HEP-05-0036.R1 Susceptibility to Antivirals of an HBV Strain With Mutations Conferring Resistance to Both Lamivudine and Adefovir

Abstract Mutations within the Hepatitis B virus (HBV) polymerase gene conferring drug -resistance are selected during prolonged lamivudine (3TC) or adefovir dipivoxil (ADV) treatment. As there is no other appro ved drug against HBV, treatments with 3TC or ADV are used either sequentially or in addition depending on treatment response or failure. Considering the use of de novo or add -on 3TC+ADV bitherapy, we investigated the possibility of emergence of an HBV stra in harboring polymerase mutations conferring resistance to both 3TC (rtL180M+M204V) and ADV (rtN236T). We constructed the L180M+M204V+N236T mutant and determined its replication capacity and its susceptibility to different nucleos(t)ide analogs in transien tly transfected hepatoma cell lines. The triple mutant replicates its genome in vitro , but less efficiently than either the wild -type (wt) HBV or L180M+M204V and N236T mutants. Phenotypic assays indicated that the L180M+M204V+N236T mutant is resistant to p yrimidine analogs (3TC, -FTC, E -L -FD4C, L -FMAU). Compared to wt HBV, this mutant displays a 6 fold decreased susceptibility to ADV and entecavir and a 4 fold decreased susceptibility to tenofovir. Interferon D inhibited equally the replication of wt and L1 80M+M204V+N236T HBV. In conclusion, the combination of rtL180M+M204V and rtN236T mutations impairs HBV replication and confers resistance to both 3TC and ADV in vitro . This suggests that the emergence of the triple mutant may be delayed and associated with viral resistance in patients treated with 3TC+ADV. However, other nucleos(t)ide analogs in development showed an antiviral activity against this multiresistant strain in vitro . This provides a rationale for the clinical evaluation of de novo combination t herapies. inserm-00133179, version 1 - 3 Nov 2009