Immunity and malignant mesothelioma: From mesothelial cell damage to tumor development and immune response-based therapies

Haptoglobin phenotype: A germline risk factor for malignant pleural mesothelioma? A case-control study

PURPOSE

The pathogenesis of malignant pleural mesothelioma (MPM) is linked to asbestos-induced chronic inflammation, oxidant formation, hemolysis and subsequent hemoglobin (Hb) release, potentiating oxidative injury. Haptoglobin (Hp) serves as a major antioxidant by binding free Hb in order to prevent its harmful effects. Dependent on the Hp-phenotype, this complexing can be divergent, leading to additional formation of reactive oxygen species (ROS) above those directly induced by asbestos or released by inflammatory cells. In order to determine the Hp-phenotype as a risk factor in MPM, this case-control study compared the Hp-phenotype distribution in MPM patients with asymptomatic persons with former occupational asbestos exposure (AEx) and controls from a European population.

MATERIALS AND METHODS

Hp-phenotyping was done on serum samples of 118 MPM patients and 96 AEx subjects by starch gel electrophoresis. The frequencies of Hp phenotypes (Hp 1-1, Hp 2-1 and Hp 2-2) and alleles (Hp1, Hp2) were compared with those from 918 healthy control subjects.

RESULTS

The Hp 1-1 phenotype was overrepresented in MPM patients compared to AEx persons (P = 0.001) and healthy controls (P = 0.005). The relative risk for developing MPM when having the Hp 1-1 phenotype was 3.05 (1.47-6.34) for AEx subjects and 1.74 (1.19-2.54) for healthy controls compared to other phenotypes.

CONCLUSION

Our results indicate an important role of the Hp-phenotype in MPM pathogenesis suggesting that Hp 1-1 phenotypic persons are more prone for MPM development. Apart from the asbestos-induced radical formation, this finding confirms the role of oxidative stress in cancer development.

Antitumoral effects of Bortezomib in malignant mesothelioma: evidence of mild endoplasmic reticulum stress in vitro and activation of T cell response in vivo

BACKGROUND

Malignant mesothelioma (MM) is a rare tumor with a dismal prognosis. The low efficacy of current treatment options highlights the urge to identify more effective therapies aimed at improving MM patients' survival. Bortezomib (Bor) is a specific and reversible inhibitor of the chymotrypsin-like activity of the 20S core of the proteasome, currently approved for the treatment of multiple myeloma and mantle cell lymphoma. On the other hand, Bor appears to have limited clinical effects on solid tumors, because of its low penetration and accumulation into tumor tissues following intravenous administration. These limitations could be overcome in MM through intracavitary delivery, with the advantage of increasing local drug concentration and decreasing systemic toxicity.

METHODS

In this study, we investigated the effects of Bor on cell survival, cell cycle distribution and modulation of apoptotic and pro-survival pathways in human MM cell lines of different histotypes cultured in vitro. Further, using a mouse MM cell line that reproducibly forms ascites when intraperitoneally injected in syngeneic C57BL/6 mice, we investigated the effects of intraperitoneal Bor administration in vivo on both tumor growth and the modulation of the tumor immune microenvironment.

RESULTS

We demonstrate that Bor inhibited MM cell growth and induced apoptosis. Further, Bor activated the Unfolded Protein Response, which however appeared to participate in lowering cells' sensitivity to the drug's cytotoxic effects. Bor also affected the expression of EGFR and ErbB2 and the activation of downstream pro-survival signaling effectors, including ERK1/2 and AKT. In vivo, Bor was able to suppress MM growth and extend mice survival. The Bor-mediated delay of tumor progression was sustained by increased activation of T lymphocytes recruited to the tumor microenvironment.

CONCLUSIONS

The results presented herein support the use of Bor in MM and advocate future studies aimed at defining the therapeutic potential of Bor and Bor-based combination regimens for this treatment-resistant, aggressive tumor.

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

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

Inhibition of the Histone Methyltransferase EZH2 Enhances Protumor Monocyte Recruitment in Human Mesothelioma Spheroids

Malignant pleural mesothelioma (MPM) is a highly aggressive cancer with a long latency period and dismal prognosis. Recently, tazemetostat (EPZ-6438), an inhibitor of the histone methyltransferase EZH2, has entered clinical trials due to the antiproliferative effects reported on MPM cells. However, the direct and indirect effects of epigenetic reprogramming on the tumor microenvironment are hitherto unexplored. To investigate the impact of tumor-associated macrophages (TAMs) on MPM cell responsiveness to tazemetostat, we developed a three-dimensional MPM spheroid model that recapitulates in vitro, both monocytes’ recruitment in tumors and their functional differentiation toward a TAM-like phenotype (Mo-TAMs). Along with an increased expression of genes for monocyte chemoattractants, inhibitory immune checkpoints, immunosuppressive and M2-like molecules, Mo-TAMs promote tumor cell proliferation and spreading. Prolonged treatment of MPM spheroids with tazemetostat enhances both the recruitment of Mo-TAMs and the expression of their protumor phenotype. Therefore, Mo-TAMs profoundly suppress the antiproliferative effects due to EZH2 inhibition in MPM cells. Overall, our findings indicate that TAMs are a driving force for MPM growth, progression, and resistance to tazemetostat; therefore, strategies of TAM depletion might be evaluated to improve the therapeutic efficacy of pharmacological inhibition of EZH2.

Intrapleural immunotherapy: An update on emerging treatment strategies for pleural malignancy

OBJECTIVES

Malignant pleural mesothelioma and malignant pleural effusions are a major therapeutic challenge, and are associated with impairment in quality of life and increased mortality. Advances in systemic therapies of malignant pleural mesothelioma have demonstrated limited clinical benefit and there is ongoing interest in intrapleural immunotherapies which have been demonstrated to be well tolerated overall with variable clinical responses. We have reviewed the literature to provide a comprehensive summary of novel intrapleural immunotherapeutic paradigms, including oncolytic virus therapy, gene-mediated cytotoxic immunotherapy, direct cytokine-mediated immunotherapies, innate immunomodulators and adoptive transfer of intrapleural chimeric antigen receptor T-cell therapy.

