Preclinical evaluation of CDK4 phosphorylation predicts high sensitivity of pleural mesotheliomas to CDK4/6 inhibition

Malignant pleural mesothelioma (MPM) is an aggressive cancer with limited therapeutic options. We evaluated the impact of CDK4/6 inhibition by palbociclib in 28 MPM cell lines including 19 patient-derived ones, using various approaches including RNA-sequencing. Palbociclib strongly and durably inhibited the proliferation of 23 cell lines, indicating a unique sensitivity of MPM to CDK4/6 inhibition. When observed, insensitivity to palbociclib was mostly explained by the lack of active T172-phosphorylated CDK4. This was associated with high p16INK4A (CDKN2A) levels that accompany RB1 defects or inactivation, or (unexpectedly) CCNE1 overexpression in the presence of wild-type RB1. Prolonged palbociclib treatment irreversibly inhibited proliferation despite re-induction of cell cycle genes upon drug washout. A senescence-associated secretory phenotype including various potentially immunogenic components was irreversibly induced. Phosphorylated CDK4 was detected in 80% of 47 MPMs indicating their sensitivity to CDK4/6 inhibitors. Its absence in some highly proliferative MPMs was linked to very high p16 (CDKN2A) expression, which was also observed in public datasets in tumours from short-survival patients. Our study supports the evaluation of CDK4/6 inhibitors for MPM treatment, in monotherapy or combination therapy.

Pleural mesothelioma: a snapshot of emerging drug targets and opportunities for non-surgical therapeutic advancement

INTRODUCTION

Pleural mesothelioma is a rare and aggressive cancer originating in the pleura, with a devastating prognosis and limited treatment options. There have been significant advancements in the management of this disease in recent years. Since 2021, nivolumab and ipilimumab immune checkpoint inhibitors have become the new standard of care for first-line treatment of pleural mesothelioma.

AREAS COVERED

While a combination of chemotherapy and immune checkpoint inhibitors appears to be the next step, targeted therapies are emerging thanks to our understanding of the oncogenesis of pleural mesothelioma. Moreover, several new strategies are currently being investigated, including viral therapy, antibody-drug conjugates, and even cell therapies with CAR-T cells or dendritic cells. In this review, we will explore the various future opportunities that could potentially transform patients' lives in light of the clinical trials that have been conducted.

EXPERT OPINION

Future clinical studies aim to rebiopsy patients after disease progression to identify new molecular alterations and to be associated with ancillary studies, guiding subsequent therapy decisions. Predicting and investigating treatment resistance mechanisms will lead to innovative approaches and improved treatment outcomes.

Multiomic analysis of malignant pleural mesothelioma identifies molecular axes and specialized tumor profiles driving intertumor heterogeneity

Malignant pleural mesothelioma (MPM) is an aggressive cancer with rising incidence and challenging clinical management. Through a large series of whole-genome sequencing data, integrated with transcriptomic and epigenomic data using multiomics factor analysis, we demonstrate that the current World Health Organization classification only accounts for up to 10% of interpatient molecular differences. Instead, the MESOMICS project paves the way for a morphomolecular classification of MPM based on four dimensions: ploidy, tumor cell morphology, adaptive immune response and CpG island methylator profile. We show that these four dimensions are complementary, capture major interpatient molecular differences and are delimited by extreme phenotypes that-in the case of the interdependent tumor cell morphology and adapted immune response-reflect tumor specialization. These findings unearth the interplay between MPM functional biology and its genomic history, and provide insights into the variations observed in the clinical behavior of patients with MPM.

A10 OVEREXPRESSION OF ASCL2 ALTERS DIFFERENTIATION, CELL CYCLE AND RESISTANCE TO ANTI-CANCER TREATMENT IN ESOPHAGEAL ORGANOIDS

Background

The esophagus is in constant contact with the austere environment caused by food and gastric reflux. It is protected by a squamous epithelium which maintenance is provided by a rare subpopulation of basal cells: Keratin 15+ (Krt15+) stem cells. However, little is known about the mechanisms underlying the expansion and the function of these stem cells. It was shown that the transcription factor ASCL2 is strongly upregulated in Krt15+ cells compared to Krt15- cells. Interestingly, ASCL2 is a gene target of the Wnt/β-catenin pathway, which acts as a regulator of proliferation and maintenance of the stemness state.

Purpose

The ultimate goal of my research project is to determine the role of ASCL2 in the maintenance of esophageal stem cells. To do so, I will investigate the role of ASCL2 in esophageal epithelial biology.

Method

Lentiviral infection approach was used to obtain mouse esophageal organoids overexpressing ASCL2 (ASCL2^OE). Organoid culture, immunostaining (such as IF and H&E), qPCR, WB, mass spectrometry and proliferation assay were used to characterize the effect of ASCL2^OE on morphology, differentiation, proliferation, self-renewal, and gene expression.

Result(s)

ASCL2^OE severely altered the morphology of organoids, which were smaller and less differentiated. Defects in differentiation was investigated by IF which showed that some cells expressed both p63 and K13, respectively basal and suprabasal markers. Thus, cells seem to be blocked in an intermediate state of differentiation suggesting a default in cell fate decision. Mass spectrometry analysis confirmed a change in biological processes related to differentiation of keratinocytes and of epithelial cells. We also investigated the role of ASCL2 in self-renewal and observed that organoid formation rate (OFR) was reduced in ASCL2^OE organoids. Furthermore, proliferation was also reduced in WST-1 and EdU assays. We then observed significant changes in the cell cycle by flow cytometry: there is an increased in the number of cells in G0/G1 and a major decrease in G2/M cells, suggesting a blockade in G1. Interestingly, CDNK2a (p16INK4a), an inhibitor of cell cycle progression, was increased in our mass spectrometry results. Finally, ASCL2 could also play a role in radio and chemoresistance of Krt15+ stem cells, as ASCL2^OE organoids are less sensitive to radiation and chemotherapy agents than control.

Conclusion(s)

ASCL2 could play a role in orchestrating cell fate decision in the esophageal epithelium as ASCL2^OE organoids showed alteration in differentiation, proliferation, and cell cycle.

Please acknowledge all funding agencies by checking the applicable boxes below

Other

Please indicate your source of funding;

NSERC, Canada Research Chairs and CRCHUS scolarship

Disclosure of Interest

None Declared

Deep dive into the immune response against murine mesothelioma permits design of novel anti-mesothelioma therapeutics

Given the need to improve the efficacy of standard-of-care immunotherapy (anti-CTLA-4 + anti-PD-1) in human malignant pleural mesothelioma (hMPM), we thoroughly characterized the immunobiology of the AB12 murine mesothelioma (MM) model, aiming to increase its accuracy in predicting the response of hMPM to immunotherapy and in designing novel anti-hMPM treatments. Specifically, we used immunologic, transcriptomic and survival analyses, to synchronize the MM tumor growth phases and immune evolution with the histo-molecular and immunological characteristics of hMPM while also determining the anti-MM efficacy of standard-of-care anti-hMPM immunotherapy as a benchmark that novel therapeutics should meet. We report that early-, intermediate- and advanced- AB12 tumors are characterized by a bell-shaped anti-tumor response that peaks in intermediate tumors and decays in advanced tumors. We further show that intermediate- and advanced- tumors match with immune active ("hot") and immune inactive ("cold") hMPM respectively, and that they respond to immunotherapy in a manner that corresponds well with its performance in real-life settings. Finally, we show that in advanced tumors, addition of cisplatin to anti CTLA-4 + anti PD-1 can extend mice survival and invigorate the decaying anti-tumor response. Therefore, we highlight this triple combination as a worthy candidate to improve clinical outcomes in hMPM.

