Characterization of herpes simplex virus 1 strains as platforms for the development of oncolytic viruses against liver cancer.

Background: Diverse oncolytic viruses (OV) are being designed for the treatment of cancer. The characteristics of the parental virus strains may influence the properties of these agents. Aims: To characterize two herpes simplex virus 1 strains (HSV-1 17syn + and HFEM) as platforms for virotherapy against liver cancer. Methods: The luciferase reporter gene was introduced in the intergenic region 20 locus of both HSV-1 strains, giving rise to the Cgal-Luc and H6-Luc viruses. Their properties were studied in hepatocellular carcinoma (HCC) cells in vitro. Biodistribution was monitored by bioluminescence imaging (BLI) in athymic mice and immune-competent Bab/c mice. Immunogenicity was studied by MHC-tetramer staining, in vivo killing assays and determination of specific antibody production. Intratumoural transgene expression and oncolytic effect were studied in HuH-7 xenografts. Results: The H6-Luc virus displayed a syncytial phenotype and showed higher cytolytic effect on some HCC cells. Upon intravenous or intrahepatic injection in mice, both viruses showed a transient transduction of the liver with rapid relocalization of bioluminescence in adrenal glands, spinal cord, uterus and ovaries. No significant differences were observed in the immunogenicity of these viruses. Local intratumoural administration caused progressive increase in transgene expression during the first 5 days and persisted for at least 2 weeks. H6-Luc achieved faster amplification of transgene expression and stronger inhibition of tumour growth than CgalLuc, although toxicity of these non-attenuated viruses should be reduced to obtain a therapeutic effect. Conclusions: The syncytial H6-Luc virus has a strong oncolytic potential on human HCC xenografts and could be the basis for potent OV. Oncolytic viruses (OV) are emerging as promising options for the treatment of cancer, especially if they are used in combination with standard therapies or if they are adapted as vectors to deliver therapeutic genes. Herpes simplex virus type 1 (HSV-1) is an interesting platform for the development of OV, because of its wide cellular tropism, its potent cytolytic effect and its large DNA genome, which allows incorporation of foreign material of considerable size (1). Wild type HSV-1 is a human pathogen that usually causes self-limited skin lesions, but it has the potential to produce life-threatening diseases such as herpetic encephalitis. For safety reasons, early generation HSV-1 OV were based on attenuated viruses with deletions in one or both copies of genes implicated in neurovirulence, typically c134.5 (2, 3). In addition, the lack of c134.5 confers certain cancer specificity because it is necessary to counteract the early antiviral responses in normal cells. Preferential replication in tumours can also be obtained by selective mutation of certain viral genes such as ribonucleotide reductase or thymidine kinase that can be partially complemented in cancer cells, but not in normal resting cells (4–6). Apart from these modifications, the intrinsic properties of the parental HSV-1 strains can influence