1. ¹Cancer Gene Therapy Group, Molecular Cancer Biology Program and Haartman Institute, University of Helsinki, Helsinki, Finland
2. ²Department of Oncology and HUSLAB Laboratory of Transplantation Pathology, Helsinki University Central Hospital, Helsinki, Finland
3. ³Department of Obstetrics and Gynecology, Duesseldorf University Medical Center, Heinrich-Heine University, Germany
4. ⁴Biostatistics and Bioinformatics Unit, Comprehensive Cancer Center, University of Alabama at Birmingham, Birmingham, AL, USA
5. ⁵Department of Obstetrics and Gynecology, Helsinki University Central Hospital, Helsinki, Finland

Correspondence: Dr A Hemminki, Cancer Gene Therapy Group, Molecular Cancer Biology Program and Haartman Institute, University of Helsinki, PO Box 63, 00014 Helsinki, Finland. E-mail: akseli.hemminki@helsinki.fi

Received 13 March 2007; Revised 26 April 2007; Accepted 6 May 2007; Published online 5 July 2007.

Abstract

Arming oncolytic adenoviruses with therapeutic transgenes and enhancing transduction of tumor cells are useful strategies for eradication of advanced tumor masses. Herpes simplex virus thymidine kinase (TK) together with ganciclovir (GCV) has been promising when coupled with viruses featuring low oncolytic potential, but their utility is unknown in the context of highly effective infectivity-enhanced viruses. We constructed Ad5/3-24-TK-GFP, a serotype 3 receptor-targeted, Rb/p16 pathway-selective oncolytic adenovirus, where a fusion gene encoding TK and green fluorescent protein (GFP) was inserted into 6.7K/gp19K-deleted E3 region. Ad5/3-24-TK-GFP killed ovarian cancer cells effectively, which correlated with GFP expression. Delivery of GCV immediately after infection abrogated viral replication, which might have utility as a safety switch. Due to the bystander effect, killing of some cell lines in vitro was enhanced by GCV regardless of timing. In murine models of metastatic ovarian cancer, Ad5/3-24-TK-GFP improved antitumor efficacy over the respective replication-deficient virus with GCV. However, GCV did not further enhance efficacy of Ad5/3-24-TK-GFP in vivo. Simultaneous detection of tumor load and virus replication with bioluminescence and fluorescence imaging provided insight into the in vivo kinetics of oncolysis. In summary, TK/GCV may not add antitumor activity in the context of highly potent oncolysis.