Heterogeneous RNA editing and influence of ADAR2 on mesothelioma chemoresistance and the tumor microenvironment

We previously observed increased levels of adenosine-deaminase-acting-on-dsRNA (Adar)-dependent RNA editing during mesothelioma development in mice exposed to asbestos. The aim of this study was to characterize and assess the role of ADAR-dependent RNA editing in mesothelioma. We found that tumors and mesothelioma primary cultures have higher ADAR-mediated RNA editing compared to mesothelial cells. Unsupervised clustering of editing in different genomic regions revealed heterogeneity between tumor samples as well as mesothelioma primary cultures. ADAR2 expression levels are higher in BRCA1-associated protein 1 wild-type tumors, with corresponding changes in RNA editing in transcripts and 3'UTR. ADAR2 knockdown and rescue models indicated a role in cell proliferation, altered cell cycle, increased sensitivity to antifolate treatment, and type-1 interferon signaling upregulation, leading to changes in the microenvironment in vivo. Our data indicate that RNA editing contributes to mesothelioma heterogeneity and highlights an important role of ADAR2 not only in growth regulation in mesothelioma but also in chemotherapy response, in addition to regulating inflammatory response downstream of sensing nucleic acid structures.

A Community-Driven, Openly Accessible Molecular Pathway Integrating Knowledge on Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a highly aggressive malignancy mainly triggered by exposure to asbestos and characterized by complex biology. A significant body of knowledge has been generated over the decades by the research community which has improved our understanding of the disease toward prevention, diagnostic opportunities and new treatments. Omics technologies are opening for additional levels of information and hypotheses. Given the growing complexity and technological spread of biological knowledge in MPM, there is an increasing need for an integrating tool that may allow scientists to access the information and analyze data in a simple and interactive way. We envisioned that a platform to capture this widespread and fast-growing body of knowledge in a machine-readable and simple visual format together with tools for automated large-scale data analysis could be an important support for the work of the general scientist in MPM and for the community to share, critically discuss, distribute and eventually advance scientific results. Toward this goal, with the support of experts in the field and informed by existing literature, we have developed the first version of a molecular pathway model of MPM in the biological pathway database WikiPathways. This provides a visual and interactive overview of interactions and connections between the most central genes, proteins and molecular pathways known to be involved or altered in MPM. Currently, 455 unique genes and 247 interactions are included, derived after stringent manual curation of an initial 39 literature references. The pathway model provides a directly employable research tool with links to common databases and repositories for the exploration and the analysis of omics data. The resource is publicly available in the WikiPathways database (Wikipathways : WP5087) and continues to be under development and curation by the community, enabling the scientists in MPM to actively participate in the prioritization of shared biological knowledge.

A16 ESOPHAGEAL ORGANOID PROLIFERATION AND DIFFERENTIATION ARE ALTERED BY LOSS OF MSH2

Background

The stratified epithelium of the esophagus includes Krt15+ basal stem cells that display self-renewing and regenerative capacity, and multipotency. However, the mechanisms that specifically control their functions remain unknown. Interestingly, RNA sequencing and GSEA revealed an enrichment of a gene set associated with DNA repair in Krt15+ cells vs Krt15- cells. We also observed that Msh2 (DNA mismatch repair pathway) is the most significantly upregulated gene in Krt15+ stem cells.

Aims

To determine the effect of Msh2 loss on self-renewal and differentiation of esophageal organoids.

Methods

Esophageal epithelial cells were isolated from a wild-type mouse. Using flow cytometry, esophageal Krt15+ (GFP+) and Krt15- (GFP-) cells were sorted from Krt15-CrePR1 (R26^mT/mG) mice. All cell populations were grown as organoids and Msh2 was depleted using a CRISPR/Cas9 approach. Impact of Msh2 loss on self-renewal and differentiation in esophageal epithelial organoids was evaluated through organoid formation assays, WST-1 proliferation assays and histological analysis.

Results

At baseline, organoids depleted for Msh2 formed more poorly differentiated and less well-differentiated organoids than controls. Lower expression of differentiation gene Krt13 was also observed in Msh2-depleted organoids, confirming an altered differentiation pattern. Furthermore, these organoids showed a higher organoid formation rate and proliferation by WST-1 assay, suggesting that self-renewal capacity and viability are increased when Msh2 is depleted. Interestingly, following radiation, organoids depleted for Msh2 showed higher residual levels of p-H2AX (DNA damage marker), suggesting that their capacity to cope with DNA damages is altered. As mentioned above, we previously reported that Msh2 is the most upregulated gene in Krt15+ vs Krt15- cells. Therefore, to determine if Msh2 role is distinct in both populations, we depleted Msh2 in Krt15+ and Krt15- cells-derived organoids. Interestingly, our preliminary results suggest that Msh2 deletion led to increased p-H2AX and decreased Krt13 levels in Krt15+ organoids but not in Krt15- organoids.

Conclusions

Our results show that Msh2 is potentially a key contributor of esophageal stemness in homeostatic and injured conditions.

Funding Agencies

CIHRCanada Research Chair

A21 OVEREXPRESSION OF ASCL2 ALTERS DIFFERENTIATION IN ESOPHAGEAL ORGANOIDS

Background

The first population of stem cells in the esophageal epithelium was recently identified with the marker Keratin 15 ( Krt15). However, little is known about the mechanisms underlying the expansion and the function of these stem cells. It was shown that the transcription factor ASCL2 is upregulated in Krt15+ cells compared to Krt15- cells. Interestingly, ASCL2 is a gene target of the Wnt/β-catenin pathway, which acts as a regulator of proliferation and maintenance of the stemness state. The ultimate goal of my research project is to determine the role of ASCL2 in the maintenance of esophageal stem cells and to identify its binding partners.

Aims

Investigate the role of ASCL2 in esophageal epithelial biology.

Methods

Lentiviral infection approach was used to obtain mouse esophageal organoids overexpressing ASCL2. Organoid culture, immunostaining (such as IF and H&E), qPCR, WB and proliferation assay were used to characterize the effect of ASCL2 overexpression on morphology, differentiation, proliferation, self-renewal and gene expression.

Results

First, ASCL2 overexpression was confirmed by WB. Interestingly, the morphology of organoid overexpressing ASCL2 was severely altered: organoids were smaller and less differentiated. Defect in differentiation was investigated by qPCR and IF using relevant markers such as p63, Krt13, Wnt5a and NT5E. Indeed, we observed an increase in basal marker ( p63), a decrease in suprabasal markers ( Krt13, Wnt5a) and in a stem cell marker ( NT5E). We also investigated the role of ASCL2 in self-renewal and observed that organoid formation capacity was reduced in ASCL2-overexpressing organoids. Furthermore, proliferation was also reduced in WST-1 assays. We also observed lower expression of the gene Top2a, a recently identified marker of the proliferative basal cell population in the human esophagus. Finally, we observed significant changes in the expression of genes associated with quiescent stem cells (Clu, ZFP36L2 and Anxa1).

Conclusions

ASCL2 overexpression alters differentiation and proliferation in organoids. ASCL2 could play a role in orchestrating cell fate decision in the esophageal epithelium.

Funding Agencies

NSERC, Canada Research Chair

KRAS signaling in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) arises from mesothelial cells lining the pleural cavity of asbestos‐exposed individuals and rapidly leads to death. MPM harbors loss‐of‐function mutations in BAP1, NF2, CDKN2A, and TP53, but isolated deletion of these genes alone in mice does not cause MPM and mouse models of the disease are sparse. Here, we show that a proportion of human MPM harbor point mutations, copy number alterations, and overexpression of KRAS with or without TP53 changes. These are likely pathogenic, since ectopic expression of mutant KRAS^G12D in the pleural mesothelium of conditional mice causes epithelioid MPM and cooperates with TP53 deletion to drive a more aggressive disease form with biphasic features and pleural effusions. Murine MPM cell lines derived from these tumors carry the initiating KRAS^G12D lesions, secondary Bap1 alterations, and human MPM‐like gene expression profiles. Moreover, they are transplantable and actionable by KRAS inhibition. Our results indicate that KRAS alterations alone or in accomplice with TP53 alterations likely play an important and underestimated role in a proportion of patients with MPM, which warrants further exploration.

