ATPS-70USING CYSTEINE KNOT PROTEINS TO RETARGET AN ONCOLYTIC VIRUS TO NOVEL CELL SURFACE ANTIGENS

Abstract

INTRODUCTION: Modified measles virus (MV) is an effective oncolytic virus and is currently being investigated in clinical trials for various cancer types. An advantage of MV is the ease of retargeting the virus to a receptor of choice. We investigated the use of cysteine knot proteins (CKP) to direct MV activity. CKP are short polypeptides that bind their targets with high affinity. A library of these proteins has been made, and a CKP that binds both αv-β3 and αv-β5 integrins with single digit nanomolar affinity has been isolated. We have used this CKP to target MV to the integrins. METHODS: We made a modified MV by inserting the integrin-binding CKP coding sequence at the carboxy-terminus of a mutated H protein that does not bind to its normal receptors (MV-CKP). We tested the virus for specificity for the integrins by assessing cell killing and MV replication in vitro. RESULTS: MV-CKP killed and replicated in U87 glioma cells, which express the target integrins. The virus did not kill and did not replicate in cells in which intregrin expression was knocked down with an αv antisense lentivirus. MV-CKP activity was blocked by echistatin, an integrin binding peptide. When the CKP was cleaved from the virus at an inserted protease site, virus activity was abrogated. CONCLUSIONS: These results indicate that CKP can be used to selectively target MV. Because the integrins targeted are expressed by tumor endothelium and not by normal endothelium and because the CKP used has been shown to localize to tumor when injected IV, MV-CKP may be effective as IV therapy, a major step forward in the use of MV. In addition, the CKP library can be screened for other CKPs of interest. Lastly, the use of CKP to target viruses is applicable to many viruses other than MV.