2nd PSL Chemical Biology Symposium (2019): At the Crossroads of Chemistry and Biology.

Chemical Biology is the science of designing chemical tools to dissect and manipulate biology at different scales. It provides the fertile ground from which to address important problems of our society, such as human health and environment.

Immobilization of multivalent glycoprobes on gold surfaces for sensing proteins and macrophages.

The multivalent display of carbohydrates on the cell surface provides cooperative binding to improve the specific biological events. In addition to multivalency, the spatial arrangement and orientation of sugars with respect to external stimuli also trigger carbohydrate-protein interactions. Herein, we report a non-covalent host-guest strategy to immobilize heptavalent glyco-ß-cyclodextrin on gold-coated glass slides to study multivalent carbohydrate-protein interactions. We have found that the localization of sugar entities on surfaces using ß-cyclodextrin (ß-CD) chemistry increased the avidity of carbohydrate-protein and carbohydrate-macrophage interactions compared to monovalent-ß-CD sugar coated surfaces. This platform is expected to be a promising tool to amplify the avidity of sugar-mediated interactions on surfaces and contribute to the development of next generation bio-medical products.

Supramolecular metalloglycodendrimers selectively modulate lectin binding and delivery of Ru(ii) complexes into mammalian cells.

A host-guest interaction between Ru(ii)-complexes and sugar-capped ß-cyclodextrin was employed to synthesize metalloglycodendrimers. These glycodendrimers demonstrated selective carbohydrate-protein interactions and controlled the delivery of the Ru(ii) complexes into cancer cells, which may facilitate cell-specific apoptosis. Lectin binding assay revealed micromolar range IC50 values with different plant lectins. Cell viability assay and confocal imaging studies of Ru(ii) complexes exhibited cytotoxic activities in cancer cells compared to normal cells with IC50 values close to other literature Ru(ii) complexes. The cell death inducer was found to accumulate favorably to the endoplasmic reticulum (ER) and induced ER stress in cells. The upregulation of CHOP, caspase-3 and caspase-12 disturbed the ER morphology initiating the apoptosis pathway.

Correction: Supramolecular metalloglycodendrimers selectively modulate lectin binding and delivery of Ru(ii) complexes into mammalian cells.

Correction for 'Supramolecular metalloglycodendrimers selectively modulate lectin binding and delivery of Ru(ii) complexes into mammalian cells' by Harikrishna Bavireddi, et al., Org. Biomol. Chem., 2016, DOI: 10.1039/c6ob01546h.

Glyco-ß-cyclodextrin capped quantum dots: synthesis, cytotoxicity and optical detection of carbohydrate-protein interactions.

Highly fluorescent water soluble glyco-quantum dots were synthesized using a sonochemical procedure. The synthetic approach is based on specific host-guest interactions between ß-cyclodextrin (ß-CD) and trioctylphosphine oxide (TOPO) surfactant on quantum dots. The modified QDs were analyzed by a combination of FT-IR, (1)H-NOESY NMR spectroscopy and by TEM. The high sugar density on QDs resulted in selective colloidal aggregation with ConcanavalinA (ConA), Galanthus nivalis lectin (GNA) and Peanut agglutinin (PNA) lectins. Subsequently, in vitro studies indicated that ß-CD modification of QDs enabled good cell viability of human hepatocellular carcinoma cell line (HepG2) cells. Finally, flow cytometry and confocal imaging studies revealed that ßCDgal capped QDs undergo preferential binding with HepG2 cells. These results clearly demonstrate that ß-CD capped QDs could be a promising candidate for further carbohydrate-based biomedical applications.

Imaging and Targeting of the α(2-6) and α(2-3) Linked Sialic Acid Quantum Dots in Zebrafish and Mouse Models.

Sialic acid-conjugated nanocarriers have emerged as attractive biomarkers with promising biomedical applications. The translation of these nanocarriers into clinical applications requires in-depth assessment in animal models. However, due to the complexity, ethical concerns, and cost of the high-order animal system, there is an immediate need of information-rich simple animal models to decipher the biological significance. Herein, we performed in vivo head-to-head comparison of Neu5Acα(2-6) and α(2-3)Gal conjugated quantum dots (QDs) toxicity, biodistribution, and sequestration in wild-type zebrafish ( Danio rerio) and mouse model (C57BL). The fluorescent properties and cadmium composition of quantum dots were used to map the blood clearance, biodistribution, and sequestration of the sialylated QDs in major organs of both models. We observed that α(2-6) sialylated QDs preferentially have prolonged circulating half-life and broader biodistribution in both models. On the contrary, α(2-3) sialic acid and galactose-conjugated QDs have shortened blood circulation time and are sequestered in the liver, and cleared after several hours in both models. These results demonstrate the applicability of the zebrafish and sialylated QDs to target specific organs, as well as drug delivery and biomedical diagnostics.

