Feline Immunodeficiency Virus, a Model for Reverse Transcriptase-targeted Chemotherapy for Acquired Immune Deficiency Syndrome

Feline immunodeficiency virus (FIV), formerly called feline T-lymphotropic lentivirus, causes an immune deficiency in cats that is very similar to the acquired immune deficiency syndrome in humans (N. C. Pedersen, E. M. Ho, M. L. Brown, and J. K. Yamamoto, Science 235:790-793, 1987). We have examined the reverse transcriptase of this virus to determine whether it is similar enough to the reverse transcriptase of the human immunodeficiency virus type 1 (HIV-1) to enable its use as a model for chemotherapy for acquired immune deficiency syndrome. The FIV reverse transcriptase is similar to that of HIV-1 in sensitivity to the noncompetitive inhibitor phosphonoformate (Ki, 0.3 microM) and relative insensitivity to phosphonoacetate. This enzyme was also sensitive to two competitive inhibitors, the 5'-triphosphates of 2', 3'-dideoxythymidine (Ki, 3.4 nM) and 3'-azido-3'-deoxythymidine (AZT; Ki, 6.2 nM). The ratios of Ki/Km for these two competitive inhibitors are similar to the ratios calculated from previously reported data for the HIV-1 enzyme assayed under identical conditions. In contrast, the FIV enzyme is different from the reverse transcriptase of avian myeloblastosis virus in sensitivity to those inhibitors. The replication of FIV in Crandell feline kidney cells was inhibited by AZT; virus production was inhibited more than 95% by 1.0 microM AZT.