Novel hyperbranched glycomimetics recognized by the human mannose receptor: quinic or shikimic acid derivatives as mannose bioisosteres

Applications of mannose-binding lectins and mannan glycoconjugates in nanomedicine

Glycosylated nanoparticles (NPs) have drawn a lot of attention in the biomedical field over the past few decades, particularly in applications like targeted drug delivery. Mannosylated NPs and mannan-binding lectins/proteins (MBL/MBP) are emerging as promising tools for delivery of drugs, medicines, and enzymes to targeted tissues and cells as nanocarriers, enhancing their therapeutic benefits while avoiding the adverse effects of the drug. The occurrence of plenty of lectin receptors and their mannan ligands on cell surfaces makes them multifaceted carriers appropriate for specific delivery of bioactive drug materials to their targeted sites. Thus, the present review describes the tethering of mannose (Man) to several nanostructures, like micelles, liposomes, and other NPs, applicable for drug delivery systems. Bioadhesion through MBL-like receptors on cells has involvements applicable to additional arenas of science, for example gene delivery, tissue engineering, biomaterials, and nanotechnology. This review also focuses on the role of various aspects of drug/antigen delivery using (i) mannosylated NPs, (ii) mannosylated lectins, (iii) amphiphilic glycopolymer NPs, and (iv) natural mannan-containing polysaccharides, with most significant applications of MBL-based NPs as multivalent scaffolds, using different strategies.

GRAPHICAL ABSTRACT

Mannosylated NPs and/or MBL/MBP are coming up as viable and versatile tools as nanocarriers to deliver drugs and enzymes precisely to their target tissues or cells. The presence of abundant number of lectin receptors and their mannan ligands on cell surfaces makes them versatile carriers suitable for the targeted delivery of bioactive drugs.

Plant callus-derived shikimic acid regenerates human skin through converting human dermal fibroblasts into multipotent skin-derived precursor cells

Background

The human skin-derived precursors (SKPs) are a good cell source for regeneration. However, the isolation of SKP from human skin is limited. To overcome this drawback, we hypothesized that the component of plant stem cells could convert human fibroblasts to SKPs.

Methods

Human dermal fibroblasts were treated with shikimic acid, a major component of Sequoiadendron giganteum callus extract. The characteristics of these reprogrammed cells were analyzed by qPCR, western blot, colony-forming assay, and immunofluorescence staining. Artificial human skin was used for CO₂ laser-induced wound experiments. Human tissues were analyzed by immunohistochemistry.

Results

The reprogrammed cells expressed nestin (a neural precursor-specific protein), fibronectin, and vimentin and could differentiate into the ectodermal and mesodermal lineage. Nestin expression was induced by shikimic acid through the mannose receptor and subsequent MYD88 activation, leading to P38 phosphorylation and then CREB binding to the nestin gene promoter. Finally, we confirmed that shikimic acid facilitated the healing of cut injury and enhanced dermal reconstruction in a human artificial skin model. Moreover, in a clinical study with healthy volunteers, plant callus extracts increased the expression of stem cell markers in the basal layer of the epidermis and collagen deposit in the dermis.

Conclusions

These results indicate that shikimic acid is an effective agent for tissue regeneration.

Supplementary Information

The online version contains supplementary material available at 10.1186/s13287-021-02409-3.

Shikimic acid, a mannose bioisostere, promotes hair growth with the induction of anagen hair cycle

Shikimic acid (SA) has recently been found to be a major component of plant stem cells. The exact effects of SA on human hair follicles (HFs) is unknown. The purpose of this study was to examine the effects of SA on hair growth. We investigated the effect of SA on an in vivo C57BL/6 mouse model. We examined the expression of mannose receptor (MR), which is a known receptor of SA, in human HFs and the effect of SA on human dermal papilla cells (hDPCs), outer root sheath cells (hORSCs), and on ex vivo human hair organ culture. SA significantly prolonged anagen hair growth in the in vivo mouse model. We confirmed expression of the MR in human HFs, and that SA increased the proliferation of hDPCs and hORSCs. It was found that SA enhanced hair shaft elongation in an ex vivo human hair organ culture. SA treatment of hDPCs led to increased c-myc, hepatocyte growth factor, keratinocyte growth factor and vascular endothelial growth factor levels and upregulation of p38 MAPK and cAMP response element-binding protein levels. Our results show that SA promotes hair growth and may serve as a new therapeutic agent in the treatment of alopecia.

