DRUG DEVELOPMENT Peptide Sugar Mimetics Prevent HIV Type 1 Replication in Peripheral Blood Mononuclear Cells in the Presence of HIV-Positive Antiserum Laura L. Eggink, 1 Maria Salas, 2 Carl V. Hanson, 2 and J. Kenneth Hoober 1 Abstract Cells of the immune system express a number of receptors that bind carbohydrate ligands. We questioned whether peptide mimetics of these ligands will activate phagocytic cells and thereby enhance an antiviral response. Short peptide sequences were identified by computational modeling of docking to glycan-specific lectins, selected as receptor analogs, and incorporated into quadravalent structures by peptide synthesis. A peptide with the se- quence HPSLK bound to several lectins specific for monosaccharides and to lectins specific for Neu5Ac- Gal-containing complex glycans, whereas a longer sequence, NPSHPLSG, bound only lectins specific for the more complex glycans. In cultures of peripheral blood mononuclear cells (PBMCs) these peptides stimulated phago- cytosis of opsonized microspheres. The peptides inhibited replication of HIV-1 in PBMC cultures by 20–80% at concentrations between 1 nM and 1 mM but inhibited replication 100% in the presence of diluted HIV-positive antiserum that alone inhibited replication by 30%. HPSLK caused about 50% loss of viability of cells at 1 mM, a concentration 10 6 -fold higher than an effective inhibitory concentration, but no toxicity was observed with NPSHPLSG. These results demonstrated that peptidomimetics of glycan ligands of cellular receptors are effective in activating phagocytosis, which may be a factor in providing complete inhibition of HIV-1 replication in vitro. Introduction H IV-1, as other enveloped viruses, 1 initiates infection by entering cells through an endocytic pathway. 2 The viral content then gains access to the cytoplasm by fusion of its envelope with the endosomal membrane. This pathway attenuates the effectiveness of antibodies to eliminate the virus through Fc-mediated phagocytosis. Although virion- antibody complexes bind to Fc-receptor-bearing phagocytic cells, 3–9 the activity of these cells becomes suppressed as the infection progresses. 3,10,11 Elimination of the virus could possibly be favorably manipulated by stimulation of the phagocytic pathway. 12,13 Phagocytic cells are regulated by an extensive array of cell surface receptors. Some are C-type lectins, which bind sugars in a calcium-dependent manner. 14,15 A C-type N- acetylgalactosamine (GalNAc)-binding receptor, CD301, is expressed on the surface of macrophages and immature dendritic cells and is involved in endocytosis. 16,17 C-type lectins that also undergo endocytosis include DC-SIGN and the mannose (Man) receptor, which bind Man; Langerin, which binds galactose (Gal); and Dectin-1, a b-glucan recep- tor. 15 Other receptors are the I-type lectins that belong to the immunoglobulin superfamily. The best characterized mem- bers of I-type lectins are siglecs (sialic acid-binding Ig-like lectins), which bind sialic acid (5-acetylneuraminic acid, Neu5Ac)-Gal-containing glycans and modulate signaling events in the immune system. 18,19 Several siglecs, particularly CD22 (siglec-2), 20 CD33 (siglec-3), 21 siglec-5, 22 and siaload- hesin (CD169), 18,19,23 undergo endocytosis on binding of sia- lylated ligands. Whereas most siglecs contain an inhibitory immunoreceptor tyrosine-based inhibitory motif (ITIM) se- quence in their cytoplasmic domain, 18,19 siglec-14 and siglec- 15 lack this domain and function in conjunction with an activating adaptor protein, DAP10 or DAP12, which contain an immunoregulatory tyrosine-based activating motif (ITAM) domain. 24,25 Glycans have several drawbacks as therapeutic agents, in particular, their difficult synthesis and stability. Conse- quently, peptide mimetics of sugars are gaining interest as substitutes. 26 We questioned whether short peptides would mimic sugar components of natural ligands of receptors that function to stimulate phagocytosis. Peptide mimetics of sug- ars have potential advantages over glycans and glycoproteins 1 Susavion Biosciences, Inc., Tempe, Arizona 85281. 2 Viral and Rickettsial Disease Laboratory, California Department of Public Health, Richmond, California 94804. AIDS RESEARCH AND HUMAN RETROVIRUSES Volume 26, Number 2, 2010 ª Mary Ann Liebert, Inc. DOI: 10.1089=aid.2009.0155 149