Systemic blockade of sialylation in mice with a global inhibitor of sialyltransferases

A review on the development of sialyltransferase inhibitors

Sialylation of terminal glycoconjugates is involved in many important physiological and pathological processes such as tumor metastasis, drug resistance, organismal immunity, and viral infections. Sialyltransferases are enzymes responsible for sialylation modification in organisms, and potent sialyltransferase inhibitors can not only serve as probes for glycobiology studies, but also hold great promise to become agents for tumor therapy and viral infection control in the clinic. This review summarizes the latest progress in the development and application of various sialyltransferase inhibitors. The current challenges and development trends are also discussed.

Cell membrane sialome machinery and regulation of receptor tyrosine kinases in gliomas: The functional relevance and therapeutic perspectives

Gliomas are the most common primary brain tumors characterized by high aggressive potential, poor therapeutic response, and significantly reduced overall patient survival. Despite significant progress in the diagnosis and therapy of cancer, gliomas remain a clinical challenge due to the high molecular and cellular heterogeneity, which provides for multiple mechanisms of chemoresistance and adaptive plasticity. A better understanding of cellular regulatory mechanisms of intracellular signal transduction enables the development of targeted drug therapies and clinical application. The increasing evidence confirms the role of sialoglycans in the processing of cell membrane receptors via altered dimerization, activation, and autophosphorylation, which results in changes in cellular signaling and promotes cancer progression. Hence, the modified sialylation patterns, as a hallmark of cancer, have been described as modulators of chemotherapy effectiveness and drug resistance. The receptor tyrosine kinases (RTKs)-mediated signaling in glial tumors control cell growth, survival, migration, and angiogenesis. Here, we focus on the engagement of the sialome machinery in RTKs processing in gliomas and its importance as a suitable therapeutic target. The analysis of the sialylation pattern and its impact on the activity of growth factor receptors provides valuable insights into our understanding of the molecular and cellular complexity of glial tumors. This highlights the novel treatment approaches that could improve prognosis and patients' overall survival.

Novel anticancer drug discovery efforts targeting glycosylation: the emergence of fluorinated monosaccharides analogs

INTRODUCTION

Glycosylation is an essential enzymatic process of building glycan structures that occur mainly within the cell and gives rise to a diversity of cell surface and secreted glycoconjugates. These glycoconjugates play vital roles, for instance in cellcell adhesion, interaction and communication, activation of cell surface receptors, inflammatory response and immune recognition. This controlled and wellcoordinated enzymatic process is altered in cancer, leading to the biosynthesis of cancerassociated glycans, which impact glycandependent biological roles.

AREAS COVERED

In this review, the authors discuss the importance of targeting cancerassociated glycans through potent glycan biosynthesis inhibitors. It focuses on the use of analogs, providing an overview of findings involving these in cancer. The highly explored fluorinated monosaccharide analogs targeting aberrant glycosylation are described, aiming to inspire advances in the field.

EXPERT OPINION

Altered glycosylation, such as increased sialylation and fucosylation, is a feature in cancer and has been shown to play key roles in several malignant properties of cancer cells. Strategies aiming at remodeling cancer cells´ glycome are emerging and present a huge potential for cancer therapy. Fluorinated monosaccharides have been gathering promising preclinical results as novel cancer drugs. Nevertheless, cancer specific targeting strategies must be considered to avoid significant sideeffects.

Specifically Editing Cancer Sialoglycans for Enhanced In Vivo Immunotherapy through Aptamer-Enzyme Chimeras

Immune checkpoint blockade (ICB) therapies have demonstrated remarkable clinical success in treating cancer. However, their objective response rate remains suboptimal because current therapies rely on limited immune checkpoints that fail to cover the multiple immune evasion pathways of cancer. To explore potential ICB strategies, we propose a glycoimmune checkpoint elimination (glycoICE) therapy based on targeted editing of sialoglycans on the tumor cell surface using an aptamer-enzyme chimera (ApEC). The ApEC can be readily generated via a one-step bioorthogonal procedure, allowing for large-scale and uniform production. It specifically targets and desialylates cancer cells, disrupting the sialoglycan-Siglec axis to activate immune cells and enhance immunotherapy efficacy, while its high tumor selectivity minimizes side effects from indiscriminate desialylation of normal tissues. Furthermore, the ApEC has the potential to be a versatile platform for specific editing of sialoglycans in different tumor models by adjusting the aptamer sequences to target specific protein markers. This research not only introduces a novel molecular tool for the effective editing of sialoglycans in complex environments, but also provides valuable insights for advancing DNA-based drugs towards in vivo and clinical applications.

Preventing human influenza and coronaviral mono or coinfection by blocking virus-induced sialylation

Influenza A viruses (IAVs) and endemic coronaviruses (eCoVs) are common etiologic agents for seasonal respiratory infections. The human H1N1 of IAV and coronavirus OC43 (HCoV-OC43) can result in hospitalization, acute respiratory distress syndrome (ARDS), and even death, particularly in immunocompromised individuals. They infect the epithelium of the respiratory tract by interacting with host cell sialic acid (Sia)- linked receptors whose synthesis is catalyzed by sialyltransferases (STs). Viral coinfection is challenging to treat because of the need to target specific components of two or more distinct pathogens. Emerging drug and vaccine resistance due to the high mutation rate of viral genomes further complicates the treatment and prevention of viral infection. Sialylation mediated by STs may be a potential drug target for treating viral diseases. ST is an attractive target because it could be effective before identifying the pathogen that has occurred, providing a novel direction for overcoming drug resistance and achieving a broad-spectrum antiviral effect. We developed an H1N1 and OC43 mono or coinfection model using 14 days post-plating (14 PP) human primary small airway epithelial cells (HSAEC) grown on transwell inserts at an air-fluid interface (ALI), mimicking in vivo cellular dynamics. Using this model, we have observed that mono or coinfection with OC43 and H1N1 results in increased sialic acid levels and synergistic viral infection. We showed for the first time that H1N1 and OC43 mono- and coinfection in HSAEC caused increased expression and activity of STs, which can be blocked by pan-STs inhibitor (3Fax-Peracetyl Neu5Ac) with no host cell toxicity.

