Belgian Society for Microbiology meeting location:Brussels date:27 November 2013
The CD4 cell surface protein is the primary receptor used by the human immunodeficiency virus (HIV) for the entry and infection of host cells, such as T-helper lymphocytes. Efficient infection of HIV requires a high cellular expression level of CD4, together with the chemokine co-receptors CCR5 or CXCR4. Previous attempts to block the viral access to CD4 by using truncated soluble forms of CD4 as decoy receptor were unsuccessful. However, clinical studies with anti-CD4 monoclonal antibodies (Ibalizumab) showed efficacy in HIV-infected individuals. We have previously reported a class of HIV entry inhibitor compounds called cyclotriazadisulfonamides (CADA). These small synthetic compounds specifically down-modulate the expression level of the CD4 protein on the cell surface and subsequent prevent HIV infection of target cells. Here, we describe how structural variations in CADA derivatives affect the compounds’ ability to lower the CD4 expression level and how this correlates with their anti-HIV potency. Seventeen new CADA compounds were synthesized with variations in the sulfonamide chains, triaza ring substituents and ring size. The CD4 down-modulating activity of the compounds was independent of the cell type used: similar relative effects on CD4 were observed for the different analogs in MT-4 lymphoblastoma cells and in a CHO cell line, expressing a CD4-YFP reporter protein (R = 0.95, p < 0.001). The level of CD4 down-modulation evoked by the compounds and their anti-HIV activity correlated well: the pearson correlation of the comparison between the CD4 expression levels and HIV NL4.3 infection levels in MT-4 cells was 0.92 (p < 0.001). The correlation between our different assays confirmed the link between CD4 expression levels and the efficiency of infection by HIV. From our structure-activity data, we concluded that compounds with a high electron density in one of the sulfonamide chains showed the highest potency. Variations in the ring substituents had a minor adverse effect but methylation of a nitrogen atom in the ring caused significant loss of activity. Also, the higher activity of unsymmetrical CADA analogs suggested a bimolecular binding model for the CADA compounds. Remarkably, analogs with a smaller 11-ring backbone retained CD4 down-modulating activity and showed a consistent twofold reduction in compound potency as compared to their 12-ring counterparts. Thus, besides optimization of the sulfonamide side chains, size variations in the essential cyclic backbone are feasible, enabling the future exploration of more variations in triaza ring size to generate more potent CADA analogs as a new class of HIV entry inhibitors.