Primary Mesothelioma Cell Research Articles

The Impact of 3D Nichoids and Matrix Stiffness on Primary Malignant Mesothelioma Cells.

Malignant mesothelioma is a type of cancer that affects the mesothelium. It is an aggressive and deadly form of cancer that is often caused by exposure to asbestos. At the molecular level, it is characterized by a low number of genetic mutations and high heterogeneity among patients. In this work, we analyzed the plasticity of gene expression of primary mesothelial cancer cells by comparing their properties on 2D versus 3D surfaces. First, we derived from primary human samples four independent primary cancer cells. Then, we used Nichoids, which are micro-engineered 3D substrates, as three-dimensional structures. Nichoids limit the dimension of adhering cells during expansion by counteracting cell migration between adjacent units of a substrate with their microarchitecture. Tumor cells grow effectively on Nichoids, where they show enhanced proliferation. We performed RNAseq analyses on all the samples and compared the gene expression pattern of Nichoid-grown tumor cells to that of cells grown in a 2D culture. The PCA analysis showed that 3D samples were more transcriptionally similar compared to the 2D ones. The 3D Nichoids induced a transcriptional remodeling that affected mainly genes involved in extracellular matrix assembly. Among these genes responsible for collagen formation, COL1A1 and COL5A1 exhibited elevated expression, suggesting changes in matrix stiffness. Overall, our data show that primary mesothelioma cells can be effectively expanded in Nichoids and that 3D growth affects the cells' tensegrity or the mechanical stability of their structure.

Abstract 6086: Clonal biallelic inactivation of NF2 is an evolutionary bottleneck that exposes a vulnerability to CDK7 inhibition in mesothelioma

Abstract Background: Mesothelioma, a cancer caused by asbestos is lethal and lacks molecularly targeted therapy. The tumor suppressor NF2 constitutes a frequent, positively selected somatic alteration warranting synthetic lethal approaches to target this driver. NF2 inactivation drives nuclearization of YAP to mediate TEAD dependent oncogenic transcriptional program. YAP is stabilized by CDK7 through phosphorylation of S169/S128/S90, inhibiting the E3 ligase complex CDL4DCAF12. We hypothesized that biallelic NF2 inactivation would be vulnerable to augmentation of CRL4DCAF12 through inhibition of CDK7. Methods: 50 Patients (the MEDUSA cohort) undergoing routine extended pleurectomy decortications consented to have multiregional sampling of their mesotheliomas at resection at 4-5 stereotyped locations, followed by multiregional whole exome sequencing (mWES 200x), phylogenetic deconvolution and transfer learning to examine evolutionary trajectories. Bulk RNA sequencing enabled gene set enrichment analysis, and spatial YAP phenotyping using tissue microarrays were conducted on the mWES profiled cohort. Primary cell lines were generated from a subset of mesotheliomas and whole exome sequenced. Results: NF2 exhibited biallelic inactivation involving copy number/mutation allelic heterogeneity in 42% of mesotheliomas. Double hits were predominantly clonal. Hippo signalosome exhibited additional clonal somatic alterations in 26% of mesotheliomas, with biallelic inactivation being observed in LATS2 (8%) and LATS1 (4%). Transfer learning identified NF2 inactivation as a predominantly secondary clonal event, constituting an evolutionary bottleneck. Random forest analysis revealed YAP dependent transcription, epithelial mesenchymal transition and spindle checkpoint transcriptional signature enrichments in NF2 double hit mesotheliomas. We conducted drug screening of NF2 wild type versus inactivated primary mesothelioma cell lines, which revealed selective sensitivity to CDK7 inhibitors THZ1 and YKL-5-124 in NF2 inactivated but not wild type MEDUSA cell lines. Conclusions: NF2 biallelic inactivation constitutes an evolutionary bottleneck during early mesothelioma evolution, associated with a specific vulnerability to CDK7 highlighting a potential path to clinical stratified therapy. Citation Format: Essa Y. Baitei, Min Zhang, Qianqian Sun, Jin-Li Luo, Philip Zhang, Tamihiro Kamata, James Harber, Aleksandra Bzura, Peter W. Jordan, Charlotte Poile, Alan Dawson, Apostolos Nakas, Cathy Richards, Hongji Yang, Ed Hollox, Dean A. Fennell. Clonal biallelic inactivation of NF2 is an evolutionary bottleneck that exposes a vulnerability to CDK7 inhibition in mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 6086.

Abstract 1613: Systematic screening for genomic vulnerabilities as drug targets for mesothelioma

