Quantum dots with phenylboronic acid tags for specific labeling of sialic acids on living cells

Biosensors with Boronic Acid-Based Materials as the Recognition Elements and Signal Labels

It is of great importance to have sensitive and accurate detection of cis-diol-containing biologically related substances because of their important functions in the research fields of metabolomics, glycomics, and proteomics. Boronic acids can specifically and reversibly interact with 1,2- or 1,3-diols to form five or six cyclic esters. Based on this unique property, boronic acid-based materials have been used as synthetic receptors for the specific recognition and detection of cis-diol-containing species. This review critically summarizes the recent advances with boronic acid-based materials as recognition elements and signal labels for the detection of cis-diol-containing biological species, including ribonucleic acids, glycans, glycoproteins, bacteria, exosomes, and tumor cells. We also address the challenges and future perspectives for developing versatile boronic acid-based materials with various promising applications.

Enhancement of anti-neoplastic effects of cuminaldehyde against breast cancer via mesoporous silica nanoparticle based targeted drug delivery system

AIMS

Synthesis of novel drug delivery system for targeted delivery of cuminaldehyde to breast cancer cells and the subsequent analyses of anti-neoplastic potential of the drug.

MAIN METHODS

3-carboxy-phenyl boronic acid (PBA) conjugated and polyacrylic acid (PAA) gated mesoporous silica nanoparticles (MSNs) were synthesized for the targeted delivery of cuminaldehyde (CUM) to breast cancer cells. Enhancement of anti-neoplastic effects of cuminaldehyde (4-isopropylbenzaldehyde) by the nanoconjugates was assessed.

KEY FINDINGS

The anti-cancer effects of non-targeted and targeted drug-nanoconjugates were examined in vitro and in vivo. The targeted drug-nanoconjugates caused cell cycle arrest and induced the intrinsic pathway of apoptosis in MCF-7 cells through mitochondrial damage. In vivo intravenous injection of the targeted drug-nanoconjugates led to effective reduction in growth of 4 T1 induced mammary pad tumor in female BALB/c mice via augmented accumulation of cuminaldehyde. The drug-nanoconjugates did not exhibit any systemic toxicity.

SIGNIFICANCE

Therefore, MSN-PBA-CUM-PAA represents a potent therapeutic model for breast cancer treatment.

Determination of the Influence of Various Factors on the Character of Surface Functionalization of Copper(I) and Copper(II) Oxide Nanosensors with Phenylboronic Acid Derivatives

In this work, we attempt to determine the influence of the oxidation state of copper [Cu(I) vs Cu(II)], the nature of the interface (solid/aqueous vs solid/air), the incubation time, and the structure of N-substituted phenylboronic acids (PBAs) functionalizing the surface of copper oxide nanostructures (NSs) on the mode of adsorption. For this purpose, 4-[(N-anilino)(phosphono)-S-methyl]phenylboronic acid (1-PBA) and its two analogues (2-PBA and bis{1-PBA}) and the copper oxide NSs were synthesized in a surfactant-/ion-free solution via a synthetic route that allows controlling the size and morphology of NSs. The NSs were characterized by scanning electron microscopy, ultraviolet-visible spectroscopy, Raman spectroscopy, and X-ray diffraction, which confirmed the formation of spherical Cu2O nanoparticles (Cu2ONPs) with a size of 1.5 μm to 600 nm crystallized in a cubic cuprite structure and leaf-like CuO nanostructures (CuONSs) with dimensions of 80-180 nm in width and 400-700 nm in length and crystallized in a monoclinic structure. PBA analogues were deposited on the surface of the copper oxide NSs, and adsorption was investigated using surface-enhanced Raman spectroscopy (SERS). The changes in the orientation of the molecule relative to the substrate surface caused by the abovementioned factors were described, and the signal enhancement on the copper oxide NSs was determined. This is the first study using vibrational spectroscopy for these compounds.

Fabrication of phenyl boronic acid modified pH-responsive zinc oxide nanoparticles as targeted delivery of chrysin on human A549 cells

Recently, different natural bioactive compounds have been used as anticancer agents for their various therapeutic benefits and non-toxic nature to other organs. However, they have various restrictions in preclinical and clinical studies due to their non-targeting nature and insufficient bioavailability. As a result, a zinc oxide nanoparticle (ZnO) based drug delivery medium was constructed which has good bio-compatibility and bio-degradability. It also displays cancer cell-specific drug delivery in a targeted and controlled way. In the present study, phenylboronic acid (PBA) tagged ZnO nanoparticles (ZnO-PBA) was fabricated and in the next step, chrysin (a natural bio-active molecule) was loaded to it to form the nanoconjugate (ZnO-PBA-Chry). Different characterization techniques were used to confirm the successful fabrication of ZnO-PBA-Chry. PBA-tagging to the nanoparticle helps in targeted delivery of chrysin in lung cancer cells (A549) as PBA binds with sialic acid receptors which are over-expressed on the surface of A549 cells. As ZnO dissociates in acidic pH, it shows stimuli-responsive release of chrysin in tumor microenvironment. Application of ZnO-PBA-Chry nanohybrid in lung cancer cell line A549 caused oxidative stress mediated intrinsic cell death and cell cycle arrest. ZnO-PBA-Chry downregulated MMP-2 and VE-Cadherin, thereby inhibiting metastasis and the invasive property of A549 cells.

