654. Oncolytic Vesicular Stomatitis Virus Retargeted to the Tumor Stem Cell Marker CD133

Therapy resistance and tumor recurrence are often linked to cancer stem cells (CSCs) which represent a minor proportion of highly refractory cancer-propagating cells within a tumor. A putative marker of CSCs is CD133 (prominin-1) which has been suggested to define the tumorigenic population in glioma and hepatocellular cancer (HCC). Moreover, poor prognosis correlates with CD133 expression in cancer biopsies. CD133 is therefore a prime target for novel anti-tumoral strategies. We have previously developed a strategy by which the envelope protein complex of oncolytic measles virus (MV) can be engineered to use CD133 as receptor for cell entry. Notably, MV-CD133 was more effective in killing tumors than non-targeted MV when treating tumors with a high percentage of CD133-positive cells (Bach et al., 2013; Can Res 73, 865). We have meanwhile extended the receptor usage of MV-CD133 to CD46 to effectively infect both CD133-negative and -positive tumor cells. Moreover, to take advantage of the faster replication kinetics and superior cytotoxic activity of the vesicular stomatitis virus (VSV), we used the MV envelope glycoproteins to develop hybrid viruses. The resulting oncolytic virus VSV-CD133 is deleted for its glycoprotein gene G and instead equipped with the mutated MV hemagglutinin (H) and fusion (F) glycoproteins displaying a single-chain antibody (scFv) specific for CD133. The data show that VSV-CD133 infects CD133-positive tumor cells as selectively as MV-CD133, while MV-CD133/CD46 in addition infected CD133−/CD46+ tumor cells. We further studied the cytotoxic activity of VSV-CD133 compared to its MV counterpart. Even though both were effective at killing tumor cells, VSV-CD133 induced cell death more rapidly and at lower MOI than MV-CD133. In a mouse tumor model with subcutaneously transplanted HuH7 cells VSV-CD133 reduced the tumor burden more efficiently than MV-CD133 or MV-CD133/CD46. Most importantly, this increase in efficacy did not come at the expense of safety, as CD133+ human hematopoietic stem cells (HSCs) were neither susceptible to infection nor impaired in growth and differentiation into hematopoietic lineages. Ongoing studies will determine whether the superior oncolytic effects of VSV-CD133 translate into prolonged survival in a mouse model with orthotopically transplanted human primary glioblastoma cells.