Abstract Mesothelioma is a rare, lethal cancer caused by asbestos. Despite recent advances molecularly stratified therapy is lacking, in part due to the challenge of targeting the preponderance of tumor suppressors. Recent efforts to select therapy from our group have focused on poly(ADP-ribose) polymerase (PARP) and cyclin-dependent kinase 4/6 (CDK4/6) however the molecular determinants of response to therapy are unknown. To address this knowledge gap, we have undertaken high-throughput screening of exome sequenced primary mesothelioma cell lines alongside haploid cell lines harboring CRISPR knockouts of key, positively selected drivers BAP1, NF2 and MTAP. This strategy should enable us to identify robust and repeated drug-gene interactions using ensemble machine learning methods across a drug panel of drugs, both novel and in the clinic. Our platform encompasses multiple cross validation with both primary mesothelioma explants and clinical trial drug-response data. Patients were consented for extended pleurectomy decortication (EPD) and tissue sampled, disaggregated and cultured for no more than four passages to establish cell lines. Immunophenotyping and whole exome sequencing was conducted to validate their mesothelioma origins across an initial panel of 20 cell lines comprising primary cell lines established at the NKI (Netherlands) and Cardiff University (United Kingdom). To further characterize these, we investigated the response of the cell lines to 58 clinically approved cancer drugs using Imagen’s 3-day PredictRx assay. In addition, cell lines were treated with PARP inhibitors, olaparib, rucaparib, niraparib and talazoparib and incubated for 7 days. Cell count and cell death endpoints were captured in addition to phospho-H2AX immunofluorescence. Mesothelioma patient cells displayed differential sensitivity to targeted and non-targeted drugs. There were more nuanced responses amongst the targeted drugs, where for example epithelioid subtypes showed a greater sensitivity to mTOR, VEGFR and HDAC inhibitors in the 3-day assay. Compared with wild type cells, the haploid knockout cells were broadly 3-fold more sensitive to PARP inhibitors; mesothelioma primary cell lines showed exquisite sensitivity to talazoparib (IC50 < 0.1 µM). Multiple cross validation of our results across exome sequenced primary mesothelioma explants and patient tumors (PARP Phase II) is ongoing (data to be presented), leveraging machine learning based prediction of sensitivity, to be further validated in an upcoming PARP randomized trial. Citation Format: Gareth J. Griffiths, Dominic I. James, Beth Dyson, Immaculate M. Nalubowa, Apostolos Nakas, Paul Baas, Zsuzsanna Tabi, Min Zhang, Qianqian Sun, Daniel Faulkner, Nada Nusrat, Essa Y. Baitei, Joanna Dzialo, Alan Dawson, Charlotte Poile, Jake Spicer, Aleksandra Bzura, Jin-Li Luo, Hongji Yang, Cathy Richards, Dean A. Fennell. Systematic screening for genomic vulnerabilities as drug targets for mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 1613.

Integrated genomics point to immune vulnerabilities in pleural mesothelioma

Pleural mesothelioma is an aggressive malignancy with limited effective therapies. In order to identify therapeutic targets, we integrated SNP genotyping, sequencing and transcriptomics from tumours and low-passage patient-derived cells. Previously unrecognised deletions of SUFU locus (10q24.32), observed in 21% of 118 tumours, resulted in disordered expression of transcripts from Hedgehog pathways and the T-cell synapse including VISTA. Co-deletion of Interferon Type I genes and CDKN2A was present in half of tumours and was a predictor of poor survival. We also found previously unrecognised deletions in RB1 in 26% of cases and show sub-micromolar responses to downstream PLK1, CHEK1 and Aurora Kinase inhibitors in primary mesothelioma cells. Defects in Hippo pathways that included RASSF7 amplification and NF2 or LATS1/2 mutations were present in 50% of tumours and were accompanied by micromolar responses to the YAP1 inhibitor Verteporfin. Our results suggest new therapeutic avenues in mesothelioma and indicate targets and biomarkers for immunotherapy.

Abstract 1766: Triggering the resolution of inflammation with agonistic anti-ChemR23 antibody dampens inflammation-driven carcinogenesis

Abstract Chronic inflammation is associated with abnormal non-phlogistic clearance (efferocytosis) of apoptotic cells by macrophages and a defect of the resolution of inflammation pathways. The resolution of inflammation is an active immunological process mediated by specialized pro-resolving mediator (SPM) which target specific resolutive G-protein coupled receptors expressed by different immune cells and participate to the tissue homeostasis return after an injury. Defects in the clearance of (chemotherapy-induced) apoptotic tumor cell debris strengthens inflammation and has been associated with exacerbated tumor growth in several preclinical models. Proresolutive therapeutic approaches, such as using exogenous resolvin E1 (RvE1), the natural lipidic proresolutive ligand of the GPCR ChemR23, have been shown to dampen tumor-associated inflammation and to reduce tumor growth. Using single-cell RNA sequencing analysis, we found that ChemR23 is mainly expressed by tumor-associated macrophages in melanoma and lung cancers. Moreover, ChemR23 expression was barely expressed in non-inflamed tissues indicating a preferential expression on the inflamed or tumor site. We screened and identified an anti-ChemR23 mAb which induces RvE1-like Akt and ERK signaling in mouse and human macrophages and favors macrophage polarization towards a pro-resolutive phenotype. In vitro, the agonist antibody significantly increased the phagocytosis of apoptotic tumor primary mesothelioma cells by human tumor-polarized macrophages. In vivo, the agonist ChemR23 mAb accelerates the resolution of inflammation in an acute inflammatory model, as illustrated by a significant decrease of inflammatory macrophages and neutrophils infiltrates as compared to isotype control groups both in mice and non-human primate models. Similarly, ChemR23 triggering with the anti-ChemR23 mAb improved weight recovery, reduced diarrhea and decreased the development of colon neoplastic foci in a chronic colitis model coupled with the injection of a carcinogen agent. Furthermore, the administration of the anti-ChemR23 mAb as a monotherapy displayed some partial and complete antitumor responses in immunocompetent mouse models of subcutaneous colon carcinoma (MC38 and CT26) as well as orthotopic mesothelioma (AK7). Finally, using an orthotopic triple-negative breast cancer model (4T1), while we observed a limited impact on primary tumor growth, spontaneous metastasis development in the lung was significantly inhibited by the ChemR23 agonist mAb monotherapy. Our study reveals for the first time the therapeutic potential of triggering the proresolutive pathways using an anti-ChemR23 agonistic mAb to limit chronic inflammation in the tumor microenvironment and inhibit metastasis development. Citation Format: Vanessa Gauttier, Margot Lavy, Charlène Trilleaud, Kévin Biteau, Isabelle Girault, Lyssia Belarif, Géraldine Teppaz, Caroline Mary, Virginie Thépénier, Christophe Blanquart, Sophie Barillé-Nion, Nicolas Poirier. Triggering the resolution of inflammation with agonistic anti-ChemR23 antibody dampens inflammation-driven carcinogenesis [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 1766.

