A novel SV40 TAg transgenic model of asbestos-induced mesothelioma: malignant transformation is dose dependent

The MexTAg collaborative cross: host genetics affects asbestos related disease latency, but has little influence once tumours develop

Objectives: This study combines two innovative mouse models in a major gene discovery project to assess the influence of host genetics on asbestos related disease (ARD). Conventional genetics studies provided evidence that some susceptibility to mesothelioma is genetic. However, the identification of host modifier genes, the roles they may play, and whether they contribute to disease susceptibility remain unknown. Here we report a study designed to rapidly identify genes associated with mesothelioma susceptibility by combining the Collaborative Cross (CC) resource with the well-characterised MexTAg mesothelioma mouse model. Methods: The CC is a powerful mouse resource that harnesses over 90% of common genetic variation in the mouse species, allowing rapid identification of genes mediating complex traits. MexTAg mice rapidly, uniformly, and predictably develop mesothelioma, but only after asbestos exposure. To assess the influence of host genetics on ARD, we crossed 72 genetically distinct CC mouse strains with MexTAg mice and exposed the resulting CC-MexTAg (CCMT) progeny to asbestos and monitored them for traits including overall survival, the time to ARD onset (latency), the time between ARD onset and euthanasia (disease progression) and ascites volume. We identified phenotype-specific modifier genes associated with these traits and we validated the role of human orthologues in asbestos-induced carcinogenesis using human mesothelioma datasets. Results: We generated 72 genetically distinct CCMT strains and exposed their progeny (2,562 in total) to asbestos. Reflecting the genetic diversity of the CC, there was considerable variation in overall survival and disease latency. Surprisingly, however, there was no variation in disease progression, demonstrating that host genetic factors do have a significant influence during disease latency but have a limited role once disease is established. Quantitative trait loci (QTL) affecting ARD survival/latency were identified on chromosomes 6, 12 and X. Of the 97-protein coding candidate modifier genes that spanned these QTL, eight genes (CPED1, ORS1, NDUFA1, HS1BP3, IL13RA1, LSM8, TES and TSPAN12) were found to significantly affect outcome in both CCMT and human mesothelioma datasets. Conclusion: Host genetic factors affect susceptibility to development of asbestos associated disease. However, following mesothelioma establishment, genetic variation in molecular or immunological mechanisms did not affect disease progression. Identification of multiple candidate modifier genes and their human homologues with known associations in other advanced stage or metastatic cancers highlights the complexity of ARD and may provide a pathway to identify novel therapeutic targets.

Exploring the Expression of the «Dark Matter» of the Genome in Mesothelioma for Potentially Predictive Biomarkers for Prognosis and Immunotherapy

Recent high-throughput RNA sequencing technologies have confirmed that a large part of the non-coding genome is transcribed. The priority for further investigations is nevertheless generally given in cancer to coding sequences, due to the obvious interest of finding therapeutic targets. In addition, several RNA-sequencing pipelines eliminate repetitive sequences, which are difficult to analyze. In this review, we shall focus on endogenous retroviruses. These sequences are remnants of ancestral germline infections by exogenous retroviruses. These sequences represent 8% of human genome, meaning four-fold the fraction of the genome encoding for proteins. These sequences are generally mostly repressed in normal adult tissues, but pathological conditions lead to their de-repression. Specific mesothelioma-associated endogenous retrovirus expression and their association to clinical outcome is discussed.

Using the Collaborative Cross and Diversity Outbred Mice in Immunology

The Collaborative Cross (CC) and the Diversity Outbred (DO) stock mouse panels are the most powerful murine genetics tools available to the genetics community. Together, they combine the strength of inbred animal models with the diversity of outbred populations. Using the 63 CC strains or a panel of DO mice, each derived from the same 8 parental mouse strains, researchers can map genetic contributions to exceptionally complex immunological and infectious disease traits that would require far greater powering if performed by genome-wide association studies (GWAS) in human populations. These tools allow genes to be studied in heterozygous and homozygous states and provide a platform to study epistasis between interacting loci. Most importantly, once a quantitative phenotype is investigated and quantitative trait loci are identified, confirmatory genetic studies can be performed, which is often problematic using the GWAS approach. In addition, novel stable mouse models for immune phenotypes are often derived from studies utilizing the DO and CC mice that can serve as stronger model systems than existing ones in the field. The CC/DO systems have contributed to the fields of cancer immunology, autoimmunity, vaccinology, infectious disease, allergy, tissue rejection, and tolerance but have thus far been greatly underutilized. In this article, we present a recent review of the field and point out key areas of immunology that are ripe for further investigation and awaiting new CC/DO research projects. We also highlight some of the strong computational tools that have been developed for analyzing CC/DO genetic and phenotypic data. Additionally, we have formed a centralized community on the CyVerse infrastructure where immunogeneticists can utilize those software tools, collaborate with groups across the world, and expand the use of the CC and DO systems for investigating immunogenetic phenomena. © 2022 Wiley Periodicals LLC.

Sera from Patients with Malignant Pleural Mesothelioma Tested Positive for IgG Antibodies against SV40 Large T Antigen: The Viral Oncoprotein

Malignant pleural mesothelioma (MPM), a fatal tumor, is mainly linked to the asbestos exposure. It has been reported that together with the inhalation of asbestos fibers, other factors are involved in the MPM onset, including simian virus 40 (SV40). SV40, a polyomavirus with oncogenic potential, induces (i) in vitro the mesenchymal cell transformation, whereas (ii) in vivo the MPM onset in experimental animals. The association between MPM and SV40 in humans remains to be elucidated. Sera (n = 415) from MPM-affected patients (MPM cohort 1; n = 152) and healthy subjects (HSs, n = 263) were investigated for their immunoglobulin G (IgG) against simian virus 40 large tumor antigen (Tag), which is the transforming protein. Sera were investigated with an indirect enzyme-linked immunosorbent assay (ELISA) using two synthetic peptides from SV40 Tag protein. SV40 Tag protein was evaluated by immunohistochemical (IHC) staining on MPM samples (MPM cohort 2; n = 20). Formalin-fixed and paraffin-embedded (FFPE) samples were obtained from MPM patients unrelated to MPM serum donors. The proportion of sera, from MPM patients, showing antibodies against SV40 Tag (34%) was significantly higher compared to HSs (20%) (odds ratio 2.049, CI 95% 1.32-3.224; p=0.0026). Immunohistochemical staining (IHS) assays showed SV40 Tag expression in 8/20, 40% of MPM specimens. These results indicate that SV40 is linked to a large fraction of MPM. It is worth noting that the prevalence of SV40 Tag antibodies detected in sera from cohort 1 of MPM patients is similar to the prevalence of SV40 Tag found to be expressed in FFPE tissues from MPM cohort 2.

Preclinical Models and Resources to Facilitate Basic Science Research on Malignant Mesothelioma - A Review

Malignant mesothelioma is an aggressive cancer with poor prognosis, predominantly caused by human occupational exposure to asbestos. The global incidence of mesothelioma is predicted to increase as a consequence of continued exposure to asbestos from a variety of sources, including construction material produced in the past in developed countries, as well as those currently being produced in developing countries. Mesothelioma typically develops after a long latency period and consequently it is often diagnosed in the clinic at an advanced stage, at which point standard care of treatment, such as chemo- and radio-therapy, are largely ineffective. Much of our current understanding of mesothelioma biology, particularly in relation to disease pathogenesis, diagnosis and treatment, can be attributed to decades of preclinical basic science research. Given the postulated rising incidence in mesothelioma cases and the limitations of current diagnostic and treatment options, continued preclinical research into mesothelioma is urgently needed. The ever-evolving landscape of preclinical models and laboratory technology available to researchers have made it possible to study human disease with greater precision and at an accelerated rate. In this review article we provide an overview of the various resources that can be exploited to facilitate an enhanced understanding of mesothelioma biology and their applications to research aimed to improve the diagnosis and treatment of mesothelioma. These resources include cell lines, animal models, mesothelioma-specific biobanks and modern laboratory techniques/technologies. Given that different preclinical models and laboratory technologies have varying limitations and applications, they must be selected carefully with respect to the intended objectives of the experiments. This review therefore aims to provide a comprehensive overview of the various preclinical models and technologies with respect to their advantages and limitations. Finally, we will detail about a highly valuable preclinical laboratory resource to curate high quality mesothelioma biospecimens for research; the biobank. Collectively, these resources are essential to the continued advancement of precision medicine to curtail the increasing health burden caused by malignant mesothelioma.

