We use lentiviral-delivered RNA interference (RNAi) to inhibit the growth of a model of primary effusion lymphoma (PEL) in vitro and in vivo. RNAi is a phenomenon allowing the sequencespecific targeting and silencing of exogenous and endogenous gene expression and is being applied to inhibit viral replication both in vitro and in vivo. We show that silencing of genes believed to be essential for the Kaposi sarcomaassociated herpesvirus (KSHV) latent life cycle (the oncogenic cluster) has a varied effect in PEL cell lines cultured in vitro, however, concomitant silencing of the viral cyclin (vcyclin) and viral FLICE (Fasassociating protein with death domainlike interleukin-1-converting enzyme) inhibitory protein (vFLIP) caused efficient apoptosis in all PEL lines tested. We demonstrate that in a murine model of PEL, lentiviral-mediated RNA interference both inhibits development of ascites and can act as a treatment for established ascites. We also show that the administered lentiviral vectors are essentially limited to the peritoneal cavity, which has advantages for safety and dosage in a therapeutic setting. This shows the use of lentiviral-mediated RNA interference in vivo as a potential therapeutic against a virally driven human cancer.
IntroductionRNA interference (RNAi) is being exploited to treat or prevent infection and as a therapeutic against cancer. 1,2 Attractive targets include foreign (eg, viral) and mutated, fused, or overexpressed genes (ie, cancer). [3][4][5] In vitro, RNAi has been shown to block infection and replication of various pathogens including human immunodeficiency virus (HIV-1), 6,7 influenza, 8 and viruses implicated in oncogenesis such as Epstein Barr virus (EBV), 9,10 hepatitis B, 11,12 hepatitis C, 13 and human papilloma virus (HPV). 14,15 In experimental in vivo models, RNAi has been shown to prevent chemical-and viral-induced hepatitis. [16][17][18] The efficient delivery of therapies that knock-down specific RNA remains one obstacle to translate RNAi into a realistic treatment option for human disease. 19 The direct delivery of antisense RNA to treat or prevent CMV retinitis is one of the few successful clinical applications thus far of RNA-targeted treatment. 20,21 Although antisense provides significantly less robust inhibition of gene expression compared to RNAi, the major problem with both therapies remains effective delivery to the site of disease. One use of RNAi is based around injecting large quantities of synthetic double-stranded RNA (dsRNA) or DNA encoding short hairpin RNA (shRNA) intravenously or using hydrodynamic transfection. 16,18 This approach is not realistic for treating human disease, except for diseases involving sites where delivery of synthetic dsRNA is more straightforward. The development of shRNA to knock-down gene expression 22,23 and the incorporation of shRNA into lentiviral- 24,25 or adenoviral-based 26,27 vectors offers the opportunity to use these vectors to target RNA efficiently in vivo. Vesicular stomatitis virus-g envelope (VSV-g)-pseudoty...