Development of HBV S gene mutants in chronic hepatitis B patients receiving nucleotide/nucleoside analogue therapy.
Structurally modified nucleotide/nucleoside analogues can exert potent inhibitory effect on HBV polymerase activities. Some of these agents have been approved for the treatment of chronic hepatitis B. Because of a high risk of reactivation upon drug withdrawal, continuous long-term therapy is recommended to maintain maximal viral suppression. Consequently, drug resistance has developed in a significant proportion of patients. During long-term therapy, mutations occur not only in the polymerase gene but also in the S gene, resulting in the emergence of surface protein mutants. Two types of surface protein mutants are recognized. The first type arises as a result of amino acid substitutions caused by primary and compensatory resistance mutations in the polymerase gene, which concomitantly generate S gene mutations owing to overlapping S and polymerase genes. The second type occurs because of prolonged viral suppression leading to seroclearance of HBV surface antigen, where vaccine-escape-like mutants might be selected. The second type of mutants does not possess primary resistance mutations in the polymerase gene. Some drug-related S gene mutations are nonsense mutations, leading to truncation of the surface proteins. Among them, the rtA181T/sW172* mutant has a dominant negative secretion effect as well as an increased oncogenic potential. The clinical consequences of infection by these S gene mutants demand further clarification. Judicious selection of the antiviral agents and vigilant monitoring of viral mutants during the course of therapy are advised.
Yeh
Chau-Ting
CT
Liver Research Center, Chang Gung Memorial Hospital, Taipei, Taiwan. chautingy@gmail.com
D000818:Animals; D000998:Antiviral Agents / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D024882:Drug Resistance, Viral; D006514:Hepatitis B Surface Antigens / Q000187:drug effects / Q000235:genetics*; D006515:Hepatitis B virus / Q000187:drug effects / Q000235:genetics; D019694:Hepatitis B, Chronic / Q000188:drug therapy* / Q000821:virology; D006801:Humans; D051379:Mice; D009154:Mutation; D009705:Nucleosides / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D009711:Nucleotides / Q000737:chemistry / Q000494:pharmacology / Q000627:therapeutic use*; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology / Q000627:therapeutic use
D000998:Antiviral Agents; D006514:Hepatitis B Surface Antigens; D009705:Nucleosides; D009711:Nucleotides; D018894:Reverse Transcriptase Inhibitors