Use of preclinical models for malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer most commonly caused by prior exposure to asbestos. Median survival is 12-18 months, since surgery is ineffective and chemotherapy offers minimal benefit. Preclinical models that faithfully recapitulate the genomic and histopathological features of cancer are critical for the development of new treatments. The most commonly used models of MPM are two-dimensional cell lines established from primary tumours or pleural fluid. While these have provided some important insights into MPM biology, these cell models have significant limitations. In order to address some of these limitations, spheroids and microfluidic chips have more recently been used to investigate the role of the three-dimensional environment in MPM. Efforts have also been made to develop animal models of MPM, including asbestos-induced murine tumour models, MPM-prone genetically modified mice and patient-derived xenografts. Here, we discuss the available in vitro and in vivo models of MPM and highlight their strengths and limitations. We discuss how newer technologies, such as the tumour-derived organoids, might allow us to address the limitations of existing models and aid in the identification of effective treatments for this challenging-to-treat disease.

How to Better Understand the Influence of Host Genetics on Developing an Effective Immune Response to Thoracic Cancers

Thoracic cancers pose a significant global health burden. Immune checkpoint blockade therapies have improved treatment outcomes, but durable responses remain limited. Understanding how the host immune system interacts with a developing tumor is essential for the rational development of improved treatments for thoracic malignancies. Recent technical advances have improved our understanding of the mutational burden of cancer cells and changes in cancer-specific gene expression, providing a detailed understanding of the complex biology underpinning tumor-host interactions. While there has been much focus on the genetic alterations associated with cancer cells and how they may impact treatment outcomes, how host genetics affects cancer development is also critical and will greatly determine treatment response. Genome-wide association studies (GWAS) have identified genetic variants associated with cancer predisposition. This approach has successfully identified host genetic risk factors associated with common thoracic cancers like lung cancer, but is less effective for rare cancers like malignant mesothelioma. To assess how host genetics impacts rare thoracic cancers, we used the Collaborative Cross (CC); a powerful murine genetic resource designed to maximize genetic diversity and rapidly identify genes associated with any biological trait. We are using the CC in conjunction with our asbestos-induced MexTAg mouse model, to identify host genes associated with mesothelioma development. Once genes that moderate tumor development and progression are known, human homologues can be identified and human datasets interrogated to validate their association with disease outcome. Furthermore, our CC-MexTAg animal model enables in-depth study of the tumor microenvironment, allowing the correlation of immune cell infiltration and gene expression signatures with disease development. This strategy provides a detailed picture of the underlying biological pathways associated with mesothelioma susceptibility and progression; knowledge that is crucial for the rational development of new diagnostic and therapeutic strategies. Here we discuss the influence of host genetics on developing an effective immune response to thoracic cancers. We highlight current knowledge gaps, and with a focus on mesothelioma, describe the development and application of the CC-MexTAg to overcome limitations and illustrate how the knowledge gained from this unique study will inform the rational design of future treatments of mesothelioma.

Mouse models for mesothelioma drug discovery and development

INTRODUCTION

Mesothelioma is an aggressive mesothelial lining tumor. Available drug therapies include chemotherapeutic agents, targeted molecular therapies, and immune system modulators. Mouse models were instrumental in the discovery and evaluation of such therapies, but there is need for improved understanding of the role of inflammation, tumor heterogeneity, mechanisms of carcinogenesis, and the tumor microenvironment. Novel mouse models may provide new insights and drive drug therapy discovery that improves efficacy.

AREAS COVERED

This review concerns available mouse models for mesothelioma drug discovery and development including the advantages and disadvantages of each. Gaps in current knowledge of mesothelioma are highlighted, and future directions for mouse model research are considered.

EXPERT OPINION

Soon, CRISPR-Cas gene-editing will improve understanding of mesothelioma mechanisms foundational to the discovery and testing of efficacious therapeutic targets. There are at least two likely areas of upcoming methodology development. One is concerned with precise modeling of inflammation - is it a causal process whereby inflammatory signals contribute to tumor initiation, or is it a secondary passenger process driven by asbestos exposure effects? The other area of methods improvement regards the availability of humanized immunocompromised mice harboring patient-derived xenografts. Combining human tumors in an environment with human immune cells will enable rapid innovation in immuno-oncology therapeutics.

Voluntary exercise in mesothelioma: effects on tumour growth and treatment response in a murine model

Objective

There is substantial evidence that exercise can safely reduce the risk of cancer and improve survival in different human cancer populations. Long latency periods associated with carcinogen–induced cancers like asbestos induced mesothelioma provide an opportunity to implement exercise as an intervention to delay or prevent disease development. However, there are limited studies investigating the ability of exercise to prevent or delay cancer, and exercise as a preventive strategy has never been assessed in models with a known carcinogen. We investigated the potential of voluntary exercise (VE) to delay development of asbestos related disease (ARD) in our well-characterised, asbestos induced MexTAg model of mesothelioma.

Results

Asbestos exposed MexTAg mice were given continuous or delayed access to VE and ARD assessed over time. We found that the addition of VE did not affect ARD development in asbestos exposed MexTAg mice. However, non–asbestos exposed, aged matched control mice participated in significantly more VE behaviours, suggesting subclinical development of ARD after asbestos exposure had a greater impact on VE participation than age alone. These data highlight the importance of model choice and the potential limitation that some pre–clinical studies may not accurately represent the clinical paradigm, particularly in the context of prevention studies.

Preclinical Models of Malignant Mesothelioma

Rodent models of malignant mesothelioma help facilitate the understanding of the biology of this highly lethal cancer and to develop and test new interventions. Introducing the same genetic lesions as found in human mesothelioma in mice results in tumors that show close resemblance with the human disease counterpart. This includes the extensive inflammatory responses that characterize human malignant mesothelioma. The relatively fast development of mesothelioma in mice when the appropriate combination of lesions is introduced, with or without exposure to asbestos, make the autochthonous models particularly useful for testing new treatment strategies in an immunocompetent setting, whereas Patient-Derived Xenograft models are particularly useful to assess effects of inter- and intra-tumor heterogeneity and human-specific features of mesothelioma. It is to be expected that new insights obtained by studying these experimental systems will lead to new more effective treatments for this devastating disease.

