Siglec Signaling in the Tumor Microenvironment

MicroRNA:Siglec crosstalk in cancer progression

Aberrant Siglec expression in the tumour microenvironment has been implicated in tumour malignancies and can impact tumour behaviour and patient survival. Further to this, engagement with sialoglycans induces masked antigen recognition and promotes immune evasion, highlighting deregulated immune function. This necessitates the elucidation of their expression profiles in tumour progression. MicroRNAs (miRNAs) mediated targeting represents a novel approach to further elucidate Siglec potential and clinical relevance. Although miRNA activity in Siglec expression remains limited, we highlight current literature detailing miRNA:Siglec interactions within the tumour landscape and provide insights for possible diagnostic and therapeutic strategies in targeting the Siglec/sialic acid axis.

Tumor glucose metabolism and the T cell glycocalyx: implication for T cell function

The T cell is an immune cell subset highly effective in eliminating cancer cells. Cancer immunotherapy empowers T cells and occupies a solid position in cancer treatment. The response rate, however, remains relatively low (<30%). The efficacy of immunotherapy is highly dependent on T cell infiltration into the tumor microenvironment (TME) and the ability of these infiltrated T cells to sustain their function within the TME. A better understanding of the inhibitory impact of the TME on T cells is crucial to improve cancer immunotherapy. Tumor cells are well described for their switch into aerobic glycolysis (Warburg effect), resulting in high glucose consumption and a metabolically distinct TME. Conversely, glycosylation, a predominant posttranslational modification of proteins, also relies on glucose molecules. Proper glycosylation of T cell receptors influences the immunological synapse between T cells and tumor cells, thereby affecting T cell effector functions including their cytolytic and cytostatic activities. This review delves into the complex interplay between tumor glucose metabolism and the glycocalyx of T cells, shedding light on how the TME can induce alterations in the T cell glycocalyx, which can subsequently influence the T cell's ability to target and eliminate tumor cells.

From mechanism to therapy: the journey of CD24 in cancer

CD24 is a glycosylphosphatidylinositol-anchored protein that is expressed in a wide range of tissues and cell types. It is involved in a variety of physiological and pathological processes, including cell adhesion, migration, differentiation, and apoptosis. Additionally, CD24 has been studied extensively in the context of cancer, where it has been found to play a role in tumor growth, invasion, and metastasis. In recent years, there has been growing interest in CD24 as a potential therapeutic target for cancer treatment. This review summarizes the current knowledge of CD24, including its structure, function, and its role in cancer. Finally, we provide insights into potential clinical application of CD24 and discuss possible approaches for the development of targeted cancer therapies.

Adipose microenvironment promotes hypersialylation of ovarian cancer cells

Sialylation, the addition of negatively charged sialic acid sugars to terminal ends of glycans, is upregulated in most cancers. Hypersialylation supports multiple pro-tumor mechanisms such as enhanced migration and invasion, resistance to apoptosis and immune evasion. A current gap in knowledge is the lack of understanding on how the tumor microenvironment regulates cancer cell sialylation. The adipose niche is a main component of most peritoneal cancers' microenvironment. This includes ovarian cancer (OC), which causes most deaths from all gynecologic cancers. In this report, we demonstrate that the adipose microenvironment is a critical regulator of OC cell sialylation. In vitro adipose conditioning led to an increase in both ⍺2,3- and ⍺2,6-linked cell surface sialic acids in both human and mouse models of OC. Adipose-induced sialylation reprogramming was also observed in vivo from intra-peritoneal OC tumors seeded in the adipose-rich omentum. Mechanistically, we observed upregulation of at least three sialyltransferases, ST3GAL1, ST6GAL1 and ST3GALNAC3. Hypersialylated OC cells consistently formed intra-peritoneal tumors in both immune-competent mice and immune-compromised athymic nude mice. In contrast, hyposiaylated OC cells persistently formed tumors only in athymic nude mice demonstrating that sialylation impacts OC tumor formation in an immune dependent manner. To our knowledge, this is the first demonstration of the effect of adipose microenvironment on OC tumor sialylation. Our results set the stage for translational applications targeting sialic acid pathways in OC and other peritoneal cancers.

Glycans in melanoma: Drivers of tumour progression but sweet targets to exploit for immunotherapy

Aberrant glycosylation recently emerged as an unmissable hallmark of cancer progression in many cancers. In melanoma, there is growing evidence that the tumour 'glycocode' plays a major role in promoting cell proliferation, invasion, migration, but also dictates the nature of the immune infiltrate, which strongly affects immune cell function, and clinical outcome. Aberrant glycosylation patterns dismantle anti-tumour defence through interactions with lectins on immune cells, which are crucial to shape anti-tumour immunity but also to trigger immune evasion. The glycan/lectin axis represents a new immune subversion pathway that is exploited by melanoma to hijack immune cells and escape from immune control. In this review, we describe the glycosylation features of melanoma tumour cells, and further gather findings related to the role of glycosylation in melanoma tumour progression, deciphering in detail its impact on immunity. We also depict glycan-based strategies aiming at restoring a functional anti-tumour response in melanoma patients. Glycans/lectins emerge as key immune checkpoints with promising translational properties. Exploitation of these pathways could reshape potent anti-tumour immunity while impeding immunosuppressive circuits triggered by aberrant tumour glycosylation patterns, holding great promise for cancer therapy.

Increased Siglec-9/Siglec-9L interactions on NK cells predict poor HCC prognosis and present a targetable checkpoint for immunotherapy

BACKGROUND & AIMS

Natural killer (NK) cell-based anti-hepatocellular carcinoma (HCC) therapy is an increasingly attractive approach that warrants further study. Siglec-9 interacts with its ligand (Siglec-9L) and restrains NK cell functions, suggesting it is a potential therapeutic target. However, in situ Siglec-9/Siglec-9L interactions in HCC have not been reported, and a relevant interventional strategy is lacking. Herein, we aim to illustrate Siglec-9/Siglec-9L-mediated cell sociology and identify small-molecule inhibitors targeting Siglec-9 that could improve the efficacy of NK cell-based immunotherapy for HCC.

METHODS

Multiplexed immunofluorescence staining was performed to analyze the expression pattern of Siglec-7, -9 and their ligands in HCC tissues. Then we conducted docking-based virtual screening combined with bio-layer interferometry assays to identify a potent small-molecule Siglec-9 inhibitor. The therapeutic potential was further evaluated in vitro and in hepatoma-bearing NCG mice.