In vivo targeting of DNA vaccines to dendritic cells using functionalized gold nanoparticles

The clinical success of dendritic cell (DC)-based genetic immunization remains critically dependent on the availability of effective and safe nano-carriers for targeting antigen-encoded DNA vaccines to DCs, the most potent antigen-presenting cells in the human body in vivo. Recent studies revealed the efficacies of mannose receptor-mediated in vivo DC-targeted genetic immunization by liposomal DNA vaccine carriers containing both mannose-mimicking shikimoyl and transfection enhancing guanidinyl functionalities. However, to date, the efficacies of this approach have not been examined for metal-based nanoparticle DNA vaccine carriers. Herein, we report for the first time, the design, synthesis, physico-chemical characterization and bioactivities of gold nanoparticles covalently functionalized with a thiol ligand containing both shikimoyl and guanidinyl functionalities (Au-SGSH). We show that Au-SGSH nanoparticles can deliver DNA vaccines to mouse DCs under in vivo conditions. Subcutaneous administration of near infrared (NIR) dye-labeled Au-SGSH showed significant accumulation of the NIR dye in the DCs of the nearby lymph nodes compared to that for the non-targeting NIR-labeled Au-GSH nanoconjugate containing only a covalently tethered guanidinyl group, not the shikimoyl-functionality. Under prophylactic settings, in vivo immunization (s.c.) with the Au-SGSH-pCMV-MART1 nanoplex induced a long-lasting (180 days) immune response against murine melanoma. Notably, mannose receptor-mediated in vivo DC-targeted immunization (s.c.) with the Au-SGSH-MART1 nanoplex significantly inhibited established melanoma growth and increased the overall survivability of melanoma-bearing mice under therapeutic settings. The Au-SGSH nanoparticles reported herein have potential use for in vivo DC-targeted genetic immunization against cancer and infectious diseases.

Shikimoyl-ligand decorated gold nanoparticles for use in ex vivo engineered dendritic cell based DNA vaccination

Since mannose receptors (MRs) are expressed on the surfaces of dendritic cells (DCs), the most professional antigen presenting cells in our body, DNA vaccine carriers containing either covalently grafted mannosyl- or mannose-mimicking shikimoyl-ligands are being increasingly used in ex vivo DC-transfection based DNA vaccination. To this end, we have recently demonstrated that ex vivo immunization of mice with liposomes of shikimoylated cationic amphiphiles containing a 6-amino hexanoic acid spacer group in the head-group region in complexation with melanoma antigen (MART1) encoded DNA vaccine (pCMV-MART1) induces long lasting anti-melanoma immune responses (C. Voshavar, et al., J. Med. Chem., 2017, 60, 1605-1610). This finding prompted us to examine, in the present investigation, the efficacies of gold nanoparticles conjugated to the mannose-mimicking shikimoyl ligand (SL) via a 6-amino hexane thiol spacer (AuNPs-SL) for use in ex vivo DC-transfection based genetic immunization. Herein, we report on the design, synthesis, physico-chemical characterization and bioactivities of AuNPs-SL. Dynamic light scattering and transmission electron microscopy studies revealed the hydrodynamic diameters of theAuNPs-SL nanoconjugates to be within the range of 23-44 nm and their surface potentials within the range of 9-28 mV. MTT-assay showed the non-cytotoxic nature of AuNPs-SL and the findings in the electrophoretic gel retardation assays revealed strong DNA binding properties of the AuNPs-SL. Importantly, subcutaneous immunization of C57BL/6J mice with DCs ex vivo transfected with an electrostatic complex of AuNPs-SL & melanoma antigen (MART1) encoded DNA vaccine (p-CMV-MART1) induced a long lasting (100 days) anti-tumor immune response in immunized mice upon subsequent challenge with a lethal dose of melanoma. Notably, mice immunized with either autologous mbmDCs ex vivo pre-transfected with nanoplexes of shikimoylated AuNPs-SL & an irrelevant pCMV-SPORT-β-gal plasmid (without having encoded melanoma antigen) or untransfected DCs showed no lasting protection against subsequent tumor challenge. The presently described shikimoyl-decorated gold nanoparticles (AuNPs-SL) are expected to find future use in ex vivo DC-transfection based genetic immunization against cancer and other infectious diseases.

