Asbestos-induced Inflammation Research Articles

Targeting inflammatory factors for chemoprevention and cancer interception to tackle malignant mesothelioma.

Mesothelioma is an incurable cancer of the mesothelial lining often caused by exposure to asbestos. Asbestos-induced inflammation is a significant contributing factor in the development of mesothelioma, and genetic factors also play a role in the susceptibility to this rapidly progressive and treatment-resistant malignancy. Consequently, novel approaches are urgently needed to treat mesothelioma and prevent or reduce the overall incidence of this fatal disease. In this research perspective, we review the current state of chemoprevention and cancer interception progress in asbestos-induced mesothelioma. We discuss the different preclinical mouse models used for these investigations and the inflammatory factors that may be potential targets for mesothelioma prevention. Preliminary studies with naturally occurring phytochemicals and synthetic agents are reviewed. Results of previous clinical chemoprevention trials in populations exposed to asbestos and considerations regarding future trials are also presented.

Ki67 Tumor Expression Predicts Treatment Benefit Achieved by Macroscopic Radical Lung-Preserving Surgery in Pleural Mesothelioma-A Retrospective Multicenter Analysis.

Pleural mesothelioma (PM), linked to asbestos-induced inflammation, carries a poor prognosis. Therapy ranges from therapy limitation to aggressive multimodality treatment. Given the uncertainty about treatment benefits for patients, this study aimed to assess the role of Ki67 as a prognostic and predictive parameter in PM. Ki67 was measured in the specimens of 70 PM patients (17 female, 53 male) from two centers and correlated to overall survival (OS) and therapy outcome. The median OS was 16.1 months. The level of Ki67 expression was divided into low (≤15%) and high (>15%). A low value of Ki67 expression was associated with a longer OS (Ki67 ≤ 15%: 31.2 (95% CI 6.5-55.8) months vs. Ki67 > 15%: 11.1 (95% CI 7.7-14.6) months, p = 0.012). The 5-year survival represents 22% in the low Ki67 expression group, in contrast to 5% in the high Ki67 expression group. We found a significant interaction term of Ki67 with multimodality treatment (p = 0.031) translating to an OS of 48.1 months in the low expression Ki67 group compared to 24.3 months in the high Ki67 expression group when receiving surgery within multimodality therapy. Therefore, Ki67 stands out as a validated prognostic and, most importantly, novel predictive biomarker for treatment benefits, particularly regarding surgery within multimodality therapy.

Validation of Inflammatory Prognostic Biomarkers in Pleural Mesothelioma.

Evoked from asbestos-induced inflammation, pleural mesothelioma represents a fatal diagnosis. Therapy ranges from nihilism to aggressive multimodality regimens. However, it is still unclear who ultimately benefits from which treatment. We aimed to re-challenge inflammatory-related biomarkers' prognostic value in times of modern immune-oncology and lung-sparing surgery. The biomarkers (leukocytes, hemoglobin, platelets, neutrophils, lymphocytes, monocytes, neutrophil-lymphocyte ratio (NLR), lymphocyte-monocyte ratio (LMR), platelet-lymphocyte ratio (PLR), C-reactive protein (CRP)) and clinical characteristics (age, sex, histology, therapy) of 98 PM patients were correlated to overall survival (OS). The median OS was 19.4 months. Significant OS advantages (Log-Rank) were observed in multimodal treatment vs. others (26.1 vs. 7.2 months, p < 0.001), surgery (pleurectomy/decortication) vs. no surgery (25.5 vs. 3.8 months, p < 0.001), a high hemoglobin level (cut-off 12 g/dL, 15 vs. 24.2 months, p = 0.021), a low platelet count (cut-off 280 G/L, 26.1 vs. 11.7 months, p < 0.001), and a low PLR (cut-off 194.5, 25.5 vs. 12.3 months, p = 0.023). Histology (epithelioid vs. non-epithelioid, p = 0.002), surgery (p = 0.004), CRP (cut-off 1 mg/dL, p = 0.039), and platelets (p = 0.025) were identified as independent prognostic variables for this cohort in multivariate analysis (Cox regression, covariates: age, sex, histology, stage, CRP, platelets). Our data verified the previously shown prognostic role of systemic inflammatory parameters in patients treated with lung-sparing surgery within multimodality therapy.

