Sequential polydepsipeptides as biodegradable carriers for drug delivery systems

Sequential polydepsipeptides containing both peptide and ester bonds, poly[(L-alanyl)n-gamma-ethyl L-glutamyl-L-lactyl] (n = 0, 1, 2, and 3) (poly[(Ala)n-Glu(OEt)-Lac]), were prepared for application as biodegradable carriers for drug delivery systems. The in vivo degradation of these polymers was evaluated by subcutaneous implantation in the backs of male rats, and was strongly influenced by the number (n) of Ala units in poly[(Ala)n-Glu(OEt)-Lac]. The resulting poly(Ala-Ala-Glu(OEt)-Lac) gave the highest degradability, in which 100% degradation was observed 24 weeks from the start of implantation. A luteinizing-hormone-releasing hormone agonist des-Gly10-[D-Leu6]-LH-RH ethylamide (LH-RH agonist), was incorporated into a sequential poly(Ala-Ala-Glu(OEt)-Lac) carrier by the melt-pressing technique, which gave fine cylindrical polymer formulations with different structures of drug dispersion, e.g., blend-type and sandwich-type formulations. The rate of in vivo release of LH-RH agonist from a blend-type formulation showed a linear decrease with time until its release was finished after 6 weeks' implantation. In contrast, in a sandwich-type formulation, the in vivo release rate was apparently maintained constant over a period of 16 weeks (24 +/- 14 micrograms/day).     

Amine-modified hyperbranched polyesters as non-toxic, biodegradable gene delivery systems

For chronic non-viral gene therapy, biodegradable carriers with low cytotoxicity are essential. To create a series of non-toxic and biodegradable gene carriers, hyperbranched polymers based on 2,2-bis-(methylol)propionic acid (bis-MPA); (Boltorn H^®) were modified by introducing tertiary amines. The terminal OH groups were modified with diethylaminopropylamine (DEAPA) by carbonyldiimidazole (CDI) chemistry. The resulting polymers were characterized by ¹H, ¹³C NMR, IR and GPC. Degradability and degradation rate were investigated with respect to the degree of amine substitution. The toxicity of all hyperbranched polyesters was generally very low compared to polyethyleneimine (PEI). Measurements of size and zeta potential showed that small nano-complexes with a positive zeta potential were formed. Dependency of the degree of amine substitution on interaction with DNA was studied by agarose gel retardation assay and ethidium bromide exclusion assay. Influence of the amine substitution on transfection efficiency of the different polymers demonstrated that a certain amine substitution degree was required to achieve transfection efficiency. These carriers provide degradability, very low toxicity and the ability to transfect cells which can be influenced by the degree of amine substitution.     

Starch-based biodegradable hydrogels with potential biomedical applications as drug delivery systems

The design and preparation of novel biodegradable hydrogels developed by the free radical polymerization of acrylamide and acrylic acid, and some formulations with bis-acrylamide, in the presence of a corn starch/ethylene-co-vinyl alcohol copolymer blend (SEVA-C), is reported. The redox system benzoyl peroxide (BPO) and 4-dimethylaminobenzyl alcohol (DMOH) initiated the polymerization at room temperature. Xerogels were characterized by 1H NMR and FTIR spectroscopies. Swelling studies were performed as a function of pH in different buffer solutions determining the water-transport mechanism that governs the swelling behaviour. Degradation studies of the hydrogels were performed in simulated physiological solutions for time up to 90 days, determining the respective weight loss, and analyzing the solution residue by 1H NMR. The mechanical properties of the xerogels were characterized by tensile and compressive tests, as well as by dynamo-mechanical analysis (DMA). Dynamo-mechanical parameters are also reported for hydrated samples.     

