Saccharide-Peptide Hybrid Copolymers as Biomaterials

Recent Progress on Transition Metal Catalyzed Macrocyclizations Based on C-H Bond Activation at Heterocyclic Scaffolds

Macrocycles are essential in protein-protein interactions and the preferential intake of bioactive scaffolds. Macrocycles are commonly synthesized by late-stage macrolactonizations, macrolactamizations, transition metal-catalyzed ring-closing metathesis, S-S bond-forming reactions, and copper-catalyzed alkyne-azide cycloaddition. Recently, transition metal-catalyzed C-H activation strategies have gained significant interest among chemists to synthesize macrocycles. This article provides a comprehensive overview of the transition metal-catalyzed macrocyclization via C-H bond functionalization of heterocycle-containing peptides, annulations, and heterocycle-ring construction through direct C-H bond functionalization. In the first part, palladium salt catalyzed coupling with indolyl C(sp3)-H and C(sp2)-H bonds for macrocyclization is reported. The second part summarizes rhodium-catalyzed macrocyclizations via site-selective C-H bond functionalization. Earth-abundant, less toxic 3d metal salt Mn-catalyzed cyclizations are reported in the latter part. This summary is expected to spark interest in emerging methods of macrocycle production among organic synthesis and chemical biology practitioners, helping to develop the discipline. We hope that this mini-review will also inspire synthetic chemists to explore new and broadly applicable C-C bond-forming strategies for macrocyclization via intramolecular C-H activation.

Multifunctional Dendronized Polypeptides for Controlled Adjuvanticity

Vaccination has been playing an important role in treating both infectious and cancerous diseases. Nevertheless, many diseases still lack proper vaccines due to the difficulty to generate sufficient amounts of antigen-specific antibodies or T cells. Adjuvants provide an important route to improve and direct immune responses. However, there are few adjuvants approved clinically and many of them lack the clear structure/adjuvanticity relationship. Here, we synthesized and evaluated a series of dendronized polypeptides (denpols) functionalized with varying tryptophan/histidine (W/H) molar ratios of 0/100, 25/75, 50/50, 75/25, and 100/0 as tunable synthetic adjuvants. The denpols showed structure-dependent inflammasome activation in THP1 monocytic cells and structure-related activation and antigen cross-presentation in vitro in bone marrow-derived dendritic cells. We used the denpols with bacterial pathogen Coxiella burnetii antigens in vivo, which showed both high and tunable adjuvating activities, as demonstrated by the antigen-specific antibody and T cell responses. The denpols are easy to make and scalable, biodegradable, and have highly adjustable chemical structures. Taken together, denpols show great potential as a new and versatile adjuvant platform that allows us to adjust adjuvanticity based on structure-activity correlation with the aim to fine-tune the immune response, thus advancing vaccine development.

Sulfated poly-amido-saccharides (sulPASs) are anticoagulants in vitro and in vivo

Anticoagulant therapeutics are a mainstay of modern surgery and of clotting disorder management such as venous thrombosis, yet performance and supply limitations exist for the most widely used agent - heparin. Herein we report the first synthesis, characterization, and performance of sulfated poly-amido-saccharides (sulPASs) as heparin mimetics. sulPASs inhibit the intrinsic pathway of coagulation, specifically FXa and FXIa, as revealed by ex vivo human plasma clotting assays and serine protease inhibition assays. sulPASs activity positively correlates with molecular weight and degree of sulfation. Importantly, sulPASs are not degraded by heparanases and are non-hemolytic. In addition, their activity is reversed by protamine sulfate, unlike small molecule anticoagulants. In an in vivo murine model, sulPASs extend clotting time in a dose dependent manner with bleeding risk comparable to heparin. These findings support continued development of synthetic anticoagulants to address the clinical risks and shortages associated with heparin.

A Synthetic Bioinspired Carbohydrate Polymer with Mucoadhesive Properties

Mucoadhesive polymers are of significant interest to the pharmaceutical, medical device, and cosmetic industries. Polysaccharides possessing charged functional groups, such as chitosan, are known for mucoadhesive properties but suffer from poor chemical definition and solubility, while the chemical synthesis of polysaccharides is challenging with few reported examples of synthetic carbohydrate polymers with engineered-in ionic functionality. We report the design, synthesis, and evaluation of a synthetic, cationic, enantiopure carbohydrate polymer inspired by the structure of chitosan. These water-soluble, cytocompatible polymers are prepared via an anionic ring-opening polymerization of a bicyclic β-lactam sugar monomer. The synthetic method provides control over the site of amine functionalization and the length of the polymer while providing narrow dispersities. These well-defined polymers are mucoadhesive as documented in single-molecule scale (AFM), bulk solution phase (FRAP), and ex vivo tissue experiments. Polymer length and functionality affects bioactivity as long, charged polymers display higher mucoadhesivity than long, neutral polymers or short, charged polymers.

