CD22-Antagonists with nanomolar potency: The synergistic effect of hydrophobic groups at C-2 and C-9 of sialic acid scaffold

Abstract

In earlier studies, we identified the C-9 amido derivative 1 (9-(4'-hydroxy-4-biphenyl)acetamido-9-deoxy-Neu5Gcα2-6GalOMP) and the C-9 amino derivative 2 (9-(4'-hydroxy-4-biphenyl)methylamino-9-deoxy-Neu5Gcα2-6GalOMP) have the most promising affinity for mouse CD22 and human CD22, respectively. Replacing the subterminal galactose residue (2-6Gal-OMP) of 1 with benzyl (5) or biphenylmethyl (6) as aglycone led to even higher potency for mCD22. In this study, both compounds showed improved potency and selectivity for CD22 (IC50 70 nM) and 712-fold more selective for CD22 than for MAG. The corresponding derivatives of 2, compounds 8 and 9, showed comparable activity to 2 but lower potency and selectivity than 5 and 6. Although compounds 5-9 are simple and small molecular weight antagonists, they showed much high potency and selectivity than the corresponding compounds having α 2-6Gal linkage. Both biological and computational docking simulation studies suggest that the 2-6Gal-OMP residues of 1 and 2 are not critical for binding process and could be replaced with hydrophobic non carbohydrate moieties. The data presented herein has significant implications for the design and discovery of next-generation CD22-antagonists

From a Library of MAG Antagonists to Nanomolar CD22 Ligands

“…Surprisingly, 17 a (Entry 26) does not bind to CD22, although the o-nosyl substituent does not prohibit binding of 9 k. As reported by Kiso and colleagues, [19] intramolecular attraction between benzyl at the 2-position and biphenyl at the 9-position can lead to a hydrophobic collapse. The introduction of an onosyl group at the 5-position may further support this process, abolishing the binding of 17 a.…”

“…[16,17] CD22 recognizes sialic acid a2,6-linked to d-Gal, d-GalNAc (!1), or d-GlcNAc. A decrease in the structural complexity yielded sialic acid derivatives 2-4 [15,18,19] ( Figure 1), indicating that a biphenyl carboxamide moiety at the 9-position can improve affinity substantially. When this extension in the 9-position was applied to the disaccharide epitope, ligands such as 5 and 6 exhibiting sub-micromolar affinities were identified.…”

“…[20] Finally, benzyl substituents at the reducing end of the disaccharide epitope led to a further improvement in affinity. [19,21] When testing in B-cell based assays, a further aspect, the socalled density-dependent binding, must be considered. [22] In tests of monomeric sialosides (e.g., 7 [23] or 8, [24] Figure 1) coupled to various supports such as a polyacrylamide backbone, [23] a glutamate cluster, [18] or a polymer obtained by ring-opening metathesis, [25] a substantial increase in binding affinity relative to monovalent sialosides was observed.…”

Disubstituted sialic acid ligands targeting siglecs CD33 and CD22 associated with myeloid leukaemias and B cell lymphomas

“…In contrast, several groups have generated ligands of CD22 with 100-1000 fold higher affinity than the natural ligand, but the best of these have not demonstrated adequate selectivity. 36, 38, 39, 41 For example, although we have shown that doxorubicin-loaded liposomes displaying a high affinity ligand of CD22 (Fig. 1, compound 4 ) are effective in prolonging life in a murine model of disseminated human B cell lymphoma, this ligand exhibits a major cross-reactivity with sialoadhesin (Siglec-1, mSn), expressed on macrophages, which mediate rapid clearance of the liposomes.…”

Extensive crosslinking of CD22 by epratuzumab triggers BCR signaling and caspase-dependent apoptosis in human lymphoma cells

“…Thus, besides the routine measurement of intracellular calcium as a marker for B-cell activation and cell surface binding to assess the affinity for CD22, the biological significance of CD22-targeting agents, particularly those derived from synthetic sialosides, 40,41,[45][46][47] should be substantiated with a suitable cytotoxicity assay, as exemplified by the capability of liposomal nanoparticles displaying both antigen and CD22L to induce antigen-specific B-cell apoptosis. 5 mg/mL; GAH, 10 mg/mL), and Wet-III (lane 7; hLL2, 7.5 mg/mL; GAH, 10 mg/mL; anti-IgM, 1 mg/mL).…”