In vivo-in vitro study of biodegradable methadone delivery systems

Three one-week controlled-release methadone formulations: polylactic acid microspheres (F-PLA) and poly(lactide-co-glycolide) microspheres (F-PLGA) with 24 and 30% methadone content, respectively, and an implant of 50:50 poly(lactide-co-glycolide): methadone, were evaluated in vitro and in vivo. The implant released the total amount of methadone in vitro while microsphere formulations released the methadone incompletely, 63% from F-PLA and 85% from F-PLGA in a week. Methadone release in vivo was estimated by deconvolution, F-PLGA giving a bioavailability >99% (methadone was totally released in 48h), while the estimated bioavailability of F-PLA was lower than expected. The bioavailability of the implant by deconvolution was around 60%, but absence of methadone in the implant indicated its complete release. These differences are due to an increase in methadone clearance after 72 h of the in vivo experimental period had passed, disturbing a good in vivo-in vitro correlation. A linear correlation between in vitro methadone release and in vivo release calculated from the amount of drug remaining within the implant, was found until the drug was completely released.     

Polyethylenimine-grafted polycarbonates as biodegradable polycations for gene delivery

Polycations as one of non-viral vectors have gained increasing attentions. In this paper, polyethylenimine(PEI)-grafted polycarbonates (PMAC-g-PEIx) were synthesized as a kind of biodegradable polycations for gene delivery. Backbone polymer, poly(5-methyl-5-allyloxycarbonyl-trimethylene carbonate) (PMAC), was synthesized in bulk catalyzed by immobilized porcine pancreas lipase (IPPL). Then, PMAC–O, the allyl epoxidation product of PMAC, was further modified by PEIx with low molecular weight (x = 423, 800 and 1800). The MWs of PMAC-g-PEIx, measured by GPC–MALLS, were 81,900, 17,9900 and 200,600 g/mol with polydispersities of 1.2, 1.4 and 1.7, respectively. PMAC-g-PEIx could form positively charged nano-sized particles (30–90 nm) with pDNA, and all the three PAMC-g-PEIx/DNA polyplexes had similar buffer capabilities. In vitro experiments demonstrated that the PAMC-g-PEIx showed much low cytotoxicity and enhanced transfection efficiency could be found in comparison with PEI25K in 293T cells. Furthermore, pre-incubation of PMAC-g-PEI1800 showed a weakening binding capacity with DNA. The biodegradability of PMAC-g-PEIx can facilitate the efficient release of pDNA from polyplexes and reduce cell cytotoxicity. These results suggested that PMAC-g-PEIx would be a promising non-viral biodegradable vector for gene delivery system.     

Preparation and characterization of cationic PLGA nanospheres as DNA carriers

Nanoparticles formulated from biodegradable polymers such as poly(lactic acid) (PLA) and poly(lactide-co-glycolide) (PLGA) are being extensively investigated as non-viral gene delivery systems due to their controlled release characteristics and biocompatibility. PLGA nanoparticles for DNA delivery are mainly formulated by an emulsion-solvent evaporation technique using PVA as a stabilizer generating negatively charged particles and heterogeneous size distribution. The objective of the present study was to formulate cationically modified PLGA nanoparticles with defined size and shape that can efficiently bind DNA. An Emulsion-diffusion-evaporation technique to make cationic nanospheres composed of biodegradable and biocompatible co-polyester PLGA has been developed. PVA-chitosan blend was used to stabilize the PLGA nanospheres. The nanospheres were characterized by atomic force microscopy (AFM), photon-correlation spectroscopy (PCS), and Fourier transform infrared spectroscopy (FTIR). Zeta potential and gel electrophoresis studies were also performed to understand the surface properties of nanospheres and their ability to condense negatively charged DNA. The designed nanospheres have a zeta potential of 10mV at pH 7.4 and size under 200nm. From the gel electrophoresis studies we found that the charge on the nanospheres is sufficient to efficiently bind the negatively charged DNA electrostatically. These cationic PLGA nanospheres could serve as potential alternatives of the existing negatively charged nanoparticles.     

Development of retroviral vectors as safe, targeted gene delivery systems

The transfer of genes of potential therapeutic benefit is presently being attempted in the clinic to treat a number of genetic and virally induced diseases. Many of these protocols use retroviral vectors derived from murine leukemia retroviruses as gene delivery systems. Although these viral delivery systems are well suited for this purpose, a number of their characteristics, some of which are discussed here, are still troublesome. Future retroviral vectors will incorporate nonretroviral features and will be tailored to desired needs for specific uses. These vectors will be safer, more efficient, and targeted in their delivery. Further, expression of the therapeutic genes carried will be limited to the specific target cell type. Some of the recent advances that have been made towards this goal are reviewed here.     