Somatic Epigenetic Silencing of RIPK3 Inactivates Necroptosis and Contributes to Chemoresistance in Malignant Mesothelioma.

Receptor-interacting protein kinase 3 (RIPK3) phosphorylates effector molecule MLKL to trigger necroptosis. Although RIPK3 loss is seen in several human cancers, its role in malignant mesothelioma is unknown. This study aimed to determine whether RIPK3 functions as a potential tumor suppressor to limit development of malignant mesothelioma. RIPK3 expression was examined in 66 malignant mesothelioma tumors and cell lines. Promoter methylation and DNMT1 siRNA studies were performed to assess the mode of RIPK3 silencing in RIPK3-deficient malignant mesothelioma cells. Restoration of RIPK3 expression in RIPK3-negative malignant mesothelioma cells, either by treatment with 5-aza-2'-deoxycytidine or lentiviral expression of cDNA, was performed to assess effects on cell viability, necrosis, and chemosensitization. Loss of RIPK3 expression was observed in 42/66 (63%) primary malignant mesotheliomas and malignant mesothelioma cell lines, and RT-PCR analysis demonstrated that downregulation occurs at the transcriptional level, consistent with epigenetic silencing. RIPK3-negative malignant mesothelioma cells treated with 5-aza-2'-deoxycytidine resulted in reexpression of RIPK3 and chemosensitization. Ectopic expression of RIPK3 also resulted in chemosensitization and led to necroptosis, the latter demonstrated by phosphorylation of downstream target MLKL and confirmed by rescue experiments. Mining of RIPK3 expression and survival outcomes among patients with malignant mesothelioma available from The Cancer Genome Atlas repository revealed that promoter methylation of RIPK3 is associated with reduced RIPK3 expression and poor prognosis. These data suggest that RIPK3 acts as a tumor suppressor in malignant mesothelioma by triggering necroptosis and that epigenetic silencing of RIPK3 by DNA methylation impairs necroptosis and contributes to chemoresistance and poor survival in this incurable disease.

Exploring High Aspect Ratio Gold Nanotubes as Cytosolic Agents: Structural Engineering and Uptake into Mesothelioma Cells.

The generation of effective and safe nanoagents for biological applications requires their physicochemical characteristics to be tunable, and their cellular interactions to be well characterized. Here, the controlled synthesis is developed for preparing high-aspect ratio gold nanotubes (AuNTs) with tailorable wall thickness, microstructure, composition, and optical characteristics. The modulation of optical properties generates AuNTs with strong near infrared absorption. Surface modification enhances dispersibility of AuNTs in aqueous media and results in low cytotoxicity. The uptake and trafficking of these AuNTs by primary mesothelioma cells demonstrate their accumulation in a perinuclear distribution where they are confined initially in membrane-bound vesicles from which they ultimately escape to the cytosol. This represents the first study of the cellular interactions of high-aspect ratio 1D metal nanomaterials and will facilitate the rational design of plasmonic nanoconstructs as cytosolic nanoagents for potential diagnosis and therapeutic applications.

Mesothelioma Cells Depend on the Antiapoptotic Protein Bcl-xL for Survival and Are Sensitized to Ionizing Radiation by BH3-Mimetics

The incidence of mesothelioma continues to rise and prognosis remains dismal owing to resistance to conventional therapies and few novel treatment options. Failure to activate apoptotic cell death is a resistance mechanism that may be overcome by inhibition of antiapoptotic Bcl-2 proteins using BH3-mimetic drugs. We investigated the role of antiapoptotic proteins in the radioresistance of mesothelioma, identifying clinically relevant targets for radiosensitization and evaluating the activity of BH3-mimetics alone and in combination with radiation therapy in preclinical models. Mesothelioma cell lines 211H, H2052, and H226 exposed to BH3-mimetics demonstrated Bcl-xL dependence that correlated with protein expression and was confirmed by genetic knockdown. The Bcl-xL inhibitor A1331852 exhibited cytotoxic (EC50, 0.13-1.42 μmol/L) and radiosensitizing activities (sensitizer enhancement ratios, 1.3-1.8). Cytotoxicity was associated with induction of mitochondrial outer membrane permeabilization and caspase-3/7 activation. Efficacy was maintained in a 3-dimensional model in which combination therapy completely eradicated mesothelioma spheroids. Clinical applicability was confirmed by immunohistochemical analysis of Bcl-2 proteins in patient samples and radiosensitizing activity of A1331852 in primary patient-derived mesothelioma cells. Mesothelioma cells exhibit addiction to the antiapoptotic protein Bcl-xL, and their intrinsic radioresistance can be overcome by small molecule inhibition of this novel therapeutic target.

Targeting the Temporal Dynamics of Hypoxia-Induced Tumor-Secreted Factors Halts Tumor Migration.