Zeolites ameliorate asbestos toxicity in a transgenic model of malignant mesothelioma

Malignant mesothelioma (MM) is an almost invariably fatal cancer caused by asbestos exposure. The toxicity of asbestos fibers is related to their physicochemical properties and the generation of free radicals. We set up a pilot study to investigate the potential of the zeolite clinoptilolite to counteract the asbestos carcinogenesis by preventing the generation of reactive nitrogen and oxygen radicals. In cell culture experiments, clinoptilolite prevented asbestos-induced cell death, reactive oxygen species production, DNA degradation, and overexpression of genes known to be up-regulated by asbestos. In an asbestos-induced transgenic mouse model of MM, mice were injected intraperitoneal injections with blue asbestos, with or without clinoptilolite, and monitored for 30 weeks. By the end of the trial all 13 mice injected with asbestos alone had reached humane end points, whereas only 7 of 29 mice receiving crocidolite and clinoptilolite reached a similar stage of disease. Post-mortem examination revealed pinpoint mesothelioma-like tumors in affected mice, and the absence of tumor formation in surviving mice. Interestingly, the macrophage clearance system, which was largely suppressed in asbestos-treated mice, exhibited evidence of increased phagocytosis in mice treated with asbestos and clinoptilolite. Our study suggests that inhibiting the asbestos-induced generation of reactive oxygen species and stimulating the macrophage system may represent a pathway to amelioration of asbestos-induced toxicity. Additional studies are warranted to explore the underlying mechanisms responsible for our observations.

Association Between Simian Virus 40 and Human Tumors

Simian virus 40 (SV40) is a small DNA tumor virus of monkey origin. This polyomavirus was administered to human populations mainly through contaminated polio vaccines, which were produced in naturally infected SV40 monkey cells. Previous molecular biology and recent immunological assays have indicated that SV40 is spreading in human populations, independently from earlier SV40-contaminated vaccines. SV40 DNA sequences have been detected at a higher prevalence in specific human cancer specimens, such as the brain and bone tumors, malignant pleural mesotheliomas, and lymphoproliferative disorders, compared to the corresponding normal tissues/specimens. However, other investigations, which reported negative data, did not confirm an association between SV40 and human tumors. To circumvent the controversies, which have arisen because of these molecular biology studies, immunological researches with newly developed indirect ELISA tests were carried out in serum samples from patients affected by the same kind of tumors as mentioned above. These innovative indirect ELISAs employ synthetic peptides as mimotopes/specific SV40 antigens. SV40 mimotopes do not cross-react with the homologous human polyomaviruses, BKPyV, and JCPyV. Immunological data obtained from indirect ELISAs, using SV40 mimotopes, employed to analyze serum samples from oncological patients, have indicated that these sera had a higher prevalence of antibodies against SV40 compared to healthy subjects. The main data on (i) the biology and genetics of SV40; (ii) the epidemiology of SV40 in the general population, (iii) the mechanisms of SV40 transformation; (iv) the putative role of SV40 in the onset/progression of specific human tumors, and (v) its association with other human diseases are reported in this review.

Does Simian Virus 40 (SV40) Have a Role in UK Malignant Pleural Mesothelioma? No Role is Identified in a Sensitive RNA In Situ Hybridization Study on Potentially Affected Birth Cohorts

BACKGROUND

Simian virus 40 (SV40)-contaminated polio vaccine was accidentally administered to about one-third of the UK population receiving polio vaccines between 1956 and 1962. SV40 was subsequently demonstrated to be a carcinogenic virus in experimental and animal models. Since then, the SV40 oncogenic protein large T antigen (SV40 Tag) has been shown to cause malignant transformation of asbestos-treated human pleural mesothelial cells and malignant pleural mesotheliomas in asbestos-exposed SV40 Tag transgenic mice. The present study was designed to investigate the possible association of SV40 Tag with human malignant pleural mesothelioma samples from birth cohorts of the UK population exposed to combined peak levels of asbestos and SV40-contaminated polio vaccines.

MATERIALS AND METHODS

Tumor and background lung tissue microarrays prepared from archival surgical specimens of 139 pleural mesothelioma cases, collected over a period of 8 years (1998 to 2005), were analyzed. These represented birth cohorts overlapping with the period 1950 to 1960, exposed to a high level of both asbestos and SV40-contaminated live polio vaccines. SV40 Tag mRNA expression was investigated using a highly sensitive and specific SV40 Tag RNA in situ hybridization detection method on the basis of the novel RNAscope technology.

RESULTS

SV40 Tag RNA was not detected in any of the 127 evaluable tumor cases, despite appropriate results obtained for the external positive and negative controls included.

CONCLUSION

The complete absence of SV40 Tag mRNA in this large series of cases contradicts experimental evidence suggestive of SV40 link with asbestos-exposed malignant pleural mesotheliomas in the UK population. Alternative explanations of the negative findings are discussed to exclude possible confounding factors.

The Future of Mesothelioma Research: Basic Science Research

Our current understanding of mesothelioma in terms of disease induction, development, and treatment is underpinned by decades of basic laboratory science. In this chapter, we discuss the tools that have been developed to aid our understanding of mesothelioma such as cell lines and animal models. We then go on to detail the current use and understanding of conventional therapies for mesothelioma, e.g. chemotherapy, surgery, and radiotherapy, plus their mechanisms of action, and why they may be ineffective. Finally, we discuss a range of newer treatments that are either undergoing clinical trials or are still in the earlier stages of preclinical investigation. These include a growing number of immunotherapies (e.g. checkpoint inhibitors), plus targeted therapies, the search for clinical biomarkers to predict whether patients with mesothelioma might respond to particular treatments, and combined therapies where conventional treatments may be added to newer drugs. The strategy of repositioning existing drugs, approved for other diseases, to treat mesothelioma is also discussed.

Imaging in pleural mesothelioma: A review of the 14th International Conference of the International Mesothelioma Interest Group

Mesothelioma patients rely on the information their clinical team obtains from medical imaging. Whether x-ray-based computed tomography (CT) or magnetic resonance imaging (MRI) based on local magnetic fields within a patient's tissues, different modalities generate images with uniquely different appearances and information content due to the physical differences of the image-acquisition process. Researchers are developing sophisticated ways to extract a greater amount of the information contained within these images. This paper summarizes the imaging-based research presented orally at the 2018 International Conference of the International Mesothelioma Interest Group (iMig) in Ottawa, Ontario, Canada, held May 2-5, 2018. Presented topics included advances in the imaging of preclinical mesothelioma models to inform clinical therapeutic strategies, optimization of the time delay between contrast administration and image acquisition for maximized enhancement of mesothelioma tumor on CT, an investigation of image-based criteria for clinical tumor and nodal staging of mesothelioma by contrast-enhanced CT, an investigation of methods for the extraction of mesothelioma tumor volume from MRI and the association of volume with patient survival, the use of deep learning for mesothelioma tumor segmentation in CT, and an evaluation of CT-based radiomics for the prognosis of mesothelioma patient survival.

Calretinin promotes invasiveness and EMT in malignant mesothelioma cells involving the activation of the FAK signaling pathway

Calretinin (CR) is used as a positive marker for human malignant mesothelioma (MM) and is essential for mesothelioma cell growth/survival. Yet, the putative role(s) of CR during MM formation in vivo, binding partners or CR's influence on specific signaling pathways remain unknown. We assessed the effect of CR overexpression in the human MM cell lines MSTO-211H and SPC111. CR overexpression augmented the migration and invasion of MM cells in vitro. These effects involved the activation of the focal adhesion kinase (FAK) signaling pathway, since levels of total FAK and phospho-FAK (Tyr³⁹⁷) were found up-regulated in these cells. CR was also implicated in controlling epithelial-to-mesenchymal transition (EMT), evidenced by changes of the cell morphology and up-regulation of typical EMT markers. Co-IP experiments revealed FAK as a new binding partner of CR. CR co-localized with FAK at focal adhesion sites; moreover, CR-overexpressing cells displayed enhanced nuclear FAK accumulation and an increased resistance towards the FAK inhibitor VS-6063. Finally, CR downregulation via a lentiviral shRNA against CR (CALB2) resulted in a significantly reduced tumor formation in vivo in an orthotopic xenograft mouse model based on peritoneal MM cell injection. Our results indicate that CR might be considered as a possible target for MM treatment.