RESULTS

Siglec-9 expression, rather than Siglec-7, was markedly upregulated on tumor-infiltrating NK cells, which correlated significantly with reduced survival of patients with HCC. Moreover, the number of Siglec-9L+ cells neighboring Siglec-9+ NK cells was increased in HCC tissues and was also associated with tumor recurrence and reduced survival, further suggesting that Siglec-9/Siglec-9L interactions are a potential therapeutic target in HCC. In addition, we identified a small-molecule Siglec-9 inhibitor MTX-3937 which inhibited phosphorylation of Siglec-9 and downstream SHP1 and SHP2. Accordingly, MTX-3937 led to considerable improvement in NK cell function. Notably, MTX-3937 enhanced cytotoxicity of both human peripheral and tumor-infiltrating NK cells. Furthermore, transfer of MTX-3937-treated NK92 cells greatly suppressed the growth of hepatoma xenografts in NCG mice.

CONCLUSIONS

Our study provides the rationale for HCC treatment by targeting Siglec-9 on NK cells and identifies a promising small-molecule inhibitor against Siglec-9 that enhances NK cell-mediated HCC surveillance.

IMPACT AND IMPLICATIONS

Herein, we found that Siglec-9 expression is markedly upregulated on tumor-infiltrating natural killer (TINK) cells and correlates with reduced survival in patients with hepatocellular carcinoma (HCC). Moreover, the number of Siglec-9L+ cells neighboring Siglec-9+ NK cells was increased in HCC tissues and was also associated with tumor recurrence and reduced survival. More importantly, we identified a small-molecule inhibitor targeting Siglec-9 that augments NK cell functions, revealing a novel immunotherapy strategy for liver cancer that warrants further clinical investigation.

Engagement of sialylated glycans with Siglec receptors on suppressive myeloid cells inhibits anticancer immunity via CCL2

The overexpression of sialic acids on glycans, called hypersialylation, is a common alteration found in cancer cells. Sialylated glycans can enhance immune evasion by interacting with sialic acid-binding immunoglobulin-like lectin (Siglec) receptors on tumor-infiltrating immune cells. Here, we investigated the effect of sialylated glycans and their interaction with Siglec receptors on myeloid-derived suppressor cells (MDSCs). We found that MDSCs derived from the blood of lung cancer patients and tumor-bearing mice strongly express inhibitory Siglec receptors and are highly sialylated. In murine cancer models of emergency myelopoiesis, Siglec-E knockout in myeloid cells resulted in prolonged survival and increased tumor infiltration of activated T cells. Targeting suppressive myeloid cells by blocking Siglec receptors or desialylation strongly reduced their suppressive potential. We further identified CCL2 as a mediator involved in T-cell suppression upon interaction between sialoglycans and Siglec receptors on MDSCs. Our results demonstrated that sialylated glycans inhibit anticancer immunity by modulating CCL2 expression.

Pancreatic cancer-associated fibroblasts modulate macrophage differentiation via sialic acid-Siglec interactions

Despite recent advances in cancer immunotherapy, pancreatic ductal adenocarcinoma (PDAC) remains unresponsive due to an immunosuppressive tumor microenvironment, which is characterized by the abundance of cancer-associated fibroblasts (CAFs). Once identified, CAF-mediated immune inhibitory mechanisms could be exploited for cancer immunotherapy. Siglec receptors are increasingly recognized as immune checkpoints, and their ligands, sialic acids, are known to be overexpressed by cancer cells. Here, we unveil a previously unrecognized role of sialic acid-containing glycans on PDAC CAFs as crucial modulators of myeloid cells. Using multiplex immunohistochemistry and transcriptomics, we show that PDAC stroma is enriched in sialic acid-containing glycans compared to tumor cells and normal fibroblasts, and characterized by ST3GAL4 expression. We demonstrate that sialic acids on CAF cell lines serve as ligands for Siglec-7, -9, -10 and -15, distinct from the ligands on tumor cells, and that these receptors are found on myeloid cells in the stroma of PDAC biopsies. Furthermore, we show that CAFs drive the differentiation of monocytes to immunosuppressive tumor-associated macrophages in vitro, and that CAF sialylation plays a dominant role in this process compared to tumor cell sialylation. Collectively, our findings unravel sialic acids as a mechanism of CAF-mediated immunomodulation, which may provide targets for immunotherapy in PDAC.

Unveiling the hub genes in the SIGLECs family in colon adenocarcinoma with machine learning

Background

Despite the recognized roles of Sialic acid-binding Ig-like lectins (SIGLECs) in endocytosis and immune regulation across cancers, their molecular intricacies in colon adenocarcinoma (COAD) are underexplored. Meanwhile, the complicated interactions between different SIGLECs are also crucial but open questions.

Methods

We investigate the correlation between SIGLECs and various properties, including cancer status, prognosis, clinical features, functional enrichment, immune cell abundances, immune checkpoints, pathways, etc. To fully understand the behavior of multiple SIGLECs' co-evolution and subtract its leading effect, we additionally apply three unsupervised machine learning algorithms, namely, Principal Component Analysis (PCA), Self-Organizing Maps (SOM), K-means, and two supervised learning algorithms, Least Absolute Shrinkage and Selection Operator (LASSO) and neural network (NN).

Results

We find significantly lower expression levels in COAD samples, together with a systematic enhancement in the correlations between distinct SIGLECs. We demonstrate SIGLEC14 significantly affects the Overall Survival (OS) according to the Hazzard ratio, while using PCA further enhances the sensitivity to both OS and Disease Free Interval (DFI). We find any single SIGLEC is uncorrelated to the cancer stages, which can be significantly improved by using PCA. We further identify SIGLEC-1,15 and CD22 as hub genes in COAD through Differentially Expressed Genes (DEGs), which is consistent with our PCA-identified key components PC-1,2,5 considering both the correlation with cancer status and immune cell abundance. As an extension, we use SOM for the visualization of the SIGLECs and show the similarities and differences between COAD patients. SOM can also help us define subsamples according to the SIGLECs status, with corresponding changes in both immune cells and cancer T-stage, for instance.

Conclusion

We conclude SIGLEC-1,15 and CD22 as the most promising hub genes in the SIGLECs family in treating COAD. PCA offers significant enhancement in the prognosis and clinical analyses, while using SOM further unveils the transition phases or potential subtypes of COAD.

Sialic Acid Conjugate-Modified Cationic Liposomal Paclitaxel for Targeted Therapy of Lung Metastasis in Breast Cancer: What a Difference the Cation Content Makes

Cationic lipids play a pivotal role in developing novel drug delivery systems for diverse biomedical applications, owing to the success of mRNA vaccines against COVID-19 and the Phase III antitumor agent EndoTAG-1. However, the therapeutic potential of these positively charged liposomes is limited by dose-dependent toxicity. While an increased content of cationic lipids in the formulation can enhance the uptake and cytotoxicity toward tumor-associated cells, it is crucial to balance these advantages with the associated toxic side effects. In this work, we synthesized the cationic lipid HC-Y-2 and incorporated it into sialic acid (SA)-modified cationic liposomes loaded with paclitaxel to target tumor-associated immune cells efficiently. The SA-modified cationic liposomes exhibited enhanced binding affinity toward both RAW264.7 cells and 4T1 tumor cells in vitro due to the increased ratios of cationic HC-Y-2 content while effectively inhibiting 4T1 cell lung metastasis in vivo. By leveraging electrostatic forces and ligand-receptor interactions, the SA-modified cationic liposomes specifically target malignant tumor-associated immune cells such as tumor-associated macrophages (TAMs), reduce the proportion of cationic lipids in the formulation, and achieve dual objectives: high cellular uptake and potent antitumor efficacy. These findings highlight the potential advantages of this innovative approach utilizing cationic liposomes.