Synthetic Secoisolariciresinol Diglucoside (LGM2605) Prevents Asbestos-Induced Inflammation and Genotoxic Cell Damage in Human Mesothelial Cells.

Although alveolar macrophages play a critical role in malignant transformation of mesothelial cells following asbestos exposure, inflammatory and oxidative processes continue to occur in the mesothelial cells lining the pleura that may contribute to the carcinogenic process. Malignant transformation of mesothelial cells following asbestos exposure occurs over several decades; however, amelioration of DNA damage, inflammation, and cell injury may impede the carcinogenic process. We have shown in an in vitro model of asbestos-induced macrophage activation that synthetic secoisolariciresinol diglucoside (LGM2605), given preventively, reduced inflammatory cascades and oxidative/nitrosative cell damage. Therefore, it was hypothesized that LGM2605 could also be effective in reducing asbestos-induced activation and the damage of pleural mesothelial cells. LGM2605 treatment (50 µM) of huma n pleural mesothelial cells was initiated 4 h prior to exposure to asbestos (crocidolite, 20 µg/cm2). Supernatant and cells were evaluated at 0, 2, 4, and 8 h post asbestos exposure for reactive oxygen species (ROS) generation, DNA damage (oxidized guanine), inflammasome activation (caspase-1 activity) and associated pro-inflammatory cytokine release (IL-1β, IL-18, IL-6, TNFα, and HMGB1), and markers of oxidative stress (malondialdehyde (MDA) and 8-iso-prostaglandin F2a (8-iso-PGF2α). Asbestos induced a time-dependent ROS increase that was significantly (p < 0.0001) reduced (29.4%) by LGM2605 treatment. LGM2605 pretreatment also reduced levels of asbestos-induced DNA damage by 73.6% ± 1.0%. Although levels of inflammasome-activated cytokines, IL-1β and IL-18, reached 29.2 pg/mL ± 0.7 pg/mL and 43.9 pg/mL ± 0.8 pg/mL, respectively, LGM2605 treatment significantly (p < 0.0001) reduced cytokine levels comparable to baseline (non-asbestos exposed) values (3.8 pg/mL ± 0.2 pg/mL and 5.4 pg/mL ± 0.2 pg/mL, respectively). Furthermore, levels of IL-6 and TNFα in asbestos-exposed mesothelial cells were high (289.1 pg/mL ± 2.9 pg/mL and 511.3 pg/mL ± 10.2 pg/mL, respectively), while remaining undetectable with LGM2605 pretreatment. HMGB1 (a key inflammatory mediator and initiator of malignant transformation) release was reduced 75.3% ± 0.4% by LGM2605. Levels of MDA and 8-iso-PGF2α, markers of oxidative cell injury, were significantly (p < 0.001) reduced by 80.5% ± 0.1% and 76.6% ± 0.3%, respectively. LGM2605, given preventively, reduced ROS generation, DNA damage, and inflammasome-activated cytokine release and key inflammatory mediators implicated in asbestos-induced malignant transformation of normal mesothelial cells.

Asbestos-induced chronic inflammation in malignant pleural mesothelioma and related therapeutic approaches-a narrative review.

