New insights into understanding the mechanisms, pathogenesis, and management of malignant mesotheliomas

Mechanisms and shapes of causal exposure-response functions for asbestos in mesotheliomas and lung cancers

This paper summarizes recent insights into causal biological mechanisms underlying the carcinogenicity of asbestos. It addresses their implications for the shapes of exposure-response curves and considers recent epidemiologic trends in malignant mesotheliomas (MMs) and lung fiber burden studies. Since the commercial amphiboles crocidolite and amosite pose the highest risk of MMs and contain high levels of iron, endogenous and exogenous pathways of iron injury and repair are discussed. Some practical implications of recent developments are that: (1) Asbestos-cancer exposure-response relationships should be expected to have non-zero background rates; (2) Evidence from inflammation biology and other sources suggests that there are exposure concentration thresholds below which exposures do not increase inflammasome-mediated inflammation or resulting inflammation-mediated cancer risks above background risk rates; and (3) The size of the suggested exposure concentration threshold depends on both the detailed time patterns of exposure on a time scale of hours to days and also on the composition of asbestos fibers in terms of their physiochemical properties. These conclusions are supported by complementary strands of evidence including biomathematical modeling, cell biology and biochemistry of asbestos-cell interactions in vitro and in vivo, lung fiber burden analyses and epidemiology showing trends in human exposures and MM rates.

TROP2 expression and SN38 antitumor activity in malignant pleural mesothelioma cells provide a rationale for antibody-drug conjugate therapy

OBJECTIVES

Malignant pleural mesothelioma (MPM) is an aggressive cancer which at large is not amenable to curative surgery. Despite the recent approval of immune checkpoint inhibitor therapy, the response rates and survival following systemic therapy is still limited. Sacituzumab govitecan is an antibody-drug conjugate targeting the topoisomerase I inhibitor SN38 to trophoblast cell-surface antigen 2 (TROP-2)-positive cells. Here we have explored the therapeutic potential of sacituzumab govitecan in MPM models.

MATERIALS AND METHODS

TROP2 expression was analyzed in a panel of two well established and 15 pleural effusion derived novel lines by RT-QPCR and immunoblotting, TROP2 membrane-localization was studied by flow cytometry and immunohistochemistry. Cultured mesothelial cells and pneumothorax pleura served as controls. The sensitivity of MPM cell lines to irinotecan and SN38 was studied using cell viability, cell cycle, apoptosis and DNA damage assays. Drug sensitivity of cell lines was correlated with RNA expression of DNA repair genes. Drug sensitivity was defined as an IC50 below 5 nM in the cell viability assay.

RESULTS

TROP2 expression was detected at RNA and protein level in 6 of the 17 MPM cell lines, but not in in cultured mesothelial control cells or in the mesothelial layer of the pleura. TROP2 was detectable on the cell membrane in 5 MPM lines and was present in the nucleus in 6 cell models. Ten of 17 MPM cell lines showed sensitivity to SN38 treatment, among those 4 expressed TROP2. High AURKA RNA expression and high proliferation rate correlated with sensitivity to SN38-induced cell death, DNA damage response, cell cycle arrest and cell death. Sacituzumab govitecan treatment effectively induced cell cycle arrest and cell death in TROP2-positive MPM cells.

CONCLUSION

TROP2 expression and sensitivity to SN38 in MPM cell lines support biomarker-selected clinical exploration of sacituzumab govitecan in patients with MPM.

Evaluation of DNA/RNA quality from cell block of malignant mesothelioma and lung adenocarcinoma

Malignant mesothelioma (MM) is a rare and highly lethal tumor that arises from mesothelial tissue on the surface of the chest and abdominal cavity. Cytological examination of body fluids, including pleural fluid and ascites, is essential for the differentiation of malignant mesothelioma from other carcinomas, such as lung and gastrointestinal carcinomas and metastatic tumors. To evaluate the effectiveness of cell block preparation procedures, which are used for immunocytochemical staining and genetic panel analysis of tumor-specific gene mutations, we used various fixatives. We also evaluated the effects of immunostaining, and the quality of nucleic acids for genetic analysis.

METHODS

Cell blocks were prepared using the malignant mesothelioma cell lines MESO4 and H226 and non-small cell lung carcinoma cell line HCC78. The cells were fixed using 10% neutral buffered formalin and four different fixatives for liquid cytology. Fixed cells were formed into cell clusters using sodium alginate or centrifugation, and paraffin-embedded cell blocks were prepared.

RESULTS

Cell blocks were morphologically evaluated by hematoxylin and eosin and immunocytological staining, and the nucleic acid quality was evaluated by DNA/RNA extraction, qPCR, and next-generation sequence analysis. D2-40 and WT1 staining differed depending on the fixation solution and the cell cluster formation method; however, the degree of nucleic acid degradation was not impaired by any method.

CONCLUSION

Although the morphological evaluation of cytology specimens is affected by the method of cell block preparation, it is still useful for nucleic acid extraction and gene panel analysis, as long as there are sufficient amounts of tumor cells.

ECM Mechanoregulation in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma is a relatively rare, but devastating tumor, because of the difficulties in providing early diagnosis and effective treatments with conventional chemo- and radiotherapies. Patients usually present pleural effusions that can be used for diagnostic purposes by cytological analysis. This effusion cytology may take weeks or months to establish and has a limited sensitivity (30%-60%). Then, it is becoming increasingly urgent to develop alternative investigative methods to support the diagnosis of mesothelioma at an early stage when this cancer can be treated successfully. To this purpose, mechanobiology provides novel perspectives into the study of tumor onset and progression and new diagnostic tools for the mechanical characterization of tumor tissues. Here, we report a mechanical and biophysical characterization of malignant pleural mesothelioma cells as additional support to the diagnosis of pleural effusions. In particular, we examined a normal mesothelial cell line (Met5A) and two epithelioid mesothelioma cell lines (REN and MPP89), investigating how malignant transformation can influence cellular function like proliferation, cell migration, and cell spreading area with respect to the normal ones. These alterations also correlated with variations in cytoskeletal mechanical properties that, in turn, were measured on substrates mimicking the stiffness of patho-physiological ECM.

Malignant Peritoneal Mesothelioma Associated With Endometriosis: A Clinicopathologic Study of 15 Cases

Only a few cases of malignant peritoneal mesothelioma (MPeM) associated with endometriosis have been published; with chronic inflammation of the peritoneum associated with the latter being postulated as an inducing factor in the pathogenesis of this tumor. We assessed the clinicopathologic characteristics of MPeM associated with endometriosis to determine if there were other factors besides inflammation that may contribute to the pathogenesis in this patient population. Fifteen MPeM associated with endometriosis were retrieved from our files. Most presented with abdominal/pelvic pain, mass or distention; median age was 45 yr. Only 16% of patients had a history of asbestos exposure. In contrast, a third of the patients had a personal history of other neoplasms, and >80% had a family history of malignancies. Although most tumors had gross and microscopic features typical of MPeM, some had confounding features including "adhesion-like" appearance or gelatinous cysts/nodules, and signet ring cells. Tumors were epithelioid (9) and biphasic (6). MPeM was misdiagnosed as Müllerian carcinoma in 40% of cases. All patients (n=15) had cytoreductive surgery in addition to other therapies. Only 2/12 patients died of disease (17%). The 3- and 5-yr overall survival was 90%. MPeM associated with endometriosis tends to occur in patients with personal/familial history of malignancies, which may be a predisposing factor. In light of this finding, the role of endometriosis in the pathogenesis of MPeM is likely less relevant. The favorable outcome seen in these patients may be related to germline mutations or the hormonal milieu and needs further investigation.

