MeT-5A Cells Research Articles

Patient-derived and artificial ascites have minor effects on MeT-5A mesothelial cells and do not facilitate ovarian cancer cell adhesion.

The presence of ascites in the peritoneal cavity leads to morphological and functional changes of the peritoneal mesothelial cell layer. Cells loose cell-cell interactions, rearrange their cytoskeleton, activate the production of fibronectin, and change their cell surface morphology in a proinflammatory environment. Moreover, ovarian cancer cell adhesion has been shown to be facilitated by these changes due to increased integrin- and CD44-mediated binding sites. In this study, the biological responsiveness of the human pleural mesothelial cell line MeT-5A to patient-derived and artificial ascites was studied in vitro and adhesion of ovarian cancer cells, i.e. SKOV-3 cells, investigated. Changes were mainly observed in cells exposed to artificial ascites containing higher cytokine concentrations than patient-derived ascites. Interestingly, reduced cell-cell interactions were already observed in untreated MeT-5A cells and effects on tight junction protein expression and permeability upon exposure to ascites were minor. Ascites induced upregulation of CDC42 effector protein 2 expression, which affects stress fiber formation, however significant F-actin reorganization was not observed. Moreover, fibronectin production remained unchanged. Analysis of mesothelial cell surface characteristics showed upregulated expression of intercellular adhesion molecule 1, slightly increased hyaluronic acid secretion and decreased microvillus expression upon exposure to ascites. Nevertheless, the observed changes were not sufficient to facilitate adhesion of SKOV-3 cells on MeT-5A cell layer. This study revealed that MeT-5A cells show a reduced biological responsiveness to the presence of ascites, in contrast to published studies on primary human peritoneal mesothelial cells.

Identification of CD24 as a potential diagnostic and therapeutic target for malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive malignancy of the pleura that is currently incurable due to the lack of an effective early diagnostic method and specific medication. The CDKN2A (p16) and NF2 genes are both frequently mutated in MPM. To understand how these mutations contribute to MPM tumor growth, we generated NF2/p16 double-knockout (DKO) cell clones using human MeT-5A and HOMC-B1 mesothelial cell lines. Cell growth and migration activities were significantly increased in DKO compared with parental cells. cDNA microarray analysis revealed differences in global gene expression profiles between DKO and parental cells. Quantitative PCR and western blot analyses showed upregulation of CD24 concomitant with increased phosphorylation of AKT, p70S6K, and c-Jun in DKO clones. This upregulation was abrogated by exogenous expression of NF2 and p16. CD24 knockdown in DKO cells significantly decreased TGF-β1 expression and increased expression of E-cadherin, an epithelial–mesenchymal transition marker. CD24 was highly expressed in human mesothelioma tissues (28/45 cases, 62%) and associated with the loss of NF2 and p16. Public data analysis revealed a significantly shorter survival time in MPM patients with high CD24 gene expression levels. These results strongly indicate the potential use of CD24 as a prognostic marker as well as a novel diagnostic and therapeutic target for MPM.

Transmembrane protein 88 inhibits transforming growth factor-β1-induced-extracellular matrix accumulation and epithelial-mesenchymal transition program in human pleural mesothelial cells through modulating TGF-β1/Smad pathway

Pleural fibrosis is an irreversible pathological process occurred in the development of several lung diseases. TMEM88 is a member of transmembrane (TMEM) family and has been found to be involved in the regulation of fibrogenesis. However, the role of TMEM88 in pleural fibrosis remains unknown. In this study, we aimed to explore the role of TMEM88 in pleural fibrosis in vitro using transforming growth factor-β1 (TGF-β1)-induced human pleural mesothelial cell line MeT-5A cells. Our results showed that the expression levels of TMEM88 were downregulated in pleural fibrosis tissues and TGF-β1-treated Met-5A cells. Overexpression of TMEM88 inhibited the proliferation of Met-5A cells under TGF-β1 stimulation. In addition, TMEM88 overexpression prevented TGF-β1-induced extracellular matrix (ECM) accumulation and epithelial-mesenchymal transition (EMT) in Met-5A cells with decreased expression levels of Col I and fibronectin, increased levels of cytokeratin-8 and E-cadherin, as well as decreased levels of vimentin and α-SMA. Furthermore, overexpression of TMEM88 inhibited the expression of TGF-β receptor I (TβRI) and TβRII and suppressed the phosphorylation of Smad2 and Smad3 in Met-5A cells. In conclusion, these results indicated that TMEM88 exhibited an anti-fibrotic activity in pleural fibrosis via inhibiting the activation of TGF-β1/Smad signaling pathway.

