ARC-521 + entecavir

ARC-521 + entecavir is a **combination therapy** for chronic hepatitis B virus (HBV) infection. ARC-521 is an investigational RNA interference (RNAi) therapeutic agent designed to silence HBV gene expression by targeting HBV mRNA transcripts from both covalently closed circular DNA (cccDNA) and integrated viral DNA, thus reducing the production of viral proteins and viral replication intermediates[4][6]. Entecavir is a nucleoside analogue reverse transcriptase inhibitor approved for treating chronic HBV infection, and works by inhibiting viral DNA synthesis, thus suppressing replication of HBV. The rationale for combining these agents is that entecavir suppresses viral replication while ARC-521 reduces viral antigen production, aiming to enhance immune-mediated clearance of the virus and achieve a functional cure[6]. ARC-521 has been evaluated in Phase 1/2 clinical studies together with standard-of-care nucleos(t)ide analogs such as entecavir[6]. The combination is designed to address patient populations with lower cccDNA levels, in whom reduction of viral antigens rather than DNA alone is needed for functional cure. ARC-521 acts through the delivery of small interfering RNAs (siRNAs), engaging cellular RNAi machinery to specifically cleave HBV transcripts[4][6]. Entecavir is administered orally, while ARC-521 is given intravenously[6].