Targeting of adenovirus to endothelial cells by a bispecific single-chain diabody directed against the adenovirus fiber knob domain and human endoglin (CD105)

The use of adenoviruses for antivascular cancer gene therapy is limited by their low transduction efficiency for endothelial cells. We have developed a recombinant bispecific antibody as a molecular bridge, linking the adenov irus capsid to the endothelial cell surface protein endoglin, for vascular targeting of adenoviruses. Endoglin (CD105), a component of the transformin g growth factor beta receptor complex, represents a promising target for an tivascular cancer therapy. Endoglin is expressed predominantly on endotheli al cells and is upregulated in angiogenic areas of tumors. We isolated sing le-chain Fv fragments directed against human endoglin from a human semisynt hetic antibody library. One of the isolated scFv fragments (scFv C4) bound specifically to various proliferating primary endothelial cells or cell lin es including HUVEC, HDMEC, HMVEC, and HMEC. ScFv C4 was therefore used to c onstruct a bispecific single-chain diabody directed against endoglin and th e adenovirus fiber knob domain (scDb EDC-Ad). This bispecific molecule medi ated enhanced and selective adenovirus transduction of HUVECs, which was in dependent from binding to the coxsackievirus and adenovirus receptor (CAR) and alpha (v)-integrins. Thus, adenovirus infection was redirected to a new cellular receptor (CD105) and cell entry pathway. These results demonstrat e the utility of bispecific single-chain diabodies, which can be produced i n large quantities in bacteria, for the retargeting of adenoviruses in canc er gene therapy.