SIRT1-modified human umbilical cord mesenchymal stem cells ameliorate experimental peritoneal fibrosis by inhibiting the TGF-\u03b2/Smad3 pathway

IntroductionPeritoneal fibrosis is a serious complication of long-term peritoneal dialysis (PD). Combination therapies are emerging as a promising treatment for tissue damage. Here, we investigated the therapeutic potential of SIRT1-modified human umbilical cord mesenchymal stem cells (hUCMSCs) for peritoneal fibrosis.MethodsSIRT1 was overexpressed in hUCMSCs to establish SIRT1-modified hUCMSCs. Co-culture and transplantation experiments were performed in TGF-β-stimulated Met-5A cells and peritoneal damage rodent model to assess the therapeutic potential of SIRT1-modified hUCMSCs for peritoneal fibrosis through qPCR, Western blot, and peritoneal function analyses.ResultsSIRT1-modified hUCMSC administration had more potent anti-fibrosis ability than hUCMSCs, which significantly inhibited the expression of fibrotic genes and suppressed EMT process, increased ultrafiltration volume, and restored homeostasis of bioincompatible factors in dialysis solution. Mechanistically, SIRT1-modified hUCMSCs attenuated peritoneal fibrosis through reducing peritoneal inflammation and inhibiting the TGF-β/Smad3 pathway in peritoneal omentum tissues.ConclusionSIRT1-modified hUCMSCs might work as a promising therapeutic strategy for the treatment of peritoneal dialysis-induced peritoneal damage and fibrosis.

Abstract B10: Evaluating YAP and TAZ as therapeutic targets for treating malignant mesothelioma with Hippo pathway disruptions

Abstract Malignant mesotheliomas (MMs) are tumors originating from the mesothelial lining of internal organs. Hippo pathway disruptions are common in MMs; up to 50% of cases exhibit NF2 deficiency and other pathway genes such as LATS2 are also mutated (1). This suggests hyperactivity of YAP and TAZ as a likely oncogenic driver in MMs and a potential axis to exploit therapeutically (2). Before committing to such an approach, a dependence of MMs on YAP/TAZ for survival needs to be tested. We investigated this using different MM cell line models cultured in vitro. The impact of Hippo pathway mutations on YAP and TAZ activity in mesothelial cells was assessed using an NF2 mutant isogenic system in an immortalized mesothelial cell line (Met5A.) YAP activation levels were probed through immunoblotting for YAP S127 phosphorylation, immunofluorescence, and RNA sequencing (RNAseq). YAP and TAZ were inhibited through RNAi-mediated depletion or treatment with simvastatin or verteporfin in a panel of 7 MM cell lines, including 3 with mutations in known Hippo pathway genes and 4 lacking such mutations, and cell viability was measured using an Alamar Blue assay. We found that Hippo pathway-mediated phosphorylation of YAP at S127, and YAP cytoplasmic abundance, was reduced in NF2 mutant Met5A cells compared to isogenic nonmutant cells. Consistent with this, RNAseq analysis showed elevated YAP activity in NF2 mutant Met5A cells. However, RNAi-mediated depletion of YAP and TAZ in a panel of mesothelioma cell lines did not reveal a clear correlation between dependence on YAP/TAZ for survival and aberrant Hippo signaling. There was also a comparable level of sensitivity of NF2 wild-type and NF2 mutant Met5A cells to YAP/TAZ knockdown. Additionally, treatment with verteporfin and simvastatin did not show increased toxicity in cell lines with Hippo pathway mutations relative to nonmutant cells. Our findings confirm that Hippo pathway mutations drive YAP/TAZ hyperactivity in mesothelial cells. However, they show that pathway mutation status does not always correlate with a dependence on YAP and TAZ for mesothelioma cell survival, at least when cultured in vitro. Clearly, a more in-depth analysis of the Hippo pathway in MMs is required to determine the potential of this pathway as a therapeutic target for this disease.

Role of inflammation in the malignant transformation of pleural mesothelial cells induced by multi-walled carbon nanotubes

