The viral replication cycle is critical for a virus to spread in the body and cause disease. Focusing on this cycle in hepatitis A virus (HAV), UNC School of Medicine scientists discovered that replication requires specific interactions between the human ZCCHC14 protein and a group of enzymes called TENT4 poly(A) polymerases. They also found that the oral compound RG7834 stopped replication at a key step, making it impossible for the virus to infect liver cells.
These findings, published in the Proceedings of the National Academy of Sciences, are the first to demonstrate effective drug treatment against HAV in an animal model of the disease.
“Our study demonstrates that targeting this protein complex with an orally delivered small molecule therapeutic halts viral replication and reverses liver inflammation in a mouse model of hepatitis A, providing proof of principle for an antiviral therapy and means to halt the spread of hepatitis A in an epidemic setting,” said senior author Stanley M. Lemon, MD, professor in the UNC Department of Medicine and the UNC Department of Microbiology and Immunology and a member of the UNC Institute for Global Health and Infectious Diseases.
Lemon, who in the 1970s and 1980s was part of the Walter Reed Army Medical Center research team that developed the first inactivated HAV vaccine administered to humans, said research on HAV declined after the vaccine became widely available in the mid-1990s. Cases declined sharply in the 2000s as vaccination rates skyrocketed. The researchers turned their attention to hepatitis B and C viruses, both of which are very different from HAV and cause chronic disease. “It’s like comparing apples with turnips,” Lemon said. “The only similarity is that they all cause inflammation of the liver.” HAV is not even part of the same virus family as the hepatitis B and C viruses.
Hepatitis A outbreaks have been increasing since 2016, even though the HAV vaccine is very effective. Not everyone gets vaccinated, Lemon pointed out, and HAV can exist for long periods of time in the environment — such as on our hands, in food and water — resulting in more than 44,000 cases, 27,000 hospitalizations and 400 deaths in United States since 2016, according to the CDC.
Several outbreaks have occurred in the past few years, including in San Diego in 2017, caused largely by homelessness and illegal drug use, causing severe illness in about 600 people and killing 20. In 2022, there was a small outbreak linked to organic strawberries in multiple states, resulting in about a dozen hospitalizations. Another outbreak in 2019 was linked to fresh blackberries. Worldwide, tens of millions of HAV infections occur each year. Symptoms include fever, abdominal pain, jaundice, nausea, and loss of appetite and sense of taste. Once sick, there is no cure.
In 2013, Lemon and colleagues discovered that the hepatitis A virus changes dramatically in the human liver. The virus hijacks parts of the cell membrane as it leaves the liver cells, cloaking itself from antibodies that would otherwise quarantine the virus before it spreads widely in the bloodstream. This work was published in Nature and gave an idea of how much researchers have not yet learned about this virus, which was discovered 50 years ago and probably caused a disease dating back to ancient times.
A few years ago, researchers found that hepatitis B virus requires TENT4A/B for its replication. Meanwhile, Lemon’s lab ran experiments to look for human proteins that HAV needs to replicate, and they found ZCCHC14, a specific protein that interacts with zinc and binds to RNA.
“That was the turning point for the current study,” Lemon said. “We found that ZCCHC14 binds very specifically to a certain part of the HAV RNA, the molecule that contains the genetic information of the virus. And as a result of this binding, the virus is able to recruit TENT4 from the human cell.
In normal human biology, TENT4 is part of an RNA modification process during cell growth. Essentially, HAV hijacks TENT4 and uses it to replicate its own genome.
This work suggests that stopping the recruitment of TENT4 can stop viral replication and limit disease. Next, Lemon’s lab tested the compound RG7834, which had previously been shown to actively block the hepatitis B virus by targeting TENT4. In the PNAS paper, the researchers detailed the precise effects of oral RG7834 on HAV in the liver and feces, and how the virus’ ability to cause liver damage was dramatically reduced in mice that had been genetically engineered to develop HAV infection and disease. The study suggests that the compound is safe at the dose used in this study and in the acute time period of the study.
“This compound is a long way from human use,” Lemon said, “But it points the way to an effective way to treat a disease for which we have no treatment at all.”
The pharmaceutical company Hoffmann-La Roche developed RG7834 for use against chronic hepatitis B infections and is testing it in humans in a phase 1 trial, but animal studies suggest it may be too toxic for long-term use.
“Cure for hepatitis A will be short-term,” Lemon said, “and more importantly, our group and others are working on compounds that would hit the same target without toxic effects.”
Reference: Lemon SM and others. The ZCCHC14/TENT4 complex is required for hepatitis A virus RNA synthesis. PNAS; 2022. doi:10.1073/pnas.2204511119
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