Using boronolectin in MALDI-MS imaging for the histological analysis of cancer tissue expressing the sialyl Lewis X antigen

Retro Diels-Alder Fragmentation of Fulvene-Maleimide Bioconjugates for Mass Spectrometric Detection of Biomolecules

Diels-Alder chemistry is a well-explored avenue for the synthesis of bioactive materials; however, its potential applications have recently expanded following the development of reactions that can be performed in buffered aqueous environments at low temperatures, including fulvene-maleimide [4 + 2] cycloadditions. In this study, we synthesized two novel amine-reactive fulvene linkers to demonstrate the application of this chemistry for generating mass spectrometry-cleavable labels ("mass tags"), which can be used for the labeling and detection of proteins. Successful conjugation of these linkers to maleimide-labeled peptides was observed at low temperatures in phosphate-buffered saline, allowing the non-destructive modification of proteins with such mass tags. The labile nature of fulvene-maleimide adducts in the gas phase also makes them suitable for both matrix-assisted laser desorption/ionization (MALDI) and electrospray ionization (ESI) mass spectrometric analysis. Unlike previous examples of MALDI mass tags, we show that fulvene-maleimide cycloaddition adducts fragment predictably upon gas-phase activation without the need for bulky photocleavable groups. Further exploration of this chemistry could therefore lead to new approaches for mass spectrometry-based bioassays.

Enhanced cellular uptake efficiency of DCM probes or SN38 conjugating with phenylboronic acids

High-level of sialic acid (SA) expression on the surface of cancer cells is observed extremely common. Phenylboronic acids (PBAs) have a high affinity with SA. The cellular uptake efficiency could be enhanced by the strategy of introducing PBA fragments to the compounds. In this work, we synthesized five new probes with the Dicyanomethylene-4H-pyran (DCM) fluorophore, three of them conjugated with different phenylboronic acid fragments. By cellular uptake experiments, DLCB and DLAB showed enhanced cellular uptake abilities compared with DLN and DLO. These two effective phenylboronic acid fragments were then conjugated with SN-38 and the conjugates showed enhanced cellular uptake abilities by 3-fold or 7-fold compared with irinotecan. In summary, the strategy of introducing 4-carboxyphenylboronic acid and 3-amino-benzoxaborole groups shows great potential in drug delivery system. Moreover, the released linkers between boric acid and drugs deserve further studies.

The mechanisms of boronate ester formation and fluorescent turn-on in ortho-aminomethylphenylboronic acids

ortho-Aminomethylphenylboronic acids are used in receptors for carbohydrates and various other compounds containing vicinal diols. The presence of the o-aminomethyl group enhances the affinity towards diols at neutral pH, and the manner in which this group plays this role has been a topic of debate. Further, the aminomethyl group is believed to be involved in the turn-on of the emission properties of appended fluorophores upon diol binding. In this treatise, a uniform picture emerges for the role of this group: it primarily acts as an electron-withdrawing group that lowers the pKa of the neighbouring boronic acid thereby facilitating diol binding at neutral pH. The amine appears to play no role in the modulation of the fluorescence of appended fluorophores in the protic-solvent-inserted form of the boronic acid/boronate ester. Instead, fluorescence turn-on can be consistently tied to vibrational-coupled excited-state relaxation (a loose-bolt effect). Overall, this Review unifies and discusses the existing data as of 2019 whilst also highlighting why o-aminomethyl groups are so widely used, and the role they play in carbohydrate sensing using phenylboronic acids.

Bifunctional cleavable probes for in situ multiplexed glycan detection and imaging using mass spectrometry

In situ analysis of glycans is of great significance since they mediate a range of biological activities. Aberrant changes of glycosylation are closely related to cancer onset and progression. In this work, bifunctional laser cleavable mass probes (LCMPs) were developed for in situ glycan detection from both cells and tissues using laser desorption ionization mass spectrometry (LDI-MS). Specific recognition of glycans was achieved by lectins, and inherent signal amplification was achieved by the conversion of the detection of glycans to that of mass tags which overcame the low ionization efficiency and complicated mass spectra of glycans. Multiplexed glycan profiling was easy to implement due to the simple and generic synthetic route to LCMPs and serial alternative mass tags, which offers high sensitivity, low interference and in situ detection of glycans. Moreover, as an excellent inherent matrix, LCMPs facilitated direct glycan detection from the cell surface and tissue imaging using LDI-MS. Intrinsic and fine glycan distribution in human cancer and paracancerous tissues was strictly demonstrated by MS imaging to explore the correlation between glycosylation and various cancers. This approach presented a versatile LDI-MS based platform for fast and in situ multiplexed glycan engineering, thus providing a new perspective in glycobiology and clinical diagnosis.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: An update for 2011-2012

This review is the seventh update of the original article published in 1999 on the application of MALDI mass spectrometry to the analysis of carbohydrates and glycoconjugates and brings coverage of the literature to the end of 2012. General aspects such as theory of the MALDI process, matrices, derivatization, MALDI imaging, and fragmentation are covered in the first part of the review and applications to various structural types constitute the remainder. The main groups of compound are oligo- and poly-saccharides, glycoproteins, glycolipids, glycosides, and biopharmaceuticals. Much of this material is presented in tabular form. Also discussed are medical and industrial applications of the technique, studies of enzyme reactions, and applications to chemical synthesis. © 2015 Wiley Periodicals, Inc. Mass Spec Rev 36:255-422, 2017.