Multi-walled carbon nanotubes (MWCNTs) are one of the most widely used types of novel nano-fiber materials. The aim of this study was to establish an experimental system based on actual exposure dosage and environments and explore the roles and mechanisms of inflammation in the malignant transformation of pleural mesothelial cells induced by MWCNTs after low doses and long-term exposure. Here, we established an in vitro system by co-culturing macrophages and mesothelial cells and exposing these cells to high aspect ratio MWCNTs (0.1 μg/mL) for three months. Results indicated that IL-1β, secreted by macrophages stimulated by MWCNTs, may significantly enhance the release of inflammatory cytokines, such as IL-8, TNF-α, and IL-6, from mesothelial cells. Results obtained from proliferation, migration, invasion, colony formation, and chromosomal aberration studies indicated that MWCNTs may promote malignant transformation of mesothelial cells after long-term and low-dose exposure via inflammation. Furthermore, the obtained results demonstrated that the NF-κB/IL-6/STAT3 pathway was active in the malignant transformation of Met 5A cells, induced by MWCNTs, and played an important role in the process. In conclusion, our results showed that the NF-κB (p65)/IL-6/STAT3 molecular pathway, which was mediated by inflammation, played an important role in the malignant transformation of pleural mesothelial cells induced by MWCNTs. These findings also provide novel ideas and references for the treatment of mesothelioma and offers options for the occupational safety of nanomaterial practitioners.

Overexpression of miR-199/214 is a distinctive feature of iron-induced and asbestos-induced sarcomatoid mesothelioma in rats.

Malignant mesothelioma (MM) is one of the most lethal tumors in humans. The onset of MM is linked to exposure to asbestos, which generates reactive oxygen species (ROS). ROS are believed to be derived from the frustrated phagocytosis and the iron in asbestos. To explore the pathogenesis of MM, peritoneal MM was induced in rats by the repeated intraperitoneal injection of iron saccharate and nitrilotriacetate. In the present study, we used microarray techniques to screen the microRNA (miR) expression profiles of these MM. We observed that the histological subtype impacted the hierarchical clustering of miR expression profiles and determined that miR‐199/214 is a distinctive feature of iron saccharate‐induced sarcomatoid mesothelioma (SM). Twist1, a transcriptional regulator of the epithelial‐mesenchymal transition, has been shown to activate miR‐199/214 transcription; thus, the expression level of Twist1 was examined in iron‐induced and asbestos‐induced mesotheliomas in rats. Twist1 was exclusively expressed in iron saccharate‐induced SM but not in the epithelioid subtype. The Twist1‐miR‐199/214 axis is activated in iron saccharate‐induced and asbestos‐induced SM. The expression levels of miR‐214 and Twist1 were correlated in an asbestos‐induced MM cell line, suggesting that the Twist1‐miR‐199/214 axis is preserved. MeT5A, an immortalized human mesothelial cell line, was used for the functional analysis of miR. The overexpression of miR‐199/214 promoted cellular proliferation, mobility and phosphorylation of Akt and ERK in MeT5A cells. These results indicate that miR‐199/214 may affect the aggressive biological behavior of SM.

Molecular hydrogen regulates PTEN-AKT-mTOR signaling via ROS to alleviate peritoneal dialysis-related peritoneal fibrosis.

As a convenient, effective and economical kidney replacement therapy for end-stage renal disease (ESRD), peritoneal dialysis is available in approximately 11% of ESRD patients worldwide. However, long-term peritoneal dialysis treatment causes peritoneal fibrosis. In recent years, the application potential of molecular hydrogen in the biomedicine has been well recognized. Molecular hydrogen selectively scavenges cytotoxic reactive oxygen species (ROS) and acts as an antioxidant. In this experiment, a high glucose-induced peritoneal fibrosis mouse model was successfully established by intraperitoneal injection of high glucose peritoneal dialysate, and peritoneal fibrosis mice were treated with hydrogen-rich peritoneal dialysate. In addition, in vitro studies of high glucose-induced peritoneal fibrosis were performed using MeT-5A cells. In vitro and in vivo experiments show that molecular hydrogen could inhibit peritoneal fibrosis progress induced by high glucose effectively. Furthermore, it has been found that molecular hydrogen alleviate fibrosis by eliminating intracellular ROS and inhibiting the activation of the PTEN/AKT/mTOR pathway. The present data proposes that molecular hydrogen exerts the capacity of anti-peritoneal fibrosis through the ROS/PTEN/AKT/mTOR pathway. Therefore, molecule hydrogen is a potential, safe, and effective treatment agent, with peritoneal protective property and great clinical significance.

