Fully retargeted measles viruses for cancer therapy Free

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Attenuated replication-competent Edmonston lineage strains of measles virus (MV-Edm) have proven anti-tumor activity against xenograft models of human multiple myeloma, ovarian cancer, lymphoma and glioma. The virus is selectively oncolytic, causing extensive lethal cell to cell fusion via CD46, which is more highly expressed on tumor cells than normal cells. However, MV-Edm retains the capacity to infect a variety of nontransformed cell types via its native receptors, CD46 and SLAM. CD46 is a ubiquitous regulator of complement activation, which is found on all human nucleated cells. SLAM (signaling lymphocyte activation molecule) is expressed only on activated T and B cells, dendritic cells and macrophages. Therefore, there is a chance that oncolytic MV-Edm may cause immunosupression, or other unwanted damage to normal tissues. One approach to avoid this risk is to engineer the viral attachment protein to ablate its natural tropisms and at the same time, redirect its specificity to interact with alternative tumor specific receptors. The measles Hemagglutinin (H) protein recognizes CD46 or SLAM, and this leads to membrane fusion triggered by the viral Fusion protein (F). We previously engineered the H protein of measles virus to restrict and retarget membrane fusion through various antibody-receptor interactions (Nakamura T. et. al., Nature Biotechnology, 2004). However, ablation of the native receptor interactions makes it difficult to grow the virus on Vero cells. To address this limitation, we have developed pseudoreceptor system “STAR”, which allows rescue and propagation of fully retargeted viruses with modified H proteins that no longer bind to the native measles receptors. The H proteins of the fully retargeted viruses are tagged with a C-terminal peptide tag comprising six histidine residues (H6). The recombinant viruses can then be grown on a Vero-αHis cell line that expresses a membrane-anchored single-chain antibody recognizing the H6 peptide. For validation of the system we rescued three fully retargeted viruses incorporating single chain antibodies against CD38, epidermal growth factor receptor (EGFR), or EGFR mutant vIII, each one tagged with the H6 peptide and displayed at the C-terminus of an ablated H protein. These retargeted viruses propagated efficiently on Vero-αHis cells (but not on parental Vero cells) and efficiently entered target cells through their respective targeted receptors in vitro and in vivo, but not through CD46 and SLAM. When administered intratumorally or intravenously to mice bearing human CD38 or EGFR-positive human tumor xenografts, the targeted viruses demonstrated specific receptor-mediated anti-tumor activity. Fully retargeted MV-Edms may prove to be more selective and safer oncolytic agents than wild-type MV-Edm. Also, our data suggest that receptor choice is not a significant limitation for targeting oncolytic measles viruses and that it should therefore be possible to target a variety of tumors.