Mesothelioma Malignancy and the Microenvironment: Molecular Mechanisms

Several studies have reported that cellular and soluble components of the tumor microenvironment (TME) play a key role in cancer-initiation and progression. Considering the relevance and the complexity of TME in cancer biology, recent research has focused on the investigation of the TME content, in terms of players and informational exchange. Understanding the crosstalk between tumor and non-tumor cells is crucial to design more beneficial anti-cancer therapeutic strategies. Malignant pleural mesothelioma (MPM) is a complex and heterogenous tumor mainly caused by asbestos exposure with few treatment options and low life expectancy after standard therapy. MPM leukocyte infiltration is rich in macrophages. Given the failure of macrophages to eliminate asbestos fibers, these immune cells accumulate in pleural cavity leading to the establishment of a unique inflammatory environment and to the malignant transformation of mesothelial cells. In this inflammatory landscape, stromal and immune cells play a driven role to support tumor development and progression via a bidirectional communication with tumor cells. Characterization of the MPM microenvironment (MPM-ME) may be useful to understand the complexity of mesothelioma biology, such as to identify new molecular druggable targets, with the aim to improve the outcome of the disease. In this review, we summarize the known evidence about the MPM-ME network, including its prognostic and therapeutic relevance.

Histological comparison of malignant epithelioid mesothelioma in young and adult cattle

The histology and immunohistochemistry of pleomorphic and conventional epithelioid mesotheliomas were examined. The former was detected in two young calves aged 2 and 4 months and was characterized by pleomorphic and atypical cells with decreased expression of cytokeratin 7 (CK7). In contrast, the latter was found in a 31-month-old heifer, consisting of tumor cells uniform in size and shape with CK7 expression in nearly all cells. Production of collagen by tumor cells was demonstrated in both histological types, and was considered to be characteristic of bovine epithelioid mesothelioma. Pleomorphic mesothelioma is far more pleomorphic and mitotically active than conventional mesothelioma, and its normal counterpart may be immature mesothelial cells with high proliferation potential, which exist in fetal life and early calfhood.

Asbestos and Zeolites: from A to Z via a Common Ion

Asbestos and zeolites are silicate-based minerals, linked inextricably via paradoxical similarities and differences which have emanated from different geological epochs. Both have been employed in the service of humanity through millennia: asbestos, for its "inextinguishable" quality of being an insulator against heat and fire; zeolite, a "boiling stone" with its volcanic and marine sedimentary rock origins, for its propensity to adsorb water and remove metals and toxins. Serious adverse health effects observed in asbestos miners as long ago as the 1st Century AD did not halt the rising popularity of asbestos. As the miracle material of the 1900s, asbestos production and consumption exploded, culminating in its ubiquity in ships, vehicles, homes, commercial buildings, and over 3000 different industrial and household products. Through the 1940s and 1950s, epidemiological studies concluded that asbestos was a likely cause of asbestosis, lung cancer, and malignant mesothelioma, and it is now banned in many but far from all countries. The long latency between exposure to asbestos and the occurrence of cancer has obscured the deadly consequences of asbestos exposure for centuries. Even today, a considerable part of the world population is insufficiently aware of the dangers of asbestos, and millions of tons of this carcinogen continue to be mined and used worldwide. Zeolites, both natural and synthetic, are microporous aluminosilicate minerals commonly used in a myriad of processes, in the petrochemical industry, in domestic appliances and cleaning agents, as commercial adsorbents and exchangers for toxins and pollutants, and as catalysts. Zeolites are found in agriculture, veterinary science, and human health. More recently, new materials such as carbon nanotubes are being employed in materials requiring durability and thermal and electrical conductivity, yet nanotubes are now joining the ranks of more established particulates such as asbestos and silica, in causing human disease. In this review, we compare and contrast the similarities and differences of these two groups of silicate minerals and their waxing and waning use in the employ of humanity.

C1q-HA Matrix Regulates the Local Synthesis of Hyaluronan in Malignant Pleural Mesothelioma by Modulating HAS3 Expression

Simple Summary

Malignant pleural mesothelioma (MPM) is a rare and aggressive tumor characterized by poor prognosis due to late diagnosis and the absence of efficient first-line treatments. Hyaluronic acid (HA) and the complement protein C1q represent two pivotal players in the MPM tumor microenvironment by acting in association with effects on cancer cell adhesion, migration and proliferation. The aim of the current study is to prove HA production by MPM primary cells and to understand whether HA metabolism modulation could be considered a potential target for future therapeutic approaches in MPM.

Abstract

Increased hyaluronic acid (HA) production is often associated with cancer progression. In malignant pleural mesothelioma (MPM), HA is found at elevated levels in pleural effusions and sera of patients, and it has been widely debated whether MPM cells are able to produce HA by themselves or through the release of growth factors stimulating other cells. Another key component of the MPM microenvironment is C1q, which can act as a pro-tumorigenic factor favoring cell adhesion, migration and proliferation. The aim of the current study was to prove that MPM primary cells are able to synthesize HA and to inquire the stimulus given by C1q–HA matrix to HA synthesis. We confirmed the presence of a HA coat and cable-like structures around MPM primary cells, as well as an intracellular pool, mainly localized in the cytoplasmic and perinuclear region. After evaluating HA synthase (HAS) enzymes’ basal expression in MPM primary cells, we found that C1q bound to HA was able to impinge upon HA homeostasis by upregulating HAS3 both at the mRNA and the protein levels. High expression of HAS3 has been correlated with a shorter life expectancy in MPM by bioinformatical analysis. These data confirmed that C1q bound to HA may exert pro-tumorigenic activity and identified HAS3 as a potential target in MPM.

Sensitive Blood-Based Detection of Asbestos-Associated Diseases Using Cysteine-Rich Angiogenic Inducer 61 as Circulating Protein Biomarker

BACKGROUND

Detection of asbestos-associated diseases like asbestosis or mesothelioma is still challenging. We sought to improve the diagnosis of benign asbestos-associated disease (BAAD) by detection of the protein cysteine-rich angiogenic inducer 61 (Cyr61) in human plasma.

METHODS

Plasma Cyr61 was quantified using an enzyme-linked immunosorbent assay. Plasma samples from males diagnosed with BAAD, but without a malignant disease (n = 101), and malignant mesothelioma (n = 21; 15 males, 6 females), as well as nonasbestos-exposed healthy control participants (n = 150; 58 males, 92 females) were analyzed. Clinical sensitivity and specificity of Cyr61 were determined by receiver operating characteristic analysis.

RESULTS

The median plasma Cyr61 concentration for healthy control participants was 0.27 ng/mL. Cytoplasmic Cyr61 in peripheral blood mononuclear cells from healthy control participants was evenly distributed, as detected by immunofluorescent staining. The increase in plasma Cyr61 concentrations in the BAAD study group was statistically significant compared to the healthy control participants (P < 0.0001). For the detection of BAAD vs male healthy control participants, clinical sensitivity was 88% and clinical specificity 95% with an area under the curve of 0.924 at maximal Youden Index. For a predefined clinical specificity of 100%, the clinical sensitivity was 76%. For male mesothelioma patients vs male healthy control participants, the clinical sensitivity at maximal Youden Index was 95% with a clinical specificity of 100% (area under the curve, 0.997) and for a predefined clinical specificity of 100%, the clinical sensitivity was 93%.

