| Summary: | <p>This thesis describes the design of a virotherapy strategy capable of destroying both breast cancer vasculature and tumour cells, using an oncolytic adenovirus expressing angiogenesis-regulating proteins. Five oncolytic adenoviruses were compared to identify the best virotherapy agent for breast cancer, including measurement of cytotoxicity <em>in vitro</em>, and replication, intra-tumoural spread and anticancer efficacy <em>in vivo</em>. The viruses tested were Ad-dl922-947 (targets G1-S checkpoint defects); Ad-Onyx-015 and Ad-Onyx-017 (target p53/mRNA nuclear export defects); Ad-vKH1 (targets Wnt pathway defects) and AdEHE2F (targets estrogen receptor/G1-S checkpoint/hypoxia signalling defects).</p> <p>AdEHE2F demonstrated optimal oncolytic activity and selectivity against breast cancer, accordingly this virus was engineered to express potent regulatory angiogenic proteins, namely soluble Flt1 and soluble Delta like-4 (Dll4). sFlt1 is the soluble extra-cellular domain of VEGFR1 and binds to and sequesters VEGF-A, thereby preventing VEGFR2 stimulation which is crucial to trigger angiogenesis. sDll4 is the soluble extracellular domain of Dll4 and has been previously shown to block Dll4/Notch signalling. Dll4/Notch signalling increases a chaotic and non-functional angiogenesis which ultimately delays tumour growth. Importantly, VEGF and Dll4 are the only angiogenesis genes reported to be haploinsufficient in vascular development and both have been shown to have a good anti-tumour effect.</p> <p>sFlt1 and sDll4 genes were substituted for the viral genes E3 6.7K/gp19K of AdEHE2F, thereby using endogenous adenoviral machinery to drive production. The activities of AdEHE2F viruses expressing either sFlt1 or sDll4 were compared <em>in vitro</em> and <em>in vivo</em>. sFlt1 (expressed from AdEHE2F) inhibited endothelial cell proliferation and sprouting whereas sDll4 increased proliferation and branching <em>in vitro</em>. <em>In vivo</em> AdEHE2F expressing sFlt1 or sDll4 both showed superior anticancer activity compared to parental AdEHE2F, indicating at least additive efficacy between virotherapy and regulatory angiogenic approaches.</p>
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