Antibodies reacting to mimotopes of Simian virus 40 large T antigen, the viral oncoprotein, in sera from children

Recent data indicate that the Simian virus 40 (SV40) infection appears to be transmitted in humans independently from early SV40-contaminated antipolio vaccines. Serum antibodies against SV40 large T antigen (Tag) were analyzed in children/adolescents and young adults. To investigate antibodies reacting to SV40 Tag antigens, serum samples ( n = 812) from children and young adults were analyzed by indirect ELISAs using specific SV40 Tag mimotopes. Mimotopes were synthetic peptides corresponding to SV40 Tag epitopes. In sera ( n = 412) from healthy children up to 17 years old, IgG antibodies against SV40 Tag mimotopes reached an overall prevalence of 15%. IgM antibodies against SV40 Tag were detected in sera of children 6-8 months old confirming and extending the knowledge that SV40 seroconversion occurs early in life. In children/adolescents affected by different diseases ( n = 180) SV40 Tag had a prevalence of 18%, being the difference no significant compared to healthy subjects ( n = 220; 16%) of the same age. Our immunological data indicate that SV40 circulates in children and young adults, both in healthy conditions and affected by distinct diseases. The IgM detection in sera from healthy children suggests that the SV40 infection/seroconversion occurs early in life (>6 months). Our immunological data support the hypothesis that SV40, or a closely related still unknown polyomavirus, infects humans. The SV40 seroprevalence is lower than common polyomaviruses, such as BKPyV and JCPyV, and other new human polyomaviruses. In addition, our immunological surveillance indicates a lack of association between different diseases, considered herein, and SV40.

Zeolite protects mice from iron-induced damage in a mouse model trial

For centuries, zeolites have been used for their utility in binding metals, and they feature in a multitude of agricultural and industrial applications in which the honeycombed zeolite structures form ideal ion exchangers, catalysts and binding agents. Zeolites are currently in a transition period, moving towards implementation in human ailments and diseases. Here, we postulated that zeolites may be able to counter the effects of excess iron and conducted a mouse model trial to gauge the utility of this notion. We used the transgenic mouse strain MexTAg299 for a thirty‐week pilot trial in which iron polymaltose and/or the zeolite clinoptilolite was injected into the peritoneum twice weekly. Mice were sacrificed at the end of the trial period and examined by postmortem and histology for significant physiological differences between mouse subgroups. In this study, we demonstrated that a common zeolite, clinoptilolite, is able to maintain the general health and well‐being of mice and prevent iron‐induced deleterious effects following iron overload. When zeolites are given with iron biweekly as intraperitoneal injections, mice showed far less macroscopic visual organ discoloration, along with near normal histology, under iron overload conditions when compared to mice injected with iron only. The purpose of the present pilot study was to examine potential alternatives to current iron chelation treatments, and the results indicate an advantage to using zeolites in conditions of iron excess. Zeolites may have translational potential for use in cases of human iron overload.

Mesotheliomas in Genetically Engineered Mice Unravel Mechanism of Mesothelial Carcinogenesis

Malignant mesothelioma (MM), a rare and severe cancer, mainly caused as a result of past-asbestos exposure, is presently a public health concern. Current molecular studies aim to improve the outcome of the disease, providing efficient therapies based on the principles of precision medicine. To model the molecular profile of human malignant mesothelioma, animal models have been developed in rodents, wild type animals and genetically engineered mice harbouring mutations in tumour suppressor genes, especially selecting genes known to be inactivated in human malignant mesothelioma. Animals were either exposed or not exposed to asbestos or to other carcinogenic fibres, to understand the mechanism of action of fibres at the molecular level, and the role of the selected genes in mesothelial carcinogenesis. The aim of the manuscript was to compare mesothelioma models to human malignant mesothelioma and to specify the clue genes playing a role in mesothelial carcinogenesis. Collectively, MM models recapitulate the clinical features of human MM. At least two altered genes are needed to induce malignant mesothelioma in mice. Two pathways regulated by Cdkn2a and Trp53 seem independent key players in mesothelial carcinogenesis. Other genes and pathways appear as bona fide modulators of the neoplastic transformation.

Pre-clinical Models for Malignant Mesothelioma Research: From Chemical-Induced to Patient-Derived Cancer Xenografts

Malignant mesothelioma (MM) is a rare disease often associated with environmental exposure to asbestos and other erionite fibers. MM has a long latency period prior to manifestation and a poor prognosis. The survival post-diagnosis is often less than a year. Although use of asbestos has been banned in the United States and many European countries, asbestos is still being used and extracted in many developing countries. Occupational exposure to asbestos, mining, and migration are reasons that we expect to continue to see growing incidence of mesothelioma in the coming decades. Despite improvements in survival achieved with multimodal therapies and cytoreductive surgeries, less morbid, more effective interventions are needed. Thus, identifying prognostic and predictive biomarkers for MM, and developing novel agents for targeted therapy, are key unmet needs in mesothelioma research and treatment. In this review, we discuss the evolution of pre-clinical model systems developed to study MM and emphasize the remarkable capability of patient-derived xenograft (PDX) MM models in expediting the pre-clinical development of novel therapeutic approaches. PDX disease model systems retain major characteristics of original malignancies with high fidelity, including molecular, histopathological and functional heterogeneities, and as such play major roles in translational research, drug development, and precision medicine.

Asbestos and SV40 in Malignant Pleural Mesothelioma from a Hyperendemic Area of North-Eastern Italy

Aims and background

Malignant mesothelioma is a fatal cancer of increasing incidence in north-eastern Italy. Together with asbestos, the polyomavirus SV40 was hypothesized to contribute to the onset of malignant mesothelioma. To investigate the putative role of SV40 in the individual susceptibility to asbestos-induced malignant mesothelioma, we conducted a molecular epidemiological study on a series of malignant mesothelioma patients from an area in north-eastern Italy hyperendemic for malignant pleural mesothelioma.

Methods and study design

We collected 63 mesothelioma samples from incidence cases of patients diagnosed with malignant pleural mesothelioma in the period 2009–2010. DNA was extracted from patients’ tissue biopsies using the BioRobot EZ1 Qiagen workstation. SV40 sequence detection and quantification was performed by specific real time PCR. The 74.6% of the 63 enrolled patients had a history of asbestos exposure. The epithelioid histotype was more prevalent in males (64.0%) and the mixed in females (61.5%) who showed significantly higher cancer co-morbidity (46.1% vs 12%, P = 0.005). SV40 was detected in 22% of MM tumors, with a low viral load. In SV40-positive patients, a threefold increased risk of asbestos exposure was observed, more evident in females (OR 4.32) than in males (OR 1.20).

Conclusions

Our findings indicate that a high prevalence of SV40 was present in malignant mesothelioma incident cases from an area hyperendemic for malignant mesothelioma in north-eastern Italy. Although asbestos is considered the main risk factor in malignant mesothelioma onset, a role for SV40 could be hypothesized.

Identification of cis- and trans-acting elements regulating calretinin expression in mesothelioma cells

Calretinin (CALB2) is a diagnostic marker for epithelioid mesothelioma. It is also a prognostic marker since patients with tumors expressing high calretinin levels have better overall survival. Silencing of calretinin decreases viability of epithelioid mesothelioma cells. Our aim was to elucidate mechanisms regulating calretinin expression in mesothelioma. Analysis of calretinin transcript and protein suggested a control at the mRNA level. Treatment with 5-aza-2′-deoxycytidine and analysis of TCGA data indicated that promoter methylation is not likely to be involved. Therefore, we investigated CALB2 promoter by analyzing ~1kb of genomic sequence surrounding the transcription start site (TSS) + 1 using promoter reporter assay. Deletion analysis of CALB2 proximal promoter showed that sequence spanning the −161/+80bp region sustained transcriptional activity. Site-directed analysis identified important cis-regulatory elements within this −161/+80bp CALB2 promoter. EMSA and ChIP assays confirmed binding of NRF-1 and E2F2 to the CALB2 promoter and siRNA knockdown of NRF-1 led to decreased expression of calretinin. Cell synchronization experiment showed that calretinin expression was cell cycle regulated with a peak of expression at G1/S phase. This study provides the first insight in the regulation of CALB2 expression in mesothelioma cells.