CONCLUSIONS

In our study, plasma Cyr61 protein concentrations showed to be a new biomarker for asbestos-associated diseases like BAAD and mesothelioma in men, which deserves further investigation in large-scale cohort studies.

Tumor Microenvironment-Associated Immune-Related Genes for the Prognosis of Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a rare but highly aggressive thoracic malignancy. ESTIMATE algorithm-derived immune scores are commonly used to quantify the immune and stromal components in tumors. Thus, this algorithm may help determine the tumor microenvironment (TME)-related gene expression profile associated with tumor immunity. This study aimed at mining public databases to determine a potential correlation between differentially expressed genes (DEGs) and survival in patients with MPM. We categorized patients from the Gene Expression Omnibus database according to their immune/stromal scores into high- and low-score groups. Functional enrichment analysis and the construction of protein-protein interaction networks showed that the DEGs identified were primarily involved in the TME. Furthermore, we validated these genes in an independent cohort of patients with MPM from The Cancer Genome Atlas database. DEG analysis showed that 29 DEGs were cancer driver genes. Subsequently, 14 TME-related genes, which have been previously neglected, were shown to exhibit significant prognostic potential in MPM. In conclusion, immune/stromal scores are novel predictors of a poor prognosis in patients with MPM. We identified DEGs that are involved in immunity against MPM and may contribute to patient survival. Owing to their potential as prognostic factors for MPM, these 14 TME-related genes need to be studied in detail in the future.

Carbon Nanotubes under Scrutiny: Their Toxicity and Utility in Mesothelioma Research

Research on the toxicity of engineered carbon nanotubes (CNT) was initiated by Belgian academic chemists and toxicologists more than 15 years ago. It is now undisputed that some of these attractive nanomaterials induce serious illness such as fibrosis and cancer. The physico-chemical determinants of CNT-induced adverse effects are now elucidated and include shape, nanoscale diameter, and structural defects. Generated in vitro and in vivo data on their inflammogenic and fibrogenic activities were combined and translated in AOP (adverse outcome pathways) available for risk assessment and regulatory policies. The asbestos-like carcinogenic effect of CNT, notably their capacity to induce malignant mesothelioma (MM), remain, however, a cause of concern for public health and strongly curb the craze for CNT in industries. MM still represents a real challenge for clinicians and a highly refractory cancer to existing therapeutic strategies. By comparing mesotheliomagenic CNT (needle-like CNT-N) to non mesotheliomagenic CNT (tangled-like CNT-T), our group generated a relevant animal model that highlights immune pathways specifically associated to the carcinogenic process. Evidence indicates that only CNT-N possess the intrinsic capacity to induce a preferential, rapid, and sustained accumulation of host immunosuppressive cells that subvert immune surveillance and suppress anti-mesothelioma immunity. This new concept offers novel horizons for the clinical management of mesothelioma and represents an additional tool for predicting the mesotheliomagenic activity of newly elaborated CNT or nanoparticles.

HEG1-responsive microRNA-23b regulates cell proliferation in malignant mesothelioma cells

Malignant mesothelioma (MM) is a fatal tumor, and the absence of a specific diagnostic marker and/or a pathogenic molecule-targeting drug is a major issue for its pathological diagnosis and for targeting therapy. The molecular target of MM has not been elucidated because of unknown survival, death, and cytotoxic signals in MM. HEG homolog 1 (HEG1) is a mucin-like membrane protein that contains epidermal growth factor-like domains, and it plays an important role in cancers through aberrant signaling, including that during cell adhesion, as well as through protection from invasion of tumor cells. HEG1 expression supports the survival and proliferation of MM cells. In this study, functional analysis of HEG1 and microRNAs using MM cell lines (H226, MESO4, H2052) was performed. The MTS assay revealed that cell proliferation was significantly reduced upon transient transfection with microRNA-23b (miR-23b) inhibitor and/or HEG1 siRNA. The Annexin V assay revealed that apoptosis was induced upon suppression of miR-23b and/or HEG1. Western blotting showed that the autophagy-related protein LC3-II was induced upon suppression of miR-23b and/or HEG1. These results revealed that miR-23b contributes to HEG1-dependent cell proliferation through evasion of cytotoxicity induced by apoptosis and autophagy in MM cells. HEG1-dependent/mediated miR-23b signaling may therefore be a potential target for MM diagnosis and therapy.

Pleural mesothelioma and lung cancer: the role of asbestos exposure and genetic variants in selected iron metabolism and inflammation genes

Two of the major cancerous diseases associated with asbestos exposure are malignant pleural mesothelioma (MPM) and lung cancer (LC). In addition to asbestos exposure, genetic factors have been suggested to be associated with asbestos-related carcinogenesis and lung genotoxicity. While genetic factors involved in the susceptibility to MPM were reported, to date the influence of individual genetic variations on asbestos-related lung cancer risk is still poorly understood. Since inflammation and disruption of iron (Fe) homeostasis are hallmarks of asbestos exposure affecting the pulmonary tissue, this study aimed at investigating the association between Fe-metabolism and inflammasome gene variants and susceptibility to develop LC or MPM, by comparing an asbestos-exposed population affected by LC with an "asbestos-resistant exposed population". A retrospective approach similar to our previous autopsy-based pilot study was employed in a novel cohort of autoptic samples, thus giving us the possibility to corroborate previous findings obtained on MPM by repeating the analysis in a novel cohort of autoptic samples. The protective role of HEPH coding SNP was further confirmed. In addition, the two non-coding SNPs, either in FTH1 or in TF, emerged to exert a similar protective role in a new cohort of LC exposed individuals from the same geographic area of MPM subjects. No association was found between NLRP1 and NLRP3 polymorphisms with susceptibility to develop MPM and LC. Further research into a specific MPM and LC "genetic signature" may be needed to broaden our knowledge of the genetic landscape attributed to result in MPM and LC.

Targeting Calcium Signalling in Malignant Mesothelioma

Calcium ions (Ca²⁺) are central in cancer development and growth, serving as a major signaling system determining the cell’s fate. Therefore, the investigation of the functional roles of ion channels in cancer development may identify novel approaches for determining tumor prognosis. Malignant mesothelioma is an aggressive cancer that develops from the serosal surface of the body, strictly related to asbestos exposure. The treatment of malignant mesothelioma is complex and the survival outcomes, rather than the overall survival data are, to date, disappointedly daunting. Nevertheless, conventional chemotherapy is almost ineffective. The alteration in the expression and/or activity of Ca²⁺ permeable ion channels seems to be characteristic of mesothelioma cells. In this review, we explore the involvement of the Ca²⁺toolkit in this disease. Moreover, the established sensitivity of some Ca²⁺channels to selective pharmacological modulators makes them interesting targets for mesothelioma cancer therapy.

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.