DATA SOURCES

A review of PubMed for original manuscripts and conference reports published between 1998 and 2018 pertaining to intrapleural immunotherapy, as well as examination of reference lists from reviewed manuscripts.

STUDY SELECTION

Human clinical trials on intrapleural immunotherapies in subjects with malignant pleural mesothelioma or malignant pleural effusion were included in this review, including some relevant preclinical studies and anticipated ongoing trials reported on Clinicaltrials.gov.

RESULTS

Twenty-six clinical trials were identified, in addition to three trials currently in progress.

CONCLUSION

Intrapleural immunotherapies for pleural malignancy have demonstrated promise with regard to generating durable tumor-specific immune responses with possible clinical benefits which merit further investigation as part of multimodal chemotherapeutic and immunotherapeutic regimens.

Complex Immune Contextures Characterise Malignant Peritoneal Mesothelioma: Loss of Adaptive Immunological Signature in the More Aggressive Histological Types

Malignant peritoneal mesothelioma (MpM), arising in the setting of local inflammation, is a rare aggressive tumour with a poor prognosis and limited therapeutic options. The three major MpM histological variants, epithelioid (E-MpMs), biphasic, and sarcomatoid MpMs (S-MpMs), are characterised by an increased aggressiveness and enhanced levels of EZH2 expression. To investigate the MpM immune contexture along the spectrum of MpM histotypes, an extended in situ analysis was performed on a series of 14 cases. Tumour-infiltrating immune cells and their functionality were assessed by immunohistochemistry, immunofluorescence, qRT-PCR, and flow cytometry analysis. MpMs are featured by a complex immune landscape modulated along the spectrum of MpM variants. Tumour-infiltrating T cells and evidence for pre-existing antitumour immunity are mainly confined to E-MpMs. However, Th1-related immunological features are progressively impaired in the more aggressive forms of E-MpMs and completely lost in S-MpM. Concomitantly, E-MpMs show also signs of active immune suppression, such as the occurrence of Tregs and Bregs and the expression of the immune checkpoint inhibitory molecules PD1 and PDL1. This study enriches the rising rationale for immunotherapy in MpM and points to the E-MpMs as the most immune-sensitive MpM histotypes, but it also suggests that synergistic interventions aimed at modifying the tumour microenvironment (TME) should be considered to make immunotherapy beneficial for these patients.

Loss of C/EBP-β LIP drives cisplatin resistance in malignant pleural mesothelioma

OBJECTIVES

Cisplatin-based chemotherapy is moderately active in malignant pleural mesothelioma (MPM) due to intrinsic drug resistance and to low immunogenicity of MPM cells. CAAT/enhancer binding protein (C/EBP)-β LIP is a pro-apoptotic and chemosensitizing transcription factor activated in response to endoplasmic reticulum (ER) stress.

MATERIALS AND METHODS

We investigated if LIP levels can predict the clinical response to cisplatin and survival of MPM patients receiving cisplatin-based chemotherapy. We studied the LIP-dependent mechanisms determining cisplatin-resistance and we identified pharmacological approaches targeting LIP, able to restore cisplatin sensitiveness, in patient-derived MPM cells and animal models. Results were analyzed by a one-way analysis of variance test.

RESULTS

We found that LIP was degraded by constitutive ubiquitination in primary MPM cells derived from patients poorly responsive to cisplatin. LIP ubiquitination was directly correlated with cisplatin chemosensitivity and was associated with patients' survival after chemotherapy. Overexpression of LIP restored cisplatin's pro-apoptotic effect by activating CHOP/TRB3/caspase 3 axis and up-regulating calreticulin, that triggered MPM cell phagocytosis by dendritic cells and expanded autologous anti-tumor CD8⁺CD107⁺T-cytotoxic lymphocytes. Proteasome inhibitor carfilzomib and lysosome inhibitor chloroquine prevented LIP degradation. The triple combination of carfilzomib, chloroquine and cisplatin increased ER stress-triggered apoptosis and immunogenic cell death in patients' samples, and reduced tumor growth in cisplatin-resistant MPM preclinical models.

CONCLUSION

The loss of LIP mediates cisplatin resistance, rendering LIP a possible predictor of cisplatin response in MPM patients. The association of proteasome and lysosome inhibitors reverses cisplatin resistance by restoring LIP levels and may represent a new adjuvant strategy in MPM treatment.

Curcumin blocks autophagy and activates apoptosis of malignant mesothelioma cell lines and increases the survival of mice intraperitoneally transplanted with a malignant mesothelioma cell line

Malignant mesothelioma (MM) is a primary tumor arising from the serous membranes. The resistance of MM patients to conventional therapies, and the poor patients’ survival, encouraged the identification of molecular targets for MM treatment. Curcumin (CUR) is a “multifunctional drug”. We explored the in vitro effects of CUR on cell proliferation, cell cycle regulation, pro-survival signaling pathways, apoptosis, autophagy of human (MM-B1, H-Meso-1, MM-F1), and mouse (#40a) MM cells. In addition, we evaluated the in vivo anti-tumor activities of CUR in C57BL/6 mice intraperitoneally transplanted with #40a cells forming ascites.

CUR in vitro inhibited MM cells survival in a dose- and time-dependent manner and increased reactive oxygen species’intracellular production and induced DNA damage. CUR triggered autophagic flux, but the process was then blocked and was coincident with caspase 8 activation which activates apoptosis. CUR-mediated apoptosis was supported by the increase of Bax/Bcl-2 ratio, increase of p53 expression, activation of caspase 9, cleavage of PARP-1, increase of the percentage of cells in the sub G1 phase which was reduced (MM-F1 and #40a) or abolished (MM-B1 and H-Meso-1) after MM cells incubation with the apoptosis inhibitor Z-VAD-FMK. CUR treatment stimulated the phosphorylation of ERK1/2 and p38 MAPK, inhibited that of p54 JNK and AKT, increased c-Jun expression and phosphorylation and prevented NF-κB nuclear translocation. Intraperitoneal administration of CUR increased the median survival of C57BL/6 mice intraperitoneally transplanted with #40a cells and reduced the risk of developing tumors. Our findings may have important implications for the design of MM treatment using CUR.