Hybrid polymers bearing oligo-l-lysine(carboxybenzyl)s: synthesis and investigations of secondary structure

Hybrid polymers of peptides resembling (partially) folded protein structures are promising materials in biomedicine, especially in view of folding-interactions between different segments. In this study polymers bearing repetitive peptidic folding elements, composed of N-terminus functionalized bis-ω-ene-functional oligo-l-lysine(carboxybenzyl(Z))s (Lys_n) with repeating units (n) of 3, 6, 12, 24 and 30 were successfully synthesized to study their secondary structure introduced by conformational interactions between their chains. The pre-polymers of ADMET, narrowly dispersed Lys_ns, were obtained by ring opening polymerization (ROP) of N-carboxyanhydride (NCA) initiated with 11-amino-undecene, following N-terminus functionalization with 10-undecenoyl chloride. The resulting Lys_ns were subsequently polymerized via ADMET polymerization by using Grubbs’ first generation (G1) catalyst in 1,1,1,3,3,3-hexafluoroisopropanol (HFIP) generating the ADMET polymers (A-[Lys_n]_m) (m = 2–12) with molecular weights ranging from 3 to 28 kDa, displaying polydispersity (Đ) values in the range of 1.5–3.2. After chemical analyses of Lys_ns and A-[Lys_n]_ms by ¹H-NMR, GPC and MALDI-ToF MS, secondary structural investigations were probed by CD spectroscopy and IR spectroscopy in 2,2,2-trifluoroethanol (TFE). In order to study A-[Lys_n]_ms with defined molecular weights and low polydispersity values (Đ = 1.03–1.48), the ADMET polymers A-[Lys_n=3]_m=3 and A-[Lys_n=24]_m=4 were fractionated by preparative GPC, and subsequently analysed by ¹H-NMR, analytical GPC, MALDI-ToF MS and CD spectroscopy. We can demonstrate the influence of chain length of the generated polymers on the formation of secondary structures by comparing Lys_ns with varying n values to the ADMET-polymers with the help of spectroscopic techniques such as CD and FTIR-spectroscopy in a helicogenic solvent.

We demonstrate the influence of chain length of segmented polymers bearing dynamic folding elements onto the formation of secondary structures with the help of spectroscopic techniques such as CD and FTIR-spectroscopy in a helicogenic solvent.

Cationic poly-amido-saccharides: stereochemically-defined, enantiopure polymers from anionic ring-opening polymerization of an amino-sugar monomer

We expand the scope of the PAS methodology and evaluate multiple synthetic routes to generate a regioselectively-functionalized 6-amino carbohydrate polymer sharing key properties with natural polysaccharides, including high water-solubility.

Self-sensibilized polymeric prodrug co-delivering MMP-9 shRNA plasmid for combined treatment of tumors

Polymeric prodrugs are of immense interest as anticancer drug-delivery system owing to their superior drug stability during circulation and satisfactory drug loading capacity. However, they are usually less effective than free drugs due to imperfect degradable characteristics or active sites blockage. A polymeric prodrug (HPAA-MTX) with chemotherapeutic self-sensibilization effect consisting of glutathione (GSH)-triggered hyperbranched poly(amido amine) (HPAA) and methotrexate (MTX) was designed and synthesized in this work. This prodrug not only showed better inhibition effect on the tumor cells proliferation compared with free MTX, but also displayed selective sensibilization to tumor cells rather than normal cells. Meanwhile, HPAA-MTX was also explored as a MMP-9 shRNA plasmid delivery vector due to their rich amino group of HPAA, accompanying with MTX for simultaneous inhibiting tumor cells proliferation and migration. As expected, HPAA-MTX possessed excellent gene delivery capacity with significant down-regulation expression of MMP-9 protein and further inhibition of MCF-7 cells migration. Benefiting from the self-sensibilization effect and MTX/MMP-9 co-delivery strategy, this HPAA-MTX/MMP-9 co-delivery system exhibited significantly improved therapeutic efficacy to breast cancer in a combined manner which was confirmed through in vitro and in vivo assays. The strategy established in this study provided a facile "all-in-one" platform to integrate the drug/gene co-delivery strategy and self-sensibilization effect into one single nanocomposite for potential cancer treatment.