In Vitro Characterization of Cisplatin and Pemetrexed Effects in Malignant Pleural Mesothelioma 3D Culture Phenotypes

Malignant pleural mesothelioma (MPM) is an aggressive cancer with poor prognosis. The main treatment for MPM is doublet chemotherapy with Cisplatin and Pemetrexed, while ongoing trials test the efficacy of pemetrexed monotherapy. However, there is lack of evidence regarding the effects of Cisplatin and Pemetrexed on MPM cell phenotypes, especially in three-dimensional (3D) cell cultures. In this study, we evaluated the effects Cisplatin and Pemetrexed on cell viability using homologous cell derived extracellular matrix (hECM) as substratum and subsequently in the following 3D cell culture phenotypes: tumor spheroid formation, tumor spheroid invasion, and collagen gel contraction. We used benign mesothelial MeT-5A cells as controls and the MPM cell lines M14K (epithelioid), MSTO (biphasic), and ZL34 (sarcomatoid). Cell viability of all cell lines was significantly decreased with all treatments. Mean tumor spheroid perimeter was reduced after treatment with Pemetrexed or the doublet therapy in all cell lines, while Cisplatin reduced the mean spheroid perimeter of MeT-5A and MSTO cells. Doublet treatment reduced the invasive capacity of spheroids of cell lines into collagenous matrices, while Cisplatin lowered the invasion of the MSTO and ZL34 cell lines, and Pemetrexed lowered the invasion of MeT-5A and ZL34 cell lines. Treatment with Pemetrexed or the combination significantly reduced the collagen gel contraction of all cell lines, while Cisplatin treatment affected only the MeT-5A and M14K cells. The results of the current study can be used as an in vitro 3D platform for testing novel drugs against MPM for ameliorating the effects of first line chemotherapeutics.

Pleural Effusion IL-33/sST2 Levels and Effects of Low and High IL-33/sST2 Levels on Human Mesothelial Cell Adhesion and Migration.

Interleukin 33 (IL-33) is an alarmin with multiple roles in immunity and cell homeostasis, highly expressed in barrier sites, acting via the suppression of tumorigenicity 2 receptor (ST2). Production of IL-33 and soluble ST2 (sST2), a decoy receptor for IL-33, has been implicated in several pulmonary diseases, but both have been scarcely investigated in pleural diseases. The aim of this study was to determine the levels of IL-33 and sST2 in transudative (TrPEs), malignant (MPEs), and parapneumonic (PPEs) pleural effusions (PEs) and investigate the effect of PE fluids from each group with low and high IL-33/sST2 levels on MeT-5A cell adhesion and migration. IL-33 and sST2 pleural fluid levels were similar among TrPEs, MPEs, and PPEs. However, a significant correlation was found between IL-33 and LDH and in sST2 levels with lymphocyte counts in TrPEs. Additionally, in MPEs the levels of IL-33 correlated with the levels of sST2 and with the red blood cell counts. Furthermore, incubation of MeT-5A cells with MPEs and PPEs bearing low or high levels of IL-33/sST2 yielded significant differential effects on MeT-5A cell adhesion and migration. In MPEs, high IL-33/sST2 levels led to increased adhesion and migration of MeT-5A cells, while in PPEs the effect was the opposite, while no effect in both cell phenotypes was determined for TrPEs. These results reveal a clinical context dependent effect of the IL-33/sST2 axis in PEs.

Exosomal transfer of miR-126 promotes the anti-tumour response in malignant mesothelioma: Role of miR-126 in cancer-stroma communication.

MiR-126 has been shown to suppress malignant mesothelioma (MM) by targeting cancer-related genes without inducing toxicity or histopathological changes. Exosomes provide the opportunity to deliver therapeutic cargo to cancer stroma. Here, a tumour stromal model composed of endothelial cells (HUVECs), fibroblasts (IMR-90 cells), non-malignant mesothelial cells (Met-5A cells) and MM cells (H28 and MM-B1 cells) was used. The cells were treated with exosomes from HUVECs carrying endogenous (exo-HUVEC) and enriched miR-126 (exo-HUVECmiR-126), and the uptake/turnover of exosomes; miR-126 distribution within the stroma; and effect of miR-126 on cell signalling, angiogenesis and cell proliferation were evaluated. Based on the sensitivity of MM cells to exo-HUVEC miR-126 treatment, miR-126 was distributed differently across stromal cells. The reduced miR-126 content in fibroblasts in favour of endothelial cells reduced angiogenesis and suppressed cell growth in an miR-126-sensitive environment. Conversely, the accumulation of miR-126 in fibroblasts and the reduced level of miR-126 in endothelial cells induced tube formation in an miR-126-resistant environment via VEGF/EGFL7 upregulation and IRS1-mediated cell proliferation. These findings suggest that transfer of miR-126 via HUVEC-derived exosomes represents a novel strategy to inhibit angiogenesis and cell growth in MM.

2-Deoxy-glucose Enhances the Effect of Cisplatin and Pemetrexed in Reducing Malignant Pleural Mesothelioma Cell Proliferation But Not Spheroid Growth.