Whole exome sequencing of an asbestos-induced wild-type murine model of malignant mesothelioma

BACKGROUND

Malignant mesothelioma (MM) is an aggressive cancer of the pleural and peritoneal cavities caused by exposure to asbestos. Asbestos-induced mesotheliomas in wild-type mice have been used extensively as a preclinical model because they are phenotypically identical to their human counterpart. However, it is not known if the genetic lesions in these mice tumours are similar to in the human disease, a prerequisite for any new preclinical studies that target genetic abnormalities.

METHODS

We performed whole exome sequencing of fifteen asbestos-induced murine MM tumour cell lines from BALB/c, CBA and C57BL/6 mouse strains and compared the somatic mutations and copy number variations with those recurrently reported in human MM. We then catalogued and characterised the mutational landscape of the wild-type murine MM tumours. Quantitative RT-PCR was used to interrogate the expression of key MM genes of interest in the mRNA.

RESULTS

Consistent with human MM tumours, we identified homozygous loss of the tumour suppressor Cdkn2a in 14/15 tumours. One tumour retained the first exon of both of the p16INK4a and p19ARF isoforms though this tumour also contained genetic amplification of Myc resulting in increased expression of the c-Myc proto-oncogene in the mRNA. There were no chromosomal losses in either the Bap1 or Nf2 regions. One tumour harbored homozygous loss of Trp53 in the DNA. Mutation rates were similar in tumours generated in the CBA and C57BL/6 strains when compared to human MM. Interestingly, all BALB/c tumour lines displayed high mutational loads, consistent with the known mutator phenotype of the host strain. The Wnt, MAPK and Jak-STAT signaling pathways were found to be the most commonly affected biological pathways. Mutations and copy number deletions also occurred in the Hedgehog and Hippo pathways.

CONCLUSIONS

These data suggest that in the wild-type murine model asbestos causes mesotheliomas in a similar way to in human MM. This further supports the notion that the murine model of MM represents a genuine homologue of the human disease, something uncommon in cancer, and is thus a valuable tool to provide insight into MM tumour development and to aide the search for novel therapeutic strategies.

A Subset of Malignant Mesothelioma Tumors Retain Osteogenic Potential

Malignant mesothelioma (MM) is an aggressive serosal tumor associated with asbestos exposure. We previously demonstrated that mesothelial cells differentiate into cells of different mesenchymal lineages and hypothesize that osseous tissue observed in a subset of MM patients is due to local differentiation of MM cells. In this study, the capacity of human and mouse MM cells to differentiate into osteoblast-like cells was determined in vitro using a functional model of bone nodule formation and in vivo using an established model of MM. Human and murine MM cell lines cultured in osteogenic medium expressed alkaline phosphatase and formed mineralized bone-like nodules. Several human and mouse MM cell lines also expressed a number of osteoblast phenotype markers, including runt-related transcription factor 2 (RUNX2), osteopontin, osteonectin and bone sialoprotein mRNA and protein. Histological analysis of murine MM tumors identified areas of ossification within the tumor, similar to those observed in human MM biopsies. These data demonstrate the ability of MM to differentiate into another mesenchymal cell type and suggest that MM cells may contribute to the formation of the heterologous elements observed in MM tumors.

Investigating palygorskite's role in the development of mesothelioma in southern Nevada: Insights into fiber-induced carcinogenicity

Similar to asbestos fibers, nonregulated mineral fibers can cause malignant mesothelioma (MM). Recently, increased proportions of women and young individuals with MM were identified in southern Nevada, suggesting that environmental exposure to carcinogenic fibers was causing the development of MM. Palygorskite, a fibrous silicate mineral with a history of possible carcinogenicity, is abundant in southern Nevada. In this study, our aim was to determine whether palygorskite was contributing to the development of MM in southern Nevada. While palygorskite, in vitro, displayed some cytotoxicity toward primary human mesothelial (HM) cells and reduced their viability, the effects were roughly half of those observed when using similar amounts of crocidolite asbestos. No Balb/c (0/19) or MexTAg (0/18) mice injected with palygorskite developed MM, while 3/16 Balb/c and 13/14 MexTAg mice injected with crocidolite did. Lack of MM development was associated with a decreased acute inflammatory response, as injection of palygorskite resulted in lower percentages of macrophages (p = .006) and neutrophils (p = .02) in the peritoneal cavity 3 d after exposure compared to injection of crocidolite. Additionally, compared to mice injected with crocidolite, palygorskite-injected mice had lower percentages of M2 (tumor-promoting) macrophages (p = .008) in their peritoneal cavities when exposed to fiber for several weeks. Our study indicates that palygorskite found in the environment in southern Nevada does not cause MM in mice, seemingly because palygorskite, in vivo, fails to elicit inflammation that is associated with MM development. Therefore, palygorskite is not a likely contributor to the MM cases observed in southern Nevada.

Consistent gene expression profiles in MexTAg transgenic mouse and wild type mouse asbestos-induced mesothelioma

Background

The MexTAg transgenic mouse model of mesothelioma replicates many aspects of human mesothelioma, including induction by asbestos, pathogenicity and response to cytotoxic chemotherapy, despite high levels of the SV40 large T Antigen (TAg) in the mesothelial compartment. This model enables analysis of the molecular events associated with asbestos induced mesothelioma and is utilised here to investigate the molecular dynamics of tumours induced in these mice, using gene expression patterns as a read out.

Methods

Gene expression of MexTAg mesothelioma cell lines bearing a high or low number of copies of the TAg transgene were compared to wild type mouse mesotheliomas and normal mouse mesothelial cells using Affymetrix microarray. These data were then compared to a similar published human microarray study using the same platform.

Results

The main expression differences between transgenic mouse and wild type mouse mesotheliomas occurred for genes involved in cell cycle regulation and DNA replication, as would be expected from overexpression of the TAg oncogene. Quantitative PCR confirmed that E2F and E2F regulated genes were significantly more upregulated in MexTAg mesotheliomas and MexTAg mesothelial cells compared to wild type mesotheliomas. Like human mesothelioma, both MexTAg and wild type mesotheliomas had more genes underexpressed than overexpressed compared to normal mouse mesothelial cells. Most notably, the cdkn2 locus was deleted in the wild type mouse mesotheliomas, consistent with 80 % human mesotheliomas, however, this region was not deleted in MexTAg mesotheliomas. Regardless of the presence of TAg, all mouse mesotheliomas had a highly concordant set of deregulated genes compared to normal mesothelial cells that overlapped with the deregulated genes between human mesotheliomas and mesothelial cells.

Conclusions

This investigation demonstrates that the MexTAg mesotheliomas are comparable with wild type mouse mesotheliomas in their representation of human mesothelioma at the molecular level, with some key gene expression differences that are attributable to the TAg transgene expression. Of particular note, MexTAg mesothelioma development was not dependent on cdkn2 deletion.

Electronic supplementary material

The online version of this article (doi:10.1186/s12885-015-1953-y) contains supplementary material, which is available to authorized users.

