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

Abstract

We investigated two recently synthesized and characterized sialyl derivatives, bearing the Neu5Ac‐α‐(2‐6)‐Gal epitope, as promising binders for Siglec‐7, an inhibitory Siglec mainly found on natural killer cells. A variety of sialoglycan structures can be recognized by Siglec‐7 with implications in the modulation of immune responses. Notably, overexpression of sialylated glycans recognized by Siglec‐7 can be associated with the progression of several tumors, including melanoma and renal cell carcinoma. NOE‐based NMR techniques, including Saturation Transfer Difference and transferred‐NOESY NMR, together with molecular docking and dynamic simulations were combined to shed light on the molecular basis of Siglec‐7 recognition of two conformationally constrained Sialyl‐Tn antigen analogs. We, therefore, identify the ligands epitope mapping and their conformational features and propose 3D models accurately describing the protein‐ligand complexes. We found that the binding site of Siglec‐7 can accommodate both synthetic analogs, with the sialic acid mainly involved in the interaction. Moreover, the flexibility of Siglec‐7 loops allows a preferred accommodation of the more rigid compound bearing a biphenyl moiety at position 9 of the sialic acid that contributed to the interaction to a large extent. Our findings provided insights for developing potential novel high affinity ligands for Siglec‐7 to hinder tumor evasion.

Directing in Vitro Selection towards G‐quadruplex‐forming Aptamers to Inhibit HMGB1 Pathological Activity

“…With the aim of validating the ELONA assay and prove the specificity of the selected sequences for HMGB1, the described assay was also used to evaluate the affinity of the best‐performing aptamers for the following additional targets of biological interest: i) VEGF‐A, which is the protein used for the negative selection step in the SELEX procedure, in consideration of its high serum levels in cancer and inflammation, [42,43] analogously to HMGB1; ii) Galectin‐3, [56] which is a circulating protein involved in several biological processes, including apoptosis, cell proliferation and inflammation; iii) Siglec‐7, [57] a membrane protein found in innate lymphoid natural killer (NK) cells, blood monocytes and dendritic cells, involved in the maintenance of immune homeostasis; iv) CD19, [58] a membrane protein expressed on the surface of B and plasma cells involved in establishing intrinsic B cell signaling thresholds. In addition, VEGF‐A is also a G4 binding protein (G4BP) which showed high affinity for parallel G‐quadruplex aptamers [43,51,52,59] .…”