A138

Oncolytic virus therapy is an area in experimental cancer therapy that is under active investigation. A wide variety of viruses have shown huge potent oncolytic activity against human tumors in cell and animal models without major side effects. Several strains have already being tested in clinical trials in patients. Virotherapy is making promising progress for the treatment of malignancies. Nonetheless, when used in patients, the response rate to oncolytic virus is low. One of the main ways to increase oncolytic capacity is to refuse of excessive attenuation and to use the wild type of oncolytic strains. Naturally occurring oncolytic viruses (OVs) have shown their high cancer-targeted antitumor effects with selectively replication and destroying tumor cells while sparing normal cells, because of defects in IFN-signaling pathways in tumor cell lines. Newcastle disease virus (NDV) is one of the promising therapeutic agent for virotherapy. It belongs to avian paramyxovirus (APMV-1) that is able to infect over 240 species of birds and induce severe disease. However, NDV is not a human pathogen. Newcastle disease virus exhibits effectively oncolytic activity in a range of tumors in pre-clinical and clinical studies. We have previously reported in vitro oncolytic effects of three wild NDV strains. Here we demonstrate data that describe oncolytic capacity NDV collection gathered in 2008–2014, Russia. Antitumor effect of NDV strains on a panel of tumor human cell lines (HCT116, MCF7, A549, HeLa, Skbr, H1299) were investigated. Cell viability was examined over 96 hours by MTT assay. Dose-dependent cell cytotoxicity was demonstrated. In vitro study shows the capacity of several wild NDV strains to lyse tumor cell lines. Two strains of them have significant strong oncolytic activity on human tumor cells of various histogenesis. Recent work in our research also describes the results of in vivo experiments. One of them consists of comparing the efficacy of NDV strain to exhibit specific oncolytic activity in C57Bl/6 mice on subcutaneous murine tumors (LLC and B16) . Our results show that both intravenous and intratumoral injections with multiple doses of wild NDV strain lead to survival prolongation in B16- and LLC-bearing mice and prevent tumor development. We demonstrate antitumor activity of NDV/Altai/pigeon/770/2011 against murine KREBS-2 solid tumor in preclinical model on immunocompetent BALB/c mice. Recently we have demonstrated that NDV/Altai/pigeon/770/2011 can destroy murine KREBS-2 cells in vitro. Moreover, in pilot study we have shown that intratumoral NDV injections decrease of tumor volume and result in complete regression of KREBS-2 tumor in MRI images. Here we test intratumoral administration of NDV and show suppression of Krebs-2 tumor growth in intramuscularly allograft model (2.6-fold less size that in untreated group). Importantly, spread of the virus causes significant tumor necrosis in Krebs-2 tumors. By 20 days after virotherapy, widespread necrosis of NDV-treated tumor is observed. We describe that the vast fields of necrosis in NDV-treated group are the results of formation of ischemic foci in tumor tissue with the rapid development of tumor node and slow neoangiogenesis. Histological examinations and morphometric analysis of tumors in NDV-treated and control groups show that the number of blood vessels including the newly formed in the untreated group is significantly higher than in the experimental group. Immunohistochemical staining (CD34, VEGFR) shows that blood vessels in tumor tissue is strongly reduced to 20 days post-treatment and neoangiogenesis progresses in untreated tumor tissue. Thus, results suggest that vascular disruption in the NDV-treated group indicates the virus ability to directly or indirectly affect tumor angiogenesis and regulate tissue trophism in that way. Understanding how and in which step this effect occurs may provide capacity to use oncolytic NDV strains for therapeutic benefit.