Production and Synthetic Modifications of Shikimic Acid

Shikimic acid is a natural product of industrial importance utilized as a precursor of the antiviral Tamiflu. It is nowadays produced in multihundred ton amounts from the extraction of star anise ( Illicium verum) or by fermentation processes. Apart from the production of Tamiflu, shikimic acid has gathered particular notoriety as its useful carbon backbone and inherent chirality provide extensive use as a versatile chiral precursor in organic synthesis. This review provides an overview of the main synthetic and microbial methods for production of shikimic acid and highlights selected methods for isolation from available plant sources. Furthermore, we have attempted to demonstrate the synthetic utility of shikimic acid by covering the most important synthetic modifications and related applications, namely, synthesis of Tamiflu and derivatives, synthetic manipulations of the main functional groups, and its use as biorenewable material and in total synthesis. Given its rich chemistry and availability, shikimic acid is undoubtedly a promising platform molecule for further exploration. Therefore, in the end, we outline some challenges and promising future directions.

Clustered carbohydrates in synthetic vaccines

Are there general rules to obtain efficient immunization against carbohydrate antigens? Thanks to technological advances in glycobiology and glycochemistry we entered a new era in which the rational design of carbohydrate vaccines has become an achievable goal. The aim of this Tutorial Review is to present the most recent accomplishments in the field of semi and fully synthetic carbohydrate vaccines against viruses, bacteria and cancer. It is also pointed out that the understanding of the chemical and biochemical processes related to immunization allows the modern chemist to rationally design carbohydrate vaccines with improved efficiency.

Design and creativity in synthesis of multivalent neoglycoconjugates

From the authors' opinion, this chapter constitutes a modest extension of the seminal and inspiring contribution of Stowell and Lee on neoglycoconjugates published in this series [C. P. Stowell and Y. C. Lee, Adv. Carbohydr. Chem. Biochem., 37 (1980) 225-281]. The outstanding progresses achieved since then in the field of the "glycoside cluster effect" has witnessed considerable creativity in the design and synthetic strategies toward a vast array of novel carbohydrate structures and reflects the dynamic activity in the field even since the recent chapter by the Nicotra group in this series [F. Nicotra, L. Cipolla, F. Peri, B. La Ferla, and C. Radaelli, Adv. Carbohydr. Chem. Biochem., 61 (2007) 353-398]. Beyond the more classical neoglycoproteins and glycopolymers (not covered in this work) a wide range of unprecedented and often artistically beautiful multivalent and monodisperse nanostructures, termed glycodendrimers for the first time in 1993, has been created. This chapter briefly surveys the concept of multivalency involved in carbohydrate-protein interactions. The topic is also discussed in regard to recent steps undertaken in glycobiology toward identification of lead candidates using microarrays and modern analytical tools. A systematic description of glycocluster and glycodendrimer synthesis follows, starting from the simplest architectures and ending in the most complex ones. Presentation of multivalent glycostructures of intermediate size and comprising, calix[n]arene, porphyrin, cyclodextrin, peptide, and carbohydrate scaffolds, has also been intercalated to better appreciate the growing synthetic complexity involved. A subsection describing novel all-carbon-based glycoconjugates such as fullerenes and carbon nanotubes is inserted, followed by a promising strategy involving dendrons self-assembling around metal chelates. The chapter then ends with those glycodendrimers that have been prepared using commercially available dendrimers possessing varied functionalities, or systematically synthesized using either divergent or convergent strategies.