Targeting Siglec-Sialylated MUC1 Immune Axis in Cancer

Siglecs play a key role in mediating cell-cell interactions via the recognition of different sialylated glycoconjugates, including tumor-associated MUC1, which can lead to the activation or inhibition of the immune response. The activation occurs through the signaling of Siglecs with the cytoplasmic immunoreceptor tyrosine-based activation motif (ITAM)-containing proteins, while the inhibition signal is a result of the interaction of intracellular immunoreceptor tyrosine-based inhibition motif (ITIM)-bearing receptors. The interaction of tumor-associated MUC1 sialylated glycans with Siglecs via ITIM motifs decreases antitumor immunity. Consequently, these interactions are expected to play a key role in tumor evasion. Efforts to modulate the response of immune cells by blocking the immune-suppressive effects of inhibitory Siglecs, driving immune-activating Siglecs, and/or altering the synthesis and expression of the sialic acid glycocalyx are new therapeutic strategies deserving further investigation. We will highlight the role of Siglec's family receptors in immune evasion through interactions with glycan ligands in their natural context, presented on the protein such as MUC1, factors affecting their fine binding specificities, such as the role of multivalency either at the ligand or receptor side, their spatial organization, and finally the current and future therapeutic interventions targeting the Siglec-sialylated MUC1 immune axis in cancer.

Therapeutic and immunomodulatory potentials of mesenchymal stromal/stem cells and immune checkpoints related molecules

Mesenchymal stromal/stem cells (MSCs) are used in many studies due to their therapeutic potential, including their differentiative ability and immunomodulatory properties. These cells perform their therapeutic functions by using various mechanisms, such as the production of anti-inflammatory cytokines, growth factors, direct cell-to-cell contact, extracellular vesicles (EVs) production, and mitochondrial transfer. However, mechanisms related to immune checkpoints (ICPs) and their effect on the immunomodulatory ability of MSCs are less discussed. The main function of ICPs is to prevent the initiation of unwanted responses and to regulate the immune system responses to maintain the homeostasis of these responses. ICPs are produced by various types of immune system regulatory cells, and defects in their expression and function may be associated with excessive responses that can ultimately lead to autoimmunity. Also, by expressing different types of ICPs and their ligands (ICPLs), tumor cells prevent the formation and durability of immune responses, which leads to tumors' immune escape. ICPs and ICPLs can be produced by MSCs and affect immune cell responses both through their secretion into the microenvironment or direct cell-to-cell interaction. Pre-treatment of MSCs in inflammatory conditions leads to an increase in their therapeutic potential. In addition to the effect that inflammatory environments have on the production of anti-inflammatory cytokines by MSCs, they can increase the expression of various types of ICPLs. In this review, we discuss different types of ICPLs and ICPs expressed by MSCs and their effect on their immunomodulatory and therapeutic potential.

Targeting myeloid cells for cancer immunotherapy: Siglec-7/9/10/15 and their ligands

Advances in immunotherapy have revolutionized cancer treatment, yet many patients do not show clinical responses. While most immunotherapies target T cells, myeloid cells are the most abundant cell type in solid tumors and are key orchestrators of the immunosuppressive tumor microenvironment (TME), hampering effective T cell responses. Therefore, unraveling the immune suppressive pathways within myeloid cells could unveil new avenues for cancer immunotherapy. Over the past decade, Siglec receptors and their ligand, sialic acids, have emerged as a novel immune checkpoint on myeloid cells. In this review, we highlight key findings on how sialic acids modify immunity in the TME through engagement of Siglec-7/9/10/15 expressed on myeloid cells, and how the sialic acid-Siglec axis can be targeted for future cancer immunotherapies.

Targeting CD24/Siglec-10 signal pathway for cancer immunotherapy: recent advances and future directions

The small, heavily glycosylated protein CD24 is primarily expressed by many immune cells and is highly expressed mostly in cancer cells. As one of the most crucial biomarkers of cancers, CD24 is frequently highly expressed in solid tumors, while tumor-associated macrophages express Siglec-10 at high levels, Siglec-10 and CD24 can interact on innate immune cells to lessen inflammatory responses to a variety of disorders. Inhibiting inflammation brought on by SHP-1 and/or SHP-2 phosphatases as well as cell phagocytosis by macrophages, the binding of CD24 to Siglec-10 can prevent toll-like receptor-mediated inflammation. Targeted immunotherapy with immune checkpoint inhibitors (ICI) has lately gained popularity as one of the best ways to treat different tumors. CD24 is a prominent innate immune checkpoint that may be a useful target for cancer immunotherapy. In recent years, numerous CD24/Siglec-10-related research studies have made tremendous progress. This study discusses the characteristics and workings of CD24/Siglec-10-targeted immunotherapy and offers a summary of current advances in CD24/Siglec-10-related immunotherapy research for cancer. We then suggested potential directions for CD24-targeted immunotherapy, basing our speculation mostly on the results of recent preclinical and clinical trials.

Identification of therapeutic targets and prognostic biomarkers in the Siglec family of genes in tumor immune microenvironment of sarcoma

Sarcomas (SARC) are a highly heterogeneous cancer type that is prone to recurrence and metastasis. Numerous studies have confirmed that Siglecs are involved in immune signaling and play a key role in regulating immune responses in inflammatory diseases and various cancers. However, studies that systematically explore the therapeutic and prognostic value of Siglecs in SARC patients are very limited. The online databases GEPIA, UALCAN, TIMER, The Kaplan-Meier Plotter, GeneMANIA, cBioPortal, and STING were used in this study. IHC staining was performed on the collected patient tissues, and clinical data were statistically analyzed. The transcript levels of most Siglec family members showed a high expression pattern in SARC. Compared with normal tissues, Siglec-5, Siglec-10, and Siglec-12 were abnormally highly expressed in tumor tissues. Importantly, Siglec-15 was significantly associated with poor prognosis. Functional enrichment analysis showed that the Siglec family was mainly enriched in hematopoietic cell lineages. The genes associated with molecular mutations in the Siglec family were mainly TP53 and MUC16, among which Siglec-2 and Siglec-15 were significantly associated with the survival of patients. The expression levels of all Siglec family members were significantly correlated with various types of immune cells (B cells, CD8 + T cells, CD4 + T cells, macrophages, neutrophils and dendritic cells). Furthermore, a significant correlation was found between the somatic copy number changes of all Siglec molecules and the abundance of immune infiltrates. Our study paints a promising vision for the development of immunotherapy drugs and the construction of prognostic stratification models by investigating the therapeutic and prognostic potential of the Siglec family for SARC.