A Kinetic Trapping Approach for Facile Access to 3FaxNeu5Ac and a Photo-Cross-Linkable Sialyltransferase Probe

Sialic acid (Neu5Ac) is installed onto glycoconjugates by sialyltransferases (STs) using cytidine monophosphate-Neu5Ac (CMP-β-d-Neu5Ac) as their donor. The only class of cell-active ST inhibitors are those based on a 3FaxNeu5Ac scaffold, which is metabolically converted into CMP-3FaxNeu5Ac within cells. It is essential for the fluorine to be axial, yet stereoselective installation of fluorine in this specific orientation is challenging. Sialic acid aldolase can convert 3-fluoropyruvate and 2-acetamido-2-deoxy-d-mannopyranose (ManNAc) to 3FNeu5Ac, but stereocontrol of the fluorine in the product has not been possible. We hypothesized that the 3Fax kinetic product of a sialic acid aldolase reaction could be trapped by coupling with CMP-sialic acid synthetase to yield CMP-3FaxNeu5Ac. Here, we report that highly active CMP-sialic acid synthetase and short reaction times produce exclusively CMP-3FaxNeu5Ac. Removal of CMP from CMP-3FaxNeu5Ac under acidic conditions unexpectedly led to 3-fluoro-β-d-Neu5Ac 2-phosphate (3FaxNeu5Ac-2P). Alkaline phosphatase successfully converted 3FaxNeu5Ac-2P to 3FaxNeu5Ac, enabling stereochemically controlled access to 3FaxNeu5Ac, which is effective in lowering the sialoglycan ligands for Siglecs on cells. Moreover, our kinetic trapping approach could be used to access CMP-3FaxNeu5Ac with modifications at the C5, C9, or both positions, which enabled the chemoenzymatic synthesis of a photo-cross-linkable version of CMP-3FaxNeu5Ac that selectively photo-cross-linked to ST6GAL1 over two other STs.

Biological function of sialic acid and sialylation in human health and disease

Sialic acids are predominantly found at the terminal ends of glycoproteins and glycolipids and play key roles in cellular communication and function. The process of sialylation, a form of post-translational modification, involves the covalent attachment of sialic acid to the terminal residues of oligosaccharides and glycoproteins. This modification not only provides a layer of electrostatic repulsion to cells but also serves as a receptor for various biological signaling pathways. Sialylation is involved in several pathophysiological processes. Given its multifaceted involvement in cellular functions, sialylation presents a promising avenue for therapeutic intervention. Current studies are exploring agents that target sialic acid residues on sialoglycans or the sialylation process. These efforts are particularly focused on the fields of cancer therapy, stroke treatment, antiviral strategies, and therapies for central nervous system disorders. In this review, we aimed to summarize the biological functions of sialic acid and the process of sialylation, explore their roles in various pathophysiological contexts, and discuss their potential applications in the development of novel therapeutics.

Identification of Siglec-10 as a new dendritic cell checkpoint for cervical cancer immunotherapy

BACKGROUND

The occurrence of chronic inflammation resulting from infection with human papillomaviruses is an important factor in the development of cervical cancer (CC); thus, deciphering the crosstalk between the tumor microenvironment and innate immune cells during the establishment of immune tolerance is vital for identifying potential treatment strategies.

METHODS

Single-cell RNA sequencing data and primary tumor samples from patients with CC were used to evaluate the functional role of Siglec-10 on dendritic cells (DCs). Patient-derived tumor fragment platforms were used to examine the ability of Siglec-10 blockade to reinvigorate DC-mediate T-cell activation and tumor clearance.

RESULTS

Here, we demonstrated that Siglec-10 is a prominent inhibitory checkpoint for DCs infiltrated in CC. CC epithelial cells use their aberrant surface sialylated structures to induce the transformation of conventional DCs into phenotypes characterized by low immunogenicity and high immunotolerance. Additionally, Siglec-10+ DCs suppress the function of adaptive T cells via galectin-9 signaling to strengthen the immunosuppressive CC microenvironment. Disturbance of Siglec-10 signaling restored the DC-mediated tumoricidal response and increased adaptive T cells sensitivity to programmed cell death protein 1 inhibition.

CONCLUSION

Our study confirms the checkpoint role of Siglec-10 on DCs and proposes that targeting Siglec-10 may be a promising avenue for immunotherapy against CC.

Synthesis of α-Hydroxy-1,2,3-Triazole-linked Sialyltransferase Inhibitors and Evaluation of Selectivity Towards ST3GAL1, ST6GAL1 and ST8SIA2

Tumour-derived sialoglycans, bearing the charged nonulosonic sugar sialic acid at their termini, play a critical role in tumour cell adhesion and invasion, as well as evading cell death and immune surveillance. Sialyltransferases (ST), the enzymes responsible for the biosynthesis of sialylated glycans, are highly upregulated in cancer, with tumour hypersialylation strongly correlated with tumour growth, metastasis and drug resistance. As a result, desialylation of the tumour cell surface using either targeted delivery of a pan-ST inhibitor (or sialidase) or systemic delivery of a non-toxic selective ST inhibitors are being pursued as potential new anti-metastatic strategies against multiple cancers including pancreatic, ovarian, breast, melanoma and lung cancer. Herein, we have employed molecular modelling to give insights into the selectivity observed in a series of selective ST inhibitors that incorporate a uridyl ring in place of the cytidine of the natural donor (CMP-Neu5Ac) and replace the charged phosphodiester linker of classical ST inhibitors with a neutral α-hydroxy-1,2,3-triazole linker. The inhibitory activities of the nascent compounds were determined against recombinant human ST enzymes (ST3GAL1, ST6GAL1, ST8SIA2) showing promising activity and selectivity towards specific ST sub-types. Our ST inhibitors are non-toxic and show improved synthetic accessibility and drug-likeness compared to earlier nucleoside-based ST inhibitors.

Reduced sialylation of airway mucin impairs mucus transport by altering the biophysical properties of mucin

Mucus stasis is a pathologic hallmark of muco-obstructive diseases, including cystic fibrosis (CF). Mucins, the principal component of mucus, are extensively modified with hydroxyl (O)-linked glycans, which are largely terminated by sialic acid. Sialic acid is a negatively charged monosaccharide and contributes to the biochemical/biophysical properties of mucins. Reports suggest that mucin sialylation may be altered in CF; however, the consequences of reduced sialylation on mucus clearance have not been fully determined. Here, we investigated the consequences of reduced sialylation on the charge state and conformation of the most prominent airway mucin, MUC5B, and defined the functional consequences of reduced sialylation on mucociliary transport (MCT). Reduced sialylation contributed to a lower charged MUC5B form and decreased polymer expansion. The inhibition of total mucin sialylation de novo impaired MCT in primary human bronchial epithelial cells and rat airways, and specific α-2,3 sialylation blockade was sufficient to recapitulate these findings. Finally, we show that ST3 beta-galactoside alpha-2,3-sialyltransferase (ST3Gal1) expression is downregulated in CF and partially restored by correcting CFTR via Elexacaftor/Tezacaftor/Ivacaftor treatment. Overall, this study demonstrates the importance of mucin sialylation in mucus clearance and identifies decreased sialylation by ST3Gal1 as a possible therapeutic target in CF and potentially other muco-obstructive diseases.

