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 solubil...     

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.     

Separation of phosphorylated peptides utilizing dual pH- and temperature-responsive chromatography

The phosphorylation of a peptide is considered to be one of the most important post-translational modification reactions that can alter protein function in mammalian cells. To separate and purify, we developed a dual temperature- and pH-responsive chromatography based on terpolymer composed of N-isopropylacrylamide, N,N'-dimethylaminopropylacrylamide and butylmethacrylate. The property of the surface of the terpolymer-grafted stationary phase altered from hydrophilic to hydrophobic, and from changed to non-charged by changes in the temperature and the pH, respectively. In addition, it was possible to appear and hide ion-exchange groups on the polymer chain surface by temperature changes. These phenomena resulted from changes in the charge and the hydrophobicity of the pH- and temperature-responsive polymer on the stationary surface by controlling the temperature. In the developed environmental-responsive chromatographic system, the ionizable dimethylamino group of N,N'-dimethylaminopropylacrylamide in terpolymer played a key role for the separation. We applied the developed chromatographic system to the separation of phosphorylated compounds, such as phospho-tyrosine, phosphopeptide and oligonucleotides. At a low column temperature, the electrostatic interaction plays a predominant role for retain anionic phosphorylated compounds, because of the strong interaction between the cationic dimethylamino group in the stationary phase and the anionic phosphoric group in the analyte. On the contrary, the hydrophobic interaction became predominant upon increasing the temperature. The results showed that both the electrostatic and the hydrophobic interactions became controllable with a temperature change during the chromatographic process. Dual pH- and temperature-responsive chromatography would be very useful for biomacromolecules separation and purification.     

Drug release of pH/temperature-responsive calcium alginate/poly(N-isopropylacrylamide) semi-IPN beads

A series of semi-interpenetrating, polymer network (semi-IPN), hydrogel beads, composed of calcium alginate (Ca-alginate) and poly(N-isopropylacrylamide) (PNIPAAM), were prepared for a pH/temperature-sensitive drug delivery study. The equilibrium swelling showed the independent pH- and thermo- responsive nature of the developed materials. At pH=2.1, the release amount of indomethacin incorporated into these beads was about 10% within 400 min, while this value approached to 95% at pH=7.4. The release rate of the drug was higher at 37 degrees C than that at 25 degrees C and increased slightly with increasing PNIPAAM content. These results suggest that the Ca-alginate/PNIPAAM beads have the potential to be used as an effective pH/temperature sustainable delivery system of bioactive agents. [GRAPHS: SEE TEXT] A summary of the temperature- and pH-dependence on the release of the drug over a period of 450 min. The effect of the temperature on the swelling of the beads is shown in the inset.     

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.     

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.     

Enzyme and pH dual responsive l‐amino acid based biodegradable polymer nanocarrier for multidrug delivery to cancer cells

We report a new pH and enzyme dual responsive biodegradable polymer nanocarrier to deliver multiple anticancer drugs at the intracellular compartment in cancer cells. Natural l ‐aspartic acid was converted into multifunctional monomer and polymerized to yield new classes of biodegradable aliphatic polyester in‐build with pH responsiveness. The transformation of side chain BOC urethanes into cationic in the acidic endosomal environment disassembled the polymers nanoparticles (pH trigger‐1). The biodegradation of aliphatic polyester backbone by esterase enzyme ruptured the nanoassemblies and released the drugs in the cytoplasm (trigger‐2). The polymer scaffolds were capable of delivering multiple drugs such as doxorubicin, topotecan, and curcumin (CUR). The cytotoxicity of the nascent and drug‐loaded nanoparticles were tested in cervical (HeLa) and breast (MCF‐7) cancer cell lines. The nascent polymer nanoscaffolds were found to be nontoxic to cells whereas their drug‐loaded nanoparticles exhibited excellent killing. Confocal microscopic images revealed that the drug‐loaded polymer nanoparticles were taken up by the cells and the dual degradation process delivered the drugs to nucleus and established the proof‐of‐concept. The present investigation opens up new platform for l ‐amino acid based polyester scaffolds, for the first time, in the intracellular drug delivery in cancer treatment. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 3279–3293     

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     

Synthesis of narrow‐polydispersity degradable dendronized aliphatic polyesters

The divergent dendronization of an ?‐caprolactone‐based polymer has been performed to provide access to dendronized polymers with sufficient biocompatibility and degradability for use as drug‐delivery scaffolds. The synthesis was performed through the tin(II) 2‐ethylhexanoate‐catalyzed polymerization of a γ‐functionalized ?‐caprolactone monomer, followed by the divergent growth of pendant polyester dendrons at each repeat unit. The resulting dendronized polymers were obtained up to the fourth generation with molecular weights as high as 80,000 Da and with polydispersities between 1.11 and 1.22. The fourth‐generation hydroxyl‐terminated dendronized polymer was degradable under a variety of aqueous conditions. A comparison of the dendronization approach with a procedure involving the ring‐opening polymerization of a second‐generation dendritic macromonomer reveals that the former procedure is best suited for the preparation of this family of dendronized polyesters because it requires shorter reaction times and affords materials with higher degrees of polymerization. © 2004 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 42: 3563–3578, 2004     

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.     