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pH-responsive PBA functionalized ZnO nanoparticle was fabricated.

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Chrysin was loaded as a bioactive anticancer agent into ZnO nanoparticle.

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ZnO-PBA-Chry induced intrinsic cell death and cell cycle arrest in A549 cells.

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It inhibited metastasis and invasive properties of A549 cells.

Group VIII Metal Carbonyl Cluster-Boronic Acid Conjugates: Cytotoxicity and Mode of Action Studies

A set of metal carbonyl cluster-boronic acid conjugates of the group VIII metals (Fe, Ru, and Os) were synthesized and their antiproliferative effects measured against two breast cancer cell lines (MCF-7 and MDA-MB-231) and a noncancerous breast epithelial (MCF-10A) cell line. The cytotoxicity followed the order Ru > Os > Fe for the MDA-MB-231 cells, although the latter two exhibited similar cytotoxicity against MCF-7 and MCF-10A cells. The osmium species {Os₃(CO)₁₀(μ-H)[μ-SC₆H₄-p-B(OH)₂]} (2) could be chemically oxidized to its hydroxy analogue [Os₃(CO)₁₀(μ-H)(μ-SC₆H₄ -p-OH)] (2-OH), which showed comparable cytotoxicity. Mode of action studies pointed to an apoptotic pathway for cell death.

Turn-On Fluorescent Probe Based on a Dansyl Triarginine Peptide for Ganglioside Imaging

Gangliosides play pivotal biological roles in the animal cell membranes, and it is vital to develop fluorescent probes for imaging them. To date, various artificial receptors for ganglioside imaging have been developed; however, turn-on fluorescence imaging for gangliosides with high contrast has not been achieved. We developed a simple fluorescent probe on the basis of a dansyl triarginine peptide for turn-on ganglioside imaging on the liposome membrane. The probe bound to monosialyl gangliosides and other anionic lipids with association constants was 10⁵ M^-1, which enhanced from 6-fold to 7-fold the fluorescence intensity. Upon binding to monosialyl ganglioside-containing giant liposomes, the turn-on probe selectively enhanced the fluorescence intensity compared with the other anionic lipids. This simple peptide probe for turn-on fluorescence imaging of gangliosides would provide a novel molecular tool for chemical biology.

Glycan Labeling and Analysis in Cells and In Vivo

As one of the major types of biomacromolecules in the cell, glycans play essential functional roles in various biological processes. Compared with proteins and nucleic acids, the analysis of glycans in situ has been more challenging. Herein we review recent advances in the development of methods and strategies for labeling, imaging, and profiling of glycans in cells and in vivo. Cellular glycans can be labeled by affinity-based probes, including lectin and antibody conjugates, direct chemical modification, metabolic glycan labeling, and chemoenzymatic labeling. These methods have been applied to label glycans with fluorophores, which enables the visualization and tracking of glycans in cells, tissues, and living organisms. Alternatively, labeling glycans with affinity tags has enabled the enrichment of glycoproteins for glycoproteomic profiling. Built on the glycan labeling methods, strategies enabling cell-selective and tissue-specific glycan labeling and protein-specific glycan imaging have been developed. With these methods and strategies, researchers are now better poised than ever to dissect the biological function of glycans in physiological or pathological contexts.

Boronic-Acid-Modified Nanomaterials for Biomedical Applications

Boronic-acid-modified nanomaterials have inspired significant research interest owing to their unique biocompatibility and excellent reversible interaction with diol groups containing saccharides, protein, DNA, and other related glucose compounds. However, the different sources and methods change the application of nanomaterials. Thus, surface-functionalized nanomaterials are of interest as one of the best ways to improve the application of the biomedical field. In this mini-review, we summarize recent studies on boronic-acid-modified nanomaterials, based on the carbon dot group and graphene oxides, which have been used in the fields of bioimaging, biosensing, antiviral inhibitors, etc. Moreover, the multivalent interaction on boronic-acid-modified materials has become the main key improvement for targeting treatment in the future. We mainly focused on any previously reported papers for synergistic future opportunities of superior biomedical applications of carbon dots (CDs) in the management and diagnostics of nanomedicine fields.

In vivo therapeutic evaluation of a novel bis-lawsone derivative against tumor following delivery using mesoporous silica nanoparticle based redox-responsive drug delivery system

Herein, we have evaluated the in vivo therapeutic efficacy and systemic toxicity profile of a synthetic anticancer compound [3,3'-((4-(trifluoromethyl)phenyl)methylene)bis(2-hydroxynaphthalene-1,4-dione)]. A multifunctional mesoporous silica nanoparticle (MSN) based drug delivery network was also fabricated which specifically showed targeting nature towards the cancer cell. The mesopores of silica nanoparticles were tagged with phenyl boronic acid (PBA) for targeted drug delivery into tumor tissue. 1j was then loaded inside the nanocarriers followed by pore blocking with gold nanoparticles (GN) to attain a redox-responsive controlled drug delivery pattern. The synthesized nanocarriers (1j@-MSN-PBA-GN) having mean diameter of ~86 nm exhibited a moderate 1j loading content of 13.68% with overall negative surface charge. Both the targeted and non-targeted nanoformulations were tested for their anticancer activities both in vitro and in vivo models, and found more effective as compared with free 1j treatment. However, the targeted nanoformulations showed higher therapeutic effect due to increased cellular internalization and caused mitochondria-dependent apoptosis in MCF-7 cells via oxidative stress. Besides, the targeted nanoformulation significantly inhibited in the development of solid tumor in comparison to non-targeted nanoformulations and free 1j as a consequence of increased internalization of the drug-candidate in tumor tissue. Therefore, this study proposes that 1j can be considered as a potent anti-carcinogenic compound in vivo and its therapeutic potential is further increased by using PBA functionalized and GN gated MSN-based controlled drug delivery system without showing any significant systemic toxicity.

