Role of hedgehog signaling in malignant pleural mesothelioma

Unleashing precision: A review of targeted approaches in pleural mesothelioma

This review delves into the intricate landscape of pleural mesothelioma (PM), emphasizing the need for nuanced therapeutic strategies. While platinum-based chemotherapy remains a cornerstone, the advent of immune checkpoint inhibitors (ICIs), notably through the Checkmate 743 trial, has reshaped treatment paradigms. Challenges persist due to patient heterogeneity and a lack of specific biomarkers. Targeting genotypic and phenotypic alterations emerges as a promising avenue, demanding precision oncology in this rare disease. CDKN2A loss, prevalent in PM, may respond to CDK4/6 inhibitors. Defects in MMR and HR suggest tailored approaches with ICI or PARP inhibitors, respectively. Ongoing trials explore novel inhibitors and promising targets like mesothelin. Implementing these strategies requires overcoming challenges in patient selection, combination therapies, biomarker identification, and cost considerations. Collaboration is crucial for transforming these insights into impactful clinical interventions, heralding the era of personalized and precision medicine for PM.

Deciphering signaling pathway interplay via miRNAs in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a highly invasive form of lung cancer that adversely affects the pleural and other linings of the lungs. MPM is a very aggressive tumor that often has an advanced stage at diagnosis and a bad prognosis (between 7 and 12 months). When people who have been exposed to asbestos experience pleural effusion and pain that is not explained, MPM should be suspected. After being diagnosed, most MPM patients have a one- to four-year life expectancy. The life expectancy is approximately six months without treatment. Despite the plethora of current molecular investigations, a definitive universal molecular signature has yet to be discovered as the causative factor for the pathogenesis of MPM. MicroRNAs (miRNAs) are known to play a crucial role in the regulation of gene expression at the posttranscriptional level. The association between the expression of these short, non-coding RNAs and several neoplasms, including MPM, has been observed. Although the incidence of MPM is very low, there has been a significant increase in research focused on miRNAs in the past few years. In addition, miRNAs have been found to have a role in various regulatory signaling pathways associated with MPM, such as the Notch signaling network, Wnt/β-catenin, mutation of KRAS, JAK/STAT signaling circuit, protein kinase B (AKT), and Hedgehog signaling pathway. This study provides a comprehensive overview of the existing understanding of the roles of miRNAs in the underlying mechanisms of pathogenic symptoms in MPM, highlighting their potential as viable targets for therapeutic interventions.

High Expression of SMO and GLI1 Genes with Poor Prognosis in Malignant Mesothelioma

Background

To investigate the value of SMO and GLI1 genes in the hedgehog pathway in malignant mesothelioma specimens. Further study on the expression and prognosis of SMO and GLI1 in malignant mesothelioma tissues and the relationship between the two and the molecular mechanisms of mesothelioma immunity and to further investigate the prognostic value of mesothelioma expression.

Materials and Methods

Immunohistochemistry and RT-qPCR were applied to detect the expression of SMO and GLI1 proteins and mRNA in biopsy specimens and plasma cavity effusion specimens from malignant mesothelioma (n = 130) and benign mesothelial tissues (n = 50) and to analyze the clinicopathological significance and survival risk factors of SMO and GLI1 protein expression in mesothelioma. The mechanisms of mesothelioma cell expression and immune cell infiltration were investigated using bioinformatics methods.

Results

SMO and GLI1 in mesothelioma tissues detected high concordance between the diagnostic results of mesothelioma biopsy specimens and plasma cavity effusion specimens. The expression levels of SMO and GLI1 protein and mRNA in mesothelioma tissues were higher than those in benign mesothelioma tissues. The expression levels of SMO and GLI1 protein were correlated with the age, site, and asbestos exposure history of patients with mesothelioma. The expression levels of SMO and GLI1 protein were correlated with the expressions of ki67 and p53 (P < 0.05). SMO and GLI1 gene expression levels were negatively correlated with good prognosis in mesothelioma patients (P < 0.05). Cox proportional risk model indicated that protein expressions of invasion, lymph node metastasis, distant metastasis, staging, and genes were independent prognostic factors of mesothelioma. The GEPIA database showed the overall survival rate and the disease-free survival rate of mesothelioma patients in the high SMO and GLI1 expression groups; the UALCAN database analysis showed lower SMO expression levels in mesothelioma patients with more pronounced TP53 mutations (P = 0.001); GLI1 gene expression levels were strongly correlated with lymph node metastasis in mesothelioma patients (P = 0.009). Timer database analysis showed that the mechanism of immune cell infiltration was closely related to SMO and GLI1 expression. The degree of immune cell infiltration was strongly correlated with the prognosis of mesothelioma patients (P < 0.05).

Conclusion

The expression levels of both SMO and GLI1 proteins were higher than those of normal mesothelial tissues, and the mRNA expression levels also changed in the same direction. SMO and GLI1 gene expressions in mesothelioma were negatively correlated with age, site of occurrence, and history of asbestos exposure. Positive expression of SMO and GLI1 was negatively correlated with patient survival. The Cox proportional risk model showed that gender, history of asbestos exposure, site of occurrence, SMO, and GLI1 were independent prognostic factors for mesothelioma. The mechanism of immune cell infiltration in mesothelioma is closely related to the gene expression of both and the survival prognosis of mesothelioma patients.

Genomic and transcriptomic analysis of a diffuse pleural mesothelioma patient-derived xenograft library

BACKGROUND

Diffuse pleural mesothelioma (DPM) is an aggressive malignancy that, despite recent treatment advances, has unacceptably poor outcomes. Therapeutic research in DPM is inhibited by a paucity of preclinical models that faithfully recapitulate the human disease.

METHODS

We established 22 patient-derived xenografts (PDX) from 22 patients with DPM and performed multi-omic analyses to deconvolute the mutational landscapes, global expression profiles, and molecular subtypes of these PDX models and compared features to those of the matched primary patient tumors. Targeted next-generation sequencing (NGS; MSK-IMPACT), immunohistochemistry, and histologic subtyping were performed on all available samples. RNA sequencing was performed on all available PDX samples. Clinical outcomes and treatment history were annotated for all patients. Platinum-doublet progression-free survival (PFS) was determined from the start of chemotherapy until radiographic/clinical progression and grouped into < or ≥ 6 months.

RESULTS

PDX models were established from both treatment naïve and previously treated samples and were noted to closely resemble the histology, genomic landscape, and proteomic profiles of the parent tumor. After establishing the validity of the models, transcriptomic analyses demonstrated overexpression in WNT/β-catenin, hedgehog, and TGF-β signaling and a consistent suppression of immune-related signaling in PDXs derived from patients with worse clinical outcomes.

CONCLUSIONS

These data demonstrate that DPM PDX models closely resemble the genotype and phenotype of parental tumors, and identify pathways altered in DPM for future exploration in preclinical studies.

Analysis of Primary Cilium Expression and Hedgehog Pathway Activation in Mesothelioma Throws Back Its Complex Biology

The primary cilium (PC) is a sensory organelle present on the cell surface, modulating the activity of many pathways. Dysfunctions in the PC lead to different pathologic conditions including cancer. Hedgehog signaling (Hh) is regulated by PC and the loss of its control has been observed in many cancers, including mesothelioma. Malignant pleural mesothelioma (MPM) is a fatal cancer of the pleural membranes with poor therapeutic options. Recently, overexpression of the Hh transcriptional activator GL1 has been demonstrated to be associated with poor overall survival (OS) in MPM. However, unlike other cancers, the response to G-protein-coupled receptor smoothened (SMO)/Hh inhibitors is poor, mainly attributable to the lack of markers for patient stratification. For all these reasons, and in particular for the role of PC in the regulation of Hh, we investigated for the first time the status of PC in MPM tissues, demonstrating intra- and inter-heterogeneity in its expression. We also correlated the presence of PC with the activation of the Hh pathway, providing uncovered evidence of a PC-independent regulation of the Hh signaling in MPM. Our study contributes to the understanding MPM heterogeneity, thus helping to identify patients who might benefit from Hh inhibitors.