Objective:The aim of this review is addressing the mechanisms of asbestos carcinogenesis, including chronic inflammation and autophagy-mediated cell survival, and propose potential innovative therapeutic targets to prevent mesothelioma development or improve drug efficacy by reducing inflammation and autophagy.Background:Diffuse malignant pleural mesothelioma is an aggressive cancer predominantly related to chronic inflammation caused by asbestos exposure. Millions of individuals have been exposed to asbestos or to other carcinogenic mineral fibers occupationally or environmentally, resulting in an increased risk of developing mesothelioma. Overall patient survival rates are notably low (about 8–14 months from the time of diagnosis) and mesothelioma is resistant to existing therapies. Additionally, individuals carrying inactivating germline mutations in the BRCA-associated protein 1 (BAP1) gene and other genes are predisposed to developing cancers, prevalently mesothelioma. Their risk of developing mesothelioma further increases upon exposure to asbestos. Recent studies have revealed the mechanisms and the role of inflammation in asbestos carcinogenesis. Biomarkers for asbestos exposure and malignant mesothelioma have also been identified. These findings are leading to the development of novel therapeutic approaches to prevent or delay the growth of mesothelioma.Methods:Review of full length manuscripts published in English from January 1980 to February 2021 gathered from PubMed.gov from the National Center of Biotechnology Information and the National Library of Medicine were used to inform this review.Conclusion:Key regulators of chronic inflammation mediate asbestos-driven mesothelial cell transformation and survival through autophagic pathways. Recent studies have elucidated some of the key mechanisms involved in asbestos-induced chronic inflammation, which are largely driven by extracellular high mobility group box 1 (HMGB1). Upon asbestos exposure, mesothelial cells release HMGB1 from the nucleus to the cytoplasm and extracellular space, where HMGB1 initiates an inflammatory response. HMGB1 translocation and release also activates autophagy and other pro-survival mechanisms, which promotes mesothelioma development. HMGB1 is currently being investigated as a biomarker to detect asbestos exposure and to detect mesothelioma development in its early stage when therapy is more effective. In parallel, several approaches inhibiting HMGB1 activities have been studied and have shown promising results. Moreover, additional cytokines, such as IL-1β and TNF-α are being targeted to interfere with the inflammatory process that drives mesothelioma growth. Developing early detection methods and novel therapeutic strategies is crucial to prolong overall survival of patients with mesothelioma. Novel therapies targeting regulators of asbestos-induced inflammation to reduce mesothelioma growth may lead to clinical advancements to benefit patients with mesothelioma.

HMGB1 as a Potential Biomarker and Therapeutic Target for Malignant Mesothelioma.

Malignant mesothelioma (MM) is a rare, aggressive, and highly lethal cancer that is substantially induced by exposure to asbestos fibers. High-mobility group box 1 (HMGB1) is an intriguing proinflammatory molecule involved in MM. In this review, we describe the possible crucial roles of HMGB1 in carcinogenic mechanisms based on in vivo and in vitro experimental evidence and outline the clinical findings of epidemiological investigations regarding the possible roles of HMGB1 as a biomarker for MM. We conclude that novel strategies targeting HMGB1 may suppress MM cells and interfere with asbestos-induced inflammation.

Abstract 5763: Investigating the carcinogenic potential of various types of mineral fibers in the development of mesothelioma

Abstract Malignant mesothelioma is a very aggressive tumor and has been linked to occupational and environmental exposure to carcinogenic mineral fibers such as asbestos. It was discovered recently that individuals carrying germline BAP1 mutations are predisposed to mesothelioma in presence of even minimal exposure to carcinogenic mineral fibers. Mesothelioma causes about 3,200 deaths per year in the U.S. and over 40,000 deaths per year worldwide. Most malignant mesothelioma studies have focused on carcinogenesis due to occupational exposure to the six regulated industrial mineral fibers collectively called ‘asbestos’. Besides this family of six regulated asbestos minerals, there are other non-regulated fibers that possess physical and chemical structures that are similar to industrial asbestos, and may also be carcinogenic. However, many of those mineral fibers are unknown for their carcinogenesis. We conducted serious studies on this topic and established in vitro and in vivo assays to help determine the carcinogenesis of various types of mineral fibers. We found that high mobility box 1 protein (HMGB1) is a key initiator of asbestos-induced inflammation, which plays critical roles in the development and growth of mesothelioma, and that HMGB1 may be a good indicator for fiber carcinogenesis and a biomarker for fibers exposure. Moreover, we found that specific immune system changes that occur after exposure to carcinogenic fibers, which may be a useful tool to help interrogate the carcinogenic potential of mineral fibers. In particular, the ability to induce an M2 macrophage response appears related to the potent tumor-inducing capacity of carcinogenic mineral fibers. Citation Format: David Larson, Mika Tanji, Andrea Napolitano, Sandra Pastorino, Michele Carbone, Haining Yang. Investigating the carcinogenic potential of various types of mineral fibers in the development of mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2017; 2017 Apr 1-5; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2017;77(13 Suppl):Abstract nr 5763. doi:10.1158/1538-7445.AM2017-5763