Self-Assembled Nanorods of Phenylboronic Acid Functionalized Pyrene for In Situ Two-Photon Imaging of Cell Surface Sialic Acids and Photodynamic Therapy

Sialic acid (SA) plays important roles in various biological and pathological processes. Methods for monitoring and detection of SA are of great significance in terms of fundamental research, cancer diagnostics, and therapeutics, which are still limited until now. Here, a phenylboronic acid (PBA)-functionalized pyrene derivative, 4-(4-(pyren-1-yl)butyramido)phenylboronic acid (Py-PBA), was synthesized and used as a building block for self-assembling into hydrophilic nanorods. The Py-PBA nanorods (Py-PBA NRs) featured highly specific and efficient imaging of SA on living cells with the advantages of excellent fluorescence stability, good biocompatibility, and unique two-photon fluorescence properties. Meanwhile, the assembled Py-PBA NRs could efficiently generate ¹O₂ under two-photon irradiation, making it an excellent candidate for photodynamic therapy. This nanoplatform realized in situ recognition and two-photon imaging of SA on the cell surface as well as effective cancer cell therapy, providing a potential method for simple and selective analysis of SA in living cells and a new prospect for image-guided therapy.

Quantum dots functionalized with 3-mercaptophenylboronic acids as novel nanoplatforms to evaluate sialic acid content on cell membranes

Sialic acids (SAs) modulate essential physiological and pathological conditions, including cell-cell communication, immune response, neurological disorders, and cancer. Besides, SAs confer negative charges to cell membranes, also contributing to hemorheology. Phenylboronic acids, called as mimetic lectins, have been highlighted to study SA profiles. The association of these interesting molecules with the optical properties of quantum dots (QDs) can provide a deeper/complementary understanding of mechanisms involving SAs. Herein, we explored the thiol affinity to the QD surface to develop a simple, fast and direct attachment procedure to functionalize these nanocrystals with 3-mercaptophenylboronic acids (MPBAs). The functionalization was confirmed by fluorescence correlation spectroscopy and inductively coupled plasma spectrometry. The conjugate specificity/efficiency was proved in experiments using red blood cells (RBCs). A labeling >90% was found for RBCs incubated with conjugates, which reduced to 17% after neuraminidase pretreatment. Moreover, QDs-MPBA conjugates were applied in a comparative study using acute (KG-1) and chronic (K562) myelogenous leukemia cell lines. Results indicated that KG-1 membranes have a greater level of SA, with 100% of cells labeled and a median of fluorescence intensity of ca. 2.5-fold higher when compared to K562 (94%). Therefore, this novel QDs-MPBA conjugate can be considered a promising nanoplatform to evaluate SA contents in a variety of biological systems.

Boronate affinity material-based sensors for recognition and detection of glycoproteins

This review comprehensively presents the current overview and development potential of BAMs-based sensors for glycoprotein recognition and detection.

A Versatile Strategy for Surface Functionalization of Hydrophobic Nanoparticle by Boronic Acid Modified Polymerizable Diacetylene Derivatives

The flourishing advancements in nanotechnology significantly boost their application in biomedical fields. Whereas, inorganic nanomaterials are normally prepared and capped with hydrophobic ligands, which require essential surface modification to increase their biocompatibility and endow extra functions. Phenylboronic acid derivatives have long been known for its capacity for selective recognition of saccharides. Herein, we demonstrated a versatile surface modification strategy to directly convert hydrophobic inorganic nanocrystals into water-dispersible and targeting nanocomposites by employing boronic acid modified photo-polymerizable 10,12-pentacosadiynoicacid and further explore its potentials in selective cancer cell imaging.

A Quantum Dot-Based FLIM Glucose Nanosensor

In the last few years, quantum dot (QD) nanoparticles have been employed for bioimaging and sensing due to their excellent optical features. Most studies have used photoluminescence (PL) intensity-based techniques, which have some drawbacks, especially when working with nanoparticles in intracellular media, such as fluctuations in the excitation power, fluorophore concentration dependence, or interference from cell autofluorescence. Some of those limitations can be overcome with the use of time-resolved spectroscopy and fluorescence lifetime imaging microscopy (FLIM) techniques. In this work, CdSe/ZnS QDs with long decay times were modified with aminophenylboronic acid (APBA) to achieve QD-APBA conjugates, which can act as glucose nanosensors. The attachment of the boronic acid moiety on the surface of the nanoparticle quenched the PL average lifetime of the QDs. When glucose bonded to the boronic acid, the PL was recovered and its lifetime was enhanced. The nanosensors were satisfactorily applied to the detection of glucose into MDA-MB-231 cells with FLIM. The long PL lifetimes of the QD nanoparticles made them easily discernible from cell autofluorescence, thereby improving selectivity in their sensing applications. Since the intracellular levels of glucose are related to the metabolic status of cancer cells, the proposed nanosensors could potentially be used in cancer diagnosis.