Reversible covalent interactions of β-aminoboronic acids with carbohydrate derivatives

β-Aminoalkylboronic acids are capable of binding to carbohydrate derivatives through reversible covalent interactions. An anthracene-bearing β-aminoboronic acid has been synthesized, enabling determinations of association constants for binding of sugars by fluorescence spectroscopy. The diol-binding properties of β-aminoboronic acids are also useful in catalysis: one such compound displays remarkably high activity for regioselective O-acylation of a pyranoside derivative.

DNA-mediated cell surface engineering for multiplexed glycan profiling using MALDI-TOF mass spectrometry

Glycans are crucial for many key biological processes and their alterations are often a hallmark of disease. Thus, multiplexed and sensitive analysis of glycans is of intense interest. Here we report a novel approach using DNA-mediated cell surface engineering for glycan profiling by MALDI-TOF mass spectrometry (MS). Following lectin binding, DNA amplification and hybridization, glycans on the cell surface are specifically labeled by short DNA probes, which can be facilely released, ionized and detected in MALDI-TOF MS. This strategy converts the analysis of glycans to the detection of DNA probes, overcoming the complicated composition and low ionization efficiency of glycans, enabling in situ detection and facilitating multiplex analysis. The amplification procedure also improves the sensitivity. This approach has been applied to evaluate glycomic alterations in cancer cells and provided the intrinsic distribution of glycans in tissues using MALDI imaging mass spectrometry.

Detection, quantification, and profiling of PSA: current microarray technologies and future directions

The death rate of 13% among the men diagnosed with prostate cancer makes it a second leading cause of cancer death. This critical review evaluates DNA and protein microarray based methods for detection, quantification, and profiling of PSA.

A triphenylcyclopropenylium mass tag: synthesis and application to ultrasensitive LC/MS analysis of amines

Thiol adducts of triphenylcyclopropenylium undergo efficient heterolytic dissociation in electrospray (ESI) or laser desorption ionization (LDI) mass spectrometry giving rise to a prominent signal of an aromatic C₃Ph₃⁺ cation.

Boronic acids for fluorescence imaging of carbohydrates

Carbohydrate biomarkers are particularly important targets for fluorescence imaging given their pivotal role in numerous important biological events. This review highlights the development of fluorescence imaging agents based on boronic acids.

Click with a boronic acid handle: a neighboring group-assisted click reaction that allows ready secondary functionalization

The feasibility of a neighboring boronic acid-facilitated facile condensation of an aldehyde is described. This reaction is bio-orthogonal, complete at room temperature within minutes, and suitable for bioconjugation chemistry. The boronic acid group serves the dual purpose of catalyzing the condensation reaction and being a handle for secondary functionalization.

A fluorescent bisboronic acid compound that selectively labels cells expressing oligosaccharide Lewis X

Two fluorescent diboronic acid compounds (6a and 6b) with a dipeptide linker were synthesized as potential sensors for cell surface saccharide Lewis X (Le(X)). Compound 6a with a dipeptide (H-Asp-Ala-) as the linker was found to selectively label CHOFUT4 cells, which express Le(x), at micromolar concentrations, while non-Le(x)-expressing control cells were not labeled.

Sugar recognition: designing artificial receptors for applications in biological diagnostics and imaging

At the cellular level, numerous processes ranging from protein folding to disease development are mediated by a sugar-based molecular information system that is much less well known than its DNA- or protein-based counterparts. The subtle structural diversity of such sugar tags nevertheless offers an excellent, if challenging, opportunity to design receptors for the selective recognition of biorelevant sugars. Over the past 40 years, growing interest in the field of sugar recognition has led to the development of several promising artificial receptors, which could soon find widespread use in medical diagnostics and cell imaging.

Glycan-based diagnostic devices: current progress, challenges and perspectives

The development of glycan-based diagnostic devices is illustrated with recent examples from both carbohydrate recognition and device design aspects.