Targeted Delivery of Arctigenin Using Sialic Acid Conjugate-Modified Liposomes for the Treatment of Breast Cancer

Arctigenin (ATG) is a broad-spectrum antitumor drug with an excellent inhibitory effect on malignant tumors such as breast cancer, glioblastoma, liver cancer, and colon cancer. However, the clinical application of ATG is limited by its poor water solubility and quick hydrolysis in the liver, intestine, and plasma, which might hinder its application. Sialic acid (SA) recognizes selectin receptors overexpressed on the surface of tumor-associated macrophages. In this study, SA was conjugated with octadecylamine (ODA) to prepare SA-ODA, which was employed to prepare SA functionalized nanoliposomes (SA-Lip) to achieve breast cancer targeting. The formulations were finely optimized using the Box-Behnken design to achieve higher ATG loading. The size, ζ potential, entrapment efficiency, drug loading, and release behavior of ATG@SA-Lip were fully investigated in comparison with conventional ATG@Lip. The ATG@SA-Lip displayed more potent cytotoxicity and higher cellular internalization compared to ATG@Sol and ATG@Lip in both MCF7 and 4T1 cells. Notably, ATG@SA-Lip showed the lowest impact on the immune system. Our study demonstrates that SA-Lip has strong potential as a delivery system for the targeted delivery of ATG.

Cell Membrane Sialome: Sialic Acids as Therapeutic Targets and Regulators of Drug Resistance in Human Cancer Management

A cellular sialome is a physiologically active and dynamically changing component of the cell membrane. Sialylation plays a crucial role in tumor progression, and alterations in cellular sialylation patterns have been described as modulators of chemotherapy effectiveness. However, the precise mechanisms through which altered sialylation contributes to drug resistance in cancer are not yet fully understood. This review focuses on the intricate interplay between sialylation and cancer treatment. It presents the role of sialic acids in modulating cell-cell interactions, the extracellular matrix (ECM), and the immunosuppressive processes within the context of cancer. The issue of drug resistance is also discussed, and the mechanisms that involve transporters, the tumor microenvironment, and metabolism are analyzed. The review explores drugs and therapeutic approaches that may induce modifications in sialylation processes with a primary focus on their impact on sialyltransferases or sialidases. Despite advancements in cellular glycobiology and glycoengineering, an interdisciplinary effort is required to decipher and comprehend the biological characteristics and consequences of altered sialylation. Additionally, understanding the modulatory role of sialoglycans in drug sensitivity is crucial to applying this knowledge in clinical practice for the benefit of cancer patients.

Beta-1,4-galactosyltransferase-3 deficiency suppresses the growth of immunogenic tumors in mice

Background

Beta-1,4-galactosyltransferase-3 (B4GALT3) belongs to the family of beta-1,4-galactosyltransferases (B4GALTs) and is responsible for the transfer of UDP-galactose to terminal N-acetylglucosamine. B4GALT3 is differentially expressed in tumors and adjacent normal tissues, and is correlated with clinical prognosis in several cancers, including neuroblastoma, cervical cancer, and bladder cancer. However, the exact role of B4GALT3 in the tumor immune microenvironment (TIME) remains unclear. Here, we aimed to elucidate the function of B4GALT3 in the TIME.

Methods

To study the functions of B4GALT3 in cancer immunity, either weakly or strongly immunogenic tumor cells were subcutaneously transplanted into wild-type (WT) and B4galt3 knockout (KO) mice. Bone marrow transplantation and CD8+ T cell depletion experiments were conducted to elucidate the role of immune cells in suppressing tumor growth in B4galt3 KO mice. The cell types and gene expression in the tumor region and infiltrating CD8+ T cells were analyzed using flow cytometry and RNA sequencing. N-glycosylated proteins from WT and B4galt3 KO mice were compared using the liquid chromatography tandem mass spectrometry (LC-MS/MS)-based glycoproteomic approach.

Results

B4galt3 KO mice exhibited suppressed growth of strongly immunogenic tumors with a notable increase in CD8+ T cell infiltration within tumors. Notably, B4galt3 deficiency led to changes in N-glycan modification of several proteins, including integrin alpha L (ITGAL), involved in T cell activity and proliferation. In vitro experiments suggested that B4galt3 KO CD8+ T cells were more susceptible to activation and displayed increased downstream phosphorylation of FAK linked to ITGAL.

Conclusion

Our study demonstrates that B4galt3 deficiency can potentially boost anti-tumor immune responses, largely through enhancing the influx of CD8+ T cells. B4GALT3 might be suppressing cancer immunity by synthesizing the glycan structure of molecules on the CD8+ T cell surface, as evidenced by the changes in the glycan structure of ITGAL in immune cells. Importantly, B4galt3 KO mice showed no adverse effects on growth, development, or reproduction, underscoring the potential of B4GALT3 as a promising and safe therapeutic target for cancer treatment.

Sialylation: An alternative to designing long-acting and targeted drug delivery system

Long-acting and specific targeting are two important properties of excellent drug delivery systems. Currently, the long-acting strategies based on polyethylene glycol (PEG) are controversial, and PEGylation is incapable of simultaneously possessing targeting ability. Thus, it is crucial to identify and develop approaches to produce long-acting and targeted drug delivery systems. Sialic acid (SA) is an endogenous, negatively charged, nine-carbon monosaccharide. SA not only mediates immune escape in the body but also binds to numerous disease related targets. This suggests a potential strategy, namely "sialylation," for preparing long-acting and targeted drug delivery systems. This review focuses on the application status of SA-based long-acting and targeted agents as a reference for subsequent research.

The role of sialylation in gynecologic cancers

Sialic acids (SA) are a kind of nine-carbon backbone sugars, serving as important molecules in cell-to-cell or cell-to-extra-cellular matrix interaction mediated by either O-linked glycosylation or N-linked glycosylation to attach the terminal end of glycans, glycoproteins, and glycolipids. All processes need a balance between sialylation by sialyltransferase (STs) and desialylation by sialidases (also known as neuraminidases, NEU). Although there is much in uncertainty whether the sialyation plays in cancer development and progression, at least four mechanisms are proposed, including surveillance of immune system, modification of cellular apoptosis and cell death, alteration of cellular surface of cancer cells and tumor associated microenvironment responsible carcinogenesis, growth and metastases. The current review focuses on the role of glycosylation in gynecologic organ-related cancers, such as ovarian cancer, cervical and endometrial cancer. Evidence shows that sialylation involving in the alternation of surface components of cells (tumor and cells in the microenvironment of host) plays an important role for carcinogenesis (escape from immunosurveillance) and dissemination (metastasis) (sloughing from the original site of cancer, migration into the circulation system, extravasation from the circulatory system to the distant site and finally deposition and establishment on the new growth lesion to complete the metastatic process). Additionally, modification of glycosylation can enhance or alleviate the aggressive characteristics of the cancer behaviors. All suggest that more understandings of glycosylation on cancers may provide a new therapeutic field to assist the cancer treatment in the near future.

