新型生物医用材料: 肽类树枝状大分子及其生物医学应用

肽类树枝状大分子是近年来发展起来的一类新型生物医用高分子材料, 它在具有普通树枝状大分子的特征如规整性、高度支化、表面呈现高密度功能团、尺度为纳米级、通过可控制备可得到单一分子量等之外, 同时还具有类似蛋白一样的球状结构、好的生物相容性、水溶性、耐蛋白酶水解、生物降解等独特的性能. 肽类树枝状大分子的上述特点, 使其在生物医学应用中显示出诱人的前景. 本综述从肽类树枝状大分子的制备出发、详尽介绍了肽类树枝状大分子的功能化及其在疾病诊断和治疗中的应用等方面的研究进展, 籍此推动肽类树枝状大分子在生物医学领域的研究与开发.     

New-generation biomedical materials: Peptide dendrimers and their application in biomedicine

Peptide dendrimers are attractive synthetic polymers and have been widely used as a new generation of biomaterials in recent years. Peptide dendrimers, as well as general dendrimers, may be synthesized to reach nano sizes, and display well-defined architectures, highly-branched structures, high density of functional terminal groups, and controllable molecular weights. On the other hand, peptide dendrimers have properties similar to proteins and some special characteristics, such as good biocompatibility, water solubility and resistance to proteolytic digestion. Due to these advantages, peptide dendrimers have received considerable attention in biomedicine. This review focuses on the development of peptide dendrimers with emphasis on their applications both in diagnostics and in therapy.     

α-环糊精/聚乙二醇自组装超分子纳米药物载体

研究了一种新型超分子纳米药物载体的制备方法及其药物释放性能. 将α-环糊精(α-CD)穿入肉桂酸改性的PEG分子链形成包含复合物(inclusion complex, IC), 通过超分子自组装成为纳米粒子. 将抗肿瘤药物阿霉素负载到纳米粒子中, 研究药物释放行为及其对肿瘤细胞的抑制效果. 以核磁共振(1H NMR)、X射线衍射(XRD)、紫外吸收光谱(UV)、动态光散射(DLS)、扫描电镜(SEM)、透射电镜(TEM)和原子力显微镜(AFM)表征了纳米粒子的结构和形貌, 用激光共聚焦显微镜(Confocal)研究了载药纳米粒子在细胞内的分布及其对肿瘤细胞的抑制效果. 结果显示超分子纳米粒子具有很好的生物相容性和药物缓释作用, 载药纳米粒子对肿瘤细胞具有很好的杀伤效果.     

Peptide‐Decorated Dendrimers and Their Bioapplications

Peptide‐decorated dendrimers (PDDs) are a class of spherical, regular, branched polymers that are modified by peptides covalently attached to their surface. PDDs have been used as protein mimetics, novel biomaterials, and in a wide range of biomedical applications. Since their design and development in the late eighties, poly‐l ‐lysine has been a preferred core structure for PDDs. However, numerous recent innovations in polymer synthesis and ligation chemistry have re‐energized the field and led to the emergence of well‐defined peptide dendrimers with more diverse core structures and functions. This Minireview highlights the development of PDDs driven by significantly improved ligation chemistry incorporating structurally well‐defined peptides and the emerging use of PDDs in imaging and drug development.     

STM vizualization of thiol-containing peptide dendrimers on Au(111)

Peptide dendrimers assembled by solid-phase peptide synthesis using a branching diamino acid at every 2(nd) or 3(rd) position provide readily accessible synthetic model systems for proteins and enzymes. They adopt a globular shape by topology rather than by folding. Peptide dendrimers of 2(nd) and 3(rd) generation functionalized with a cysteine or cystine residue in the core were adsorbed on Au(111) surface and imaged by STM at air, under UHV, or in solution. The dendrimers appear as globular features with dimensions suggesting an extended flattened conformation, forming both single globules and ordered arrays on the surface. These images represent the first direct visualization of peptide dendrimer enzyme models.     

