Glycopeptide dendrimers. Part II

Dendrimers in vaccine delivery: Recent progress and advances

Dendrimers are well-defined, highly branched, multivalent and monodisperse molecules which host a range of attractive, yet functional, chemical and biological characteristics. A dendrimers accessible surface groups enable coupling to different functional moieties (e.g., antibodies, peptides, proteins, etc), which is further assisted by the dendrimers tailored size and surface charge. This adaptability allows for the preparation of molecularly precise vaccines with highly specific and predictable properties, and in conjunction with a dendrimers immune stimulating (adjuvanting) property, makes dendrimers attractive substrates for biomedical applications, including vaccines. This review highlights the structural and synthetic evolution of dendrimers throughout history, detailing the dendrimers role as both an adjuvant and carrier system for vaccine antigens, in addition to reviewing the development of commercially available vaccines for use in humans.

Perspectives of Dendrimer-based Nanoparticles in Cancer Therapy

Currently, cancer is the second most common cause of death in the United States, exceeded only by heart disease. Chemotherapy traditionally suffers from a non-specific distribution, with only a small fraction of the drug reaching the tumor, in this sense, the use of dendrimers incorporating drugs non-covalently encapsulated inside the dendrimer or covalently conjugated have proven to be effectives against different cancer cell lines. However, at present the dendrimers used as drug-carriers still do not meet the necessary characteristic to be considered as an ideal dendrimer for drug delivery; high toxicity, bio-degradability, low toxicity, biodistribution characteristics, and favorable retention with appropriate specificity and bioavailability have not been fully covered by the current available dendrimers. However, the development and study of new dendrimers drug-carriers continues to be an important tool in the cancer therapy as they can be functionalized with varied ligands to reach the tumor tissue through the different body barriers in the body with minimal loss of activity in the bloodstream, have the ability to selectively kill tumor cells without affecting the normal cells and most important with a release mechanism controlling actively. Given the continuous efforts and research in this area of interest, we presented in this review the work done with a special emphasis on the development of dendrimers as a major tool in the combination with drugs, as a potential adjunctive agent in anticancer therapy.

Peptide dendrimers: drug/gene delivery and other approaches

Dendrimers are versatile hyperbranched molecules, which have deserved attention especially for their potential in many applications, including biological. Peptide dendrimers comprise interesting classes of dendrimers, and their use has been emphasized as a drug/bioactive compound delivery system, mostly in the antineoplastic area. The bioactive molecules can be covalently linked or entrapped inside the peptide derivative. Self-assembled nanocarriers are a recent trend in the design of potential delivery systems, and pH-sensitive carriers, one of their methods, have been designed to control their systems. In addition, the use of targeting peptides or other specific groups that direct the drug/bioactive compounds to specific organs is an important trend in the search for better drug delivery systems. Recent examples have been given in the literature, showing that gene delivery as another important peptide dendrimer application. It is worth emphasizing that some peptide dendrimers show activity per se, without bioactive compounds. Immune compounds and vaccines are presented herein, as well as uses of other peptide dendrimers are briefly discussed in this review, which encompasses around 10 years of work.

Synthesis of G0 aminopolyol and aminosugar dendrimers, controlled by NMR and MALDI TOF mass spectrometry

Organic compounds designed to serve as stable dendrimer cores were developed. A series of aminosugar and amino polyol containing G0 dendrimers were synthesized. The reaction mixture composition was checked by MALDI TOF mass spectrometry, while that of purified products – by ¹H and ¹³C NMR combined with 2D NMR spectroscopy as well as MALDI TOF MSMS mass spectra. Mass spectrometric fragmentation experiments were performed in positive ion mode in order to determine common fragmentation patterns of [M+H]⁺ ions.

Dendritic glycopolymers based on dendritic polyamine scaffolds: view on their synthetic approaches, characteristics and potential for biomedical applications

The potential of dendritic glycopolymers based on dendritic polyamine scaffolds for biomedical applications is presented and compared with that of the structurally related anti-adhesive dendritic glycoconjugates.

Sweetness and light: design and applications of photo-responsive glycoconjugates

Photoswitchable glycoconjugates are promising tools for studying biomolecular interactions and for the development of stimuli-responsive materials.

