Conformationally Constrained Sialyl Analogues as New Potential Binders of h‐CD22

Abstract

Here, two conformationally constrained sialyl analogues were synthesized and characterized in their interaction with the inhibitory Siglec, human CD22 (h-CD22). An orthogonal approach, including biophysical assays (SPR and fluorescence), ligand-based NMR techniques, and molecular modelling, was employed to disentangle the interaction mechanisms at a molecular level. The results showed that the Sialyl-TnThr antigen analogue represents a promising scaffold for the design of novel h-CD22 inhibitors. Our findings also suggest that the introduction of a biphenyl moiety at position 9 of the sialic acid hampers canonical accommodation of the ligand in the protein binding pocket, even though the affinity with respect to the natural ligand is increased. Our results address the search for novel modifications of the Neu5Ac-α(2-6)-Gal epitope, outline new insights for the design and synthesis of high-affinity h-CD22 ligands, and offer novel prospects for therapeutic intervention to prevent autoimmune diseases and B-cell malignancies.

Tumor Carbohydrate Associated Antigen Analogs as Potential Binders for Siglec‐7

“…In analog 1, φ torsion angle around Neu5Ac-α-(2-6)-Gal glycosidic linkage for approximately À 60°could be deduced, as suggested by the absence of NOE contacts between H6 of galactose and H3 (axial and equatorial protons) of Neu5Ac (Figure S2), that instead would have been observed if φ was 180°. [20] Computational studies provided further information about the interaction between Siglec-7 and analog 1 and the combination of the NMR experiments permitted to obtain a 3D model (Figure 2). Docking calculations (GLIDE SP, version 8.0) [33] unveiled the best poses of analog 1 into the binding site of Siglec-7.…”

“…[18] Interestingly, it has been shown that the flexibility of Siglec-7 allows a conformational change of the CC' loop upon binding. [19] We previously evaluated the interactions of human CD22 (h-CD22) with two synthetic analogs of the disaccharide STn, [20] a tumor carbohydrate associated antigen (TACA). These two compounds (Figure S1) shared a common structure composed of Neu5Ac-α-(2-6)-Gal linked to a lactam ring that mimics the Thr residue found on natural STn antigens but lacking the acetyl group at C2 of the galactose unit.…”

“…Both synthesized STn analogs showed higher affinity for h‐CD22 with respect to the natural ligand, due to rigidity given by the aglycon moiety. Interestingly, the presence of a biphenyl moiety at position 9 of the Neu5Ac contributes to the interaction with h‐CD22 but impedes the canonical accommodation of the ligand into the binding site [20] …”

Glycomimetics for the inhibition and modulation of lectins

“…115 Although CD22 glycomimetic recognition is mediated by a largely preformed binding site, NMR analysis highlights that the role of the biphenyl substituent is more complex and provides room for future improvement. 332,369 Besides advancement in the 5 and 9 position, further improvement came from a C-4 modified structure-based design of 9-BPC-4-mNPC-Neu5Aca2Me (76) with a sub-micromolar affinity or C-2 modifications (77). 345,346 To the best of our knowledge the only non-carbohydrate CD22 ligand is the peptide PV3, which was derived from epratuzumab Fab and binds CD22 with 9 mM affinity.…”

“…115 Although CD22 glycomimetic recognition is mediated by a largely preformed binding site, NMR analysis highlights that the role of the biphenyl substituent is more complex and provides room for future improvement. 332,369…”