Stanford University Identifies Potential Drugs to Combat Hepatitis C

Stanford University School of Medicine scientists have discovered a novel class of compounds that in experiments in vitro, inhibit the replication of the virus that is responsible for hepatitis C.

If these compounds prove effective in infected humans as well, they may accelerate efforts to confront this virus’ propensity to rapidly acquire drug resistance, while possibly skirting some of the troubling side effects common among therapies in current use and in late-stage development.

Hepatitis C Virus (HCV) is an especially tough nut to crack. Natural isolates of it cannot be grown in culture as can many other viruses, which impedes drug and vaccine research.

Virologists have developed surrogate systems that substantially duplicate the HCV replication process. These systems can be used to test compounds for effectiveness against the virus.

But even when a compound shows effectiveness, HCV mutates readily. So it can rapidly acquire drug resistance. The ultimate solution is probably to attack the virus from multiple angles all at the same time with a cocktail of compounds, each targeting a different item in the virus’s toolkit, according to Dr Jeffrey Glenn.

Animal cells are composed mainly of water and water-soluble substances, enclosed within a fatty outer membrane and segregated into distinct subcellular compartments by internal membranes. HCV replicates only in association with such membranes.

While some viruses cozy up to membranes that already exist inside living cells, HCV highjacks bits and pieces of membranes and assembles them into large clusters of tiny nested bubbles, or vesicles. The clusters are unlike anything found in a normal human cell.

Glenn and his associates identified a cylinder-shaped chunk of an HCV-encoded protein that is essential for that protein’s known vesicle-aggregating activity. A synthetic version of this cylindrical section caused vesicles to aggregate into telltale clusters.

The investigators then used this finding to attack the virus: they found that mutations in the synthesized segment destroyed the virus’s ability to replicate.

While that insight was important, it alone did not translate into a therapy. The researchers set out to detect compounds that could prevent this key protein segment from working.

They designed an assay consisting of hundreds of separate tiny depressions in a plastic laboratory dish, with each depression housing large numbers of individual tiny vesicles in solution. As expected, sprinkling some of the synthesized protein segment into a depression caused the vesicles inside to clump together.

But testing of numerous off-the-shelf compounds – a different one in each well – showed that some prevented the aggregation from happening. Two of these compounds impaired HCV’s ability to reproduce itself in the workhorse surrogate HCV replication system.

Glenn foresees a year to 18 months of extensive preclinical and animal testing before this class of compounds can gain approval by the Food and Drug Administration to enter clinical trials in humans.

Because the compounds operate by disrupting a mechanism that is only needed by the virus, he said, he hopes the drugs based on them may exhibit both viral replication-suppressing ability and a favorable toxicity profile.