Editor's Note: Clinical cure of chronic hepatitis B (CHB), also known as functional cure, is achieved when patients remain HBsAg negative after stopping treatment, with or without the presence of anti-HBs, HBV DNA levels below the detection limit, and normal liver biochemical indicators. However, HBV covalently closed circular DNA (cccDNA) may still persist in the nuclei of liver cells in these patients. Therefore, clearing HBV cccDNA remains a major obstacle to achieving complete virological cure of CHB. Recently, at the 17th National Clinical Conference on Liver Diseases held in Shenyang, "Hepatology Digest" invited Professor Jun Cheng from Hebei Wutu Pharmaceutical Co., Ltd. to discuss the clearance of HBV cccDNA and other related issues.Hepatology Digest: Could you briefly summarize the critical role of HBV cccDNA in HBV infection and disease progression?
Professor Jun Cheng: To determine whether HBV cccDNA can truly be an important target for anti-HBV therapy in the future, we need to answer two questions.
The first question is whether HBV cccDNA is important. Previous research has shown that HBV cccDNA is the material basis for the long-term presence of HBV in liver cells. HBV is difficult to clear because once HBV DNA forms cccDNA, it persists in the nuclei of liver cells. HBV cccDNA serves as the primary template for viral replication and expression, making it the source of the virus.
I believe we should actively choose anti-HBV antiviral treatment targets. In the past, interferon-based drugs worked mainly by modulating the immune mechanism, while the nucleos(t)ide analogs that appeared later worked by inhibiting HBV DNA replication. The clinical focus of the former was on the seroconversion of HBeAg, and the latter on inhibiting HBV DNA replication.
Targeting HBV cccDNA for antiviral therapy could not only inhibit viral replication but also suppress viral transcription, translation, and the expression of various viral products. Therefore, the answer to the first question is that HBV cccDNA is indeed very important.
The second question is whether HBV cccDNA can be a therapeutic target. Early studies found that the half-life of HBV cccDNA in the nuclei of liver cells is up to 14.3 years, making complete clearance very difficult. Current research indicates that the HBV cccDNA pool is in a dynamic state of continuous replenishment and consumption. If external forces reduce the replenishment or accelerate the consumption of the cccDNA pool, the half-life of cccDNA can be shortened. Thus, the answer to the second question is that HBV cccDNA can indeed be a therapeutic target.
Hepatology Digest: Considering the stability and persistence of HBV cccDNA in liver cells, what do you think is the biggest challenge in clearing HBV cccDNA?
Professor Jun Cheng: The biggest challenge is that we do not fully understand the mechanisms of HBV cccDNA formation and degradation. Based on current research, there are two main pathways to clear HBV cccDNA: one targeting the virus and the other targeting the host.
The first pathway involves the HBV core protein, which forms a 120-faceted capsid around the HBV DNA, crucial for the formation of cccDNA. If we can block the formation of this capsid, HBV cccDNA formation can be prevented.
Blocking the formation of the HBV capsid has been the goal of many pharmaceutical companies over the past decade. Related drugs are mainly divided into two categories: one blocks the formation of the capsid, and the other forms empty capsids that cannot encapsulate HBV DNA. These drugs have entered phase II and even phase III clinical trials, but progress has been slower than expected, indicating some technical challenges remain in this area of research.
The second pathway involves the host immune system, which HBV suppresses to maintain long-term infection. Recent studies have found that immune factors from the Toll-like receptor (TLR) family, such as TLR-7, TLR-8, and TLR-9, can inhibit the formation of HBV cccDNA. However, TLRs are suppressed during HBV infection, so developing TLR agonists is another important research direction. Some pharmaceutical companies have developed a series of TLR agonists, which are also in clinical trials.
While researchers have made continuous efforts to inhibit HBV capsid formation, activate TLR expression, and enhance HBV immunity, whether these strategies can ultimately be translated into drugs and play a significant role in clearing HBV cccDNA requires further research and clinical validation.
Hepatology Digest: In your presentation, you mentioned new strategies for clearing HBV cccDNA. Could you elaborate on the latest research progress and the significant efficacy achieved with these new strategies?
Professor Jun Cheng: Besides capsid inhibitors and TLR agonists, there are other mechanisms and directions worth exploring. To date, HBV can only infect humans and chimpanzees, not dogs or mice. When HBV infects humans, it can reach any cell, tissue, or organ through the bloodstream. But why does HBV only infect the liver, causing hepatitis, cirrhosis, and liver cancer? The biochemical environment in the liver is conducive to HBV DNA replication and expression, leading to liver disease. We are trying to identify key host proteins involved in the HBV DNA lifecycle from the host perspective.
In recent years, we have discovered that some host proteins, such as HBV core protein, HBeAg, and X protein, play crucial roles in HBV DNA replication and expression. We have identified host genes controlling HBV cccDNA replication and expression, preliminarily explored the related mechanisms, identified compounds, and optimized their chemical structures, obtaining chemical patents. So far, our compounds can significantly inhibit HBV DNA replication and expression in cell lines and have a strong inhibitory effect on cccDNA.
Hepatology Digest: How much potential do you think these new strategies have in achieving functional cure for hepatitis B? What key breakthroughs and progress do you believe are still needed in this field?
Professor Jun Cheng: The field of infectious liver diseases includes two major diseases: CHB and chronic hepatitis C (CHC). With the advent of direct-acting antivirals (DAAs), the cure rate for CHC has reached very high levels. However, HBV antiviral treatment still faces many bottlenecks. If we compare HBV antiviral treatment to a crown, developing drugs targeting cccDNA would be the jewel on the crown. I believe CHB will be cured in the future, with cccDNA as a crucial target.
Over the past two decades, researchers have conducted many studies on inhibiting HBV core protein, blocking capsid formation, increasing TLR expression levels, and enhancing HBV immunity. These attempts have been significant and made important progress.
Our research group has a unique focus—identifying host genes and proteins controlling HBV replication and designing critical drugs targeting these genes and proteins. Preliminary research results show that our targets, mechanisms, and new compounds perform excellently in controlling HBV cccDNA in HepG2.2.15 cell lines, transiently transfected HBV cell lines, and AD38 cell lines. However, these are only preclinical results and ultimately require clinical trials.
While progress has been made in the aforementioned studies, the final outcome remains to be determined. Additionally, our research shifts from previously pursuing HBeAg seroconversion and HBV DNA inhibition and seronegativity as treatment goals to targeting surface antigen decline and seronegativity, which is closest to the clinical cure goal for CHB. I hope this will lead to great success in antiviral treatment in the future.