Graphitic carbon nitride quantum dots as analytical probe for viewing sialic acid on the surface of cells and tissues

The abnormal expression of sialic acids (SAs) on cells and tissues is closely related to various pathophysiological states. Here we applied phenylboronic acid (PBA) functionalized graphitic carbon nitride fluorescent quantum dots (PCQDs) with sizes from 3 to 5 nm in efficient and selective labeling SAs on the surface of living cells and tissues. With abundant PBA in their structure, the water soluble PCQDs showed the relative SA level on the cell surface via selectively and efficiently staining different cell lines in 30 min and revealed that M1 macrophages may express more SAs on their surfaces compared with M0 and M2. The distinct demarcation of cancerous and para-noncancerous areas on cancer tissue sections was showed by PCQDs staining. PCQDs with their high selectivity, stable photoluminescence, low cost, and nontoxicity can be an ideal SA fluorescent probe for living cells and tissues.

Rolling "wool-balls": rapid live-cell mapping of membrane sialic acids via poly-p-benzoquinone/ethylenediamine nanoclusters

Here, we report a convenient, fast labeling strategy for the imaging of cell surface sialic acids (SAs, nine-carbon monosaccharides located at the terminals of cell surface sugar chains). This strategy is based on the synthesis of sticky, furry and fluorescent "wool-balls", which are wound into nanoclusters from p-benzoquinone/ethylenediamine polymer "wires". With abundant amino groups at the surface, the wool-balls can easily stick to the C-7 aldehyde group generated at the ends of periodate treated SAs in less than 30 min.

In Situ Modification of the Tumor Cell Surface with Immunomodulating Nanoparticles for Effective Suppression of Tumor Growth in Mice

Current cancer immunotherapies including chimeric antigen receptor (CAR)-based therapies and checkpoint immune inhibitors have demonstrated significant clinical success, but always suffer from immunotoxicity and autoimmune disease. Recently, nanomaterial-based immunotherapies are developed to precisely control in vivo immune activation in tumor tissues for reducing immune-related adverse events. However, little consideration has been put on the spatial modulation of interactions between immune cells and cancer cells to optimize the efficacy of cancer immunotherapies. Herein, a rational design of immunomodulating nanoparticles is demonstrated that can in situ modify the tumor cell surface with natural killer cell (NK cell)-activating signals to achieve in situ activation of tumor-infiltrating NK cells, as well as direction of their antitumor immunity toward tumor cells. Using these immunomodulating nanoparticles, the remarkable inhibition of tumor growth is observed in mice without noticeable side effects. This study provides an accurate immunomodulation strategy that achieves safe and effective antitumor immunity through in situ NK cell activation in tumors. Further development by constructing interactions with various immune cells can potentially make this nanotechnology become a general platform for the design of advanced immunotherapies for cancer treatments.

Progress and Current Trends in the Synthesis of Novel Polymers with Enhanced Mucoadhesive Properties

Mucoadhesion is defined as the adherence of a synthetic or natural polymer to a mucosal membrane via physical or chemical interactions. Mucoadhesive materials are widely used to develop dosage forms for transmucosal drug delivery via ocular, nasal, esophageal, oral, vaginal, rectal, and intravesical routes of administration. This review will discuss some of the most prominent and recent synthetic methodologies employed to modify polymeric materials in order to enhance their mucoadhesive properties. This includes chemical conjugation of polymers with molecules bearing thiol-, catechol-, boronate-, acrylate-, methacrylate-, maleimide-, and N-hydroxy(sulfo)succinimide ester- groups.

Targeted delivery of quercetin via pH-responsive zinc oxide nanoparticles for breast cancer therapy

Naturally occurring bioactive compounds are gaining much importance as anti-tumor agents in recent times due to their high therapeutic potential and less systemic toxicity. However, different preclinical and clinical studies have noted significant shortcomings, such as nonspecific tumor targeting and low bioavailability which limit their usage in therapeutics. Therefore, a safe and compatible nanoparticle mediated controlled drug delivery system is in high demand to enable effective transport of the drug candidates in the tumor tissue. Herein, we have synthesized phenylboronic acid (PBA) conjugated Zinc oxide nanoparticles (PBA-ZnO), loaded with quercetin (a bioflavonoid widely found in plants), with zeta potential around -10.2 mV and diameter below 40 nm. Presence of PBA moieties over the nanoparticle surface facilitates targeted delivery of quercetin to the sialic acid over-expressed cancer cells. Moreover, Quercetin loaded PBA-ZnO nanoparticles (denoted as PBA-ZnO-Q) showed pH responsive drug release behavior. Results suggested that PBA-ZnO-Q induced apoptotic cell death in human breast cancer cells (MCF-7) via enhanced oxidative stress and mitochondrial damage. In line with the in vitro results, PBA-ZnO-Q was found to be effective in reducing tumor growth in EAC tumor bearing mice. Most interestingly, PBA-ZnO-Q is found to reduce tumor associated toxicity in liver, kidney and spleen. The cytotoxic potential of the nanohybrid is attributed to the combinatorial cytotoxic effects of quercetin and ZnO in the cancer cells. Overall, the presented data highlighted the chemotherapeutic potential of the novel nanohybrid, PBA-ZnO-Q which can be considered for clinical cancer treatment.

