Angiogenic response caused by oncolytic herpes simplex virus-induced reduced thrombospondin expression can be prevented by specific viral mutations or by administering a thrombospondin-derived peptide

Abstract

Wild-type (WT) herpes simplex virus (HSV) causes some pathology, such as ocular keratitis, by increasing infected tissue vascularity, possibly reflecting altered angiogenic factor expression in infected cells. Oncolytic HSVs possess specific mutations enabling selective replication in tumor cells. We investigated whether this ability to enhance infected tissue vascularity is retained in oncolytic HSV, which could be an undesirable effect of oncolytic HSVs that may need to be addressed when treating tumors with oncolytic HSVs. s.c. tumors derived from U87 human glioma cells in athymic mice were treated with oncolytic HSVs G207 or 647Δ in the presence or absence of a recombinant protein composed of the three type-1 repeats (3TSR) of thrombospondin-1 (TSP-1). Real-time reverse transcription-PCR and Western blot of infected cultured cells measured angiogenic factor expression. Microvessel density was assessed using immunofluorescence. G207-treated U87 s.c. tumors had elevated microvessel densities compared with saline- and G47Δ-treated tumors, and G207 treatment caused delayed tumor growth resumption. G207-infected U87 and U373 cells exhibited reduced protein, not mRNA, expression of angiogenesis inhibitors TSP-1 and thrombospondin-2 (TSP-2). 3TSR restored the G207-treated tumor microvessel density to the low level of G47Δ-treated tumors and prevented delayed growth resumption. Oncolytic HSV G207 thus retains the ability of WT HSV to increase infected tissue vascularity. In infected tumors, this increased vascularity is mediated by reduced TSP-1 and TSP-2 levels and causes delayed tumor growth resumption. Incorporating viral mutations, such as those seen in G47Δ or administering thrombospondin-derived peptides, counteracts the angiogenic effect of oncolytic HSV and should be considered when designing oncolytic HSV therapies. ©2007 American Association for Cancer Research.