Anticancer approach by targeted activation of a global inhibitor of sialyltransferases with acrolein

Cells are covered with a thick layer of sugar molecules known as glycans. Abnormal glycosylation is a hallmark of cancer, and hypersialylation increases tumor metastasis by promoting immune evasion and inducing tumor cell invasion and migration. Inhibiting sialylation is thus a potential anticancer treatment strategy. However, targeting sialic acids is difficult because of the lack of selective delivery tools. Here, we present a prodrug strategy for selectively releasing the global inhibitor of sialylation peracetylated 3Fax-Neu5Ac (PFN) in cancer cells using the reaction between phenyl azide and endogenous acrolein, which is overproduced in most cancer cells. The prodrug significantly suppressed tumor growth in mice as effectively as PFN without causing kidney dysfunction, which is associated with PFN. The use of sialylated glycans as immune checkpoints is gaining increasing attention, and the proposed method for precisely targeting aberrant sialylation provides a novel avenue for expanding current cancer treatments.

Blockade of Sialylation with Decrease in Polysialic Acid Levels Counteracts Transforming Growth Factor β1-Induced Skin Fibroblast-to-Myofibroblast Transition

Aberrant sialylation with overexpression of the homopolymeric glycan polysialic acid (polySia) was recently reported in fibroblasts from fibrotic skin lesions. Yet, whether such a rise in polySia levels or sialylation in general may be functionally implicated in profibrotic activation of fibroblasts and their transition to myofibroblasts remains unknown. Therefore, we herein explored whether inhibition of sialylation could interfere with the process of skin fibroblast-to-myofibroblast transition induced by the master profibrotic mediator transforming growth factor β1 (TGFβ1). Adult human skin fibroblasts were pretreated with the competitive pan-sialyltransferase inhibitor 3-Fax-peracetyl-Neu5Ac (3-Fax) before stimulation with recombinant human TGFβ1, and then analyzed for polySia expression, cell viability, proliferation, migratory ability, and acquisition of myofibroblast-like morphofunctional features. Skin fibroblast stimulation with TGFβ1 resulted in overexpression of polySia, which was effectively blunted by 3-Fax pre-administration. Pretreatment with 3-Fax efficiently lessened TGFβ1-induced skin fibroblast proliferation, migration, changes in cell morphology, and phenotypic and functional differentiation into myofibroblasts, as testified by a significant reduction in FAP, ACTA2, COL1A1, COL1A2, and FN1 gene expression, and α-smooth muscle actin, N-cadherin, COL1A1, and FN-EDA protein levels, as well as a reduced contractile capability. Moreover, skin fibroblasts pre-administered with 3-Fax displayed a significant decrease in Smad3-dependent canonical TGFβ1 signaling. Collectively, our in vitro findings demonstrate for the first time that aberrant sialylation with increased polySia levels has a functional role in skin fibroblast-to-myofibroblast transition and suggest that competitive sialyltransferase inhibition might offer new therapeutic opportunities against skin fibrosis.

Sialic acid blockade inhibits the metastatic spread of prostate cancer to bone

BACKGROUND

Bone metastasis is a common consequence of advanced prostate cancer. Bisphosphonates can be used to manage symptoms, but there are currently no curative treatments available. Altered tumour cell glycosylation is a hallmark of cancer and is an important driver of a malignant phenotype. In prostate cancer, the sialyltransferase ST6GAL1 is upregulated, and studies show ST6GAL1-mediated aberrant sialylation of N-glycans promotes prostate tumour growth and disease progression.

METHODS

Here, we monitor ST6GAL1 in tumour and serum samples from men with aggressive prostate cancer and using in vitro and in vivo models we investigate the role of ST6GAL1 in prostate cancer bone metastasis.

FINDINGS

ST6GAL1 is upregulated in patients with prostate cancer with tumours that have spread to the bone and can promote prostate cancer bone metastasis in vivo. The mechanisms involved are multi-faceted and involve modification of the pre-metastatic niche towards bone resorption to promote the vicious cycle, promoting the development of M2 like macrophages, and the regulation of immunosuppressive sialoglycans. Furthermore, using syngeneic mouse models, we show that inhibiting sialylation can block the spread of prostate tumours to bone.

INTERPRETATION

Our study identifies an important role for ST6GAL1 and α2-6 sialylated N-glycans in prostate cancer bone metastasis, provides proof-of-concept data to show that inhibiting sialylation can suppress the spread of prostate tumours to bone, and highlights sialic acid blockade as an exciting new strategy to develop new therapies for patients with advanced prostate cancer.

FUNDING

Prostate Cancer Research and the Mark Foundation For Cancer Research, the Medical Research Council and Prostate Cancer UK.

Reduced Sialylation of Airway Mucin Impairs Mucus Transport by Altering the Biophysical Properties of Mucin

Mucus stasis is a pathologic hallmark of muco-obstructive diseases, including cystic fibrosis (CF). Mucins, the principal component of mucus, are extensively modified with hydroxyl (O)-linked glycans, which are largely terminated by sialic acid. Sialic acid is a negatively charged monosaccharide and contributes to the biochemical/biophysical properties of mucins. Reports suggest that mucin sialylation may be altered in CF; however, the consequences of reduced sialylation on mucus clearance have not been fully determined. Here, we investigated the consequences of reduced sialylation on the charge state and conformation of the most prominent airway mucin, MUC5B, and defined the functional consequences of reduced sialylation on mucociliary transport (MCT). Reduced sialylation contributed to a lower charged MUC5B form and decreased polymer expansion. The inhibition of total mucin sialylation de novo impaired MCT in primary human bronchial epithelial cells and rat airways, and specific α-2,3 sialylation blockade was sufficient to recapitulate these findings. Finally, we show that ST3 beta-galactoside alpha-2,3-sialyltransferase (ST3Gal1) expression is downregulated in CF and partially restored by correcting CFTR via Elexacaftor/Tezacaftor/Ivacaftor treatment. Overall, this study demonstrates the importance of mucin sialylation in mucus clearance and identifies decreased sialylation by ST3Gal1 as a possible therapeutic target in CF and potentially other muco-obstructive diseases.

The glycosylation landscape of prostate cancer tissues and biofluids

An overview of the role of glycosylation in prostate cancer (PCa) development and progression is presented, focusing on recent advancements in defining the N-glycome through glycomic profiling and glycoproteomic methodologies. Glycosylation is a common post-translational modification typified by oligosaccharides attached N-linked to asparagine or O-linked to serine or threonine on carrier proteins. These attached sugars have crucial roles in protein folding and cellular recognition processes, such that altered glycosylation is a hallmark of cancer pathogenesis and progression. In the past decade, advancements in N-glycan profiling workflows using Matrix Assisted Laser Desorption/Ionization Mass Spectrometry Imaging (MALDI-MSI) technology have been applied to define the spatial distribution of glycans in PCa tissues. Multiple studies applying N-glycan MALDI-MSI to pathology-defined PCa tissues have identified significant alterations in N-glycan profiles associated with PCa progression. N-glycan compositions progressively increase in number, and structural complexity due to increased fucosylation and sialylation. Additionally, significant progress has been made in defining the glycan and glycopeptide compositions of prostatic-derived glycoproteins like prostate-specific antigen in tissues and biofluids. The glycosyltransferases involved in these changes are potential drug targets for PCa, and new approaches in this area are summarized. These advancements will be discussed in the context of the further development of clinical diagnostics and therapeutics targeting glycans and glycoproteins associated with PCa progression. Integration of large scale spatial glycomic data for PCa with other spatial-omic methodologies is now feasible at the tissue and single-cell levels.

