KRAS Pathway Alterations in Malignant Pleural Mesothelioma: An Underestimated Player

Clinical Next Generation Sequencing Application in Mesothelioma: Finding a Golden Needle in the Haystack

Mesothelioma comprises a group of rare cancers arising from the mesothelium of the pleura, peritoneum, tunica vaginalis testis and pericardium. Mesothelioma is generally associated with asbestos exposure and has a dismal prognosis, with few therapeutic options. Several next generation sequencing (NGS) experiments have been performed on mesothelioma arising at different sites. These studies highlight a genomic landscape mainly characterized by a high prevalence (>20%) of genomic aberrations leading to functional losses in oncosuppressor genes such as BAP1, CDKN2A, NF2, SETD2 and TP53. Nevertheless, to date, evidence of the effect of targeting these alterations with specific drugs is lacking. Conversely, 1-2% of mesothelioma might harbor activating mutations in oncogenes with specifically approved drugs. The goal of this review is to summarize NGS applications in mesothelioma and to provide insights into target therapy of mesothelioma guided by NGS.

KRAS Mutations Are Associated with Shortened Survival in Patients with Epithelioid Malignant Pleural Mesothelioma

Malignant pleural mesothelioma (MPM) is an aggressive malignancy of the pleural surface that includes three major histologic subtypes, epitheliod, sarcomatoid and biphasic. Epithelioid mesothelioma is usually associated with better prognosis. The genetic mechanisms driving MPM, the possible target mutations and the correlation with overall survival remain largely unsettled. We performed target exome sequencing in 29 cases of MPM aimed at identifying somatic mutations and, eventually, their correlation with phenotypic traits and prognostic significance. We found that KRAS mutations, occurring in 13.7% of cases, were associated with shortened median survival (7.6 versus 32.6 months in KRAS wild-type; p = 0.005), as it was the occurrence of any ≥3 mutations (7.6 versus 37.6 months; p = 0.049). Conversely, the presence of KDR single nucleotide polymorphism p.V297I (rs2305948) resulted in a favorable variable for survival (NR versus 23.4 months; p = 0.026). With the intrinsic limitations of a small number of cases and patient heterogeneity, results of this study contribute to the characterization of the mutation profile of MPM and the impact of selected somatic mutations, and possibly KDR polymorphism, on prognosis.

MEK1 drives oncogenic signaling and interacts with PARP1 for genomic and metabolic homeostasis in malignant pleural mesothelioma

Malignant pleural mesothelioma (MPM) is a lethal malignancy etiologically caused by asbestos exposure, for which there are few effective treatment options. Although asbestos carcinogenesis is associated with reactive oxygen species (ROS), the bona fide oncogenic signaling pathways that regulate ROS homeostasis and bypass ROS-evoked apoptosis in MPM are poorly understood. In this study, we demonstrate that the mitogen-activated protein kinase (MAPK) pathway RAS-RAF-MEK-ERK is hyperactive and a molecular driver of MPM, independent of histological subtypes and genetic heterogeneity. Suppression of MAPK signaling by clinically approved MEK inhibitors (MEKi) elicits PARP1 to protect MPM cells from the cytotoxic effects of MAPK pathway blockage. Mechanistically, MEKi induces impairment of homologous recombination (HR) repair proficiency and mitochondrial metabolic activity, which is counterbalanced by pleiotropic PARP1. Consequently, the combination of MEK with PARP inhibitors enhances apoptotic cell death in vitro and in vivo that occurs through coordinated upregulation of cytotoxic ROS in MPM cells, suggesting a mechanism-based, readily translatable strategy to treat this daunting disease. Collectively, our studies uncover a previously unrecognized scenario that hyperactivation of the MAPK pathway is an essential feature of MPM and provide unprecedented evidence that MAPK signaling cooperates with PARP1 to homeostatically maintain ROS levels and escape ROS-mediated apoptosis.

The Genes-Stemness-Secretome Interplay in Malignant Pleural Mesothelioma: Molecular Dynamics and Clinical Hints

MPM has a uniquely poor somatic mutational landscape, mainly driven by environmental selective pressure. This feature has dramatically limited the development of effective treatment. However, genomic events are known to be associated with MPM progression, and specific genetic signatures emerge from the exceptional crosstalk between neoplastic cells and matrix components, among which one main area of focus is hypoxia. Here we discuss the novel therapeutic strategies focused on the exploitation of MPM genetic asset and its interconnection with the surrounding hypoxic microenvironment as well as transcript products and microvesicles representing both an insight into the pathogenesis and promising actionable targets.