STATEMENT OF SIGNIFICANCE

A cationic polymeric prodrug with chemotherapeutic self-sensibilization effect was designed and showed better inhibition effect on tumor cells proliferation compared with its free drug, as well displayed the selective sensibilization effect to tumor cells rather than normal cells. Moreover, the prodrug could also deliver MMP-9 shRNA plasmid for a combined therapy. As expected, the prodrug possessed excellent gene delivery capacity with significant down-regulation expression of MMP-9 protein and further inhibition of MCF-7 cells migration. Benefiting from the self-sensibilization effect and the drug/gene co-delivery strategy, this prodrug exhibited significantly improved therapeutic efficacy to breast cancer in a combined manner.

Star-Shaped Amphiphilic Hyperbranched Polyglycerol Conjugated with Dendritic Poly(l-lysine) for the Codelivery of Docetaxel and MMP-9 siRNA in Cancer Therapy

The drug/gene codelivery is a promising strategy for cancer treatment. Herein, to realize the codelivery of docetaxel and MMP-9 siRNA plasmid efficiently into tumor cells, a star-shaped amphiphilic copolymer consisting of hyperbranched polyglycerol derivative (HPG-C18) and dendritic poly(l-lysine) (PLLD) was synthesized by the click reaction between azido-modified HPG-C18 and propargyl focal point PLLD. The obtained HPG-C18-PLLD could form the nanocomplexes with docetaxel and MMP-9, and the complexes showed good gene delivery ability in vitro by inducing an obvious decrease in MMP-9 protein expression in MCF-7 cells. The apoptosis assay showed that the complex could induce a more significant apoptosis to breast cancer cells than that of docetaxel or MMP-9 used alone. In vivo assay indicated that the codelivery strategy displayed a better effect on tumor inhibition. Moreover, HPG-C18-PLLD displayed lower toxicity as well as better blood compatibility compared to polyethylenimine PEI-25k, which may be the result of that HPG-C18-PLLD showed the comparative MMP-9 delivery ability in vivo compared with PEI-25k even if it showed the slight lower transfection efficiency in vitro. Therefore, HPG-C18-PLLD is a safe and effective carrier for the codelivery of drug/gene, which should be encouraged in tumor therapy.

ATP triggered drug release and DNA co-delivery systems based on ATP responsive aptamers and polyethylenimine complexes

Stimuli-responsive nanocarriers for anticancer drug and gene co-delivery are a promising strategy in cancer therapy due to their combination of chemotherapy and gene therapy. In this work, we developed a facile and effective method to fabricate stimuli-responsive nanocarriers for anticancer drug and gene co-delivery based on complexes of polyethylenimine (PEI) with an adenosine triphosphate (ATP) responsive aptamer duplex (ARAD). No chemical reactions or complex modifications were used in the construction processes. In this system, Doxorubicin-loaded aptamer duplex and plasmid DNA (p53) can be bound by PEI by electronic interactions to form stable complexes which effectively protect the aptamer and p53 from DNase degradation. The intercalated Dox can be released on-demand by a structural change in the aptamer duplex in an ATP-rich environment. The morphology and average size of the nanocarriers were characterized by zeta potential and transmission electron microscopy (TEM). The nanocarriers exhibit lower cell toxicity in HeLa cell lines relative to PEI. RT-PCR and Western blot analysis confirmed that p53 could be effectively delivered and expressed in HeLa cells by PEI/ARAD/p53 complexes. Moreover, the apoptosis percentage of HeLa cells treated with PEI/ARAD/Dox/p53 complex increased to 40.8%, compared to 24.7% for PEI/ARAD/Dox complex and 11.5% for PEI/ARAD/p53, respectively. The result demonstrated that the combinatorial delivery of Dox and p53 by nanocarriers could induce synergistic actions and lead to effective cancer cell apoptosis.