Malignant pleural mesothelioma (MPM) is a therapy-resistant neoplasm of the pleura. Standard chemotherapy consists of a combination of cisplatin (CPDD) and pemetrexed (PEM). The aim of this study was to assess whether inhibition of aerobic glycolysis by 2-deoxy-glucose (2DG) would enhance the effects of standard chemotherapy. MeT-5A, M14K, MSTO and ZL34 cell lines were used. Cell viability with 2DG and cell proliferation and spheroid formation with CPDD+PEM alone and with 2-DG were tested. Viability with 2-DG was dose-dependent. Cell proliferation with CPDD+PEM on 2D surface was reduced in all cell types, 2-DG inclusion demonstrated a synergistic effect in MSTO and ZL34 cells. Spheroid growth in 3D with CPDD+PEM or CPDD+PEM+2-DG lowered spheroid growth in all cell types. 2-DG synergizes with CPDD+PEM in lowering MPM cell proliferation in 2D to <20%. In 3D MPM spheroid growth 2-DG synergism with CPDD+PEM treatment is not maintained.

Blockade of thrombospondin-1 ameliorates high glucose-induced peritoneal fibrosis through downregulation of TGF-β1/Smad3 signaling pathway.

Transforming growth factor-β1 (TGF-β1) is a profibrotic cytokine which induces mesothelial cell mesothelial-to-mesenchymal transition (MMT) and peritoneal fibrosis in patients receiving treatment of peritoneal dialysis. Because thrombospondin-1 (TSP-1) is able to activate latent TGF-β1 in vivo, we investigated whether blockade of TSP-1 could modulate mesothelial cell MMT and ameliorate peritoneal fibrosis. Human pleural mesothelial cells (Met-5A cells) were treated with TSP-1 and addition of TGF-β1 neutralizing antibody to assess the effect of TSP-1 on MMT. Furthermore, TSP-1 blocking peptide Leu-Ser-Lys-Leu (LSKL) was applied to Met-5A cells treated with 4.25% d-glucose to determine its function in high glucose-induced MMT. Consequently, a uremic dialysate injection rat model was set up to confirm the results in vivo. Exposure of Met-5A cells to TSP-1 increased TGF-β1 secretion, expression and bioactivity, triggered Smad3 phosphorylation, upregulated the expression of mesenchymal molecules including fibronectin, collagen type III, α-smooth muscle actin, Snail, and decreased calretinin expression. The effect was partially attenuated by TGF-β1 neutralizing antibody. TSP-1 expression in Met-5A cells was increased by 4.25% d-glucose, followed by increased secretion and bioactivity of TGF-β1, the onset of Smad3 phosphorylation and induction of MMT. LSKL significantly attenuated high glucose-mediated mesothelial cell MMT and ameliorated peritoneal fibrosis in uremic rats receiving dextrose dialysate injection. Taken together, these data demonstrated that TSP-1 contributes to mesothelial cell MMT by activating TGF-β1/Smad3 signaling pathway and blockade of TSP-1 attenuates high glucose-mediated mesothelial cell MMT and peritoneal fibrosis.

Benign Pleural Mesothelial Cells Have Higher Osmotic Water Permeability than Malignant Pleural Mesothelioma Cells and Differentially Respond to Hyperosmolality.

Cell volume regulation is a critical mechanism for cell homeostasis and depends on the osmotic water permeability (Pf) of the cell plasma membrane. The Pf of human mesothelial cells is unknown although they contribute to serosal fluid turnover. In this study we measured the osmotic water permeability of benign human mesothelial cells (MeT-5A) and of epithelioid (M14K) and sarcomatoid (ZL34) malignant pleural mesothelioma (MPM) cells in response to acute hyperosmotic stress. We also assessed the changes in their Pf after preconditioning with 4% glucose for 24 hours. In both cases we also assessed the role of AQP1 inhibition (0.1 mM HgCl2) on the Pf. Finally, we assessed corresponding changes in the AQP1 plasma membrane availability by immunofluorescence. We report that MeT-5A cells have a significantly higher Pf as compared to M14K and ZL34 MPM cells [4.85E-03±2.37E-03 cm/sec (n=17) versus 2.74E-03±0.74E-03 cm/sec (n=11) and 2.86E-03±0.11E-03 cm/sec (n=11)]. AQP1 inhibition significantly decreased the Pf in all cells lines (p<0.001 in all cases). High glucose preconditioning for 24 hours significantly increased MeT-5A Pf (p<0.001), did not influence M14K Pf (p=0.19) and significantly reduced ZL34 Pf (p=0.02). Comparing cell lines after high glucose preconditioning, MeT-5A Pf was significantly higher than that of M14K and ZL34 MPM cells and the AQP1 inhibition effect was significant in MeT-5A and M14K cells. These results were corroborated by AQP1 immunofluorescence. We provide evidence for a differential regulation of Pf in benign and MPM cells that require further mechanistic investigation.