可生物降解聚合物作为药物载体的应用进展

目前作为控制释放体系的药物载体材料大多是高分子聚合物材料。生物降解聚合物在一定时间内能被水解或酶解成小分子,可通过生理途径代谢排出体外,不需二次手术取出载体材料,因此比生物惰性材料更安全、更可靠,有更好的生物相容性,成为了药物载体的首选材料。简要综述了主要常用生物降解性聚合物在药物控释体系中的应用进展。     

Thermoresponsive nanostructured polycarbonate block copolymers as biodegradable therapeutic delivery carriers

Water-soluble, thermoresponsive block copolymers based on a biodegradable platform were synthesized by the ring opening polymerization of cyclic carbonate monomers functionalized with hydrophilic and hydrophobic groups for application as nanocarriers in medicine. The approach based on cyclic carbonate monomers derived from 2,2-bis(methylol)propionic acid (bis-MPA) allowed a simple and versatile route to functional monomers capable of undergoing ring opening polymerization (ROP). The resulting polymers possessed the predicted molecular weights based on the molar ratio between monomers to initiators and the narrow molecular weight distributions. Transmittance measurement for aqueous polymer solutions provided an evidence for temperature-responsiveness with lower critical solution temperature (LCST) in the range of 36?°C-60?°C, depending on the molecular weight of hydrophilic poly(ethylene glycol) (PEG) chains, compositions of copolymers, molar ratios of hydrophilic to hydrophobic monomers in the corona, and the hydrophobic core. This study showed synthetic advancement toward the design and preparation of biodegradable thermoresponsive polymers with extremely low CMC values for injectable drug delivery systems. TRC350-10,30,60, which possessed an LCST of 36?°C in PBS, was identified as a useful model polymer. Paclitaxel, an anti-cancer drug, was loaded into the micelles efficiently, giving rise to nano-sized particles with a narrow size distribution. Paclitaxel release from the micelles was faster, and cellular uptake of the micelles was higher at the body temperature (i.e. 37?°C) as compared to a temperature below the LCST. While the polymer was not cytotoxic, paclitaxel-loaded micelles killed HepG2 human liver carcinoma cells more efficiently at the body temperature as compared to free paclitaxel and paclitaxel-loaded micelles at the temperature below the LCST. These micelles are ideally suited to deliver anti-cancer drugs to tumor tissues through local injection.     

Nanocapsules as drug delivery systems

Dispersed polymer nanocapsules can serve as nano-sized drug carriers to achieve controlled release as well as efficient drug targeting. The dispersion stability and the primary physiological response are mainly determined by the type of the surfactant and the nature of the outer coating. Their release and degradation properties largely depend on the composition and the structure of the capsule walls. Another important criterion is the capsule size, where an optimum is generally seen for radii ranging between 100 and 500 nm. Nanocapsules can be prepared by four principally different approaches: interfacial polymerization, interfacial precipitation, interfacial deposition, and self assembly procedures. All these procedures offer their individual advantages and disadvantages when it comes to the design of optimized drug carrier systems. The most important capsule parameters such as capsule radius distribution, the capsule surface, the thickness and the permeability of the capsule membrane and its thermal or chemical decomposition, are discussed and examples are shown. In combination with efficient preparation procedures, nanocapsule dispersions allow for new and promising approaches in many kinds of pharmaceutical therapies.     

Hollow chitosan-silica nanospheres as pH-sensitive targeted delivery carriers in breast cancer therapy

