Design, synthesis and evaluation of potential inhibitors of HIV gp120–CD4 interactions

Neutralising properties of peptides derived from CXCR4 extracellular loops towards CXCL12 binding and HIV-1 infection

The chemokine receptor CXCR4 interacts with a single endogenous chemokine, CXCL12, and regulates a wide variety of physiological and pathological processes including inflammation and metastasis development. CXCR4 also binds the HIV-1 envelope glycoprotein, gp120, resulting in viral entry into host cells. Therefore, CXCR4 and its ligands represent valuable drug targets. In this study, we investigated the inhibitory properties of synthetic peptides derived from CXCR4 extracellular loops (ECL1-X4, ECL2-X4 and ECL3-X4) towards HIV-1 infection and CXCL12-mediated receptor activation. Among these peptides, ECL1-X4 displayed anti-HIV-1 activity against X4, R5/X4 and R5 viruses (IC50=24 to 76μM) in cell viability assay without impairing physiological CXCR4-CXCL12 signalling. In contrast, ECL2-X4 only inhibited X4 and R5/X4 strains, interfering with HIV-entry into cells. At the same time, ECL2-X4 strongly and specifically interacted with CXCL12, blocking its binding to CXCR4 and its second receptor, CXCR7 (IC50=20 and 100μM). Further analysis using mutated and truncated peptides showed that ECL2 of CXCR4 forms multiple contacts with the gp120 protein and the N-terminus of CXCL12. Chemokine neutralisation was mainly driven by four aspartates and the C-terminal residues of ECL2-X4. These results demonstrate that ECL2 represents an important structural determinant in CXCR4 activation. We identified the putative site for the binding of CXCL12 N-terminus and provided new structural elements to explain the recognition of gp120 and dimeric CXCR4 ligands.

Galectin-1-specific inhibitors as a new class of compounds to treat HIV-1 infection

Despite significant improvements, antiretroviral therapies against HIV-1 are plagued by a high frequency of therapeutic failures that have been associated with acquisition of drug resistance. We recently reported that HIV-1 exploits a host glycan binding protein, galectin-1, to increase its attachment to host cells, thereby increasing its overall infectivity in susceptible cells. This finding suggests that host molecules such as galectin-1 could reduce the expected efficiency of HIV-1 drugs targeting early steps of the replicative cycle, such as attachment and entry processes. Thus, new classes of drugs that would interfere with galectin-1/HIV-1 interactions could benefit the current antiretroviral therapy. To further explore this possibility, experiments were conducted to discover leading compounds showing specific inhibition of galectin-1 activity in a cellular model of HIV-1 infection. Three lactoside compounds were found to modestly inhibit the interaction of galectin-1 with primary human CD4(+) T cells. Interestingly, these same inhibitors reduced the galectin-1-mediated increase in HIV-1 attachment to target cells in a much more efficient manner. More important, the tested lactoside derivatives also significantly decreased the galectin-1-dependent enhancement of HIV-1 infection. These observations deserve further attention when considering that the development of new drugs to prevent and treat HIV-1 infection remains a priority.

Targeting protein-protein interactions by rational design: mimicry of protein surfaces

Protein-protein interactions play key roles in a range of biological processes, and are therefore important targets for the design of novel therapeutics. Unlike in the design of enzyme active site inhibitors, the disruption of protein-protein interactions is far more challenging, due to such factors as the large interfacial areas involved and the relatively flat and featureless topologies of these surfaces. Nevertheless, in spite of such challenges, there has been considerable progress in recent years. In this review, we discuss this progress in the context of mimicry of protein surfaces: targeting protein-protein interactions by rational design.

Interaction of monobenzamidine-linked trypanocides with the Trypanosoma brucei P2 aminopurine transporter

Single benzamidine group-carrying compounds were shown to interact with the Trypanosoma brucei P2 aminopurine transporter. Replacement of the amidine with a guanidine group decreased affinity. Trypanocidal activity was evident, but compounds were equally toxic against trypanosomes lacking the P2 transporter, which indicates additional uptake routes for monobenzamidine-derived compounds.