Development of a Novel, Potent, and Selective Sialyltransferase Inhibitor for Suppressing Cancer Metastasis

Sialyltransferase-catalyzed membrane protein and lipid glycosylation plays a vital role as one of the most abundant post-translational modifications and diversification reactions in eukaryotes. However, aberrant sialylation has been associated with cancer malignancy and metastasis. Sialyltransferases thus represent emerging targets for the development of small molecule cancer drugs. Herein, we report the inhibitory effects of a recently discovered lithocholic acid derivative FCW393 on sialyltransferase catalytic activity, integrin sialyation, cancer-associated signal transduction, MDA-MB-231 and B16F10 cell migration and invasion, and in in vivo studies, on tumor growth, metastasis, and angiogenesis. FCW393 showed effective and selective inhibition of the sialyltransferases ST6GAL1 (IC50 = 7.8 μM) and ST3GAL3 (IC50 = 9.45 μM) relative to ST3GAL1 (IC50 > 400 μM) and ST8SIA4 (IC50 > 100 μM). FCW393 reduced integrin sialylation in breast cancer and melanoma cells dose-dependently and downregulated proteins associated with the integrin-regulated FAK/paxillin and GEF/Rho/ROCK pathways, and with the VEGF-regulated Akt/NFκB/HIF-1α pathway. FCW393 inhibited cell migration (IC50 = 2.6 μM) and invasion in in vitro experiments, and in in vivo studies of tumor-bearing mice, FCW393 reduced tumor size, angiogenesis, and metastatic potential. Based on its demonstrated selectivity, cell permeability, relatively low cytotoxicity (IC50 = 55 μM), and high efficacy, FCW393 shows promising potential as a small molecule experimental tool compound and a lead for further development of a novel cancer therapeutic.

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.

Targeting aberrant sialylation and fucosylation in prostate cancer cells using potent metabolic inhibitors

Aberrant glycosylation is a hallmark of cancer and is not just a consequence, but also a driver of a malignant phenotype. In prostate cancer, changes in fucosylated and sialylated glycans are common and this has important implications for tumor progression, metastasis, and immune evasion. Glycans hold huge translational potential and new therapies targeting tumor-associated glycans are currently being tested in clinical trials for several tumor types. Inhibitors targeting fucosylation and sialylation have been developed and show promise for cancer treatment, but translational development is hampered by safety issues related to systemic adverse effects. Recently, potent metabolic inhibitors of sialylation and fucosylation were designed that reach higher effective concentrations within the cell, thereby rendering them useful tools to study sialylation and fucosylation as potential candidates for therapeutic testing. Here, we investigated the effects of global metabolic inhibitors of fucosylation and sialylation in the context of prostate cancer progression. We find that these inhibitors effectively shut down the synthesis of sialylated and fucosylated glycans to remodel the prostate cancer glycome with only minor apparent side effects on other glycan types. Our results demonstrate that treatment with inhibitors targeting fucosylation or sialylation decreases prostate cancer cell growth and downregulates the expression of genes and proteins important in the trajectory of disease progression. We anticipate our findings will lead to the broader use of metabolic inhibitors to explore the role of fucosylated and sialylated glycans in prostate tumor pathology and may pave the way for the development of new therapies for prostate cancer.

Recent advances in the development of sialyltransferase inhibitors to control cancer metastasis: A comprehensive review

Metastasis accounts for the majority of cancer-associated mortalities, representing a huge health and economic burden. One of the mechanisms that enables metastasis is hypersialylation, characterized by an overabundance of sialylated glycans on the tumor surface, which leads to repulsion and detachment of cells from the original tumor. Once the tumor cells are mobilized, sialylated glycans hijack the natural killer T-cells through self-molecular mimicry and activatea downstream cascade of molecular events that result in inhibition of cytotoxicity and inflammatory responses against cancer cells, ultimately leading to immune evasion. Sialylation is mediated by a family of enzymes known as sialyltransferases (STs), which catalyse the transfer of sialic acid residue from the donor, CMP-sialic acid, onto the terminal end of an acceptor such as N-acetylgalactosamine on the cell-surface. Upregulation of STs increases tumor hypersialylation by up to 60% which is considered a distinctive hallmark of several types of cancers such as pancreatic, breast, and ovarian cancer. Therefore, inhibiting STs has emerged as a potential strategy to prevent metastasis. In this comprehensive review, we discuss the recent advances in designing novel sialyltransferase inhibitors using ligand-based drug design and high-throughput screening of natural and synthetic entities, emphasizing the most successful approaches. We analyse the limitations and challenges of designing selective, potent, and cell-permeable ST inhibitors that hindered further development of ST inhibitors into clinical trials. We conclude by analysing emerging opportunities, including advanced delivery methods which further increase the potential of these inhibitors to enrich the clinics with novel therapeutics to combat metastasis.

Co-administration of angiotensin II and simvastatin triggers kidney injury upon heme oxygenase-1 deficiency

Kidneys are pivotal organ in iron redistribution and can be severely damaged in the course of hemolysis. In our previous studies, we observed that induction of hypertension with angiotensin II (Ang II) combined with simvastatin administration results in a high mortality rate or the appearance of signs of kidney failure in heme oxygenase-1 knockout (HO-1 KO) mice. Here, we aimed to address the mechanisms underlying this effect, focusing on heme and iron metabolism. We show that HO-1 deficiency leads to iron accumulation in the renal cortex. Higher mortality of Ang II and simvastatin-treated HO-1 KO mice coincides with increased iron accumulation and the upregulation of mucin-1 in the proximal convoluted tubules. In vitro studies showed that mucin-1 hampers heme- and iron-related oxidative stress through the sialic acid residues. In parallel, knock-down of HO-1 induces the glutathione pathway in an NRF2-depedent manner, which likely protects against heme-induced toxicity. To sum up, we showed that heme degradation during heme overload is not solely dependent on HO-1 enzymatic activity, but can be modulated by the glutathione pathway. We also identified mucin-1 as a novel redox regulator. The results suggest that hypertensive patients with less active HMOX1 alleles may be at higher risk of kidney injury after statin treatment.

