Inhibitory effects of selected antiviral compounds on human hepatitis B virus DNA synthesis

By using an assay system based on a human hepatoblastoma cell line (HB611) that continuously synthesizes hepatitis B virus DNA, the following compounds were found to inhibit hepatitis B virus DNA synthesis at concentrations that were significantly lower than their minimum cytotoxic concentrations: 9-(2-phosphonylmethoxyethyl)-2,6-diaminopurine (PMEDAP), (S)-9-(3-hydroxy-2-phosphonylmethoxypropyl)adenine, 9-(phosphonylmethoxyethyl)adenine, 2',3'-dideoxy-2',3'-didehydrocytidine, and 2',3'-dideoxycytidine. The most potent compound was PMEDAP (50% effective concentration, 0.02 micrograms/ml). The selective index, or ratio of the 50% cytotoxic concentration to 50% effective concentration, of PMEDAP was greater than 750.