Exosomal miR-16-5p as a target for malignant mesothelioma

Malignant mesothelioma (MM) is an asbestos-induced cancer arising on the mesothelial surface of organ cavities. MM is essentially incurable without a means of early diagnosis and no successful standard of care. These facts indicate a deep chasm of knowledge that needs to be filled. Our group recently delved into MM tumor biology from the perspective of exosome-contained microRNAs (miRNAs). We discovered that the most abundant miRNAs in MM cancer exosomes were tumor suppressors, particularly miR-16-5p. This observation lead us to hypothesize that MM cells preferentially secreted tumor-suppressor miRNAs via exosomes. Through separate avenues of potential therapeutic advance, we embarked on an innovative strategy to kill MM tumor cells. We employed small molecule inhibitors to block exosome secretion, thereby reducing miR-16-5p exosome loss and replenishing cellular miR-16-5p leading to reduced tumorigenic capacity and miR-16-5p target oncoproteins CCND1 and BCL2. Additionally, we force-fed MM tumor exosomes back to MM tumor cells, which led to cell death, and a reduction in the same oncoproteins. We recapitulated these results with direct transfection of miR-16-5p, confirmed that this is a cancer-cell specific effect, and elucidated a part of the miR-16-5p mechanism of exosome loading.

What can independent research for mesothelioma achieve to treat this orphan disease?

Introduction: Malignant pleural mesothelioma (MPM) is a rare neoplasm with a poor prognosis, as current therapies are ineffective. Despite the increased understanding of the molecular biology of mesothelioma, there is still a lack of drugs that dramatically enhance patient survival. Area Covered: This review discusses recent and complete clinical trials supported by the NIH, other U.S. Federal agencies, universities and organizations found on clinicaltrials.gov. Firstly, chemotherapy-based trials are described, followed by immunotherapy and multitargeted therapy. Then we introduce drug repositioning and the use of drug docking as tools to find new interesting molecules. Finally, we highlight potential molecular pathways that may play a role in mesothelioma biology and therapy. Expert Opinion: Numerous biases are present in the clinical trials due to a restricted number of cases, inappropriate endpoints and inaccurate stratification of patients which delay the finding of a treatment for MPM. The most crucial issue of independent research for MPM is the lack of more substantive funding to translate these findings to the clinical setting. However, this approach is not necessarily scientific given the low mutational load of mesothelioma relative to other cancers, and therefore patients need a more solid rationale to have a good chance of successful treatment.

CDKN2A copy number and p16 expression in malignant pleural mesothelioma in relation to asbestos exposure

Background

Deletion of the CDKN2A locus is centrally involved in the development of several malignancies. In malignant pleural mesothelioma (MPM), it is one of the most frequently reported genomic alteration. MPM is strongly associated with a patients’ asbestos exposure. However, the status of CDKN2A and the expression of the corresponding protein, p16, in relation to MPM patient’s asbestos exposure is poorly known. Copy number alterations in 2p16, 9q33.1 and 19p13 have earlier been shown to accumulate in lung cancer in relation to asbestos exposure but their status in MPM is unclear.

Methods

We studied DNA copy numbers for CDKN2A using fluorescence in situ hybridization (FISH) and p16 expression by immunohistochemistry (IHC) in 92 MPM patients, 75 of which with known asbestos exposure status. We also studied, in MPM, copy number alterations in 2p16, 9q33.1 and 19p13 by FISH.

Results

We were unable to detect an association between p16 expression and pulmonary asbestos fiber count in MPM tumor cells. However, significantly more MPM patients with high pulmonary asbestos fiber count (> 1 million fibers per gram [f/g]) had stromal p16 immunoreactivity than MPM of patients with low exposure (≤ 0.5 million f/g) (51.4% vs 16.7%; p = 0.035, Chi-Square). We found that an abnormal copy number of CDKN2A in MPM tumor cells associated with a high pulmonary asbestos fiber count (p = 0.044, Fisher’s Exact test, two-tailed). In contrast to our earlier findings in asbestos associated lung cancer, DNA copy number changes in 2p16, 9q33 and 19p13 were not frequent in MPM although single cases with variable copy numbers on those regions were seen.

Conclusions

We found two instances where the gene locus CDKN2A or its corresponding protein expression, is associated with high asbestos exposure levels. This suggests that there may be biological differences between the mesotheliomas with high pulmonary asbestos fiber count and those with low fiber count.

Electronic supplementary material

The online version of this article (10.1186/s12885-019-5652-y) contains supplementary material, which is available to authorized users.

Metadherin Is a Prognostic Apoptosis Modulator in Mesothelioma Induced via NF-κB-Mediated Signaling

Therapies against malignant pleural mesothelioma (MPM) have yielded disappointing results, in part, because pathologic mechanisms remain obscure. In searching for rational molecular targets, we identified metadherin (MTDH), a multifunctional gene associated with several tumor types but previously unrecognized in MPM. Cox proportional hazards regression analysis delineated associations between higher MTDH expression and lower patient survival from three independent MPM cohorts (n = 349 patients). Through in vitro assays with overexpression and downregulation constructs in MPM cells, we characterized the role of MTDH. We confirmed in vivo the phenotype of altered MTDH expression in a murine xenograft model. Transcriptional regulators of MTDH were identified by chromatin immunoprecipitation. Overexpression of both MTDH mRNA (12-fold increased) and protein levels was observed in tumor tissues. MTDH stable overexpression significantly augmented proliferation, invasiveness, colony formation, chemoresistance, and an antiapoptosis phenotype, while its suppression showed opposite effects in MPM cells. Interestingly, NF-κB and c-Myc (in a feed-forward loop motif) contributed to modulating MTDH expression. Knockdown of MTDH expression profoundly retarded xenograft tumor growth. Thus, our findings support the notion that MTDH integrates upstream signals from certain transcription factors and mediates pathogenic interactions contributing to MPM traits. MTDH represents a new MPM-associated gene that can contribute to insights of MPM biology and, as such, suggest other treatment strategies.

Impact of asbestos on public health: a retrospective study on a series of subjects with occupational and non-occupational exposure to asbestos during the activity of Fibronit plant (Broni, Italy)

The goal of this study is to understand more about the role of asbestos in causing human diseases, first of all mesothelioma, by investigating a large series of deaths due to asbestos-related diseases (ARDs). The main aim is to clarify if even very low amounts of asbestos can cause mesothelioma and other ARDs, as well as to find out if a different individual vulnerability can be important. This retrospective study included 188 subjects who died from asbestos related diseases in 2000-2017 in the area around Broni, Italy, where an important asbestos cement factory had been active from 1932 until 1993. In each case, a forensic autopsy has been performed. In order to perform the present study, the records were retrieved, including the clinical files, the autopsy, and the histological report. The statistical analysis performed showed that there was a significant relation between the cause of death (mesothelioma, lung cancer or asbestosis) and the kind of exposure (occupational, neighborhood or household), showing that all the subjects not exposed occupationally (and, therefore, exposed to lower amounts of asbestos) died from mesothelioma, whereas the individuals who used to work at the plant died also from other caused (asbestosis, lung cancer). Significant differences were highlighted examining the distribution of the causes of death according to the smoking habits. Moreover, among the mesothelioma patients, the survival time was shorter in the subjects with a neighborhood or household exposure than in the occupationally exposed individuals. The study provided meaningful data about the role of asbestos in causing human pathologies. In particular, the present data appear to support the hypothesis that even an exposure to a very little amount of asbestos can cause mesothelioma in hypersusceptible subjects (probably, on a genetic basis).