UV light-induced spatial loss of sialic acid capping using a photoactivatable sialyltransferase inhibitor

Sialic acids cap glycans displayed on mammalian glycoproteins and glycolipids and mediate many glycan-receptor interactions. Sialoglycans play a role in diseases such as cancer and infections where they facilitate immune evasion and metastasis or serve as cellular receptors for viruses, respectively. Strategies that specifically interfere with cellular sialoglycan biosynthesis, such as sialic acid mimetics that act as metabolic sialyltransferase inhibitors, enable research into the diverse biological functions of sialoglycans. Sialylation inhibitors are also emerging as potential therapeutics for cancer, infection, and other diseases. However, sialoglycans serve many important biological functions and systemic inhibition of sialoglycan biosynthesis can have adverse effects. To enable local and inducible inhibition of sialylation, we have synthesized and characterized a caged sialyltransferase inhibitor that can be selectively activated with UV-light. A photolabile protecting group was conjugated to a known sialyltransferase inhibitor (P-SiaFNEtoc). This yielded a photoactivatable inhibitor, UV-SiaFNEtoc, that remained inactive in human cell cultures and was readily activated through radiation with 365 nm UV light. Direct and short radiation of a human embryonic kidney (HEK293) cell monolayer was well-tolerated and resulted in photoactivation of the inhibitor and subsequent spatial restricted synthesis of asialoglycans. The developed photocaged sialic acid mimetic holds the potential to locally hinder the synthesis of sialoglycans through focused treatment with UV light and may be applied to bypass the adverse effects related to systemic loss of sialylation.

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.

Targeting stromal cell sialylation reverses T cell-mediated immunosuppression in the tumor microenvironment

Immunosuppressive tumor microenvironments (TMEs) reduce the effectiveness of immune responses in cancer. Mesenchymal stromal cells (MSCs), precursors to cancer-associated fibroblasts (CAFs), promote tumor progression by enhancing immune cell suppression in colorectal cancer (CRC). Hyper-sialylation of glycans promotes immune evasion in cancer through binding of sialic acids to their receptors, Siglecs, expressed on immune cells, which results in inhibition of effector functions. The role of sialylation in shaping MSC/CAF immunosuppression in the TME is not well characterized. In this study, we show that tumor-conditioned stromal cells have increased sialyltransferase expression, α2,3/6-linked sialic acid, and Siglec ligands. Tumor-conditioned stromal cells and CAFs induce exhausted immunomodulatory CD8+ PD1+ and CD8+ Siglec-7+/Siglec-9+ T cell phenotypes. In vivo, targeting stromal cell sialylation reverses stromal cell-mediated immunosuppression, as shown by infiltration of CD25 and granzyme B-expressing CD8+ T cells in the tumor and draining lymph node. Targeting stromal cell sialylation may overcome immunosuppression in the CRC TME.

Self-Assembled Core-Shell Nanoscale Coordination Polymer Nanoparticles Carrying a Sialyltransferase Inhibitor for Cancer Metastasis Inhibition

Despite hypersialylation of cancer cells together with a significant upregulation of sialyltransferase (ST) activity contributes to the metastatic cascade at multiple levels, there are few dedicated tools to interfere with their expression. Although transition state-based ST inhibitors are well-established, they are not membrane permeable. To tackle this problem, herein, we design and construct long-circulating, self-assembled core-shell nanoscale coordination polymer (NCP) nanoparticles carrying a transition state-based ST inhibitor, which make the inhibitor transmembrane and potently strip diverse sialoglycans from various cancer cells. In the experimental lung metastasis and metastasis prevention models, the nanoparticle device (NCP/STI) significantly inhibits metastases formation without systemic toxicity. This strategy enables ST inhibitors to be applied to cells and animals by providing them with a well-designed nanodelivery system. Our work opens a new avenue to the development of transition state-based ST inhibitors and demonstrates that NCP/STI holds great promise in achieving metastases inhibition for multiple cancers.

Attenuation of Polysialic Acid Biosynthesis in Cells by the Small Molecule Inhibitor 8-Keto-sialic acid

Sialic acids are key mediators of cell function, particularly with regard to cellular interactions with the surrounding environment. Reagents that modulate the display of specific sialyl glycoforms at the cell surface would be useful biochemical tools and potentially allow for therapeutic intervention in numerous challenging chronic diseases. While multiple strategies are being explored for the control of cell surface sialosides, none that shows high selectivity between sialyltransferases or that targets a specific sialyl glycoform has yet to emerge. Here, we describe a strategy to block the formation of α2,8-linked sialic acid chains (oligo- and polysialic acid) through the use of 8-keto-sialic acid as a chain-terminating metabolic inhibitor that, if incorporated, cannot be elongated. 8-Keto-sialic acid is nontoxic at effective concentrations and serves to block polysialic acid synthesis in cancer cell lines and primary immune cells, with minimal effects on other sialyl glycoforms.

Sialyltransferase Inhibitor Ac53FaxNeu5Ac Reverts the Malignant Phenotype of Pancreatic Cancer Cells, and Reduces Tumor Volume and Favors T-Cell Infiltrates in Mice

Hypersialylation is a feature of pancreatic ductal adenocarcinoma (PDA) and it has been related to tumor malignancy and immune suppression. In this work, we have evaluated the potential of the sialyltransferase inhibitor, Ac₅3F_axNeu5Ac, to decrease tumor sialoglycans in PDA and to revert its malignant phenotype. Sialoglycans on PDA cells were evaluated by flow cytometry, and the functional impact of Ac₅3F_axNeu5Ac was assessed using E-selectin adhesion, migration, and invasion assays. PDA tumors were generated in syngeneic mice from KC cells and treated with Ac₅3F_axNeu5Ac to evaluate tumor growth, mice survival, and its impact on blocking sialic acid (SA) and on the tumor immune component. Ac₅3F_axNeu5Ac treatment on human PDA cells decreased α2,3-SA and sialyl-Lewis^x, which resulted in a reduction in their E-selectin adhesion, and in their migratory and invasive capabilities. Subcutaneous murine tumors treated with Ac₅3F_axNeu5Ac reduced their volume, their SA expression, and modified their immune component, with an increase in CD8⁺ T-lymphocytes and NK cells. In conclusion, Ac₅3F_axNeu5Ac treatment weakened PDA cells' malignant phenotype, thereby reducing tumor growth while favoring anti-tumor immune surveillance. Altogether, these results show the positive impact of reducing SA expression by inhibiting cell sialyltransferases and open the way to use sialyltransferase inhibitors to target this dismal disease.

Insights into the Role of Sialylation in Cancer Metastasis, Immunity, and Therapeutic Opportunity

Sialylation is an enzymatic process that covalently attaches sialic acids to glycoproteins and glycolipids and terminates them by creating sialic acid-containing glycans (sialoglycans). Sialoglycans, usually located in the outmost layers of cells, play crucial biological roles, notably in tumor transformation, growth, metastasis, and immune evasion. Thus, a deeper comprehension of sialylation in cancer will help to facilitate the development of innovative cancer therapies. Cancer sialylation-related articles have consistently increased over the last four years. The primary subjects of these studies are sialylation, cancer, immunotherapy, and metastasis. Tumor cells activate endothelial cells and metastasize to distant organs in part by the interactions of abnormally sialylated integrins with selectins. Furthermore, cancer sialylation masks tumor antigenic epitopes and induces an immunosuppressive environment, allowing cancer cells to escape immune monitoring. Cytotoxic T lymphocytes develop different recognition epitopes for glycosylated and nonglycosylated peptides. Therefore, targeting tumor-derived sialoglycans is a promising approach to cancer treatments for limiting the dissemination of tumor cells, revealing immunogenic tumor antigens, and boosting anti-cancer immunity. Exploring the exact tumor sialoglycans may facilitate the identification of new glycan targets, paving the way for the development of customized cancer treatments.

