Herpes Simplex Virus Type 1 Mutant Vectors in Vivo Expression Mediated by Replication-conditional, Oncolytic Positron Emission Tomography-based Imaging of Transgene

ABSTRACT To evaluate the efficiency of gene delivery in gene therapy strategies formalignant brain tumors, it is important to determine the distribution andmagnitude of transgene expression in target tumor cells over time. Here,we assess the time- and vector dose-dependent kinetics of recombinantherpes simplex virus (HSV)-1 vector-mediated gene expression and vectorreplication in culture and in vivo by a recently developed radiotracermethod for noninvasive imaging of gene expression (J. G. Tjuvajev et al.,Cancer Res., 55: 6126–6132, 1995).The kinetics of viral infection of rat 9L gliosarcoma cells by thereplication-conditional HSV-1 vector, hrR3, was studied by measuring theaccumulation rate of 2-[ 14 C]-fluoro-5-iodo-1-b- D -arabinofuranosyl-uracil(FIAU), a selective substrate for viral thymidine kinase (TK). The level ofviral TK activity in 9L cells was monitored by the radiotracer assay toassess various vector doses and infection times, allowing vector replicationand spread. In parallel, viral yields and levels of Escherichia coli b-galactosidase activity were assessed quantitatively. To study vector repli-cation, spread and HSV-1-tkand lacZ gene coexpression in vivo, first- orsecond-generation recombinant HSV-1 vectors (hrR3 or MGH-1) wereinjected into s.c. growing rat 9L or human U87DEGFR gliomas in nuderats at various times (8 h to 8 days) and at various vector doses [1 3 10