F-127-PEI co-delivering docetaxel and TFPI-2 plasmid for nasopharyngeal cancer therapy

The co-delivery of drug and gene has become the primary strategy in cancer therapy. However, to construct one safe co-delivering system with higher drug loading and gene transfection efficiency for cancer therapy is still challenging. Herein, a novel degradable nanocarriers were synthesized and characterized in this study, which was composed of polyethylenimine (PEI)-linked PEO-PPO-PEO (Pluronic F127), called F127-PEI. Then the nanocarrier was used for hydrophobic docetaxel (DOC) and functional gene (TFPI-2 plasmid) co-delivery to treat nasopharyngeal cancer (NPC). The results indicated that F127-PEI nanocarriers had higher DOC loading amount and possessed good gene delivery effect in vitro. For co-delivery analysis, the obtained F127-PEI/DOC/TFPI-2 complexes could induce a more significant apoptosis than DOC or TFPI-2 alone, and decreased invasive capacity of NPC HNE-1 cells more obviously. Moreover, the F127-PEI copolymer exhibited better blood compatibility and lower cytotoxicity compared to PEI-25k by the hemolysis and MTT assays, which suggests a promising potential for NPC therapy.

A new boronic acid fluorescent sensor based on fluorene for monosaccharides at physiological pH

Fluorescent boronic acids are very useful fluorescent sensor for detection of biologically important saccharides. Herein we synthesized a new fluorene-based fluorescent boronic acid that shows significant fluorescence changes upon addition of saccharides at physiological pH. Upon addition of fructose, sorbitol, glucose, galactose, ribose, and maltose at different concentration to the solution of 7-(dimethylamino)-9,9-dimethyl-9H-fluoren-2-yl-2-boronic acid (7-DMAFBA, 1), significant decreases in fluorescent intensity were observed. It was found that this boronic acid has high affinity (K(a)=3582.88 M(-1)) and selectivity for fructose over glucose at pH=7.4. The sensor 1 showed a linear response toward d-fructose in the concentrations ranging from 2.5×10(-5) to 4×10(-4) mol L(-1) with the detection limit of 1.3×10(-5) mol L(-1).

Modular and orthogonal synthesis of hybrid polymers and networks

Biomaterials scientists strive to develop polymeric materials with distinct chemical make-up, complex molecular architectures, robust mechanical properties and defined biological functions by drawing inspirations from biological systems. Salient features of biological designs include (1) repetitive presentation of basic motifs; and (2) efficient integration of diverse building blocks. Thus, an appealing approach to biomaterials synthesis is to combine synthetic and natural building blocks in a modular fashion employing novel chemical methods. Over the past decade, orthogonal chemistries have become powerful enabling tools for the modular synthesis of advanced biomaterials. These reactions require building blocks with complementary functionalities, occur under mild conditions in the presence of biological molecules and living cells and proceed with high yield and exceptional selectivity. These chemistries have facilitated the construction of complex polymers and networks in a step-growth fashion, allowing facile modulation of materials properties by simple variations of the building blocks. In this review, we first summarize features of several types of orthogonal chemistries. We then discuss recent progress in the synthesis of step growth linear polymers, dendrimers and networks that find application in drug delivery, 3D cell culture and tissue engineering. Overall, orthogonal reactions and modulular synthesis have not only minimized the steps needed for the desired chemical transformations but also maximized the diversity and functionality of the final products. The modular nature of the design, combined with the potential synergistic effect of the hybrid system, will likely result in novel hydrogel matrices with robust structures and defined functions.

Codelivery of doxorubicin and p53 by biodegradable micellar carriers based on chitosan derivatives

In this work, novel biodegradable cationic micelles were prepared based on poly-(N-ε-carbobenzyloxy-l-lysine) (PZLL) and chitosan (CS) by click reaction, and applied for co-delivery of doxorubicin (DOX) and p53 plasmid.