GANT61/BI-847325 combination: a new hope in lung cancer treatment

Despite the huge efforts employed to implement novel chemotherapeutic paradigms for lung cancer, the disease still remains a major concern worldwide. Targeting molecular pathways as Hedgehog (Hh) and Mitogen-activated protein kinase (MAPK) represent a new hope in lung cancer treatment. This work was undertaken to evaluate the antitumor effects of GANT61 (5 μM), BI-847325(30 μM), and GANT61 (5 μM)/BI-847325(30 μM) combination on A549 adenocarcinoma lung cancer cell line. The growth inhibition 50 (GI50) for both drugs was performed using MTT. The protein levels of Caspase-3, Bcl-2-associated X protein (Bax), Myeloid cell leukemia sequence 1 (MCL-1), cyclin D1, vascular endothelial growth factor (VEGF), extracellular signal-regulated kinases (ERK), p-Akt, and phosphohistone H3 (pHH3) were measured using ELISA. Glioma-associated oncogene homolog 1(Gli1) gene expression was assessed by quantitative real-time PCR. The GI50 for GANT61 and BI-8473255 were 5 µM and 30 µM, respectively. Caspase-3 and Bax protein levels were significantly elevated while MCL-1, cyclin D1, VEGF, ERK 1/2, p-Akt, and pHH3 levels were significantly reduced by both drugs and their combination relative to the control group. Gli1 gene expression was down-regulated in all groups relative to the control group. GANT61, BI-847325 and their combination inhibited proliferation and angiogenesis but activated the apoptotic pathway. Both drugs conferred a profound negative impact on the crosstalk between each of Hh and MAPK pathways and Phosphoinositide 3 -kinases (PI3K)/Akt/Mammalian target of Rapamycin (mTOR). To the best of our knowledge, the antitumor effects of BI-847325/GANT61 combination have not been tested before. Further in-vitro and in-vivo studies are warranted to support the findings.

Combined treatment with inhibitors of ErbB Receptors and Hh signaling pathways is more effective than single treatment in reducing the growth of malignant mesothelioma both in vitro and in vivo

Malignant mesothelioma (MM) is a rare orphan aggressive neoplasia with low survival rates. Among the other signaling pathways, ErbB receptors and Hh signaling are deregulated in MM. Thus, molecules involved in these signaling pathways could be used for targeted therapy approaches. The aim of this study was to evaluate the effects of inhibitors of Hh- (GANT-61) and ErbB receptors (Afatinib)-mediated signaling pathways, when used alone or in combination, on growth, cell cycle, cell death and autophagy, modulation of molecules involved in transduction pathways, in three human MM cell lines of different histotypes. The efficacy of the combined treatment was also evaluated in a murine epithelioid MM cell line both in vitro and in vivo. This study demonstrated that combined treatment with two inhibitors counteracting the activation of two different signaling pathways involved in neoplastic transformation and progression, such as those activated by ErbB and Hh signaling, is more effective than the single treatments in reducing MM growth in vitro and in vivo. This study may have clinical implications for the development of targeted therapy approaches for MM.

DNA repair and damage pathways in mesothelioma development and therapy

Malignant mesothelioma (MMe) is an aggressive neoplasm that occurs through the transformation of mesothelial cells. Asbestos exposure is the main risk factor for MMe carcinogenesis. Other important etiologies for MMe development include DNA damage, over-activation of survival signaling pathways, and failure of DNA damage response (DDR). In this review article, first, we will describe the most important signaling pathways that contribute to MMe development and their interaction with DDR. Then, the contribution of DDR failure in MMe progression will be discussed. Finally, we will review the latest MMe therapeutic strategies that target the DDR pathway.

Molecular and Immunohistochemical Characterization of Mesothelioma of the Tunica Vaginalis

AIMS

Malignant mesothelioma (MM) of the tunica vaginalis (TV) is a rare and aggressive tumor, and the molecular features and staining profile with contemporary immunohistochemical (IHC) biomarkers are largely unexplored. We characterize the clinicopathologic, molecular, and IHC features of MM (N=13) and mesothelial neoplasms of uncertain malignant potential (MUMP) (N=4).

METHODS AND RESULTS

Targeted next-generation sequencing was performed on 7 MMs and 2 MUMPs. IHC was performed for MTAP, BAP1 and SOX6. 13 adenomatoid tumors were also assessed with SOX6. MM were epithelioid (7/13) or biphasic (6/13). In MM, NF2 (5/7; 71%), CDKN2A (3/7; 43%), and BAP1 (2/7; 29%) were most frequently altered. Non-recurrent driver events were identified in PTCH1 and TSC1. In contrast, none of these alterations were identified in MUMPs; however, one MUMP harbored a TRAF7 missense mutation. By IHC, loss of MTAP (2/12; 17%) and BAP1 (2/9; 22%) was infrequent in MM, whereas both were retained in the MUMPs. SOX6 was positive in 9/11 (82%) MMs, and negative in all MUMPs and adenomatoid tumors.

CONCLUSIONS

Testicular MM exhibit a similar mutational profile to those of the pleura/peritoneum; however, alterations in CDKN2A and BAP1 are less common. These findings suggest that although MTAP and BAP1 IHC are specific for MM, their sensitivity in testicular MMs appears lower. In addition, rare tumors may harbor targetable alterations in driver genes (PTCH1 and TSC1) that are unusual in MMs at other anatomic sites. SOX6 is sensitive for MM; accordingly, the presence of SOX6 expression argues against a benign neoplastic process.

The Role of Smoothened-Dependent and -Independent Hedgehog Signaling Pathway in Tumorigenesis

The Hedgehog (Hh)-glioma-associated oncogene homolog (GLI) signaling pathway is highly conserved among mammals, with crucial roles in regulating embryonic development as well as in cancer initiation and progression. The GLI transcription factors (GLI1, GLI2, and GLI3) are effectors of the Hh pathway and are regulated via Smoothened (SMO)-dependent and SMO-independent mechanisms. The SMO-dependent route involves the common Hh-PTCH-SMO axis, and mutations or transcriptional and epigenetic dysregulation at these levels lead to the constitutive activation of GLI transcription factors. Conversely, the SMO-independent route involves the SMO bypass regulation of GLI transcription factors by external signaling pathways and their interacting proteins or by epigenetic and transcriptional regulation of GLI transcription factors expression. Both routes of GLI activation, when dysregulated, have been heavily implicated in tumorigenesis of many known cancers, making them important targets for cancer treatment. Hence, this review describes the various SMO-dependent and SMO-independent routes of GLI regulation in the tumorigenesis of multiple cancers in order to provide a holistic view of the paradigms of hedgehog signaling networks involving GLI regulation. An in-depth understanding of the complex interplay between GLI and various signaling elements could help inspire new therapeutic breakthroughs for the treatment of Hh-GLI-dependent cancers in the future. Lastly, we have presented an up-to-date summary of the latest findings concerning the use of Hh inhibitors in clinical developmental studies and discussed the challenges, perspectives, and possible directions regarding the use of SMO/GLI inhibitors in clinical settings.