Promising drug nanocarriers consisting of mono-dispersed and pH sensitive chitosan-silica hollow nanospheres (CS-SiO(2) HNPs) suitable for breast cancer therapy are produced and investigated. The SiO(2) HNPs are fabricated using a one-step, one-medium process which obviates the need for post-treatment to remove the templates, additional dissolution, or calcination. Taking advantage of the cross-linking reaction with (3-Glycidyloxypropyl) trimethoxysilane (GTPMS), cationic polysaccharide-chitosan decorates the surface and produces pH sensitive CS-SiO(2) HNPs. The materials enable controlled release of loaded drugs in pericellular and interstitial environments. In particular, the antibody molecule (to ErbB 2) can be conjugated onto the surface of the CS-SiO(2) HNPs thereby allowing the hollow nanospheres to serve as a targeted delivery agent to breast cancer cells. TNF-α are delivered to MCF-7 breast cancer cells under both in vitro and in vivo conditions to suppress the growth of cancerous cells and even kill them with high therapeutic efficacy. Owing to their hollow inner cavity and porous structures, the CS-SiO(2) HNPs are excellent pH-responsive targeted nanocarriers.     

Microparticles as vaccine adjuvants and delivery systems

Adjuvants can be broadly divided into two groups, based on their principal mechanisms of action: vaccine delivery systems and immunostimulatory adjuvants. Vaccine delivery systems are generally particulate (e.g., emulsions, microparticles, immunostimulatory complexes and liposomes) and function mainly to target associated antigens into antigen-presenting cells. However, increasingly, more complex formulations are being developed in which delivery systems are exploited both for the delivery of antigens and also for the delivery of coadministered immunostimulatory adjuvants. The rationale for this approach is to ensure that both antigen and adjuvant are delivered into the same population of antigen-presenting cells. In addition, delivery systems can focus the effect of the adjuvants onto the key cells of the immune system and limit the systemic distribution of the adjuvant, to minimize its potential to induce adverse effects. The formulation and delivery of potent adjuvants in microparticles may allow the development of prophylactic and therapeutic vaccines against cancers and chronic infectious diseases, which are currently poorly controlled. In addition, microparticle formulations may also allow vaccines to be delivered mucosally.     

Synthesis and characterization of biodegradable polylactide-grafted dextran and its application as compatilizer

Brush-like biodegradable polylactide-grafted dextran copolymer (PLA-g-dextran) was by a bulk polymerization reaction using a trimethylsilyl-protected (TMS) dextran as macroinitiator and stannous octoate as catalyst. After the polymerization, the TMS groups could be easily removed by immersing the copolymer in methanol for 48 h. The PLA-g-dextran copolymers were characterized by (1)H NMR, GPC and intrinsic viscosity measurements. Besides, mouse 3T3 fibroblasts were cultured on these copolymeric substrates together with pure polylactide (PLA). Although the copolymers exhibited better hydrophilicity and cell affinity compared to pure PLA because of the incorporation of glucose units and the brush-like architecture, it was found that the cells still could not migrate into the center part of scaffold made of PLA-g-dextran copolymer. In result, PLA-g-dextran copolymers themselves were not an appropriate choice for the cell scaffold material, however, it could be used as compatilizer to ameliorate the compatibility between hydrophilic dextran and hydrophobic PLA due to its amphiphilic structure, which could improve the mechanical properties of PLA/dextran blends by reducing the phase separation between PLA and dextran. Therefore, the PLA/dextran blends, which had good cell affinity and moderate mechanical strength, might be prospect cell scaffold materials.     

Synthesis and characterization of biodegradable polyrotaxane as a novel supramolecular-structured drug carrier

Polyrotaxanes were synthesized as novel biodegradable polymers with supramolecular assembly and their properties evaluated in vitro. The synthesis of biodegradable polyrotaxanes consists of three steps: preparation of an inclusion complex consisting of α-cyclodextrins (α-CDs) and amino-terminated poly(ethylene glycol) (PEG); introduction of L-phenylalanine (L-Phe) at each complex terminal via peptide linkages; and hydroxypropylation of α-CDs in the polyrotaxanes. Succinimide ester of benzyloxycarbonyl-L-Phe was condensed with the terminal amino groups of the inclusion complex. ¹ H-NMR and GPC results showed that α-CDs were threaded onto a PEG chain and L-Phe moieties were introduced at each terminal of the PEG chain. Further, the amount of threaded α-CDs was found to be governed by the molecular weight of PEG. The hydroxypropylation of α-CDs improved the solubility of the polyrotaxanes in PBS (pH 7.4). The hydroxypropylated (HP-) polyrotaxanes were characterized by terminal peptide cleavage using papain. In vitro degradation of HP-polyrotaxanes revealed that HP-α-CDs threaded onto a PEG chain were released only when terminal peptide linkages were cleaved. Moreover, threaded HP-α-CDs onto a PEG chain was found to be completely released. Kinetics of terminal peptide cleavage were also evaluated by catalytic efficiency (k_cat/ K_m). The k_cat/ K_m values were found to be independent of the molecular weight of HP-polyrotaxanes but to be affected by terminal hydrophobic moieties. It is proposed that our designed polyrotaxanes are feasible as novel drug carriers.     

