Exciting new data presented today at the International Liver Congress™ 2013 include results from early in vitro and in vivo studies targeting covalently closed circular DNA (cccDNA), which may form the basis of a cure for chronic hepatitis B virus (HBV) infection.
HBV cccDNA is organized into mini-chromosomes within the nucleus of infected cells by histone and non-histone proteins. Despite the availability of efficient therapies against HBV, long-term persistence of cccDNA necessitates life-long treatments to suppress the virus. The following three experimental studies demonstrate effective HBV-cccDNA targeting/depletion using novel therapeutic approaches which offer the potential of a cure.
Liver regeneration induces strong reduction of viral replication and cccDNA levels, but not complete cccDNA eradication; without antiviral treatment, de novo HBV infection can be re-established.
Key findings of research in HBV-infected human hepatocytes using the uPA/SCID chimeric mouse system show that liver regeneration induces strong reduction of viral replication and cccDNA levels, with rapid formation of cccDNA-free hepatocytes. However, because complete cccDNA eradication is not achieved, in the absence of antiviral treatment, de novo HBV infection could be re-established in quiescent (non-dividing) human hepatocytes. This suggests that induction of hepatocyte turn-over together with antiviral drugs inducing viral suppression, such as nucleoside analogues and IFN, or blocking cell entry, may accelerate the clearance of the viral minichromosome.
Targeting epigenetic control of nuclear cccDNA minichromosome to suppress HBV transcription and replication may form basis for other therapeutic approaches to curing chronic HBV infection.
In the infected liver cell the rate of replication of HBV is regulated by the acetylation or methylation of histone proteins which surround the cccDNA minichromosome -- so called epigenetic regulation. In a separate innovative study, the suppression of HBV transcription and replication by small molecules that target the epigenetic control of nuclear cccDNA minichromosome was investigated. The different classes of small molecules studied included: Class I, II and III histone deacetylase inhibitors (HDACi); p300 and PCAF histone acetyltransferases (HAT) inhibitors; hSirt1 activators; JMJD3 histone demethylase inhibitors.
The combined inhibition of p300 and PCAF HATs resulted in an evident reduction of HBV replication which mirrored the decrease of pgRNA transcription. The hSirt1/2 activator MC2791 and the JMJD3 inhibitor MC3119, albeit with different efficiency, inhibited both HBV replication and cccDNA transcription. Results represent a proof of concept that activation of hSirt1 and Ezh2 (through the inhibition of its functional antagonist JMJD3) by small molecules can induce an active epigenetic suppression of HBV cccDNA minichromosome similar to that observed with IFNα, and lead to persistent cccDNA silencing.
Lymphtoxin beta receptor (LTbR) agonisation represents basis for novel alternative therapeutic approach to curing chronic HBV infection.
The final study demonstrated that stimulating the lymphtoxin beta receptor (LTbR) provides an effective, long lasting and non-cytopathic mechanism for achieving effective HBV-cccDNA depletion in infected hepatocytes. Cell culture models including HBV-infected HepaRG cells and primary human hepatocytes were used to test the effect of antibodies stimulating human LTbR (BS1 or CBE11). Results show that a strong and dose-dependent anti-HBV effect was achieved by activation of the LTbR. All HBV replication markers were decreased with this treatment, including cccDNA in cells where HBV infection was already established.
Hepatitis B is the most prevalent cause of chronic viral hepatitis and a major global health problem. Prof. Fabien Zoulim, EASL Educational Councillor commented on the exciting new data: "In chronic hepatitis B infection, the viral genome forms a stable minichromosome -- the covalently closed circular DNA (cccDNA) -- which can persist throughout the lifespan of the hepatocyte."
"Current treatments focus on suppression of HBV and discovery of compounds directly targeting cccDNA has been one of the major challenges to curing HBV infection; but these preliminary data show novel therapeutic approaches can be applied to successfully target cccDNA with the long-term aspiration of finding a cure" added Prof. Fabien Zoulim.
Using lymphotoxin-beta-receptor agonists to eradicate the HBV virus
Data from animal studies presented during the EASL meeting showed that it is possible to eradicate the HBV virus from infected cells by targeting its replication template, the so-called covalently closed circular DNA (cccDNA). These findings raise hope for an alternative therapeutic approach to cure chronic HBV infection.
