Molecular targets and targeted therapies for malignant mesothelioma

Malignant mesothelioma is a highly invasive tumor originating from the mesothelial linings of the pleura, peritoneum and pericardium. It is seldom amenable to surgical intervention and poorly responsive to radiotherapy, leaving chemotherapy as the main therapeutic option for most patients. The development of effective drug regimens against mesothelioma has proven extremely difficult and a standard first-line treatment for patients with unresectable tumors has not been established until recently. Despite the benefits obtained with this newly validated standard of care, which is based on the combination of pemetrexed and cisplatin, the prognosis for mesothelioma patients remains poor, median survival is still less than two years and more active treatments are urgently needed. This article will focus on the molecular basis providing the rationale for targeted interventions against mesothelioma and will review targeted agents under evaluation as new potential therapeutic options for mesothelioma patients. Such agents include inhibitors of growth factor receptors, ligands and intracellular effectors. The agents targeting vascular endothelial growth factor signaling are of particular interest, due to the involvement of this pathway both in tumor angiogenesis and autocrine stimulation of mesothelioma cell growth. Alternative approaches are based on inhibitors of the ubiquitin-proteasome pathway and of histone deacetylases which, notwithstanding the functional divergence of the corresponding targets, share the ability to determine a wide modulation of the cancer cell phenotype that can lead to cell cycle arrest, apoptosis and sensitization to different antineoplastic treatments. A recombinant immunotoxin targeted to the membrane antigen mesothelin is an additional agent whose activity is being evaluated in mesothelioma patients.