Synthesis and esterolytic activity of catalytic peptide dendrimers

Peptide dendrimers were prepared by solid-phase peptide synthesis. Monomeric dendrimers were first obtained by assembly of a hexapeptide sequence containing alternate standard alpha-amino acids with diamino acids as branching units. The monomeric dendrimers were then dimerized by disulfide-bridge formation at the core cysteine. The synthetic strategy is compatible with functional amino acids and different diamino acid branching units. Peptide dendrimers composed of the catalytic triad amino acids histidine, aspartate, and serine catalyzed the hydrolysis of N-methylquinolinium salts when the histidine residues were placed at the outermost position. The dendrimer-catalyzed hydrolysis of 7-isobutyryl-N-methylquinolinium followed saturation kinetics with a rate constant of catalysis/rate constant without catalysis (k(cat)/k(uncat)) value of 3350 and a rate constant of catalysis/Michaelis constant (k(cat)/K(M)) value 350-fold larger than the second-order rate constant of the 4-methylimidazole-catalyzed reaction; this corresponds to a 40-fold rate enhancement per histidine side chain. Catalysis can be attributed to the presence of histidine residues at the surface of the dendrimers.     

Synthesis of water-soluble, multiple functionalizable dendrons for the conversion of large dendrimers or other molecular objects into potential drug carriers

The synthesis of dendrons and dendrimers which carry OEG chains and bidentate ligands and/or fluorescence tags is described. The orthogonally protected functional groups of the dendrons allow modification of the substitution pattern and attachment to larger entities. Both dendrons and dendrimers are highly water-soluble. The dendrons should have considerable potential to convert, for example, commercially available, high-generation dendrimers into water-soluble, versatile support materials for antitumor therapy.     

Application of Dendrimers in Anticancer Diagnostics and Therapy

The application of dendrimeric constructs in medical diagnostics and therapeutics is increasing. Dendrimers have attracted attention due to their compact, spherical three-dimensional structures with surfaces that can be modified by the attachment of various drugs, hydrophilic or hydrophobic groups, or reporter molecules. In the literature, many modified dendrimer systems with various applications have been reported, including drug and gene delivery systems, biosensors, bioimaging contrast agents, tissue engineering, and therapeutic agents. Dendrimers are used for the delivery of macromolecules, miRNAs, siRNAs, and many other various biomedical applications, and they are ideal carriers for bioactive molecules. In addition, the conjugation of dendrimers with antibodies, proteins, and peptides allows for the design of vaccines with highly specific and predictable properties, and the role of dendrimers as carrier systems for vaccine antigens is increasing. In this work, we will focus on a review of the use of dendrimers in cancer diagnostics and therapy. Dendrimer-based nanosystems for drug delivery are commonly based on polyamidoamine dendrimers (PAMAM) that can be modified with drugs and contrast agents. Moreover, dendrimers can be successfully used as conjugates that deliver several substances simultaneously. The potential to develop dendrimers with multifunctional abilities has served as an impetus for the design of new molecular platforms for medical diagnostics and therapeutics.     

Peptide dendrimer enzyme models for ester hydrolysis and aldolization prepared by convergent thioether ligation

Peptide dendrimers with multiple histidines or N-terminal prolines efficiently catalyze ester hydrolysis or aldol reactions in aqueous medium. Part of the catalytic proficiency of these dendritic enzyme models stems from multivalency effects observed in G2, G3 and G4 dendrimers displaying multiple catalytic groups in their branches. To study multivalency in higher generation systems, G4, G5 and G6 peptide dendrimers were prepared by a convergent assembly. Thus, peptide dendrimers bearing four or eight chloroacetyl groups at their N-termini underwent multiple thioether ligation with G2 and G3 peptide dendrimers with a cysteine residue at their focal point, to give G4, G5 and G6 dendrimers containing up to 341 amino acids, including multiple histidines or N-terminal prolines. While the efficiency of the esterase catalysts was comparable to that of their lower generation analogs, a remarkable reactivity increase was observed in G5 and G6 aldolase dendrimers.     

