Screening of the Pan-African Natural Product Library Identifies Ixoratannin A-2 and Boldine as Novel HIV-1 Inhibitors

Abstract

The continued burden of HIV in resource-limited regions such as parts of sub-Saharan Africa, combined with adverse effects and potential risks of resistance to existing antiretroviral therapies, emphasize the need to identify new HIV inhibitors. Here we performed a virtual screen of molecules from the pan-African Natural Product Library, the largest collection of medicinal plant-derived pure compounds on the African continent. We identified eight molecules with structural similarity to reported interactors of Vpu, an HIV-1 accessory protein with reported ion channel activity. Using in vitro HIV-1 replication assays with a CD4+ T cell line and peripheral blood mononuclear cells, we confirmed antiviral activity and minimal cytotoxicity for two compounds, ixoratannin A-2 and boldine. Notably, ixoratannin A-2 retained inhibitory activity against recombinant HIV-1 strains encoding patient-derived mutations that confer resistance to protease, non-nucleoside reverse transcriptase, or integrase inhibitors. Moreover, ixoratannin A-2 was less effective at inhibiting replication of HIV-1 lacking Vpu, supporting this protein as a possible direct or indirect target. In contrast, boldine was less effective against a protease inhibitor-resistant HIV-1 strain. Both ixoratannin A-2 and boldine also inhibited in vitro replication of hepatitis C virus (HCV). However, BIT-225, a previously-reported Vpu inhibitor, demonstrated antiviral activity but also cytotoxicity in HIV-1 and HCV replication assays. Our work identifies pure compounds derived from African plants with potential novel activities against viruses that disproportionately afflict resource-limited regions of the world.

Novel Acylguanidine-Based Inhibitor of HIV-1

“…To investigate SM111's mechanism of action, we next tested its ability to inhibit recombinant HIV-1 NL4.3 strains carrying patient-derived sequences that harbor major resis- (Fig. 4A) (35). As expected, wild-type HIV-1 NL4.3 failed to replicate in the presence of 100 nM of each antiretroviral (ARV) (Fig.…”

“…HEK-293T cells were purchased commercially (Lenti-X 293T; Clontech Laboratories) and maintained in D10ϩ medium (Dulbecco's modified Eagle medium with 4.5 g/liter glucose and L-glutamine [Lonza] supplemented with 10% FCS, 100 U penicillin/ml, and 100 g streptomycin/ml [Sigma]). SM111, SM113, and BIT-225 were synthesized as reported previously (35,36). For each compound, a 100 mM stock solution was prepared in dimethyl sulfoxide (DMSO), aliquoted, and stored at Ϫ20°C until use.…”

“…1A) and BIT-225 (Fig. 1B), are reported to inhibit HIV-1 replication; however, both display substantial in vitro toxicity, particularly to T cells (5,6,34,35). We therefore sought to design an acylguanidine-based derivative with a reduced cytotoxic component.…”

“…Unfortunately, the high in vitro cytotoxicity of most acylguanidines with antiviral activity has precluded more detailed molecular and cellular studies (4)(5)(6). For example, while BIT-225 has shown promise in early clinical trials (33), it displays lower activity in T cell lines, where inhibitory concentrations frequently cause cell death (7,34,35).…”

Identification of Bichalcones as Sirtuin Inhibitors by Virtual Screening and <em>in Vitro </em>Testing

“…Owing to the small quantities of the isolated samples, an efficient approach for the management of the p-ANAPL library has been to only test samples of in silico hits from virtual screening. A previous successful campaign, which combined pharmacophore-based virtual screening and in vitro testing, had led to the identification of boldine and ixoratannin as anti-HIV-1 compounds [11].…”