Sialylation: A Cloak for Tumors to Trick the Immune System in the Microenvironment

The tumor microenvironment (TME), where the tumor cells incite the surrounding normal cells to create an immune suppressive environment, reduces the effectiveness of immune responses during cancer development. Sialylation, a type of glycosylation that occurs on cell surface proteins, lipids, and glycoRNAs, is known to accumulate in tumors and acts as a "cloak" to help tumor cells evade immunological surveillance. In the last few years, the role of sialylation in tumor proliferation and metastasis has become increasingly evident. With the advent of single-cell and spatial sequencing technologies, more research is being conducted to understand the effects of sialylation on immunity regulation. This review provides updated insights into recent research on the function of sialylation in tumor biology and summarizes the latest developments in sialylation-targeted tumor therapeutics, including antibody-mediated and metabolic-based sialylation inhibition, as well as interference with sialic acid-Siglec interaction.

Disruption of the sialic acid/Siglec-9 axis improves antibody-mediated neutrophil cytotoxicity towards tumor cells

Upregulation of surface expressed sialoglycans on tumor cells is one of the mechanisms which promote tumor growth and progression. Specifically, the interactions of sialic acids with sialic acid-binding immunoglobulin-like lectins (Siglecs) on lymphoid or myeloid cells transmit inhibitory signals and lead to suppression of anti-tumor responses. Here, we show that neutrophils express among others Siglec-9, and that EGFR and HER2 positive breast tumor cells express ligands for Siglec-9. Treatment of tumor cells with neuraminidases or a sialyl transferase inhibitor significantly reduced binding of a soluble recombinant Siglec-9-Fc fusion protein, while EGFR and HER2 expression remained unchanged. Importantly, the cytotoxic activity of neutrophils driven by therapeutic EGFR or HER2 antibodies in vitro was increased by blocking the sialic acid/Siglec interaction, either by reducing tumor cell sialylation or by a Siglec-9 blocking antibody containing an effector silenced Fc domain. In vivo a short-term xenograft mouse model confirmed the improved therapeutic efficacy of EGFR antibodies against sialic acid depleted, by a sialyltransferase inhibitor, tumor cells compared to untreated cells. Our studies demonstrate that sialic acid/Siglec interactions between tumor cells and myeloid cells can impair antibody dependent tumor cell killing, and that Siglec-9 on polymorphonuclear cells (PMN) is critically involved. Considering that PMN are often a highly abundant cell population in the tumor microenvironment, Siglec-9 constitutes a promising target for myeloid checkpoint blockade to improve antibody-based tumor immunotherapy.

Tumor cell-intrinsic and tumor microenvironmental conditions co-determine signaling by the glycoimmune checkpoint receptor Siglec-7

Tumors create an immunosuppressive tumor microenvironment by altering protein expression, but also by changing their glycosylation status, like altered expression of sialoglycans. Sialoglycans are capped with sialic acid sugar residues and are recognized by Siglec immune receptors. Siglec-7 is an inhibitory immune receptor similar to PD-1, and is emerging as glycoimmune checkpoint exploited by cancer cells to evade the immune system. However, the exact cellular and molecular conditions required for Siglec-7-mediated immune cell inhibition remain largely unknown. Here, we report on the development of a chimeric Siglec-7 cell system that enables dissection of Siglec-7 signaling, rather than Siglec-7 binding. Antibody-induced clustering, sialic acid-containing polymers, and highly sialylated erythrocytes effectively induced Siglec-7 signaling, thereby validating functionality of this reporter system. Moreover, the system reveals tumor cell-dependent Siglec-7 signaling. Tumor-associated conditions important for Siglec-7 signaling were defined, such as Siglec-7 ligand expression levels, presence of the known Siglec-7 ligand CD43, and sialic acid availability for sialylation of glycans. Importantly, therapeutic targeting of the Siglec-7/sialic acid axis using a sialyltransferase inhibitor resulted in strong reduction of Siglec-7 signaling. In conclusion, using a newly established cellular tool, we defined a set of tumor-associated conditions that influence Siglec-7 signaling. Moreover, the system allows to assess the efficacy of novel cancer drugs interfering with the Siglec-7/sialic acid axis as immunotherapy to treat cancer.

Breast density and estradiol are associated with distinct different expression patterns of metabolic proteins in normal human breast tissue in vivo

Background

Breast density and exposure to sex steroids are major risk factors for breast cancer. The local microenvironment plays an essential role in progression of breast cancer. Metabolic adaption is a major hallmark of cancer. Whether proteins from the extracellular space regulating metabolism are affected in breast cancer, dense breasts or by estrogen exposure are not yet fully elucidated.

Methods

Women with breast cancer, postmenopausal women with normal breast tissue with varying breast density or premenopausal women with breasts exposed to high levels of estradiol were included in the study. Microdialysis was used to collect proteins from the extracellular space in vivo in 73 women; 12 with breast cancer, 42 healthy postmenopausal women with different breast densities, and 19 healthy premenopausal women. Breast density was determined as lean tissue fraction (LTF) using magnetic resonance imaging. Data were evaluated in a murine breast cancer model. We quantified a panel of 92 key proteins regulating metabolism using proximity extension assay.

Results

We report that 29 proteins were upregulated in human breast cancer. In dense breasts 37 proteins were upregulated and 17 of these were similarly regulated as in breast cancer. 32 proteins correlated with LTF. In premenopausal breasts 19 proteins were up-regulated and 9 down-regulated. Of these, 27 correlated to estradiol, a result that was confirmed for most proteins in experimental breast cancer. Only two proteins, pro-cathepsin H and galanin peptide, were similarly regulated in breast cancer, dense- and estrogen exposed breasts.

Conclusions

Metabolic proteins may be targetable for breast cancer prevention. Depending on risk factor, this may, however, require different approaches as breast density and estradiol induce distinct different expression patterns in the breast. Additionally, metabolic proteins from the extracellular space may indeed be further explored as therapeutic targets for breast cancer treatment.