Pathophysiological relationship between hypoxia associated oxidative stress, Epithelial-mesenchymal transition, stemness acquisition and alteration of Shh/ Gli-1 axis during oral sub-mucous fibrosis and oral squamous cell carcinoma

Oral sub-mucous fibrosis (OSF) is a pathophysiological state of oral cavity or oropharynx having a high chance of conversion to oral squamous cell carcinoma (OSCC). It involves fibrotic transformation of sub-epithelial matrix along with epithelial abnormalities. The present work aims to unveil the mechanistic domain regarding OSF to OSCC conversion exploring the scenario of hypoxia associated oxidative stress, epithelial-mesenchymal transition (EMT), metastasis and stemness acquisition. The study involves histopathological analysis of the diseased condition along with the exploration of oxidative stress status, assessment of mitochondrial condition, immunohistochemical analysis of HIF-1α, E-cadherin, vimentin, ERK, ALDH-1, CD133, Shh, Gli-1 and survivin expressions in the oral epithelial region together with the quantitative approach towards collagen deposition in the sub-epithelial matrix. Oxidative stress was found to be associated with type-II EMT in case of OSF attributing the development of sub-epithelial fibrosis and type-III EMT in case of OSCC favoring malignancy associated metastasis. Moreover, the acquisition of stemness during OSCC can also be correlated with EMT. Alteration of Shh and Gli-1 expression pattern revealed the mechanistic association of hypoxia with the phenotypic plasticity and disease manifestation in case of OSF as well as OSCC. Shh/ Gli-1 signaling can also be correlated with survivin mediated cytoprotective phenomenon under oxidative stress. Overall, the study established the correlative network of hypoxia associated oxidative stress, EMT and manifestation of oral pre-cancerous and cancerous condition in a holistic approach that may throw rays of hope in the therapeutic domain of the concerned diseases.

Update of in vitro, in vivo and ex vivo fluoro-edenite effects on malignant mesothelioma: A systematic review (Review)

Fluoro-edenite (FE), asbestiform fiber found in Biancavilla (Sicily, Italy), presents various characteristics similar to the asbestos group, in particular two fibrous phases tremolite and actinolite. Indeed, epidemiological studies have shown that FE fibers have similar effects to those of asbestos fibers. Such studies have reported a high incidence of malignant mesothelioma (MM), an aggressive neoplasm of the serosal membranes lining the pleural cavity, in individuals residing there due to FE exposure in Biancavilla related to environmental contamination. Evidence has led to the classification of FE as a Group 1 human carcinogen by the International Agency for Research on Cancer (IARC). The aim of this systematic review is to compare the results achieved in in vitro, in vivo and ex vivo experimental studies involving FE in order to update the current knowledge on the pathogenesis and molecular mechanisms responsible for FE-mediated MM development as well as the availability of effective biomarkers for MM prevention and diagnosis. This review is focused on the pathophysiological mechanisms mediated by inflammation induced by FE fiber exposure and which are responsible for MM development. This review also discusses the discovery of new diagnostic and prognostic biomarkers for the management of this pathology. It is known that the risk of cancer development increases with chronic inflammation, arising from enhanced reactive oxygen species (ROS) and NO^• production stimulated by the body to remove exogenous agents, causing DNA damage and enhanced signal transduction that may lead to activation of oncogenes. Studies concerning MM biomarker discovery indicate that several biomarkers have been proposed for MM, but mesothelin is the only Food and Drug Administration (FDA)-approved biomarker for MM, with limitations. In recent studies, in silico analysis to identify selected miRNAs highly deregulated in cancer samples when compared with normal control have been developed. This in silico approach could represent an effort in the field of biomarker discovery for MM.

SMO mutations confer poor prognosis in malignant pleural mesothelioma

Background

Malignant pleural mesothelioma (MPM) is an aggressive tumor but approximately 12% of patients survive more than 3 years. The biological differences underlying better outcomes are not known. Several targeted agents and immunotherapy have been ineffective. Hedgehog (Hh) is one emerging pathway. We compared the biological profiles of patients with different survival, investigating the most frequently altered genes, including the Hh pathway.

Methods

We analyzed 56 MPM. A 36-month overall survival (OS) cut-off divided patients into 32 normo (NS) and 24 long (LS) survivors. We used next generation sequencing to test 21 genes, immunohistochemistry to evaluate SMO expression. Mutation differences between NS and LS and their associations with clinical features were analysed by Fisher’s test, OS with the Kaplan-Meier method and its association with mutations by univariate and multivariate Cox proportional hazard models.

Results

Clinical features were similar in both groups. Eighteen out of 56 patients (32%) were wild-type for the genes analysed. At least five had mutations in BAP1, NF2, TP53, SMO and PTCH1 with no significant differences between the groups except for SMO. SMO, a member of the Hh pathway, was mutated only in NS (15.6%) and only SMO mutations were significantly associated with poor prognosis at univariate (HR =4.36, 95% CI: 2.32–8.18, P<0.0001) and multivariate (HR =9.2, 95% CI: 3.0–28.4, P=0.0001) analysis. All SMO mutated patients expressed high protein levels.

Conclusions

SMO mutations were clearly associated with worse prognosis. SMO may be a therapeutic target but this needs to be confirmed in a prospective trial.

"Hedgehog pathway": a potential target of itraconazole in the treatment of cancer

PURPOSE

Itraconazole is an antifungal drug that has been clinically used for over 30 years. In recent years, scholars have discovered that it possesses an anticancer effect. Moreover, its mechanism has been clarified to some degree. What deserves to be mentioned is that itraconazole acting on the Hedgehog pathway has made a new progress in the treatment of cancers. While interestingly, studies have demonstrated that the Hedgehog pathway is largely activated in different cancer cells.

RESULT

This review tries to highlight the effect of itraconazole on smoothened receptor (SMO) in the Hedgehog pathway, thereby reducing the glioma-associated oncogene homolog (GLI) release and finally exhibiting a range of anticancer effects, promoting apoptosis of cancer cells, and inhibiting proliferation by indirect inhibition of NF-κB pathway and inflammation, moreover, promoting the expression of cyclin-dependent kinase inhibitors, inhibiting the expression of target genes transcribed by GLI such as BCL-2 and Cyclin-D1. Besides, itraconazole increases the number of Bnip3, subsequently, inducing the dissociation of the Beclin-1/BCL-2 binding complex, as a result of ultimately promoting autophagy of cancer cells.

CONCLUSION

As a new anticancer drug, whether itraconazole eventually entering clinical application requires the joint eforts of all scholars. In any case, an in-depth study on itraconazole will bring new hope for cancer patients in the near future.

Inhibition of the hedgehog pathway for the treatment of cancer using Itraconazole

Itraconazole (ITZ) is an anti-fungal drug that has been used in clinical practice for nearly 35 years. Recently, numerous experiments have shown that ITZ possesses anti-cancer properties. The Hedgehog (Hh) pathway plays a pivotal role in fundamental processes, including embryogenesis, structure, morphology and proliferation in various species. This pathway is typically silent in adult cells, and inappropriate activity is linked to various tumor types. The most important mechanism of ITZ in the treatment of cancer is inhibition of the Hh pathway through the inhibition of smoothened receptors (SMO), glioma-associated oncogene homologs (GLI), and their downstream targets. In this review, we discuss the mechanisms of ITZ in the treatment of cancer through inhibition of the Hh pathway, which includes anti-inflammation, prevention of tumor growth, induction of cell cycle arrest, induction of apoptosis and autophagy, prevention of angiogenesis, and drug resistance. We also discuss the clinical use of ITZ in many types of cancers. We hope this review will provide more information to support future studies on ITZ in the treatment of various cancers.

Misactivation of Hedgehog signaling causes inherited and sporadic cancers

The Hedgehog pathway is critical for the development of diverse organs. Misactivation of the Hedgehog pathway can cause developmental abnormalities and cancers, including medulloblastoma, the most common pediatric brain tumor, and basal cell carcinoma, the most common cancer in the United States. Here, we review how basic, translational, and clinical studies of the Hedgehog pathway have helped reveal how cells communicate, how intercellular communication controls development, how signaling goes awry to cause cancer, and how to use targeted molecular agents to treat both inherited and sporadic cancers.

Hedgehog Signaling in Lung Cancer: From Oncogenesis to Cancer Treatment Resistance

Hedgehog signaling pathway is physiologically activated during embryogenesis, especially in lung development. It is also reactivated in many solid tumors. In lung cancer, Hedgehog pathway is closely associated with cancer stem cells (CSCs). Recent works have shown that CSCs produced a full-length Sonic Hedgehog (Shh) protein, with paracrine activity and induction of tumor development. Hedgehog pathway is also involved in tumor drug resistance in lung cancer, as cytotoxic chemotherapy, radiotherapy, and targeted therapies. This review proposes to describe the activation mechanisms of Hedgehog pathway in lung cancer, the clinical implications for overcoming drug resistance, and the perspectives for further research.

