“Identification and characterization of genes involved in the Malignant Pleural Mesothelioma”

Malignant pleural mesothelioma (MPM) is an asbestos-related cancer of the pleural cavities. Since the molecular mechanisms of MPM are poorly understood, our main goal was to identify relevant genes involved in this neoplasm. Firstly, we performed an extensive literature review focused on the MPM transcriptome and a data mining (using Coremine, SNPs3D, and GeneProspector). The results from review of transcriptome studies and from data mining were intersected. Then, we undertook a validation study to verify whether 77 genes could be confirmed in their de-regulation on an independent series of specimens (20 MPM and 20 healthy pleura tissues). The genes resulted deregulated in our MPM and healthy pleural tissues, have been further validated on four MPM cell lines. The high expression levels of Mesothelin (MSLN), Calretinin (CALB2), and Platelet-derived growth factor receptor beta (PDGFRB) captured our interest. PDGFRB is a target for the tyrosine-kinase inhibitor imatinib. Personal communication (reported by Dr. L. Mutti, Hospital of Vercelli, Italy) highlighted that imatinib was assayed for compassionate use in advanced MPM patients in combination with gemcitabine. Preliminary observations reported that patients showed a good response with the stabilization or partial shrinkage of the tumor mass. However, some patients either did not respond or, after an initial response, relapsed. We hypothesized that mutations within PDGFRB, occurring during the carcinogenesis or during the therapy, could explain these observations but no mutations were found within PDGFRB in 100 surgically resected MPMs. Imatinib resistant Mero-14 cell lines did not show mutations within PDGFRB, making difficult to understand the resistance to imatinib. In order to prove that MSLN and CALB2 play a role in maintaining the malignant phenotype, rather to be simply epiphenomenons, we attempted an approach using silencing-RNA. After having switched off these targets, we analyzed the behavior of MPM cell lines for their apoptotic ability, invasion capacity, cell cycle, and in culture growth parameters. As regard the CALB2 depletion, from our findings we can hypothesize that this gene does not seem involved in triggering the disease. For MSLN, its depletion causes the arrest of some of the most important characteristics malignant phenotypes. Indeed, the specific gene silencing for MSLN decreased the viability, and the invasiveness of MPM cells. Moreover we showed that MSLN depletion sensitized Mero-14 cell lines to cisplatin, and that under this treatment, they displayed an apoptotic type of cell death, and a substantial arrest of the proliferation rate. Finally, the most important result of this work provides evidence for a possible targeting of MSLN, alone or in combination with chemotherapy, for the treatment of MPM, highlighting the importance of this target gene for novel therapies.