One-step fabrication of boronic-acid-functionalized carbon dots for the detection of sialic acid

Typically, sialic acids (SA) with a nine-carbon backbone are found at the glycan chain termini on the cell membranes, which play crucial roles in various physiological and pathological processes. The expression level of SA in the blood serum has been reported to correlate with various disease states among cancer. In this study, a novel approach for preparing fluorescent boronic-acid-modified carbon dots (C-dots) for the detection of SA was developed. The functionalized C-dots were synthesized by a facile, one-step hydrothermal method using 3-pyridineboronic acid as the sole carbon source. The added SA selectively recognized the C-dots, leading to the fluorescence quenching of the C-dots in a linear range of 80-4000 μM with a detection limit of 54 μM. The as-developed boronic-acid nanoprobe was successfully applied for the detection of SA in human serum samples with satisfactory results. In addition, this method afforded results within 4 min. Compared to other methods, this new proposed approach was simpler and exhibited excellent sensitivity and selectivity, demonstrating immense potential as an alternative for SA detection.

Integrated magneto-fluorescence nanobeads for ultrasensitive glycoprotein detection using antibody coupled boronate-affinity recognition

Herein, we report a novel magnet-mediated antibody-boronate sandwich-typed assay (ABSTA) strategy for the ultrasensitive, specific, rapid, and enzyme-free detection of glycoproteins in complex samples.

Fluorescent visual quantitation of cell-secreted sialoglycoconjugates by chemoselective recognition and hybridization chain reaction

A fluorescent visual method is developed for the quantitation of cell-secreted sialoglycoconjugates by chemoselective recognition and hybridization chain reaction.

Exploring boar sperm sialylation during capacitation using boronic acid-functionalized beads

Sialic acid (SA), which usually occupies the terminal position of oligosaccharide chains in mammalian spermatozoa, has important functions in fertilization. Compared with other methods, such as lectin probing, boronic acid could recognize and bind SA with a higher affinity and specificity at pH 6.9. In this study, two boronic acid carriers, 3-aminophenylboronic acid-labeled fluorescent latex (CML-APBA) and magnetic beads (CMM-APBA were applied to explore surface sialylation profile and sialoglycoproteins of the boar sperm. There are three binding sections of CML-APBA on the head of ejaculated sperm: acrosomal region, equatorial segment and the head posterior, which are the major regions undergoing sialylation. After capacitation in vitro, two major binding patterns of CML-APBA exists on sperm head. On some spermatozoa, sialylation exists on the equatorial segment and the posterior head, whilst on other spermatozoa, sialylation occurs on the acrosomal region and equatorial segment. Flow cytometry analysis suggested that the level of sialylation on boar sperm membrane decreases after capacitation. Furthermore, using CMM-APBA, we pulled down sialylated proteins from spermatozoa. Among them, two decapacitation factors associating on sperm surface, AWN and PSP-1, were identified. The levels of the two proteins reduced during capacitation, which might contribute to the decrease of sialylation on boar sperm surface.

Recent Chemical Biology Approaches for Profiling Cell Surface Sialylation Status

Sialic acids (SAs) often exist as the terminal sugars of glycans of either glycoproteins or glycolipids on the cell surface and thus are directly involved in biological processes, such as cell-cell, cell-ligand, and cell-pathogen interactions. Cell surface SA expression levels and their linkages are collectively termed cell surface sialylation status, which represent varying cellular states and contribute to the overall functionality of a cell. Accordingly, systemic and specific profiling of the cell surface sialyation status is critical in deciphering the structures and functions of cell surface glycoconjugates and the molecular mechanisms of their underlying biological processes. In recent decades, several advanced chemical biology approaches have been developed to profile the cell surface sialyation status of both in vitro and in vivo samples, including metabolic labeling, direct chemical modification, and boronic acid coupling approaches. Various investigative technologies have also been explored for their unique competence, including fluorescent imaging, flow cytometry, Raman imaging, magnetic resonance imaging (MRI), and matrix-assisted laser desorption ionization imaging mass spectrometry. In particular, the sialylation status of a specific glycoprotein on the cell surface has been investigated. This review highlights the recent advancements in chemical biology approaches for profiling cell surface sialyation status. It is expected that this review will provide researchers different choices for both biological and biomedical research and applications.

Efficient Assembly of Quantum Dots with Homogenous Glycans Derived from Natural N-Linked Glycoproteins

Coating inorganic nanoparticles with polyethylene glycol (PEG)-appended ligands, as means to preserve their physical characteristics and promote steric interactions with biological systems, including enhanced aqueous solubility and reduced immunogenicity, has been explored by several groups. Conversely, macromolecules present in the human serum and on the surface of cells are densely coated with hydrophilic glycans that act to reduce nonspecific interactions, while facilitating specific binding and interactions. In particular, N-linked glycans are abundant on the surface of most serum proteins and are composed of a branched architecture that is typically characterized by a significant level of molecular heterogeneity. Here we provide two distinct methodologies, covalent bioconjugation and self-assembly, to functionalize two types of Quantum Dots with a homogeneous, complex-type N-linked glycan terminated with a sialic acid moiety. A detailed physical and functional characterization of these glycan-coated nanoparticles has been performed. Our findings support the potential use of such fluorescent platforms to sense glycan-involved biological processes, such as lectin recognition and sialidase-mediated hydrolysis.