Emerging Role of Immunosuppression in Diseases Induced by Micro- and Nano-Particles: Time to Revisit the Exclusive Inflammatory Scenario

Fibrosis, cancer, and autoimmunity developing upon particle exposure have been exclusively linked with uncontrolled inflammatory processes. The critical role of inflammation is now challenged by several contradictory observations indicating that the emergence of these chronic disorders may result from non-inflammatory events. A growing number of studies reveals that micro- and nano-particles can cause exaggerated and persistent immunosuppression characterized by the release of potent anti-inflammatory cytokines (IL-10 and TGF-β), and the recruitment of major regulatory immune cells (M2 macrophages, T and B regs, and MDSC). This persistent immunosuppressive environment is initially established to limit early inflammation but contributes later to fibrosis, cancer, and infection. Immunosuppression promotes fibroblast proliferation and matrix element synthesis and subverts innate and adaptive immune surveillance against tumor cells and microorganisms. This review details the contribution of immunosuppressive cells and their derived immunoregulatory mediators and delineates the mutual role of inflammatory vs. immunosuppressive mechanisms in the pathogenesis of chronic diseases induced by particles. The consideration of these new results explains how particle-related diseases can develop independently of chronic inflammation, enriches current bioassays predicting particle toxicity and suggests new clinical strategies for treating patients affected by particle-associated diseases.

Differential regulation of the sphere formation and maintenance of cancer-initiating cells of malignant mesothelioma via CD44 and ALK4 signaling pathways

Malignant mesothelioma (MM) has a poor prognosis and is largely resistant to standard treatments, so it is important to seek novel therapeutic strategies for this disease. Cancer-initiating cells (CICs) were previously identified in MM using stem cell-associated markers in combination with spheroid cultures. However, the mechanisms underlying the induction and maintenance of CICs in MM remain to be fully explored. Here we showed that the CICs, which had high aldehyde dehydrogenase levels (ALDH^bright) and stem cell-associated genes, were expanded in MM cells cultured under sphere-forming conditions. The MM spheroids also initiated tumors in immunodeficient mice more efficiently than did conventional adherent MM cells. In the MM spheroids, the expression of hyaluronan (HA) synthases was upregulated. Inhibiting the HA synthesis or CD44 functions by gene knockdown or neutralizing antibody abolished the formation of large-sized spheroids and the expansion of ALDH^bright CICs. The expression of activin-A was also increased in the spheroids, and type I activin-A receptor subunit (ALK4) was upregulated in the ALDH^bright CICs. The neutralization of activin-A or functional inactivation of ALK4 diminished the ALDH^bright CICs without affecting spheroid formation. The knockdown of CD44 or ALK4 strongly suppressed the tumor growth in immunodeficient mice. These results together suggest that the HA–CD44 and activin-A–ALK4 pathways differentially regulate the spheroid formation and maintenance of ALDH^bright CICs in MM cells, and that both pathways play critical roles in tumor growth in immunodeficient hosts. Our findings provide a novel therapeutic option for MM that targets signaling pathways that promote the CIC compartment through CD44 and ALK4.

Pirfenidone decreases mesothelioma cell proliferation and migration via inhibition of ERK and AKT and regulates mesothelioma tumor microenvironment in vivo

Malignant mesothelioma is an aggressive cancer with poor prognosis. It is characterized by prominent extracellular matrix, mesenchymal tumor cell phenotypes and chemoresistance. In this study, the ability of pirfenidone to alter mesothelioma cell proliferation and migration as well as mesothelioma tumor microenvironment was evaluated. Pirfenidone is an anti-fibrotic drug used in the treatment of idiopathic pulmonary fibrosis and has also anti-proliferative activities. Mesothelioma cell proliferation was decreased by pirfenidone alone or in combination with cisplatin. Pirfenidone also decreased significantly Transwell migration/invasion and 3D collagen invasion. This was associated with increased BMP pathway activity, decreased GREM1 expression and downregulation of MAPK/ERK and AKT/mTOR signaling. The canonical Smad-mediated TGF-β signaling was not affected by pirfenidone. However, pirfenidone blocked TGF-β induced upregulation of ERK and AKT pathways. Treatment of mice harboring mesothelioma xenografts with pirfenidone alone did not reduce tumor proliferation in vivo. However, pirfenidone modified the tumor microenvironment by reducing the expression of extracellular matrix associated genes. In addition, GREM1 expression was downregulated by pirfenidone in vivo. By reducing two major upregulated pathways in mesothelioma and by targeting tumor cells and the microenvironment pirfenidone may present a novel anti-fibrotic and anti-cancer adjuvant therapy for mesothelioma.

Malignant peritoneal mesothelioma in patients with endometriosis

Aims

Florid mesothelial hyperplasia is known to result from endometriosis. Well-differentiated papillary mesothelioma and multiloculated peritoneal inclusion cysts have also been described in women with endometriosis. To our knowledge, peritoneal diffuse malignant mesothelioma (MM) arising in the setting of endometriosis has not been reported. The purpose of this study is to report the clinicopathological characteristics of women with MM and endometriosis.

Methods

The surgical pathology files of a tertiary academic medical centre and the consultation files of one of the study authors were reviewed for cases of MM in females with and without endometriosis.

Results

Six women with MM and endometriosis ranging in age from 29 to 55 years (median=45 years) were identified. All had peritoneal MM and endometriosis involving the peritoneum and/or adnexa. Five had epithelioid MM and one had biphasic MM. Two had paraoccupational exposure to asbestos. The median age of women with MM and endometriosis (44.5 years) was significantly less than the median age of cases without endometriosis (58.0 years) (p value=0.01).

Conclusions

To our knowledge, this is the first report of MM in women with endometriosis. Interestingly, MM in the setting of endometriosis has only been observed in the peritoneum and not in other serosal cavities. The findings in the present study suggest that chronic serosal inflammation secondary to endometriosis may be an inducing factor in rare cases of MM of the peritoneum.

Antitumor efficacy of Kisspeptin in human malignant mesothelioma cells

Purpose

Kisspeptin signaling, via its receptors GPR54, could be an essential players in the inhibition of mesothelioma progression, invasion and metastasis formation. The loss of KiSS1 by tumor cells has been associated with a metastatic phenotype but the mechanistic insights of this process are still unknown.

Experimental design

The blockade of the metastatic process at early stage is a hot topic in cancer research. We studied the role of KiSS1 on proliferation, invasiveness, migration abilities of mesothelioma cell lines focusing on the effect on epithelial-to-mesenchymal transition (EMT).

Results

Treatment with the KiSS1 peptide or with a synthesis peptide with longer half-life, the FTM080, significantly inhibited cell proliferation, migration and invasion of mesothelioma cell lines; the same treatment reduced the activity of MMP-2 and MMP-9 determining consequently a marked reduction in the invasiveness of primary tumors and metastases. Thespecificexpression of EMT markers, as E-caderin, Vimentin, Slug and Snail, suggested the inhibition of EMT after treatment with KiSS1 as well as the preservation of epithelial components.

Conclusion

Our results support anti-proliferative effect of KiSS1 in cancer cells and suggest that targeting the KiSS1/GPR54 system may represent a novel therapeutic approach for mesothelioma.

