Evaluation of HSV-tk gene therapy in a rat model of chemically induced hepatocellular carcinoma by intratumoral and intrahepatic artery routes

Transfer of the herpes simplex virus-thymidine kinase (HSV-tk) gene followe d by the administration of ganciclovir (GCV) into hepatocellular carcinoma (HCC)-derived cell Lines either in vitro or transplanted into nude mice has been shown to provide a potential strategy for HSV-tk-based gene therapy o f HCC. We report herein an analysis of the antitumoral efficacy of two reco mbinant adenoviruses (Ads), Ad.CMVtk and Ad.AFPtk, in a relevant model of m ultifocal hepatic lesions induced in rats by a potent alkylating chemical c arcinogen, diethylnitrosamine. Two routes of administration of the Ad were studied: intratumoral and intrahepatic artery injections. Both recombinant Ads, Ad.CMVtk and Ad.AFPtk, express the HSV-tk gene under the control of th e early enhancer/promoter cytomegalovirus and alpha-fetoprotein regulatory gene sequences, respectively. The antitumor response was assessed by magnet ic resonance imaging and by autopsy and histological analysis following pos tmortem. Tumor growth cessation was demonstrated by magnetic resonance imag ing in large tumor nodules of size 5-8 mm treated by intratumoral administr ation of 2 x 10(9) pfu Ad.CMVtk plus i.p. treatment with GCV, We also show an antitumor efficacy in small tumor nodules of size <3 mm treated with 2 x 10(9) pfu Ad.CMVtk plus GCV by the intrahepatic artery route, albeit assoc iated with an adverse toxicity. Iii vivo targeting of the HSV-tk gene to di ethylnitrosamine-induced HCC cells with the recombinant Ad.AFPtk suppresses the hepatic toxicity in the nontumoral liver. The Lower antitumor response would argue for the use of multiple injections of such adenoviral construc ts. These observations may lead to potential approaches for designing gene therapy destined for early treatment of dysplastic nodules or advanced HCC in cirrhosis.