Sugar-appended polyamidoamine dendrimer conjugates with cyclodextrins as cell-specific non-viral vectors

The widespread use of various cyclodextrin (CyD)-appended polymers and polyrotaxanes as gene carriers has been reported. Among the various polyamidoamine dendrimer (dendrimer) conjugates with CyDs (CDE), the dendrimer (G3) conjugate with α-CyD having an average degree of substitution (DS) of 2.4 (α-CDE (G3, DS 2)) displayed remarkable properties as DNA carriers. In an attempt to develop cell-specific gene transfer carriers, we prepared some sugar-appended α-CDEs, e.g. mannosylated, galactosylated, and lactosylated α-CDEs. In addition, PEGylated Lac-α-CDEs (G3) were prepared and evaluated as a hepatocyte-selective and serum-resistant gene transfer carrier. Moreover, PEGylated-α-CDE/CyD polypseudorotaxane systems for novel sustained DNA release system have been developed. Interestingly, glucronylglucosyl-β-cyclodextrin (GUG-β-CyD) conjugates with dendrimer (G2) (GUG-β-CDE (G2)) had superior gene transfer activity to α-CDE (G2), expecting a development of new series of sugar-appended CDEs over α-CDEs (G2). Collectively, sugar-appended α-CDEs have the potential as novel cell-specific and safe carriers for DNA.

Analysis of carbohydrates and glycoconjugates by matrix-assisted laser desorption/ionization mass spectrometry: an update for 2007-2008

This review is the fifth update of the original review, 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 2008. The first section of the review covers fundamental studies, fragmentation of carbohydrate ions, use of derivatives and new software developments for analysis of carbohydrate spectra. Among newer areas of method development are glycan arrays, MALDI imaging and the use of ion mobility spectrometry. The second section of the review discusses applications of MALDI MS to the analysis of different types of carbohydrate. Specific compound classes that are covered include carbohydrate polymers from plants, N- and O-linked glycans from glycoproteins, biopharmaceuticals, glycated proteins, glycolipids, glycosides and various other natural products. There is a short section on the use of MALDI mass spectrometry for the study of enzymes involved in glycan processing and a section on the use of MALDI MS to monitor products of the chemical synthesis of carbohydrates with emphasis on carbohydrate-protein complexes and glycodendrimers. Corresponding analyses by electrospray ionization now appear to outnumber those performed by MALDI and the amount of literature makes a comprehensive review on this technique impractical. However, most of the work relating to sample preparation and glycan synthesis is equally relevant to electrospray and, consequently, those proposing analyses by electrospray should also find material in this review of interest.

Guest-release control in enzyme-sensitive, amphiphilic-dendrimer-based nanoparticles through photochemical crosslinking

Stimuli sensitive, facially amphiphilic dendrimers have been synthesized and their enzyme-responsive nature has been determined with dual fluorescence responses of both covalently conjugated and non-covalently bound reporter units. These dual responses are correlated to ascertain the effect of enzymatic action on micellar aggregates and the consequential guest release. The release of the guest molecule is conveniently tuned by stabilizing the micellar aggregates through photochemical crosslinking of hydrophobic coumarin units. This photo-crosslinking is also utilized as a tool to investigate the mode of enzyme-substrate interaction in the context of aggregate-monomer equilibrium.

Dendri-RAFTs: a second generation of cyclopeptide-based glycoclusters

Synthetic glycoclusters and their related biological applications have stimulated increasing interest over the last decade. As a prerequisite to discovering active and selective therapeuticals, the development of multivalent glycoconjugates with diverse topologies is faced with inherent synthetic and structural characterisation difficulties. Here we describe a new series of molecularly-defined glycoclusters that were synthesized in a controlled manner using a robust and versatile divergent protocol. Starting from a Regioselectively Addressable Functionalized Template (RAFT) carrier, either a polylysine dendritic framework or a second RAFT, then 16 copies of βGal, αMan, βLac or cancer-related Thomsen-Freidenreich (αTF) antigen were successively conjugated within the same molecule using oxime chemistry. We thus obtained a new generation of dendri-RAFTs glycoclusters with high glycosidic density and variable spatial organizations. These compounds displaying 16 endgroups were unambiguously characterized by NMR spectroscopy and mass spectrometry. Further biological assays between a model lectin from Canavalia ensiformis (ConA) and mannosylated glycoclusters revealed a higher inhibition potency than the tetravalent counterpart, in particular for the hexadecavalent polylysine skeleton. Together with the efficiency of the synthetic and characterisation processes, this preliminary biological study provided clear evidence of promising properties that make the second generation of cyclopeptide-based glycoclusters attractive for biomedical applications.

Melectin MAPs: the influence of dendrimerization on antimicrobial and hemolytic activity

The recently described antimicrobial peptide melectin (MEP, GFLSILKKVLPKVMAHMK-NH2) exhibits high antimicrobial activity against Gram-positive and Gram-negative bacteria. Here we describe the synthesis and biological activities of 23 new analogues of MEP. We studied the influence of dimerization and tetramerization (MAP-constructs of MEP) on the antimicrobial and hemolytic activities, as well as the role of Met in positions 14 and 17 of the peptide chain. Oxidation of the Met to Met(O) and Met(O2) decreases antimicrobial activity of all tested bacteria if the peptide is in the monomeric form, however, only to Staphylococcus aureus if in the form of dimer or tetramer. Dimerization and tetramerization increase the undesirable hemolytic activity of the peptides. Interestingly, substitution of Leu for Val in position 6 leads to the decrease of hemolytic activity. Introduction of the isosteric amino acid Nle into positions 14 or 17 or both leads to slight increase of hemolytic activity under preservation of high antimicrobial activities. Unfortunately, dimerization again leads to an increase of hemolytic activity.

