The (-) enantiomer of cis-5-fluoro-1l-[2-(hydroxymethyl)-1,3-oxathiolan-5-yl]cytosine [(-)-FTC)], a substituted oxathiolane compound with anti-hepatitis B virus activity in vitro, was assessed for its efficacy in woodchucks with naturally acquired woodchuck hepatitis virus (WHV) infection. Pharmacokinetics and in vitro anabolism were also determined. (-)-FTC was anabolized to the 5'-triphosphate in a dose-related fashion, reaching a maximum concentration at about 24 h in cultured woodchuck hepatocytes. Following administration of a dose of 10 mg/kg of body weight intraperitoneally (i.p.), the clearance of (-)-FTC from plasma was monoexponential, the terminal half-life was 3.76 +/- 1.4 h, and the systemic clearance was 0.12 +/- 0.06 liters/h/kg. The antiviral efficacy of (-)-FTC in the woodchuck model was assessed by quantitation of serum WHV DNA levels and by WHV particle-associated DNA polymerase activity at two dosages, 30 and 20 mg/kg given i.p. twice daily (b.i.d.), respectively. The level of WHV DNA in serum was reduced 20- to 150-fold (average, 56-fold) in the 30-mg/kg-b.i.d. treatment group and 6- to 49-fold (average, 27-fold) in the 20-mg/kg-b.i.d. treatment group. Viral DNA polymerase levels diminished accordingly. One week after treatment was discontinued, WHV levels returned to pretreatment levels in both studies. These animals were biopsied before and following treatment with 30 mg of (-)-FTC per kg. Their livers were characterized by a mild increase in cytoplasmic lipid levels, but this change was not associated with altered liver enzyme levels. Serum chemistry and hematology results were within the normal ranges for all treated animals. We conclude that (-)-FTC is a potent antihepadnaviral agent and that it has no detectable toxic effects in woodchucks when given for up to 25 days. Further development of (-)-FTC as an anti-hepatitis B virus therapy for patients is warranted.

Flow cytometric analysis of the ploidy of normal and neoplastic hepatocyte nuclei obtained from adult woodchucks, a model of human hepadnavirus-induced hepatocellular carcinoma, was performed. All 36 samples of nuclei from non-neoplastic liver from woodchuck hepatitis virus-infected or uninfected liver were diploid, indicating that age-related nuclear polyploidization does not occur in this species, unlike other rodents. Individual or multiple hepatic neoplasms were obtained from each of 14 woodchuck hepatitis virus-infected woodchucks. Nineteen samples of hepatocellular carcinoma and eight adenomas were examined. Aneuploid nuclei were detected in 10 of the hepatocellular carcinomas and three of the adenoma samples. Similar DNA indexes, ranging from 1.11 to 1.22, were found in 7 of the 10 aneuploid HCCs and all 3 aneuploid adenomas. Nine of the 19 hepatocellular carcinoma samples and 5 of the 8 adenomas were diploid. Four of the diploid hepatocellular carcinomas had increased proportions of tetraploid nuclei. The presence of aneuploid nuclei was not related to histological appearance of the neoplasms or serum gamma-glutamyltranspeptidase levels. Because none of the hepatocellular carcinomas metastasized, the presence of aneuploidy could not be related to biological behavior. We determined the proportion of uninucleate and binucleate hepatocytes in hepatocellular carcinoma and nonneoplastic liver. Approximately 7% of hepatocytes were binucleate in nonneoplastic liver from woodchuck hepatitis virus-infected and uninfected liver. Only 2% of malignant hepatocytes were binucleate. The results of this study indicate that aneuploidy is a common change in hepatic neoplasms from woodchuck hepatitis virus-infected woodchucks.