Radiation Sensitization of Basal Cell and Head and Neck Squamous Cell Carcinoma by the Hedgehog Pathway Inhibitor Vismodegib

Vismodegib, an inhibitor of the Hedgehog signaling pathway, is an approved drug for monotherapy in locally advanced or metastatic basal cell carcinoma (BCC). Data on combined modality treatment by vismodegib and radiation therapy, however, are rare. In the present study, we examined the radiation sensitizing effects of vismodegib by analyzing viability, cell cycle distribution, cell death, DNA damage repair and clonogenic survival in three-dimensional cultures of a BCC and a head and neck squamous cell carcinoma (HNSCC) cell line. We found that vismodegib decreases expression of the Hedgehog target genes glioma-associated oncogene homologue (GLI1) and the inhibitor of apoptosis protein (IAP) Survivin in a cell line- and irradiation-dependent manner, most pronounced in squamous cell carcinoma (SCC) cells. Furthermore, vismodegib significantly reduced proliferation in both cell lines, while additional irradiation only slightly further impacted on viability. Analyses of cell cycle distribution and cell death induction indicated a G1 arrest in BCC and a G2 arrest in HNSCC cells and an increased fraction of cells in SubG1 phase following combined treatment. Moreover, a significant rise in the number of phosphorylated histone-2AX/p53-binding protein 1 (γH2AX/53BP1) foci in vismodegib- and radiation-treated cells was associated with a significant radiosensitization of both cell lines. In summary, these findings indicate that inhibition of the Hedgehog signaling pathway may increase cellular radiation response in BCC and HNSCC cells.

Non-Coding Transcript Heterogeneity in Mesothelioma: Insights from Asbestos-Exposed Mice

Mesothelioma is an aggressive, rapidly fatal cancer and a better understanding of its molecular heterogeneity may help with making more efficient therapeutic strategies. Non-coding RNAs represent a larger part of the transcriptome but their contribution to diseases is not fully understood yet. We used recently obtained RNA-seq data from asbestos-exposed mice and performed data mining of publicly available datasets in order to evaluate how non-coding RNA contribute to mesothelioma heterogeneity. Nine non-coding RNAs are specifically elevated in mesothelioma tumors and contribute to human mesothelioma heterogeneity. Because some of them have known oncogenic properties, this study supports the concept of non-coding RNAs as cancer progenitor genes.

Drug repurposing in malignant pleural mesothelioma: a breath of fresh air?

Drug repurposing is the use of known drugs for new indications. Malignant pleural mesothelioma (MPM) is a rare cancer with a poor prognosis. So far, few treatments have been approved in this disease. However, its incidence is expected to increase significantly, particularly in developing countries. Consequently, drug repurposing appears as an attractive strategy for drug development in MPM, since the known pharmacology and safety profile based on previous approvals of repurposed drugs allows for faster time-to-market for patients and lower treatment cost. This is critical in low- and middle-income countries where access to expensive drugs is limited. This review assesses the published preclinical and clinical data about drug repurposing in MPM.In this review, we identified 11 therapeutic classes that could be repositioned in mesothelioma. Most of these treatments have been evaluated in vitro, half have been evaluated in vivo in animal models of MPM and only three (i.e. valproate, thalidomide and zoledronic acid) have been investigated in clinical trials, with limited benefits so far. Efforts could be coordinated to pursue further investigations and test promising drugs identified in preclinical experiments in appropriately designed clinical trials.

How asbestos drives the tissue towards tumors: YAP activation, macrophage and mesothelial precursor recruitment, RNA editing, and somatic mutations

Chronic exposure to intraperitoneal asbestos triggered a marked response in the mesothelium well before tumor development. Macrophages, mesothelial precursor cells, cytokines, and growth factors accumulated in the peritoneal lavage. Transcriptome profiling revealed YAP/TAZ activation in inflamed mesothelium with further activation in tumors, paralleled by increased levels of cells with nuclear YAP/TAZ. Arg1 was one of the highest upregulated genes in inflamed tissue and tumor. Inflamed tissue showed increased levels of single-nucleotide variations, with an RNA-editing signature, which were even higher in the tumor samples. Subcutaneous injection of asbestos-treated, but tumor-free mice with syngeneic mesothelioma tumor cells resulted in a significantly higher incidence of tumor growth when compared to naïve mice supporting the role of the environment in tumor progression.

Live-Cell Mesothelioma Biobank to Explore Mechanisms of Tumor Progression

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

Old Sonic Hedgehog, new tricks: a new paradigm in thoracic malignancies

The Sonic Hedgehog (Shh) pathway is physiologically involved during embryogenesis, but is also activated in several diseases, including solid cancers. Previous studies have demonstrated that the Shh pathway is involved in oncogenesis, tumor progression and chemoresistance in lung cancer and mesothelioma. The Shh pathway is also closely associated with epithelial-mesenchymal transition and cancer stem cells. Recent findings have revealed that a small proportion of lung cancer cells expressed an abnormal full-length Shh protein, associated with cancer stem cell features. In this paper, we review the role of the Shh pathway in thoracic cancers (small cell lung cancer, non-small cell lung cancer, and mesothelioma) and discuss the new perspectives of cancer research highlighted by the recent data of the literature.

Identification of cis- and trans-acting elements regulating calretinin expression in mesothelioma cells

Calretinin (CALB2) is a diagnostic marker for epithelioid mesothelioma. It is also a prognostic marker since patients with tumors expressing high calretinin levels have better overall survival. Silencing of calretinin decreases viability of epithelioid mesothelioma cells. Our aim was to elucidate mechanisms regulating calretinin expression in mesothelioma. Analysis of calretinin transcript and protein suggested a control at the mRNA level. Treatment with 5-aza-2′-deoxycytidine and analysis of TCGA data indicated that promoter methylation is not likely to be involved. Therefore, we investigated CALB2 promoter by analyzing ~1kb of genomic sequence surrounding the transcription start site (TSS) + 1 using promoter reporter assay. Deletion analysis of CALB2 proximal promoter showed that sequence spanning the −161/+80bp region sustained transcriptional activity. Site-directed analysis identified important cis-regulatory elements within this −161/+80bp CALB2 promoter. EMSA and ChIP assays confirmed binding of NRF-1 and E2F2 to the CALB2 promoter and siRNA knockdown of NRF-1 led to decreased expression of calretinin. Cell synchronization experiment showed that calretinin expression was cell cycle regulated with a peak of expression at G1/S phase. This study provides the first insight in the regulation of CALB2 expression in mesothelioma cells.

Heterogeneous Contributing Factors in MPM Disease Development and Progression: Biological Advances and Clinical Implications

Malignant pleural mesothelioma (MPM) tumors are remarkably aggressive and most patients only survive for 5–12 months; irrespective of stage; after primary symptoms appear. Compounding matters is that MPM remains unresponsive to conventional standards of care; including radiation and chemotherapy. Currently; instead of relying on molecular signatures and histological typing; MPM treatment options are guided by clinical stage and patient characteristics because the mechanism of carcinogenesis has not been fully elucidated; although about 80% of cases can be linked to asbestos exposure. Several molecular pathways have been implicated in the MPM tumor microenvironment; such as angiogenesis; apoptosis; cell-cycle regulation and several growth factor-related pathways predicted to be amenable to therapeutic intervention. Furthermore, the availability of genomic data has improved our understanding of the pathobiology of MPM. The MPM genomic landscape is dominated by inactivating mutations in several tumor suppressor genes; such as CDKN2A; BAP1 and NF2. Given the complex heterogeneity of the tumor microenvironment in MPM; a better understanding of the interplay between stromal; endothelial and immune cells at the molecular level is required; to chaperone the development of improved personalized therapeutics. Many recent advances at the molecular level have been reported and several exciting new treatment options are under investigation. Here; we review the challenges and the most up-to-date biological advances in MPM pertaining to the molecular pathways implicated; progress at the genomic level; immunological progression of this fatal disease; and its link with developmental cell pathways; with an emphasis on prognostic and therapeutic treatment strategies.

