The use of so-called 'suicide' genes to activate prodrugs approach but reveal that hepatic expression of HSVtk, both has been effective in animal models for several solid tumor in tumor bearing and in tumor-free rats, provokes severe types and is now in phase I and II clinical trials. We have liver dysfunction and mortality upon GCV administration. exploited adenovirus vectors (Ad) for transfer and These data show, that in contrast to the common assumpexpression of the herpes simplex virus thymidine kinase tion, normally non-mitotic tissues too, can be affected by (HSVtk) gene to render rat colorectal liver metastases adenovirus-mediated HSVtk transfer and subsequent GCV sensitive to the anti-herpetic agent ganciclovir (GCV). The treatment. Given the hepatotropic nature of systemically efficacy and toxicity of this enzyme-prodrug combination administered adenovirus type 2-and 5-derived vectors, it were tested after in situ transduction of rat colorectal tumor will be essential to monitor liver functions of patients cells and after intraportal administration of the vector included in all gene therapy trials involving adenoviral vecAd.CMV.TK. Our results demonstrate the validity of the tors with the HSVtk gene.

Targeted gene delivery is essential for gene therapy involvPerfusion with chelating agents (1 mM EGTA, or 2 mM ing in vivo gene transfer. In the present study we analyzed EDTA) prior to the administration of the vector increased the efficiency and tissue-specificity of gene transfer into the the efficiency to at least 40%. Similar efficiencies were liver with recombinant adenoviruses. Adenovirus vectors obtained in experiments with liver lobes of Rhesus monkcarrying the E. coli lacZ gene (Ad.RSV.␤-gal) and the firefly eys. In vivo administration of AdCMV-luc via ILP resulted luciferase gene (AdCMV-luc) as reporters were adminisin a significantly more efficient (P = 0.028) and also more tered to the liver of adult Wistar rats, either via infusion into reproducible gene transfer when compared to IPI. Although the portal vein (intraportal infusion; IPI) or via perfusion of detectable in both groups, extrahepatic luciferase the vascularly isolated liver (isolated liver perfusion; ILP).expression was considerably reduced in the ILP group. Our Ex vivo liver perfusion experiments with Ad.RSV.␤-gal data demonstrate that IPL can be used for efficient and were used to optimize the conditions for hepatic gene reproducible liver-specific gene delivery. Therefore, we transfer. Ex vivo perfusion of rat livers with 2 × 10 9 plaque think that the perfusion of vascularly isolated organs is useforming units (p.f.u.) Ad.RSV.␤-gal was sufficient to ful as a modality for the tissue-specific administration of infect about 20% of the liver parenchymal cells. recombinant adenovirus vectors.