CHAPEL HILL, NC — The viral replication cycle is critical for a virus to spread in the body and cause disease. By focusing on that cycle in the hepatitis A virus (HAV), scientists at the UNC School of Medicine found that replication requires specific interactions between the human protein ZCCHC14 and a group of enzymes called TENT4 poly(A) polymerases. . They also found that the oral compound RG7834 stopped replication in a key step, preventing the virus from infecting 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 administered small molecule therapeutic agent halts viral replication and reverses liver inflammation in a mouse model of hepatitis A, providing a proof-of-principle for antiviral therapy and the means to spread of hepatitis A in outbreak situations,” said senior author Stanley M. Lemon, MDprofessor in the UNC Department of Medicine and UNC Department of Microbiology & Immunology, and member of the UNC Institute for Global Health and Infectious Diseases.
Lemon, who was part of a research team at Walter Reed Army Medical Center in the 1970s and 1980s that developed the first inactivated HAV vaccine given to humans, said research on HAV waned after the vaccine was launched in the mid-1990s. became widely available. Cases plummeted in the 2000s as vaccination rates skyrocketed. 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 to turnips,” Lemon said. “The only similarity is that they all cause inflammation of the liver.” HAV does not even belong to the same virus family as hepatitis B and C viruses.
Hepatitis A outbreaks have been increasing since 2016, although the HAV vaccine is very effective. Not everyone gets vaccinated, Lemon noted, and HAV can be present in the environment for long periods of time — such as on our hands and in food and water — resulting in more than 44,000 cases, 27,000 hospitalizations and 400 deaths in the United States since 2016, according to the CDC†
Several outbreaks have occurred in recent years, including in San Diego in 2017, largely caused by homelessness and illegal drug use, which left about 600 people seriously ill and 20 people dead. In 2022 there was a small outbreak linked to organic strawberries in multiple states, leading to about a dozen hospitalizations. Another outbreak in 2019 was linked to fresh blackberries. Tens of millions of HAV infections occur worldwide every year. Symptoms include fever, abdominal pain, jaundice, nausea, and loss of appetite and taste. Once sick, there is no treatment.
In 2013, Lemon and colleagues found that the hepatitis A virus changes dramatically in the human liver. The virus hijacks bits of cell membrane as it exits the liver cells and cloaks itself against antibodies that would otherwise have quarantined the virus before it spread widely through the bloodstream. This work, published in Nature, provided insight into how much researchers still had to learn about this virus that was discovered 50 years ago and likely caused disease dating back to ancient times.
A few years ago, researchers discovered that the hepatitis B virus needed TENT4A/B for its replication. Meanwhile, Lemon’s lab led experiments to look for human proteins that HAV needs to replicate, and they found ZCCHC14 — a particular protein that interacts with zinc and binds to RNA.
“This was the tipping point for this current study,” Lemon said. “We found that ZCCHC14 binds very specifically to a certain part of HAV’s RNA, the molecule that contains the genetic information of the virus. And because of that binding, the virus can 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 suggested that stopping TENT4 recruitment could halt viral replication and limit disease. Lemon’s lab then 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 describe the precise effects of oral RG7834 on HAV in liver and feces and how the virus’ ability to cause liver damage is dramatically reduced in mice that were genetically modified to develop HAV infection and disease. The study suggests that the compound was safe at the dose used in this study and in the acute time frame of the study.
“This compound is still 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 tested it in humans in a phase 1 trial, but animal studies suggested it may be too toxic for long-term use.
“The treatment for Hepatitis A would be short-lived,” Lemon said, “and, more importantly, our group and others are working on compounds that would hit the same target without toxic effects.”
This research was a collaboration between the Lemon lab and the lab of Jason Whitmire, professor of genetics at the UNC School of Medicine. Lemon and Whitmire are members of the UNC Lineberger Comprehensive Cancer Center.
The first authors of the PNAS paper are You Li and Ichiro Misumi. Other authors, all at UNC, include Tomoyuki Shiota, Lu Sun, Erik Lenarcic, Hyejeong Kim, Takayoshi Shirasaki, Adriana Hertel-Wulff, Taylor Tibbs, Joseph Mitchell, Kevin McKnight, Craig Cameron, Nathaniel Moorman, David McGivern, John Cullen, Jason K. Whitmire and Stanley M. Lemon.
This work was supported by grants from the National Institute of Allergy and Infectious Diseases (R01-AI131685), (R01-AI103083), (R01-AI150095), (R21-AI163606), (R01-AI143894), (R01-AI138337) . The UNC Pathology Services Core and UNC High-Throughput Sequencing Facility were supported in part by a National Cancer Institute Center Core Support Grant (P30CA016086) to the UNC Lineberger Comprehensive Cancer Center.
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