pH- and temperature-responsive redox behavior of hydroxyanthracenediones

The redox response of three anthracenediones; 4,8-dihydroxy-9,10-dioxo-9,10-dihydroanthracen-1-yl acetate (HACAD), 1,4,5-trihydroxyanthracene-9,10-dione (HAD) and 1,4,5-trihydroxy-2-methyl-3-(3-oxobutyl)anthracene-9,10-dione (HOAD) was probed at the surface of a glassy carbon electrode (GCE) over a wide pH range from pH 3 to pH 12 using voltammetric techniques. Cyclic voltammetry (CV) allowed us to evaluate the redox processes in general. Temperature-dependent sweep rate experiments allowed us to obtain kinetic parameters like the diffusion coefficient and the electron transfer rate constant, which were further used to evaluate the thermodynamics of the processes. Differential pulse voltammetry (DPV) allowed the determination of the number of electrons and protons involved in the Faradaic processes. In addition, square-wave voltammetry (SWV) allowed us to assess the reversible/irreversible nature of the electrode processes and allowed the determination of analytical parameters, such as the limit of detection and the limit of quantification. A thorough UV–vis spectroscopy, in a wide pH range, allowed the determination of the acid-base dissociation constant, pK_a, and of the molar extinction coefficient. The pK_a values determined by different methods were found to be in very good agreement.     

Fabrication of tunable colloid crystals from amine-terminated polyamidoamine dendrimers

A pH-responsive colloidal crystal was assembled using core-shell composite spheres, poly(styrene-methyl methacrylate-acrylic acid) (P(St-MMA-AA)) spheres covered by generation 4 amine-terminated polyamidoamine dendrimers. The light reflection of the colloidal crystal film can be tuned at different pH due to different protonation level of the dendrimers. The method shows a facile way to fabricate diffraction-based chemical and biological sensors by exploiting the effect of photonic crystal cooperated with tunable nanoparticles.     

Double targeting of tumours with pyrenyl-modified dendrimers encapsulated in an arene-ruthenium metallaprism

The self‐assembly of 2,4,6‐tris(pyridin‐4‐yl)‐1,3,5‐triazine (tpt) triangular panels with p‐cymene–ruthenium building blocks and 5,8‐dioxido‐1,4‐naphthoquinonato (donq) bridges, in the presence of pyrenyl‐containing dendrimers of different generations (P₀, P₁ and P₂), affords the triangular prismatic host–guest compounds [P_n?Ru₆(p‐cymene)₆(tpt)₂(donq)₃]⁶⁺ ([P_n? 1 ]⁶⁺). The host–guest nature of these systems, with the pyrenyl moiety being encapsulated in the hydrophobic cavity of the cage and the dendritic functional group pointing outwards, was confirmed by NMR spectroscopy (¹H, 2D and DOSY). The host–guest properties of these systems were studied in solution by NMR and UV/Vis spectroscopic methods, allowing the determination of their affinity constants (K_a). Moreover, the ability of these water‐soluble host–guest systems to carry the pyrenyl‐containing dendrimers into cancer cells was evaluated on human ovarian cancer cells. The host–guest systems are all more cytotoxic than the empty cage [ 1 ][CF₃SO₃]₆ (IC₅₀≈4 μM ), with the most active compound, [P₀? 1 ][CF₃SO₃]₆, being an order of magnitude more cytotoxic.     

“Clip” and “Click” Chemistries Combination: Toward Easy PEGylation of Degradable Aliphatic Polyesters

α‐Methoxy‐ω‐alkyne poly(ethylene glycol) (PEG) was tagged with pendent N‐hydroxy‐succinimidyl activated esters by photografting of a molecular clip. This easily synthesized heterofunctional PEG was found to be a versatile building block for (i) conjugation with an amino derivative and (ii) grafting to azido functional aliphatic polyesters backbone by Huisgen's 1,3‐dipolar cycloaddition. This original combination of “clip” and “click” reactions provides a versatile and straightforward pathway for the synthesis of functional amphiphilic and degradable copolymers valuable for biomedical applications such as in drug‐delivery.

     

Synthesis of poly(ester‐amide) dendrimers based on 2,2‐Bis(hydroxymethyl) propanoic acid and glycine

Water‐soluble, biodegradable, and biocompatible poly(ester‐amide) dendrimers with hydroxyl functional groups are synthesized from previously prepared AB₂ adduct of 2,2‐bis(hydroxymethyl) propanoic acid (bis‐MPA) and glycine as a repeating unit. Two esterification procedures using different coupling reagent/catalyst systems (DCC/DPTS or EDC/DMAP) are studied with respect to efficiency, ease of products purification, and quality of the final products. Both procedures have their own benefits and drawbacks, depending on dendrimer generation. The synthesized poly(ester‐amide) dendrimers as well as commercially available bis‐MPA dendrimers, poly(ester‐amide) hyperbranched polymer, and poly(vinyl alcohol) are used for preparation of solid dispersions of sulfonylurea antidiabetic drug glimepiride to improve its poor water‐solubility. In vitro dissolution studies show in comparison with pure glimepiride in crystalline or amorphous form, to the same extent improved glimepiride solubility for solid dispersions based on dendritic polymers, but not for poly(vinyl alcohol). The amount of glimepiride complexed with both dendrimer types increases with dendrimer generation. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 3292–3301