Whole exome sequencing of an asbestos-induced wild-type murine model of malignant mesothelioma

BACKGROUND

Malignant mesothelioma (MM) is an aggressive cancer of the pleural and peritoneal cavities caused by exposure to asbestos. Asbestos-induced mesotheliomas in wild-type mice have been used extensively as a preclinical model because they are phenotypically identical to their human counterpart. However, it is not known if the genetic lesions in these mice tumours are similar to in the human disease, a prerequisite for any new preclinical studies that target genetic abnormalities.

METHODS

We performed whole exome sequencing of fifteen asbestos-induced murine MM tumour cell lines from BALB/c, CBA and C57BL/6 mouse strains and compared the somatic mutations and copy number variations with those recurrently reported in human MM. We then catalogued and characterised the mutational landscape of the wild-type murine MM tumours. Quantitative RT-PCR was used to interrogate the expression of key MM genes of interest in the mRNA.

RESULTS

Consistent with human MM tumours, we identified homozygous loss of the tumour suppressor Cdkn2a in 14/15 tumours. One tumour retained the first exon of both of the p16INK4a and p19ARF isoforms though this tumour also contained genetic amplification of Myc resulting in increased expression of the c-Myc proto-oncogene in the mRNA. There were no chromosomal losses in either the Bap1 or Nf2 regions. One tumour harbored homozygous loss of Trp53 in the DNA. Mutation rates were similar in tumours generated in the CBA and C57BL/6 strains when compared to human MM. Interestingly, all BALB/c tumour lines displayed high mutational loads, consistent with the known mutator phenotype of the host strain. The Wnt, MAPK and Jak-STAT signaling pathways were found to be the most commonly affected biological pathways. Mutations and copy number deletions also occurred in the Hedgehog and Hippo pathways.

CONCLUSIONS

These data suggest that in the wild-type murine model asbestos causes mesotheliomas in a similar way to in human MM. This further supports the notion that the murine model of MM represents a genuine homologue of the human disease, something uncommon in cancer, and is thus a valuable tool to provide insight into MM tumour development and to aide the search for novel therapeutic strategies.

Posttranscriptional Regulation Controls Calretinin Expression in Malignant Pleural Mesothelioma

Calretinin (CALB2) is a diagnostic and prognostic marker in malignant pleural mesothelioma (MPM). We previously reported that calretinin expression is regulated at the mRNA level. The presence of a medium-sized (573 nucleotide) 3' untranslated region (3'UTR) predicted to contain binding sites for miR-30a/b/c/d/e and miR-9 as well as an adenine/uridine-rich element (ARE) in all three transcripts arising from the CALB2 gene, suggests that calretinin expression is regulated via posttranscriptional mechanisms. Our aim was to investigate the role of the CALB2-3'UTR in the posttranscriptional regulation of calretinin expression in MPM. CALB2-3'UTR was inserted downstream of the luciferase reporter gene using pmiRGLO vector and reporter expression was determined after transfection into MPM cells. Targeted mutagenesis was used to generate variants harboring mutated miR-30 family and ARE binding sites. Electrophoretic mobility shift assay was used to test for the presence of ARE binding proteins. CALB2-3'UTR significantly decreased luciferase activity in MPM cells. Analysis of mutation in the ARE site revealed a further destabilization of the reporter and human antigen R (HuR) binding to the ARE sequence was detected. The mutation of two miR-30 binding sites abolished CALB2-3'UTR destabilization effect; a transient delivery of miR-30e-5p mimics or anti-miR into MPM cells resulted in a significant decrease/increase of the luciferase reporter expression and calretinin protein, respectively. Moreover, overexpression of CALB2-3'UTR quenched the effect of miR-30e-5p mimics on calretinin protein levels, possibly by sequestering the mimics, thereby suggesting a competitive endogenous RNA network. Finally, by data mining we observed that expression of miR-30e-5p was negatively correlated with the calretinin expression in a cohort of MPM patient samples. Our data show the role of (1) adenine-uridine (AU)-binding proteins in calretinin stabilization and (2) miR-30e-5p in the posttranscriptional negative regulation of calretinin expression via interaction with its 3'UTR. Furthermore, our study demonstrates a possible physiological role of calretinin's alternatively spliced transcripts.

CK2 in Cancer: Cellular and Biochemical Mechanisms and Potential Therapeutic Target

CK2 genes are overexpressed in many human cancers, and most often overexpression is associated with worse prognosis. Site-specific expression in mice leads to cancer development (e.g., breast, lymphoma) indicating the oncogenic nature of CK2. CK2 is involved in many key aspects of cancer including inhibition of apoptosis, modulation of signaling pathways, DNA damage response, and cell cycle regulation. A number of CK2 inhibitors are now available and have been shown to have activity against various cancers in vitro and in pre-clinical models. Some of these inhibitors are now undergoing exploration in clinical trials as well. In this review, we will examine some of the major cancers in which CK2 inhibition has promise based on in vitro and pre-clinical studies, the proposed cellular and signaling mechanisms of anti-cancer activity by CK2 inhibitors, and the current or recent clinical trials using CK2 inhibitors.

A Subset of Malignant Mesothelioma Tumors Retain Osteogenic Potential

Malignant mesothelioma (MM) is an aggressive serosal tumor associated with asbestos exposure. We previously demonstrated that mesothelial cells differentiate into cells of different mesenchymal lineages and hypothesize that osseous tissue observed in a subset of MM patients is due to local differentiation of MM cells. In this study, the capacity of human and mouse MM cells to differentiate into osteoblast-like cells was determined in vitro using a functional model of bone nodule formation and in vivo using an established model of MM. Human and murine MM cell lines cultured in osteogenic medium expressed alkaline phosphatase and formed mineralized bone-like nodules. Several human and mouse MM cell lines also expressed a number of osteoblast phenotype markers, including runt-related transcription factor 2 (RUNX2), osteopontin, osteonectin and bone sialoprotein mRNA and protein. Histological analysis of murine MM tumors identified areas of ossification within the tumor, similar to those observed in human MM biopsies. These data demonstrate the ability of MM to differentiate into another mesenchymal cell type and suggest that MM cells may contribute to the formation of the heterologous elements observed in MM tumors.

Antagonizing the Hedgehog Pathway with Vismodegib Impairs Malignant Pleural Mesothelioma Growth In Vivo by Affecting Stroma

An autocrine-driven upregulation of the Hedgehog (Hh) signaling pathway has been described in malignant pleural mesothelioma (MPM), in which the ligand, desert Hh (DHH), was produced from tumor cells. However, our investigation revealed that the Hh pathway is activated in both tumor and stroma of MPM tumor specimens and an orthotopic immunocompetent rat MPM model. This was demonstrated by positive immunohistochemical staining of Glioma-associated oncogene 1 (GLI1) and Patched1 (PTCH1) in both tumor and stromal fractions. DHH was predominantly expressed in the tumor fractions. To further investigate the role of the Hh pathway in MPM stroma, we antagonized Hh signaling in the rat model of MPM using a Hh antagonist, vismodegib, (100 mg/kg orally). Daily treatment with vismodegib efficiently downregulated Hh target genes Gli1, Hedgehog Interacting Protein (Hhip), and Ptch1, and caused a significant reduction of tumor volume and tumor growth delay. Immunohistochemical analyses revealed that vismodegib treatment primarily downregulated GLI1 and HHIP in the stromal compartment along with a reduced expression of previously described fibroblast Hh-responsive genes such as Fibronectin (Fn1) and Vegfa Primary cells isolated from the rat model cultured in 3% O2 continued to express Dhh but did not respond to vismodegib in vitro However, culture supernatant from these cells stimulated Gli1, Ptch1, and Fn1 expression in mouse embryonic fibroblasts, which was suppressed by vismodegib. Our study provides new evidence regarding the role of Hh signaling in MPM stroma in the maintenance of tumor growth, emphasizing Hh signaling as a treatment target for MPM. Mol Cancer Ther; 15(5); 1095-105. ©2016 AACR.

