Inhibition of human hepatitis B virus replication by AT-61, a phenylpropenamide derivative, alone and in combination with (-)beta-L-2 ',3 '-dideoxy-3'-thiacytidine

AT-61, a member of a novel class of phenylpropenamide derivatives, was foun d to be a highly selective and potent inhibitor of human hepatitis B virus (HBV) replication in four different human hepatoblastoma cell Lines which s upport the replication of HBV (i.e., HepAD38, HepAD79, 2.2,15, and transien tly transfected HepG2 cells). This compound was equally effective at inhibi ting both the formation of intracellular immature core particles and the re lease of extracellular virions, with 50% effective concentrations ranging f rom 0.6 to 5.7 mu M. AT-61 (27 mu M) was able to reduce the amount of HBV c ovalently closed circular DNA found in the nuclei of HepAD38 cells by >99%. AT-61 at concentrations of >27 mu M had little effect on the amount of vir al RNA found within the cytoplasms of induced HepAD38 cells but reduced the number of immature virions which contained pregenomic RNA by >99%. The pot ency of AT-61 aas not affected by one of the mutations responsible for (-)- beta-L-2',3'-dideoxy-3' thiacytidine (3TC) resistance in HBV, and AT-61 act ed synergistic,vith 3TC to inhibit HBV replication. AT-61 (81 mu M) was not cytotoxic or antiproliferative to several cell lines and had no antiviral effect on woodchuck or duck HBV, human immunodeficiency virus type 1, herpe s simplex virus type 1, vesicular stomatitis virus, or Newcastle disease vi rus. Therefore, we concluded that the antiviral activity of AT-61 is specif ic for HBV replication and most likely occurs at one of the steps between t he synthesis of viral RNA and the packaging of pregenomic RNA into immature core particles.