Multi-site tumor sampling highlights molecular intra-tumor heterogeneity in malignant pleural mesothelioma

Background

Malignant pleural mesothelioma (MPM) is a heterogeneous cancer. Better knowledge of molecular and cellular intra-tumor heterogeneity throughout the thoracic cavity is required to develop efficient therapies. This study focuses on molecular intra-tumor heterogeneity using the largest series to date in MPM and is the first to report on the multi-omics profiling of a substantial series of multi-site tumor samples.

Methods

Intra-tumor heterogeneity was investigated in 16 patients from whom biopsies were taken at distinct anatomical sites. The paired biopsies collected from apex, side wall, costo-diaphragmatic, or highest metabolic sites as well as 5 derived cell lines were screened using targeted sequencing. Whole exome sequencing, RNA sequencing, and DNA methylation were performed on a subset of the cohort for deep characterization. Molecular classification, recently defined histo-molecular gradients, and cell populations of the tumor microenvironment were assessed.

Results

Sequencing analysis identified heterogeneous variants notably in NF2, a key tumor suppressor gene of mesothelial carcinogenesis. Subclonal tumor populations were shared among paired biopsies, suggesting a polyclonal dissemination of the tumor. Transcriptome analysis highlighted dysregulation of cell adhesion and extracellular matrix pathways, linked to changes in histo-molecular gradient proportions between anatomic sites. Methylome analysis revealed the contribution of epigenetic mechanisms in two patients. Finally, significant changes in the expression of immune mediators and genes related to immunological synapse, as well as differential infiltration of immune populations in the tumor environment, were observed and led to a switch from a hot to a cold immune profile in three patients.

Conclusions

This comprehensive analysis reveals patient-dependent spatial intra-tumor heterogeneity at the genetic, transcriptomic, and epigenetic levels and in the immune landscape of the tumor microenvironment. Results support the need for multi-sampling for the implementation of molecular-based precision medicine.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13073-021-00931-w.

Abstract 3128: Spatial intra-tumor molecular heterogeneity in malignant pleural mesothelioma

Introduction: Malignant pleural mesothelioma (MPM) is a heterogeneous cancer characterized by a diffuse locoregional growth within the thoracic cavity. Better knowledge of molecular and cellular intra-tumor heterogeneity throughout the thoracic cavity is required to develop efficient therapies.

Methods: Intra-tumor heterogeneity was investigated in 16 patients biopsied at distinct anatomic sites (apex, side wall, costo-diaphragmatic and highly metabolic site detected by PET scan when present). Paired biopsies and five derived primary cell lines were screened by targeted sequencing. Part of the cohort was also deeply characterized by whole exome sequencing, RNA-seq and DNA methylation profiling. Molecular classification and recently defined histo-molecular gradients were assessed, as were the cell populations infiltration of the tumor microenvironment.

Results: Sequencing analysis showed that most of the protein-altering somatic variants were common between paired samples from a given patient. However, we identified heterogeneous variants notably in NF2, the well-known mesothelioma driver tumor suppressor gene. Furthermore, we highlighted subclonal tumor populations shared among paired biopsies, suggesting a polyclonal dissemination of the tumor. Chromosomal abnormalities profiles were similar between different regions within the same tumor suggesting that the main chromosomal alterations occurring in MPM are early events of mesothelial carcinogenesis. Transcriptomic analysis showed major differential gene expression between anatomic sites, leading to the dysregulation of specific pathways notably linked to cell adhesion and extracellular matrix. Accordingly, histo-molecular gradient determining the proportions of epithelioid-like and sarcomatoid-like cellular entities varied between these samples. These changes were linked to epigenetic mechanisms in two patients. Finally, we found consequent spatial intra-tumor heterogeneity of the immune microenvironment with differential expression of immune mediators and immune checkpoints, and differential infiltration of immune populations. These changes led to a switch from a hot to a cold immune profile in three patients.

Conclusions: This study is the first to report on the multi-omics profiling of a substantial series of multi-site MPM tumor samples. Spatial intra-tumor heterogeneity is complex in MPM and varies among patients. We highlighted multiple types of heterogeneity, i.e. (i) genetic, (ii) transcriptomic, (iii) epigenetic and (iv) in the immune landscape of the tumor microenvironment. These results support the need for multi-sampling for the implementation of molecular-based precision medicine in MPM.

Citation Format: Clément Meiller, François Montagne, Théo Z. Hirsch, Stefano Caruso, Julien de Wolf, Quentin Bayard, Jean-Baptiste Assié, Léa Meunier, Yuna Blum, Lisa Quetel, Laure Gibault, Ecaterina Pintilie, Cécile Badoual, Marie-Christine Copin, Eric Letouzé, Arnaud Scherpereel, Jessica Zucman-Rossi, Françoise Le Pimpec-Barthes, Marie-Claude Jaurand, Didier Jean. Spatial intra-tumor molecular heterogeneity in malignant pleural mesothelioma [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 3128.

Involvement of the M-CSF/IL-34/CSF-1R pathway in malignant pleural mesothelioma

Background

Malignant pleural mesothelioma (MPM) is a rare and aggressive cancer related to asbestos exposure. The tumor microenvironment content, particularly the presence of macrophages, was described as crucial for the development of the disease. This work aimed at studying the involvement of the M-CSF (CSF-1)/IL-34/CSF-1R pathway in the formation of macrophages in MPM, using samples from patients.

Methods

Pleural effusions (PEs), frozen tumors, primary MPM cells and MPM cell lines used in this study belong to biocollections associated with clinical databases. Cytokine expressions were studied using real-time PCR and ELISA. The Cancer Genome Atlas database was used to confirm our results on an independent cohort. An original three-dimensional (3D) coculture model including MPM cells, monocytes from healthy donors and a tumor antigen-specific cytotoxic CD8 T cell clone was used.

Results

We observed that high interleukin (IL)-34 levels in PE were significantly associated with a shorter survival of patients. In tumors, expression of CSF1 was correlated with ‘M2-like macrophages’ markers, whereas this was not the case with IL34 expression, suggesting two distinct modes of action of these cytokines. Expression of IL34 was higher in MPM cells compared with primary mesothelial cells. Particularly, high expression of IL34 was observed in MPM cells with an alteration of CDKN2A. Finally, using 3D coculture model, we demonstrated the direct involvement of MPM cells in the formation of immunosuppressive macrophages, through activation of the colony stimulating factor-1 receptor (CSF1-R) pathway, causing the inhibition of cytotoxicity of tumor antigen-specific CD8⁺ T cells.

Conclusions

The M-CSF/IL-34/CSF-1R pathway seems strongly implicated in MPM and could constitute a therapeutic target to act on immunosuppression and to support immunotherapeutic strategies.

A53 STUDYING THE ROLE OF ASCL2 IN THE ESOPHAGEAL EPITHELIUM USING ORGANOIDS

Background

The esophagus is lined with a stratified squamous epithelium that assure protection against the austere environment found in the esophageal lumen. The maintenance of this epithelium is ensured by a rare population of cells: stem cells. Those cells have increased capacity of self-renewal and multipotency, which is the capacity to give rise to every cell types of a tissue. The marker Krt15 was used to identify the first stem cell population in the esophagus. Krt15+ cells display an extended lifespan and they are radioresistant, multipotent and capable of self-renewal. Moreover, it was observed by RNA sequencing that the expression of the transcription factor ASCL2 is strongly increased in Krt15+ cells compared to Krt15- cells. Interestingly, ASCL2 is necessary to maintain the stemness of Lgr5+ intestinal stem cells. It is also a target of the Wnt/β-catenin pathway. The overall goal of this project is to determine the role of ACSL2 in the maintenance of esophageal stem cells and to identify its binding partners since ASCL2 needs to dimerize to efficiently bind DNA.