OA22.03 HMGB1, a Target for Mesothelioma Therapy and a Biomarker to Detect Asbestos Exposure and to Identify Mesothelioma Patients

Millions of people have been potentially exposed to asbestos, the primary cause of malignant mesothelioma (MM). Presently, no reliable biomarkers are available to identify among potentially exposed people, those individuals who have actually been exposed and who are at high risk of MM. High Mobility Group Box Protein-1 (HMGB1) is a key mediator of asbestos-induced inflammation and MM pathogenesis. Recently, HMGB1 hyper-acetylation has been functionally associated to its active release by inflammatory cells. Here, we compared the serum levels of total and hyper-acetylated HMGB1 in individuals professionally exposed to asbestos, MM patients and healthy unexposed controls. We compared the serum levels of total and hyper-acetylated HMGB1 in individuals professionally exposed to asbestos, MM patients and healthy unexposed controls. Previously proposed MM biomarkers fibulin-3, osteopontin, and mesothelin were also blindly measured in blood collected from participants to the study. HMGB1 serum levels reliably distinguished asbestos-exposed individuals and MM patients from unexposed controls. Moreover, the levels of total and hyper-acetylated HMGB1 were significantly higher in MM patients compared to asbestos-exposed individuals, and did not vary with tumor stage, suggesting that early lesions are also associated to increased HMGB1 levels. At a cutoff value of 2.00 ng/mL, the sensitivity and specificity of hyper-acetylated serum HMGB1 in differentiating MM patients from asbestos-exposed individuals was 100%, outperforming, in parallel experiments, other previously proposed biomarkers: osteopontin, fibulin-3, and mesothelin. When comparing MM patients to patients with other non-MM cytologically benign or malignant pleural effusion, the combination of two biomarkers, HMGB1 and fibulin-3, provided the highest sensitivity and specificity in differentiating these two groups. Moreover, we found that HMGB1 drives MM development and sustains MM progression, and we demonstrated that targeting HMGB1 inhibits MM cell growth and motility in vitro, reduced tumor growth in vivo and prolonged survival. Despite the relatively small size of our cohorts, our results are of exceptional significance and clinical relevance as they provide the first biomarker of asbestos exposure and indicate that hyper-acetylated HMGB1 is a very sensitive and specific biomarker to differentiate MM patients from individuals occupationally exposed to asbestos and unexposed controls. Moreover, our results on HMGB1 inhibitors indicate that HMGB1 targeting hampers the malignant phenotype of MM, offering a novel potential therapeutic approach to patients afflicted with this dismal disease.