Understanding the Molecular Structure of the Sialic Acid-Phenylboronic Acid Complex by using a Combined NMR Spectroscopy and DFT Study: Toward Sialic Acid Detection at Cell Membranes

The origin of the unusually high stability of the sialic acid (SA) and phenylboronic acid (PBA) complex was investigated by a combined nuclear magnetic resonance (NMR) spectroscopy and density functional theory (DFT) study. SA is a glycan-terminating monosaccharide, and its importance as a clinical target has long been recognized. Inspired by the fact that the binding properties of SA-PBA complexation are anomalously high relative to those of typical monosaccharides, great effort has been made to build a clinical platform with the use of PBA as a SA-selective receptor. Although a number of applications have been reported in recent years, the ability of PBA to recognize SA-terminating surface glycans selectively is still unclear, because high-affinity SA-PBA complexation might not occur in a physiological environment. In particular, different forms of SA (α- and β-pyranose) were not considered in detail. To answer this question, the combined NMR spectroscopy/DFT study revealed that the advantageous binding properties of the SA-PBA complex arise from ester bonding involving the α-carboxylate moieties (C1 and C2) of β-SA but not α-SA. Moreover, the facts that the C2 atom is blocked by a glycoside bond in a physiological environment and that α-SA basically exists on membrane-bound glycans in a physiological environment lead to the conclusion that PBA cannot selectively recognize the SA unit to discriminate specific types of cells. Our results have a significant impact on the field of SA-based cell recognition.

Red fluorescent carbon dots with phenylboronic acid tags for quick detection of Fe(III) in PC12 cells

Carbon dots have attracted considerable attention in the field of biosensors and bioimaging because of their excellent optical performance and low toxicity. However, the cellular uptake of the reported carbon dots generally has a low efficiency, which limits their practical applications. In this study, we reported a novel red fluorescent sulfur and nitrogen co-doped carbon dots with small molecular phenylboronic acid tags (i.e. S, N-CDs-PBA). The S, N-CDs-PBA can be taken up rapidly by PC12 cells in twenty minutes and showed high sensitivity for the detection of Fe³⁺ ions. The maximum emission wavelength is at 593 nm under the excitation of 550 nm. The absolute fluorescence quantum yield is 23% in water. The fluorescence can be effectively and selectively quenched by Fe³⁺ ions and the linear response range of Fe³⁺ ions was obtained from 0.3 µM to 5.0 µM with a detection limit as low as 0.1 µM. It could be concluded that the rapid uptake of S, N-CDs-PBA into cells and high photoluminescence quantum yield of red emission are beneficial for quick detection of Fe³⁺ ions.

Polydiacetylene liposomes with phenylboronic acid tags: a fluorescence turn-on sensor for sialic acid detection and cell-surface glycan imaging

Sialic acid (SA) located at the terminal end of glycans on cell membranes has been shown to play an important yet distinctive role in various biological and pathological processes. Effective methods for the facile, sensitive and in situ analysis of SA on living cell surfaces are of great significance in terms of clinical diagnostics and therapeutics. Here, a new polydiacetylene (PDA) liposome-based sensor system bearing phenylboronic acid (PBA) and 1,8-naphthalimide derived fluorophore moieties was developed as a fluorescence turn-on sensor for the detection of free SA in aqueous solution and the in situ imaging of SA-terminated glycans on living cell surfaces. In the sensor system, three diacetylene monomers, PCDA-pBA, PCDA-Nap and PCDA-EA, were designed and synthesized to construct the composite PDA liposome sensor. The monomer PCDA-pBA modified with PBA molecules was employed as a receptor for SA recognition, while the monomer PCDA-Nap containing a 1,8-naphthalimide derivative fluorophore was used for fluorescence signaling. When the composite PDA liposomes were formed, the energy transfer between the fluorophore and the conjugated backbone could directly quench the fluorescence of the fluorophore. In the presence of additional SA or SA abundant cells, the strong binding of SA with PBA moieties disturbed the pendent side chain conformation, resulting in the fluorescence restoration of the fluorophore. The proposed methods realized the fluorescence turn-on detection of free SA in aqueous solution and the in situ imaging of SA on living MCF-7 cell surfaces. This work provides a new potential tool for simple and selective analysis of SA on living cell membranes.

'Borono-lectin' based engineering as a versatile platform for biomedical applications

Boronic acids are well known for their ability to reversibly interact with the diol groups, a common motif of biomolecules including sugars and ribose. Due to their ability to interact with carbohydrates, they can be regarded as synthetic mimics of lectins, termed 'borono-lectins'. The borono-lectins can be tailored to elicit a broad profile of binding strength and specificity. This special property has been translated into many creative biomedical applications in a way interactive with biology. This review provides a brief overview of recent efforts of polymeric materials-based engineering taking advantage of such virtue of 'borono-lectins' chemistry, related to the field of biomaterials and drug delivery applications.

Nanoparticles for drug delivery to the anterior segment of the eye

Commercially available ocular drug delivery systems are effective but less efficacious to manage diseases/disorders of the anterior segment of the eye. Recent advances in nanotechnology and molecular biology offer a great opportunity for efficacious ocular drug delivery for the treatments of anterior segment diseases/disorders. Nanoparticles have been designed for preparing eye drops or injectable solutions to surmount ocular obstacles faced after administration. Better drug pharmacokinetics, pharmacodynamics, non-specific toxicity, immunogenicity, and biorecognition can be achieved to improve drug efficacy when drugs are loaded in the nanoparticles. Despite the fact that a number of review articles have been published at various points in the past regarding nanoparticles for drug delivery, there is not a review yet focusing on the development of nanoparticles for ocular drug delivery to the anterior segment of the eye. This review fills in the gap and summarizes the development of nanoparticles as drug carriers for improving the penetration and bioavailability of drugs to the anterior segment of the eye.

