Chronic hepatitis B virus (HBV) infection is a major health concern worldwide, frequently leading to liver cirrhosis, liver failure and hepatocellular carcinoma. Evidence exists that high viral antigen load may play a role in chronicity. Production of viral proteins is thought to depend on transcription of viral covalently closed circular DNA (cccDNA). In a human clinical trial with ARC-520, a RNA interference (RNAi)-based therapeutic targeting HBV transcripts, HBV S antigen (HBsAg) was strongly reduced in treatment-naïve patients positive for HBV e antigen (HBeAg) but was reduced significantly less in patients that were HBeAg negative or had received long-term therapy with nucleos(t)ide viral replication inhibitors (NUCs). The molecular basis for this unexpected differential response was investigated in chimpanzees chronically infected with HBV. Several independent lines of evidence demonstrated that HBsAg was expressed not only from the episomal cccDNA minichromosome, but also from transcripts arising from HBV DNA integrated into the host genome. The latter was the dominant source in HBeAg negative chimpanzees. Many of the integrants detected in chimpanzees lacked target sites for the siRNAs in ARC-520, explaining the reduced response in HBeAg negative chimpanzees and by extension in HBeAg negative patients. Our results uncover a heretofore under-recognized source of HBsAg that may represent a strategy adopted by HBV to maintain chronicity in the presence of host immune surveillance and could alter trial design and endpoint expectations of new therapies for chronic HBV.

Background and Aims ARC‐520, the first an RNA interference (RNAi) therapeutic, was designed to reduce all RNA transcripts derived from covalently closed circular DNA, leading to a reduction in viral antigens and hepatitis B virus (HBV) DNA. Approach and Results We aimed to evaluate the depth of hepatitis B surface antigen (HBsAg) decline in response to multiple doses of ARC‐520 compared to placebo (PBO) in two randomized, multicenter studies in nucleoside/nucleotide analogue reverse‐transcriptase inhibitor (NUC)–experienced patients with hepatitis B early antigen (HBeAg)–negative (E‐neg) or HBeAg‐positive (E‐pos) disease. A total of 58 E‐neg and 32 E‐pos patients were enrolled and received four monthly doses of PBO (n = 20 E‐neg, 11 E‐pos), 1 mg/kg ARC‐520 (n = 17 E‐neg, 10 E‐pos), or 2 mg/kg ARC‐520 (n = 21 E‐neg, 11 E‐pos) concomitantly with NUC. HBsAg change from baseline to 30 days after the last ARC‐520 dose were compared to PBO. Both E‐neg and E‐pos high‐dose groups significantly reduced HBsAg compared to PBO, with mean reductions of 0.38 and 0.54 log IU/mL, respectively. HBsAg reductions persisted for approximately 85 days and >85 days after the last dose in E‐neg and E‐pos patients, respectively. The low‐dose groups did not reach statistical significance in either study. E‐pos patients showed a dose‐dependent reduction in HBeAg from baseline. Mean maximum reduction was 0.23 and 0.69 log Paul Ehrlich IUs/mL in the low‐dose and high dose ARC‐520 groups respectively. ARC‐520 was well tolerated, with only two serious adverse events of pyrexia possibly related to study drug observed. Conclusions ARC‐520 was active in both E‐neg and E‐pos, NUC‐experienced HBV patients; but absolute HBsAg reductions were moderate, possibly due to expression of HBsAg from integrated HBV DNA, indicating the need for RNAi therapeutics that can target viral transcripts regardless of origin.

ARC‐520 Injection, an RNA interference drug for the treatment of hepatitis B that targets cccDNA‐derived viral mRNA transcripts with high specificity, effectively reduces the production of viral proteins and HBV DNA. In this phase 1 randomized, double‐blind, placebo‐controlled study, 54 healthy volunteers (half male, half female) received a single, intravenous dose of 0.01–4.0 mg/kg ARC‐520 Injection (n = 36) or placebo (n = 18). Assessments included safety, tolerability, pharmacokinetics, and pharmacodynamics (cytokines and complement). Pharmacokinetics of the siRNA and peptide excipient components contained in ARC‐520 Injection showed a relatively short half‐life of 3–5 and 8–10 hours, respectively. Dose exposure linearity was demonstrated within the dose range. ARC‐520 Injection was well tolerated, with adverse‐event frequency the same as placebo and no serious adverse events. ARC‐520 Injection was initially found to induce histamine release through mast cell degranulation, resulting in 2 moderate hypersensitivity reactions. However, after initiation of pretreatment with oral antihistamine, no further hypersensitivity reactions occurred. Low‐level, transient complement induction and sporadic, mild, and transient elevations of several cytokines were observed but not associated with any symptoms. ARC‐520 Injection showed a favorable tolerability profile in this single‐dose study in healthy volunteers. Oral antihistamine pretreatment is recommended in the future to offset mast cell degranulation stimulation.

No abstract

NCT02363946.