Cul4A overexpression associated with Gli1 expression in malignant pleural mesothelioma

Malignant pleural mesothelioma (mesothelioma) is a highly aggressive cancer without an effective treatment. Cul4A, a scaffold protein that recruits substrates for degradation, is amplified in several human cancers, including mesothelioma. We have recently shown that Cul4A plays an oncogenic role in vitro and in a mouse model. In this study, we analysed clinical mesothelioma tumours and found moderate to strong expression of Cul4A in 70.9% (51/72) of these tumours, as shown by immunohistochemistry. In 72.2% mesothelioma tumours with increased Cul4A copy number identified by fluorescence in situ hybridization analysis, Cul4A protein expression was moderate to strong. Similarly, Cul4A was overexpressed and Cul4A copy number was increased in human mesothelioma cell lines. Because Gli1 is highly expressed in human mesothelioma cells, we compared Cul4A and Gli1 expression in mesothelioma tumours and found their expression associated (P < 0.05, chi-square). In mesothelioma cell lines, inhibiting Cul4A by siRNA decreased Gli1 expression, suggesting that Gli1 expression is, at least in part, regulated by Cul4A in mesothelioma cells. Our results suggest a linkage between Cul4A and Gli1 expression in human mesothelioma.

Latest developments in our understanding of the pathogenesis of mesothelioma and the design of targeted therapies

Malignant mesothelioma is an aggressive cancer whose pathogenesis is causally linked to occupational exposure to asbestos. Familial clusters of mesotheliomas have been observed in settings of genetic predisposition. Mesothelioma incidence is anticipated to increase worldwide in the next two decades. Novel treatments are needed, as current treatment modalities may improve the quality of life, but have shown modest effects in improving overall survival. Increasing knowledge on the molecular characteristics of mesothelioma has led to the development of novel potential therapeutic strategies, including: molecular targeted approaches, that is the inhibition of vascular endothelial growth factor with bevacizumab; immunotherapy with chimeric monoclonal antibody, immunotoxin, antibody drug conjugate, vaccine and viruses; inhibition of asbestos-induced inflammation, that is aspirin inhibition of HMGB1 activity may decrease or delay mesothelioma onset and/or growth. We elaborate on the rationale behind new therapeutic strategies, and summarize available preclinical and clinical results, as well as efforts still ongoing.

Inhibition of NADPH oxidase 4 induces apoptosis in malignant mesothelioma: Role of reactive oxygen species

Malignant pleural mesothelioma (MPM) is an aggressive tumor that is characterized by dysregulated growth and resistance to apoptosis. Reactive oxygen species (ROS)-generating NADPH oxidase (Nox) family enzymes have been suggested to be involved in neoplastic proliferation. Both the antioxidant N-acetylcysteine (NAC) and the inhibitor of flavoprotein-dependent oxidase, diphenylene iodonium (DPI), inhibited the cell viability of MPM cells in a dose-dependent manner. To examine whether Nox-mediated ROS generation confers antiapoptotic activity and thus a growth advantage to MPM cells, we analyzed the mRNA expression of Nox family members using quantitative RT-PCR in 7 MPM cell lines and a normal mesothelial cell line. Nox4 mRNA was expressed in all of the examined MPM cell lines, whereas little or no Nox2, Nox3 and Nox5 mRNA expression was detected. In 2 MPM cell lines, Nox4 mRNA expression was significantly higher than that in a normal mesothelial cell line. siRNAs targeting Nox4 suppressed ROS generation and cell viability in the MPM cell lines. In addition, DPI treatment and knockdown of Nox4 attenuated phosphorylation of AKT and ERK. Taken together, our results indicate that Nox4-mediated ROS, at least in part, transmit cell survival signals and their depletion leads to apoptosis, thus highlighting the Nox4-ROS-AKT signaling pathway as a potential therapeutic target for MPM treatment.

Inhibition of hedgehog signaling reduces the side population in human malignant mesothelioma cell lines

Deregulation of crucial embryonic pathways, including hedgehog signaling, has been frequently implicated in a variety of human cancers and is emerging as an important target for anticancer therapy. This study evaluated the potential anticancer effects of cyclopamine, a chemical inhibitor of hedgehog signaling, in human malignant mesothelioma (HMM) cell lines. Cyclopamine treatment significantly decreased the proliferation of HMM cells by promoting apoptosis and shifting the cell cycle toward dormant phase. The clonogenicity and mobility of HMM cells were significantly decreased by cyclopamine treatment. Treatment of HMM cells with cyclopamine significantly reduced the abundance of side population cells, which were measured using an assay composed of Hoechst 33342 dye staining and subsequent flow cytometry. Furthermore, the expression levels of stemness-related genes were significantly affected by cyclopamine treatment. Taken together, the present study showed that targeting hedgehog signaling could reduce a more aggressive subpopulation of the cancer cells, suggesting an alternative approach for HMM therapy.

Hedgehog Signaling in Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is a cancer associated with exposure to asbestos fibers, which accumulate in the pleural space, damage tissue and stimulate regeneration. Hedgehog signaling is a pathway important during embryonic mesothelium development and is inactivated in adult mesothelium. The pathway is reactivated in some MPM patients with poor clinical outcome, mainly mediated by the expression of the ligands. Nevertheless, mutations in components of the pathway have been observed in a few cases. Data from different MPM animal models and primary culture suggest that both autocrine and paracrine Hedgehog signaling are important to maintain tumor growth. Drugs inhibiting the pathway at the level of the smoothened receptor (Smo) or glioma-associated protein transcription factors (Gli) have been used mostly in experimental models. For clinical development, biomarkers are necessary for the selection of patients who can benefit from Hedgehog signaling inhibition.

Chemistry and anticarcinogenic mechanisms of glycoalkaloids produced by eggplants, potatoes, and tomatoes

Inhibition of cancer can occur via apoptosis, a genetically directed process of cell self-destruction that involves numerous biomarkers and signaling pathways. Glycoalkaloids are nitrogen-containing secondary plant metabolites found in numerous Solanaceous plants including eggplants, potatoes, and tomatoes. Exposure of cancer cells to glycoalkaloids produced by eggplants (α-solamargine and α-solasonine), potatoes (α-chaconine and α-solanine), and tomatoes (α-tomatine) or their hydrolysis products (mono-, di-, and trisaccharide derivatives and the aglycones solasodine, solanidine, and tomatidine) inhibits the growth of the cells in culture (in vitro) as well as tumor growth in vivo. This overview comprehensively surveys and consolidates worldwide efforts to define the following aspects of these natural compounds: (a) their prevalence in the three foods; (b) their chemistry and structure-activity relationships; (c) the reported factors (biomarkers, signaling pathways) associated with apoptosis of bone, breast, cervical, colon, gastric, glioblastoma, leukemia, liver, lung, lymphoma, melanoma, pancreas, prostate, and squamous cell carcinoma cell lines in vitro and the in vivo inhibition of tumor formation and growth in fish and mice and in human skin cancers; and (d) future research needs. The described results may make it possible to better relate the structures of the active compounds to their health-promoting function, individually, in combination, and in food, and allow the consumer to select glycoalkaloid-containing food with the optimal content of nontoxic beneficial compounds. The described findings are expected to be a valuable record and resource for further investigation of the health benefits of food-related natural compounds.