The discovery of compounds directly targeting HBV cccDNA has recently become one of the major challenges in hepatitis B research. Indeed, while current treatments are very potent to reduce patients’ viremia, these agents are not capable of eliminating the virus’s cccDNA. Thus, patients cannot be cured and require life-long treatments that may cause side effects.
During the EASL meeting, several early phase studies were presented suggesting different approaches to target HBV cccDNA. One of these approaches, presented by Julie Lucifora, from the team of Ulrike Protzer in Munich, Germany, showed it is possible to destroy cccDNA in infected cells by using agonists of the lymphtoxin beta receptor (LTbR).
LTbR-agonists trigger cccDNA degradation in vitro and in vivo
The researchers led their experiments in vitro in different cell culture models, including HBV-infected HepaRG cells and primary human hepatocytes, but also in vivo in mouse LTbR transgenic models. They observed that LTbR activation led to a strong dose-dependent anti-HBV effect both in vitro and in vivo, without inducing cell-toxicity. All HBV replication markers were decreased upon treatment, including cccDNA (Slide 13).
Importantly, the team showed that there was no rebound in HBV replication after stopping the LTbR treatment (Slide 14). Such a rebound is observed when using nucleos(t)ide analogues such as lamivudine.
cccDNA degradation depends on the overexpression of APOBEC3B
The team further identified the mechanism at play. LTbR-activation results in the overexpression of a protein called APOBEC3B, known for its deaminase activity. “In our experiments, the deactivation of APOBEC3B led to a full rescue of cccDNA in cells treated with the agonist,” explained Lucifora.
Dr. Lucifora proposed a model in which a signaling pathway activated by LTbR agnonists leads to the overexpression of APOBEC3B, triggering hypermutations in the cccDNA and its subsequent degradation by endonucleases.
“This is one of the first studies showing that by activating a signaling cascade we can destabilize and degrade HBV cccDNA. This provides new hopes for developing therapies which might one day be able to cure the infection,” said Dr. Lucifora, who added that one of the agonists used in her team’s experiments, CBE11, initially developed for anti-cancer therapy, has already been used in clinical phase I trials without inducing any adverse effect.
Written by Clementine Wallace, based on abstract 59, presented by Julie Lucifora, from Munich, Germany, also interviewed during the EASL congress 2013 in Amsterdam.
well done search by veteran. its like a promishing hope, finally a milestone academic step in understanding cccdna and eradicating cccdna.
now we our members have to find out alternates to stimulate same kind of immune activities using the relatives of above trial compounds or using the other currently available compounds.
This information of them knowing it was working on cancer goes as far back as 1996. http://m.jbc.org/content/271/40/24934.long
Again bio chemists were aware of this. And look at what big pharma is doing with both hiv cancer and hbv treatments. When very effective immune therapies are there.
All they could have done is try! Instead of killing people chemotherapy. Which is in itself is carcinogenic. Which all NUCs are btw. And if you ask around HIV forums they will tell you they are cancers are drug related side effects. Not so much from the affects of hiv.
Anyway here is another proof that all this is a conspiracy to create whole industries like chronic HBV treatment.
Department of Immunobiology, Biogen Idec, Cambridge, MA 02142, USA.
Abstract The lymphotoxin-beta receptor (LT beta R) is a tumor necrosis factor receptor family member critical for the development and maintenance of various lymphoid microenvironments. Herein, we show that agonistic anti-LT beta R monoclonal antibody (mAb) CBE11 inhibited tumor growth in xenograft models and potentiated tumor responses to chemotherapeutic agents. In a syngeneic colon carcinoma tumor model, treatment of the tumor-bearing mice with an agonistic antibody against murine LT beta R caused increased lymphocyte infiltration and necrosis of the tumor. A pattern of differential gene expression predictive of cellular and xenograft response to LT beta R activation was identified in a panel of colon carcinoma cell lines and when applied to a panel of clinical colorectal tumor samples indicated 35% likelihood a tumor response to CBE11. Consistent with this estimate, CBE11 decreased tumor size and/or improved long-term animal survival with two of six independent orthotopic xenografts prepared from surgical colorectal carcinoma samples. Targeting of LT beta R with agonistic mAbs offers a novel approach to the treatment of colorectal and potentially other types of cancers.
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