多肽树枝状大分子合成的研究进展

多肽树枝状大分子具有不同于链状多肽和其它树枝状大分子的物理化学性质,在化学、生物、医学等领域中有广泛应用。本文综述了近年来所报道的多肽树枝状大分子的合成进展。     

Artificial aldolases from peptide dendrimer combinatorial libraries

Peptide dendrimers were investigated as synthetic models for aldolase enzymes. Combinatorial libraries were prepared with aldolase active residues such as lysine and proline placed at the dendrimer core or near the surface. On-bead selection for aldolase activity was carried out using the dye-labelled 1,3-diketone 1a, suitable for covalent trapping of enamine-reactive side-chains, and the fluorogenic enolization probe 6. Aldolase dendrimers catalyzed the aldol reaction of acetone, dihydroxyacetone and cyclohexanone with nitrobenzaldehyde. Much like enzymes, the dendrimers exhibited strong aldolase activity in aqueous medium, but were also active in organic solvent. Dendrimer-catalyzed aldol reactions reached complete conversion in 3 h at 25 degrees C with 1 mol% catalyst and gave aldol products with up to 65% ee. A positive dendritic effect in catalysis was observed with both lysine and proline based aldolase dendrimer catalysts.     

Inhibition of mitosis by glycopeptide dendrimer conjugates of colchicine

Glycopeptide dendrimers have been prepared bearing four or eight identical glycoside moieties at their surface (beta-glucose, alpha-galactose, alpha-N-acetyl-galactose, or lactose), natural amino acids within the branches (Ser, Thr, His, Asp, Glu, Leu, Val, Phe), 2,3-diaminopropionic acid as the branching unit, and a cysteine residue at the core. These dendrimers have been used as drug-delivery devices for colchicine. Colchicine was attached to the dendrimers at the cysteine thiol group through a disulfide or thioether linkage. The biological activities of the glycopeptide dendrimer conjugates were evaluated in HeLa tumor cells and non-transformed mouse embryonic fibroblasts (MEFs). The concentrations of glycopeptide dendrimer drug conjugates required to achieve inhibition of cell proliferation by interference with the tubulin system were found to be higher (IC50 > 1 microM) compared to the required colchicine concentration. On the other hand, the glycopeptide dendrimer conjugates inhibited the proliferation of HeLa cells 20-100 times more effectively than the proliferation of MEFs. In comparison, non-glycosylated dendrimers and colchicine itself showed a selectivity of 10-fold or less for HeLa cells.     

Peptide and glycopeptide dendrimer apple trees as enzyme models and for biomedical applications

Solid phase peptide synthesis (SPPS) provides peptides with a dendritic topology when diamino acids are introduced in the sequences. Peptide dendrimers with one to three amino acids between branches can be prepared with up to 38 amino acids (MW ~ 5,000 Da). Larger peptide dendrimers (MW ~ 30,000) were obtained by a multivalent chloroacetyl cysteine (ClAc) ligation. Structural studies of peptide dendrimers by CD, FT-IR, NMR and molecular dynamics reveal molten globule states containing up to 50% of α-helix. Esterase and aldolase peptide dendrimers displaying dendritic effects and enzyme kinetics (k(cat)/k(uncat) ~ 10(5)) were designed or discovered by screening large combinatorial libraries. Strong ligands for Pseudomonas aeruginosa lectins LecA and LecB able to inhibit biofilm formation were obtained with glycopeptide dendrimers. Efficient ligands for cobalamin, cytotoxic colchicine conjugates and antimicrobial peptide dendrimers were also developed showing the versatility of dendritic peptides. Complementing the multivalency, the amino acid composition of the dendrimers strongly influenced the catalytic or biological activity obtained demonstrating the importance of the "apple tree" configuration for protein-like function in peptide dendrimers.     