Aims

Confirm that esophageal organoids are adapted to study ASCL2 in the esophagus.

Methods

Esophageal organoids were established from esophageal epithelial cells from wildtype mice. Following this, organoids were treated with an inhibitor of the Notch pathway (DAPT) to induce hyperplasia or infected with lentiviruses to invalidate Ascl2 (CRISPR/Cas9 approach).

Results

To validate that Ascl2 plays an important role in esophageal cell proliferation, Notch pathway was inhibited through DAPT treatment in esophageal organoids to induce hyperplasia, which was confirmed by increased number of proliferative cells (Ki-67+). ASCL2 protein expression was also increased in DAPT-treated organoids supporting its role in proliferation and confirming that organoid is a good model to study ASCL2 role in esophageal epithelial cells. In this optic, organoids lines invalidated for Ascl2 (CRISPR/Cas9 approach) were established. Our preliminary results suggest that Ascl2 loss affects cell proliferation and organoid size under normal conditions.

Conclusions

The expression of ASCL2 correlates with hyperplasia which supports its role in esophageal epithelium homeostasis.

Funding Agencies

Canada research chair et NSERC

A27 MSH2 CONTRIBUTES TO SELF-RENEWAL OF ESOPHAGEAL ORGANOIDS

Background

The esophagus is lined by a stratified epithelium in which basal cells can proliferate and undergo differentiation while migrating towards the lumen. In the basal layer, we also find Krt15+ stem cells that are multipotent, self-renewing and that have regenerative capacity. However, mechanisms that specifically control their functions remain unknown. Interestingly, RNA sequencing and gene set enrichment analysis (GSEA) revealed an enrichment of a gene set associated with DNA repair in Krt15+ cells in comparison to Krt15- cells. We also observed that Msh2 (MutS homolog 2), a gene associated with the DNA mismatch repair (MMR) mechanism, is the most significantly upregulated gene in Krt15+ stem cells.

Aims

To determine the impact of Msh2 loss on self-renewal of esophageal organoids under normal and stress conditions.

Methods

Esophageal epithelial cells were isolated from a wild type mouse and grown as organoids, a 3D culture model that supports stem cell growth and morphologically reproduces the tissue of origin. To determine Msh2 role in esophageal epithelium, this gene was deleted through a CRISPR/Cas9 approach in mouse esophageal organoids. Invalidation was confirmed by Western Blot and immunofluorescence. Impact of Msh2 loss on self-renewal was measured under normal condition and following radiation.

Results

At baseline, loss of Msh2 decreases the organoid formation rate of esophageal organoids. Furthermore, following high-dose radiation, Msh2 deficient cells form less organoids than control cells. These results suggest that self-renewal capacity is reduced when Msh2 is depleted. Interestingly, following radiation, organoids depleted for Msh2 show higher residual levels of p-H2AX, a DNA damage marker, and p-ATM, a key kinase in DNA damage response, suggesting that their capacity to cope with DNA damages is reduced.

Conclusions

Our results suggest that Msh2 contributes to maintaining genomic integrity in esophageal cells and that contributes to maintaining self-renewal capacity of basal cells and possibly esophageal stem cells.

Funding Agencies

Canada Research Chair.

Abstract B14: Discovery of YAP-TEAD protein-protein interaction inhibitors (PPI) for treating malignant pleural mesothelioma (MPM)

We have recently reported the development of YAP-TEAD interaction inhibitors that disrupt the YAP-TEAD complex and block proliferation of tumor cells. These compounds represent promising new treatment modalities for mesothelioma where the Hippo pathway is highly deregulated, with around 45% of MPM cases displaying a mutation of NF2 or LATS and predominantly nuclear YAP localization. MPM is an extremely aggressive disease with limited treatment options and no cure and is inherently chemoresistant, with only 50% of patients responding to the standard-of-care treatment; consequently, it has a very poor prognosis. The aim of this study was to support a multipronged approach to treat MPM. We have first established the in vitro proof of concept using siRNA experiments. Then, we have evaluated the effect of several Inventiva compounds (YAP-TEAD inhibitors) on the proliferation of a well-characterized YAP-dependent mesothelioma cell line (H2052) and on a large panel of MPM cells. We have further demonstrated the mechanism of action (MOA) of our compounds investigating the nuclear localization of YAP, the YAP-TEAD interactions, and the YAP protein expression levels in H2052 cancer cell line. To demonstrate the MOA, we have used immunofluorescence, proximity ligation assay, as well as Co-IP and Western blot experiments. Furthermore, we have examined the effect of IVA compounds in combination with the standard-of-care agent pemetrexed in a 3D spheroid model, and demonstrated the target engagement by looking at YAP-TEAD target gene expression. The effect of IVA compounds has been compared to this obtained with siRNA transfection. To assess the efficacy of pemetrexed +/- Inventiva compounds, we exposed H2052 cells to either each of the single agents or to their combination for 4 or 15 days in 2D or in 3D cultures. We used EdU incorporation assay or the measure of the spheroid area to access cell proliferation. We found a synergistic effect between YAP-TEAD inhibitors and pemetrexed, leading to a drastic inhibition of cancer cell proliferation and an increase of cytotoxicity. This suggests that YAP-TEAD inhibitors used in combination with existing chemotherapeutics could be used to attenuate multidrug resistance and resensitize chemoresistant cancer cells. We are currently exploring the effect of Inventiva compounds in H2052 mouse xenograft model. This study will be expanded to other indications and combination strategies where standard-of-care agents are ineffective and YAP is activated.

Citation Format: Anne Soudé, Martine Barth, Jean-Michel Luccarini, Séverine Delaporte, Florence Chirade, Christelle Valaire, Aude Boulay, Geneviève Cheret, Marie Dorchie, Céline Estivalet, Pascale Tuya-Boustugue, Robin Tranchand, Didier Jean, Lisa Quetel, Jean-Baptiste Assié, Irena Konstantinova, Jean-Louis Junien, Pierre Broqua. Discovery of YAP-TEAD protein-protein interaction inhibitors (PPI) for treating malignant pleural mesothelioma (MPM) [abstract]. In: Proceedings of the AACR Special Conference on the Hippo Pathway: Signaling, Cancer, and Beyond; 2019 May 8-11; San Diego, CA. Philadelphia (PA): AACR; Mol Cancer Res 2020;18(8_Suppl):Abstract nr B14.

The Biology of Malignant Mesothelioma and the Relevance of Preclinical Models

Malignant mesothelioma (MM), especially its more frequent form, malignant pleural mesothelioma (MPM), is a devastating thoracic cancer with limited therapeutic options. Recently, clinical trials that used immunotherapy strategies have yielded promising results, but the benefits are restricted to a limited number of patients. To develop new therapeutic strategies and define predictors of treatment response to existing therapy, better knowledge of the cellular and molecular mechanisms of MM tumors and sound preclinical models are needed. This review aims to provide an overview of our present knowledge and issues on both subjects. MM shows a complex pattern of molecular changes, including genetic, chromosomic, and epigenetic alterations. MM is also a heterogeneous cancer. The recently described molecular classifications for MPM could better consider inter-tumor heterogeneity, while histo-molecular gradients are an interesting way to consider both intra- and inter-tumor heterogeneities. Classical preclinical models are based on use of MM cell lines in culture or implanted in rodents, i.e., xenografts in immunosuppressed mice or isografts in syngeneic rodents to assess the anti-tumor immune response. Recent developments are tumoroids, patient-derived xenografts (PDX), xenografts in humanized mice, and genetically modified mice (GEM) that carry mutations identified in human MM tumor cells. Multicellular tumor spheroids are an interesting in vitro model to reduce animal experimentation; they are more accessible than tumoroids. They could be relevant, especially if they are co-cultured with stromal and immune cells to partially reproduce the human microenvironment. Even if preclinical models have allowed for major advances, they show several limitations: (i) the anatomical and biological tumor microenvironments are incompletely reproduced; (ii) the intra-tumor heterogeneity and immunological contexts are not fully reconstructed; and (iii) the inter-tumor heterogeneity is insufficiently considered. Given that these limitations vary according to the models, preclinical models must be carefully selected depending on the objectives of the experiments. New approaches, such as organ-on-a-chip technologies or in silico biological systems, should be explored in MM research. More pertinent cell models, based on our knowledge on mesothelial carcinogenesis and considering MM heterogeneity, need to be developed. These endeavors are mandatory to implement efficient precision medicine for MM.