Hippo/YAP pathway for targeted therapy

Malignant pleural mesothelioma (MPM) is molecularly characterized by loss of function or mutations in the neurofibromin 2 (NF2) and the cyclin-dependent kinase inhibitor 2 genes. NF2 activates a cascade of kinases, called Hippo pathway, which downregulates Yes associated protein (YAP) function as transcription co-activator for TEA domain transcription factors (TEAD). In the absence of functional NF2, the expression of genes essential for cell cycling such as survivin is increased. New therapeutic strategies aimed at interfering with YAP activity include inhibition of hedgehog pathway, which downregulates the YAP protein, verteporfin, which inhibits the assembly of a functional YAP-TEAD transcription factor, and interference with thrombin and lysophosphatidic acid (LPA) receptors downstream signalling, since upon agonist binding they activate YAP.

Personalized oncogenomics: clinical experience with malignant peritoneal mesothelioma using whole genome sequencing

Peritoneal mesothelioma is a rare and sometimes lethal malignancy that presents a clinical challenge for both diagnosis and management. Recent studies have led to a better understanding of the molecular biology of peritoneal mesothelioma. Translation of the emerging data into better treatments and outcome is needed. From two patients with peritoneal mesothelioma, we derived whole genome sequences, RNA expression profiles, and targeted deep sequencing data. Molecular data were made available for translation into a clinical treatment plan. Treatment responses and outcomes were later examined in the context of molecular findings. Molecular studies presented here provide the first reported whole genome sequences of peritoneal mesothelioma. Mutations in known mesothelioma-related genes NF2, CDKN2A, LATS2, amongst others, were identified. Activation of MET-related signaling pathways was demonstrated in both cases. A hypermutated phenotype was observed in one case (434 vs. 18 single nucleotide variants) and was associated with a favourable outcome despite sarcomatoid histology and multifocal disease. This study represents the first report of whole genome analyses of peritoneal mesothelioma, a key step in the understanding and treatment of this disease.

[Role of the Sonic Hedgehog pathway in thoracic cancers]

INTRODUCTION

Sonic Hedgehog (Shh) pathway is physiologically activated during embryogenesis and development. It plays a role in idiopathic lung fibrosis and is also activated in several solid cancers.

STATE OF THE ART

Shh pathway is reactivated in thoracic cancers, as small cell lung carcinoma, non-small cell lung carcinoma and malignant pleural mesothelioma. Shh pathway is associated with cancer stem cells and seems to have a crucial role in tumor proliferation, aggressiveness and chemoresistance in these cancers. This review describes the activation mode of Shh pathway in thoracic cancers and its role in small cell lung carcinoma, non-small cell lung carcinoma and malignant pleural mesothelioma, using in vitro and in vivo models. Notably, data from literature show that inhibition of Shh pathway has an antitumor action and sensitizes to chemotherapy.

PERSPECTIVES

These results incite to develop targeted therapies against Shh pathway in the treatment of thoracic cancers.

CK2α, over-expressed in human malignant pleural mesothelioma, regulates the Hedgehog signaling pathway in mesothelioma cells

Background

The Hedgehog (Hh) signaling pathway has been implicated in stem cell maintenance and its activation is aberrant in several types of cancer including mesothelioma. Protein kinase CK2 affects several cell signaling pathways through the mechanism of phosphorylation.

Methods

Protein and mRNA levels of CK2α and Gli1 were tested by quantitative RT-PCR and immunohistochemistry staining in mesothelioma samples and cell lines. Down-regulated Gli1 expression and transcriptional activity were demonstrated by RT-PCR, Western blot and luciferase reporter assay.

Results

In this study, we show that CK2α is over-expressed and a positive regulator of Hegdehog/Gli1 signaling in human malignant pleural mesothelioma. First of all, we found that the mRNA levels of CK2α and Gli1 were broadly elevated and correlated (n = 52, r = 0.401, P < 0.05), compared with LP9 (a normal mesothelial cell line). We then investigated their expression at the protein level, and found that all the 7 mesothelioma cell lines tested showed positive staining in CK2α and Gli1 immunohistochemistry. Correlation analysis by Pearson test for CK2α and Gli1 expression in the 75 mesothelioma tumors and the 7 mesothelioma cell lines showed that the two protein expression was significantly correlated (n = 82, r = 0.554, P < 0.01). Furthermore, we demonstrated that Gli1 expression and transcriptional activity were down-regulated after CK2α was silenced in two mesothelioma cell lines (H28 and H2052). CK2α siRNA also down-regulated the expression of Hh target genes in these cell lines. Moreover, treatment with a small-molecule CK2α inhibitor CX-4945 led to dose-dependent inhibition of Gli1 expression and transcriptional activity. Conversely, forced over-expression of CK2α resulted in an increase in Gli1 transcriptional activity in H28 cells.

Conclusions

Thus, we report for the first time that over-expressed CK2α positively regulate Hh/Gli1 signaling in human mesothelioma.

Electronic supplementary material

The online version of this article (doi:10.1186/s13046-014-0093-6) contains supplementary material, which is available to authorized users.

Evaluation of imaging techniques for the assessment of tumour progression in an orthotopic rat model of malignant pleural mesothelioma†

OBJECTIVES

An orthotopic rat tumour recurrence model for malignant pleural mesothelioma (MPM) provides clinical similarity to patients and is useful for drug testing combined with surgical intervention. Importantly, a reliable imaging method is required allowing for noninvasive and repetitive evaluation of the tumour load. We compared the tumour load assessed by bioluminescence and magnetic resonance imaging (MRI) to the macroscopic tumour volume as a reference standard.

METHODS

A total of 500,000 syngeneic rat MPM cells transfected with luciferase were implanted underneath the parietal pleura of immunocompetent rats (n=13). From the second day after implantation, bioluminescence measurements of the tumour load expressed as the maximum bioluminescent intensity (photon/second) were performed daily after intraperitoneal injection of the luciferase substrate, d-luciferin, to observe the first occurrence of tumour. Six days after the first detection of tumour, bioluminescence, MRI and macroscopic tumour volume measurement were conducted. For MRI, a 4.7-Tesla small animal imager equipped with a 1H whole-body rat coil was employed using T2-weighted fast spin-echo sequences. Tumour burden (mm3) was quantified from magnetic resonance transverse images by two independent readers by manual segmentation. Finally, the tumour burden assessed by bioluminescence and MRI was correlated (Pearson's correlation) with the macroscopic measurement of tumour (ellipsoid) volume.

RESULTS

In all rats, a single tumour nodule was found at the inoculation site with a median macroscopic volume of 46 mm3 (18-377 mm3). For tumour burden quantification of MRIs, we observed good interobserver correlation (R2=0.81, P<0.0001) as well as significant association with the macroscopic tumour volume (R2=0.59, P=0.002). However, the signal intensity of bioluminescence did not correspond to the macroscopic tumour volume (R2=0.01, P=0.76).

CONCLUSIONS

MRI is a reliable and reproducible noninvasive in vivo imaging method for MPM tumour burden assessment for the present MPM model.

GAS5 long non-coding RNA in malignant pleural mesothelioma

Background

Malignant pleural mesothelioma (MPM) is an aggressive cancer with short overall survival. Long non-coding RNAs (lncRNA) are a class of RNAs more than 200 nucleotides long that do not code for protein and are part of the 90% of the human genome that is transcribed. Earlier experimental studies in mice showed GAS5 (growth arrest specific transcript 5) gene deletion in asbestos driven mesothelioma. GAS5 encodes for a lncRNA whose function is not well known, but it has been shown to act as glucocorticoid receptor decoy and microRNA “sponge”. Our aim was to investigate the possible role of the GAS5 in the growth of MPM.

Methods

Primary MPM cultures grown in serum-free condition in 3% oxygen or MPM cell lines grown in serum-containing medium were used to investigate the modulation of GAS5 by growth arrest after inhibition of Hedgehog or PI3K/mTOR signalling. Cell cycle length was determined by EdU incorporation assay in doxycycline inducible short hairpinGAS5 clones generated from ZL55SPT cells. Gene expression was quantified by quantitative PCR. To investigate the GAS5 promoter, a 0.77 kb sequence was inserted into a pGL3 reporter vector and luciferase activity was determined after transfection into MPM cells. Localization of GAS5 lncRNA was identified by in situ hybridization. To characterize cells expressing GAS5, expression of podoplanin and Ki-67 was assessed by immunohistochemistry.