Abstract 842: The NALP3 inflammasome and IL-1â signaling link asbestos-induced inflammation with the development of malignant mesothelioma

Abstract Exposure to asbestos is causally associated with the development of malignant mesothelioma (MM), a cancer of cells lining the internal body cavity. MM is an aggressive cancer that is resistant to all current therapies. Once inhaled or ingested, asbestos causes inflammation in and around tissues that come in contact with these carcinogenic fibers. Recent studies suggest that inflammation is a major contributing factor in the development of many types of cancer, including MM. The NALP3 inflammasome, including the component ASC, is an important mediator of inflammation that senses extracellular insults, such as infection or asbestos, and activates a signaling cascade resulting in release of mature IL-1â and recruitment of inflammatory cells. To determine if inflammasome-mediated inflammation contributes to asbestos-induced MM, we chronically exposed Asc-deficient mice to asbestos and evaluated tumor incidence, latency and overall survival. Asc-deficient mice showed a significant delay in tumor onset compared to wild-type animals, suggesting that the NALP3 inflammasome plays a role in MM carcinogenesis. We also tested whether inflammation-related release of IL-1â promotes tumor development in an accelerated mouse model of asbestos-induced MM. Nf2+/-;Cdkn2a+/- mice exposed to asbestos in the presence of the IL-1â antagonist, anakinra, showed a 50% longer disease-free survival than in similarly exposed mice given vehicle control, consistent with IL-1â signaling contributing significantly to MM development. Collectively, these studies provide evidence for a link between asbestos-associated inflammation/IL-1â signaling and the development of MM; furthermore, these findings provide rationale for chemoprevention strategies targeting inflammation-related IL-1â signaling in high risk, asbestos-exposed populations. Citation Format: Yuwaraj Kadariya, Craig W. Menges, Jacqueline Talarchek, Qi Cai, Andres J. Klein-Szanto, Ralph A. Pietrofesa, Melpo Christofidou-Solomidou, Brooke T. Mossman, Arti Shukla, Joseph R. Testa. The NALP3 inflammasome and IL-1â signaling link asbestos-induced inflammation with the development of malignant mesothelioma. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 842.

Abstract 3112: HMGB1 and its isoform are sensitive and specific biomarkers to detect asbestos exposure and to identify mesothelioma patients

Abstract Millions of people have been potentially exposed to asbestos, the primary cause of malignant mesothelioma (MM). Presently, no reliable biomarkers are available to identify among potentially exposed people, those individuals who have actually been exposed and who are at high risk of MM. High Mobility Group Box Protein-1 (HMGB1) is a key mediator of asbestos-induced inflammation and MM pathogenesis. Recently, HMGB1 hyper-acetylation has been functionally associated to its active release by inflammatory cells. Here, we compared the serum levels of total and hyper-acetylated HMGB1 in individuals professionally exposed to asbestos, MM patients and healthy unexposed controls. HMGB1 serum levels reliably distinguished asbestos-exposed individuals and MM patients from unexposed controls. Moreover, the levels of total and hyper-acetylated HMGB1 were significantly higher in MM patients compared to asbestos-exposed individuals, and did not vary with tumor stage, suggesting that early lesions are also associated to increased HMGB1 levels. At a cutoff value of 2.00 ng/mL, the sensitivity and specificity of hyper-acetylated serum HMGB1 in differentiating MM patients from asbestos-exposed individuals was 100%, outperforming, in parallel experiments, other previously proposed biomarkers: osteopontin, fibulin-3, and mesothelin. When comparing MM patients to patients with other non-MM cytologically benign or malignant pleural effusion, the combination of two biomarkers, HMGB1 and fibulin-3, provided the highest sensitivity and specificity in differentiating these two groups. We propose total and hyper-acetylated HMGB1 as valuable biomarkers to differentiate MM patients from individuals professionally exposed to asbestos and from unexposed people. Citation Format: Andrea Napolitano, Daniel J. Antoine, Laura Pellegrini, Francine Baumann, Ian Pagano, Sandra Pastorino, Chandra M. Goparaju, Kirill Prokrym, Claudia Canino, Harvey I. Pass, Michele Carbone, Haining Yang. HMGB1 and its isoform are sensitive and specific biomarkers to detect asbestos exposure and to identify mesothelioma patients. [abstract]. In: Proceedings of the 107th Annual Meeting of the American Association for Cancer Research; 2016 Apr 16-20; New Orleans, LA. Philadelphia (PA): AACR; Cancer Res 2016;76(14 Suppl):Abstract nr 3112.