Establishment of immortalized murine mesothelial cells and a novel mesothelioma cell line

Mesothelial cells are susceptible to asbestos fiber-induced cytotoxicity and on longer time scales to transformation; the resulting mesothelioma is a highly aggressive neoplasm that is considered as incurable at the present time Zucali et al. (Cancer Treatment Reviews 37:543–558, 2011). Only few murine cell culture models of immortalized mesothelial cells and mesothelioma cell lines exist to date. We generated SV40-immortalized cell lines derived from wild-type (WT) and neurofibromatosis 2 (merlin) heterozygote (Nf2+/−) mice, both on a commonly used genetic background, C57Bl/6J. All immortalized mesothelial clones consistently grow in DMEM supplemented with fetal bovine serum. Cells can be passaged for more than 40 times without any signs of morphological changes or a decrease in proliferation rate. The tumor suppressor gene NF2 is one of the most frequently mutated genes in human mesothelioma, but its detailed function is still unknown. Thus, these genotypically distinct cell lines likely relevant for malignant mesothelioma formation are expected to serve as useful in vitro models, in particular to compare with in vivo studies in mice of the same genotype. Furthermore, we generated a novel murine mesothelioma cell line RN5 originating from an Nf2+/− mouse subjected to repeated crocidolite exposure. RN5 cells are highly tumorigenic.

Absence of germline mutations in BAP1 in sporadic cases of malignant mesothelioma

Malignant mesothelioma (MM) is a uniformly fatal tumour caused predominantly by exposure to asbestos. It is not known why some exposed individuals get mesothelioma and others do not. There is some epidemiological evidence of host susceptibility. BAP1 gene somatic mutations and allelic loss are common in mesothelioma and recently a BAP1 cancer syndrome was described in which affected individuals and families had an increased risk of cancer of multiple types, including MM. To determine if BAP1 mutations could underlie any of the sporadic mesothelioma cases in our cohort of patients, we performed targeted deep sequencing of the BAP1 exome on the IonTorrent Proton sequencer in 115 unrelated MM cases. No exonic germline BAP1 mutations of known functional significance were observed, further supporting the notion that sporadic germline BAP1 mutations are not relevant to the genetic susceptibility of MM.

Malignant pleural mesothelioma: history, controversy and future of a manmade epidemic

Asbestos is the term for a family of naturally occurring minerals that have been used on a small scale since ancient times. Industrialisation demanded increased mining and refining in the 20th century, and in 1960, Wagner, Sleggs and Marchand from South Africa linked asbestos to mesothelioma, paving the way to the current knowledge of the aetiology, epidemiology and biology of malignant pleural mesothelioma. Pleural mesothelioma is one of the most lethal cancers, with increasing incidence worldwide. This review will give some snapshots of the history of pleural mesothelioma discovery, and the body of epidemiological and biological research, including some of the controversies and unresolved questions. Translational research is currently unravelling novel circulating biomarkers for earlier diagnosis and novel treatment targets. Current breakthrough discoveries of clinically promising noninvasive biomarkers, such as the 13-protein signature, microRNAs and the BAP1 mesothelioma/cancer syndrome, are highlighted. The asbestos history is a lesson to not be repeated, but here we also review recent in vivo and in vitro studies showing that manmade carbon nanofibres could pose a similar danger to human health. This should be taken seriously by regulatory bodies to ensure thorough testing of novel materials before release in the society.

Malignant pleural mesothelioma is a cancer with increasing death tolls due to the past and present use of asbestoshttp://ow.ly/DhA2y

Mouse models of mesothelioma: strengths, limitations and clinical translation

SUMMARY 

Mouse models of cancer are invaluable for obtaining detailed knowledge about tumor development and for screening therapeutic and preventive approaches. Mesothelioma is an unusual cancer because the same carcinogen, asbestos, causes a similar disease in both humans and animals. Unlike most other cancers, murine mesothelioma can therefore be regarded as a disease homolog, rather than a model as such. However, because asbestos-induced cancer has low penetrance and a long lag time, most translational studies have utilized more efficient models such as tumor transplantation. In consequence, many promising results have not translated into positive findings in patients. Here, we describe the widely used murine mesothelioma models and critically discuss their relative advantages and disadvantages. We emphasize the use of the appropriate model for the specific research question and the need to use multiple models in order to obtain robust and translatable data.

Effect of NSAIDS and COX-2 inhibitors on the incidence and severity of asbestos-induced malignant mesothelioma: evidence from an animal model and a human cohort

OBJECTIVES

Non-steroidal anti-inflammatory drugs (NSAIDs) and COX-2 inhibitors have been associated with lower incidence rates of some cancers. Because asbestos can cause chronic inflammation at the pleural and peritoneal surfaces we hypothesised that NSAID and COX-2 inhibitors would inhibit the development of asbestos-induced mesothelioma.

MATERIALS AND METHODS

A murine model of asbestos-induced mesothelioma was used to test this hypothesis by providing the NSAID, aspirin, daily in the feed at 50mg/kg or 250 mg/kg. In a parallel study, the relationship between the use of NSAID and COX-2 inhibitors and mesothelioma was investigated in a human cohort of 1738 asbestos exposed people living or working in Wittenoom, Western Australia (a crocidolite mine site).

RESULTS

Aspirin did not alter the rate of disease development or increase the length of time that mice survived. Aspirin had a small but significant effect on disease latency (the time between asbestos exposure and first evidence of disease; p<0.05) but disease progression was not affected by the continued presence of the drug. In the Wittenoom cohort, individuals who reported use of NSAIDs, COX-2 inhibitors or both did not have a lower incidence of mesothelioma (HR=0.85; 95% CI=0.53-1.37, p=0.50), (HR=0.69; 95% CI=0.21-2.30, p=0.55) and (HR=0.43; 95% CI=0.16-1.13, p=0.087) respectively.

CONCLUSION

We conclude that NSAIDs and COX-2 inhibitors do not moderate mesothelioma development or progression in a human cohort exposed to asbestos and this result is confirmed in an autochthonous mouse model.

Statins do not alter the incidence of mesothelioma in asbestos exposed mice or humans

Mesothelioma is principally caused by asbestos and may be preventable because there is a long latent period between exposure and disease development. The most at-risk are a relatively well-defined population who were exposed as a consequence of their occupations. Although preventative agents investigated so far have not been promising, discovery of such an agent would have a significant benefit world-wide on healthcare costs and personal suffering. Statins are widely used for management of hypercholesterolemia and cardiovascular risk; they can induce apoptosis in mesothelioma cells and epidemiological data has linked their use to a lower incidence of cancer. We hypothesised that statins would inhibit the development of asbestos-induced mesothelioma in mice and humans. An autochthonous murine model of asbestos-induced mesothelioma was used to test this by providing atorvastatin daily in the feed at 100 mg/kg, 200 mg/kg and 400 mg/kg. Continuous administration of atorvastatin did not alter the rate of disease development nor increase the length of time that mice survived. Latency to first symptoms of disease and disease progression were also unaffected. In a parallel study, the relationship between the use of statins and development of mesothelioma was investigated in asbestos-exposed humans. In a cohort of 1,738 asbestos exposed people living or working at a crocidolite mine site in Wittenoom, Western Australia, individuals who reported use of statins did not have a lower incidence of mesothelioma (HR = 1.01; 95% CI = 0.44–2.29, p = 0.99). Some individuals reported use of both statins and non-steroidal anti-inflammatory drugs or COX-2 inhibitors, and these people also did not have an altered risk of mesothelioma development (HR = 1.01; 95% CI = 0.61–1.67, p = 0.97). We conclude that statins do not moderate the rate of development of mesothelioma in either a mouse model or a human cohort exposed to asbestos.

SV40 TAg mouse models of cancer

The discovery of a number of viruses with the ability to induce tumours in animals and transform human cells has vastly impacted cancer research. Much of what is known about tumorigenesis today regarding tumour drivers and tumour suppressors has been discovered through experiments using viruses. The SV40 virus has proven extremely successful in generating transgenic models of many human cancer types and this review provides an overview of these models and seeks to give evidence as to their relevance in this modern era of personalised medicine and technological advancements.