Results

GAS5 expression was lower in MPM cell lines compared to normal mesothelial cells. GAS5 was upregulated upon growth arrest induced by inhibition of Hedgehog and PI3K/mTOR signalling in in vitro MPM models. The increase in GAS5 lncRNA was accompanied by increased promoter activity. Silencing of GAS5 increased the expression of glucocorticoid responsive genes glucocorticoid inducible leucine-zipper and serum/glucocorticoid-regulated kinase-1 and shortened the length of the cell cycle. Drug induced growth arrest was associated with GAS5 accumulation in the nuclei. GAS5 was abundant in tumoral quiescent cells and it was correlated to podoplanin expression.

Conclusions

The observations that GAS5 levels modify cell proliferation in vitro, and that GAS5 expression in MPM tissue is associated with cell quiescence and podoplanin expression support a role of GAS5 in MPM biology.

Exemestane blocks mesothelioma growth through downregulation of cAMP, pCREB and CD44 implicating new treatment option in patients affected by this disease

Background

Recent evidence suggests that aromatase may be involved in the pathogenesis of malignant mesothelioma. Here, we evaluated the effect of exemestane, an inhibitor of aromatase, in the treatment of mesothelioma using in vitro and in vivo preclinical models.

Results

We show a significant reduction of cell proliferation, survival, migration and block of cells in S phase of cell cycle in mesothelioma cells upon exemestane treatment. Moreover, we find that CD44, which is involved in mesothelioma cells migration, was modulated by exemestane via cAMP and pCREB. Most importantly, in mice mesothelioma xenograft exemestane causes a significant decrease in tumor size and the association pemetrexed/exemestane is more effective than pemetrexed/cisplatin.

Conclusion

The preclinical mesothelioma model suggests that exemestane might be beneficial in mesothelioma treatment.

Biomolecular and clinical practice in malignant pleural mesothelioma and lung cancer: what thoracic surgeons should know

Today, molecular-profile-directed therapy is a guiding principle of modern thoracic oncology. The knowledge of new biomolecular technology applied to the diagnosis, prognosis, and treatment of lung cancer and mesothelioma should be part of the 21st century thoracic surgeons' professional competence. The European Society of Thoracic Surgeons (ESTS) Biology Club aims at providing a comprehensive insight into the basic biology of the diseases we are treating. During the 2013 ESTS Annual Meeting, different experts of the field presented the current knowledge about diagnostic and prognostic biomarkers in malignant pleural mesothelioma including new perspectives as well as the role and potential application of microRNA and genomic sequencing for lung cancer, which are summarized in the present article.

Targeting of the Hedgehog signal transduction pathway suppresses survival of malignant pleural mesothelioma cells in vitro

OBJECTIVE

The present study sought to determine whether the Hedgehog (Hh) pathway is active and regulates the cell growth of cultured malignant pleural mesothelioma (MPM) cells and to evaluate the efficacy of pathway blockade using smoothened (SMO) antagonists (SMO inhibitor GDC-0449 or the antifungal drug itraconazole [ITRA]) or Gli inhibitors (GANT61 or the antileukemia drug arsenic trioxide [ATO]) in suppressing MPM viability.

METHODS

Selective knockdown of SMO to inhibit Hh signaling was achieved by small interfering RNA in 3 representative MPM cells. The growth inhibitory effect of GDC-0449, ITRA, GANT61, and ATO was evaluated in 8 MPM lines, with cell viability quantified using the 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay. Cell death was determined by annexinV/propidium iodide staining and flow cytometry.

RESULTS

SMO small interfering RNA mediated a two- to more than fivefold reduction of SMO and Gli1 gene expression as determined by real-time quantitative reverse-transcriptase polymerase chain reaction, indicating significant Hh pathway blockade. This was associated with significantly reduced cell viability (34% ± 7% to 61% ± 14% of nontarget small interfering RNA controls; P = .0024 to P = .043). Treating MPM cells with Hh inhibitors resulted in a 1.5- to 4-fold reduction of Gli1 expression. These 4 Hh antagonists strongly suppressed MPM cell viability. More importantly, ITRA, ATO, GANT61 induced significant apoptosis in the representative MPM cells.

CONCLUSIONS

Hh signaling is active in MPM and regulates cell viability. ATO and ITRA were as effective as the prototypic SMO inhibitor GDC-0449 and the Gli inhibitor GANT61 in suppressing Hh signaling in MPM cells. Pharmaceutical agents Food and Drug Administration-approved for other indications but recently found to have anti-Hh activity, such as ATO or ITRA, could be repurposed to treat MPM.

Mutational analysis of hedgehog signaling pathway genes in human malignant mesothelioma

BACKGROUND

The Hedgehog (HH) signaling pathway is critical for embryonic development and adult homeostasis. Recent studies have identified regulatory roles for this pathway in certain cancers with mutations in the HH pathway genes. The extent to which mutations of the HH pathway genes are involved in the pathogenesis of malignant mesothelioma (MMe) is unknown.

METHODOLOGY/PRINCIPAL FINDINGS

Real-time PCR analysis of HH pathway genes PTCH1, GLI1 and GLI2 were performed on 7 human MMe cell lines. Exon sequencing of 13 HH pathway genes was also performed in cell lines and human MMe tumors. In silico programs were used to predict the likelihood that an amino-acid substitution would have a functional effect. GLI1, GLI2 and PTCH1 were highly expressed in MMe cells, indicative of active HH signaling. PTCH1, SMO and SUFU mutations were found in 2 of 11 MMe cell lines examined. A non-synonymous missense SUFU mutation (p.T411M) was identified in LO68 cells. In silico characterization of the SUFU mutant suggested that the p.T411M mutation might alter protein function. However, we were unable to demonstrate any functional effect of this mutation on Gli activity. Deletion of exons of the PTCH1 gene was found in JU77 cells, resulting in loss of one of two extracellular loops implicated in HH ligand binding and the intracellular C-terminal domain. A 3-bp insertion (69_70insCTG) in SMO, predicting an additional leucine residue in the signal peptide segment of SMO protein was also identified in LO68 cells and a MMe tumour.

CONCLUSIONS/SIGNIFICANCE

We identified the first novel mutations in PTCH1, SUFU and SMO associated with MMe. Although HH pathway mutations are relatively rare in MMe, these data suggest a possible role for dysfunctional HH pathway in the pathogenesis of a subgroup of MMe and help rationalize the exploration of HH pathway inhibitors for MMe therapy.

Expression of smoothened protein in colon cancer and its prognostic value for postoperative liver metastasis

BACKGROUDS: The hedgehog (Hh) signaling pathway is composed of patched (PTCH) and smoothened (SMO), two transmembrane proteins, and downstream glioma-associated oncogene homolog (Gli) transcription factors. Hh signaling plays a pathological role in the occurrence and development of various cancers.

METHODS

To investigate the expression of SMO protein in colon cancer and its association with clinicopathological parameters and postoperative liver metastasis, immunohistochemistry was performed with paraffin-embedded specimens of 96 cases. Relationships between SMO protein expression and clinicopathological parameters, postoperative liver metastasis were analyzed.

RESULTS

IHC examination showed that SMO protein expression was significantly increased in colon cancer tissues compared to normal colon tissues (P = 0.042), positively related to lymph node metastases (P = 0.018) and higher T stages (P = 0.026). Postoperative live metastasis-free survival was significantly longer in the low SMO expression group than in those with high SMO expression (48.7 ± 8.02 months vs 28.0 ± 6.86 months, P=0.036). Multivariate analysis showed SMO expression level to be an independent prognostic factor for postoperative live metastasis-free survival (95% confidence interval [CI] =1.46-2.82, P = 0.008).

CONCLUSIONS

Our results suggest that in patients with colon cancer, the SMO expression level is an independent biomarker for postoperative liver metastasis, and SMO might play an important role in colon cancer progression.