Genetic alterations of malignant pleural mesothelioma: association with tumor heterogeneity and overall survival

Development of precision medicine for malignant pleural mesothelioma (MPM) requires a deep knowledge of tumor heterogeneity. Histologic and molecular classifications and histo‐molecular gradients have been proposed to describe heterogeneity, but a deeper understanding of gene mutations in the context of MPM heterogeneity is required and the associations between mutations and clinical data need to be refined. We characterized genetic alterations on one of the largest MPM series (266 tumor samples), well annotated with histologic, molecular and clinical data of patients. Targeted next‐generation sequencing was performed focusing on the major MPM mutated genes and the TERT promoter. Molecular heterogeneity was characterized using predictors allowing classification of each tumor into the previously described molecular subtypes and the determination of the proportion of epithelioid‐like and sarcomatoid‐like components (E/S.scores). The mutation frequencies are consistent with literature data, but this study emphasized that TERT promoter, not considered by previous large sequencing studies, was the third locus most affected by mutations in MPM. Mutations in TERT promoter, NF2, and LATS2 were more frequent in nonepithelioid MPM and positively associated with the S.score. BAP1, NF2, TERT promoter, TP53, and SETD2 mutations were enriched in some molecular subtypes. NF2 mutation rate was higher in asbestos unexposed patient. TERT promoter, NF2, and TP53 mutations were associated with a poorer overall survival. Our findings lead to a better characterization of MPM heterogeneity by identifying new significant associations between mutational status and histologic and molecular heterogeneity. Strikingly, we highlight the strong association between new mutations and overall survival.

Frequent Homozygous Deletions of Type I Interferon Genes in Pleural Mesothelioma Confer Sensitivity to Oncolytic Measles Virus

INTRODUCTION

Oncolytic immunotherapy is based on the use of nonpathogenic replicative oncolytic viruses that infect and kill tumor cells exclusively. Recently, we found that the spontaneous oncolytic activity of the Schwarz strain of measles virus (MV) against human malignant pleural mesothelioma (MPM) depends on defects in the antiviral type I interferon (IFN-I) response in tumor cells.

METHODS

In this study, we studied three independent human MPM bio-collections to identify the defects in the IFN-I responses in tumor cells.

RESULTS

We show that the most frequent defect is the homozygous deletions (HDs) of all the 14 IFN-I genes (IFN-α and IFN-β) that we found in more than half of MV-sensitive MPM cell lines. These HDs occur together with the HDs of the tumor suppressor gene CDKN2A also located in the 9p21.3 chromosome region. Therefore, the IFN-I^-/- MPM cell lines develop a partial and weak IFN-I response when they are exposed to the virus compared with that of normal cells and MV-resistant MPM cell lines. This response consists of the expression of a restricted number of IFN-stimulated genes that do not depend on the presence of IFN-I. In addition, the IFN-I^-/- MPM cell lines infected by MV also develop a pro-inflammatory response associated with stress of the endoplasmic reticulum.

CONCLUSION

Our study emphasizes the link between HDs of IFN-I encoding genes and the CDKN2A gene in MPM and sensitivity to MV oncolytic immunotherapy.

Combined MEK and PI3K/p110β Inhibition as a Novel Targeted Therapy for Malignant Mesothelioma Displaying Sarcomatoid Features

Among malignant mesotheliomas (MM), the sarcomatoid subtype is associated with higher chemoresistance and worst survival. Due to its low incidence, there has been little progress in the knowledge of the molecular mechanisms associated with sarcomatoid MM, which might help to define novel therapeutic targets. In this work, we show that loss of PTEN expression is frequent in human sarcomatoid MM and PTEN expression levels are lower in sarcomatoid MM than in the biphasic and epithelioid subtypes. Combined Pten and Trp53 deletion in mouse mesothelium led to nonepithelioid MM development. In Pten;Trp53-null mice developing MM, the Gαi2-coupled receptor subunit activated MEK/ERK and PI3K, resulting in aggressive, immune-suppressed tumors. Combined inhibition of MEK and p110β/PI3K reduced mouse tumor cell growth in vitro. Therapeutic inhibition of MEK and p110β/PI3K using selumetinib (AZD6244, ARRY-142886) and AZD8186, two drugs that are currently in clinical trials, increased the survival of Pten;Trp53-null mice without major toxicity. This drug combination effectively reduced the proliferation of primary cultures of human pleural (Pl) MM, implicating nonepithelioid histology and high vimentin, AKT1/2, and Gαi2 expression levels as predictive markers of response to combined MEK and p110β/PI3K inhibition. Our findings provide a rationale for the use of selumetinib and AZD8186 in patients with MM with sarcomatoid features. This constitutes a novel targeted therapy for a poor prognosis and frequently chemoresistant group of patients with MM, for whom therapeutic options are currently lacking. SIGNIFICANCE: Mesothelioma is highly aggressive; its sarcomatoid variants have worse prognosis. Building on a genetic mouse model, a novel combination therapy is uncovered that is relevant to human tumors.

Unraveling the cellular heterogeneity of malignant pleural mesothelioma through a deconvolution approach

We determined the proportions of epithelioid-like and sarcomatoid-like cellular entities within malignant pleural mesothelioma samples, by deconvolution of their transcriptomes. These proportions are associated with prognosis and may guide therapeutic strategies. This novel approach describes both intra- and inter-tumor heterogeneity and provides a new way of thinking about cancer pathology.

Dissecting heterogeneity in malignant pleural mesothelioma through histo-molecular gradients for clinical applications

Malignant pleural mesothelioma (MPM) is recognized as heterogeneous based both on histology and molecular profiling. Histology addresses inter-tumor and intra-tumor heterogeneity in MPM and describes three major types: epithelioid, sarcomatoid and biphasic, a combination of the former two types. Molecular profiling studies have not addressed intra-tumor heterogeneity in MPM to date. Here, we use a deconvolution approach and show that molecular gradients shed new light on the intra-tumor heterogeneity of MPM, leading to a reconsideration of MPM molecular classifications. We show that each tumor can be decomposed as a combination of epithelioid-like and sarcomatoid-like components whose proportions are highly associated with the prognosis. Moreover, we show that this more subtle way of characterizing MPM heterogeneity provides a better understanding of the underlying oncogenic pathways and the related epigenetic regulation and immune and stromal contexts. We discuss the implications of these findings for guiding therapeutic strategies, particularly immunotherapies and targeted therapies.

Assessment of signaling pathway inhibitors and identification of predictive biomarkers in malignant pleural mesothelioma

OBJECTIVES

Malignant pleural mesothelioma (MPM) is an aggressive tumor with limited therapeutic options, requiring the development of efficient targeted therapies based on molecular phenotype of the tumor and to identify predictive biomarkers of the response.

MATERIALS AND METHODS

The effect of inhibitors was investigated by cell viability assessment on primary MPM cell lines established in our laboratory from patient tumors, well characterized at the molecular level. Effects on apoptosis, cell proliferation and viability on MPM growing in multicellular spheroid were also assessed for verteporfin. Gene and protein expression, and gene knockdown by RNA interference were used to define mechanism of inhibition and specific predictive biomarkers.

