ROLE OF ADDITIONAL MUTATIONS OUTSIDE THE YMDD MOTIF OF HEPATITIS-B VIRUS POLYMERASE IN L(-)SDDC (3TC) RESISTANCE

L(-)SddC (3TC) has been shown to be the most promising nucleoside anal ogue used for the treatment of hepatitis B virus (HBV) infection. Unfo rtunately, it has been reported that about 12% of HBV-infected patient s experience a recurrence of HBV after a period of treatment with 3TC. Point mutations were detected in the HBV polymerase of those viruses from 3TC-resistant patients. A common mutation occurred at methionine in the YMDD motif. In this report, we present mutants that were genera ted from the HBV genome (adr subtype) by site-directed mutagenesis bas ed on clinical reports from other investigators. With the transient tr ansfection system, it was found that by changing methionine to valine or isoleucine at the YMDD motif, the viral DNA replication would be mo re than 100-fold less efficient than that of the wild-type virus. Some additional mutations outside the YMDD motif could enhance the replica tion of the virus containing a YMDD mutation. Various levels of resist ance to 3TC were observed in HBV mutants containing point mutations bo th inside and outside the YMDD motif. These results suggest. that the mutations outside the YMDD motif compensate the YMDD mutation to some extent for the viral replication and may also contribute to clinical v iral resistance to 3TC. (C) 1998 Elsevier Science Inc.