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

Abstract

The siglec family of sialic acid-binding proteins are endocytic immune cell receptors that are recognized as potential targets for cell directed therapies. CD33 and CD22 are prototypical members and are validated candidates for targeting acute myeloid leukaemia and non-Hodgkin’s lymphomas due to their restricted expression on myeloid cells and B-cells, respectively. While nanoparticles decorated with high affinity siglec ligands represent an attractive platform for delivery of therapeutic agents to these cells, a lack of ligands with suitable affinity and/or selectivity has hampered progress. Herein we describe selective ligands for both of these siglecs, which when displayed on liposomal nanoparticles, can efficiently target the cells expressing them in peripheral human blood. Key to their identification was the development of a facile method for chemo-enzymatic synthesis of disubstituted sialic acid analogues, combined with iterative rounds of synthesis and rapid functional analysis using glycan microarrays.

CD22 Ligands on a Natural N-Glycan Scaffold Efficiently Deliver Toxins to B-Lymphoma Cells

“…The 9-C and 5-C sialic acids were prepared similarly to our published methods 21 with some modifications as described in Experimental Procedures and Supplementary Information. These sialic acid analogs, 1a–c are readily prepared to gram scale.…”

“…41–42 The Chinese hamster ovary (CHO) parental (wild type) cell line (WT-CHO) and cells expressing human or murine Siglecs (Siglec-CHO) were described previously. 21, 36 The recombinant siglec-Fc chimeras, hCD22 Fc 23 and mSn Fc 36 , were prepared as previously described. A polymeric CD22 ligand (1 M Da), Neu5Gcα2–6LacNAc-PAA-Biotin (Neu5Gc-PAA), was obtained from the Consortium for Functional Glycomics (CFG #: PA365).…”

“…1, 17–18 To overcome the low avidity of natural sialosides, several groups have employed sialic acid analogues with substituents at the C-9 and/or C-5 positions to increase avidity and selectivity for CD22. 1, 17–19 Exemplary analogs for human CD22 are 9-N-biphenyl carboxamide-Neu5Ac ( BPC Neu5Ac; 1a ) 20 and 9-N-m-phenoxybenzamide-Neu5FAc ( MPB Neu5FAc; 1c ) 21 that have affinities in the low micromolar range. Yet they do not have enough avidity to compete with natural glycoprotein ligands on B cells, so called cis -ligands, 22 requiring multivalent presentation on polymers or nanoparticles for stable binding to and uptake by cells.…”

Synthesis and biological evaluation of 9- N -oxamyl sialosides as Siglec-7 ligands

“…[7][8][9][10][11][12][13][14][15] Further affinity enhancing substitutions, including a Siglec-7 selective ligand, were found by screening a set of substituted di-and trisaccharides. 8,[16][17][18][19] Previously, high affinity Siglec ligands proved to be very useful to study the biological function of their lectin domain. [20][21][22] Selective ligands were used as well for cell specific delivery of toxic agents to kill malignant cells, for delivery of antigens to improve vaccinations and for tolerance induction.…”

Detection of mSiglec-E, in solution and expressed on the surface of Chinese hamster ovary cells, using sialic acid functionalised gold nanoparticles

“…18 hSiglec-7, overexpressed on a variety of cancer cells, 19 has been used as a target for the drug delivery of antibody-functionalised poly(lactide-co-glycolide) nanoparticles. 20 Recently, the use of liposomal nanoparticles functionalised with glycan ligands that bind specifically to a Siglec of interest such as hCD33 and hCD22, 21 sialoadhesin/Siglec-1, 22 Siglec-9 23 and Siglec-7 24 has been extensively reported by Paulson and co-workers. These studies use fluorescence-based techniques to elucidate the behaviour of the nanoparticles within the cells.…”