| Summary: | Pancreatic ductal adenocarcinoma (PDA) is one of the leading causes of cancer-related deaths worldwide and the development of new treatment strategies for patients suffering from PDA is of crucial importance. Virotherapy uses natural or engineered oncolytic viruses (OVs) to selectively kill tumour cells. Although various OVs are being investigated as agents for pancreatic cancer treatment, due to the genetic heterogeneity of PDA cells and their consequent mixed permissiveness to viruses, virotherapy should not rely on a short list of possible candidates. As such, preliminary data from our group demonstrating the potent pro-apoptotic effect of the low pathogenicity avian influenza virus (LPAIV) H7N3 A/turkey/Italy/2962/03 in PDA cells, previously established to be resistant to other OVs, suggested that this virus might be effective against specific sub-classes of pancreatic cancer. Therefore, in the present studies, the avian isolate was selected for further development. Preferential replication of the H7N3 virus in IFN-deficient cells, a trait of the majority of PDA cell lines, was improved by the truncation of the viral NS1 protein (NS1-77), which compromised the virus' ability to counteract the IFN-mediated antiviral response and, as bystander effect, enhanced the killing of uninfected cancer cells by stimulating IFN expression from healthy cells. Introduction of L75H mutation within the mitochondrial targeting sequence (MTS) of the viral protein PB1-F2 increased virus replication in permissive IFN deficient cells and also lessened PB1-F2's ability to counter the IFN response induced by overexpression of mitochondrial antiviral signalling protein (MAVS), further enhancing selectivity for PDA cells. Substitution of the genes expressing avian surface antigens haemagglutinin (HA) and neuraminidase (NA) with those of the well characterized human H1N1 A/Puerto Rico/8/1934 virus eliminated the potential risk of reassortment of the H7N3 virus with circulating human influenza strains that might result in a new pandemic virus, nonetheless, preserving the oncolytic properties of the parental isolate. Finally, to promote anti-tumour immunity, the newly generated PR8 H1/N1-2962 NS1-77 virus was 'armed' to express the human granulocyte-macrophage colony-stimulating factor (GM-CSF) gene during infection. Taken together our data demonstrate the possibility to select an IAV from the avian reservoir on the basis of its strain-specific oncolytic skills in PDA cells and, through engineering, improve its selectivity, safety and tumour debulking activity.
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