Targeted Osmotic Lysis of H28 Mesothelioma Cells

Mesothelioma is an aggressive cancer of the pleura cells of the chest cavity commonly linked to asbestos exposure. With a post‐diagnosis prognosis of between 6 and 12 months. Traditional chemotherapy increases survival time by only 11 weeks. Targeted Osmotic Lysis (TOL) is a novel cancer therapeutic that exploits cancer cells' upregulation of Voltage‐Gated Sodium Channels (VGSC) by pairing a pharmacological blocker of Na+, K+‐ATPase (sodium pumps), such as digoxin or ouabain, with electric or magnetic stimulation of VGSCs. The increase in intracellular Na+ causes an osmotic lysis of cells that over‐express VGSCs. TOL has been shown to selectively lyse highly invasive breast cancer cells, such as MDA‐MB 231, while leaving the normal tissue intact. To test the hypothesis that TOL would be an effective treatment for mesothelioma, we incubated H28 mesothelioma cells or MeT‐5A normal pleural effusion cells in 0–500 nM digoxin for 10 min, then activated the VGSCs with a 0–5 VDC electric current for 30 min. Using video microscopy, lysis was assessed by two independent observers with cytosolic extrusion as the measure. TOL effectively lysed H28 cells dose‐ and stimulus‐dependently, with a maximum cell death of 94.2% Less than 5% of cells in the Drug only, Stimulation only, and Non‐treated groups died (p&lt;.0001). MeT‐5A cells did not lyse. Likewise, when we used a pulsed magnetic field (90 mT, 25 pps) to stimulate VGSCs, H28 cells lysed dose‐ and stimulation‐dependently, whereas control treatments and Met‐5a cells did not. Together these results are evidence that TOL causes significant cell death in mesothelioma cells compared to the normal cells. Thus, TOL may be an effective treatment for mesothelioma.Support or Funding InformationThis research was supported by a grant from Oleander Medical TechnologiesThis abstract is from the Experimental Biology 2019 Meeting. There is no full text article associated with this abstract published in The FASEB Journal.

Epithelial to Mesenchymal Transition in Human Mesothelial Cells Exposed to Asbestos Fibers: Role of TGF-β as Mediator of Malignant Mesothelioma Development or Metastasis via EMT Event.

Asbestos exposure increases the risk of asbestosis and malignant mesothelioma (MM). Both fibrosis and cancer have been correlated with the Epithelial to Mesenchymal Transition (EMT)—an event involved in fibrotic development and cancer progression. During EMT, epithelial cells acquire a mesenchymal phenotype by modulating some proteins. Different factors can induce EMT, but Transforming Growth Factor β (TGF-β) plays a crucial role in promoting EMT. In this work, we verified if EMT could be associated with MM development. We explored EMT in human mesothelial cells (MeT-5A) exposed to chrysotile asbestos: we demonstrated that asbestos induces EMT in MeT-5A cells by downregulating epithelial markers E-cadherin, β-catenin, and occludin, and contemporarily, by upregulating mesenchymal markers fibronectin, α-SMA, and vimentin, thus promoting EMT. In these cells, this mechanism is mediated by increased TGF-β secretion, which in turn downregulates E-cadherin and increases fibronectin. These events are reverted in the presence of TGF-β antibody, via a Small Mother Against Decapentaplegic (SMAD)-dependent pathway and its downstream effectors, such as Zinc finger protein SNAI1 (SNAIL-1), Twist-related protein (Twist), and Zinc Finger E-Box Binding Homeobox 1 (ZEB-1), which downregulate the E-cadherin gene. Since SNAIL-1, Twist, and ZEB-1 have been shown to be overexpressed in MM, these genes could be considered possible predictive or diagnostic markers of MM development.