Oligomerization of the macrophage mannose receptor enhances gp120-mediated binding of HIV-1

C-type lectin receptors expressed on the surface of dendritic cells and macrophages are able to bind glycoproteins of microbial pathogens via mannose, fucose, and N-acetylglucosamine. Langerin on Langerhans cells, dendritic cell-specific intercellular adhesion molecule 3-grabbing nonintegrin on dendritic cells, and mannose receptor (MR) on dendritic cells and macrophages bind the human immunodeficiency virus (HIV) envelope protein gp120 principally via high mannose oligosaccharides. These C-type lectin receptors can also oligomerize to facilitate enhanced ligand binding. This study examined the effect of oligomerization of MR on its ability to bind to mannan, monomeric gp120, native trimeric gp140, and HIV type 1 BaL. Mass spectrometry analysis of cross-linked MR showed homodimerization on the surface of primary monocyte-derived dendritic cells and macrophages. Both monomeric and dimeric MR were precipitated by mannan, but only the dimeric form was co-immunoprecipitated by gp120. These results were confirmed independently by flow cytometry analysis of soluble monomeric and trimeric HIV envelope and a cellular HIV virion capture assay. As expected, mannan bound to the carbohydrate recognition domains of MR dimers mostly in a calcium-dependent fashion. Unexpectedly, gp120-mediated binding of HIV to dimers on MR-transfected Rat-6 cells and macrophages was not calcium-dependent, was only partially blocked by mannan, and was also partially inhibited by N-acetylgalactosamine 4-sulfate. Thus gp120-mediated HIV binding occurs via the calcium-dependent, non-calcium-dependent carbohydrate recognition domains and the cysteine-rich domain at the C terminus of MR dimers, presenting a much broader target for potential inhibitors of gp120-MR binding.

Influence of ligand valency on the targeting of immature human dendritic cells by mannosylated liposomes

An important challenge for the development of new generations of vaccines is the efficient delivery of antigens to antigen presenting cells such as dendritic cells. In the present study we compare the interaction of plain and targeted liposomes, containing mono-, di-, and tetraantennary mannosyl lipid derivatives, with human monocyte-derived immature dendritic cells (iDCs). Whereas efficient mannose receptor-mediated endocytosis by iDCs was observed for the mannosylated liposomes, in contrast, only nonspecific interaction with little uptake was observed with plain liposomes. In accordance with the clustering effect, liposomes prepared with multibranched mannosylated lipids displayed higher binding affinity for the mannose receptor than vesicles containing the monomannosylated analogs. Importantly, we have found that dimannosylated ligands present at the surface of the liposomes were as efficient as tetramannosylated ones to engage in multidentate interactions with the mannose receptor of iDCs, resulting in both cases in an effective uptake/endocytosis. This result will greatly facilitate, from a practical standpoint, the design of mannose-targeted vaccination constructs. Moreover, we showed that mannose-mediated uptake of liposomes did not result in an activation of iDCs. Altogether, our results suggest that antigen-associated targeted liposomes containing diantennary mannosylated lipids could be effective vectors for vaccines when combined with additional DC activation signals.

Toward targeted oral vaccine delivery systems: selection of lectin mimetics from combinatorial libraries

PURPOSE

Various lectins bind specifically to oligosaccharides on intestinal cells. Exploiting this specificity, Ulex europaeus agglutinin I (UEA1) has been used as a ligand for targeted oral vaccine delivery to M cells (antigen-presenting cells) in follicle-associated epithelium. In this study we characterized compounds identified from mixture-based positional scanning synthetic combinatorial libraries, which mimic UEA1 and, thus, may have properties applicable to targeted drug delivery.

METHODS

Two UEA1 mimetics were synthesized and their activity was verified on live cells. The ability of the lead compound, a tetragalloyl D-Lysine amide construct (4-copy gallic acid construct), to deliver dye-loaded polystyrene particles to M cells was assessed in an in situ mouse gut loop model.