Dietary vitamin D supplementation does not reduce the incidence or severity of asbestos-induced mesothelioma in a mouse model

Epidemiological studies suggest that vitamin and mineral intake is associated with cancer incidence. A prevention strategy based on diet or dietary supplementation could have enormous benefit, both directly, by preventing disease, and indirectly by alleviating fear in millions of people worldwide who have been exposed to asbestos. We have previously shown that dietary supplementation with the antioxidants vitamins A, E, and selenium does not affect overall survival nor the time to progression of asbestos-induced mesothelioma in MexTAg mice. Here we have extended our analysis to vitamin D. We compared survival of asbestos-exposed MexTAg mice provided with diets that were deficient or supplemented with 4500 IU/kg vitamin D (cholecalciferol). Survival of supplemented mice was significantly shorter than mice given a standard AIN93 diet containing 1000 IU/kg cholecalciferol (median survival was 29 and 32.5 weeks respectively). However, mice deficient in vitamin D had the same rate of mesothelioma development as control mice. Neither the latency time from asbestos exposure to diagnosis nor disease progression after diagnosis were significantly different between mice on these diets. We conclude that vitamin D is unlikely to moderate the incidence of disease in asbestos-exposed populations or to ameliorate the pathology in patients with established mesothelioma.

The role of key genes and pathways involved in the tumorigenesis of Malignant Mesothelioma

Malignant Mesothelioma (MM) is a very aggressive cancer with low survival rates and often diagnosed at an advanced stage. Several players have been implicated in the development of this cancer, such as asbestos, erionite and the simian virus 40 (SV40). Here, we have reviewed the involvement of erionite, SV40, as well as, the role of several genes (p16(INK4a), p14(ARF), NF2, LATS2, SAV, CTNNB1 and among others), the pathways (RAS, PI3K, Wnt, BCL and Hippo), and their respective roles in the development of MM.

High prevalence of serum antibodies reacting with simian virus 40 capsid protein mimotopes in patients affected by malignant pleural mesothelioma

Human malignant pleural mesothelioma (MPM) is considered a rare tumor, but recent estimations indicate that one-quarter million people will die of this neoplasm in Europe in the next three decades. The mineral asbestos is considered the main causative agent of this neoplasm. MPM is largely unresponsive to conventional chemotherapy/radiotherapy. In addition to asbestos exposure, genetic predisposition to asbestos carcinogenesis and to simian virus (SV)40 infection has also been suggested. SV40 is a DNA tumor virus found in some studies to be associated at high prevalence with MPM. SV40 sequences have also been detected, although at a lower prevalence than in MPM, in blood specimens from healthy donors. However, some studies have failed to reveal SV40 footprints in MPM and its association with this neoplasm. These conflicting results indicate the need for further investigations with new approaches. We report on the presence of antibodies in serum samples from patients affected by MPM that specifically react with two different SV40 mimotopes. The two SV40 peptides used in indirect ELISAs correspond to viral capsid proteins. ELISA with the two SV40 mimotopes gave overlapping results. Our data indicate that in serum samples from MPM-affected patients (n = 97), the prevalence of antibodies against SV40 viral capsid protein antigens is significantly higher (26%, P = 0.043) than in the control group (15%) represented by healthy subjects (n = 168) with the same median age (66 y) and sex. Our results suggest that SV40 is associated with a subset of MPM and circulates in humans.

NLRP1 polymorphisms in patients with asbestos-associated mesothelioma

Background

An increasing incidence of malignant mesothelioma (MM) cases in patients with low levels of asbestos exposure suggests the interference of alternative cofactors. SV40 infection was detected, as co-morbidity factor, only in 22% of asbestos-MM patients from a North-Eastern Italy area. An additional mechanism of injury related to asbestos exposure in MM development has been recently associated to inflammatory responses, principally driven by interleukin (IL)-1 beta (ß) activated within the inflammasome complex.

NLRP3 inflammosome has been described as the intracellular sensor for asbestos able to induce inflammasome activation and IL-1ß secretion while NLRP1 is expressed in lung epithelial cells and alveolar macrophages and contributes to the immune response and to survival/apoptosis balance. This study proposes to evaluate the impact of known NLRP3 and NLRP1 polymorphisms in the individual susceptibility to asbestos-induced mesothelioma in subjects from a hyperendemic area for MM.

Methods

134 Italian patients with diagnosis of mesothelioma due (MMAE, n=69) or not (MMAF, n=65) to asbestos, 256 healthy Italian blood donors and 101 Italian healthy subjects exposed to asbestos (HCAE) were genotyped for NLRP1 (rs2670660 and rs12150220) and NLRP3 (rs35829419 and rs10754558) polymorphisms.

Results

While NLRP3 SNPs were not associated to mesothelioma, the NLRP1 rs12150220 allele T was significantly more frequent in MMAE (0.55) than in HCAE (0.41) (p=0.011; OR=1.79) suggesting a predisponent effect of this allele on the development of mesothelioma. This effect was amplified when the NLRP1 rs2670660 allele was combined with the NLRP1 rs12150220 allele (p=0.004; OR=0.52).

Conclusion

Although NLRP3 SNPs was not involved in mesothelioma predisposition, these data proposed NLRP1 as a novel factor possibly involved in the development of mesothelioma.

NLRP3 promotes inflammation-induced skin cancer but is dispensable for asbestos-induced mesothelioma

Asbestos exposure can result in serious and frequently lethal diseases, including malignant mesothelioma. The host sensor for asbestos-induced inflammation is the NLRP3 inflammasome and it is widely assumed that this complex is essential for asbestos-induced cancers. Here, we report that acute interleukin-1β production and recruitment of immune cells into peritoneal cavity were significantly decreased in the NLRP3-deficient mice after the administration of asbestos. However, NLRP3-deficient mice displayed a similar incidence of malignant mesothelioma and survival times as wild-type mice. Thus, early inflammatory reactions triggered by asbestos are NLRP3-dependent, but NLRP3 is not critical in the chronic development of asbestos-induced mesothelioma. Notably, in a two-stage carcinogenesis-induced papilloma model, NLRP3-deficient mice showed a resistance phenotype in two different strain backgrounds, suggesting a tumour-promoting role of NLRP3 in certain chemically-induced cancer types.

Mesothelioma not associated with asbestos exposure

CONTEXT

Despite asbestos being identified as the single most important cause of malignant mesothelioma, the tumor is known to occur in only 10% to 20% of heavily exposed individuals. In addition, about 20% of the patients have no history of asbestos exposure even after detailed assessment. Therefore, there has been speculation for some time that asbestos alone may not be sufficient to cause mesothelioma and that other factors may be involved either as cocarcinogens or as independent mechanisms of cancer causation.

OBJECTIVE

To give a brief review of nonasbestos fiber erionite and therapeutic radiation as 2 established examples of asbestos-independent mechanisms, of the potential emerging role of man-made fibers such as carbon nanotubes, and of polyoma virus SV40 (simian virus 40) as a potential example of the cocarcinogenic mode of involvement.

DATA SOURCES

Relevant recent literature has been surveyed to portray and provide the evidence in favor of the examples.

CONCLUSIONS

Erionite has emerged as the most important example of nonasbestos-mediated cause of mesothelioma in regions such as Turkey where exposure to this type of fiber is highly prevalent. Recently, the polyoma virus SV40 has been unexpectedly discovered as an effective cocarcinogen of asbestos in the causation of animal mesothelioma, though despite considerable research, its potential role in human mesothelioma remains unproven.

Construction and identification of ATP4B-SV40T-IRES-GFP transgenic vector

AIM: To construct and identify ATP4B-SV40T-IRES-GFP transgenic vector.

