Short hairpin RNA-expressing oncolytic adenovirus-mediated inhibition of IL-8: effects on antiangiogenesis and tumor growth inhibition

RNA interference, due to its target specificity, may be highly effective as a novel therapeutic modality, but direct delivery of synthetic small interfering RNA still remains a major obstacle for this approach. To induce long-term expression and specific gene silencing, novel delivery vector system is also required. In this study, we have generated an efficient oncolytic adenovirus ( Ad)- based short hairpin ( shRNA) expression system (Ad-Delta B7- U6shIL8) against IL-8, a potent proangiogenic factor. To demonstrate IL-8- specificity of this newly engineered Ad-based shRNA, we also manufactured replication- incompetent Ads (Ad-Delta E1- CMVshIL8 and Ad Delta E1- U6shIL8) under the control of the cytomegalovirus (CMV) and U6 promoters, respectively. Ad- Delta E1- U6shIL8 was highly effective in reducing IL- 8 expression, and was much more effective in driving IL- 8- specific shRNA than the CMV promoter- driven vector. The reduced IL- 8 expression then translated into decreased angiogenesis in vitro as measured by migration, tube formation and rat aortic ring sprouting assays. In addition to its effect on endothelial cells, Ad-Delta E1- U6shIL8 also effectively suppressed the migration and invasion of cancer cells. In vivo, intratumoral injection of Ad-Delta B7- U6shIL8 significantly inhibited the growth of Hep3B and A549 human tumor xenografts. Histopathological analysis of Ad-Delta B7- U6shIL8- treated tumors revealed an increase in apoptotic cells and a reduction in vessel density. Finally, Ad- Delta B7- U6shIL8 was also shown to inhibit the growth of disseminated MDA- MB- 231 breast cancer metastases. Taken together, these findings demonstrate the utility and antitumor effectiveness of oncolytic Ad expressing shRNA against IL-8.