RESULTS

Anti-tumor effect of eight major signaling pathways inhibitors involved in mesothelial carcinogenesis was investigated. Three inhibitors were more efficient than cisplatin, the drug used as first-line chemotherapy in patients with MPM: verteporfin, a putative YAP inhibitor, defactinib, a FAK inhibitor and NSC668394, an Ezrin inhibitor. Verteporfin, the most efficient inhibitor, induced cell proliferation arrest and cell death, and is effective on 3D spheroid multicellular model. Verteporfin sensitivity was YAP-independent and related to molecular classification of the tumors. Biomarkers based on gene expression were identified to predict accurately sensitivity to these three inhibitors.

CONCLUSION

Our study shows that drug screening on well-characterized MPM cells allows for the identification of novel potential therapeutic strategies and defining specific biomarkers predictive of the drug response.

Brain-derived neurotrophic factor, a new soluble biomarker for malignant pleural mesothelioma involved in angiogenesis

Malignant pleural mesothelioma (MPM) is a rare and aggressive cancer related to asbestos exposure. The discovery of soluble biomarkers with diagnostic/prognostic and/or therapeutic properties would improve therapeutic care of MPM patients. Currently, soluble biomarkers described present weaknesses preventing their use in clinic. This study aimed at evaluating brain-derived neurotrophic factor (BDNF), we previously identified using transcriptomic approach, in MPM. We observed that high BDNF expression, at the mRNA level in tumors or at the protein level in pleural effusions (PE), was a specific hallmark of MPM samples. This protein presented significant but limited diagnostic properties (area under the curve (AUC) = 0.6972, p < 0.0001). Interestingly, high BDNF gene expression and PE concentration were predictive of shorter MPM patient survival (13.0 vs 8.3 months, p < 0.0001, in PE). Finally, BDNF did not affect MPM cell oncogenic properties but was implicated in PE-induced angiogenesis. In conclusion, BDNF appears to be a new interesting biomarker for MPM and could also be a new therapeutic target regarding its implication in angiogenesis.

Mesotheliomas in Genetically Engineered Mice Unravel Mechanism of Mesothelial Carcinogenesis

Malignant mesothelioma (MM), a rare and severe cancer, mainly caused as a result of past-asbestos exposure, is presently a public health concern. Current molecular studies aim to improve the outcome of the disease, providing efficient therapies based on the principles of precision medicine. To model the molecular profile of human malignant mesothelioma, animal models have been developed in rodents, wild type animals and genetically engineered mice harbouring mutations in tumour suppressor genes, especially selecting genes known to be inactivated in human malignant mesothelioma. Animals were either exposed or not exposed to asbestos or to other carcinogenic fibres, to understand the mechanism of action of fibres at the molecular level, and the role of the selected genes in mesothelial carcinogenesis. The aim of the manuscript was to compare mesothelioma models to human malignant mesothelioma and to specify the clue genes playing a role in mesothelial carcinogenesis. Collectively, MM models recapitulate the clinical features of human MM. At least two altered genes are needed to induce malignant mesothelioma in mice. Two pathways regulated by Cdkn2a and Trp53 seem independent key players in mesothelial carcinogenesis. Other genes and pathways appear as bona fide modulators of the neoplastic transformation.

Modulating BAP1 expression affects ROS homeostasis, cell motility and mitochondrial function

The tumor suppressor BAP1 associates with ASXL1/2 to form the core Polycomb complex PR-DUB, which catalyzes the removal of mono-ubiquitin from several substrates including histone H2A. This complex also mediates the poly-deubiquitination of HCFC1, OGT and PCG1-α, preventing them from proteasomal degradation. Surprisingly, considering its role in a Polycomb complex, no transcriptional signature was consistently found among BAP1-inactivated tumor types. It was hypothesized that BAP1 tumor suppressor activity could reside, at least in part, in stabilizing proteins through its poly-deubiquitinase activity. Quantitative mass spectrometry and gene expression arrays were used to investigate the consequences of BAP1 expression modulation in the NCI-H226 mesothelioma cell line. Analysis of differentially expressed proteins revealed enrichment in cytoskeleton organization, mitochondrial activity and ROS management, while gene expression analysis revealed enrichment in the epithelial-to-mesenchymal transition pathway. Functional assessments in BAP1 inactivated, BAP1 wild-type and BAP1 catalytically dead-expressing NCI-H226 and QR mesothelioma cell lines confirmed alteration of these pathways and demonstrated that BAP1 deubiquitinase activity was mandatory to maintain these phenotypes. Interestingly, monitoring intracellular ROS levels partly restored the morphology and the mitochondrial activity. Finally, the study suggests new tumorigenic and cellular functions of BAP1 and shows for the first time the interest of studying the proteome as readout of BAP1 inactivation.

Co-occurring Mutations of Tumor Suppressor Genes, LATS2 and NF2, in Malignant Pleural Mesothelioma

Purpose: To better define malignant pleural mesothelioma (MPM) heterogeneity and identify molecular subtypes of MPM, we focus on the tumor suppressor gene LATS2, a member of the Hippo signaling pathway, which plays a key role in mesothelial carcinogenesis.Experimental Design: Sixty-one MPM primary cultures established in our laboratory were screened for mutations in LATS2 Gene inactivation was modeled using siRNAs. Gene and protein expressions were analyzed by quantitative RT-PCR, Western blot analysis, and reverse phase protein array. Cell proliferation, viability, apoptosis, mobility, and invasion were determined after siRNA knockdown or YAP (verteporfin), mTOR (rapamycin), and mTOR/PI3K/AKT (PF-04691502) inhibitor treatment.Results: The LATS2 gene was altered in 11% of MPM by point mutations and large exon deletions. Genetic data coupled with transcriptomic data allowed the identification of a new MPM molecular subgroup, C2^LN, characterized by a co-occurring mutation in the LATS2 and NF2 genes in the same MPM. MPM patients of this subgroup presented a poor prognosis. Coinactivation of LATS2 and NF2 leads to loss of cell contact inhibition between MPM cells. Hippo signaling pathway activity, mTOR expression, and phosphorylation were altered in the C2^LN MPM subgroup. MPMs of this new subgroup show higher sensitivity to PF-04691502 inhibitor. The MOK gene was identified as a potential biomarker of the C2^LN MPM subgroup and PF-04691502 sensitivity.Conclusions: We identified a new MPM molecular subgroup that shares common genetic and transcriptomic characteristics. Our results made it possible to highlight a greater sensitivity to an anticancer compound for this MPM subgroup and to identify a specific potential biomarker. Clin Cancer Res; 23(12); 3191-202. ©2016 AACR.

Abstract 112: Genetic alterations in molecular tumor subgroups of malignant pleural mesothelioma

Background: Malignant pleural mesothelioma (MPM) is a very aggressive neoplasm linked to asbestos exposure. In spite of research efforts to develop more effective therapeutic approaches, its prognosis remains poor, because of the absence of curative treatment. The identification of molecular profiles by omic analyses is a powerful approach to better define MPM subclasses and new targeted therapies. A recent transcriptomic analysis allowed to define a robust MPM classification and to identify two subgroups, C1 and C2, linked to histology and survival. The main finding was to separate epitheloid MPM, the most frequent histologic subtype, within these two subgroups. Epitheloid MPM with a worse survival prognosis were classified in the C2 subgroup. To better define the heterogeneity of MPM and establish a more precise classification, we determined genetic alterations in C1 and C2 MPM.