Photoresponsive nanocarriers based on PAMAM dendrimers with a o‐nitrobenzyl shell

Gn (n = 3, 4, and 5) poly(amidoamine) (PAMAM) dendrimers were synthesized and peripherally modified with photocleavable o‐nitrobenzyl (NB) groups by reacting o‐nitrobenzaldehyde with the terminal amine groups of PAMAM dendrimers, followed by reducing the imine to amine groups with NaBH₄. The NB‐modified dendrimers, Gn‐NB (n = 3, 4, and 5), were characterized by nuclear magnetic resonance and fourier transform infrared spectroscopy. The results showed that the NB groups were successfully attached on the periphery of the dendrimers with near 100% grafting efficiency. Such a photosensitive NB shell could be cut off on irradiation with 365 nm ultraviolet (UV) light. The encapsulation and release of guest molecules, that is, salicylic acid (SA) and adriamycin (ADR), by Gn‐NB were explored. The encapsulation capability of these dendrimers was found to increase as the guest molecular size was decreased and have dependence on the generation of dendrimers as well. For both of SA and ADR, the average encapsulation numbers per dendrimer decreased in the order of G4‐NB > G5‐NB > G3‐NB, indicating that the fourth generation dendrimer was a better container for the guest molecules. The rate of SA release was found to be greater with UV irradiation than that without, suggesting that the NB‐shelled PAMMAM dendrimers could function as a molecular container/box with photoresponsive characteristics. © 2009 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 48: 551–557, 2010     

Degradable dual pH- and temperature-responsive photoluminescent dendrimers

Poly(β-aminoester) dendrimers have been prepared. These systems represent the first degradable dual pH- and temperature-responsive dendrimers displaying photoluminescence. The pH/temperature sensitivities are interrelated; the lower critical solution temperature of the dendrimer decreases as the pH of the solution is increased. The sensitivities are mainly due to phase changes of the surface groups with changes in pH or temperature. These dual-responsive dendrimers are very useful in drug delivery. They may be loaded with a hydrophobic drug at low temperature without using organic solvents. The loaded drug is released very slowly and steadily at 37 °C and physiological pH, but can be quickly released at acidic pH, for example the lysosomal pH (pH 4-5), for intracellular drug release. These dendrimers also display strong photoluminescence, which can be exploited for monitoring drug loading and release. Thus, poly(β-aminoester) dendrimers constitute ideal drug carriers since their thermal sensitivity allows the loading of drugs without using organic solvents, their pH sensitivity permits fast intracellular drug release, and their photoluminescence provides a means of monitoring drug loading and release.     

Water-soluble carbosilane dendrimers: synthesis biocompatibility and complexation with oligonucleotides; evaluation for medical applications

Novel amine- or ammonium-terminated carbosilane dendrimers of type nG-[Si{OCH2(C6H3)-3,5-(OCH2CH2NMe2)2}]x, nG-[Si{O(CH2)2N(Me)(CH2)2NMe2}]x and nG-[Si{(CH2)3NH2}]x or nG-[Si{OCH2(C6H3)-3,5-(OCH2CH2NMe3 +I-)2}]x, nG-[Si{O(CH2)2N(Me)(CH2)2NMe3 +I-}]x, and nG-[Si{(CH2)3NH3 +Cl-}]x have been synthesized and characterized up to the third generation by two strategies: 1) alcoholysis of Si--Cl bonds with amino alcohols and subsequent quaternization with MeI, and 2) hydrosilylation of allylamine with Si--H bonds of the dendritic systems and subsequent quaternization with HCl. Quaternized carbosilane dendrimers are soluble in water, although degradation is apparent due to hydrolysis of Si--O bonds. However, dendrimers containing Si--C bonds are water-stable. The biocompatibility of the second-generation dendrimers in primary cell cultures of peripheral blood mononuclear cells (PBMCs) and erythrocytes have been analyzed, and they show good toxicity profiles over extended periods. In addition, we describe a study on the interactions between the different carbosilane dendrimers and DNA oligodeoxynucleotides (ODNs) and plasmids along with a comparative analysis of their toxicity. They can form complexes with DNA ODNs and plasmids at biocompatible doses via electrostatic interaction. Also a preliminary transfection assay has been accomplished. These results demonstrate that the new ammonium-terminated carbosilane dendrimers are good base molecules to be considered for biomedical applications.     