Targeting microenvironmental factors that foster migratory cell phenotypes is a promising strategy for halting tumor migration. However, lack of mechanistic understanding of the emergence of migratory phenotypes impedes pharmaceutical drug development. Using our three-dimensional microtumor model with tight control over tumor size, we recapitulated the tumor size-induced hypoxic microenvironment and emergence of migratory phenotypes in microtumors from epithelial breast cells and patient-derived primary metastatic breast cancer cells, mesothelioma cells, and lung cancer xenograft cells. The microtumor models from various patient-derived tumor cells and patient-derived xenograft cells revealed upregulation of tumor-secreted factors, including matrix metalloproteinase-9 (MMP9), fibronectin (FN), and soluble E-cadherin, consistent with clinically reported elevated levels of FN and MMP9 in patient breast tumors compared with healthy mammary glands. Secreted factors in the conditioned media of large microtumors induced a migratory phenotype in nonhypoxic, nonmigratory small microtumors. Subsequent mathematical analyses identified a two-stage microtumor progression and migration mechanism whereby hypoxia induces a migratory phenotype in the initialization stage, which then becomes self-sustained through a positive feedback loop established among the tumor-secreted factors. Computational and experimental studies showed that inhibition of tumor-secreted factors effectively halts microtumor migration despite tumor-to-tumor variation in migration kinetics, while inhibition of hypoxia is effective only within a time window and is compromised by tumor-to-tumor variation, supporting our notion that hypoxia initiates migratory phenotypes but does not sustain it. In summary, we show that targeting temporal dynamics of evolving microenvironments, especially tumor-secreted factors during tumor progression, can halt tumor migration. SIGNIFICANCE: This study uses state-of-the-art three-dimensional microtumor models and computational approaches to highlight the temporal dynamics of tumor-secreted microenvironmental factors in inducing tumor migration.

Abstract LB-014: Pirfenidone as a new potential therapy for malignant mesothelioma

Abstract The purpose of this study was to examine pirfenidone (PFD) as a potential new therapy for malignant pleural mesothelioma. PFD is an anti-fibrotic drug used to treat idiopathic pulmonary fibrosis (IPF). PFD reduces fibrous tissue formation e.g. by downregulating the production of fibroblasts and procollagens and inhibiting TGFß, TNFα and PDGF pathways. Since mesothelioma shares characteristics with IPF alongside with the activation of PI3K/Akt/mTOR, EGF, PDGF, HGF, VEGF, FGF and TGF-β pathways, we assessed the effect of PFD on mesothelioma cells in vitro and in vivo. In vitro studies were carried out using mesothelioma cell lines (JL-1, H2052, AB12) and primary mesothelioma cells. Cells treated with PFD and/or other agents (cisplatin, pemetrexed, MK-2206, PD98059, MG132) were subjected to cell viability assays, Transwell migration assays and 3D collagen or Matrigel growth and invasion assays. TGFβ/BMP, MAPK/Erk and Akt pathway activities were studied using luciferase reporter assays and human phospho-kinase array and validated with ELISA, RT-qPCR and Western blotting. For in vivo xenograft studies mice were injected subcutaneously with primary human mesothelioma cells expressing luciferase marker. Mice were treated with pirfenidone daily for 60 days and tumor growth was followed by bioluminescent imaging. Proliferation was studied by IHC. Differential gene expression in treated vs. untreated tumors was analyzed using RNA sequencing. We demonstrated that PFD treatment reduced significantly mesothelioma cell proliferation, migration and invasive growth in 3D in a concentration-dependent manner. The inhibitory effect of PFD increased when combined with cisplatin treatment in vitro. We also observed reduction of Akt and MAPK/Erk pathway activities and increase in BMP signaling in PFD treated tumor cells. Preliminary analyses of in vivo experiment revealed differential expression of multiple genes in pirfenidone treated vs. untreated tumors associated with a shift to more anti-fibrotic tumor microenvironment in PFD treated tumors. Expression profiles are currently under closer investigation. We identified pirfenidone as an inhibitor of mesothelioma invasive growth and showed that it has anti-fibrotic effects to tumor microenvironment. Since mesotheliomas are often inherently chemoresistant in fibrotic microenvironment, the use of pirfenidone could aid in overcoming chemoresistance by loosening ECM barrier for better drug penetration into the tumor tissue. Based on the current research we suggest that pirfenidone should be subjected to more intensive study as potential adjuvant-therapy for malignant mesotheliomas. Citation Format: Chang Li, Veronika Rezov, Emmi I. Joensuu, Ville Vartiainen, Mikko Rönty, Miao Yin, Marjukka Myllärniemi, Katri Koli. Pirfenidone as a new potential therapy for malignant mesothelioma [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2018; 2018 Apr 14-18; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2018;78(13 Suppl):Abstract nr LB-014.

Trophoblast Glycoprotein is Associated With a Favorable Outcome for Mesothelioma and a Target for Antibody Drug Conjugates.