Cationic charged helical glycopolypeptide using ring opening polymerization of 6-deoxy-6-azido-glyco-N-carboxyanhydride

Glycopolypeptides with a defined secondary structure are of significance in understanding biological phenomena. Synthetic glycopolypeptides, or polypeptides featuring pendant carbohydrate moieties, have been of particular interest in the field of tissue engineering and drug delivery. In this work, we have synthesized charged water-soluble glycopolypeptides that adopt a helical conformation in water. This was carried out by the synthesis of a glyco-N-carboxyanhydride (glyco-NCA) containing an azide group at the sixth position of the carbohydrate ring. Subsequently, the NCA was polymerized to obtain azide-containing glycopolypeptides having good control over molecular weight and polydispersity index (PDI) in high yields. We were also able to control the incorporation of the azide group by synthesizing random co-glycopolypeptide containing 6-deoxy-6-azido and regular 6-OAc functionalized glucose. This azide functionality allows for the easy attachment of a bioactive group, which could potentially enhance the biological activity of the glycopolypeptide. We were able to obtain water-soluble charged glycopolypeptides by both reducing the azide groups into amines and using CuAAC with propargylamine. These charged glycopolypeptides were shown to have a helical conformation in water. Preliminary studies showed that these charged glycopolypeptides showed good biocompatibility and were efficiently taken up by HepG2 cells.

Star-shaped cyclodextrin-poly(l-lysine) derivative co-delivering docetaxel and MMP-9 siRNA plasmid in cancer therapy

A new cyclodextrin derivative (CD-PLLD) consisting of a β-cyclodextrin core and poly(l-lysine) dendron arms was prepared by the click conjugation of per-6-azido-b-cyclodextrin with propargyl focal point poly(l-lysine) dendron of third generation, and then used for docetaxel (DOC) and the best siRNA plasmid targeting MMP-9 (pMR3) co-delivery. Different from commonly used amphiphilic copolymers with cationic character, the as obtained cyclodextrin derivative may be used directly for the combinatorial delivery of nucleic acid and lipophilic anticancer drugs without a complicated micellization process. It was found that CD-PLLD/pMR3 nanocomplex showed a good gene transfection efficiency in vitro, and could mediate the reduce of MMP-9 protein in HNE-1 cells. For co-delivery analysis, the obtained CD-PLLD/DOC/pMR3 complexes could induce a more significant apoptosis than DOC or pMR3 used only, and decreased invasive capacity of HNE-1 cells. Moreover, the star-shaped copolymer exhibited better blood compatibility and lower cytotoxicity compared to PEI-25k in the hemolysis and MTT assays, which should be encouraged in nasopharyngeal cancer therapy.

Spectral properties of highly selective chemosensor for Hg2+

A (E)-2-(2-(2-(1H-indol-3-yl)vinyl)-4H-chromen-4-ylidene)malononitrile (dye 1) was synthesized and its cation sensing properties in DMSO were investigated by UV-vis spectroscopy. Upon the addition of Hg2+, the solution of dye 1 showed color change and the absorption band shows a formation of a 1:1 dye 1-Hg2+ coordination complex. The dye 1 exhibited high selectivity for Hg2+ as compared with other cations. Interestingly, the dye 1-F- complex also could be recovered by adding Hg2+. We have investigated the ability of complex formation based on the association constant, Kass; the binding ability for the complex formation of dye 1-F- and Hg2+ is greater than that of the dye 1 with F-.

A facile channel for D-glucose detection in aqueous solution

Three facile ensembles for sensing D-glucose are designed and constructed. The ensembles are comprised of fluorescent dye (NAHBDS) and boronic acid substituted viologens (BBVs) quenchers/receptors. The sensing processes of three ensembles (NAHBDS/o-BBV, NAHBDS/m-BBV and NAHBDS/p-BBV) to D-glucose were determined by fluorescence spectra at pH 7.4 buffer solution. The results show that NAHBDS/o-BBV and NAHBDS/m-BBV ensembles embody higher sensitivity for D-glucose with reversible "on-off" fluorescence response. More importantly, the recovery of relative intensity has good linear relation to low concentration of D-glucose. The action between the ensemble with D-glucose is dynamically reversible equilibrium process. The research results provide a new mode to design highly selective probe.

Surfactant-free synthesis of biodegradable, biocompatible, and stimuli-responsive cationic nanogel particles

