Lamivudine Therapy of WHV-Infected Woodchucks

Abstract

Hepatitis B viruses establish a chronic, productive, and noncytopathic infection of hepatocytes. Viral products are produced by transcription from multiple copies (5-50) of covalently closed circular (ccc) viral DNA. This cccDNA does not replicate, but can be replaced by DNA precursors that are synthesized in the cytoplasm. The present study was carried out to determine if long-term treatment with an inhibitor of viral DNA synthesis would lead to loss of virus products, including cccDNA, from the liver of woodchucks chronically infected with woodchuck hepatitis virus. Viral DNA synthesis was inhibited with the nucleoside analog, lamivudine (2'-deoxy-3'-thiacytidine). Lamivudine treatment produced a slow but progressive decline in viral titers in serum, to about 0.3% or less of the initial level. However, even after maintenance of drug therapy for 3-12 months, > 95% of the hepatocytes in most animals were still infected. Significant declines in the percentage of infected hepatocytes and of intrahepatic cccDNA levels were observed in only three woodchucks, two in the group receiving lamivudine and one in the placebo control group. Moreover, virus titers eventually rose in woodchucks receiving lamivudine, suggesting that drug-resistant viruses began to spread through the liver starting at least as early as 9-12 months of treatment. Three types of mutation that may be associated with drug resistance were found at this time, in a region upstream of the YMDD motif in the active site of the viral reverse transcriptase. The YMDD motif itself remained unchanged. Not unexpectedly, the lamivudine therapy did not have a impact on development of liver cancer.

Week 48 resistance surveillance in two phase 3 clinical studies of adefovir dipivoxil for chronic hepatitis B

“…Although the woodchuck animal model was used to select lamivudine-resistant woodchuck hepatitis virus, this model did not select the clinically relevant YMDD mutations in woodchuck hepatitis virus. 25 Furthermore, the previously known adefovir-resistant HIV mutations (K65R and K70E 26,27 ) did not provide guidance for searching for adefovir-resistant HBV mutations because this region of HIV RT is conserved poorly in HBV polymerase. Therefore, we entered phase 3 clinical studies without a prior knowledge of where in the HBV genome adefovir resistance mutations might emerge.…”

Early Detection of Viral Resistance by Determination of Hepatitis B Virus Polymerase Mutations in Patients Treated by Lamivudine for Chronic Hepatitis B

“…44 Furthermore, results of experiments performed in the woodchuck model have shown that early therapeutic intervention may be required to prevent or delay the occurrence of hepatocellular carcinoma via a decrease in hepatocyte turnover. 45 Although this was not the major aim of this retrospective study, we have analyzed the effect of famciclovir and interferon therapy on viral replication in patients with lamivudine resistance. First, we found that famciclovir had no significant effect on viral DNA levels in these patients.…”

Repopulation of mouse liver with human hepatocytes and in vivo infection with hepatitis B virus

“…3 Chimpanzees are the only animal species infectable with HBV, 4,5 but studies with these animals and evaluation of antiviral therapies are severely restricted because of their limited availability and high costs. Animal models based on HBV-related hepadnaviruses, such as woodchuck and Pekin duck hepatitis B viruses, are often used for assessment of antiviral drugs [6][7][8] and have provided important information about factors involved in establishment of virus infection, viral persistence, and hepatocarcinogenesis. [9][10][11][12][13][14] However, woodchucks are relatively large animals of outbred origins that are difficult to handle in many laboratories, and chronic hepadnavirus infection in birds does not lead to cancer.…”