Tamoxifen Modulates the Immune Landscape of the Tumour Microenvironment: The Paired Siglec-5/14 Checkpoint in Anti-Tumour Immunity in an In Vitro Model of Breast Cancer

Since the role of sialome–Siglec axis has been described as a regulatory checkpoint of immune homeostasis, the promotion of stimulatory or inhibitory Siglec-related mechanisms is crucial in cancer progression and therapy. Here, we investigated the effect of tamoxifen on the sialic acid–Siglec interplay and its significance in immune conversion in breast cancer. To mimic the tumour microenvironment, we used oestrogen-dependent or oestrogen-independent breast cancer cells/THP-1 monocytes transwell co-cultures exposed to tamoxifen and/or β-estradiol. We found changes in the cytokine profiles accompanied by immune phenotype switching, as measured by the expression of arginase-1. The immunomodulatory effects of tamoxifen in THP-1 cells occurred with the altered SIGLEC5 and SIGLEC14 genes and the expression of their products, as confirmed by RT-PCR and flow cytometry. Additionally, exposure to tamoxifen increased the binding of Siglec-5 and Siglec-14 fusion proteins to breast cancer cells; however, these effects appeared to be unassociated with oestrogen dependency. Our results suggest that tamoxifen-induced alterations in the immune activity of breast cancer reflect a crosstalk between the Siglec-expressing cells and the tumour’s sialome. Given the distribution of Siglec-5/14, the expression profile of inhibitory and activatory Siglecs in breast cancer patients may be useful in the verification of therapeutic strategies and predicting the tumour’s behaviour and the patient’s overall survival.

Targeting of TAMs with freeze-dried monosialotetrahexosylganglioside and sialic acid-octadecylamine co-modified liposomes remodels the tumor microenvironment and enhances anti-tumor activity

Although anti-tumor strategies targeting tumor-associated immune cells were being rapidly developed, the preparations were usually limited in targeting efficiency. To overcome this barrier, this study reported a novel sialic acid-octadecylamine (SA-ODA) and monosialotetrahexosylganglioside (GM1) co-modified epirubicin liposomes (5-5-SAGL-EPI), which improved tumor-targeting ability through the active targeting of tumor-associated macrophages (TAMs) by SA-ODA and the long circulation of GM1. Thus, we evaluated 5-5-SAGL-EPI in vitro and in vivo. Analysis of cellular uptake by RAW264.7 cells using flow cytometry and confocal microscopy showed a higher rate of cellular uptake for 5-5-SAGL-EPI than for the common liposomes (CL-EPI). In pharmacokinetic studies using Wistar rats, compared to CL-EPI, 5-5-SAGL-EPI showed a higher circulation time in vivo. Tissue distribution studies in Kunming mice bearing S180 tumors revealed increased distribution of 5-5-SAGL-EPI in tumor tissues compared with liposomes modified with single ligands (SA-ODA [5-SAL-EPI] or GM1 [5-GL-EPI]). In vivo anti-tumor experiments using the S180 tumor-bearing mice revealed a high tumor inhibition rate and low toxicity for 5-5-SAGL-EPI. Moreover, freeze-dried 5-5-SAGL-EPI had good storage stability, and the anti-tumor effect was comparable to that before freeze-drying. Overall, 5-5-SAGL-EPI exhibited excellent anti-tumor effects before and after lyophilization.

Immuno-PET Imaging of Siglec-15 Using the Zirconium-89-Labeled Therapeutic Antibody, NC318

Objective. Sialic acid-binding immunoglobulin-like lectin 15 (Siglec-15) is overexpressed in various cancers which has led to the development of therapeutic anti-Siglec-15 monoconal antibodies (mAbs). In these preclinical studies, the therapeutic mAb, NC318 (antihuman/murine Siglec-15 mAb), was labeled with zirconium-89 and evaluated in human Siglec-15 expressing cancer cells and mouse xenografts for potential use as a clinical diagnostic imaging agent. Methods. Desferrioxamine-conjugated NC318 was radiolabeled with zirconium-89 to synthesize [89Zr]Zr-DFO-NC318. Cancer cell lines expressing variable Siglec-15 levels were used for in vitro cell binding studies and tumor xenograft mouse models for biodistributions. [89Zr]Zr-DFO-NC318 biodistribution and PET imaging studies to determine tissue uptakes (tissue : muscle ratios, T : M) included pharmacokinetic evaluation in Siglec-15+tumor xenografts and immunocompetent mice, blocking with nonradioactive NC318 (20, 100, and 300 μg) and xenografts with low/negligible Siglec-15 expressing tumors. Results. [89Zr]Zr-DFO-NC318 exhibited high affinity ( $K_d$ ~4 nM) for Siglec-15 and distinguished between moderate and negligible Siglec-15 expression levels in cancer cell lines. The highest [89Zr]Zr-DFO-NC318 uptakes occurred in the spleen and lymph nodes of the Siglec-15+tumor xenografts at all time points followed by Siglec-15+tumor uptake which was lower although highly retained. In immunocompetent mice, the spleen and lymph nodes exhibited lower uptakes indicating that the athymic xenografts had increased Siglec-15+ immune cells. Specific [89Zr]Zr-DFO-NC318 binding to Siglec-15 was proven with NC318 blocking studies in which dose-dependent decreases in Siglec-15+tumor T : Ms were observed. Higher than expected, tumor T : Ms were seen in lower expressing tumors likely due to the contribution of murine Siglec-15+ immune cells in the tumor microenvironment as confirmed by immunohistochemistry. Siglec-15+tumors were identified on PET images whereas low/negligible expressing tumors showed lower uptakes. Conclusions. In vitro and in vivo [89Zr]Zr-DFO-NC318 uptakes correlated with Siglec-15 expression levels in target tissues. Despite uptake in immune cell subsets in the tumor microenvironment, these results suggest that clinical [89Zr]Zr-DFO-NC318 PET imaging may have value in selecting patients for Siglec-15-targeted therapies.

The Blessed Union of Glycobiology and Immunology: A Marriage That Worked

In this article, we discuss the main aspects regarding the recognition of cell surface glycoconjugates and the immunomodulation of responses against the progression of certain pathologies, such as cancer and infectious diseases. In the first part, we talk about different aspects of glycoconjugates and delve deeper into the importance of N-glycans in cancer immunotherapy. Then, we describe two important lectin families that have been very well studied in the last 20 years. Examples include the sialic acid-binding immunoglobulin (Ig)-like lectins (siglecs), and galectins. Finally, we discuss a topic that needs to be better addressed in the field of glycoimmunology: the impact of oncofetal antigens on the cells of the immune system. New findings in this area are of great importance for advancement, especially in the field of oncology, since it is already known that cellular interactions mediated by carbohydrate-carbohydrate and/or carbohydrate proteins are able to modulate the progression of different types of cancer in events that compromise the functionality of the immune responses.