Nanogels have attracted much attention lately because of their many potential applications, including as nanocarriers for drug and gene delivery. Most nanogels reported previously, however, are not biodegradable, and their synthesis often requires the use of surfactants. Herein we report a surfactant-free method for the preparation of biodegradable, biocompatible, and stimuli-responsive cationic nanogels. The nanogels were synthesized by simply coaservating linear polymer precursors in mixed solvents followed by in situ cross-linking with homobifunctional cross-linkers. The versatility of this approach has been demonstrated by employing two different polymers and various cross-linkers to prepare nanogel particles with diameters ranging from 170 to 220 nm. Specifically, disulfide-containing tetralysine (TetK)- and oligoethylenimine (OEI)-based prepolymers were prepared and the subsequent nanogels were formed by covalently cross-linking the polymer coacervate phase. Nanogel particles are responsive to pH changes, increasing in size and zeta-potential with concomitant lowering of solution pH. Furthermore, as revealed by AFM imaging, nanogel particles were degradable in the presence of glutathione at concentrations similar to those in intracellular environment (10 mM). Both the nanogel and the polymer precursors were determined to exhibit minimal cytotoxicity against fibroblast 3T3 cells by flow cytometric analyses and fluorescent imaging. This study demonstrates a new surfactant-free method for preparing biodegradable, biocompatible, and stimuli-responsive nanogels as potential nanocarriers for the delivery of drugs and genes.

Star-shaped polymer consisting of a porphyrin core and poly(L-lysine) dendron arms: synthesis, drug delivery, and in vitro chemo/photodynamic therapy

A novel star-shaped polymer, porphyrin-poly(L-lysine) dendrons (PP-PLLD), is synthesized by the click reaction between azido-modified porphyrin and propargyl focal point poly(L-lysine) dendrons. Its chemical structure is characterized by (1) H nuclear magnetic resonance, Fourier transform infrared spectroscopy, and gel permeation chromatography (GPC) is analyses etc. Due to its amphiphilic property, the obtained PP-PLLD has a low critical micelle concentration in an aqueous solution, and can load doxorubicin (DOX) with a loading amount of 64 μg mg(-1) . By in vitro toxicity assay, PP-PLLD has no dark cytotoxicity but has significant phototoxicity. Moreover, DOX-loaded PP-PLLD shows a higher cytotoxicity under the light condition than PP-PLLD or DOX alone, suggesting PP-PLLD has a potential application in combined photodynamic therapy and chemotherapy.

Modulation of chondrocyte behavior through tailoring functional synthetic saccharide-peptide hydrogels

Tailoring three-dimensional (3D) biomaterial environments to provide specific cues in order to modulate function of encapsulated cells could potentially eliminate the need for addition of exogenous cues in cartilage tissue engineering. We recently developed saccharide-peptide copolymer hydrogels for cell culture and tissue engineering applications. In this study, we aim to tailor our saccharide-peptide hydrogel for encapsulating and culturing chondrocytes in 3D and examine the effects of changing single amino acid moieties differing in hydrophobicity/hydrophilicity (valine (V), cysteine (C), tyrosine (Y)) on modulation of chondrocyte function. Encapsulated chondrocytes remained viable over 21 days in vitro. Glycosaminoglycan and collagen content was significantly higher in Y-functionalized hydrogels compared to V-functionalized hydrogels. Extensive matrix accumulation and concomitant increase in mechanical properties was evident over time, particularly with the presence of Y amino acid. After 21 days in vitro, Y-functionalized hydrogels attained a modulus of 193 ± 46 kPa, compared to 44 ± 21 kPa for V-functionalized hydrogels. Remarkably, mechanical and biochemical properties of chondrocyte-laden hydrogels were modulated by change in a single amino acid moiety. This unique property, combined with the versatility and biocompatibility, makes our saccharide-peptide hydrogels promising candidates for further investigation of combinatorial effects of multiple functional groups on controlling chondrocyte and other cellular function and behavior.

Highly selective ensembles for D-fructose based on fluorescent method in aqueous solution

Three highly sensitive and selective switches for monosaccharides were composed by anionic polyelectrolyte PPPSO(3)Na and cationic viologen quencheres BBVs. The sensing processes of three ensembles (PPPSO(3)Na/o-BBV, PPPSO(3)Na/m-BBV and PPPSO(3)Na/p-BBV) to common seven monosaccharides have been determined by fluorescence spectra at pH 7.4 buffer solution. The results show that the three sensing ensembles all embody higher selectivity and sensitivity for d-fructose with reversible "on-off-on" fluorescence response. The research results can provide a new mode for developing highly selective probes.