Heterogeneity in Immune Cell Content in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a highly aggressive cancer with limited therapy options and dismal prognosis. In recent years, the role of immune cells within the tumor microenvironment (TME) has become a major area of interest. In this review, we discuss the current knowledge of heterogeneity in immune cell content and checkpoint expression in MPM in relation to prognosis and prediction of treatment efficacy. Generally, immune-suppressive cells such as M2 macrophages, myeloid-derived suppressor cells and regulatory T cells are present within the TME, with extensive heterogeneity in cell numbers. Infiltration of effector cells such as cytotoxic T cells, natural killer cells and T helper cells is commonly found, also with substantial patient to patient heterogeneity. PD-L1 expression also varied greatly (16-65%). The infiltration of immune cells in tumor and associated stroma holds key prognostic and predictive implications. As such, there is a strong rationale for thoroughly mapping the TME to better target therapy in mesothelioma. Researchers should be aware of the extensive possibilities that exist for a tumor to evade the cytotoxic killing from the immune system. Therefore, no "one size fits all" treatment is likely to be found and focus should lie on the heterogeneity of the tumors and TME.

AMD3100 Augments the Efficacy of Mesothelin-Targeted, Immune-Activating VIC-008 in Mesothelioma by Modulating Intratumoral Immunosuppression

AMD3100 (plerixafor), a CXCR4 antagonist, has been demonstrated to suppress tumor growth and modulate intratumoral T-cell trafficking. However, the effect of AMD3100 on immunomodulation remains elusive. Here, we explored immunomodulation and antitumor efficacy of AMD3100 in combination with a previously developed mesothelin-targeted, immune-activating fusion protein, VIC-008, in two syngeneic, orthotopic models of malignant mesothelioma in immunocompetent mice. We showed that combination therapy significantly suppressed tumor growth and prolonged animal survival in two mouse models. Tumor control and survival benefit were associated with enhanced antitumor immunity. VIC-008 augmented mesothelin-specific CD8⁺ T-cell responses in the spleen and lymph nodes and facilitated intratumoral lymphocytic infiltration. However, VIC-008 treatment was associated with increased programmed cell death protein-1 (PD-1) expression on intratumoral CD8⁺ T cells, likely due to high CXCL12 in the tumor microenvironment. AMD3100 alone and in combination with VIC-008 modulated immunosuppression in tumors and the immune system through suppression of PD-1 expression on CD8⁺ T cells and conversion of regulatory T cells (T_regs) into CD4⁺CD25^-Foxp3⁺IL2⁺CD40L⁺ helper-like cells. In mechanistic studies, we demonstrated that AMD3100-driven T_reg reprogramming required T cell receptor (TCR) activation and was associated with loss of PTEN due to oxidative inactivation. The combination of VIC-008 augmentation of tumor-specific CD8⁺ T-cell responses with AMD3100 abrogation of immunosuppression conferred significant benefits for tumor control and animal survival. These data provide new mechanistic insight into AMD3100-mediated immunomodulation and highlight the enhanced antitumor effect of AMD3100 in combination with a tumor antigen-targeted therapy in mouse malignant mesothelioma, which could be clinically relevant to patients with this difficult-to-treat disease. Cancer Immunol Res; 6(5); 539-51. ©2018 AACR.

SIRT1 at the crossroads of AKT1 and ERβ in malignant pleural mesothelioma cells

In this report, we show that malignant pleural mesothelioma (MPM) patients whose tumors express high levels of AKT1 exhibit a significantly worse prognosis, whereas no significant correlation with AKT3 expression is observed. We provide data that establish a phosphorylation independent role of AKT1 in affecting MPM cell shape and anchorage independent cell growth in vitro and highlight the AKT1 isoform-specific nature of these effects.

We describe that AKT1 activity is inhibited by the loss of SIRT1-mediated deacetylation and identify, by mass spectrometry, 11 unique proteins that interact with acetylated AKT1.

Our data demonstrate a role of the AKT1/SIRT1/FOXM1 axis in the expression of the tumor suppressor ERβ. We further demonstrate an inhibitory feedback loop by ERβ, activated by the selective agonist KB9520, on this axis both in vitro and in vivo.

Our data broaden the current knowledge of ERβ and AKT isoform-specific functions that could be valuable in the design of novel and effective therapeutic strategies for MPM.

Extracellular signal regulated kinase 5 and inflammasome in progression of mesothelioma

Malignant mesothelioma is an aggressive cancer in desperate need of treatment. We have previously shown that extracellular signaling regulated kinase 5 (ERK5) plays an important role in mesothelioma pathogenesis using ERK5 silenced human mesothelioma cells exhibiting significantly reduced tumor growth in immunocompromised mice. Here, we used a specific ERK 5 inhibitor, XMD8-92 in various in vitro and in vivo models to demonstrate that inhibition of ERK5 can slow down mesothelioma tumorigenesis. First, we show a dose dependent toxicity of XMD8-92 to 2 human mesothelioma cell lines growing as a monolayer. We also demonstrate the inhibition of ERK5 phosphorylation in various human mesothelioma cell lines by XMD8-92. We further confirmed the toxicity of XMD8-92 towards mesothelioma cell lines grown as spheroids in a 3-D model as well as in intraperitoneal (immune-competent) and intrapleural (immune-deficient) mouse models with and without chemotherapeutic drugs. To ascertain the mechanism, we explored the role of the nod-like receptor family member containing a pyrin domain 3 (NLRP3) inflammasome in the process. We found XMD8-92 attenuated naïve and chemotherapeutic-induced inflammasome priming and activation in mesothelioma cells. It can thus be concluded that ERK5 inhibition attenuates mesothelioma tumor growth and this phenomenon in part is regulated by the inflammasome.

Targeting mesothelin receptors with drug-loaded bacterial nanocells suppresses human mesothelioma tumour growth in mouse xenograft models

Human malignant mesothelioma is a chemoresistant tumour that develops from mesothelial cells, commonly associated with asbestos exposure. Malignant mesothelioma incidence rates in European countries are still rising and Australia has one of the highest burdens of malignant mesothelioma on a population basis in the world. Therapy using systemic delivery of free cytotoxic agents is associated with many undesirable side effects due to non-selectivity, and is thus dose-limited which limits its therapeutic potential. Therefore, increasing the selectivity of anti-cancer agents has the potential to dramatically enhance drug efficacy and reduce toxicity. EnGeneIC Dream Vectors (EDV) are antibody-targeted nanocells which can be loaded with cytotoxic drugs and delivered to specific cancer cells via bispecific antibodies (BsAbs) which target the EDV and a cancer cell-specific receptor, simultaneously. BsAbs were designed to target doxorubicin-loaded EDVs to cancer cells via cell surface mesothelin (MSLN). Flow cytometry was used to investigate cell binding and induction of apoptosis, and confocal microscopy to visualize internalization. Mouse xenograft models were used to assess anti-tumour effects in vivo, followed by immunohistochemistry for ex vivo evaluation of proliferation and necrosis. BsAb-targeted, doxorubicin-loaded EDVs were able to bind to and internalize within mesothelioma cells in vitro via MSLN receptors and induce apoptosis. In mice xenografts, the BsAb-targeted, doxorubicin-loaded EDVs suppressed the tumour growth and also decreased cell proliferation. Thus, the use of MSLN-specific antibodies to deliver encapsulated doxorubicin can provide a novel and alternative modality for treatment of mesothelioma.