Interaction and cellular uptake of surface-modified carbon dot nanoparticles by J774.1 macrophages

Carbon dot (Cdot) nanoparticles are an emerging class of carbon nanomaterials with a promising potential for drug delivery and bio imaging applications. Although the interaction between Cdots and non-immune cell types has been well studied, Cdot interactions with macrophages have not been investigated. Exposure of Cdot nanoparticles to J774.1 cells, a murine macrophage cell line, resulted in minimal toxicity, where notable toxicity was only seen with Cdot concentrations higher than 0.5 mg/ml. Flow cytometric analysis revealed that Cdots prepared from citric acid were internalized at significantly higher levels by macrophages compared with those prepared from bamboo leaves. Interestingly, macrophages preferentially took up phenylboronic acid (PB)-modified nanoparticles. By fluorescence microscopy, strong blue light-specific punctate Cdot fluorescence resembling Cdot structures in the cytosolic space was mostly observed in J774.1 macrophages exposed to PB-modified nanoparticles and not unmodified Cdot nanoparticles. PB binds to sialic acid residues that are overexpressed on diseased cell surfaces. Our findings demonstrate that PB-conjugated Cdots can be taken up by macrophages with low toxicity and high efficiency. These modified Cdots can be used to deliver drugs to suppress or eliminate aberrant immune cells such as macrophages associated with tumors such as tumor-associated macrophages.

Heterocyclic boronic acids display sialic acid selective binding in a hypoxic tumor relevant acidic environment

A group of heterocyclic boronic acids demonstrating unusually high affinity and selectivity for sialic acids are described, with strong interactions under the weakly acidic pH conditions associated with a hypoxic tumoral microenvironment.

Boronic acids are well known for their ability to reversibly interact with the diol groups found in sugars and glycoproteins. However, they are generally indiscriminate in their binding. Herein we describe the discovery of a group of heterocyclic boronic acids demonstrating unusually high affinity and selectivity for sialic acids (SAs or N-acetylneuraminic acid), which are sugar residues that are intimately linked with tumor growth and cancer progression. Remarkably, these interactions strengthen under the weakly acidic pH conditions associated with a hypoxic tumoral microenvironment. In vitro competitive binding assays uncovered a significantly higher ability of 5-boronopicolinic acid, one of the derivatives identified in this work as a strong SA-binder, to interact with cell surface SA in comparison to a gold-standard structure, 3-propionamidophenylboronic acid, which has proven to be an efficient SA-binder in numerous reports. This structure also proved to be suitable for further chemical conjugation with a well-preserved SA-binding capability. These findings suggest an attractive alternative to other ongoing boronic acid based chemistry techniques aiming to achieve tumor-specific chemotherapies and diagnoses.

Sialic Acid-Targeted Biointerface Materials and Bio-Applications

Sialic acids (SAs) are typically found as terminal monosaccharides attached to cell surface glycoconjugates, which play crucial roles in various biological processes, and aberrant sialylation is closely associated with many diseases, particularly cancers. As SAs are overexpressed in tumor-associated glycoproteins, the recognition and specific binding of SA are crucial for monitoring, analyzing and controlling cancer cells, which would have a considerable impact on diagnostic and therapeutic application. However, both effective and selective recognition of SA on the cancer cell surface remains challenging. In recent years, SA-targeted biointerface materials have attracted great attention in various bio-applications, including cancer detection and imaging, drug delivery for cancer therapy and sialylated glycopeptide separation or enrichment. This review provides an overview of recent advances in SA-targeted biointerface materials and related bio-applications.

High-Precision Profiling of Sialic Acid Expression in Cancer Cells and Tissues Using Background-Free Surface-Enhanced Raman Scattering Tags

Precise profiling of the sialic acid (SA) expression on the membrane of cancer cells is critical for early identification of cancers and assessment of cancer metastasis. However, the complex physiological environments often result in false positives with currently available imaging technologies. Herein, we have established a background-free surface-enhanced Raman scattering (SERS) imaging platform that allows high-precision profiling of SA expression in cancer cells and differentiation of clinically relevant cancer tissues with various metastasis degrees. Three-dimensional Raman imaging technique provided a deeper insight into visualizing the probe distribution and thus the SA expression at the single-cell level, without destructing the cells. This noninvasive, high-precision imaging technique could favor early diagnosis, staging, and monitoring therapeutic responses of cancers that are highly essential in clinical settings.