Circulating exosomal immuno-oncological checkpoints and cytokines are potential biomarkers to monitor tumor response to anti-PD-1/PD-L1 therapy in non-small cell lung cancer patients

Immune checkpoint inhibitors (ICIs) including anti-PD-1 and anti-PD-L1 antibodies, have significantly changed the treatment outcomes of NSCLC patients with better overall survival. However, 15-40% of the patients still fail to respond to ICIs therapy. Identification of biomarkers associated with responses are mandated in order to increase the efficacy of such therapy. In this study we evaluated 27 serum-derived exosomal immuno-oncological proteins and 44 cytokines/chemokines before and after ICIs therapy in 17 NSCLC patients to identify surrogate biomarkers for treatment/monitoring patient stratification for maximum therapeutic benefit. We first confirmed the identity of the isolated exosomes to have their specific markers (CD63, CD81, HSP70 and CD91). We have demonstrated that baseline concentration of exosomal-PD-L1 (p<0.0001), exosomal-PD-L2 (p=0.0413) and exosomal-PD-1 (p=0.0131) from NSCLC patients were significantly higher than their soluble-free forms. Furthermore, the exosomal-PD-L1 was present in all the patients (100%), while only 71% of patients expressed tissue PD-L1. This indicates that exosomal-PD-L1 is a more reliable diagnostic biomarker. Interestingly, exosomal-PD-L2 expression was significantly higher (p=0.0193) in tissue PD-L1-negative patients compared to tissue PD-L1-positive patients. We have also shown that immuno-oncological proteins isolated from pre-ICIs treated patients were significantly higher in exosomes compared to their soluble-free counterparts (CD152, p=0.0008; CD80, p=0.0182; IDO, p=0.0443; Arginase, p<0.0001; Nectin-2, p<0.0001; NT5E, p<0.0001; Siglec-7, p<0.0001; Siglec-9, p=0.0335; CD28, p=0.0092; GITR, p<0.0001; MICA, p<0.0001). Finally, the changes in the expression levels of exosomal immuno-oncological proteins/cytokines and their correlation with tumor response to ICIs treatment were assessed. There was a significant downregulation of exosomal PD-L1 (p=0.0156), E-Cadherin (p=0.0312), ULBP1 (p=0.0156), ULBP3 (p=0.0391), MICA (p=0.0391), MICB (p=0.0469), Siglec7 (p=0.0078) and significant upregulation of exosomal PD-1 (p=0.0156) and IFN- γ (p=0.0156) in responding patients. Non-responding patients showed a significant increase in exosomal-PD-L1 (p=0.0078). Furthermore, responding-patients without liver-metastasis showed significant-upregulation of PD-1 (p=0.0070), and downregulation of ULBP1 (p=0.0137) and Siglec-7 (p=0.0037). Non-responding patients had significant-downregulation of ULBP3 (p=0.0317) in patient without brain-metastasis and significant-upregulation/downregulation of PD-L1 and ULBP3 (p=0.0262/0.0286) in patients with pulmonary-metastasis. We demonstrated for the first time that exosomal immuno-oncological proteins/cytokines are potential biomarkers to monitor response to ICIs therapy and can predict the clinical outcomes in NSCLC patients.

Targeting the Siglec-Sialic Acid Immune Axis in Cancer: Current and Future Approaches

The sialic acid-binding immunoglobulin-like lectin (Siglec)-sialic acid immune axis is an evolutionarily conserved immunoregulatory pathway that provides a mechanism for establishing self-recognition and combatting invasive pathogens. Perturbations in the pathway lead to many immune dysregulated diseases, including autoimmunity, neurodegeneration, allergic conditions, and cancer. The purpose of this review is to provide a brief overview of the relationship between Siglecs and sialic acid as they relate to human health and disease, to consider current Siglec-based therapeutics, and to discuss new therapeutic approaches targeting the Siglec-sialic acid immune axis, with a focus on cancer.

Targeted nanomedicines remodeling immunosuppressive tumor microenvironment for enhanced cancer immunotherapy

Cancer immunotherapy has significantly flourished and revolutionized the limited conventional tumor therapies, on account of its good safety and long-term memory ability. Discouragingly, low patient response rates and potential immune-related side effects make it rather challenging to literally bring immunotherapy from bench to bedside. However, it has become evident that, although the immunosuppressive tumor microenvironment (TME) plays a pivotal role in facilitating tumor progression and metastasis, it also provides various potential targets for remodeling the immunosuppressive TME, which can consequently bolster the effectiveness of antitumor response and tumor suppression. Additionally, the particular characteristics of TME, in turn, can be exploited as avenues for designing diverse precise targeting nanomedicines. In general, it is of urgent necessity to deliver nanomedicines for remodeling the immunosuppressive TME, thus improving the therapeutic outcomes and clinical translation prospects of immunotherapy. Herein, we will illustrate several formation mechanisms of immunosuppressive TME. More importantly, a variety of strategies concerning remodeling immunosuppressive TME and strengthening patients' immune systems, will be reviewed. Ultimately, we will discuss the existing obstacles and future perspectives in the development of antitumor immunotherapy. Hopefully, the thriving bloom of immunotherapy will bring vibrancy to further exploration of comprehensive cancer treatment.

Mass spectrometry-based shotgun glycomics for discovery of natural ligands of glycan-binding proteins

The non-covalent associations of complex carbohydrates (glycans) with glycan-binding proteins mediate many important physiological and pathophysiological processes. Identifying these interactions is essential to understanding their diverse biological functions and enables the development of new disease treatments and diagnostics. Knowledge of the repertoire of glycans recognized by most glycan-binding proteins and their affinities is incomplete. Mass spectrometry-based screening of natural glycan libraries has emerged as a promising approach to defining the glycan interactome of glycan-binding proteins. Here, we review recent advances in mass spectrometry-based natural library screening that have led to the discovery of glycan ligands of endogenous and exogenous proteins and illuminated their binding specificities.

Whole-cell tumor vaccines desialylated to uncover tumor antigenic Gal/GalNAc epitopes elicit anti-tumor immunity

BACKGROUND

Aberrant sialoglycans on the surface of tumor cells shield potential tumor antigen epitopes, escape recognition, and suppress activation of immunocytes. α2,3/α2,6Gal- and α2,6GalNAc (Gal/GalNAc)-linked sialic acid residues of sialoglycans could affect macrophage galactose-type lectins (MGL) mediated-antigen uptake and presentation and promote sialic acid-binding immunoglobulin-like lectins (Siglecs) mediated-immunosuppression. Desialylating sialoglycans on tumor cells could present tumor antigens with Gal/GalNAc residues and overcome glyco-immune checkpoints. Thus, we explored whether vaccination with desialylated whole-cell tumor vaccines (DWCTVs) triggers anti-tumor immunity in ovarian cancer (OC).

