Bepirovirsen

CAS 1403787-62-1

NA SALT 1403787-62-1

Formula	C230H309N88O115P19S19
Molar mass	7344.14 g·mol−1

FDA 2026, APPROVALS 2026, Hibsago, hepatitis B

To treat chronic hepatitis B virus infection in certain adults without cirrhosis, in combination with existing antiviral therapy

Bepirovirsen (sold as Hibsago) is a first-in-class antisense oligonucleotide injection developed by GSK and Ionis Pharmaceuticals to treat chronic hepatitis B (CHB). It acts as a potential functional cure by targeting viral RNA, reducing surface antigen levels, and stimulating the immune system.

What It Does & How It Works

• Mechanism of Action: A non-GalNAc-conjugated antisense oligonucleotide that recognizes and destroys hepatitis B virus RNA, lowers viral protein production, and activates immune responses.
• Functional Cure Definition: Achieves sustained HBV DNA suppression and undetectable hepatitis B surface antigen (HBsAg) for at least 24 weeks after stopping all treatments.
• Clinical Trial Results: In the Phase 3 B-Well 1 and B-Well 2 trials, 19% to 24% of eligible patients achieved a functional cure and safely discontinued existing antiviral medications.

Regulatory Status & Approvals

• United States: Approved by the FDA in October 2026 for use in certain adults without cirrhosis who have been on antiviral therapy for at least six months and have HBsAg levels of 3,000 IU/mL or less. It features a boxed warning for potential serious liver reactions and low platelet counts.
• Japan: Approved as the first functional cure option for chronic hepatitis B under the brand name Hibsago.
• Other Designations: Granted Breakthrough Therapy and Priority Review designations in China and SENKU designation in Japan.

Bepirovirsen, sold under the brand name Hibsago, is an antisense oligonucleotide gapmer developed to treat hepatitis B infection.^[1]

PAT

WO2012145697

PAT

WO2024214041A1

https://patents.google.com/patent/WO2024214041A1/en

Bepirovirsen is an ASO currently in clinical evaluation for treating Chronic HBV infections. It is compound ISIS No. 505358 as disclosed in WO2012/145697. Bepirovirsen has 20 linked nucleosides and has a nucleobase sequence of 5′-GCAGAGGTGAAGCGAAGTGC- 3′ (SEQ ID NO: 1), and it includes: a gap segment consisting of ten linked deoxynucleosides, a 5′ wing segment consisting of 5 linked nucleosides, and a 3′ wing segment consisting of 5 linked nucleosides, wherein the gap segment is positioned between the 5′ wing segment and the 3′ wing segment, wherein each nucleoside of each wing segment includes a 2′-O-methoxyethyl sugar, wherein each intemucleoside linkage is a phosphorothioate linkage, and wherein each cytosine is a 5 -methylcytosine. The CAS Registry Number of bepirovirsen is 1403787-62-1.

AHB-137 is an unconjugated ASO that is believed to have the same nucleobase sequence as bepirovirsen. AHB-137 is developed by Ausper Biopharma Co., Ltd. and is currently investigated in clinical studies for treating HBV infections. See WO2023/131098; Qiu, X. et al., “AHB-137, a novel and potent hepatitis B virus antisense oligonucleotide with a favorable preclinical pharmacokinetics and safety profile,” EASL 2023, Abstract No. SAT-178 (concluding that “the novel HBV ASO AHB-137 has demonstrated a favorable preclinical pharmacokinetics and safety profile”); Wu, X. et al., “AHB-137, a novel hepatitis B virus antisense oligonucleotide with substantially enhanced in vitro and in vivo antiviral activity,” EASL 2023, Abstract No. SAT-173 (concluding that “AHB-137 has more potent activity in reducing serum HBsAg than BPV [bepirovirsen] across multiple in vitro and in vivo HBV models, by reducing intrahepatic HBV RNA and HBsAg”).

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References

Mak, Lung-Yi; Hui, Rex Wan-Hin; Fung, James; Seto, Wai-Kay; Yuen, Man-Fung (2 November 2023). “Bepirovirsen (GSK3228836) in chronic hepatitis B infection: an evaluation of phase II progress”. Expert Opinion on Investigational Drugs. 32 (11): 971–983. doi:10.1080/13543784.2023.2277389. PMID 37902953. S2CID 264672407.

Clinical data
Trade names	Hibsago
Other names	GSK3228836
Identifiers
IUPAC name
CAS Number	1403787-62-1
UNII	Z87O6SM01N
ChEMBL	ChEMBL4650468
Chemical and physical data
Formula	C230H309N88O115P19S19
Molar mass	7344.14 g·mol−1
SMILES
InChI

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