Gremlin-1 is a key regulator of the invasive cell phenotype in mesothelioma

Malignant mesothelioma originates from mesothelial cells and is a cancer type that aggressively invades into the surrounding tissue, has poor prognosis and no effective treatment. Gremlin-1 is a cysteine knot protein that functions by inhibiting BMP-pathway activity during development. BMP-independent functions have also been described for gremlin-1. We have previously shown high gremlin-1 expression in mesothelioma tumor tissue. Here, we investigated the functions of gremlin-1 in mesothelioma cell migration and invasive growth. Gremlin-1 promoted mesothelioma cell sprouting and invasion into three dimensional collagen and Matrigel matrices. The expression level of gremlin-1 was linked to changes in the expression of SNAI2, integrins, matrix metalloproteinases (MMP) and TGF-β family signaling - all previously associated with a mesenchymal invasive phenotype. Small molecule inhibitors of MMPs completely blocked mesothelioma cell invasive growth. In addition, inhibitors of TGF-β receptors significantly reduced invasive growth. This was associated with reduced expression of MMP2 but not SNAI2, indicating that gremlin-1 has both TGF-β pathway dependent and independent mechanisms of action. Results of in vivo mesothelioma xenograft experiments indicated that gremlin-1 overexpressing tumors were more vascular and had a tendency to send metastases. This suggests that by inducing a mesenchymal invasive cell phenotype together with enhanced tumor vascularization, gremlin-1 drives mesothelioma invasion and metastasis. These data identify gremlin-1 as a potential therapeutic target in mesothelioma.

Novel insights into mesothelioma biology and implications for therapy

Malignant mesothelioma is a universally lethal cancer that is increasing in incidence worldwide. There is a dearth of effective therapies, with only one treatment (pemetrexed and cisplatin combination chemotherapy) approved in the past 13 years. However, the past 5 years have witnessed an exponential growth in our understanding of mesothelioma pathobiology, which is set to revolutionize therapeutic strategies. From a genomic standpoint, mesothelioma is characterized by a preponderance of tumour suppressor alterations, for which novel therapies are currently in development. Other promising antitumour agents include inhibitors against angiogenesis, mesothelin and immune checkpoints, which are at various phases of clinical trial testing.

Immune checkpoint therapy of mesothelioma: Pre-clinical bases and clinical evidences

Treatment with immune-checkpoint blocking monoclonal antibody (mAb) is demonstrating a significant efficacy in different tumor types. Here, we discuss the impact of this promising approach in malignant mesothelioma (MM), a still dreadful disease in which medical treatment has been set on platinum based chemotherapy for decades with unsatisfactory results.

DCLK1 is correlated with MET and ERK5 expression, and associated with prognosis in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer for which more effective treatments are needed. In this study, strong to moderate staining of MET and ERK5 was detected in 67.1 and 48% of the analyzed 73 human mesothelioma tumors, and significant correlation of MET and ERK5 expression was identified (P<0.05). We evaluated the doublecortin-like kinase 1 (DCLK1) expression in human mesothelioma tumors. Our results showed that 50.7% of the immunohistochemistry analyzed human mesothelioma tumors have strong to moderate staining of DCLK1, and its expression is significantly correlated with MET or ERK5 expression (P<0.05). Also, the upregulation of DCLK1 is correlated with poor prognosis in MPM patients (P=0.0235). To investigate whether DCLK1 is downstream of MET/ERK5 signaling in human mesothelioma, the effect of DCLK1 expression was analyzed after treatments with either the MET inhibitor XL184 or the ERK5 inhibitor XMD8-92 in human mesothelioma cell lines. Our results showed that the MET inhibitor XL184 reduced the expression of phospho‑ERK5 and DCLK1 expression in human mesothelioma cell lines. In addition, the ERK5 inhibitor XMD8-92 reduced the expression of phospho-ERK5 and DCLK1 expression in human mesothelioma cell lines. Furthermore, XML184 and XMD8-92 treatment impaired invasion and tumor sphere formation ability of H290 mesothelioma cells. These results suggest that DCLK1 is regulated by MET/ERK5 signaling in human mesothelioma, and the MET/ERK5/DCLK1 signaling cascade could be further developed into a promising therapeutic target against mesothelioma.

In vitro experimental models of mesothelioma revisited

Malignant pleural mesothelioma (MPM) is a biologically unusual, highly aggressive cancer that defies current multimodality treatments. Epidemiologic data suggest that this malignancy has not abated despite increasingly strict environmental regulations on asbestos, the putative causative agent for sporadic cases. An incomplete understanding of all the factors mechanistically driving mesothelioma is largely responsible for the current lack of curative treatments. Many approaches have been employed to ascertain the step-by-step molecular events involved in mesothelioma oncogenesis including in vitro, small animal in vivo, and human experimental models; though clearly defined, druggable mechanisms still are elusive. Importantly, the foundation of the latest accepted model of tumor initiation is derived from in vitro systems. A thorough review of in vitro mesothelioma oncogenesis models may suggest further opportunities for discovery.

Evaluating the mechanistic evidence and key data gaps in assessing the potential carcinogenicity of carbon nanotubes and nanofibers in humans

In an evaluation of carbon nanotubes (CNTs) for the IARC Monograph 111, the Mechanisms Subgroup was tasked with assessing the strength of evidence on the potential carcinogenicity of CNTs in humans. The mechanistic evidence was considered to be not strong enough to alter the evaluations based on the animal data. In this paper, we provide an extended, in-depth examination of the in vivo and in vitro experimental studies according to current hypotheses on the carcinogenicity of inhaled particles and fibers. We cite additional studies of CNTs that were not available at the time of the IARC meeting in October 2014, and extend our evaluation to include carbon nanofibers (CNFs). Finally, we identify key data gaps and suggest research needs to reduce uncertainty. The focus of this review is on the cancer risk to workers exposed to airborne CNT or CNF during the production and use of these materials. The findings of this review, in general, affirm those of the original evaluation on the inadequate or limited evidence of carcinogenicity for most types of CNTs and CNFs at this time, and possible carcinogenicity of one type of CNT (MWCNT-7). The key evidence gaps to be filled by research include: investigation of possible associations between in vitro and early-stage in vivo events that may be predictive of lung cancer or mesothelioma, and systematic analysis of dose-response relationships across materials, including evaluation of the influence of physico-chemical properties and experimental factors on the observation of nonmalignant and malignant endpoints.

The resistance related to targeted therapy in malignant pleural mesothelioma: Why has not the target been hit yet?

Malignant pleural mesothelioma (MPM) is an aggressive tumor of the pleura with a poor prognosis. The most active first-line regimens are platinum compounds and pemetrexed. There is no standard second-line treatment in MPM. Advances in the understanding of tumor molecular biology have led to the development of several targeted treatments, which have been evaluated in clinical trials. Unfortunately none of the explored targeted treatments can currently be recommended as routine treatment in MPM. We reviewed the biological pathways involved in MPM, the clinical trials about targeted therapy, and possible related mechanisms of resistance. We suggest that specific genetic markers are needed as targets of selective therapy. By this way the selection of patients based on the molecular profile may facilitate a therapeutic strategy that allows the use of the most appropriate drug for each patient.

