Abstract 1381: The vascular targeted and antitumor effects of gene electrotransfer of plasmid silencing endoglin with tissue specific and constitutive promoter

Endoglin, the transforming growth factor-β (TGF-β) co-receptor, mediates proliferation, differentiation and migration of endothelial cells forming neovasculature. It is promising target for vascular targeted therapies for the treatment of cancer, although its specific, safe and long-lasting targeting remains the challenge. One of the options for targeted and prolonged silencing is gene electrotransfer (GET) of plasmid DNA encoding shRNA against endoglin. In our study we used two plasmid DNAs; one with tissue specific promoter for endothelial cells (TS plasmid) and the other with constitutive promoter (CON promoter). In vitro, we evaluated the transfection efficacy using flow cytometry measurement of transfected cells and determined the vascular targeted effects by tube formation assay. The therapeutic potential of the GET of plasmids and comparison of theirs efficacies in vitro was obtained by measuring tumor growth and by analyzing histological sections for determining area of necrosis and a number of activated blood vessels. In vitro, we demonstrated the tissue specificity of TS plasmid on several cell lines, and the antiangiogenic efficacy of GET of either of both plasmids, as reduced tube formation of 2H11 endothelial cells. In vivo, on a murine mammary TS/A tumor model, we demonstrated good antitumor effect of GET of either of both plasmids in treatment of smaller tumors in avascular phase of growth, as well as on bigger tumors, already well vascularized, possibly due to both, the antiangiogenic and vascular disrupting effect. In order to support that, the histological analysis has demonstrated an increase in necrosis and a decrease in the number of blood vessels in therapeutic groups. Therefore, using GET of TS plasmid we were able to demonstrate that it is specific, safe and has quite the same efficacy as the GET of CON plasmid. Therefore, our approach can represent a novel alternative to other therapeutic approaches that aim at silencing endoglin, which represents also an alternative target in VEGF resistant (unresponsive) tumors. Citation Format: Monika Stimac, Tanja Dolinsek, Ursa Lampreht, Maja Cemazar, Gregor Sersa. The vascular targeted and antitumor effects of gene electrotransfer of plasmid silencing endoglin with tissue specific and constitutive promoter. [abstract]. In: Proceedings of the 106th Annual Meeting of the American Association for Cancer Research; 2015 Apr 18-22; Philadelphia, PA. Philadelphia (PA): AACR; Cancer Res 2015;75(15 Suppl):Abstract nr 1381. doi:10.1158/1538-7445.AM2015-1381