Strategies to enhance the efficacy of oncolytic virotherapy in Malignant Pleural Mesothelioma treatment

Malignant Pleural Mesothelioma (MPM) is a rare and aggressive type of cancer that results from the neoplastic transformation of mesothelial cells and more than 80% of MPM cases are related to previous asbestos exposure on the workplace. The median overall survival (OS) for MPM patients is less than 1 year from the diagnosis, and this is due to the currently available treatment strategies such as surgery, chemotherapy and radiotherapy, which can help to improve patients’ prognosis and life expectancy, nevetheless they cannot be considered resolutive. For these reasons, new strategies for MPM treatment are in high demand and, among all options, immunotherapies represent a very promising alternative. Oncolytic viruses are a new frontier of immunotherapy whose anticancer effect is based on a dual mechanism: a direct lytic effect on infected cancer cell, while spearing the healthy ones, and the boosting of the natural antitumor immunity. Herein, the aim of this project was to design and test a novel oncolytic adenovirus, AdV5/3-∆24-ICOSL-CD40L, which was engineered to selectively replicate in cancer cells and to express two potent immunostimulatory transgenes, enhancing its clinical efficacy. After demonstrating the identity and the genetic stability of the vector, the anticancer activity of the newly cloned oncolytic virus, alone and in combination with an anti PD-1 (Pembrolizumab), was first tested in vitro, both on murine Ab12 and human H226 mesothelioma cell lines. In both cases, high levels of expression of adenoviral receptors ensured that the novel oncolytic virus could be internalized effectively into the host cells, where it exerted a strong cell killing activity, as confirmed by the cell viability analysis; furthermore, high levels of extracellular ATP and calreticulin confirmed the immunogenic profile of the viral-induced cell death. In the case of H226 cell line, also the type and mechanisms of cell death have been analyzed, revealing a higher percentage of apoptotic cells for the groups treated with the virus only and with the combination of both the virus and the anti-PD1. Subsequently in vivo experiments were conducted at first on Balb/c immunocompetent mice engrafted with Ab12 cells and, then, in Balb/c nude mice engrafted with H226 cells. In both cases, the group treated with the combination regime of both AdV5/3-∆24-ICOSL-CD40L and anti-PD-1 registered the lowest tumor volume and the lowest ex vivo tumor weight at the end of the observation period, confirming the superiority of the proposed treatment strategy. Thus, these findings represent the scientific rationale to carry on with further in vivo experiments on humanized mice: in this platform, both the tumor and the immune system will be human, meaning that it will allow to study the efficacy of the treatment on a murine system that is as close as possible to the human physiology. Altogether, the obtained results suggest how the newly cloned oncolytic virus AdV5/3-∆24-ICOSL-CD40L, either alone or in combination with Pembrolizumab, represents a promising alternative for the treatment of mesothelioma patients and to increase their life expectancy. For sure, the continuation of studies according to the projects illustrated will hep to affirm the efficacy of the treatment and to further clarify its anticancer mechanism.