RNA Interference Inhibits HBV Replication

拉米夫定

By Karla Gale

Hepatitis B (HBV) viral RNA interference reduced the ability of HBV to replicate in mice, scientists in California report in the advance issue of Nature Biotechnology, published online May 12.

"We have worked for 10 years on gene therapies for hepatitis, and this is the first that I believe really looks promising," senior author Dr. Mark A. Kay of Stanford University School of Medicine, California, told Reuters Health.

RNA interference can inhibit viral replication in cell culture and target viral sequences in vivo, but thus far no one has shown the ability of this technique to prevent viral replication in vivo, Dr. Kay and associates explain.

When they transfected cultured human hepatoma cells with plasmids expressing one of seven short hairpin RNAs (shRNA) directed against sequences conserved among major HBV genotypes, all but one significantly reduced the amount of HBV surface antigen in culture. The most effective shRNA reduced antigen expression by 94.2% after 8 days.

The researchers transfected mice with the plasmid that most reduced HBV surface antigen in culture. In immunocompetent mice, treatment resulted in 77% less HBV RNA transcripts in liver compared to controls, while RNA was reduced 92% in immunocompromised mice. Treatment reduced replicated HBV DNA to undetectable levels.

The differences between immunocompetent and immunocompromised mice were "not substantial," Dr. Kay said. However, "there is the possibility of a synergistic effect between the host immune response and shRNA," he added.

In mice lacking B and T lymphocytes, plasmid treatment reduced serum levels of HBV surface antigen by 88% at day 4.

Dr. Kay said that he does not expect that an immune response would be generated to interfering RNA, and his group observed no obvious toxicity in plasmid-treated mice.

He suggested three possible scenarios for RNA silencing in hepatitis B infection. "In the best scenario, the body is purged of virus and cured." Another possibility is a significant reduction in viral load, "which may buy someone 20 or 30 more years before developing liver disease."

He also believes that combining RNA interference treatment with drug therapy would provide a synergistic effect.

"In theory, any viral disorder" could be treated in this manner, he added, noting that another research group is experimenting with RNA silencing for treatment of HIV.

He and his associates now plan to transfect small mammals using viral vectors instead of plasmids. If successful, "I think 2 to 3 years would be a reasonable time frame" for initiating phase I trials in humans.