Glycine-amide is an active metabolite of the antiretroviral tripeptide glycyl-prolyl-glycine-amide

The chemically modified tripeptide glycyl-prolyl-glycine-amide (GPG-NH2) inhibits replication of human immunodeficiency virus (HIV) type 1 (HIV-1) in vitro, probably by interfering with capsid formation. The aim of the present study was to determine whether the metabolites glycyl-proline (GP-OH), glycine (G-OH), prolyl-glycine-amide (PG-NH2), proline (P-OH), and glycine-amide (G-NH2) from proteolytic cleavage may inhibit the replication of HIV-1 in vitro. PG-NH2 has previously been shown to have a modest effect on HIV-1 replication. In the present study we show that G-NH2 exhibits a pronounced inhibitory effect on HIV-1. This effect was not due to a decrease in cell proliferation or viability and could not be shown for herpes simplex virus type 1. The G-NH2 concentration that inhibited virus replication by 50% (IC50) was equimolar to that of GPG-NH2 and ranged from 3 to 41 muM. Transmission electron microscopy revealed that the effect of G-NH2 on HIV-1 morphology was equivalent to that of GPG-NH2 and showed disarranged capsid structures, indicating interference with capsid formation. Serial passage of HIV-infected cells with G-NH2 for more than 20 subcultivations did not decrease the susceptibility to the compound. The results from this study suggest that GPG-NH2 might act as a prodrug and that G-NH2 is an active antiretroviral metabolite.