Management of hepatitis delta: Need for novel therapeutic options

Hepatitis D virus (HDV) is the smallest single stranded RNA virus infecting humans. The hepatitis B surface antigen envelope protein protects the HDV nucleocapsid antigen and provides a means for the virus to enter and exit the hepatocyte. Hepatitis B and D viruses exploit the human sodium taurocholate co-transporting polypeptide (NTCP), a receptor, for their entry into hepatocytes. Prenylation of the large delta antigen is a critical determinant of HDV particle assembly. Treatment with pegylated interferon results in sustained virological response six months post-treatment in one fourth of the patients. Nucleos(t)ide analogs (NAs) have been widely tested in hepatitis delta, but they appear to be ineffective. Combination treatment of NAs with interferon also proved to be disappointing so there is a need for novel therapeutic options. The receptor function of NTCP is blocked by Myrcludex B, a synthetic N-acylated preS1 lipopeptide that competes with infectious virions for receptor binding. There are already some approved drugs available, including irbesartan, ezetimibe, and ritonavir and cyclosporin A, with documented inhibitory effects on NTCP's metabolic function. These drugs may have a role in HDV treatment. Interference with hostmediated post-translational changes of proteins that are crucial to the HDV life cycle, such as prenylation may become an important tool to control HDV infection and prevent replication. Lonafarnib, a prenylation inhibitor significantly reduces virus levels in hepatitis delta patients. Antisense oligodeoxynucleotides which are complementary to genomic HDV ribozyme self-cleavage site and stem I regions can inhibit genomic HDV ribozyme activity.