The prognosis for patients with mesothelioma is poor, which prompts the need for the development of better treatment options. Antibody drug conjugates (ADCs) are gaining interest as a therapeutic strategy in mesothelioma. Trophoblast glycoprotein (5T4) is an oncofetal protein overexpressed in mesothelioma with low expression in normal tissue and therefore a good candidate for ADC treatment. Here,we evaluated and manipulated 5T4 as a suitable antigen for ADC targeted therapy in patients with mesothelioma. Expression of the 5T4 antigen is evaluated in (primary) mesothelioma cell lines and biopsy specimens, and correlated with clinical outcome. Internalization was assessed in 5T4 expressing cells. The cytotoxicity of three different 5T4-targeting ADCs was tested on (primary) mesotheliomacells. 5T4 was expressed in 10 of 12 (primary) cell lines. Most biopsy specimens stained positive for the 5T4 antigen, with marked differences in staining intensity and percentage of positive cells. High expression correlated with long progression-free survival. Both free antibody and ADCs targeting 5T4 were internalized and entered lysosomal compartments. Cytotoxicity experiments showed that cell lines with a high expression for 5T4 were sensitive to two of three ADCs. Lack of efficacy for the third ADC could be restored by neutralizing lysosomal compartments with chloroquine. The 5T4 antigen is expressed in mesothelioma and 5T4-based ADCs are internalized in lysosomes. Two of three ADCs were capable of killing the mesothelioma cells; the third ADC required additional lysosomal neutralization for its effect. 5T4-based ADCs would be a selective strategy for the treatment of mesothelioma.

Live-Cell Mesothelioma Biobank to Explore Mechanisms of Tumor Progression.

Experimental models closely representing in vivo conditions allow investigating mechanisms of resistance. Our aims were to establish a live-cell biobank of malignant pleural mesothelioma (MPM) samples and to obtain proof of principle that primary culture chemoresistant models, mimicking tumor progression observed in patients, can be obtained in vitro, providing a useful tool to investigate underlying mechanisms. Primary mesothelioma cultures were established from 235 samples between 2007 and 2014. Of two MPM patients, primary cultures obtained at different time points: at initial diagnosis, after neoadjuvant treatment at surgery and/or after tumor recurrence, were deeply investigated. Cells and corresponding tumor tissue were characterized by mesothelial protein and gene expression analysis. In addition, primary cultures from chemo naive patients were exposed to increasing doses of cisplatin/pemetrexed during three months and compared with non-treated cells in a cytotoxicity assay, and by selected profiling of senescence markers. In vitro chemoresistance in the primary mesothelioma cell cultures was associated with increased Thy1 (CD90) expression. Thy1 expression in MPM samples was significantly associated with poor overall survival in the TCGA MPM cohort. Our results illustrate that the establishment of a large live-cell MPM biobank contributes to a better understanding of therapy resistance observed in vivo, which eventually may lead to a more logical approach for developing new treatment strategies.

Abstract 1894: Gremlin-1 is an important regulator of invasiveness in malignant mesothelioma

Abstract The purpose of this study was to clarify the role of BMP inhibitor gremlin 1 in invasion and migration in mesothelioma. Primary mesothelioma cells isolated from patient pleural fluid as well as mesothelioma cell lines were used for in vitro studies. Cells were transfected with siRNAs or transduced with lentiviral expression vectors. Invasive growth was analyzed in 3D Matrigel or collagen I matrices. mRNA expressions were analyzed using a commercial PCR array and quantitative RT-PCR. Migration assays were performed using scratch wound assay or transwell migration assay with fibronectin or collagen coating. TGF-β and BMP signaling activity was measured with luciferase reporter assays. For in vivo mouse xenograft experiment cells were additionally transduced to express a luciferase marker. Subcutaneous cell injection with Matrigel matrix was performed in the flank of nude mice. Malignant mesothelioma is an aggressive cancer that develops from mesothelial cells, most often in the pleural lining of the lung. We have previously shown that the BMP inhibitor protein gremlin 1 is highly expressed in mesothelioma and induces a mesenchymal and chemoresistant phenotype in mesothelioma cells. Since mesothelioma tumors are locally very invasive and has poor prognosis, we analyzed the role of gremlin 1 in mesothelioma cell migration and invasive growth. We found that mesothelioma cells expressing gremlin 1 showed invasive sprouting when tumor cell spheroids were imbedded into 3D collagen matrix. Silencing of gremlin 1 expression significantly reduced invasive growth. In addition, cells overexpressing gremlin 1 gained more invasive phenotype. This was associated with increased mRNA expression levels of Slug and matrix metalloproteinases (MMP) as well as reduced expression of E-cadherin. The cells were more migratory and exhibited increased expression of certain integrins, especially the αv subunit. Gremlin 1 induced invasive growth was dependent on MMP activity and associated with increased TGF-β activity. Intrapleural injection of mesothelioma cells overexpressing gremlin 1 isolated from a patient with epithelioid mesothelioma, produced tumors in 2/4 mice over 5 months after injection. Mice with cells transduced with vector only did not develop tumors (0/4). When cells were injected subcutaneously together with Matrigel gremlin 1 overexpressing tumors appeared more slowly, but exhibited comparable luciferase signal 2.5 months after injection. However, gremlin 1 tumors showed more vascularization and in contrast to control tumors some also developed metastases (2/6 mice). As conclusion, we identified gremlin 1 as an important regulator of mesothelioma invasive growth and chemoresistance. Blocking gremlin 1 function may overcome drug resistance and reduce invasive behavior of mesothelioma. Citation Format: Miao Yin, Mira Tissari, Emmi I. Joensuu, Jenni Tamminen, Irene Ylivinkka, Mikko Rönty, Kaisa Lehti, Marko Hyytiäinen, Marjukka Myllärniemi, Katri Koli. Gremlin-1 is an important regulator of invasiveness in malignant 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 1894. doi:10.1158/1538-7445.AM2017-1894

Efficacy of Anti-mesothelin Immunotoxin RG7787 plus Nab-Paclitaxel against Mesothelioma Patient-Derived Xenografts and Mesothelin as a Biomarker of Tumor Response.