P2X7 targeting inhibits growth of human mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive tumor refractory to anti-blastic therapy. MPM cells show several genetic and biochemical defects, e.g. overexpression of oncogenes, downregulation of onco-suppressor genes, dysregulation of microRNA, or alteration of intracellular Ca²⁺ homeostasis and of apoptosis. No information is as yet available on purinergic signalling in this tumor. Signalling via the P2×7 (P2RX7 or P2×7R) purinergic receptor is attracting increasing attention as a pathway involved in cancer cell death or proliferation. In this report we show that the P2×7R is expressed by three MPM cell lines established from MPM patients but not by mesothelial cells from healthy subjects (healthy mesothelial cells, HMCs). MPM cell proliferation was inhibited by in vitro incubation in the presence of selective P2×7R antagonists, as well as by stimulation with the P2×7R agonist BzATP. Systemic administration of the selective P2×7R blocker AZ10606120 inhibited in vivo growth of MPM tumors whether implanted subcutaneously (s.c.) or intraperitoneally (i.p.). Our findings suggest that the P2×7R might be a novel target for the therapy of mesothelioma.

Bromodomain inhibition exerts its therapeutic potential in malignant pleural mesothelioma by promoting immunogenic cell death and changing the tumor immune-environment

Systemic treatment of malignant pleural mesothelioma (MPM) is moderately active for the intrinsic pharmacological resistance of MPM cell and its ability to induce an immune suppressive environment. Here we showed that the expression of bromodomain (BRD) proteins BRD2, BRD4 and BRD9 was significantly higher in human primary MPM cells compared to normal mesothelial cells (HMC). Nanomolar concentrations of bromodomain inhibitors (BBIs) JQ1 or OTX015 impaired patient-derived MPM cell proliferation and induced cell-cycle arrest without affecting apoptosis. Importantly, BBIs primed MPM cells for immunogenic cell death, by increasing extracellular release of ATP and HMGB1, and by promoting membrane exposure of calreticulin and ERp57. Accordingly, BBIs activated dendritic cell (DC)-mediated phagocytosis and expansion of CD8⁺ T-lymphocyte clones endorsed with antitumor cytotoxic activity. BBIs reduced the expression of the immune checkpoint ligand PD-L1 in MPM cells; while both CD8⁺ and CD4⁺ T-lymphocytes co-cultured with JQ1-treated MPM cells decreased PD-1 expression, suggesting a disruption of the immune-suppressive PD-L1/PD-1 axis. Additionally, BBIs reduced the expansion of myeloid-derived suppressor cells (MDSC) induced by MPM cells. Finally, a preclinical model of MPM confirmed that the anti-tumor efficacy of JQ1 was largely due to its ability to restore an immune-active environment, by increasing intra-tumor DC and CD8⁺ T-lymphocytes, and decreasing MDSC. Thereby, we propose that, among novel drugs, BBIs should be investigated for MPM treatment for their combined activity on both tumor cells and surrounding immune-environment.

Abundant expression of TIM-3, LAG-3, PD-1 and PD-L1 as immunotherapy checkpoint targets in effusions of mesothelioma patients

Malignant pleural mesothelioma (MPM) is an aggressive cancer with an increasing incidence, poor prognosis and limited effective treatment options. Hence, new treatment strategies are warranted which include immune checkpoint blockade approaches with encouraging preliminary data. Research on the immunological aspects of the easily accessible mesothelioma microenvironment could identify prognostic and/or predictive biomarkers and provide useful insights for developing effective immunotherapy. In this context, we investigated the immune cell composition of effusions (pleural and ascites fluids) from 11 different chemotherapy-treated MPM patients. We used multicolor flow cytometry to describe different subsets of immune cells and their expression of immune checkpoint molecules TIM-3, LAG-3, PD-1 and PD-L1. We demonstrate a patient-dependent inter- and intraspecific variation comparing pleural and ascites fluids in immune cell composition and immune checkpoint expression. We found CD4⁺ and CD8⁺ T cells, B cells, macrophages, natural killer cells, dendritic cells and tumor cells in the fluids. To the best of our knowledge, we are the first to report TIM-3 and LAG-3 expression and we confirm PD-1 and PD-L1 expression on different MPM effusion-resident immune cells. Moreover, we identified two MPM effusion-related factors with clinical value: CD4+ T cells were significantly correlated with better response to chemotherapy, while the percentage of PD-L1⁺ podoplanin (PDPN)⁺ tumor cells is a significant prognostic factor for worse outcome. Our data provide a basis for more elaborate research on MPM effusion material in the context of treatment follow-up and prognostic biomarkers and the development of immune checkpoint-targeted immunotherapy.

Determination of PD-L1 expression in effusions from mesothelioma by immuno-cytochemical staining

BACKGROUND

Malignant mesothelioma (MM) is an aggressive, fatal tumor. Current therapeutic options only marginally improve survival. Programmed cell death ligand 1 (PD-L1) is a dominant mediator of immunosuppression, binding to programmed cell death 1 (PD-1). PD-L1 is up-regulated in cancer cells, and the PD-1/PD-L1 pathway plays a critical role in tumor immune evasion, thus providing a target for antitumor therapy. Further, a correlation between PD-L1 expression and prognosis has been reported. Studies performed on histological material have revealed expression of PD-L1 in MM, but no study has been performed on MM effusions thus far.

METHODS

PD-L1 expression was determined by a commercially available antibody (clone 28-8) in 74 formalin-fixed, paraffin-embedded cell blocks from body effusions obtained at diagnosis from patients with MM. The presence of MM cells was confirmed with CK5/6, calretinin, and EMA and the admixture of macrophages was assessed with CD68. Only cases containing more than 100 tumor cells were assessed. Membranous staining in tumor cells was considered positive. Survival time was calculated from the appearance of the first malignant effusion until death.

RESULTS

Reactivity was observed in 23 of 61 (38%) of cases and was classified as ≥1%-5% (n = 9 cases), >5%-10% (n = 4 cases), >10%-50% (n = 4 cases), and >50% (n = 6 cases) positive cells. Survival times did not differ significantly between patients with PD-L1-positive and PD-L1-negative tumors.