Selective catalysis with peptide dendrimers

Peptide dendrimers incorporating 3,5-diaminobenzoic acid 1 as a branching unit (B) were prepared by solid-phase synthesis of ((Ac-A(3))(2)B-A(2))(2)B-Cys-A(1)-NH(2) followed by disulfide bridge formation. Twenty-one homo- and heterodimeric dendrimers were obtained by permutations of aspartate, histidine, and serine at positions A(1), A(2), and A(3). Two dendrimers catalyzed the hydrolysis of 7-hydroxy-N-methyl-quinolinium esters (2-5), and two other dendrimers catalyzed the hydrolysis of 8-hydroxy-pyrene-1,3,6-trisulfonate esters (10-12). Enzyme-like kinetics was observed in aqueous buffer pH 6.0 with multiple turnover, substrate binding (K(M) = 0.1-0.5 mM), rate acceleration (k(cat)/k(uncat) > 10(3)), and chiral discrimination (E = 2.8 for 2-phenylpropionate ester 5). The role of individual amino acids in catalysis was investigated by amino acid exchanges, highlighting the key role of histidine as a catalytic residue, and the importance of electrostatic and hydrophobic interactions in modulating substrate binding. These experiments demonstrate for the first time selective catalysis in peptide dendrimers.     

Convergent assembly and surface modification of multifunctional dendrimers by three consecutive click reactions

Multifunctional dendrimers bearing two or more surface functionalities have the promise to provide smart drug delivery devices that can for example combine tissue targeting and imaging or be directed more precisely to a specific tissue or cell type. We have developed a concise synthetic methodology for efficient dendrimer assembly and heterobifunctionalization based on three sequential azide-alkyne cycloadditions. The methodology is compatible with biologically important compounds rich in chemical functionalities such as peptides, carbohydrates, and fluorescent tags. In the approach, a strain-promoted azide-alkyne cycloaddition (SPAAC) between polyester dendrons modified at the focal point with an azido and 4-dibenzocyclooctynol (DIBO) moiety provided dendrimers bearing terminal and TMS-protected (TMS=trimethylsilyl) alkynes at the periphery. The terminal alkynes were outfitted with azido-modified polyethylene glycol (PEG) chains or galactosyl residues by using Cu(I) -catalyzed azide-alkyne cycloadditions (CuAAC). Next, a one-pot TMS deprotection and second click reaction of the resulting terminal alkyne with azido-containing compounds gave multifunctional dendrimers bearing complex biologically active moieties at the periphery.     

Dendrimer as a versatile platform for biomedical application: A review

Modern chemistry is vastly fascinated by dendrimer chemistry, an area that is rapidly expanding and brimming with potential applications. Dendrimers are highly branched polymers that have multiple peripheral groups, interior cavities and they have many structural properties therefore Dendrimers play a crucial role in the fields of nanotechnology, pharmaceuticals, and medicinal chemistry. The terminal functional groups of dendrimers may be chemically linked to other moieties in order to adjust surface properties for applications such as biomimetic nanodevices. A variety of biologically active agents can be incorporated into dendrimers to create biologically active conjugates, including novel drug carriers, by utilizing the homogeneity of their three-dimensional architecture. The purpose of this review is to provide a brief overview of bio-inspired dendrimer applications, highlighting their use as drug and gene delivery agents, and biomedical diagnostic agents. In addition, the review mentions briefly some dendrimer applications in cosmetics, agrochemicals, and catalyst.     

Two Decades of Triazine Dendrimers

For two decades, methods for the synthesis and characterization of dendrimers based on [1,3,5]-triazine have been advanced by the group. Motivated by the desire to generate structural complexity on the periphery, initial efforts focused on convergent syntheses, which yielded pure materials to generation three. To obtain larger generations of dendrimers, divergent strategies were pursued using iterative reactions of monomers, sequential additions of triazine and diamines, and ultimately, macromonomers. Strategies for the incorporation of bioactive molecules using non-covalent and covalent strategies have been explored. These bioactive materials included small molecule drugs, peptides, and genetic material. In some cases, these constructs were examined in both in vitro and in vivo models with a focus on targeting prostate tumor subtypes with paclitaxel conjugates. In the materials realm, the use of triazine dendrimers anchored on solid surfaces including smectite clay, silica, mesoporous alumina, polystyrene, and others was explored for the separation of volatile organics from gas streams or the sequestration of atrazine from solution. The combination of these organics with metal nanoparticles has been probed. The goal of this review is to summarize these efforts.