Purpose: The purpose of this study was to evaluate the antitumor efficacy of the reduced immunogenicity anti-mesothelin immunotoxin RG7787 plus nab-paclitaxel against primary mesothelioma cell lines and tumor xenografts and the utility of mesothelin as a biomarker of tumor response.Experimental Design: Early-passage human malignant mesothelioma cell lines NCI-Meso16, NCI-Meso19, NCI-Meso21, and NCI-Meso29 were evaluated for sensitivity to RG7787 or nab-paclitaxel alone or in combination. In addition, the antitumor activity of RG7787 plus nab-paclitaxel was evaluated using NCI-Meso16, NCI-Meso21, and NCI-Meso29 tumor xenografts in immunodeficient mice. Serum mesothelin was measured at different time points to determine whether its levels correlated with tumor response.Results: All four primary mesothelioma cell lines highly expressed mesothelin with 41 × 103 to 346 × 103 mesothelin sites per cell and were sensitive to RG7787, with IC50 ranging from 0.3 to 10 ng/mL. Except for NCI-Meso19, these cells were also sensitive to nab-paclitaxel, with IC50 of 10 to 25 ng/mL. In vitro, RG7787 plus nab-paclitaxel led to decreased cell viability compared with either agent alone. In NCI-Meso16 tumor xenografts, treatment with RG7787 plus nab-paclitaxel led to sustained complete tumor regressions. Similar antitumor efficacy was observed against NCI-Meso21 and NCI-Meso29 tumor xenografts. In all three tumor xenograft models, changes in human serum mesothelin correlated with response to therapy and were undetectable in mice with complete tumor regression with RG7787 and nab-paclitaxel.Conclusions: RG7787 plus nab-paclitaxel is very active against primary human mesothelioma cells in vitro as well as in vivo, with serum mesothelin levels correlating with tumor response. These results indicate that this combination could be useful for treating patients with mesothelioma. Clin Cancer Res; 23(6); 1564-74. ©2016 AACR.

OA02.02 Gremlin-1 is a Key Regulator of the Invasive Phenotype in Mesothelioma

Malignant mesothelioma is an aggressive cancer that develops from mesothelial cells, most often in the pleural lining of the lung. We have previously shown that the BMP inhibitor protein gremlin-1 is highly expressed in mesothelioma and induces a mesenchymal and chemoresistant phenotype in mesothelioma cells. Since mesothelioma tumors are locally highly invasive, we analyzed the role of gremlin-1 in mesothelioma cell migration and invasive growth. Primary mesothelioma cells isolated from patient pleural fluid as well as mesothelioma cell lines were used for in vitro studies. Cells were transfected with siRNAs or transduced with lentiviral expression vectors. Invasive growth was analyzed in 3D matrigel or collagen I matrices. mRNA expression was analyzed using a commercial PCR array and quantitative RT-PCR. Migration assays were performed using scratch wound assay or Transwell migration assay with fibronectin or collagen coating. TGF-β and BMP signaling activity was measured with reporter-luciferase assays. For in vivo mouse xenograft experiment cells were additionally transduced to express a luciferase marker. Subcutaneous cell injection with matrigel matrix was performed in the flank of nude mice. Mesothelioma cells expressing gremlin-1 showed invasive sprouting when tumor cell spheroids were imbedded into 3D collagen matrix. Silencing of gremlin-1 expression significantly reduced invasive growth. In addition, cells overexpressing gremlin-1 gained invasive growth ability. This was associated with increased mRNA expression levels of Slug and matrix metalloproteinases (MMP) as well as reduced expression of E-cadherin. The cells were more migratory and exhibited increased expression of certain integrins, especially the αv subunit. Gremlin-1 induced invasive growth was dependent on MMP activity and associated with increased TGF-β activity. Intrapleural injection of gremlin-1 overexpressing mesothelioma cells isolated from a patient with epithelioid mesothelioma, produced tumors in 2/4 mice over 4 months after injection. Cells transduced with vector only did not produced tumors (0/4). When cells were injected subcutaneously together with matrigel gremlin-1 overexpressing tumors appeared more slowly, but exhibited comparable luciferase signal 2.5 months after injection. However, gremlin-1 tumors showed more local spreading and in contrast to control tumors some also developed metastasis (2/6 mice). Mesothelioma invades locally and has poor prognosis. We have identified gremlin-1 as an important regulator of mesothelioma chemoresistance and invasive growth behavior. Blocking gremlin function may overcome drug resistance and reduce invasion of mesothelioma.