Material and Methods: Using a gene candidate approach, we performed Next-Generation Sequencing (Miseq, Illumina) in 84 MPM including 49 MPM primary cultures and 35 frozen tumors to identify genetic alterations in specific genes with a 200X depth. We selected 22 genes including key altered genes in mesothelial carcinogenesis (NF2, CDKN2A, CDKN2B BAP1, TP53 and LATS2) previously sequenced by Sanger method, genes mutated at low frequency in MPM (KRAS, HRAS, EGFR⋯) and genes recently suggested as altered in MPM (CUL1, KMT2D, SETD2⋯).

Results: Previous mutations identified by Sanger sequencing in our collection have been confirmed. The results showed an enrichment in C&gt;T transitions, which was already observed in an exome sequencing study in MPM. We identified 93 variants inducing protein structure modification. Among them, 70% were deleterious to the function of the protein (deletion/insertion, splice-site mutation, substitutions nonsense and damaging missense predicted by SIFT or Polyphen). For most of the genes, the mutation frequency was consistent with literature data. The highest alteration frequency was found in CDKN2A, CDKN2B, NF2 and BAP1 genes (over 25%), lower frequencies were found in TP53, LATS2, KMT2D and SETD2 genes (5% to 20%). The alteration frequency of four genes was different between C1 and C2 tumor subgroups. BAP1 mutations were more frequent in C1 MPM, as we showed previously. We also identified new relevant mutations notably in the methyltransferases SETD2 and KMT2D that are also associated to C1 MPM. Mutations in TP53 were significantly associated with C2 MPM.

Conclusion: We defined the genetic alterations signatures of C1 and C2 tumor subgroups. Mutations in enzymes involved in chromatin organization seem to be characteristic of the C1 subgroup. Interestingly, TP53 mutations, which are known to provide tumor aggressiveness, are found in the C2 subgroup gathering patients with the worse prognosis. Ongoing analysis of 83 additional MPM would allow to confirm statistically all the associations we observed.

Citation Format: Lisa Quetel, Robin Tranchant, Clément Meiller, Sandrine Imbeaud, Annie Renier, Françoise Le Pimpec-Barthes, Jessica Zucman-Rossi, Marie-Claude Jaurand, Didier Jean. Genetic alterations in molecular tumor subgroups of malignant pleural 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 112.

Five years update on relationships between malignant pleural mesothelioma and exposure to asbestos and other elongated mineral particles

Despite the reduction of global asbestos consumption and production due to the ban or restriction of asbestos uses in more than 50 countries since the 1970s, malignant mesothelioma remains a disease of concern. Asbestos is still used, imported, and exported in several countries, and the number of mesothelioma deaths may be expected to increase in the next decades in these countries. Asbestos exposure is the main risk factor for malignant pleural mesothelioma, but other types of exposures are linked to the occurrence of this type of cancer. Although recent treatments improve the quality of life of patients with mesothelioma, malignant pleural mesothelioma remains an aggressive disease. Recent treatments have not resulted in appreciable improvement in survival, and thus development of more efficient therapies is urgently needed. The development of novel therapeutic strategies is dependent on our level of knowledge of the physiopathological and molecular changes that mesothelial cells acquired during the neoplastic process. During the past 5 years, new findings have been published on the etiology, epidemiology, molecular changes, and innovative treatments of malignant pleural mesothelioma. This review aims to update the findings of recent investigations on etiology, epidemiology, and molecular changes with a focus on (1) attributable risk of asbestos exposure in men and women and (2) coexposure to other minerals and other elongated mineral particles or high aspect ratio nanoparticles. Recent data obtained on genomic and gene alterations, pathways deregulations, and predisposing factors are summarized.

Causes and pathophysiology of malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) results from the neoplastic transformation of pleural mesothelial cells. Asbestos exposure is a major risk factor for MPM, but epidemiologic studies demonstrated the occurrence of MPM in populations exposed to other fibers, and an excess of MPM in populations occupationally exposed to man-made vitreous fibers and previously to asbestos. The development of nanotechnologies also raises some concern about the potential health effects of new particles of high aspect ration, such as carbon nanotubes. Toxicological studies investigated the mechanism of asbestos-induced transformation of mesothelial cells, and molecular analyses defined the genomic and physiopathological changes in MPM. These findings allowed identifying some key events accounting for the neoplastic process. This article summarizes the known and suspected causes of MPM, the cellular events and responses of mesothelial cells to asbestos fibers and the alterations of key genes and regulatory pathways involved in the pathological mechanism.

Molecular classification of malignant pleural mesothelioma: identification of a poor prognosis subgroup linked to the epithelial-to-mesenchymal transition

PURPOSE

Despite research efforts to develop more effective diagnostic and therapeutic approaches, malignant pleural mesothelioma (MPM) prognosis remains poor. The assessment of tumor response to therapy can be improved by a deeper phenotypical classification of the tumor, with emphasis on its clinico-biological heterogeneity. The identification of molecular profiles is a powerful approach to better define MPM subclasses and targeted therapies.

EXPERIMENTAL DESIGN

Molecular subclasses were defined by transcriptomic microarray on 38 primary MPM cultures. A three-gene predictor, identified by quantitative reverse transcription PCR, was used to classify an independent series of 108 frozen tumor samples. Gene mutations were determined in BAP1, CDKN2A, CDKN2B, NF2, and TP53. Epithelial-to-mesenchymal transition (EMT) markers were studied at the mRNA and protein levels.

RESULTS

Unsupervised hierarchical clustering on transcriptomic data defined two robust MPM subgroups (C1 and C2), closely related to prognosis and partly to histologic subtypes. All sarcomatoid/desmoplastic MPM were included in the C2 subgroup. Epithelioid MPM were found in both subgroups, with a worse survival prognosis in the C2 subgroup. This classification and its association with histologic subtypes and survival were validated in our independent series using the three-gene predictor. Similar subgroups were found after classification of other MPM series from transcriptomic public datasets. C1 subgroup exhibited more frequent BAP1 alterations. Pathway analysis revealed that EMT was differentially regulated between MPM subgroups. C2 subgroup is characterized by a mesenchymal phenotype.

CONCLUSIONS

A robust classification of MPM that defines two subgroups of epithelioid MPM, characterized by different molecular profiles, gene alterations, and survival outcomes, was established.

Molecular changes in mesothelioma with an impact on prognosis and treatment

CONTEXT

In recent decades, research on malignant pleural mesothelioma (MPM) has been developed to improve patients' outcomes by increasing the level of confidence in MPM diagnosis and prognosis.

OBJECTIVE

To summarize data on genetic and epigenetic abnormalities in MPM that may be of interest for a better management of patients with MPM.

DATA SOURCES

Data were obtained from scientific publications on genetic and epigenetic abnormalities in MPM by studying gene mutations, DNA methylation, and gene and microRNA expression profiling.

CONCLUSIONS

Molecular changes in MPM consist in altered expression and in activation or inactivation of critical genes in oncogenesis, especially tumor suppressor genes at the INK4 and NF2 loci. Activation of membrane receptor tyrosine kinases and deregulation of signaling pathways related to differentiation, survival, proliferation, apoptosis, cell cycle control, metabolism, migration, and invasion have been demonstrated. Alterations that could be targeted at a global level (methylation) have been recently reported. Experimental research has succeeded especially in abolishing proliferation and triggering apoptosis in MPM cells. So far, targeted clinical approaches focusing on receptor tyrosine kinases have had limited success. Molecular analyses of series of MPM cases have shown that defined alterations are present in MPM subsets, consistent with interindividual variations of molecular alterations, and suggesting that identification of patient subgroups will be essential to develop more specific therapies.

Respiratory and metabolic effects of massive administration of isotonic saline solution in heaves-affected and control horses

REASONS FOR PERFORMING STUDY

It has been suggested that rapid administration of isotonic saline solution relieves airway obstruction in heaves-affected horses, but the efficacy and tolerability of this treatment is poorly documented.

OBJECTIVES

To determine the respiratory and metabolic effects of a rapid administration of isotonic saline solution in control horses and those with heaves.