CONCLUSION

MM effusions are suitable for immune-cytochemical assessment of PD-L1 expression in malignant cells and the results are similar to those reported for histological specimens. Cancer Cytopathol 2017;125:908-17. © 2017 American Cancer Society.

CAR T-cell immunotherapy of MET-expressing malignant mesothelioma

Mesothelioma is an incurable cancer for which effective therapies are required. Aberrant MET expression is prevalent in mesothelioma, although targeting using small molecule-based therapeutics has proven disappointing. Chimeric antigen receptors (CARs) couple the HLA-independent binding of a cell surface target to the delivery of a tailored T-cell activating signal. Here, we evaluated the anti-tumor activity of MET re-targeted CAR T-cells against mesothelioma. Using immunohistochemistry, MET was detected in 67% of malignant pleural mesotheliomas, most frequently of epithelioid or biphasic subtype. The presence of MET did not influence patient survival. Candidate MET-specific CARs were engineered in which a CD28+CD3ζ endodomain was fused to one of 3 peptides derived from the N and K1 domains of hepatocyte growth factor (HGF), which represents the minimum MET binding element present in this growth factor. Using an NIH3T3-based artificial antigen-presenting cell system, we found that all 3 candidate CARs demonstrated high specificity for MET. By contrast, these CARs did not mediate T-cell activation upon engagement of other HGF binding partners, namely CD44v6 or heparan sulfate proteoglycans, including Syndecan-1. NK1-targeted CARs demonstrated broadly similar in vitro potency, indicated by destruction of MET-expressing mesothelioma cell lines, accompanied by cytokine release. In vivo anti-tumor activity was demonstrated following intraperitoneal delivery to mice with an established mesothelioma xenograft. Progressive tumor regression occurred without weight loss or other clinical indicators of toxicity. These data confirm the frequent expression of MET in malignant pleural mesothelioma and demonstrate that this can be targeted effectively and safely using a CAR T-cell immunotherapeutic strategy.

In Vitro and In Vivo Anti-tumoral Effects of the Flavonoid Apigenin in Malignant Mesothelioma

Malignant mesothelioma (MM) is a tumor arising from mesothelium. MM patients’ survival is poor. The polyphenol 4′,5,7,-trihydroxyflavone Apigenin (API) is a “multifunctional drug”. Several studies have demonstrated API anti-tumoral effects. However, little is known on the in vitro and in vivo anti-tumoral effects of API in MM. Thus, we analyzed the in vitro effects of API on cell proliferation, cell cycle regulation, pro-survival signaling pathways, apoptosis, and autophagy of human and mouse MM cells. We evaluated the in vivo anti-tumor activities of API in mice transplanted with MM #40a cells forming ascites. API inhibited in vitro MM cells survival, increased reactive oxygen species intracellular production and induced DNA damage. API activated apoptosis but not autophagy. API-induced apoptosis was sustained by the increase of Bax/Bcl-2 ratio, increase of p53 expression, activation of both caspase 9 and caspase 8, cleavage of PARP-1, and increase of the percentage of cells in subG1 phase. API treatment affected the phosphorylation of ERK1/2, JNK and p38 MAPKs in a cell-type specific manner, inhibited AKT phosphorylation, decreased c-Jun expression and phosphorylation, and inhibited NF-κB nuclear translocation. Intraperitoneal administration of API increased the median survival of C57BL/6 mice intraperitoneally transplanted with #40a cells and reduced the risk of tumor growth. Our findings may have important implications for the design of MM treatment using API.

Prognostic and predictive aspects of the tumor immune microenvironment and immune checkpoints in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive cancer with a poor prognosis and an increasing incidence, for which novel therapeutic strategies are urgently required. Since the immune system has been described to play a presumed role in the protection against MPM, characterization of its tumor immune microenvironment (TME) and immune checkpoints can identify new immunotherapeutic targets and their predictive and/or prognostic value. To characterize the TME and the immune checkpoint expression profile, we performed immunohistochemistry (IHC) on formalin-fixed paraffin embedded (FFPE) tissue sections from 54 MPM patients (40 at time of diagnosis; 14 treated with chemotherapy). We stained for PD-1, PD-L1, TIM-3, LAG-3, CD4, CD8, CD45RO, granzyme B, FoxP3 and CD68. Furthermore, we analyzed the relationship between the immunological parameters and survival, as well as response to chemotherapy. We found that TIM-3, PD-1 and PD-L1 were expressed on both immune and tumor cells. Strikingly, PD-1 and PD-L1 expression on tumor cells was only seen in unpretreated samples. No LAG-3 expression was observed. CD45RO expression in the stroma was an independent negative predictive factor for response on chemotherapy, while CD4 and TIM-3 expression in lymphoid aggregates were independent prognostic factors for better outcome. Our data propose TIM-3 as a promising new target in mesothelioma. Chemotherapy influences the expression of immune checkpoints and therefore further research on the best combination treatment schedule is required.

Switching off malignant mesothelioma: exploiting the hypoxic microenvironment

Malignant mesotheliomas are aggressive, asbestos-related cancers with poor patient prognosis, typically arising in the mesothelial surfaces of tissues in pleural and peritoneal cavity. The relative unspecific symptoms of mesotheliomas, misdiagnoses, and lack of precise targeted therapies call for a more critical assessment of this disease. In the present review, we categorize commonly identified genomic aberrations of mesotheliomas into their canonical pathways and discuss targeting these pathways in the context of tumor hypoxia, a hallmark of cancer known to render solid tumors more resistant to radiation and most chemo-therapy. We then explore the concept that the intrinsic hypoxic microenvironment of mesotheliomas can be Achilles' heel for targeted, multimodal therapeutic intervention.

Mesothelioma response to carbon nanotubes is associated with an early and selective accumulation of immunosuppressive monocytic cells

Background

The asbestos-like toxicity of some engineered carbon nanotubes (CNT), notably their capacity to induce mesothelioma, is a serious cause of concern for public health. Here we show that carcinogenic CNT induce an early and sustained immunosuppressive response characterized by the accumulation of monocytic Myeloid Derived Suppressor Cells (M-MDSC) that counteract effective immune surveillance of tumor cells.

