Anti-human immunodeficiency virus activity of YK-FH312 (a betulinic acid derivative), a novel compound blocking viral maturation

Betulinic acid, a triterpenoid isolated from the methyl alcohol extract of the leaves of Syzigium claviflorum, was found to have a potent inhibitory a ctivity against human immunodeficiency virus type 1 (HIV-1). Betulinic acid derivatives were synthesized to enhance the anti-HIV activity. Among the d erivatives, 3-0-(3',3'-dimethylsuccinyl) betulinic acid, designated YK-FH31 2, showed the highest activity against HIV-induced cytopathic effects in HT V-1-infected MT-4 cells. To determine the step(s) of HIV replication affect ed by YK-FH312, a syncytium formation inhibition assay in MOLT-4/HIV-1(IIIB ) and MOLT-4 coculture, a multinuclear-activation-of galactosidase-indicato r (MAGI) assay in MAGI-CCR5 cells, electron microscopic observation, and a time-of-addition assay were performed. In the syncytium formation inhibitio n assay or in the MAGI assay for de novo infection, the compound did not sh ow inhibitory effects against HIV replication. Conversely, no virions were detected in HIV-1-infected cell cultures treated with YK-FH312 either by el ectron microscopic observation or by viral yield in the supernatant, In acc ordance with a p24 enzyme-linked immunosorbent assay of culture supernatant in the time-of-addition assay, YK-FH312 inhibited virus expression in the supernatant when it was added 18 h postinfection, However, Western blot ana lysis of the cells in the time-of-addition assay revealed that the producti on of viral proteins in the cells was not inhibited completely by YK-FH312, These results suggest that YK-FH312 might affect the step(s) of virion ass embly and/or budding of virions, and this is a novel mechanism of action of an anti-HIV compound.