Flaxseed lignans enriched in secoisolariciresinol diglucoside prevent acute asbestos-induced peritoneal inflammation in mice.

Malignant mesothelioma (MM), linked to asbestos exposure, is a highly lethal form of thoracic cancer with a long latency period, high mortality and poor treatment options. Chronic inflammation and oxidative tissue damage caused by asbestos fibers are linked to MM development. Flaxseed lignans, enriched in secoisolariciresinol diglucoside (SDG), have antioxidant, anti-inflammatory and cancer chemopreventive properties. As a prelude to chronic chemoprevention studies for MM development, we tested the ability of flaxseed lignan component (FLC) to prevent acute asbestos-induced inflammation in MM-prone Nf2(+/mu) mice. Mice (n = 16-17 per group) were placed on control (CTL) or FLC-supplemented diets initiated 7 days prior to a single intraperitoneal bolus of 400 µg of crocidolite asbestos. Three days post asbestos exposure, mice were evaluated for abdominal inflammation, proinflammatory/profibrogenic cytokine release, WBC gene expression changes and oxidative and nitrosative stress in peritoneal lavage fluid (PLF). Asbestos-exposed mice fed CTL diet developed acute inflammation, with significant (P < 0.0001) elevations in WBCs and proinflammatory/profibrogenic cytokines (IL-1ß, IL-6, TNFα, HMGB1 and active TGFß1) relative to baseline (BL) levels. Alternatively, asbestos-exposed FLC-fed mice had a significant (P < 0.0001) decrease in PLF WBCs and proinflammatory/profibrogenic cytokine levels relative to CTL-fed mice. Importantly, PLF WBC gene expression of cytokines (IL-1ß, IL-6, TNFα, HMGB1 and TGFß1) and cytokine receptors (TNFαR1 and TGFßR1) were also downregulated by FLC. FLC also significantly (P < 0.0001) blunted asbestos-induced nitrosative and oxidative stress. FLC reduces acute asbestos-induced peritoneal inflammation, nitrosative and oxidative stress and may thus prove to be a promising agent in the chemoprevention of MM.

Abstract 5542: Flaxseed and its lignan component protect from asbestos-induced inflammation in mice

Abstract Introduction/Background: Malignant mesothelioma (MM) is a highly lethal form of thoracic cancer with high mortality and poor treatment options. Development of MM has been linked directly to exposure to asbestos fibers, but with a long latency period. Recent studies have indicated that the pathogenesis of asbestos-induced cancers is due, in part, to chronic inflammation and oxidative tissue damage caused by persistent asbestos fibers. Whole grain flaxseed (FS) has known antioxidant, anti-inflammatory and cancer chemopreventive properties. Rationale: As a prelude to future chemoprevention studies, we tested the ability of oral FS and its lignan component, FLC which is enriched in the lignan secoisolariciresinol diglucoside (SDG), to prevent acute asbestos-induced inflammation and inflammatory cytokine release in MM-prone Nf2+/mut;Cdkn2a+/mut mice. Methods: Mice were given a single ip bolus of 400 mM of crocidolite asbestos. They were then placed on 10% FS or 10% FLC supplemented diets 1 day prior (-1) to or after (+1) asbestos instillation. All mice were evaluated 3 days after injection of asbestos for abdominal inflammation and proinflammatory cytokine release. The Nf2+/mut;Cdkn2a+/mut model was selected as it develops an accelerated form of MM when exposed to asbestos. Results: Using liquid chromatography and tandem mass spectrometry (LC/MS/MS), we showed that systemic levels (plasma) of flaxseed lignan metabolites (such as the mammalian lignans Enterolactone (EL) and Enterodiol (ED)) were comparable to those in other mouse models where FS was shown to be an effective chemopreventive agent. The numbers of macrophages (MF) and neutrophils (PMN) in peritoneal lavage fluid indicated that both FS and FLC blunted acute abdominal inflammation induced by asbestos. In addition, the levels of pro-inflammatory cytokines TNF alpha and IL-1 beta in lavage fluid were also decreased by the dietary agents. Conclusions: Our findings suggest that the known chemopreventive properties of FS and its lignan component appear to reduce short-term asbestos-induced inflammation and may thus prove to be a promising dietary agent in the chemoprevention of MM. Funding: This study was supported in part by Penn's SRP Center Grant (P42 ES027320), “Asbestos fate, exposure, remediation and adverse health effects” from the National Institute of Environmental Health (NIEHS) and 1R03CA180548-02 (MCS). Citation Format: Steven M. Albelda, Ralph A. Pietrofesa, Craig W. Menges, Joseph R. Testa, Melpo Christofidou-Solomidou. Flaxseed and its lignan component protect from asbestos-induced inflammation in mice. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 5542. doi:10.1158/1538-7445.AM2015-5542