Methods

Wistar rats and C57BL/6 mice were intraperitoneally injected with carcinogenic multi-walled Mitsui-7 CNT (CNT-7) or crocidolite asbestos. Peritoneal mesothelioma development and immune cell accumulation were assessed until 12 months. Leukocyte sub-populations were identified by recording expression of CD11b/c and His48 by flow cytometry. The immunosuppressive activity on T lymphocytes of purified peritoneal leukocytes was assessed in a co-culture assay with activated spleen cells.

Results

We demonstrate that long and short mesotheliomagenic CNT-7 injected in the peritoneal cavity of rats induced, like asbestos, an early and selective accumulation of monocytic cells (CD11b/c^int and His48^hi) which possess the ability to suppress polyclonal activation of T lymphocytes and correspond to M-MDSC. Peritoneal M-MDSC persisted during the development of peritoneal mesothelioma in CNT-7-treated rats but were only transiently recruited after non-carcinogenic CNT (CNT-M, CNT-T) injection. Peritoneal M-MDSC did not accumulate in mice which are resistant to mesothelioma development.

Conclusions

Our data provide new insights into the initial pathogenic events induced by CNT, adding a new component to the adverse outcome pathway leading to mesothelioma development. The specificity of the M-MDSC response after carcinogenic CNT exposure highlights the interest of this response for detecting the ability of new nanomaterials to cause cancer.

Electronic supplementary material

The online version of this article (doi:10.1186/s12989-016-0158-0) contains supplementary material, which is available to authorized users.

The Potential Protective Effects of Polyphenols in Asbestos-Mediated Inflammation and Carcinogenesis of Mesothelium

Malignant Mesothelioma (MM) is a tumor of the serous membranes linked to exposure to asbestos. A chronic inflammatory response orchestrated by mesothelial cells contributes to the development and progression of MM. The evidence that: (a) multiple signaling pathways are aberrantly activated in MM cells; (b) asbestos mediated-chronic inflammation has a key role in MM carcinogenesis; (c) the deregulation of the immune system might favor the development of MM; and (d) a drug might have a better efficacy when injected into a serous cavity thus bypassing biotransformation and reaching an effective dose has prompted investigations to evaluate the effects of polyphenols for the therapy and prevention of MM. Dietary polyphenols are able to inhibit cancer cell growth by targeting multiple signaling pathways, reducing inflammation, and modulating immune response. The ability of polyphenols to modulate the production of pro-inflammatory molecules by targeting signaling pathways or ROS might represent a key mechanism to prevent and/or to contrast the development of MM. In this review, we will report the current knowledge on the ability of polyphenols to modulate the immune system and production of mediators of inflammation, thus revealing an important tool in preventing and/or counteracting the growth of MM.

Precision immunotherapy; dynamics in the cellular profile of pleural effusions in malignant mesothelioma patients

OBJECTIVES

Clinical studies have proven the potential of immunotherapy in malignancies. To increase efficacy, a prerequisite is that treatment is tailored, so precision immune-oncology is the logical next step. In order to tailor treatment, characterization of the patient's tumor environment is key. Pleural effusion (PE) often accompanies malignant pleural mesothelioma (MPM) and is an important part of the MPM environment. Furthermore, the composition of PE is used as surrogate for the tumor. In this study, we provide an insight in the dynamics of the MPM environment through characterization of PE composition over time and show that the immunological characteristics of PE do not necessarily mirror those of the tumor.

MATERIALS AND METHODS

From 5 MPM patients, PE and tumor biopsies were acquired at the same time point. From one of these patients multiple PEs were obtained. PEs were acquired performing thoracocenteses and total cell amounts were determined. Immunohistochemistry was performed to quantify immune cell composition (T cells, macrophages) and tumor cells in PE derived cytospins and tumor biopsies.

RESULTS

The PE amount and (immune) cellular composition varied considerably over time between multiple (n=10) thoracocenteses. These dynamics could in part be attributed to the treatment regimen consisting of standard chemotherapy and dendritic cell (DC)-based immunotherapy. In addition, the presence of T cells and macrophages in PE did not necessarily mirror the infiltration of these immune cells within tumor biopsies in 4 out of 5 patients.

CONCLUSIONS

In this proof-of-concept study with limited sample size, we demonstrate that the composition of PE is dynamic and influenced by treatment. Furthermore, the immune cell composition of PE does not automatically reflect the properties of tumor tissue. This has major consequences when applying precision immunotherapy based on PE findings in patients. Furthermore, it implies a regulated trafficking of immune regulating cells within the tumor environment.

Zoledronic acid overcomes chemoresistance and immunosuppression of malignant mesothelioma

The human malignant mesothelioma (HMM) is characterized by a chemoresistant and immunosuppressive phenotype. An effective strategy to restore chemosensitivity and immune reactivity against HMM is lacking. We investigated whether the use of zoledronic acid is an effective chemo-immunosensitizing strategy.

We compared primary HMM samples with non-transformed mesothelial cells.

HMM cells had higher rate of cholesterol and isoprenoid synthesis, constitutive activation of Ras/extracellular signal-regulated kinase1/2 (ERK1/2)/hypoxia inducible factor-1α (HIF-1α) pathway and up-regulation of the drug efflux transporter P-glycoprotein (Pgp). By decreasing the isoprenoid supply, zoledronic acid down-regulated the Ras/ERK1/2/HIF-1α/Pgp axis and chemosensitized the HMM cells to Pgp substrates. The HMM cells also produced higher amounts of kynurenine, decreased the proliferation of T-lymphocytes and expanded the number of T-regulatory (Treg) cells. Kynurenine synthesis was due to the transcription of the indoleamine 1,2 dioxygenase (IDO) enzyme, consequent to the activation of the signal transducer and activator of transcription-3 (STAT3). By reducing the activity of the Ras/ERK1/2/STAT3/IDO axis, zoledronic acid lowered the kyurenine synthesis and the expansion of Treg cells, and increased the proliferation of T-lymphocytes.

