Pradimicin S, a Highly Soluble Nonpeptidic Small-Size Carbohydrate-Binding Antibiotic, Is an Anti-HIV Drug Lead for both Microbicidal and Systemic Use

Pradimicin S (PRM-S) is a highly water-soluble, negatively charged derivative of the antibiotic pradimicin A (PRM-A) in which the terminal xylose moiety has been replaced by 3-sulfated glucose. PRM-S does not prevent human immunodeficiency virus (HIV) adsorption on CD4(+) T cells, but it blocks virus entry into its target cells. It inhibits a wide variety of HIV-1 laboratory strains and clinical isolates, HIV-2, and simian immunodeficiency virus (SIV) in various cell culture systems (50% and 90% effective concentrations [EC(50)s and EC(90)s] invariably in the lower micromolar range). PRM-S inhibits syncytium formation between persistently HIV-1- and SIV-infected cells and uninfected CD4(+) T lymphocytes, and prevents dendritic cell-specific intercellular adhesion molecule-3-grabbing nonintegrin (DC-SIGN)-mediated HIV-1 and SIV capture and subsequent virus transmission to CD4(+) T cells. Surface plasmon resonance (SPR) studies revealed that PRM-S strongly binds to gp120 in a Ca2+-dependent manner at an affinity constant (K-D) in the higher nanomolar range. Its anti-HIV activity and HIV-1 gp120-binding properties can be dose-dependently reversed in the presence of an (alpha-1,2) mannose trimer. Dose-escalating exposure of HIV-1- infected cells to PRM-S eventually led to the isolation of mutant virus strains that had various deleted N-glycosylation sites in the envelope gp120 with a strong preference for the deletion of the high-mannose-type glycans. Genotypic resistance development occurred slowly, and significant phenotypic resistance occurred only after the sequential appearance of up to six mutations in gp120, pointing to a high genetic barrier of PRM-S. The antibiotic is nontoxic against a variety of cell lines, is not mitogenic, and does not induce cytokines and chemokines in peripheral blood mononuclear cells as determined by the Bio-Plex human cytokine 27-plex assay. It proved stable at high temperature and low pH. Therefore, PRM-S may qualify as a potential anti-HIV drug candidate for further (pre) clinical studies, including its microbicidal use.