METHODS

Thirty litres isotonic saline solution were administered i.v. to 5 control (Group C) and 9 heaves-affected horses (Group H). Pulmonary function testing and arterial blood gas analysis were performed prior to saline infusion, at 90 and 180 mins after starting the infusion, and 1, 3, 6 and 10 days later. PCV, plasma total solids, plasma electrolytes (Na+, Cl- and K+) and venous blood gas analysis were performed prior, during and after saline infusion.

RESULTS

Rapid saline administration was shown to have no beneficial effects on lung function during infusion in Group H. On the contrary, they had significantly increased pulmonary resistance (RL) at 180 mins following the initiation of saline administration compared to baseline. In Group C, saline administration resulted in a significant increase in RL at 180 mins and a significant decrease in PaO2 at 90 mins. These results suggest a transient decrement in lung function caused by rapid saline administration. Group H had a metabolic alkalosis with hypochloraemia at baseline compared to control horses. This resolved following i.v. saline administration and returned to baseline within 6 h after treatment had been discontinued.

CONCLUSION

The administration of saline to Group H did not improve airway function significantly, but resulted in mild and transient side effects.

POTENTIAL RELEVANCE

Rapid administration of isotonic saline alone is not an effective therapy for heaves in horses.

Down-regulation of the expression of RB18A/MED1, a cofactor of transcription, triggers strong tumorigenic phenotype of human melanoma cells

The RB18A/MED1 human gene, also named TRAP220, DRIP205 and PBP, encodes for a single 205 kDa component, which interacts with nuclear receptors and transcription factors. RB18A/MED1 chromosome localization on locus 17q12-q21.1 suggests its involvement in human cancers. We herein analyzed RB18A/MED1 expression in human melanoma cell lines. We found that RB18A/MED1 is either highly or weakly expressed in melanoma cells, depending on their respectively non or highly-tumorigenic phenotype. We therefore investigated the possible existence of a relationship between the RB18A/MED1 expression level and melanoma cell phenotype. For this purpose, we down-regulated RB18A/MED1 expression by transfecting melanoma cells with a RB18A/MED1 small interfering RNA (siRNA), specific to the 3'-untranslated region of native RB18A/MED1 RNA, already demonstrated to inhibit specifically RB18A/MED1 protein expression. A nonspecific (scrambled) siRNA was used as control. This RB18A/MED1 siRNA did not modify the expression of cathepsin L forms or lamin A/C, nor the secretion of procathepsin L and MMP2 in transfected cells. Analysis using a microarray membrane with 113 cancer-related genes, western blot and specific tests, demonstrated that RB18A/MED1 knockdown significantly inhibits tissue inhibitor of metalloproteinase-3 expression, and increases uPAR expression, two genes well known to be involved in melanoma cell invasion, through modifications of the tumor microenvironment. Indeed, RB18A/MED1 knockdown in melanoma cells in vitro increased their invasive properties, without modification of cell proliferation. Furthermore, RB18A/MED1 knockdown in vivo switched melanoma phenotype from non to strongly-tumorigenic in nude mice. Our data thus demonstrated for the first time that a decrease of RB18A/MED1 expression in human melanoma cells increases their tumorigenic phenotype.

Detection of rib trauma in newborn foals in an equine critical care unit: a comparison of ultrasonography, radiography and physical examination

REASONS FOR PERFORMING STUDY

Previous studies have shown that in man ultrasonography is more accurate than radiography for detecting rib fractures.

OBJECTIVES

To describe clinical, radiographic and ultrasonographic findings related with rib fractures in newborn foals in an equine critical care unit; and to compare diagnostic accuracy of ultrasonography to radiography.

METHODS

A prospective ultrasonographic study was performed on 29 foals presented to the emergency unit. This study was performed at the Centre Hospitalier Universitaire Vétérinaire (CHUV), University of Montreal. Physical examination as well as radiographic and ultrasonographic examinations were performed.

RESULTS

Thoracic radiographs revealed 10 rib fractures in 5 of 26 (19%) foals. Ultrasonography revealed 49 fractures in 19 of 29 (65%) foals of which fillies (n = 13; 68%) were significantly over represented as were fractures to the left thorax (n = 15; 78%). Seventeen of 19 foals (90%) had rib fractures located 3 cm or less from the costochondral junction, the distal part of the rib being displaced laterally in all cases. In 2 foals, where both thoracic radiographs and ultrasonography detected rib fractures, the site of fractures was located on the mid portion of the rib. Rib fractures were detected only by thoracic radiographs in one foal. Sixty-five percent (32/49) of fractured ribs had a moderate displacement (1-4 mm).

CONCLUSIONS

Rib fractures are seen frequently in newborn foals in equine critical care units. Ultrasonography is more accurate than radiography and reveals fractures in most patients presented in emergency. The position (costochondral junction) of rib fractures and of the fragments suggest that most thoracic trauma probably occurs during parturition.

POTENTIAL RELEVANCE

Ultrasound imaging increases awareness and improves the diagnosis of rib fractures in newborn foals.

Pharmacological activity of three commercialHypericum perforatum preparations in mice

St John's Wort (Hypericum perforatum) is the main herbal species used to treat depression. The products available on the pharmaceutical and dietary supplement markets are obtained by a variety of preparation processes and their pharmacological effects may differ significantly. The purpose of this study therefore was to investigate the effect of different St John's Wort commercial preparations available on the French market. Only one preparation gave significant results in the forced swimming test.

Infection of human B lymphoma cells by Mycoplasma fermentans induces interaction of its elongation factor with the intracytoplasmic domain of Epstein-Barr virus receptor (gp140, EBV/C3dR, CR2, CD21)

Human cell lines are often infected by mycoplama strains. We have demonstrated that when infected by Mycoplasma fermentans, human B lymphoma cell proliferation increased strongly. These infected B cells expressed a p45 kDa protein which interacted with the intracellular domain of CD21, the EBV/C3d receptor. p45 analysis demonstrated that this is a new gene which encodes an elongation factor originating from Mycoplasma fermentans. p45 interaction with CD21 was specific, there being no interaction with CD19. This is the first demonstration that Mycoplasma fermentans, in infecting human B cells, generates a p45 Mycoplasma component that interacts with CD21, which is involved in B cell proliferation.

Activation of Epstein-Barr virus/C3d receptor (gp140, CR2, CD21) on human B lymphoma cell surface triggers Cbl tyrosine phosphorylation, its association with p85 subunit, Crk-L and Syk and its dissociation with Vav

It is well established that CD21 activation on human B cell surface triggers B cell proliferation. We previously demonstrated that CD21 activation also triggers tyrosine phosphorylation of two components, p95 and p120, both interacting with SH2 domains of the p85 subunit of PI 3-kinase. We successively identified p95 as the nucleolin and the first signal transduction pathway specifically triggered by CD21 activation, i.e.: pp60Src activation, tyrosine phosphorylation of p95 nucleolin, its interaction with SH2 domains of p85 subunit and PI 3-kinase activation, followed by AKT-GSK-3 activations. We herein identified the p120 component as the protooncoprotein Cbl and the first steps associated to its activation. First, CD21 activation triggered Cbl tyrosine phosphorylation, which required c-Src kinase but not PI 3-kinase or Syk kinase activities. Involvement of Src kinase in this step was supported by inhibition of Cbl phosphorylation and its interactions with other components when cells were either preincubated with specific Src inhibitor or transfected with dominant-negative c-Src form. Second, once tyrosine phosphorylated, Cbl interacts with SH2 domains of p85 subunit, SH2 domains of Crk-L and with tyrosine phosphorylated Syk kinase. The third and unexpected feature was to found that, at the contrary of BCR or of CD19 (herein also analyzed for the first time), CD21 activation triggers dissociation of Cbl-Vav complex. Thus, these results provide the first molecular basis of a new signal transduction pathway specifically triggered by CD21 activation.