Vertex is completing midstage testing of its drug telaprevir, a hepatitis C protease inhibitor.
He designed early protease inhibitor drugs for AIDS, but the lead molecule failed in trials.
However, the protease inhibitors have been linked to skin rashes and heightened anemia in some patients.
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Vertex's stock sank 13% on Oct. 18 when Schering-Plough touted promising results for its rival protease inhibitor.
The only other frontline drugs are combinations which include protease inhibitors which are more difficult to take.
Schering is in discovery stages for a protease inhibitor that they hope to offer in pill form.
Protease inhibitors shut down AIDS enzymes by locking onto readily available toeholds, but hep-C's protease is smooth.
But others, including Schering-Plough and Vertex Pharmaceuticals, prevailed and now have protease inhibitors in early human trials.
The protease works as a molecular scissors to cut out proteins that then form new viral particles.
It took two years to get a stable, crystalline form of the hepatitis C protease enzyme for study.
Its biggest selling point: It does not seem to raise cholesterol as similar drugs, called protease inhibitors, do.
Doctors hope, ultimately, to boost cure rates by combining protease inhibitors with a second drug class called polymerase inhibitors.
Jenner and Markowitz are watching Schering-Plough's development of a protease inhibitor, as well.
However, as often happens, evolution has got to work and generated drug-resistant strains of the virus by modifying its protease.
The drugs, so-called hepatitis C protease inhibitors, represent the first class of agents that directly target the hepatitis C virus.
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Gilead is also testing a protease inhibitor for hepatitis C, a disease for which there aren't a lot of great treatments.
Once this was done, "it became clear what a remarkable challenge" designing a protease inhibitor would be, says Vertex executive John Thomson.
The leader in the pack with protease inhibitors for the hepatitis virus, say Markowitz and Jenner, is Vertex Pharmaceuticals of Cambridge, Mass.
Much attention is being lavished on two classes of enzymes inside hepatitis C that are crucial for its replication: polymerase and protease.
The surface of the hepatitis C protease turned out to be flat.
One reason is that the flat geometry of the hepatitis C protease protein made it is difficult target to hit with small-chemical drugs.
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"This has got the potential to be the best in class protease inhibitor for HIV and AIDS, " says Palmer, the chief scientific officer.
Data from a small, midstage clinical trial with its protease inhibitor, known as vx-950 or telaprevir, were "nothing short of spectacular, " says Markowitz.
It was the first to market a protease inhibitor for AIDS in the U.S., but competing medicines ended up dominating the U.S. market.
Telaprevir is a protease inhibitor that attacks the virus directly and blocks its replication, much the way antiretrovirals revolutionized the treatment of AIDS over a decade ago.
Vertex's stock sank 13% on Oct. 18 when Schering-Plough (nyse: SGP - news - people ) touted promising results for its rival protease inhibitor.
Thus far the most promising new class of such enzyme-attacking drugs looks to be protease inhibitors, best known for combating the progress of HIV infections in the body.
Vertex also is in late-stage tests of a new AIDS drug, a protease inhibitor that requires only two pills a day versus six or more for rival remedies.
In 2011, Foldit players needed only 10 days to produce an accurate 3-D model of the Mason-Pfizer monkey virus, a protease whose structure had stumped scientists for 15 years.
The agency says some drugs should never be taken with Mevacor including protease inhibitors, a class of HIV drugs and certain drugs used to treat bacterial and fungal infections.
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