Deficiency in ST6GAL1, one of the two α2,6-sialyltransferases, has only a minor effect on the pathogenesis of prion disease

Prion diseases are a group of fatal neurodegenerative diseases caused by misfolding of the normal cellular form of the prion protein or PrPC, into a disease-associated self-replicating state or PrPSc. PrPC and PrPSc are posttranslationally modified with N-linked glycans, in which the terminal positions occupied by sialic acids residues are attached to galactose predominantly via α2-6 linkages. The sialylation status of PrPSc is an important determinant of prion disease pathogenesis, as it dictates the rate of prion replication and controls the fate of prions in an organism. The current study tests whether a knockout of ST6Gal1, one of the two mammalian sialyltransferases that catalyze the sialylation of glycans via α2-6 linkages, reduces the sialylation status of PrPSc and alters prion disease pathogenesis. We found that a global knockout of ST6Gal1 in mice significantly reduces the α2-6 sialylation of the brain parenchyma, as determined by staining with Sambucus Nigra agglutinin. However, the sialylation of PrPSc remained stable and the incubation time to disease increased only modestly in ST6Gal1 knockout mice (ST6Gal1-KO). A lack of significant changes in the PrPSc sialylation status and prion pathogenesis is attributed to the redundancy in sialylation and, in particular, the plausible involvement of a second member of the sialyltransferase family that sialylate via α2-6 linkages, ST6Gal2.

Targeting cancer glycosylation repolarizes tumor-associated macrophages allowing effective immune checkpoint blockade

Immune checkpoint blockade (ICB) has substantially improved the prognosis of patients with cancer, but the majority experiences limited benefit, supporting the need for new therapeutic approaches. Up-regulation of sialic acid-containing glycans, termed hypersialylation, is a common feature of cancer-associated glycosylation, driving disease progression and immune escape through the engagement of Siglec receptors on tumor-infiltrating immune cells. Here, we show that tumor sialylation correlates with distinct immune states and reduced survival in human cancers. The targeted removal of Siglec ligands in the tumor microenvironment, using an antibody-sialidase conjugate, enhanced antitumor immunity and halted tumor progression in several murine models. Using single-cell RNA sequencing, we revealed that desialylation repolarized tumor-associated macrophages (TAMs). We also identified Siglec-E as the main receptor for hypersialylation on TAMs. Last, we found that genetic and therapeutic desialylation, as well as loss of Siglec-E, enhanced the efficacy of ICB. Thus, therapeutic desialylation represents an immunotherapeutic approach to reshape macrophage phenotypes and augment the adaptive antitumor immune response.

Aberrant Sialylation in Cancer: Therapeutic Opportunities

The surface of every eukaryotic cell is coated in a thick layer of glycans that acts as a key interface with the extracellular environment. Cancer cells have a different ‘glycan coat’ to healthy cells and aberrant glycosylation is a universal feature of cancer cells linked to all of the cancer hallmarks. This means glycans hold huge potential for the development of new diagnostic and therapeutic strategies. One key change in tumour glycosylation is increased sialylation, both on N-glycans and O-glycans, which leads to a dense forest of sialylated structures covering the cell surface. This hypersialylation has far-reaching consequences for cancer cells, and sialylated glycans are fundamental in tumour growth, metastasis, immune evasion and drug resistance. The development of strategies to inhibit aberrant sialylation in cancer represents an important opportunity to develop new therapeutics. Here, I summarise recent advances to target aberrant sialylation in cancer, including the development of sialyltransferase inhibitors and strategies to inhibit Siglecs and Selectins, and discuss opportunities for the future.

Small molecule inhibitors of mammalian glycosylation

Glycans are one of the fundamental biopolymers encountered in living systems. Compared to polynucleotide and polypeptide biosynthesis, polysaccharide biosynthesis is a uniquely combinatorial process to which interdependent enzymes with seemingly broad specificities contribute. The resulting intracellular cell surface, and secreted glycans play key roles in health and disease, from embryogenesis to cancer progression. The study and modulation of glycans in cell and organismal biology is aided by small molecule inhibitors of the enzymes involved in glycan biosynthesis. In this review, we survey the arsenal of currently available inhibitors, focusing on agents which have been independently validated in diverse systems. We highlight the utility of these inhibitors and drawbacks to their use, emphasizing the need for innovation for basic research as well as for therapeutic applications.

Targeting hypersialylation in multiple myeloma represents a novel approach to enhance NK cell-mediated tumor responses

Hypersialylation in MM facilitates immune evasion of NK cells but can be overcome by targeted desialylation or genetic deletion of Siglec-7.

Desialylation unmasks CD38 expression on MM cells, enhancing NK cell–mediated ADCC induced by CD38 targeting of monoclonal antibodies.

Abnormal glycosylation is a hallmark of cancer, and the hypersialylated tumor cell surface facilitates abnormal cell trafficking and drug resistance in several malignancies, including multiple myeloma (MM). Furthermore, hypersialylation has also been implicated in facilitating evasion of natural killer (NK) cell–mediated immunosurveillance but not in MM to date. In this study, we explore the role of hypersialylation in promoting escape from NK cells. We document strong expression of sialic acid-derived ligands for Siglec-7 (Siglec-7L) on primary MM cells and MM cell lines, highlighting the possibility of Siglec-7/Siglec-7L interactions in the tumor microenvironment. Interactomics experiments in MM cell lysates revealed PSGL-1 as the predominant Siglec-7L in MM. We show that desialylation, using both a sialidase and sialyltransferase inhibitor (SIA), strongly enhances NK cell–mediated cytotoxicity against MM cells. Furthermore, MM cell desialylation results in increased detection of CD38, a well-validated target in MM. Desialylation enhanced NK cell cytotoxicity against CD38⁺ MM cells after treatment with the anti-CD38 monoclonal antibody daratumumab. Additionally, we show that MM cells with low CD38 expression can be treated with all trans-retinoic acid (ATRA), SIA and daratumumab to elicit a potent NK cell cytotoxic response. Finally, we demonstrate that Siglec-7^KO potentiates NK cell cytotoxicity against Siglec-7L⁺ MM cells. Taken together, our work shows that desialylation of MM cells is a promising novel approach to enhance NK cell efficacy against MM, which can be combined with frontline therapies to elicit a potent anti-MM response.

