Development of a second-generation oncolytic Herpes simplex virus expressing TNFα for cancer therapy

Abstract

Background: Tumour necrosis factor alpha (TNFα) therapy is a promising anti-cancer treatment when combined with radiotherapy due to as potent radio sensitising effects, but systemic toxicity has limited its clinical use. Previously, non-replicative adenovirus vectors have been used to deliver TNFα directly to the tumour, including under the control of a radiation sensitive promoter. Here, we have used an ICP34.5 deleted, oncolytic herpes simplex virus (HSV) for delivery to increase expression levels and spread through the turnout, and the use of the US11 true late HSV promoter to limit expression to where the virus replicates, i.e. selectively in meaner tissue. Methods: TNFα expression under the CMV or US11 promoter was compared on cell lines CT26, BHK and Fadu. To further compare the activities of the promoters, expression of human TNFα was analysed in the presence and absence of acyclovir- an inhibitor of viral DNA replication and on HSV/ICP34.5- non-permissive cell line 3T6. The in vivo efficacy and toxicity of TNFα viruses were compared using A20 double flank tumour model in Balb/C mice and Fadu tumour model in nude mice. Results: The results demonstrated that the US11 promoter significantly reduced and delayed TNFα, expression as computed to use of the CMV promoter, especially in non-permissive cells or in the presence of acyclovir. Despite the reduced and more selective expression levels, US11 driven TNFα showed improved anti-turnour effects compared to CMV driven TNFα, and without the toxic side effects. Conclusions: This approach is therefore beneficial in increasing localised TNFα expression as compared to the use of non-replicative approaches, and combines the effects of TNFα, with oncolytic virus replication which is expected to further enhance the efficacy of radiotherapy in a combined treatment approach. Copyright © 2007 John Wiley & Sons, Ltd.