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.

Evaluation of clonal origin of malignant mesothelioma.

BackgroundThe hypothesis that most cancers are of monoclonal origin is often accepted as a fact in the scientific community. This dogma arose decades ago, primarily from the study of hematopoietic malignancies and sarcomas, which originate as monoclonal tumors. The possible clonal origin of malignant mesothelioma (MM) has not been investigated. Asbestos inhalation induces a chronic inflammatory response at sites of fiber deposition that may lead to malignant transformation after 30-50 years latency. As many mesothelial cells are simultaneously exposed to asbestos fibers and to asbestos-induced inflammation, it may be possible that more than one cell undergoes malignant transformation during the process that gives rise to MM, and result in a polyclonal malignancy.Methods and resultsTo investigate the clonality patterns of MM, we used the HUMARA (Human Androgen Receptor) assay to examine 16 biopsies from 14 women MM patients. Out of 16 samples, one was non-informative due to skewed Lyonization in its normal adjacent tissue. Fourteen out of the 15 informative samples revealed two electrophoretically distinct methylated HUMARA alleles, the Corrected Allele Ratio (CR) calculated on the allele peak areas indicating polyclonal origin MM.ConclusionsOur results show that MM originate as polyclonal tumors and suggest that the carcinogenic “field effect” of mineral fibers leads to several premalignant clones that give rise to these polyclonal malignancies.Electronic supplementary materialThe online version of this article (doi:10.1186/s12967-014-0301-3) contains supplementary material, which is available to authorized users.

Cancer-promoting role of adipocytes in asbestos-induced mesothelial carcinogenesis through dysregulated adipocytokine production

Like many other human cancers, the development of malignant mesothelioma is closely associated with a chronic inflammatory condition. Both macrophages and mesothelial cells play crucial roles in the inflammatory response caused by asbestos exposure. Here, we show that adipocytes can also contribute to asbestos-induced inflammation through dysregulated adipocytokine production. 3T3-L1 preadipocytes were differentiated into mature adipocytes prior to use. These cells took up asbestos fibers (chrysotile, crocidolite and amosite) but were more resistant to asbestos-induced injury than macrophages and mesothelial cells. Expression microarray analysis followed by reverse transcription-PCR revealed that adipocytes respond directly to asbestos exposure with an increased production of proinflammatory adipocytokines [e.g. monocyte chemoattractant protein-1 (MCP-1)], whereas the production of anti-inflammatory adipocytokines (e.g. adiponectin) is suppressed. This was confirmed in epididymal fat pad of mice after intraperitoneal injection of asbestos fibers. Such dysregulated adipocytokine production favors the establishment of a proinflammatory environment. Furthermore, MCP-1 marginally promoted the growth of MeT-5A mesothelial cells and significantly enhanced the wound healing of Y-MESO-8A and Y-MESO-8D human mesothelioma cells. Our results suggest that increased levels of adipocytokines, such as MCP-1, can potentially contribute to the promotion of mesothelial carcinogenesis through the enhanced recruitment of inflammatory cells as well as a direct growth and migration stimulatory effect on mesothelial and mesothelioma cells. Taken together, our findings support a potential cancer-promoting role of adipocytes in asbestos-induced mesothelial carcinogenesis.

