The 3-O-(3′,3′-dimethylsuccinyl) derivative of betulinic acid (DSB) inhibits the assembly of virus-like particles in HIV-1 Gag precursor-expressing cells

Abstract

Background: The 3-O-(3′,3′-dimethylsuccinyl) derivative of betulinic acid (DSB) blocks HIV-1 maturation by interfering with viral protease (PR) at the capsid (CA)-SP1 cleavage site, a crucial region in HIV-1 morphogenesis. Methods: We analysed the effect of DSB on the assembly of HIV-1 Gag precursor (Pr55GagHIV) into membrane-enveloped virus-like particles (VLP) in baculovirus-infected cells expressing Pr55GagHIV, in a cellular context devoid of viral PR. Results: DSB showed a dose-dependent negative effect on VLP assembly, with an IC50∼10 μM. The DSB inhibitory effect was p6-independent and was also observed for intracellular assembly of non-N-myristoylated Gag core-like particles. HIV-1 VLP assembled in the presence of DSB exhibited a lower stability of their inner cores upon membrane delipidation compared with control VLP, suggesting weaker Gag-Gag interactions. DSB also inhibited the assembly of simian immunodeficiency virus SIVmac251 VLP, although with a twofold lower efficacy (IC50∼20 μM). No detectable inhibitory activity was observed for murine leukaemia virus (MLV) VLP; however, fusion of the SP1-NC-p6 domains from HIV-1 to the matrix (MA)-CA domains from MLV conferred DSB sensitivity to the chimaeric Gag precursor Pr72GagMLV-HIV (IC50=30 μM). This observation suggested that the main DSB target on Pr55Gag was the SP1 domain, but the higher degree of DSB resistance for Pr72GagMLV-HIV compared with Pr55GagHIV implied that other upstream Gag region(s) might contribute to DSB reactivity. Conclusions: Sequence alignment and three-dimensional modelling by homology of the CA-SP1-NC junction in HIV-1, SIVmac251 and Pr72GagMLV-HIV suggested that a higher hydrophilic character of the CA region immediately upstream to the HIV-1 CA-SP1 junction, as occurred in Pr72GagMLV-HIV, correlated with a lower DSB sensitivity. © 2007 International Medical Press.