Abstract
Transcriptional targeting of viral genes is a promising strategy to achieve tumor-specific replication of oncolytic viruses. Due to its natural tropism, herpes simplex virus type 1 (HSV-1) may be an ideal tool for oncolytic therapy of brain tumors such as malignant glioblastoma. To study whether glioma-specific gene expression can be accomplished within the HSV-1 genome, four cellular regulatory elements were exemplarily studied. Whereas the human telomerase reverse transcriptase (hTERT) and survivin promoters and the nestin and vascular endothelial growth factor A (VEGF-A) enhancers displayed pronounced glioma specificity after plasmid transfection, only the nestin enhancer conferred a certain selectivity for glioma cells and notable activity when transferred into the viral genome. The nestin enhancer was also found to be highly useful for tumor cell-specific expression of a therapeutically relevant gene (interleukin-2) when tested in combination with the hTERT or simian virus 40 (SV40) early promoter in the HSV-1 genome. Because activity of the chosen promoter in a tumor is a prerequisite for the successful application of an oncolytic virus, we examined whether the activity of a promoter can be deduced from the amounts of cellular mRNA or protein expressed under its control. We found little correlation between promoter activity and mRNA levels of the corresponding gene, whereas protein expression was more closely related to promoter activity. We conclude that the cellular elements are differently regulated in the viral and cellular genomes. Mechanistic insight into the differential regulation is required to improve and refine the design of transcriptionally targeted HSV vectors.
Acknowledgements
The authors thank Yasushi Kawaguchi for providing the HSV-1 BAC as well as Maureen Murphy and Franck Schnieders for the survivin promoter reporter and the mIL2 plasmids, respectively. The authors are indebted to Darius Moharregh-Khiabani for providing primary astrocytes. They thank the members of the group, in particular Penelope Kay-Jackson, for critical reading of the manuscript and for helpful comments. This work was supported by the Wilhelm-Sander-Stiftung (grant 2004.075.1) and the Else Kröner-Fresenius-Stiftung (grant P35/04/A45/04).
Declaration of interest: The authors report no conflicts of interest. The authors alone are responsible for the content and writing of the paper.