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.

Molecular Pathways: Targeting Mechanisms of Asbestos and Erionite Carcinogenesis in Mesothelioma

Malignant mesothelioma is an aggressive malignancy related to asbestos and erionite exposure. AP-1 transcriptional activity and the NF-κB signaling pathway have been linked to mesothelial cell transformation and tumor progression. HGF and c-Met are highly expressed in mesotheliomas. Phosphoinositide 3-kinase, AKT, and the downstream mTOR are involved in cell growth and survival, and they are often found to be activated in mesothelioma. p16(INK4a) and p14(ARF) are frequently inactivated in human mesothelioma, and ∼50% of mesotheliomas contain the NF2 mutation. Molecular therapies aimed at interfering with these pathways have not improved the dismal prognosis of mesothelioma, except possibly for a small subset of patients who benefit from certain therapies. Recent studies have shown the importance of asbestos-induced inflammation in the initiation and growth of mesothelioma, and HMGB1 and Nalp3 inflammasome have been identified as key initiators of this process. Asbestos induces cell necrosis, causing the release of HMGB1, which in turn may activate Nalp3 inflammasome, a process that is enhanced by asbestos-induced production of reactive oxygen species. HMGB1 and Nalp3 induce proinflammatory responses and lead to interleukin-1β and TNF-α secretion and NF-κB activity, thereby promoting cell survival and tumor growth. Novel strategies that interfere with asbestos- and erionite-mediated inflammation might prevent or delay the onset of mesothelioma in high-risk cohorts, including genetically predisposed individuals, and/or inhibit tumor growth. The very recent discovery that germline BAP1 mutations cause a new cancer syndrome characterized by mesothelioma, uveal melanoma, and melanocytic tumors provides researchers with a novel target for prevention and early detection.

How Frustration Leads to Inflammation

A molecular basis for asbestos-induced inflammation may lie in a particular component of the inflammasome protein complex.

Asbestos-Induced Inflammation and Fibrosis are Regulated by Rac1

Asbestos-Induced Inflammation and Fibrosis are Regulated by Rac1

Increased Localization and Substrate Activation of Protein Kinase Cδ in Lung Epithelial Cells following Exposure to Asbestos

The protein kinase C (PKC) family consists of several isozymes whose substrates may be necessary for the regulation of key cellular events important in the pathogenesis of proliferative diseases. Asbestos is a carcinogen and fibroproliferative agent in lung that may cause cell signaling events through activation of PKC. Here we used a murine inhalation model of asbestos-induced inflammation and fibrosis to examine immunoreactivity of PKC delta and its substrate, phosphorylated-adducin (p-adducin), in cells of the lung. Moreover, we characterized PKC delta and p-adducin expression in a pulmonary epithelial cell line (C10) in both log versus confluent cells and in cells after mechanical wounding or crocidolite asbestos exposure. Both PKC delta and p-adducin were almost exclusively expressed in bronchiolar and alveolar type II (ATII) epithelial cells in lung sections and increased in these cell types after inhalation of asbestos by mice. Increases in membrane and nuclear localization of PKC delta were seen in log phase as compared to confluent C10 cells. Moreover, enhanced immunoreactivity of PKC delta was observed in epithelial cells expressing proliferating cell nuclear antigen (PCNA) after mechanical wounding or exposure to asbestos fibers. These studies show that activated PKC delta in pulmonary epithelial cells is a consequence of inhalation of asbestos and may be linked to the activation of cell proliferation.