Synthesis of water-soluble poly(α-hydroxy acids) from living ring-opening polymerization of O-benzyl-L-serine carboxyanhydrides

O-benzyl-L-serine carboxyanhydrides were synthesized via diazotization of O-benzyl-L-serine with sodium nitrite in aqueous sulfuric acid solution followed by cyclization of the resulting serine-based α-hydroxy acid with phosgene. Degradable, water-soluble poly(α-hydroxy acids) bearing pendant hydroxyl groups were readily prepared under mild conditions via ring-opening polymerization of O-benzyl-L-serine carboxyanhydrides followed by removal of the benzyl group and showed excellent cell compatibility, suggesting their potential being used as novel materials in constructing drug delivery systems and as hydrogel scaffolds for tissue engineering applications.

Biodegradable and biocompatible synthetic saccharide-Peptide hydrogels for three-dimensional stem cell culture

Saccharide-peptide hydrogels have been developed in our laboratory as new synthetic extracellular matrices for regenerative medicine applications. In this work, we have expanded on our previously reported system and applied copolymerization of cysteine (Cys) and vinyl sulfone (VS)-functionalized saccharide-peptide polymers via Michael-type addition for encapsulation and 3D culture of cells. Specifically, our aims were to (1) develop a novel hydrogel platform, which could be applied for encapsulating and culturing mesenchymal stem cells (MSCs) in a 3D environment, (2) characterize the tunable properties of the hydrogel, specifically, degradation, mechanical, and gel network properties, and (3) determine the biocompatibility of the saccharide-peptide hydrogel material with MSCs. Hydrogel mechanical properties were tunable by varying the VS:Cys ratio (= 0.5, 1, or 2) as well as the pH (6, 7, or 8) of the cross-linking components. Stiffer gels were formed at VS:Cys = 1 and pH 6 or 7. Gels formed at pH 8 or with excess Cys (VS:Cys = 0.5) or VS (VS:Cys = 2) were significantly softer. Cross-linking pH and VS:Cys ratio also had an effect on the degradation behavior of the VS:Cys gels, with higher cross-linking pH resulting in an accelerated loss of mass. On the basis of environmental scanning electron microscopy (ESEM) analysis and fluorescence microscopy, all hydrogels appeared to exhibit porous gel networks. MSCs cultured in monolayer and exposed to soluble Cys or VS copolymers (0.1-5 mg/mL) did not exhibit measurable cytotoxicity. In addition, MSCs were cultured in 3D for up to 14 days in vitro without deleterious effects on cell viability. In summary, we have established and characterized a tunable 3D saccharide-peptide hybrid copolymer hydrogel platform for culturing MSCs. Future studies will focus on utilizing the hydrogel system for controlling the differentiation of MSCs.

Direct synthesis of polyamides via catalytic dehydrogenation of diols and diamines

We report a direct synthesis of polyamides via catalytic dehydrogenation of diols and diamines. A PNN pincer ruthenium complex, the Milstein catalyst, was used for this reaction and polyamides with number average molecular weight from ∼10 to 30 kDa could be obtained from a wide variety of diols and diamines bearing aliphatic or aromatic, linear or cyclic spacers. Because of the high catalytic selectivity of primary amine over secondary amine, polyamines could be conveniently incorporated into linear polyamides without tedious protection/deprotection steps. Compared with conventional condensation method, this catalytic system avoids the requirement of stoichiometric preactivation or in situ activation reagents and provides a much cleaner process with high atomic economy.

Degradation of poly(glycoamidoamine) DNA delivery vehicles: polyamide hydrolysis at physiological conditions promotes DNA release

Poly(glycoamidoamine)s (PGAAs) are a group of efficient and degradable gene delivery vehicles that consist of three main functionalities: carbohydrate groups, secondary amines, and amide bonds. Herein, we have created nonhydroxylated models to these structures by polymerizing oxylate, succinate, or adipate groups with pentaethylenehexamine. The resulting polymers (named O4, S4, and A4, respectively) were created to understand how the absence of hydroxyl groups and changes in the amide bond spacing affect polymer degradation, plasmid DNA (pDNA) complexation, toxicity, and transfection efficiency in vitro. An additional model was also created that retains a galactaramide unit, but we have replaced the secondary amines with ethyleneoxide units (GO2) to understand the effects of the amine groups on polymer degradation. We have found that the secondary amines and hydroxyls are necessary to facilitate rapid degradation of these polymers, and analogues lacking hydroxyls or amines did not degrade over the time course of the study. Through electron-withdrawing and hydrogen bonding, the hydroxyls appear to activate the carbonyls of the amide bond to hydrolysis via an inductive electron withdrawing effect. Through titration experiments, PGAA degradation appears not to affect the polymer buffering capacity. Furthermore, we have found that PGAA degradation may enhance gene expression by releasing pDNA from polyplexes (polymer-pDNA complexes) and, thus, exposing it to undergo transcription and translation. The difference in the optimal pH that promotes degradation of the PGAAs and the hydroxyl-free analogues may prove to be a useful means to achieve pH-regulated DNA release from polyplexes by specifically modulating the chemical structures.