RESULTS

The 4-copy gallic acid construct inhibited UEA1 binding to Caco-2 cell membranes with an IC50 of 3 microM, a 650- to 5000-fold increase over the natural UEA1 substrate alpha-L-fucose. The biotin-labeled derivative of this construct demonstrated comparable binding activity as verified on live cells by fluorescence-activated cell sorting. Preclinical studies confirmed its ability to mediate M cell-specific delivery of streptavidin-coated particles in vivo.

CONCLUSIONS

Polyphenolic compounds, D-Lysine scaffolds with multiple galloyl groups, can mimic functional activities of UEA1. Properties of such molecules, including low molecular weight, stability, ease of synthesis and low cost, highlight their potential for application in targeted vaccine delivery.

Synthesis and mannose receptor-mediated uptake of clustered glycomimetics by human dendritic cells: effect of charge

Effect of charge and shape of multivalent lysine-based cluster glycomimetics on their mannose receptor-mediated uptake by human dendritic cells has been evaluated: The capture is strongly affected by the shape of the ligands. The effect of charge is less pronounced although positive charges on the ligands seem to favor non-specific endocytosis capture.

Combined thioether/hydrazone chemoselective ligation reactions for the synthesis of glycocluster-antigen peptide conjugates

Hydrazone/thioether ligation reactions show promise for the synthesis of clustered glycosides-antigen conjugates. Due to its propensity to aggregate, tetanus toxoid-derived epitopic peptide TT(830-846) was elected to further evaluate this three-component ligation process. This difficult sequence was supplemented by a hydrazine or a glyoxylyl group either at its C- or N-terminus. The peptide-hydrazines or peptide-aldehydes thus obtained were coupled with glyoxylyl- (or hydrazino-) N-chloroacetylated-L-lysinyl trees and 2-thioethyl-alpha-D-mannopyranoside. As anticipated the ligations were controlled by the nature of the peptide and proved difficult for the C-terminal aldehyde derivative. However, when the process was performed in absence of buffer and using mannitol as a dispersing agent, all combinations finally led to the expected glycoconjugates in 40-60% purified yields.

Analysis of binding of mannosides in relation to Langerin (CD207) in Langerhans cells of normal and transformed epithelia

Tandem-repeat C-type lectins (pattern-recognition receptors) with specificity for mannosides are intimately involved in antigen recognition, uptake, routing and presentation in macrophages and dendritic cells. In Langerhans cells, Langerin (CD207), a type-II transmembrane protein with a single C-type carbohydrate recognition domain attached to a heptad repeat in the neck region, which is likely to establish oligomers with an alpha-coiled-coil stalk, has been implicated in endocytosis and the formation of Birbeck granules. The structure of Langerin harbours essential motifs for Ca2+-binding and sugar accommodation. Lectin activity has previously been inferred by diminished antibody binding to cells in the presence of the glycan ligand mannan. In view of the complexity of the C-type lectin/lectin-like network, it is unclear what role Langerin plays for Langerhans cells in binding mannosides. In order to reveal in frozen tissue sections to what extent mannose-binding activity co-localizes with Langerin, we have used a synthetic marker, i.e. a neoglycoprotein carrying mannose maxiclusters, as a histochemical ligand, and computer-assisted fluorescence monitoring in a double-labelling procedure. Mannoside-binding capacity was detected in normal epithelial cells. Double labelling ensured the unambiguous assessment of the binding of the neoglycoprotein in Langerhans cells. Light-microscopically, its localization profile resembled the pattern of immunohistochemical detection of Langerin. This result has implications for suggesting rigorous controls in histochemical analysis of this cell type, because binding of kit reagents, i.e. mannose-rich glycoproteins horseradish peroxidase or avidin, to Langerin (or a spatially closely associated lectin) could yield false-positive signals. To show that recognition of carbohydrate ligands in dendritic cells is not restricted to mannose clusters, we have also documented binding of carrier-immobilized histo-blood group A trisaccharide, a ligand of galectin-3, which was not affected by the presence of a blocking antibody to Langerin. Remarkably, access to the carbohydrate recognition domain of Langerin appeared to be impaired in proliferatively active environments (malignancies, hair follicles), indicating presence of an endogenous ligand with high affinity to saturate the C-type lectin under these conditions.