METHODS: The mouse ATP4B gene promoter was amplified and inserted into IRES-GFP vector after the addition of restriction enzyme sites to result in ATP4B-IRES-GFP. After restriction enzyme digestion, the SV40T gene sequence was inserted into ATP4B-IRES-GFP. The resultant recombinant plasmid was identified by digestion with restriction enzymes PstI and AseⅠ.

RESULTS: The recombinant plasmids ATP4B-IRES-GFP and ATP4B-SV40T-IRES-GFP have been successfully constructed and can be used to generate transgenic mice.

CONCLUSION: The recombinated plasmid ATP4B-SV40T-IRES-GFP was constructed successfully and it could be used to construct the transgenic mice with primary gastric cancer.

The antioxidants vitamins A and E and selenium do not reduce the incidence of asbestos-induced disease in a mouse model of mesothelioma

Epidemiological evidence indicates that supplementation with some dietary factors is associated with a lower incidence of cancer. An effective cancer prevention strategy for the millions of people worldwide who have been exposed to asbestos could have enormous benefit. We tested whether dietary supplementation of the antioxidants vitamin A, E, and selenium could alter the pattern of disease in the MexTAg transgenic mouse model, in which mice uniformly develop mesothelioma after asbestos exposure. We focused on antioxidants because one of the most widely accepted hypotheses for the mechanism by which asbestos fibers cause cancer proposes the involvement of reactive oxygen and nitrogen species. We compared the survival of MexTAg mice that had been inoculated with asbestos fed on diets supplemented with 250,000 IU/kg vitamin A (retinoic acid), or 1,000 mg/kg vitamin E (α-tocopherol acetate) or 3 mg/kg selenium, or both vitamin E and selenium concurrently and, additionally, diets deficient in each antioxidant. We found that neither the time to develop symptoms of disease nor overall survival times were altered by any of the diets. We conclude that the data do not support the notion that dietary antioxidants will moderate the rate of mesothelioma in asbestos-exposed populations.

Simian virus 40 transformation, malignant mesothelioma and brain tumors

Simian virus 40 (SV40) is a DNA virus isolated in 1960 from contaminated polio vaccines, that induces mesotheliomas, lymphomas, brain and bone tumors, and sarcomas, including osteosarcomas, in hamsters. These same tumor types have been found to contain SV40 DNA and proteins in humans. Mesotheliomas and brain tumors are the two tumor types that have been most consistently associated with SV40, and the range of positivity has varied about from 6 to 60%, although a few reported 100% of positivity and a few reported 0%. It appears unlikely that SV40 infection alone is sufficient to cause human malignancy, as we did not observe an epidemic of cancers following the administration of SV40-contaminated vaccines. However, it seems possible that SV40 may act as a cofactor in the pathogenesis of some tumors. In vitro and animal experiments showing cocarcinogenicity between SV40 and asbestos support this hypothesis.

Malignant mesothelioma: facts, myths, and hypotheses

Malignant mesothelioma (MM) is a neoplasm arising from mesothelial cells lining the pleural, peritoneal, and pericardial cavities. Over 20 million people in the US are at risk of developing MM due to asbestos exposure. MM mortality rates are estimated to increase by 5-10% per year in most industrialized countries until about 2020. The incidence of MM in men has continued to rise during the past 50 years, while the incidence in women appears largely unchanged. It is estimated that about 50-80% of pleural MM in men and 20-30% in women developed in individuals whose history indicates asbestos exposure(s) above that expected from most background settings. While rare for women, about 30% of peritoneal mesothelioma in men has been associated with exposure to asbestos. Erionite is a potent carcinogenic mineral fiber capable of causing both pleural and peritoneal MM. Since erionite is considerably less widespread than asbestos, the number of MM cases associated with erionite exposure is smaller. Asbestos induces DNA alterations mostly by inducing mesothelial cells and reactive macrophages to secrete mutagenic oxygen and nitrogen species. In addition, asbestos carcinogenesis is linked to the chronic inflammatory process caused by the deposition of a sufficient number of asbestos fibers and the consequent release of pro-inflammatory molecules, especially HMGB-1, the master switch that starts the inflammatory process, and TNF-alpha by macrophages and mesothelial cells. Genetic predisposition, radiation exposure and viral infection are co-factors that can alone or together with asbestos and erionite cause MM. J. Cell. Physiol. 227: 44-58, 2012. © 2011 Wiley Periodicals, Inc.

Adult mouse epicardium modulates myocardial injury by secreting paracrine factors

The epicardium makes essential cellular and paracrine contributions to the growth of the fetal myocardium and the formation of the coronary vasculature. However, whether the epicardium has similar roles postnatally in the normal and injured heart remains enigmatic. Here, we have investigated this question using genetic fate-mapping approaches in mice. In uninjured postnatal heart, epicardial cells were quiescent. Myocardial infarction increased epicardial cell proliferation and stimulated formation of epicardium-derived cells (EPDCs), which remained in a thickened layer on the surface of the heart. EPDCs did not adopt cardiomyocyte or coronary EC fates, but rather differentiated into mesenchymal cells expressing fibroblast and smooth muscle cell markers. In vitro and in vivo assays demonstrated that EPDCs secreted paracrine factors that strongly promoted angiogenesis. In a myocardial infarction model, EPDC-conditioned medium reduced infarct size and improved heart function. Our findings indicate that epicardium modulates the cardiac injury response by conditioning the subepicardial environment, potentially offering a new therapeutic strategy for cardiac protection.

Merkel cell polyomavirus is not detected in mesotheliomas

BACKGROUND

Merkel cell polyomavirus (MCPyV) is the first polyoma virus consistently linked to the etiology of a human cancer. Serological studies indicate that the virus is commonly acquired in childhood, with seroprevalence reaching 50% or higher among young adults. The modes of MCPyV transmission are still unclear, but it has been identified in respiratory tract samples. Given its respiratory tropism, we examined whether MCPyV could be detected in mesothelioma tissue, a malignancy induced in animal models by another polyomavirus, SV40.

OBJECTIVE

To determine if MCPyV DNA can be detected in mesothelioma.

STUDY DESIGN

DNA was extracted from 45 fresh-frozen mesothelioma samples. PCR was used to detect and quantify the abundance of MCPyV DNA, and a human control gene, in duplicates of the tissues. DNA from a sequence verified MCC tumor was used as a positive control.

RESULTS

The human control gene was detected at high levels in all but three mesothelioma tissues. MCPyV DNA was detected in only one mesothelioma, and the level of viral DNA was very low.

CONCLUSIONS

These results are inconsistent with the hypothesis that MCPyV is etiologically linked to mesothelioma.

Animal models of malignant pleural effusion

PURPOSE OF REVIEW

Malignant pleural effusion (MPE) poses a common and significant clinical problem. Its pathogenesis is poorly understood and therapeutic options are limited. Herein are summarized animal models of MPE and their contributions in unveiling new aspects of the pathobiology of the condition.

RECENT FINDINGS

In recent years, different groups have developed novel models of MPE, including a genetic mouse model of spontaneous mesothelioma development, a model of adenocarcinoma-induced MPE in immunocompetent mice, as well as models of human cancer-induced MPE in immunocompromised animals, all relevant to the human condition to a different extent. Work using these models has yielded novel insights into the pathogenesis of mesothelioma as well as into the mechanisms of intrapleural malignant effusion accumulation and tumor dissemination. The data produced underline the significance of tumor-associated inflammation, angiogenesis, and vascular hyperpermeability in the pathogenesis of MPE.

SUMMARY

In the past few years, novel approaches to induce experimental MPE have yielded new insights into its pathogenesis and have identified possible therapeutic targets to block pleural fluid exudation induced by primary and metastatic cancer cells in the pleural space.