Malignant Mesothelioma Effusions Are Infiltrated by CD3+ T Cells Highly Expressing PD-L1 and the PD-L1+ Tumor Cells within These Effusions Are Susceptible to ADCC by the Anti–PD-L1 Antibody Avelumab

IntroductionThe functional aspects of programmed death 1 (PD-1) and PD ligand 1 (PD-L1) immune checkpoints in malignant mesothelioma have not been studied. MethodsTumor samples from 65 patients with mesothelioma were evaluated for PD-L1 expression by immunohistochemistry, and its prognostic significance was examined. Malignant effusions from patients with pleural and peritoneal mesothelioma were evaluated for PD-1–positive and PD-L1–positive infiltrating lymphocytes and their role in inducing PD-L1 expression in tumor cells. Antibody-dependent cellular cytotoxicity (ADCC) of avelumab, a fully humanized immunoglobulin G1 anti PD-L1 antibody against primary mesothelioma cell lines, was evaluated in presence of autologous and allogeneic natural killer cells. ResultsOf 65 pleural and peritoneal mesothelioma tumors examined, 41 (63%) were PD-L1–positive, which was associated with slightly inferior overall survival compared to patients with PD-L1–negative tumors (median 23.0 versus 33.3 months, p = 0.35). The frequency of PD-L1 expression was similar in patients with pleural and peritoneal mesothelioma, with 62% and 64% of samples testing positive, respectively. In nine mesothelioma effusion samples evaluated, the fraction of cells expressing PD-L1 ranged from 12% to 83%. In seven patients with paired malignant effusion and peripheral blood mononuclear cell (PBMC) samples, PD-L1 expression was significantly higher on CD3-positive T cells present in malignant effusions as compared with PBMCs (p = 0.016). In addition, the numbers of CD14-positive PD-1–positive cells were increased in malignant effusions compared with PBMCs (p = 0.031). The lymphocytes present in malignant effusions recognized autologous tumor cells and induced interferon-γ–mediated PD-L1 expression on the tumor cell surface. Of the three primary mesothelioma cell lines tested, two were susceptible to avelumab-mediated ADCC in the presence of autologous natural killer cells. ConclusionsMost pleural as well as peritoneal mesotheliomas express PD-L1. Malignant effusions in this disease are characterized by the presence of tumor cells and CD3-positive T cells that highly express PD-L1. In addition, mesothelioma tumor cells are susceptible to ADCC by the anti–PD-L1 antibody avelumab.

Abstract 332: Spliceosome inhibition as novel strategy against diffuse malignant peritoneal mesothelioma

Abstract Background: Diffuse malignant peritoneal mesothelioma (DMPM) is an aggressive tumor of the lining of the abdomen, characterized by late clinical symptoms and poor prognosis. Systemic chemotherapy together with cytoreductive surgery and intraperitoneal hyperthermic therapy has been introduced as the best treatment option, resulting in an overall 5-year survival rate of approximately 50%. To further increase survival, novel drugs targeting key molecular factors in DMPM are warranted. Analogous to pleural mesothelioma, such a factor may be alternative splicing which can be modulated by inhibiting the SF3B subunit of the spliceosome. This strategy is an emerging therapeutic opportunity for a number of solid tumors and hematological malignancies. In particular, the spliceosome inhibitor Pladienolide B (PB) has low nanomolar IC50 values against a range of cancer cell lines and leukemic cells, but no data are available regarding its antitumor efficacy in DMPM. Aims: This study investigates (1) the activity of PB (alone or in combination with standard chemotherapeutics) in primary peritoneal mesothelioma cells through in vitro and in vivo assays, and (2) the molecular mechanisms of splicing inhibition through whole-genome RNA-seq and PCR of selected genes involved in apoptosis and invasion. Methods: The antiproliferative effect of PB was investigated using the SRB assay on two primary mesothelioma cell cultures (MESOII and STO), obtained from resected tumors with well-annotated clinical characteristics. Further in vitro studies were performed to evaluate the pro-apoptotic and anti-invasive activities, while splicing profiles of treated and untreated cells were determined with RNA-seq. Results: PB impaired DMPM cell growth in a dose-dependent manner, with IC50 values of 1.57 ± 0.30 nM in MESOII and 1.18 ± 0.16 nM in STO (n = 3, mean ± standard deviation). The specific activity on the spliceosome was demonstrated by PB induced time- and dose-dependent alterations of splicing patterns for several apoptotic genes, such as Mcl-1, Bcl-X, Fas, and for the pro-metastatic tyrosine kinase receptor RON, which was shifted to its un-spliced and non-functional variant. In addition, RNA-seq showed several differentially expressed alternatively spliced genes in PB treated samples. The DMPM cells have also been genetically engineered to express Firefly- and Gaussia- luciferases, enabling monitoring of tumor growth inhibition by PB in in vivo orthotopic models. Conclusions: These data provide evidence that PB has a strong antitumor activity against relevant models of DPMP, associated with modulation of splicing, induction of apoptosis and inhibition of invasion. RNA-seq represents a powerful tool for the identification of alternatively spliced genes that could serve as useful diagnostic markers as well as potential therapeutic targets for DMPM. Citation Format: Rocco Sciarrillo, Valentina E. Gomez, Marzia Pennati, Anna Wojtuszkiewicz, Gert-Jan L. Kaspers, Carla Molthoff, Nadia Zaffaroni, Godefridus J. Peters, Gerrit Jansen, Elisa Giovannetti. Spliceosome inhibition as novel strategy against diffuse malignant peritoneal 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 332.