Boronic acid-tethered amphiphilic hyaluronic acid derivative-based nanoassemblies for tumor targeting and penetration

(3-Aminomethylphenyl)boronic acid (AMPB)-installed hyaluronic acid-ceramide (HACE)-based nanoparticles (NPs), including manassantin B (MB), were fabricated for tumor-targeted delivery. The amine group of AMPB was conjugated to the carboxylic acid group of hyaluronic acid (HA) via amide bond formation, and synthesis was confirmed by spectroscopic methods. HACE-AMPB/MB NPs with a 239-nm mean diameter, narrow size distribution, negative zeta potential, and >90% drug encapsulation efficiency were fabricated. Exposed AMPB in the outer surface of HACE-AMPB NPs (in the aqueous environment) may react with sialic acid of cancer cells. The improved cellular accumulation efficiency, in vitro antitumor efficacy, and tumor penetration efficiency of HACE-AMPB/MB NPs, compared with HACE/MB NPs, in MDA-MB-231 cells (CD44 receptor-positive human breast adenocarcinoma cells) may be based on the CD44 receptor-mediated endocytosis and phenylboronic acid-sialic acid interaction. Enhanced in vivo tumor targetability, infiltration efficiency, and antitumor efficacies of HACE-AMPB NPs, compared with HACE NPs, were observed in a MDA-MB-231 tumor-xenografted mouse model. In addition to passive tumor targeting (based on an enhanced permeability and retention effect) and active tumor targeting (interaction between HA and CD44 receptor), the phenylboronic acid-sialic acid interaction can play important roles in augmented tumor targeting and penetration of HACE-AMPB NPs. STATEMENT OF SIGNIFICANCE: (3-Aminomethylphenyl)boronic acid (AMPB)-tethered hyaluronic acid-ceramide (HACE)-based nanoparticles (NPs), including manassantin B (MB), were fabricated and their tumor targeting and penetration efficiencies were assessed in MDA-MB-231 (CD44 receptor-positive human adenocarcinoma) tumor models. MB, which exhibited antitumor efficacies via the inhibition of angiogenesis and hypoxia inducible factor (HIF)-1, was entrapped in HACE-AMPB NPs in this study. Phenylboronic acid located in the outer surface of HACE-AMPB/MB NPs (in the aqueous milieu) may react with the sialic acid over-expressed in cancer cells and intramolecular B‒O bond can be formed. This phenylboronic acid-sialic acid interaction may provide additional tumor targeting and penetration potentials together with an enhanced permeability and retention (EPR) effect (passive tumor targeting) and HA-CD44 receptor interaction (active tumor targeting). Developed HACE-AMPB NP may be one of promising nanocarriers for the imaging and therapy of CD44 receptor-expressed cancers.

A silica-based SERS chip for rapid and ultrasensitive detection of fluoride ions triggered by a cyclic boronate ester cleavage reaction

Chemical sensing for the convenient detection of trace aqueous fluoride ions (F^-) has been widely explored with the use of various sensing materials and techniques. It still remains a challenge to achieve ultrasensitive but simple, rapid, and inexpensive detection of F^- for environmental monitoring and protection. Here we reported a novel surface-enhanced Raman scattering (SERS) nanosensor, fluorescein phenylboronic acid covalently linked to 1,4-dimercapto-2,3-butanediol modified Au@Ag NPs by a cyclic boronate ester (Flu-PBA-Diol-Au@Ag NPs), for the rapid and ultrasensitive detection of F^-. Once the Flu-PBA approached the surface of Au@Ag NPs, the Raman signals of Flu-PBA were remarkably enhanced due to the strong SERS effect. However, the presence of F^- will induce the cleavage reaction of the cyclic boronate ester into the trifluoroborate anion (3F-Flu-PBA) and diol. The 3F-Flu-PBA molecules exfoliated from the surface of Au@Ag NPs, and the SERS signals of the nanosensor were quenched. Following the sensing mechanism, a silica-based SERS chip has been fabricated by the assembly of Flu-PBA-Diol-Au@Ag NPs on a piece of silicon wafer. The silica-based SERS chips showed high sensitivity for aqueous F^-, and the limit of detection (LOD) could reach as low as 0.1 nM. Each test using the SERS chip only needs a droplet of 20 μL sample and is accomplished within ∼10 min. The silica-based SERS chip has also been applied to the quantification of F^- in tap water and lake water.

Preparation of Sialic Acid-Imprinted Fluorescent Conjugated Nanoparticles and Their Application for Targeted Cancer Cell Imaging

Fluorescent conjugated polymer nanoparticles have attracted great interest for applications in biological imaging owing to their excellent optical properties and low cytotoxicity; however, a lack of effective targeting limits their use. In this work, we design and synthesize a fluorescent conjugated polymer modified with a phenylboronic acid group, which can covalently bind with cis-diol-containing compounds, such as sialic acid (SA), by forming a cyclic ester. However, the obtained conjugated polymer nanoparticles failed to discriminate between cancer cells, with or without SA overexpressed surfaces (such as DU 145 and HeLa cells, respectively). To address this problem, we introduced SA template molecules into the polymer nanoparticles during the reprecipitation process and then removed the template by adjusting the solution pH. The SA-imprinted nanoparticles showed a uniform size around 30 nm and enhanced fluorescence intensity compared with unmodified polymer nanoparticles. The SA-imprinted nanoparticles exhibited selective staining for DU 145 cancer cells and did not enter HeLa cells even after long incubation times. Thus, we present a facile method to prepare fluorescent nanoparticles for applications in targeted cancer cell imaging.

Aqueous synthesis of dual-targeting Gd-doped CuInS2/ZnS quantum dots for cancer-specific bi-modal imaging

CIGS/ZnS@FA|APBA q-dots were synthesized in an aqueous phase; these quantum dots exhibited great potential as dual-modal nanoprobes for optical/MR imaging.