen amino acids (T1-127) was sufficient to sensitize cells. A C-terminal segment consisting of T-antigen amino acids 251 to 708 (T251-708) also sensitized cells to 5-FU-induced apoptosis. This sensitization did not occur when T251-708 was targeted to the nucleus by inclusion of the SV40 nuclear localization signal. The introduction of mutations into the T-antigen J domain resulted in mutation-specific and variable inhibition of apoptosis. This result suggested that either the structural or the functional integrity of the J domain is required to sensitize cells to apoptosis. Treatment of REF or REF expressing full-length T antigen, an N-terminal segment, or T251-708 resulted in increased expression of the p53-responsive MDM2 gene; apoptosis occurred through a p53-dependent pathway, as p53-null cells expressing these T antigens were resistant to 5-FU-induced apoptosis. Possible mechanisms involved in sensitizing cells to a p53-dependent apoptosis pathway in spite of the ability of T antigen to bind and inactivate the transcriptional transactivating activity of p53 are discussed.

T antigens of simian virus 40: molecular chaperones for viral replication and tumorigenesis

Simian virus 40 (SV40) is a small DNA tumor virus that has been extensively characterized due to its relatively simple genetic organization and the ease with which its genome is manipulated. The large and small tumor antigens (T antigens) are the major regulatory proteins encoded by SV40. Large T antigen is responsible for both viral and cellular transcriptional regulation, virion assembly, viral DNA replication, and alteration of the cell cycle. Deciphering how a single protein can perform such numerous and diverse functions has remained elusive. Recently it was established that the SV40 T antigens, including large T antigen, are molecular chaperones, each with a functioning DnaJ domain. The molecular chaperones were originally identified as bacterial genes essential for bacteriophage growth and have since been shown to be conserved in eukaryotes, participating in an array of both viral and cellular processes. This review discusses the mechanisms of DnaJ/Hsc70 interactions and how they are used by T antigen to control viral replication and tumorigenesis. The use of the DnaJ/Hsc70 system by SV40 and other viruses suggests an important role for these molecular chaperones in the regulation of the mammalian cell cycle and sheds light on the enigmatic SV40 T antigen-a most amazing molecule.

Regions and activities of simian virus 40 T antigen that cooperate with an activated ras oncogene in transforming primary rat embryo fibroblasts

Prolonged expression of a ras oncogene in primary cells accelerates the natural process of senescence. This ras-induced permanent growth arrest is bypassed in cells expressing the simian virus 40 large T antigen. Previously we showed that two regions of T antigen, a region consisting of the N-terminal 147 amino acids and a region consisting of amino acids 251 to 708 (T251-708), independently overcome ras-induced senescence. Coexpression of either T-antigen fragment and Ras results in the appearance of dense foci of transformed cells. Using a series of mutants that produce shorter T-antigen fragments, we show that the C-terminal limit of the N-terminal T-antigen fragment that cooperates with Ras lies between amino acids 83 and 121. The N-terminal limit of the C-terminal T-antigen fragment lies between amino acids 252 and 271. In addition, we present evidence that cooperation between the N-terminal fragment and Ras depends upon an intact T-antigen J domain and the ability of the T antigen to bind and inactivate the growth-suppressive effect of the tumor suppressor Rb. Introduction of specific amino acid substitutions surrounding residue 400 into T251-708 prevented the fragment from cooperating with Ras. T251-708 proteins with these same substitutions inhibited the transcriptional transactivating potential of p53 as effectively as did the wild-type protein. Thus, at least one activity contained within T251-708, other than inactivating p53 as a transcriptional transactivator, is likely to be required to bypass Ras-induced senescence.

MUC1-specific CTLs are non-functional within a pancreatic tumor microenvironment

Pancreatic cancer is a highly aggressive, treatment refractory disease and is the fourth leading cause of death in the United States. In humans, 90% of pancreatic adenocarcinomas over-express altered forms of a tumor-associated antigen, MUC1 (an epithelial mucin glycoprotein), which is a target for immunotherapy. Using a clinically relevant mouse model of pancreas cancer that demonstrates peripheral and central tolerance to human MUC1 and develops spontaneous tumors of the pancreas, we have previously reported the presence of functionally active, low affinity, MUC1-specific precursor cytotoxic T cells (pCTLs). Hypothesis for this study is that MUC1-based immunization may enhance the low level MUC1-specific immunity that may lead to an effective anti-tumor response. Data demonstrate that MUC1 peptide-based immunization elicits mature MUC1-specific CTLs in the peripheral lymphoid organs. The mature CTLs secrete IFN-gamma and are cytolytic against MUC1-expressing tumor cells in vitro. However, active CTLs that infiltrate the pancreas tumor microenvironment become cytolytically anergic and are tolerized to MUC1 antigen, allowing the tumor to grow. We demonstrate that the CTL tolerance could be reversed at least in vitro with the use of anti-CD40 co-stimulation. The pancreas tumor cells secrete immunosuppressive cytokines, including IL-10 and TGF-beta that are partly responsible for the down-regulation of CTL activity. In addition, they down-regulate their MHC class I molecules to avoid immune recognition. CD4+ CD25+ T regulatory cells, which secrete IL-10, were also found in the tumor environment. Together these data indicate the use of several immune evasion mechanisms by tumor cells to evade CTL killing. Thus altering the tumor microenvironment to make it more conducive to CTL killing may be key in developing a successful anti-cancer immunotherapy.