Abstract 3103: The reduced immunogenicity anti-mesothelin immunotoxin RG7787 in combination with nab-paclitaxel has significant anti-tumor efficacy against primary mesothelioma cell lines and patient derived mesothelioma tumor xenografts

Abstract Mesothelin is a tumor differentiation antigen that is highly expressed in many cancers including malignant mesothelioma. RG7787 is a second-generation anti-mesothelin immunotoxin that is designed to be less immunogenic in patients and has reduced non-specific toxicity in pre-clinical studies. In this study, we evaluated the anti-tumor efficacy of RG7787 alone and in combination with nab-paclitaxel using primary mesothelioma cell lines obtained from patients with pleural or peritoneal mesothelioma. Four early passage malignant mesothelioma cell lines: NCI-Meso16, NCI-Meso19, NCI-Meso21 and NCI-Meso29 were evaluated for mesothelin expression and have 18×103- 56×103 mesothelin sites/cell. All four cell lines were sensitive to RG7787 with IC50s of 0.3 to 10 ng/ml. Three of the cell lines: NCI-Meso 16, NCI-Meso 21 and NCI-Meso 29 were also sensitive to nab-paclitaxel with IC50s of 4, 40 and 2 ng/ml respectively while, NCI-Meso 19 was resistant with IC50 >100 ng/ml. Synergistic in vitro cell cytotoxicity was observed with both NCI-Meso16 and NCI-Meso21 cells, when treated with the combination of RG7787 and nab-paclitaxel. To evaluate the efficacy of RG7787 with nab-paclitaxel in vivo, athymic nude mice were inoculated subcutaneously with 5×106 NCI-Meso 16 cells. When the tumors reached 100 mm3 in size, mice (n = 7 in each group) were treated with 2 cycles (separated by 3 days) of either RG7787 2.5 mg/kg every other day x 3 doses, nab-paclitaxel 100 mg/kg on day 1, a combination of RG7787 and nab-paclitaxel at the same dose and schedule as for single agent therapy, or received no treatment (control). Although treatment with RG7787 and nab-paclitaxel alone resulted in tumor shrinkage compared to control mice, none of the mice had complete tumor regressions. However, in mice treated with RG7787 plus nab-paclitaxel all mice had complete tumor regressions by day 64 that persisted in 7/7 mice when the experiment was terminated 100 days after starting treatment. In the slow growing NCI-Meso 21 in-vivo model, we also observed similar synergistic anti-tumor effects with the combination of RG7787 and nab-paclitaxel. Taken together, our findings show that RG7787 in combination with nab-paclitaxel has significant anti-tumor activity against primary mesothelioma cell lines both in vitro and in vivo, suggesting that this combination treatment could be useful to treat patients with mesothelioma. Citation Format: Jingli Zhang, Qun Jiang, Christine Alewine, Swati Khanna, Betsy Morrow, Anish Thomas, Ira Pastan, Raffit Hassan. The reduced immunogenicity anti-mesothelin immunotoxin RG7787 in combination with nab-paclitaxel has significant anti-tumor efficacy against primary mesothelioma cell lines and patient derived mesothelioma tumor xenografts. [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 3103.

Molecular profiling reveals primary mesothelioma cell lines recapitulate human disease

Malignant mesothelioma (MM) is an aggressive, fatal tumor strongly associated with asbestos exposure. There is an urgent need to improve MM patient outcomes and this requires functionally validated pre-clinical models. Mesothelioma-derived cell lines provide an essential and relatively robust tool and remain among the most widely used systems for candidate drug evaluation. Although a number of cell lines are commercially available, a detailed comparison of these commercial lines with freshly derived primary tumor cells to validate their suitability as pre-clinical models is lacking. To address this, patient-derived primary mesothelioma cell lines were established and characterized using complementary multidisciplinary approaches and bioinformatic analysis. Clinical markers of mesothelioma, transcriptional and metabolic profiles, as well as the status of p53 and the tumor suppressor genes CDKN2A and NF2, were examined in primary cell lines and in two widely used commercial lines. Expression of MM-associated markers, as well as the status of CDKN2A, NF2, the ‘gatekeeper' in MM development, and their products demonstrated that primary cell lines are more representative of the tumor close to its native state and show a degree of molecular diversity, thus capturing the disease heterogeneity in a patient cohort. Molecular profiling revealed a significantly different transcriptome and marked metabolic shift towards a greater glycolytic phenotype in commercial compared with primary cell lines. Our results highlight that multiple, appropriately characterised, patient-derived tumor cell lines are required to enable concurrent evaluation of molecular profiles versus drug response. Furthermore, application of this approach to other difficult-to-treat tumors would generate improved cellular models for pre-clinical evaluation of novel targeted therapies.

New high affinity monoclonal antibodies recognize non-overlapping epitopes on mesothelin for monitoring and treating mesothelioma.

Mesothelin is an emerging cell surface target in mesothelioma and other solid tumors. Most antibody drug candidates recognize highly immunogenic Region I (296–390) on mesothelin. Here, we report a group of high-affinity non-Region I rabbit monoclonal antibodies. These antibodies do not compete for mesothelin binding with the immunotoxin SS1P that binds Region I of mesothelin. One pair of antibodies (YP218 and YP223) is suitable to detect soluble mesothelin in a sandwich ELISA with high sensitivity. The new assay can also be used to measure serum mesothelin concentration in mesothelioma patients, indicating its potential use for monitoring patients treated with current antibody therapies targeting Region I. The antibodies are highly specific and sensitive in immunostaining of mesothelioma. To explore their use in tumor therapy, we have generated the immunotoxins based on the Fv of these antibodies. One immunotoxin (YP218 Fv-PE38) exhibits potent anti-tumor cytotoxicity towards primary mesothelioma cell lines in vitro and an NCI-H226 xenograft tumor in mice. Furthermore, we have engineered a humanized YP218 Fv that retains full binding affinity for mesothelin-expressing cancer cells. In conclusion, with their unique binding properties, these antibodies may be promising candidates for monitoring and treating mesothelioma and other mesothelin-expressing cancers.