Thanks to its ability to decrease Ras/ERK1/2 activity, which is responsible for both Pgp-mediated chemoresistance and IDO-mediated immunosuppression, zoledronic acid is an effective chemo-immunosensitizing agent in HMM cells.

Targeting immune checkpoints: New opportunity for mesothelioma treatment?

Malignant pleural mesothelioma is an aggressive cancer linked to asbestos exposure in most patients. Due to the long latency between exposure and presentation, incidence is expected to further increase in the next decade, despite the ban on asbestos import which occurred at the end of last century in industrialized countries. Platinum-based palliative chemotherapy is the only treatment with proven benefit on outcome, resulting in selected patients in a median overall survival of about 1 year. Therefore, there is room for therapeutic improvement using a new strategy to prolong survival. Dealing with cancer cell induced immunosuppression is a promising approach. Reactivating immune responses that are silenced by immune checkpoints recently gained a lot of interest. Checkpoint blockade has already shown promising preclinical and clinical results in several cancer types and is currently also being investigated in mesothelioma. Here, we discuss the expression patterns and mechanisms of action of CTLA-4 and PD-1 as the two most studied and of TIM-3 and LAG-3 as two interesting upcoming immune checkpoints. Furthermore, we review the clinical results of molecules blocking these immune checkpoints and point out their future opportunities with a special focus on mesothelioma.

Human mesothelioma induces defects in dendritic cell numbers and antigen-processing function which predict survival outcomes

Mesothelioma is an almost invariably fatal tumor with chemotherapy extending survival by a few months. One immunotherapeutic strategy is to target dendritic cells (DCs), key antigen-presenting cells involved in antigen presentation, to induce antigen-specific T cell responses. However, DC-targeting will only be effective if DCs are fit-for-purpose, and the functional status of DCs in mesothelioma patients was not clear. We found that mesothelioma patients have significantly decreased numbers of circulating myeloid (m)DC1 cells, mDC2 cells and plasmacytoid (p)DCs relative to healthy age and gender-matched controls. Blood monocytes from patients could not differentiate into immature monocyte-derived DCs (MoDCs), indicated by a significantly reduced ability to process antigen and reduced expression of costimulatory (CD40, CD80 and CD86) and MHC (HLA-DR) molecules, relative to controls. Activation of mesothelioma-derived MoDCs with LPS+/-IFNγ generated partially mature MoDCs, evident by limited upregulation of the maturation marker, CD83, and the costimulatory markers. Attempts to rescue mesothelioma-derived DC function using CD40Ligand(L) also failed, indicated by maintenance of antigen-processing capacity and limited upregulation of CD40, CD83, CD86 and HLA-DR. These data suggest that mesothelioma patients have significant numerical and functional DC defects and that their reduced capacity to process antigen and reduced expression of costimulatory molecules could induce anergized/tolerized T cells. Nonetheless, survival analyses revealed that individuals with mesothelioma and higher than median levels of mDC1s and/or whose MoDCs matured in response to LPS, IFNγ or CD40L lived longer, implying their selection for DC-targeting therapy could be promising especially if combined with another treatment modality.

Research priorities in mesothelioma: A James Lind Alliance Priority Setting Partnership

BACKGROUND

In the UK, despite the import and use of all forms of asbestos being banned more than 15 years ago, the incidence of mesothelioma continues to rise. Mesothelioma is almost invariably fatal, and more research is required, not only to find more effective treatments, but also to achieve an earlier diagnosis and improve palliative care. Following a debate in the House of Lords in July 2013, a package of measures was agreed, which included a James Lind Alliance Priority Setting Partnership, funded by the National Institute for Health Research. The partnership brought together patients, carers, health professionals and support organisations to agree the top 10 research priorities relating to the diagnosis, treatment and care of patients with mesothelioma.

METHODS

Following the established James Lind Alliance priority setting process, mesothelioma patients, current and bereaved carers, and health professionals were surveyed to elicit their concerns regarding diagnosis, treatment and care. Research questions were generated from the survey responses, and following checks that the questions were currently unanswered, an interim prioritisation survey was conducted to identify a shortlist of questions to take to a final consensus meeting.

FINDINGS

Four hundred and fifty-three initial surveys were returned, which were refined into 52 unique unanswered research questions. The interim prioritisation survey was completed by 202 responders, and the top 30 questions were taken to a final meeting where mesothelioma patients, carers, and health professionals prioritised all the questions, and reached a consensus on the top 10.

INTERPRETATION

The top 10 questions cover a wide portfolio of research (including assessing the value of immunotherapy, individualised chemotherapy, second-line treatment and immediate chemotherapy, monitoring patients with pleural thickening, defining the management of ascites in peritoneal mesothelioma, and optimising follow-up strategy). This list is an invaluable resource, which should be used to inform the prioritisation and funding of future mesothelioma research.

Surgical cytoreduction restores the antitumor efficacy of a Listeria monocytogenes vaccine in malignant pleural mesothelioma

Recent studies suggest that immunotherapy may offer a promising treatment strategy for early-stage malignant pleural mesothelioma (MPM), but advanced tumor burden may limit the efficacy of immunotherapy. Therefore, we hypothesized that surgical cytoreduction could restore the efficacy of vaccine-based immunotherapy for MPM. We developed a murine model of MPM through transduction of a mesothelioma cell line with mesothelin. We used this model to evaluate the efficacy of a Listeria monocytogenes vaccine expressing mesothelin. Tumor growth was significantly inhibited at four weeks in animals vaccinated two weeks prior to tumor cell inoculation as compared to those given an empty vector control (1371 ± 420 mm(3) versus 405 ± 139 mm(3); p < 0.01). Mice vaccinated one week prior to tumor challenge also displayed significant reduction in tumor volume (1227 ± 406 mm(3) versus 309 ± 173 mm(3); p < 0.01). The vaccine had no effect when administered concurrently with tumor challenge, or after tumors were established. Flow cytometry showed reduced mesothelin expression in large tumors, as well as tumor-associated immunosuppression due to increased myeloid derived suppressor cells (MDSCs). These factors may have limited vaccine efficacy for advanced disease. Surgical cytoreduction of established tumors restored the antitumor potency of the therapeutic vaccine, with significantly reduced tumor burden at post-operative day 18 (397 ± 103 mm(3) versus 1047 ± 258 mm(3); p < 0.01). We found that surgery reduced MDSCs to levels comparable to those in tumor-naïve mice. This study demonstrates that cytoreduction surgery restores the efficacy of cancer vaccines for MPM by reducing tumor-related immunosuppression that impairs immunotherapy.