Spontaneous adenocarcinoma mouse models for immunotherapy

Recent discoveries regarding the identification of tumor-associated antigens and antigen presentation have made successful immunotherapy strategies possible with little, if any, toxicity. Here, we describe transgenic mammary, pancreas, prostate, stomach and lung adenocarcinoma animal models that can be used to study various immunotherapeutic strategies. The challenge in developing a tumor vaccine is effective antigen presentation that elicits anti-tumor immune responses without precipitating autoimmunity. Clinical trials must be preceded by appropriate animal studies to demonstrate that the concepts can be translated into efficacious therapy for cancer. Although many xenograph or transplantable tumor models have been used, the most effective studies are in spontaneous tumor models. These models are clinically relevant, as tumors arise in an appropriate tissue background and in a host conditioned by the physiological events of neoplastic progression and tumorigenesis and in the context of a viable immune system.

Mice with spontaneous pancreatic cancer naturally develop MUC-1-specific CTLs that eradicate tumors when adoptively transferred

Pancreatic cancer is a highly aggressive, treatment refractory cancer and is the fourth leading cause of death in the United States. In humans, 90% of pancreatic adenocarcinomas overexpress altered forms of a tumor-specific Ag, mucin 1 (MUC1; an epithelial mucin glycoprotein), which is a potential target for immunotherapy. We have established a clinically relevant animal model for pancreatic cancer by developing a double transgenic mouse model (called MET) that expresses human MUC1 as self molecule and develops spontaneous tumors of the pancreas. These mice exhibit acinar cell dysplasia at birth, which progresses to microadenomas and acinar cell carcinomas. The tumors express large amounts of underglycosylated MUC1 similar to humans. Tumor-bearing MET mice develop low affinity MUC1-specific CTLs that have no effect on the spontaneously occurring pancreatic tumors in vivo. However, adoptive transfer of these CTLs was able to completely eradicate MUC1-expressing injectable tumors in MUC1 transgenic mice, and these mice developed long-term immunity. These CTLs were MHC class I restricted and recognized peptide epitopes in the immunodominant tandem repeat region of MUC1. The MET mice appropriately mimic the human condition and are an excellent model with which to elucidate the native immune responses that develop during tumor progression and to develop effective antitumor vaccine strategies.

The N-terminal common domain of simian virus 40 large T and small t antigens acts as a transformation suppressor of the HER-2/neu oncogene

Overexpression of HER-2/neu (also known as c-erbB-2) proto-oncogene frequently occurs in many different types of human cancers, including ovarian carcinoma, and is known to enhance tumor metastasis and chemoresistance. Previous studies showed that inhibition of HER-2/neu expression by various agents, such as adenovirus E1A and simian virus 40 large T, can lead to suppression of tumorigenicity of HER-2/neu-overexpressing cancer cells. Here we report that T/t-common, which contains the N-terminal common domain of simian virus 40 large T and small t antigens, could specifically repress the HER-2/neu promoter. When the coding sequence of T/t-common was stably transfected into the HER-2/neu-overexpressing human ovarian carcinoma SK-OV-3 cells, the expression of HER-2/neu was dramatically reduced by the expression of T/t-common. Accordingly the tumorigenic potential of these T/t-common-expressing clones, including the ability to grow anchorage-independently and the ability to induce tumor in nu/nu mice, was also drastically suppressed. Furthermore, when T/t-common was transiently cotransfected with the activated genomic neu into NIH3T3 cells, the transforming activity of the latter was suppressed by T/t-common in soft-agarose microcolony formation assays. Taken together, these data suggest that T/t-common may act as a transformation suppressor of the HER-2/neu oncogene. Oncogene (2000).

Transactivation of a ribosomal gene by simian virus 40 large-T antigen requires at least three activities of the protein

Simian virus 40 large-T antigen transactivates the ribosomal genes which are transcribed by RNA polymerase (pol I), as well as genes that are dependent on either pol II or pol III. This report identifies regions and activities of T antigen that are required to transactivate a pol I-dependent rat ribosomal gene promoter. By using the rat ribosomal gene (rDNA) promoter linked to a chloramphenicol acetyltransferase gene, we show that at least three separable T-antigen regions are necessary to achieve wild-type levels of transactivation of rDNA in transiently transfected monkey cells. One activity depends on the region of T antigen shared with small-t antigen (T/t common region). A second activity maps to amino acids 109 to 626 and is highly sensitive to mutational inactivation. Complementation analyses suggest that at least one activity in this region is independent of and must be in cis with the activity within the T/t common region. In addition, a functional nuclear localization signal is required for maximal T-antigen-mediated transactivation of rat rDNA. The three activities work in concert to override cellular species-specific controls and transactivate the rat ribosomal gene promoter. Finally, we provide evidence that although the tumor suppressor protein Rb has been shown to repress a pol I-dependent promoter, transactivation of the rat rDNA promoter does not depend on T antigen's ability to bind the tumor suppressor product Rb.