Modeling Glyco-Collagen Conjugates Using a Host-Guest Strategy To Alter Phenotypic Cell Migration and in Vivo Wound Healing.

The constructs and study of combinatorial libraries of structurally defined homologous extracellular matrix (ECM) glycopeptides can significantly accelerate the identification of cell surface markers involved in a variety of physiological and pathological processes. Herein, we present a simple and reliable host-guest approach to design a high-throughput glyco-collagen library to modulate the primary and secondary cell line migration process. 4-Amidoadamantyl-substituted collagen peptides and ß-cyclodextrin appended with mono- or disaccharides were used to construct self-assembled glyco-collagen conjugates (GCCs), which were found to be thermally stable, with triple-helix structures and nanoneedles-like morphologies that altered cell migration processes. We also investigated the glycopeptide's mechanisms of action, which included interactions with integrins and cell signaling kinases. Finally, we report murine wound models to demonstrate the real-time application of GCCs. As a result of our observations, we claim that the host-guest model of ECM glycopeptides offers an effective tool to expedite identification of specific glycopeptides to manipulate cell morphogenesis, cell differentiation metastatic processes, and their biomedical applications.

Understanding carbohydrate-protein interactions using homologous supramolecular chiral Ru(ii)-glyconanoclusters.

Multivalent glycodendrimers make promising tools to tackle the basic and translational research in the field of carbohydrate-mediated interactions. Despite advances in glycodendrimers and glycopolymers, the multivalent probes available to date are still far from being ideal biological mimics. This work demonstrates the inherent chirality of glycodendrimers to be one of the promising factors to generate different spatial carbohydrate micro-environments to modulate specific carbohydrate-protein interactions. By exploiting the host-guest strategy, chiral Ru(ii) complexes (Δ and Λ) and mannose capped ß-cyclodextrin (ß-CD), we generated a library of homologous metallo-glycodendrimers (MGDs) with sizes of 50-70 nm. These nanoclusters can enantioselectively bind to specific C-type lectins and displayed selectivity in cellular uptake. We also discovered their potential clathrin-mediated endocytotic pathway in DC-SIGN and SIGNR3-transfected cell lines. Finally, in vivo biodistribution and sequestration of MGDs was determined to understand the role of chirality mediated spatial arrangement in carbohydrate-mediated interactions.

Exploiting the lactose-GM3 interaction for drug delivery.

Protein-protein and protein-carbohydrate interactions as a means to target the cell surface for therapeutic applications have been extensively investigated. However, carbohydrate-carbohydrate interactions (CCIs) have largely been overlooked. Here, we investigate the concept of CCI-mediated drug delivery. Lactose-functionalized ß-cyclodextrin (L-ß-CD) hosting doxorubicin (Dox) was evaluated for site-specific delivery to cancer cells via interaction with GM3 , a cell-surface carbohydrate. The host-guest complex was evaluated in B16 melanoma cells, which express exceptionally high levels of GM3 , and acute monocytic leukemia (THP-1) and mouse fibroblast (NIH-3T3) cells, which lack GM3 on the cell surface. Doxorubicin (Dox) was delivered more efficiently into B16 cells compared with NIH-3T3 and THP-1 cells. In B16 cells pretreated with sialidase or sodium periodate, thus preventing CCI formation, drug uptake was significantly decreased. Taken together, the results of these studies strongly support CCI-mediated uptake via the GM3 -lactose interaction as the mechanism of controlled drug delivery.

Probing carbohydrate-carbohydrate interactions by photoswitchable supramolecular glycoclusters.

The synthesis of photo-switchable glycoclusters with distinct sugar arrangements is described and the use of these clusters to study carbohydrate-carbohydrate interactions (CCIs) is demonstrated.

Use of Boolean and fuzzy logics in lactose glycocluster research.

Fuzzy logic systems can be exploited for defining the degrees of true or false binding between calcium mediated multivalent lactose and peanut agglutinin lectin, which are difficult to define with Boolean logic.