Protease pretreatment increases the efficacy of adenovirus-mediated gene therapy for the treatment of an experimental glioblastoma model

Effective virus-mediated gene therapy For cancer will he facilitated by pro cedures that enhance the low level of gene transfer mediated by replication -deficient, recombinant viral, vectors. We found recently that protease pre treatment of solid tumors is a useful strategy for enhancing virus-mediated gene transduction in vivo. In this study, we examined the potential of pro tease pretreatment to improve the efficacy of a gene therapy strategy For p rodrug activation that depends on infection with a recombinant adenovirus e ncoding herpes simplex, virus thymidine kinase (Ad-HSV-tk). Trypsin or a di ssolved mixture of collagenase/dispase was inoculated into xenografts deriv ed from the human glioblastoma multiforme-derived cell lines, U87 or U251. Ad-HSV-tk was administered 24 h after protease pretreatment, and animals we re then treated for 10 days with ganciclovir (GCV), We found that protease pretreatment increased the efficacy of adenovirus mediated HSV-tk/GCV gene therapy in these experimental tumor models. Mice receiving Ad-HSV-tk/GCV af ter protease pretreatment demonstrated a significantly greater regression o f tumors compared with those treated with Ad-HSV-tk/GCV alone. No adverse e ffects of protease pretreatment were observed, No signs of metastasis were seen either by histological inspection of lymph nodes or by a PCR-based ana lysis of selected mouse tissues to detect human tumor cells. Our findings i ndicate that protease pretreatment may be a useful strategy to enhance the efficacy of virus-mediated cancer gene therapy.