An experimental antiviral drug that works by a different mechanism than existing drugs has been shown to suppress hepatitis C in chimpanzees and is already being tested in human clinical trials, researchers reported Thursday.
The new agent is a so-called antisense drug that binds to RNA required by the virus for replication, preventing the virus from proliferating in the liver. Preliminary tests suggest that the drug, called SPC3649, has no toxic side effects, does not allow development of resistance -- which plagues other hepatitis drugs -- and has lasting effects after treatment has stopped.
"If you had asked me five years ago, I would have been very skeptical that this approach would work," said microbiologist Peter Sarnow of Stanford University, who was not involved in the research. But the new results, reported in the online version of the journal Science, "are very exciting," he said.
An estimated 170 million people worldwide, and 3 million to 4 million Americans, have chronic hepatitis C infections. The persistent infections produce scarring of the liver, or cirrhosis, and frequently lead to liver cancer, which is the most rapidly increasing cause of cancer death in the United States, according to virologist Robert E. Lanford of the Southwest Foundation for Biomedical Research in San Antonio, Texas. Life expectancy is a year after diagnosis, he said.
The current treatment for hepatitis C combines the antiviral agent ribavirin with a long-lasting form of interferon. But the treatment has harsh side effects that cause many patients to stop using it, and is effective in about half of those who are able to finish the 48-week regimen.
It has proven difficult to come up with new, effective treatments, Lanford said. He works with chimpanzees, which are the only animals other than humans that can be infected by the virus. He has tested many experimental drugs in the animals as a last step before human testing. The most promising of these drugs usually fail after a few weeks because the virus develops resistance to them, he said.
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