10th International Virology Summit
University of Pittsburgh, USA
Title: Development of retargeted ohsv vectors for systemic treatment of breast cancer
Biography: Joseph C. Glorioso
The development of safe, oncolytic (o) HSV vectors for systemic treatment of metastatic breast cancer provides an opportunity for combining virus lytic activity with the potential to induce anti-tumor immunity. Ideally oHSV should be engineered for selective infection of tumor cells and escape from neutralizing antibodies. Complete retargeting strategies both detarget the viral attachment/entry glycoprotein gD from recognition of its cognate receptors, HVEM and nectin-1, and provide gD with a novel ligand that recognizes a highly expressed tumor-associated receptors that are poorly or not expressed on non-tumor tissue. Here we present design strategies for engineered oHSV that preferentially infect and lyse breast cancer cells by recognition of GFRα1, a receptor highly expressed on a subset of estrogen receptor-positive breast cancers. We replaced the signal peptide and HVEM binding domain of gD with pre-pro-(pp)GDNF to create a GFRα1 targeting protein, gD(Y38)-GDNF, that can still bind nectin-1. Virus expressing gD(Y38)-GDNF was propagated on cells expressing nectin-1 and purified virus was shown to enter nectin-1/HVEM-deficient J1.1-2 and B78H1 cells in a GFRα1-dependent manner. U2OS cells engineered to express GFRα1 were found to support propagation of a fully retargeted derivative virus that no longer recognizes nectin-1 but selectively infects cells through recognition of GFRα1, resulting in MOI-dependent tumor cell death in vitro. Moreover, direct intratumoral injection in nude mice showed complete tumor destruction in vivo. We have discovered, however, that retargeting can reduce the efficiency of virus entry and increase sensitivity to neutralizing (VN) antibodies, both associated with reduced retargeted gD incorporation into the virus envelope. Efficient infectivity was partially restored by selective residue changes in the downstream fusogen gB. Current studies involve engineered and selected changes in the epitope structure of retargeted gD that allow escape from VN antibodies to permit efficient systemic application of oHSV for metastatic breast cancer therapy.