PO-103 Regulation of prostate cancer cell growth and signalling by exercise

IntroductionMalignant mesothelioma (MM) is an aggressive cancer of the mesothelium. MM has a poor prognosis with a median post-diagnosis survival of 12 months. Currently, MM is treated with platinum-based chemotherapy, resulting in side-effects to the patient. Hence, efforts have been focused on genetically analysing MM tumours to improve treatment specificity. Genetically, MMs are characterised by the loss of key tumour suppressor genes such as NF2. NF2 functions as a member of the Hippo signalling pathway. The Hippo pathway consists of a tumour-suppressive kinase cascade which inactivates the proto-oncogenic transcription factors YAP and TAZ. NF2 up-regulates the Hippo pathway kinases to reduce the activity of YAP/TAZ. Hence, NF2 mutant MMs may exhibit hyperactivity of YAP/TAZ, driving oncogenic processes. So, YAP/TAZ may be ideal therapeutic targets for treating NF2 mutant MMs.Material and methodsA panel of 7 MM cell lines and one wildtype mesothelial cell line were used to assess the potential for selectively targeting YAP/TAZ to treat MMs with mutations in NF2 or in the Hippo pathway kinases LATS1/2. YAP and TAZ activity was abrogated in the cell lines using siRNA-mediated knockdown or using chemical inhibition with the drug compounds Verteporfin or Simvastatin. The viability of cell lines 96 hours post YAP/TAZ inhibition was measured using an Alamar blue viability assay. Statistical comparisons of cellular responses to YAP/TAZ inhibition were conducted using an unpaired student’s t-test.Results and discussionsThe effect of YAP/TAZ inhibition on the viability of a panel of 7 MM cell lines and a wildtype mesothelial cell line (Met5A) was assessed. Hippo pathway mutant cell lines showed the highest sensitivity to YAP/TAZ knockdown, however, two non-mutant MM cells also showed considerable sensitivity, indicating that there wasn’t a statistically significant dependence of mutant cell lines on YAP/TAZ for viability. Mutant cell lines did not show selective sensitivity to Simvastatin or Verteporfin, suggesting that these compounds may not be ideal treatment options. However, these observations were likely confounded by the heterogeneity of the panel of cell lines. As such, an isogenic system of NF2 mutant Met5A cells was developed to validate the findings.ConclusionBased on our findings, YAP and TAZ may not be ideal targets for treating Hippo pathway mutant MMs. However, the use of an NF2 mutant isogenic MM cell line system will provide a definitive outlook on their feasibility as therapeutic candidates.

PO-100 Targeting YAP and TAZ to treat hippo pathway mutant malignant mesotheliomas

IntroductionMalignant mesothelioma (MM) is an aggressive cancer of the mesothelium. MM has a poor prognosis with a median post-diagnosis survival of 12 months. Currently, MM is treated with platinum-based chemotherapy, resulting in side-effects to the patient. Hence, efforts have been focused on genetically analysing MM tumours to improve treatment specificity. Genetically, MMs are characterised by the loss of key tumour suppressor genes such as NF2. NF2 functions as a member of the Hippo signalling pathway. The Hippo pathway consists of a tumour-suppressive kinase cascade which inactivates the proto-oncogenic transcription factors YAP and TAZ. NF2 up-regulates the Hippo pathway kinases to reduce the activity of YAP/TAZ. Hence, NF2 mutant MMs may exhibit hyperactivity of YAP/TAZ, driving oncogenic processes. So, YAP/TAZ may be ideal therapeutic targets for treating NF2 mutant MMs.Material and methodsA panel of 7 MM cell lines and one wildtype mesothelial cell line were used to assess the potential for selectively targeting YAP/TAZ to treat MMs with mutations in NF2 or in the Hippo pathway kinases LATS1/2. YAP and TAZ activity was abrogated in the cell lines using siRNA-mediated knockdown or using chemical inhibition with the drug compounds Verteporfin or Simvastatin. The viability of cell lines 96 hours post YAP/TAZ inhibition was measured using an Alamar blue viability assay. Statistical comparisons of cellular responses to YAP/TAZ inhibition were conducted using an unpaired student’s t-test.Results and discussionsThe effect of YAP/TAZ inhibition on the viability of a panel of 7 MM cell lines and a wildtype mesothelial cell line (Met5A) was assessed. Hippo pathway mutant cell lines showed the highest sensitivity to YAP/TAZ knockdown, however, two non-mutant MM cells also showed considerable sensitivity, indicating that there wasn’t a statistically significant dependence of mutant cell lines on YAP/TAZ for viability. Mutant cell lines did not show selective sensitivity to Simvastatin or Verteporfin, suggesting that these compounds may not be ideal treatment options. However, these observations were likely confounded by the heterogeneity of the panel of cell lines. As such, an isogenic system of NF2 mutant Met5A cells was developed to validate the findings.ConclusionBased on our findings, YAP and TAZ may not be ideal targets for treating Hippo pathway mutant MMs. However, the use of an NF2 mutant isogenic MM cell line system will provide a definitive outlook on their feasibility as therapeutic candidates.