Raw and thermally treated cement asbestos exerts different cytotoxicity effects on A549 cells in vitro

Raw cement asbestos (RCA) undergoes a complete solid state transformation when heated at high temperatures. The secondary raw material produced, high temperatures-cement asbestos (HT-CA) is composed of newly-formed crystals in place of the asbestos fibers present in RCA. Our previous study showed that HT-CA exerts lower cytotoxic cell damage compared to RCA. Nevertheless further investigations are needed to deepen our understanding of pathogenic pathways involving oxidative and nitrative damage. Our aim is to deepen the understanding of the biological effects on A549 cells of these materials regarding DNA damage related proteins (p53, its isoform p73 and TRAIL) and nitric oxide (NO) production during inducible nitric oxide synthase (iNOS)-mediated inflammation. Increments of p53/p73 expression, iNOS positive cells and NO concentrations were found with RCA, compared to HT-CA and controls mainly at 48 h. Interestingly, ferrous iron causing reactive oxygen species (ROS)-mediated DNA damage was found in RCA as a contaminant. HT-CA thermal treatment induces a global recrystallization with iron in a crystal form poorly released in media. HT-CA slightly interferes with genome expression and exerts lower inflammatory potential compared to RCA on biological systems. It could represent a safe approach for storing or recycling asbestos and an environmentally friendly alternative to asbestos waste.

Intratumoral delivery of recombinant vaccinia virus encoding for ErbB2/Neu inhibits the growth of salivary gland carcinoma cells

Background

The antitumor activity induced by intratumoral vaccination with poxvirus expressing a tumor antigen was shown to be superior to that induced by subcutaneous vaccination. Salivary gland carcinomas overexpress ErbB2. Trastuzumab, a monoclonal antibody to ErbB2, was proposed for salivary gland tumors treatment. We explored the effectiveness of intratumoral vaccination with the recombinant vaccinia virus ErbB2/Neu (rV-neuT) vaccine in hampering the growth of transplanted Neu-overexpressing BALB-neuT salivary gland cancer cells (SALTO) in BALB-neuT mice.

Methods

BALB-neuT male mice were subcutaneously injected with SALTO tumor cells and intratumorally vaccinated twice with different doses of either rV-neuT or V-wt (wild-type). Tumors were measured weekly. The presence of anti-ErbB2/Neu antibodies was assayed by ELISA, immunoprecipitation or indirect immunofluorescence. Biological activity of immune sera was investigated by analyzing antibody-dependent cellular cytotoxicity (ADCC), SALTO cells proliferation and apoptosis, ErbB2/Neu receptor down regulation and ERK1/2 phosphorylation. Anti-Neu T cell immunity was investigated by determining the release of IL-2 and IFN-gamma in T cells supernatant. Survival curves were determined using the Kaplan-Meier method and compared using the log-rank test. Differences in tumor volumes, number of apoptotic cells, titer of the serum, percentage of ADCC were evaluated through a two-tailed Student’s t-test.

Results

rV-neuT intratumoral vaccination was able to inhibit the growth of SALTO cancer cells in a dose-dependent manner. The anti-Neu serum titer paralleled in vivo antitumor activity of rV-neuT vaccinated mice. rV-neuT immune serum was able to mediate ADCC, inhibition of SALTO cells proliferation, down regulation of the ErbB2/Neu receptor, inhibition of ERK1/2 phosphorylation and induction of apoptosis, thus suggesting potential mechanisms of in vivo tumor growth interference. In addition, spleen T cells of rV-neuT vaccinated mice released IFN-gamma and IL-2 upon in vitro stimulation with several Neu-specific peptides located in the extracellular domain of Neu sequence.

Conclusions

rV-neuT intratumoral vaccination could be employed to induce an efficient antitumor response and reject transplanted salivary gland tumors. Our findings may have important implications for the design of cancer vaccine protocols for the treatment of salivary gland tumors and other accessible tumors using intratumoral injection of recombinant vaccinia virus.

A molecular targeting against nuclear factor-κB, as a chemotherapeutic approach for human malignant mesothelioma

Chronic inflammation due to the absorption of asbestos is an important cause of mesothelioma. Although the increased prevalence of mesothelioma is a serious problem, the development of effective chemotherapeutic agents remains incomplete. As the nuclear factor-κB (NF-κB) pathway contributes to malignant transformation of various types of cells, we explored NF-κB activity in three different pathological types of malignant mesothelioma cells, and evaluated the therapeutic potential of a recently reported NF-κB inhibitor, IMD-0354. NF-κB was constantly activated in MSTO-211H, NCI-H28, and NCI-H2052 cells, and the proliferation of these cell lines was inhibited by IMD-0354. D-type cyclins were effectively suppressed in mixed tissue type MSTO-211H, leading to cell cycle arrest at sub G₁/G₁ phase. IMD-0354 reduced cyclin D3 in both epithelial tissue type NCI-H28 and sarcomatoid tissue type NCI-H2052. In a sphere formation assay, IMD-0354 effectively decreased the number and diameter of MSTO-211H spheres. Preincubation of MSTO-211H cells with IMD-0354 delayed tumor formation in transplanted immunodeficient mice. Furthermore, administration of IMD-0354 markedly rescued the survival rate of mice that received intrathoracic injections of MSTO-211H cells. These results indicate that a targeted drug against NF-κB might have therapeutic efficacy in the treatment of human malignant mesothelioma.

