Novel Siglec-15-Sia axis inhibitor leads to colorectal cancer cell death by targeting miR-6715b-3p and oncogenes.

Siglecs are well known immunotherapeutic targets in cancer. Current checkpoint inhibitors have exhibited limited efficacy, prompting a need for novel therapeutics for targets such as Siglec-15. Presently, small molecule inhibitors targeting Siglec-15 are not explored alongside characterised regulatory mechanisms involving microRNAs in CRC progression. Therefore, a small molecule inhibitor to target Siglec-15 was elucidated in vitro and microRNA mediated inhibitor effects were investigated. Our research findings demonstrated that the SHG-8 molecule exerted significant cytotoxicity on cell viability, migration, and colony formation, with an IC50 value of approximately 20µM. SHG-8 exposure induced late apoptosis in vitro in SW480 CRC cells. Notably, miR-6715b-3p was the most upregulated miRNA in high-throughput sequencing, which was also validated via RT-qPCR. MiR-6715b-3p may regulate PTTG1IP, a potential oncogene which was validated via RT-qPCR and in silico analysis. Additionally, molecular docking studies revealed SHG-8 interactions with the Siglec-15 binding pocket with the binding affinity of -5.4 kcal/mol, highlighting its role as a small molecule inhibitor. Importantly, Siglec-15 and PD-L1 are expressed on mutually exclusive cancer cell populations, suggesting the potential for combination therapies with PD-L1 antagonists.

Siglec and anti-Siglec therapies.

Siglecs (sialic acid-binding immunoglobulin-like lectins) are a family of receptors that bind sialic acids in specific linkages on glycoproteins and glycolipids. Siglecs play roles in immune signalling and exhibit cell-type specific expression and endocytic properties. Recent studies suggest that Siglecs are likely to function as immune checkpoints that regulate responses in cancers and inflammatory diseases. In this review, we discuss strategies to target the Siglec-sialic acid axis in human diseases, particularly cancer, and the possibility of exploiting them for therapeutic intervention.

Expedient assembly of Oligo-LacNAcs by a sugar nucleotide regeneration system: Finding the role of tandem LacNAc and sialic acid position towards siglec binding.

Sialosides containing (oligo-)N-acetyllactosamine (LacNAc, Galß(1,4)GlcNAc) as core structure are known to serve as ligands for Siglecs. However, the role of tandem inner epitope for Siglec interaction has never been reported. Herein, we report the effect of internal glycan (by length and type) on the binding affinity and describe a simple and efficient chemo-enzymatic sugar nucleotide regeneration protocol for the preparative-scale synthesis of oligo-LacNAcs by the sequential use of ß1,4-galactosyltransferase (ß4GalT) and ß1,3-N-acetylglucosyl transferase (ß3GlcNAcT). Further modification of these oligo-LacNAcs was performed in one-pot enzymatic synthesis to yield sialylated and/or fucosylated analogs. A glycan library of 23 different sialosides containing various LacNAc lengths or Lac core with natural/unnatural sialylation and/or fucosylation was synthesized. These glycans were used to fabricate a glycan microarray that was utilized to screen glycan binding preferences against five different Siglecs (2, 7, 9, 14 and 15).

Sialic Acid Mimetics to Target the Sialic Acid-Siglec Axis.

Sialic acid sugars are vital regulators of the immune system through binding to immunosuppressive sialic acid-binding immunoglobulin-like lectin (Siglec) receptors on immune cells. Aberrant sialic acid-Siglec interactions are associated with an increasing number of pathologies including infection, autoimmunity, and cancer. Therefore, the sialic acid-Siglec axis is an emerging target to prevent or affect the course of several diseases. Chemical modifications of the natural sialic acid ligands have led to sialic acid mimetics (SAMs) with improved binding affinity and selectivity towards Siglecs. Recent progress in glycobiotechnology allows the presentation of these SAMs on nanoparticles, polymers, and living cells via bioorthogonal synthesis. These developments now enable the detailed study of the sialic acid-Siglec axis including its therapeutic potential as an immune modulator.

Constitutively expressed Siglec-9 inhibits LPS-induced CCR7, but enhances IL-4-induced CD200R expression in human macrophages.

Siglecs recognize the sialic acid moiety and regulate various immune responses. In the present study, we compared the expression levels of Siglecs in human monocytes and macrophages using a quantitative real-time reverse transcription-polymerase chain reaction analysis. The differentiation of monocytes into macrophages by macrophage colony-stimulating factor or granulocyte macrophage colony-stimulating factor enhanced the expression of Siglec-7 and Siglec-9. The differentiated macrophages were stimulated by lipopolysaccharide (LPS) plus interferon (IFN)-γ or interleukin (IL)-4. The expression of Siglec-10 was enhanced by IL-4, whereas that of Siglec-7 was reduced by LPS plus IFN-γ. The expression of Siglec-9 was not affected by these stimuli. The knockdown of Siglec-9 enhanced the expression of CCR7 induced by the LPS or the LPS plus IFN-γ stimulation, and decreased the IL-4-induced expression of CD200R. These results suggest that Siglec-9 is one of the main Siglecs in human blood monocytes/macrophages and modulates innate immunity.

Antiallergic effect of anti-Siglec-F through reduction of eosinophilic inflammation in murine allergic rhinitis.

BACKGROUND: Sialic acid-binding Ig-like lectin-F (Siglec-F) in mice and its functional paralog Siglec-8 in humans are transmembrane receptors that play a role in the apoptosis of eosinophils. We aimed to evaluate the therapeutic potential of anti-Siglec-F antibodies in a murine model of allergic rhinitis. METHODS: Twenty-eight BALB/c mice were used. In group A (control group, n = 7), mice were sensitized and challenged with saline. In group B (ovalbumin [OVA] challenge group, n = 7), OVA was used for i.p. sensitization and intranasal challenge. Mice in group C (control IgG group, n = 7) or those in group D (anti-Siglec-F group, n = 7) had been given rabbit control IgG or anti-Siglec-F antibody injections, respectively. We assessed the number of nose-scratching events; serum total/OVA-specific IgE; the number of eosinophils, neutrophils, and lymphocytes in bronchoalveolar lavage (BAL) fluid; histopathological changes in nasal cavity tissues; and the levels of IL-4, IL-5, and IL-13 in BAL fluid. RESULTS: Mice in group D had significantly less nose scratching. Serum total and OVA-specific IgE were not significantly changed. The number of eosinophils in BAL fluid and in the lamina propria of the nasal cavity mucosa was significantly decreased with anti-Siglec-F antibody treatment. The levels of Th2 cytokines such as IL-4, IL-5, and IL-13 were also significantly decreased with anti-Siglec-F antibody treatment. CONCLUSION: Anti-Siglec-F antibody has beneficial effects in a mouse model of experimental allergic rhinitis.