Anti-nonspecific protein adsorption properties of biomimetic glycocalyx-like glycopolymer layers: effects of glycopolymer chain density and protein size

In many cases, biomaterials surfaces are desired to be resistant to protein adsorption. A system fulfilling this task in nature is the so-called glycocalyx. The glycocalyx is an outer layer on the cell membrane with bound glycoproteins and glycolipids, exposing a pattern of carbohydrate groups. There is a growing interest to mimic this glycocalyx layer to have a tool to overcome the problems with uncontrolled protein adsorption on biomaterials. In this work a glycocalyx-like layer is artificially imitated by surface-initiated atom transfer radical polymerization (ATRP) of a glycomonomer, D-gluconamidoethyl methacrylate (GAMA), from a mixed self-assembled monolayer (SAM) of an ATRP initiator-immobilized hydroxyl-terminated thiol and a methyl-terminated thiol as diluent. Fourier transform infrared spectroscopy (FT/IR-ATR), contact angle, and ellipsometry measurements were employed to confirm the grafting of the glycopolymer. The anti-nonspecific protein binding properties of this glycopolymer layer were then investigated with surface plasmon resonance (SPR). Three proteins with different size, lysozyme, bovine serum albumin (BSA), and fibrinogen were used as model solutes to investigate the influence of protein size on the protein resistance behavior. The glycopolymer chain density was controlled during surface-initiated ATRP by varying the ratio of the components in the mixed SAM, and the chain length was adjusted by ATRP time. The effect of chain density in combination with the protein size was also evaluated. The most important results are that poly(GAMA) layers of higher grafting density show resistance to adsorption of the model proteins used in this work and that the amount of adsorbed protein depends on the length and density of the glycopolymer chains and also on the size of the proteins.

Phage wrapping with cationic polymers eliminates nonspecific binding between M13 phage and high pI target proteins

M13 phage have provided scaffolds for nanostructure synthesis based upon self-assembled inorganic and hard materials interacting with phage-displayed peptides. Additionally, phage display has been used to identify binders to plastic, TiO(2), and other surfaces. However, synthesis of phage-based materials through the hybridization of soft materials with the phage surface remains unexplored. Here, we present an efficient "phage wrapping" strategy for the facile synthesis of phage coated with soluble, cationic polymers. Polymers bearing high positive charge densities demonstrated the most effective phage wrapping, as shown by assays for blocking nonspecific binding of the anionic phage coat to a high pI target protein. The results establish the functional group requirements for hybridizing phage with soft materials and solve a major problem in phage display-nonspecific binding by the phage to high pI target proteins.

Carbohydrate polymers for nonviral nucleic acid delivery

Carbohydrates have been investigated and developed as delivery vehicles for shuttling nucleic acids into cells. In this review, we present the state of the art in carbohydrate-based polymeric vehicles for nucleic acid delivery, with the focus on the recent successes in preclinical models, both in vitro and in vivo. Polymeric scaffolds based on the natural polysaccharides chitosan, hyaluronan, pullulan, dextran, and schizophyllan each have unique properties and potential for modification, and these results are discussed with the focus on facile synthetic routes and favorable performance in biological systems. Many of these carbohydrates have been used to develop alternative types of biomaterials for nucleic acid delivery to typical polyplexes, and these novel materials are discussed. Also presented are polymeric vehicles that incorporate copolymerized carbohydrates into polymer backbones based on polyethylenimine and polylysine and their effect on transfection and biocompatibility. Unique scaffolds, such as clusters and polymers based on cyclodextrin (CD), are also discussed, with the focus on recent successes in vivo and in the clinic. These results are presented with the emphasis on the role of carbohydrate and charge on transfection. Use of carbohydrates as molecular recognition ligands for cell-type specific delivery is also briefly reviewed. We contend that carbohydrates have contributed significantly to progress in the field of non-viral DNA delivery, and these new discoveries are impactful for developing new vehicles and materials for treatment of human disease.