Spontaneous mesotheliomas in F344/N rats are characterized by dysregulation of cellular growth and immune function pathways

Aged male Fischer 344/N rats are prone to developing spontaneous peritoneal mesotheliomas that arise predominantly from the tunica vaginalis of the testes. A definitive cause for the predominance of this neoplasm in F344/N rats is unknown. Investigation of the molecular alterations that occur in spontaneous rat mesotheliomas may provide insight into their pathogenesis as well enable a better understanding regarding the mechanisms underlying chemically induced mesothelioma in rodents. Mesothelial cell function represents a complex interplay of pathways related to host defense mechanisms and maintenance of cellular homeostasis. Global gene expression profiles of spontaneous mesotheliomas from vehicle control male F344/N rats from 2-year National Toxicology Program carcinogenicity bioassays were analyzed to determine the molecular features of these tumors and elucidate tumor-specific gene expression profiles. The resulting gene expression pattern showed that spontaneous mesotheliomas are associated with upregulation of various growth factors, oncogenes, cytokines, pattern recognition response receptors, and pathogen-associated molecular patterns receptors, and the production of reactive oxygen and nitrogen species, as well as downregulation of apoptosis pathways. Alterations in these pathways in turn trigger molecular responses that stimulate cell proliferation and promote tumor survival and progression.

Treatment of malignant pleural mesothelioma by fibroblast activation protein-specific re-directed T cells

Introduction

Malignant pleural mesothelioma (MPM) is an incurable malignant disease, which results from chronic exposition to asbestos in at least 70% of the cases. Fibroblast activation protein (FAP) is predominantly expressed on the surface of reactive tumor-associated fibroblasts as well as on particular cancer types. Because of its expression on the cell surface, FAP is an attractive target for adoptive T cell therapy. T cells can be re-directed by retroviral transfer of chimeric antigen receptors (CAR) against tumor-associated antigens (TAA) and therefore represent a therapeutic strategy of adoptive immunotherapy.

Methods

To evaluate FAP expression immunohistochemistry was performed in tumor tissue from MPM patients. CD8⁺ human T cells were retrovirally transduced with an anti-FAP-F19-∆CD28/CD3ζ-CAR. T cell function was evaluated in vitro by cytokine release and cytotoxicity assays. In vivo function was tested with an intraperitoneal xenograft tumor model in immunodeficient mice.

Results

FAP was found to be expressed in all subtypes of MPM. Additionally, FAP expression was evaluated in healthy adult tissue samples and was only detected in specific areas in the pancreas, the placenta and very weakly for cervix and uterus. Expression of the anti-FAP-F19-∆CD28/CD3ζ-CAR in CD8⁺ T cells resulted in antigen-specific IFNγ release. Additionally, FAP-specific re-directed T cells lysed FAP positive mesothelioma cells and inflammatory fibroblasts in an antigen-specific manner in vitro. Furthermore, FAP-specific re-directed T cells inhibited the growth of FAP positive human tumor cells in the peritoneal cavity of mice and significantly prolonged survival of mice.

Conclusion

FAP re-directed CD8⁺ T cells showed antigen-specific functionality in vitro and in vivo. Furthermore, FAP expression was verified in all MPM histotypes. Therefore, our data support performing a phase I clinical trial in which MPM patients are treated with adoptively transferred FAP-specific re-directed T cells.

Interleukin-17 Produced by Malignant Mesothelioma-Polarized Immune Cells Promotes Tumor Growth and Invasiveness

Malignant mesothelioma (MM) is a highly fatal tumor of inner body membranes, the extensive growth of which is supported by both a weak immunogenicity and the ability to reprogram surrounding immune cells towards tumor-supporting phenotypes. Interleukin-17 (IL-17) is a major inflammatory cytokine which is now accepted as the paradigmatic cytokine of many autoimmune diseases; however, its role in tumor immunology has only been partially unraveled, and no data exist regarding its possible involvement in MM. Thus, in this work we evaluated the ability of MM to induce IL-17 production in immune cells and the effects of IL-17 on MM growth and invasiveness. Our data show for the first time that macrophages and CD4+ T-cells are polarized by MM to produce IL-17, and that this cytokine exerts multiple tumor-supporting effects on both cell growth and invasiveness. These data provide novel evidence of the crosstalk occurring between MM and immune cells and suggest potential targets for the development of new pharmacological approaches for MM treatment.

Local radiotherapy increases the level of autoantibodies to ribosomal P0 protein but not to heat shock proteins, extracellular matrix molecules and EGFR/ErbB2 receptors in prostate cancer patients

Prostate cancer is a common cancer among men in developed countries. Although hormonotherapy and radiotherapy (RT) represent valid therapies for prostate cancer treatment, novel immunological approaches have been explored. The development of clinical trials employing cancer vaccines has indicated that immune response to tumor antigens can be boosted and that vaccine administration can improve patient survival. Immune response to tumor antigens could also be enhanced after standard therapies. In the present study, we determined the occurrence of antibodies to extracellular matrix (ECM) molecules, heat shock protein (HSP), ribosomal P0 protein, EGFR, ErbB2 and prostate-specific antigen (PSA) in 35 prostate cancer patients prior to and following local RT and hormonotherapy. We demonstrated that immunity to P0, ECM molecules [collagens (C) CI, CIII, CV, fibronectin (FN) and laminin (LM)] and to HSP90 was associated with malignancy in untreated patients. None of the patient sera showed antibodies to EGFR, while 2 and 1 patients showed reactivity to ErbB2 and PSA, respectively. We also demonstrated that 8 months after therapy the IgG serum levels to CI, CIII, FN and HSP90 significantly decreased. Conversely, the level of P0 autoantibodies increased after therapy in 10 patients. Five of the 10 patients with increased levels of P0 autoantibodies were treated with RT plus hormonotherapy. Treatment of patients did not change the levels of antibodies against EGFR, ErbB2 and PSA. Our results indicated that the modification of antibody level to self molecules after standard treatment of prostate cancer patients is influenced by the type of antigen. Ribosomal P0 protein appears to be a high immunogenic antigen and its immunogenicity increases following RT. In addition, 10 patients with increased levels of autoantibodies to P0 showed PSA mean levels lower than the remaining 25 patients at 18 months. This study may contribute to a better understanding of the immunobiological behavior of prostate cancer patients following standard treatment.