Glycopeptide dendrimer colchicine conjugates targeting cancer cells

Screening of a 65,536-member one-bead-one-compound (OBOC) combinatorial library of glycopeptide dendrimers of structure ((betaGal)(n)(+1)X(8)X(7)X(6)X(5))(2)DapX(4)X(3)X(2)X(1)(beta-Gal)(m) (betaGal=beta-galactosyl-thiopropionic acid, X(8-1)=variable amino acids, Dap=l-2,3-diaminopropionic acid, n, m=0, or 1 if X(8)=Lys resp. X(1)=Lys) for binding of Jurkat cells to the library beads in cell culture, resynthesis and testing lead to the identification of dendrimer J1 (betaGal-Gly-Arg-His-Ala)(2)Dap-Thr-Arg-His-Asp-CysNH(2) and related analogues as delivery vehicles. Cell targeting is evidenced by FACS with fluorescein conjugates such as J1F. The colchicine conjugate J1C is cytotoxic with LD(50)=1.5 microM. The beta-galactoside groups are necessary for activity, as evidenced by the absence of cell-binding and cytotoxicity in the non-galactosylated, acetylated analogue AcJ1F and AcJ1C, respectively. The pentagalactosylated dendrimer J4 betaGal(4)(Lys-Arg-His-Leu)(2)Dap-Thr-Tyr-His-Lys(betaGal)-Cys) selectively labels Jurkat cell as the fluorescein derivative J4F, but its colchicine conjugate J4C lacks cytotoxicity. Tubulin binding assays show that the colchicine dendrimer conjugates do not bind to tubulin, implying intracellular degradation of the dendrimers releasing the active drug.

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.

MAP dendrimer elicits antibodies for detecting rat and mouse GH-binding proteins

The membrane-bound rat GH-R and an alternatively spliced isoform, the soluble rat GH-BP, are comprised of identical N-terminal GH-binding domains; however, their C-terminal sequences differ. Immunological reagents are needed to distinguish between the two isoforms in order to understand their respective roles in mediating the actions of GH. Accordingly, a tetravalent MAP dendrimer with four identical branches of a C-terminal peptide sequence of the rat GH-BP (GH-BP(263-279)) was synthesized and used as an immunogen in rabbits. Solid-phase peptide synthesis of four GH-BP(263-279) segments onto a tetravalent Lys(2)-Lys-beta-Ala-OH core peptide was carried out using Fmoc chemistry. The mass of the RP-HPLC-purified synthetic product, 8398 Da, determined by ESI-MS, was identical to expected mass. Three anti-rat GH-BP(263-279) MAP antisera, BETO-8039, BETO-8040, and BETO-8041, at dilutions of 10(-3), recognized both the rat GH-BP(263-279) MAP and recombinant mouse GH-BP with ED(50)s within a range of 5-10 fmol, but did not cross-react with BSA in dot blot analyses. BETO-8041 antisera (10(-3) dilution) recognized GH-BPs of rat serum and liver having M(r)s ranging from 35 to 130 kDa, but did not recognize full-length rat GH-Rs. The antisera also detected recombinant mouse GH-BPs. In summary, the tetravalent rat GH-BP(263-279) MAP dendrimer served as an effective immunogenic antigen in eliciting high titer antisera specific for the C-termini of both rat and mouse GH-BPs. The antisera will facilitate studies aimed at improving our understanding of the biology of GH-BPs.

Glycopeptide dendrimers, part III: a review. Use of glycopeptide dendrimers in immunotherapy and diagnosis of cancer and viral diseases

Glycopeptide dendrimers containing different types of tumor associated-carbohydrate antigens (T(N), TF, sialyl-T(N), sialyl-TF, sialyl-Le(x), sialyl-Le(a) etc.) were used in diagnosis and therapy of different sorts of cancer. These dendrimeric structures with incorporated T-cell epitopes and adjuvants can be used as antitumor vaccines. Best results were obtained with multiantigenic vaccines, containing, e.g. five or six different TAAs. The topic of TAAs and their dendrimeric forms at molecular level are reviewed, including structure, syntheses, and biological activities. Use of glycopeptide dendrimers as antiviral vaccines against HIV and influenza is also described. Their syntheses, physico-chemical properties, and biological activities are given with many examples.