Abstract 523: miR-206 inhibits pleural mesothelioma by targeting an active KRAS/CDK4/CCND1 pathway

Abstract Introduction: Since there remains no effective, durable chemotherapy against malignant pleural mesothelioma (MPM), we propose to leverage microRNA(miR)-based approaches that recently reached phase I trial testing. We posit there are many miR with therapeutic potential yet to be identified in MPM. Methods/ Results: Our prior miRNA expression profiling results of MPM (GSE40345) were cross-referenced with a novel p-value minimization analytic technique to identify prognostic miRNA. Both MPM cell lines and tissues (tumors and normal pleura) were assessed using quantitative and functional biologic assays. In silico algorithms identified gene targets that were verified by 3'-UTR luciferase assay.In silico analyses showed underexpression of miR-206 by 12.1-fold in MPM tumors compared to normal pleura. Using our p-value minimization technique, we assessed the clinical impact of this underexpressed miR in TCGA data (n=73 MPM) and noted a significant association to worse survival for patients with lower miR-206 expression (p=0.024). We confirmed that miR-206 was significantly underexpressed in tumor tissues by qRT-PCR analysis of a new, randomly selected MPM cohort (n=41) versus normal pleura (n=14). In a set of established MPM cell lines with low endogenous miR-206 level, ectopic re-expression of miR-206 dramatically suppressed cell proliferation, invasiveness, colony foci formation, and growth in soft-agar. Treatment of non-malignant mesothelial cells MeT-5a and LP9 with ectopic miR-206 showed no untoward effects. In silico gene target predictions for miR-206 were summated across 3 databases and screened by prognostic effect based on Kaplan-Meier results from TCGA data (n=87 MPM). Interestingly, we noted several overexpressed MPM-prognostic genes (p&amp;lt;0.05) regulated by miR-206: KRAS, CDK4, and CCND1. qRT-PCR analysis of tissues confirmed elevated transcripts of KRAS, CDK4, and CCND1 in MPM. This signaling axis of KRAS/CDK4/CCND1 is important in MPM as it summates well-known dysregulated tyrosine kinase receptors (EGF, IGF-1, VEGF, MET, etc) that are upstream. The KRAS/CDK4/CCND1 axis is associated with cell cycle progression and survival of cancer cells, but is not an easily druggable target. miR-206 treatment significantly downregulated KRAS, CDK4 and CCND1 genes in MPM cell lines. Conclusion: In vitro, miR-206 exerts tumor suppressive effects in MPM via inhibition of KRAS/CDK4/CCND1 signaling. miR-206 restoration in MPM mimics simultaneous blocking of multiple tyrosine kinases. Loss of miR-206 and concomitant overexpression of KRAS, CDK4 and CCND1 formed a poor prognostic signature of MPM. Our results identify miR-206 as a rational therapeutic agent to studied further in preclinical MPM models. Citation Format: Anand Singh, Roma Pahwa, Li Zhang, Nathanael Pruett, R Taylor Ripley, David S. Schrump, Chuong D. Hoang. miR-206 inhibits pleural mesothelioma by targeting an active KRAS/CDK4/CCND1 pathway [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 523.

DNA methylation profiling of asbestos-treated MeT5A cell line reveals novel pathways implicated in asbestos response.

Occupational and environmental asbestos exposure is the main determinant of malignant pleural mesothelioma (MPM), however, the mechanisms by which its fibres contribute to cell toxicity and transformation are not completely clear. Aberrant DNA methylation is a common event in cancer but epigenetic modifications involved specifically in MPM carcinogenesis need to be better clarified. To investigate asbestos-induced DNA methylation and gene expression changes, we treated Met5A mesothelial cells with different concentrations of crocidolite and chrysotile asbestos (0.5 ÷ 5.0µg/cm2, 72h incubation). Overall, we observed 243 and 302 differentially methylated CpGs (≥ 10%) between the asbestos dose at 5µg/cm2 and untreated control, in chrysotile and crocidolite treatment, respectively. To examine the dose-response effect, Spearman's correlation test was performed and significant CpGs located in genes involved in migration/cell adhesion processes were identified in both treatments. Moreover, we found that both crocidolite and chrysotile exposure induced a significant up-regulation of CA9 and SRGN (log2 fold change > 1.5), previously reported as associated with a more aggressive MPM phenotype. However, we found no correlation between methylation and gene expression changes, except for a moderate significant inverse correlation at the promoter region of DKK1 (Spearman rho = - 1, P value = 0.02) after chrysotile exposure. These results describe for the first time the relationship between DNA methylation modifications and asbestos exposure. Our findings provide a basis to further explore and validate asbestos-induced DNA methylation changes, that could influence MPM carcinogenesis and possibly identifying new chemopreventive target.