Experimental Drugs Block
Hepatitis C Virus
05-08-2003
New
experimental compounds may help the body fight off hepatitis
C, researchers said Thursday. The research, done by separate
teams in the United States and Canada, also led to new
discoveries about how the body fights off infection.
While
viruses such as influenza are eventually cleared by the immune
system, hepatitis C can stay in the body permanently, eluding
the immune system's various weapons. According to CDC, 75
percent to 85 percent of those infected have chronic hepatitis
C infection. Many will develop liver damage, sometimes leading
to cirrhosis and liver cancer. The antiviral ribavirin, used
with alpha interferon, can help some patients control
hepatitis C but does not cure it.
"Just
a year ago, the hepatitis C virus field had no leads,"
said Michael Gale, a virologist at the University of Texas
Southwestern Medical Center in Dallas who led one of the
studies. "We were totally clueless." Gale's team and
a team led by John Hiscott at McGill University in Montreal
found out how the virus de-activates cell defenses so it can
stay in a cell virtually forever. The full reports were
published in the online journal Science Express (April 17,
2003; 10.1126/science.1082604) and in the Journal of Virology
(2003;77:3898-3912).
Both
teams said they found that the virus can block a cell's
production of interferon regulatory factor 3 (IRF3), which
cells produce to defend against infection and to summon more
immune system help. The McGill team also found it blocks a
second compound, IRF7.
"This
really gives us the first evidence of how it is the virus can
cause lifetime infection, as opposed to influenza which
infects you for a week," Gale said in an interview.
Gale's team also discovered that individual cells have their
own immune responses. "The whole thing works by IRF3
turning on genes in the human cell that fight off infection.
We are going to find out what those genes are, what their
products are," Gale said. This, in turn, could lead to
new ways to battle viruses from HIV to herpes.
In
the meantime, Schering-Plough and Boehringer Ingelheim have
developed compounds they hope will work against hepatitis C.
Gale's team tested the experimental Schering product, SCH-6,
and found it could protect the cell's defenses. "We found
that the new protease inhibitors could actually prevent the
virus from blocking this immune response and basically restore
the innate antiviral response in human cells," Gale said.
The
work reported in Science Express was all done in the
laboratory; Gale said the drugs will be difficult to test
because no animals are naturally infected with hepatitis C the
way humans are. However, Boehringer has reported on Phase I
clinical trials that suggest its protease inhibitor is safe
and may greatly reduce viral levels in the body.
Source:
Reuters (04.17.03) - Friday, April 25, 2003; Maggie Fox;
Courtesy of the CDC National Center for HIV, STD, and TB
Prevention.
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