FR-901724

A novel tricyclic 21-amino-acid peptide, FR901724, was isolated from the cultured broth of Streptomyces sp. No. 73264. This peptide appears to possess potent anti-human immunodeficiency virus (HIV) activity in vitro and might represent a lead to a new class of anti-HIV agents; it qualifies as an HIV-cell fusion inhibitor because of its weak inhibition of virus-cell binding and strong inhibition of syncytium formation. From the time-of-addition experiments, the mode of action of FR901724 was found to definitely differ from that of KNI-272, a peptide mimetic allophenylnorstatine-derivative HIV protease inhibitor. FR901724 appears to interact with a stage of the virus replicative cycle that may well correspond to virus-cell fusion. We also found that FR901724 was synergistic or had a strong tendency toward synergism when combined with other antiviral drugs, such as KNI-272, AZT, ddI and dextran sulfate.