Glycosylation characteristics of colorectal cancer

Glycans on proteins and lipids are known to alter with malignant transformation. The study of these may contribute to the discovery of biomarkers and treatment targets as well as understanding of cancer biology. We here describe the change of glycosylation specifically defining colorectal cancer with view on N-glycans, O-glycans, and glycosphingolipid glycans in colorectal cancer cells and tissues as well as patient sera. Glycan alterations observed in colon cancer include increased β1,6-branching and correlating higher abundance of (poly-)N-acetyllactosamine extensions of N-glycans as well as an increase in (truncated) high-mannose type glycans, while bisected structures decrease. Colorectal cancer-associated O-glycan changes are predominated by reduced expression of core 3 and 4 glycans, whereas higher levels of core 1 glycans, (sialyl) T-antigen, (sialyl) Tn-antigen, and a generally higher density of O-glycans are observed. Specific changes for glycosphingolipid glycans are lower abundances of disialylated structures as well as globo-type glycosphingolipid glycans with exception of Gb3. In general, alterations affecting all discussed glycan types are increased sialylation, fucosylation as well as (sialyl) Lewis-type antigens and type-2 chain glycans. As a consequence, interactions with glycan-binding proteins can be affected and the biological function and cellular consequences of the altered glycosylation with regard to tumorigenesis, metastasis, modulation of immunity, and resistance to antitumor therapy will be discussed. Finally, analytical approaches aiding in the field of glycomics will be reviewed with focus on binding assays and mass spectrometry.

Matrix assisted laser desorption ionization imaging mass spectrometry workflow for spatial profiling analysis of N-linked glycan expression in tissues

A new matrix assisted laser desorption ionization imaging mass spectrometry (MALDI-IMS) method to spatially profile the location and distribution of multiple N-linked glycan species in tissues is described. Application of an endoglycosidase, peptide N-glycosidase F (PNGaseF), directly on tissues followed by incubation releases N-linked glycan species amenable to detection by MALDI-IMS. The method has been designed to simultaneously profile the multiple glycan species released from intracellular organelle and cell surface glycoproteins, while maintaining histopathology compatible preparation workflows. A recombinant PNGaseF enzyme was sprayed uniformly across mouse brain tissue slides, incubated for 2 h, then sprayed with 2,5-dihydroxybenzoic acid matrix for MALDI-IMS analysis. Using this basic approach, global snapshots of major cellular N-linked glycoforms were detected, including their tissue localization and distribution, structure, and relative abundance. Off-tissue extraction and modification of glycans from similarly processed tissues and further mass spectrometry or HPLC analysis was done to assign structural designations. MALDI-IMS has primarily been utilized to spatially profile proteins, lipids, drug, and small molecule metabolites in tissues, but it has not been previously applied to N-linked glycan analysis. The translatable MALDI-IMS glycan profiling workflow described herein can readily be applied to any tissue type of interest. From a clinical diagnostics perspective, the ability to differentially profile N-glycans and correlate their molecular expression to histopathological changes can offer new approaches to identifying novel disease related targets for biomarker and therapeutic applications.

Molecular architecture and therapeutic potential of lectin mimics

Lectins are proteins of non-immune origin that bind specific carbohydrates without chemical modification. Coupled with the emerging biological and pathological significance of carbohydrates, lectins have become extensively used as research tools in glycobiology. However, lectin-based drug development has been impeded by high manufacturing costs, low chemical stability, and the potential risk of initiating an unfavorable immune response. As alternatives to lectins, non-protein small molecules having carbohydrate-binding properties (lectin mimics) are currently attracting a great deal of attention because of their ease of preparation and chemical modification. Lectin mimics of synthetic origin are divided roughly into two groups, boronic acid-dependent and boronic acid-independent lectin mimics. This article outlines their representative architectures and carbohydrate-binding properties, and discusses their therapeutic potential by reviewing recent attempts to develop antiviral and antimicrobial agents using their architectures. We also focus on the naturally occurring lectin mimics, pradimicins and benanomicins. They are the only class of non-protein natural products having a C-type lectin-like ability to recognize d-mannopyranosides in the presence of Ca^2 + ions. Their molecular basis of carbohydrate recognition and therapeutic potential are also discussed.

Carbohydrate biomarker recognition using synthetic lectin mimics

Carbohydrate biomarkers play very important roles in a wide range of biological and pathological processes. Compounds that can specifically recognize a carbohydrate biomarker are useful for targeted delivery of imaging agents and for development of new diagnostics. Furthermore, such compounds could also be candidates for the development of therapeutic agents. A tremendous amount of active work on synthetic lectin mimics has been reported in recent years. Amongst all the synthetic lectins, boronic-acid-based lectins (boronolectins) have shown great promise. Along this line, four classes of boronolectins including peptide-, nucleic-acid-, polymer-, and small-molecule-based ones are discussed with a focus on the design principles and recent advances. We hope that by presenting the potentials of this field, this review will stimulate more research in this area.

Probe-based chemical modulations of tissues for IMS

Chemical modulation imaging over a tissue is gaining momentum in the field of mass spectrometry. Some endogenous or exogenous compounds present in a tissue can be visualized by imaging mass spectrometry after chemical derivatization. This approach gives researchers the possibility to elude chemical interferences in components of the tissues, such as lipids or salts, as well as interferences caused by the matrix. The use of primary and secondary antibodies, the chemical derivatization of peptides and small molecules, and the use of (18)O labeling are various examples reviewed in this article to demonstrate the importance and potential of this emerging aspect of imaging mass spectrometry.