METHODS

Sialic acid (Sia) and Gal/GalNAc residues on OC A2780, OVCAR3, and ID8 cells treated with α2-3 neuraminidase (α2-3NA) and α2-6NA, and Sigec-9 or Siglec-E and MGL on DCs pulsed with desialylated OC cells were identified using flow cytometry (FCM); RT-qPCR determined IFNG expression of T cells, TRBV was sequenced using Sanger sequencing and cytotoxicity of αβ T cells was measured with LDH assay; Anti-tumor immunity in vivo was validated via vaccination with desialylated whole-cell ID8 vaccine (ID8 DWCTVs).

RESULTS

Gal/GalNAc but not Sia residues were significantly increased in the desialylated OC cells. α2-3NA-modified DWCTV increased MGL but decreased Siglec-9 or Siglec E expression on DCs. MGL^bright/Siglec-9^dim DCs significantly up-regulated IFNG expression and CD4/CD8 ratio of T cells and diversified the TCR repertoire of αβ T-cells that showed enhanced cytotoxic activity. Vaccination with α2-3NA-modified ID8 DWCTVs increased MGL^bright/Siglec-E^dim DCs in draining lymph nodes, limited tumor growth, and extended survival in tumor-challenged mice.

CONCLUSION

Desialylated tumor cell vaccine could promote anti-tumor immunity and provide a strategy for OC immunotherapy in a clinical setting.

CD24: A Novel Target for Cancer Immunotherapy

Cluster of differentiation 24 (CD24) is a small, highly glycosylated cell adhesion protein that is normally expressed by immune as well as epithelial, neural, and muscle cells. Tumor CD24 expression has been linked with alterations in several oncogenic signaling pathways. In addition, the CD24/Siglec-10 interaction has been implicated in tumor immune evasion, inhibiting macrophage-mediated phagocytosis as well as natural killer (NK) cell cytotoxicity. CD24 blockade has shown promising results in preclinical studies. Although there are limited data on efficacy, monoclonal antibodies against CD24 have demonstrated clinical safety and tolerability in two clinical trials. Other treatment modalities evaluated in the preclinical setting include antibody–drug conjugates and chimeric antigen receptor (CAR) T cell therapy. In this review, we summarize current evidence and future perspectives on CD24 as a potential target for cancer immunotherapy.

Differential Immune Checkpoint and Ig-like V-Type Receptor Profiles in COVID-19: Associations with Severity and Treatment

Identifying patients' immune system status has become critical to managing SARS-CoV-2 infection and avoiding the appearance of secondary infections during a hospital stay. Despite the high volume of research, robust severity and outcome markers are still lacking in COVID-19. We recruited 87 COVID-19 patients and analyzed, by unbiased automated software, 356 parameters at baseline emergency department admission including: high depth immune phenotyping and immune checkpoint expression by spectral flow cytometry, cytokines and other soluble molecules in plasma as well as routine clinical variables. We identified 69 baseline alterations in the expression of immune checkpoints, Ig-like V type receptors and other immune population markers associated with severity (O₂ requirement). Thirty-four changes in these markers/populations were associated with secondary infection appearance. In addition, through a longitudinal sample collection, we described the changes which take place in the immune system of COVID-19 patients during secondary infections and in response to corticosteroid treatment. Our study provides information about immune checkpoint molecules and other less-studied receptors with Ig-like V-type domains such as CD108, CD226, HVEM (CD270), B7H3 (CD276), B7H5 (VISTA) and GITR (CD357), defining these as novel interesting molecules in severe and corticosteroids-treated acute infections.

Advances in the Immunomodulatory Properties of Glycoantigens in Cancer

Simple Summary

This work reviews the role of aberrant glycosylation in cancer cells during tumour growth and spreading, as well as in immune evasion. The interaction of tumour-associated glycans with the immune system through C-type lectin receptors can favour immune escape but can also provide opportunities to develop novel tumour immunotherapy strategies. This work highlights the main findings in this area and spotlights the challenges that remain to be investigated.

Abstract

Aberrant glycosylation in tumour progression is currently a topic of main interest. Tumour-associated carbohydrate antigens (TACAs) are expressed in a wide variety of epithelial cancers, being both a diagnostic tool and a potential treatment target, as they have impact on patient outcome and disease progression. Glycans affect both tumour-cell biology properties as well as the antitumor immune response. It has been ascertained that TACAs affect cell migration, invasion and metastatic properties both when expressed by cancer cells or by their extracellular vesicles. On the other hand, tumour-associated glycans recognized by C-type lectin receptors in immune cells possess immunomodulatory properties which enable tumour growth and immune response evasion. Yet, much remains unknown, concerning mechanisms involved in deregulation of glycan synthesis and how this affects cell biology on a major level. This review summarises the main findings to date concerning how aberrant glycans influence tumour growth and immunity, their application in cancer treatment and spotlights of unanswered challenges remaining to be solved.

Glycosoaminoglycans in cancer therapy

Glycosaminoglycans (GAGs) are an important component of the tumor microenvironment (TME). GAGs can interact with a variety of binding partners and thereby influence cancer progression on multiple levels. GAGs can modulate growth factor and chemokine signaling, invasion and metastasis formation. Moreover, GAGs are able to change the physical property of the extracellular matrix (ECM). Abnormalities in GAG abundance and structure (e.g., sulfation patterns and molecular weight) are found across various cancer types and show biomarker potential. Targeting GAGs, as well as the usage of GAGs and their mimetics, are promising approaches to interfere with cancer progression. In addition, GAGs can be used as drug and cytokine carriers to induce an anti-tumor response. In this review, we summarize the role of GAGs in cancer and the potential use of GAGs and GAG derivatives to target cancer.

Transgenic mouse models to study the physiological and pathophysiological roles of human Siglecs

Sialic acid-binding immunoglobulin-like lectins (Siglecs) are important immunomodulatory receptors. Due to differences between human and mouse Siglecs, defining the in vivo roles for human Siglecs (hSiglecs) can be challenging. One solution is the development and use of hSiglec transgenic mice to assess the physiological roles of hSiglecs in health and disease. These transgenic mice can also serve as important models for the pre-clinical testing of immunomodulatory approaches that are based on targeting hSiglecs. Four general methods have been used to create hSiglec-expressing transgenic mice, each with associated advantages and disadvantages. To date, transgenic mouse models expressing hSiglec-2 (CD22), -3 (CD33), -7, -8, -9, -11, and -16 have been created. This review focuses on both the generation of these hSiglec transgenic mice, along with the important findings that have been made through their study. Cumulatively, hSiglec transgenic mouse models are providing a deeper understanding of the differences between human and mice orthologs/paralogs, mechanisms by which Siglecs regulate immune cell signaling, physiological roles of Siglecs in disease, and different paradigms where targeting Siglecs may be therapeutically advantageous.