Role and therapeutic implications of protein glycosylation in neuroinflammation

The importance of glycosylation (post-translational attachment of glycan residues to proteins) in the context of neuroinflammation is only now beginning to be understood. Although the glycome is challenging to investigate due to its complexity, this field is gaining interest because of the emergence of novel analytical methods. These investigations offer the possibility of further understanding the molecular signature of disorders with underlying neuroinflammatory cascades. In this review, we portray the clinically relevant trends in glyconeurobiology and suggest glyco-related paths that could be targeted therapeutically to decrease neuroinflammation. A combinatorial insight from glycobiology and neurology can be harnessed to better understand neuroinflammatory-related conditions to identify relevant molecular targets.

Sialic acid blockade in dendritic cells enhances CD8+ T cell responses by facilitating high-avidity interactions

Sialic acids are negatively charged carbohydrates that cap the glycans of glycoproteins and glycolipids. Sialic acids are involved in various biological processes including cell-cell adhesion and immune recognition. In dendritic cells (DCs), the major antigen-presenting cells of the immune system, sialic acids emerge as important regulators of maturation and interaction with other lymphocytes including T cells. Many aspects of how sialic acids regulate DC functions are not well understood and tools and model systems to address these are limited. Here, we have established cultures of murine bone marrow-derived DCs (BMDCs) that lack sialic acid expression using a sialic acid-blocking mimetic Ac53FaxNeu5Ac. Ac53FaxNeu5Ac treatment potentiated BMDC activation via toll-like receptor (TLR) stimulation without affecting differentiation and viability. Sialic acid blockade further increased the capacity of BMDCs to induce antigen-specific CD8+ T cell proliferation. Transcriptome-wide gene expression analysis revealed that sialic acid mimetic treatment of BMDCs induces differential expression of genes involved in T cell activation, cell-adhesion, and cell-cell interactions. Subsequent cell clustering assays and single cell avidity measurements demonstrated that BMDCs with reduced sialylation form higher avidity interactions with CD8+ T cells. This increased avidity was detectable in the absence of antigens, but was especially pronounced in antigen-dependent interactions. Together, our data show that sialic acid blockade in BMDCs ameliorates maturation and enhances both cognate T cell receptor-MHC-dependent and independent T cell interactions that allow for more robust CD8+ T cell responses.

A proximity labeling method for protein–protein interactions on cell membrane

Modified catalytic antibodies targeting specific antigens are employed to investigate protein interactions and antigen interaction sites.

Therapeutic Interventions Targeting Innate Immune Receptors: A Balancing Act

The innate immune system is an organism's first line of defense against an onslaught of internal and external threats. The downstream adaptive immune system has been a popular target for therapeutic intervention, while there is a relative paucity of therapeutics targeting the innate immune system. However, the innate immune system plays a critical role in many human diseases, such as microbial infection, cancer, and autoimmunity, highlighting the need for ongoing therapeutic research. In this review, we discuss the major innate immune pathways and detail the molecular strategies underpinning successful therapeutics targeting each pathway as well as previous and ongoing efforts. We will also discuss any recent discoveries that could inform the development of novel therapeutic strategies. As our understanding of the innate immune system continues to develop, we envision that therapies harnessing the power of the innate immune system will become the mainstay of treatment for a wide variety of human diseases.

Key Activating and Inhibitory Ligands Involved in the Mobilization of Natural Killer Cells for Cancer Immunotherapies

Natural killer (NK) cells are the most potent arm of the innate immune system and play an important role in immunity, alloimmunity, autoimmunity, and cancer. NK cells recognize “altered-self” cells due to oncogenic transformation or stress due to viral infection and target to kill them. The effector functions of NK cells depend on the interaction of the activating and inhibitory receptors on their surface with their cognate ligand expressed on the target cells. These activating and inhibitory receptors interact with major histocompatibility complex I (MHC I) expressed on the target cells and make decisions to mount an immune response. NK cell immune response includes cytolytic activity and secretion of cytokines to help with the ongoing immune response. The advancement of our knowledge on the expression of inhibitory and activating molecules led us to exploit these molecules in the treatment of cancer. This review discusses the importance of activating and inhibitory receptors on NK cells and their clinical importance in cancer immunotherapy.

The Metabolic Chemical Reporter Ac46AzGal Could Incorporate Intracellular Protein Modification in the Form of UDP-6AzGlc Mediated by OGT and Enzymes in the Leloir Pathway

Galactose is a naturally occurring monosaccharide used to build complex glycans that has not been targeted for labeling as a metabolic reporter. Here, we characterize the cellular modification of proteins by using Ac₄6AzGal in a dose- and time-dependent manner. It is noted that a vast majority of this labeling of Ac₄6AzGal occurs intracellularly in a range of mammalian cells. We also provided evidence that this labeling is dependent on not only the enzymes of OGT responsible for O-GlcNAcylation but also the enzymes of GALT and GALE in the Leloir pathway. Notably, we discover that Ac₄6AzGal is not the direct substrate of OGT, and the labeling results may attribute to UDP-6AzGlc after epimerization of UDP-6AzGal via GALE. Together, these discoveries support the conclusion that Ac₄6AzGal as an analogue of galactose could metabolically label intracellular O-glycosylation modification, raising the possibility of characterization with impaired functions of the galactose metabolism in the Leloir pathway under certain conditions, such as galactosemias.

Synthesis and biological evaluation of selective phosphonate-bearing 1,2,3-triazole-linked sialyltransferase inhibitors

The critical role of sialyltransferase (ST) enzymes in tumour cell growth and metastasis, as well as links to multi-drug and radiation resistance, has seen STs emerge as a target for potential antimetastatic cancer treatments. One promising class of ST inhibitors that improve upon the pharmacokinetic issues of previous inhibitors is the 1,2,3-triazole-linked transition-state analogues. Herein, we present the design and synthesis of a new generation of 1,2,3-triazole-linked sialyltransferase inhibitors, along with their biological evaluation demonstrating increased potency for phosphonate bearing compounds. The six most promising inhibitors presented in this work exhibited a greater number of binding modes for hST6Gal I over hST3Gal I, with K _i ranging from 3-55 μM. This work highlights phosphonate bearing triazole-linked compounds as a promising class of synthetically accessible ST inhibitors that warrant further investigation.

Engineering the Sialome

The surface of every eukaryotic cell is coated in a dense layer of structurally diverse glycans that together comprise the glycocalyx, a key interface between intracellular biochemistry and the external environment. Many of the glycans within the glycocalyx terminate in anionic monosaccharides belonging to the sialic acid family. Advances in our understanding of the biological processes mediated by sialic acids at the interfaces between cells have catalyzed interest in metabolic, enzymatic, and chemical strategies to edit the total complement of cellular sialic acids-the sialome. Here, we review strategies for altering the composition of the sialome with particular focus on glycan structures and state-of-the-art tools.

Sialic Acid Ligands of CD28 Suppress Costimulation of T Cells

Effector T cells comprise the cellular arm of the adaptive immune system and are essential for mounting immune responses against pathogens and cancer. To reach effector status, costimulation through CD28 is required. Here, we report that sialic acid-containing glycans on the surface of both T cells and APCs are alternative ligands of CD28 that compete with binding to its well-documented activatory ligand CD80 on the APC, resulting in attenuated costimulation. Removal of sialic acids enhances antigen-mediated activation of naïve T cells and also increases the revival of effector T cells made hypofunctional or exhausted via chronic viral infection. This occurs through a mechanism that is synergistic with antibody blockade of the inhibitory PD-1 axis. These results reveal a previously unrecognized role of sialic acid ligands in attenuation of CD28-mediated costimulation of T cells.