The endoplasmic reticulum mitochondrial calcium cross talk is downregulated in malignant pleural mesothelioma cells and plays a critical role in apoptosis inhibition

The failure of apoptosis may contribute to the formation of cancer and to its resistance to therapy. Malignant pleural mesothelioma (MPM) is an aggressive tumor that responds poorly to standard chemo- and radio-therapies. Several studies have demonstrated that a plethora of oncogenes and tumor suppressors contribute to MPM onset/progression. Importantly, most of these genes are involved in the regulation of calcium (Ca²⁺)-handling. Cellular Ca²⁺ signaling is an important regulator of many physiological processes, and it has been widely reported to participate in the regulation of apoptotic cell death in cancer cells and tissues. However, in MPM the role of cellular Ca²⁺ has been poorly investigated. Therefore, we examined whether Ca²⁺ is involved in MPM. We found that mesothelioma cell lines and short-term cultures obtained from MPM-affected patients exhibited a critical dysregulation in Ca²⁺ signaling. We determined that this characteristic was associated with resistance to apoptotic stimuli and that correction of intracellular Ca²⁺ signaling resulted in the rescue of efficient apoptotic responses. In addition, we discovered that mitochondrial Ca²⁺-uptake plays a pivotal role as an inducer of apoptosis in MPM. Altogether, these findings suggest the identification of new MPM markers, which in turn could be potential targets for new therapeutic approaches.

Malignant peritoneal mesothelioma and Crohn disease

AIMS

Mesothelial reaction simulating peritoneal diffuse malignant mesothelioma (MM) has been reported in the setting of Crohn ileitis. To our knowledge, peritoneal MM arising in patients with inflammatory bowel disease (IBD) has not been reported. The purpose of this study is to report the clinicopathological characteristics of patients with peritoneal MM and IBD.

METHODS

A database of approximately 3800 MM was reviewed for cases of MM in patients with IBD.

RESULTS

Three patients (0.08%) with peritoneal MM and Crohn disease (CD) were identified, including two women and one man ranging in age from 56 to 65 years. All had a long-standing history of diarrhoea and an established diagnosis of CD of 3 years or greater duration. Two had epithelial MM and one had biphasic MM. Only one had documented asbestos exposure.

CONCLUSIONS

Peritoneal MM occurs rarely in patients with IBD, but interestingly, has only been observed in the setting of CD and not in patients with ulcerative colitis. Chronic inflammation has been associated with the development of MM in rare instances and these three cases suggest that CD with transmural inflammation may also be a precursor. The precise role of CD-related transmural inflammation in the carcinogenesis of peritoneal MM remains to be determined.

Moving Immune Checkpoint Blockade in Thoracic Tumors beyond NSCLC

SCLC and malignant pleural mesothelioma (MPM) are historically characterized by a disappointing lack of significant therapeutic breakthroughs for novel agents, and both malignancies represent true unmet medical needs. Given the promising results of anti-cytotoxic T-lymphocyte associated protein-4 and anti-programmed cell death-1/programmed death ligand-1 antibodies in the treatment of advanced NSCLCs, these immune checkpoint inhibitors are now also under investigation in SCLC and MPM, as well as in thymic epithelial tumors (TETs). Here, we review the biological and clinical rationale for immune checkpoint inhibition in SCLC, MPM, and TETs and present preliminary clinical results with available antibodies. Immunotherapeutic perspectives for these malignancies in terms of novel agents currently under evaluation or anticipated in the near future are also discussed. Current immune checkpoint blockers targeting cytotoxic T-lymphocyte associated protein-4 and the programmed cell death-1/programmed death ligand-1 axis, administered alone or in combination and as multimodality treatment, are likely to be a valuable addition to the therapeutic array for managing SCLC and MPM; studies in TETs, which are currently in their infancy, are merited. Close attention to potential toxicities will be important to the success of such strategies in these settings.

Immunomediated Pan-cancer Regulation Networks are Dominant Fingerprints After Treatment of Cell Lines with Demethylation

Pan-cancer studies are particularly relevant not only for addressing the complexity of the inherently observed heterogeneity but also for identifying clinically relevant features that may be common to the cancer types. Immune system regulations usually reveal synergistic modulation with other cancer mechanisms and in combination provide insights on possible advances in cancer immunotherapies. Network inference is a powerful approach to decipher pan-cancer systems dynamics. The methodology proposed in this study elucidates the impacts of epigenetic treatment on the drivers of complex pan-cancer regulation circuits involving cell lines of five cancer types. These patterns were observed from differential gene expression measurements following demethylation with 5-azacytidine. Networks were built to establish associations of phenotypes at molecular level with cancer hallmarks through both transcriptional and post-transcriptional regulation mechanisms. The most prominent feature that emerges from our integrative network maps, linking pathway landscapes to disease and drug-target associations, refers primarily to a mosaic of immune-system crosslinked influences. Therefore, characteristics initially evidenced in single cancer maps become motifs well summarized by network cores and fingerprints.

Differential Susceptibility of Human Pleural and Peritoneal Mesothelial Cells to Asbestos Exposure

Malignant mesothelioma (MM) is an aggressive cancer of mesothelial cells of pleural and peritoneal cavities. In 85% of cases both pleural and peritoneal MM is caused by asbestos exposure. Although both are asbestos-induced cancers, the incidence of pleural MM is significantly higher (85%) than peritoneal MM (15%). It has been proposed that carcinogenesis is a result of asbestos-induced inflammation but it is not clear what contributes to the differences observed between incidences of these two cancers. We hypothesize that the observed differences in incidences of pleural and peritoneal MM are the result of differences in the direct response of these cell types to asbestos rather than to differences mediated by the in vivo microenvironment. To test this hypothesis we characterized cellular responses to asbestos in a controlled environment. We found significantly greater changes in genome-wide expression in response to asbestos exposure in pleural mesothelial cells as compared to peritoneal mesothelial cells. In particular, a greater response in many common genes (IL-8, ATF3, CXCL2, CXCL3, IL-6, GOS2) was seen in pleural mesothelial cells as compared to peritoneal mesothelial cells. Unique genes expressed in pleural mesothelial cells were mainly pro-inflammatory (G-CSF, IL-1β, IL-1α, GREM1) and have previously been shown to be involved in development of MM. Our results are consistent with the hypothesis that differences in incidences of pleural and peritoneal MM upon exposure to asbestos are the result of differences in mesothelial cell physiology that lead to differences in the inflammatory response, which leads to cancer.

The proliferative effects of asbestos-exposed peripheral blood mononuclear cells on mesothelial cells

Malignant mesothelioma (MM) is thought to arise from the direct effect of asbestos on mesothelial cells. However, MM takes a long time to develop following exposure to asbestos, which suggests that the effects of asbestos are complex. The present study examined the effects of asbestos exposure on the cell growth of MeT-5A human mesothelial cells via cytokines produced by immune cells. Peripheral blood mononuclear cells (PBMCs) were stimulated with antibodies against cluster of differentiation (CD)3 and CD28 upon exposure to the asbestos chrysotile A (CA) or crocidolite (CR); the growth of MeT-5A cells in media supplemented with PBMC culture supernatants was subsequently examined. MeT-5A cells exhibited an increase in proliferation when grown in supernatant from the 7-day PBMC culture exposed to CA or CR. Analysis of cytokine production demonstrated increased levels of granulocyte colony-stimulating factor (G-CSF), granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-1α, IL-1β, IL-3, IL-5, IL-13 and IL-17A in supernatants. Individual administration of these cytokines, excluding G-CSF and GM-CSF, led to an increase in cell growth of MeT-5A, whereas this effect was not observed following the combined administration of these cytokines. The results indicate that cytokines secreted by immune cells upon exposure to asbestos cause an increase in the growth activity of mesothelial cells, suggesting that alterations in the production of cytokines by immune cells may contribute to tumorigenesis in individuals exposed to asbestos.