Proteogenomic characterization of pancreatic ductal adenocarcinoma

Pancreatic ductal adenocarcinoma (PDAC) is a highly aggressive cancer with poor patient survival. Toward understanding the underlying molecular alterations that drive PDAC oncogenesis, we conducted comprehensive proteogenomic analysis of 140 pancreatic cancers, 67 normal adjacent tissues, and 9 normal pancreatic ductal tissues. Proteomic, phosphoproteomic, and glycoproteomic analyses were used to characterize proteins and their modifications. In addition, whole-genome sequencing, whole-exome sequencing, methylation, RNA sequencing (RNA-seq), and microRNA sequencing (miRNA-seq) were performed on the same tissues to facilitate an integrated proteogenomic analysis and determine the impact of genomic alterations on protein expression, signaling pathways, and post-translational modifications. To ensure robust downstream analyses, tumor neoplastic cellularity was assessed via multiple orthogonal strategies using molecular features and verified via pathological estimation of tumor cellularity based on histological review. This integrated proteogenomic characterization of PDAC will serve as a valuable resource for the community, paving the way for early detection and identification of novel therapeutic targets.

Aberrant Sialylation in Cancer: Biomarker and Potential Target for Therapeutic Intervention?

Simple Summary

Sialylation is a post-translational modification that consists in the addition of sialic acid to growing glycan chains on glycoproteins and glycolipids. Aberrant sialylation is an established hallmark of several types of cancer, including breast, ovarian, pancreatic, prostate, colorectal and lung cancers, melanoma and hepatocellular carcinoma. Hypersialylation can be the effect of increased activity of sialyltransferases and results in an excess of negatively charged sialic acid on the surface of cancer cells. Sialic acid accumulation contributes to tumor progression by several paths, including stimulation of tumor invasion and migration, and enhancing immune evasion and tumor cell survival. In this review we explore the mechanisms by which sialyltransferases promote cancer progression. In addition, we provide insights into the possible use of sialyltransferases as biomarkers for cancer and summarize findings on the development of sialyltransferase inhibitors as potential anti-cancer treatments.

Abstract

Sialylation is an integral part of cellular function, governing many biological processes including cellular recognition, adhesion, molecular trafficking, signal transduction and endocytosis. Sialylation is controlled by the levels and the activities of sialyltransferases on glycoproteins and lipids. Altered gene expression of these enzymes in cancer yields to cancer-specific alterations of glycoprotein sialylation. Mounting evidence indicate that hypersialylation is closely associated with cancer progression and metastatic spread, and can be of prognostic significance in human cancer. Aberrant sialylation is not only a result of cancer, but also a driver of malignant phenotype, directly impacting key processes such as tumor cell dissociation and invasion, cell-cell and cell-matrix interactions, angiogenesis, resistance to apoptosis, and evasion of immune destruction. In this review we provide insights on the impact of sialylation in tumor progression, and outline the possible application of sialyltransferases as cancer biomarkers. We also summarize the most promising findings on the development of sialyltransferase inhibitors as potential anti-cancer treatments.

Glycans in Immunologic Health and Disease

The surfaces of all living organisms and most secreted proteins share a common feature: They are glycosylated. As the outermost-facing molecules, glycans participate in nearly all immunological processes, including driving host-pathogen interactions, immunological recognition and activation, and differentiation between self and nonself through a complex array of pathways and mechanisms. These fundamental immunologic roles are further cast into sharp relief in inflammatory, autoimmune, and cancer disease states in which immune regulation goes awry. Here, we review the broad impact of glycans on the immune system and discuss the changes and clinical opportunities associated with the onset of immunologic disease.

Targeting glyco-immune checkpoints for cancer therapy

Introduction: Targeting immune checkpoints with antibodies has significantly improved the outcome of cancer patients, but only few patients have long-term benefits from currently used PD-1/PD-L1 and CTLA-4 inhibitors. New approaches are needed to increase the number of patients going into long-term remission after cancer immunotherapy. Glyco-immune checkpoints are new targets for cancer immunotherapy. They are defined as immune-modulatory pathways including interactions of glycans with glycan-binding proteins or lectins. The most prominent pathway is the sialoglycan-Siglec axis and inhibitors of this axis are already successfully tested in early clinical trials.Area covered: Here, we summarize the current knowledge on glyco-immune checkpoints with a focus on the sialoglycan-Siglec axis. We also provide an overview on current approaches to clinically target glyco-immune checkpoints and give an outlook for the further clinical development of glyco-immune checkpoint targeting agents.Expert opinion: Glyco-immune checkpoints are interesting new targets to improve cancer immunotherapy. Antibodies targeting the sialoglycan-Siglec axis are already in clinical development. Other approaches with higher risk of toxicity including tumor-targeted sialidases are in late stage pre-clinical development. Despite the challenges, targeting of glyco-immune checkpoints could lead to the development of a new class of drugs providing improved anti-cancer immunity and eventually benefit cancer patients.

Fluorinated carbohydrates as chemical probes for molecular recognition studies. Current status and perspectives

This review provides an extensive summary of the effects of carbohydrate fluorination with regard to changes in physical, chemical and biological properties with respect to regular saccharides. The specific structural, conformational, stability, reactivity and interaction features of fluorinated sugars are described, as well as their applications as probes and in chemical biology.

Sialyltransferase Inhibitors as Potential Anti-Cancer Agents

Sialic acid occupies a privileged position at the terminus of the glycan chain of many cell-surface glycoconjugates. Owing to both their structure and location, charged sialic acid residues mediate numerous critical interactions in cell–cell communication including cell recognition, invasion, migration, receptor binding, and immunological responses. Sialyltransferases (STs) are the enzymes involved in the biosynthesis of sialylated glycans and are highly upregulated, up to 40–60 %, in a range of cancers, with tumour hypersialylation strongly correlated with both tumour progression and treatment resistance. Accordingly, inhibiting sialylation is currently being explored by several research groups worldwide as a potential new cancer treatment strategy. However, to progress small molecule ST inhibitors into the clinic, issues around selectivity, synthetic accessibility, and cell permeability need to be addressed. Using computationally guided design principles, we produced a leading series of ST inhibitors by replacing the cytidine nucleoside with uridine and substituting the charged phosphodiester linker with a carbamate or triazole moiety. Biological evaluation of the newly developed inhibitors was performed using commercially available human ST enzymes, with the Ki inhibition values of the lead compounds ranging from 1 to 20 µM. Compared with earlier generations of sialylation inhibitors, our inhibitors are non-toxic in a range of cell studies, with improved synthetic accessibility.