Development of bioactive and biodegradable chitosan-based injectable systems containing bioactive glass nanoparticles

There is increasing interest in the development of new tissue engineering strategies to deliver cells and bioactive agents encapsulated in a biodegradable matrix through minimally invasive procedures. The present work proposes to combine chitosan-beta-glycerophosphate salt formulations with bioactive glass nanoparticles in order to conceive novel injectable thermo-responsive hydrogels for orthopaedic reconstructive and regenerative medicine applications. The initial rheological properties and the gelation points of the developed organic-inorganic in situ thermosetting systems were revealed to be adequate for intracorporal injection. In vitro bioactivity tests, using incubation protocols in simulated body fluid (SBF), allowed the observation of bone-like apatite formation in the hydrogel formulations containing bioactive nanoparticles. The density of the apatite formed increased with increasing bioactive glass content and soaking time in SBF. These results indicate that the stimuli-responsive hydrogels could potentially be used as temporary injectable scaffolds in bone tissue engineering applications.     

Reduction biodegradable brushed PDMAEMA derivatives synthesized by atom transfer radical polymerization and click chemistry for gene delivery

Novel reducible and degradable brushed poly(2-(dimethylamino) ethyl methacrylate) (PDMAEMA) derivatives were synthesized and evaluated as non-viral gene delivery vectors. First, alkyne-functionalized poly(aspartic acid) with a disulfide linker between the propargyl group and backbone poly([(propargyl carbamate)-cystamine]-α,β-aspartamide) (P(Asp-SS-AL)) was synthesized. Second, linear low molecular weight (LMW) monoazido-functionalized PDMAEMAs synthesized via atom transfer radical polymerization were conjugated to the polypeptide side-chains of P(Asp-SS-AL) via click chemistry to yield high molecular weight (HMW) polyaspartamide-based disulfide-containing brushed PDMAEMAs (PAPDEs). The PAPDEs were able to condense plasmid DNA to form 100 to 200 nm polyplexes with positive ζ-potentials. Moreover, in the presence of dithiothreitol the PAPDEs degraded into LMW PDAMEMA, resulting in disintegration of the PAPDE/DNA polyplexes and subsequent release of plasmid DNA. In vitro experiments revealed that the PAPDEs were less cytotoxic and more effective in gene transfection than control 25 kDa poly(ethyleneimine) and HMW linear PDMAEMA. In conclusion, reducible and degradable polycations composed of LMW PDMAEMAs coupled to a polypeptide backbone via reduction-sensitive disulfide bonds are effective gene vectors with an excellent cytocompatibility.     

Synthesis and characterization of pH-sensitive glycopolymers for oral drug delivery systems

pH-sensitive hydrogels are suitable candidates for oral delivery of therapeutic peptides and proteins, due to their ability to respond to environmental pH changes. New pH-sensitive glycopolymers have been developed by free-radical photopolymerization of methacrylic acid and 2-methacryloxyethyl glucoside, using tetra(ethylene glycol) dimethacrylate as a cross-linking agent. To determine the suitability of these hydrogels as carriers for oral drug delivery devices, their swelling behavior was investigated as a function of the pH and copolymer compositions, and various structural parameters such as the number-average molecular weight between cross-links, Mc, the mesh size, xi, and the cross-linking density, rho(x), were calculated. The transition between the swollen and the collapsed states of these hydrogels was at a pH of 5. The swelling ratios of the hydrogels increased at pH values above 5. The mesh sizes of the hydrogels were between 18 and 35 A in the collapsed state (at pH 2.2) and between 70 and 111 A in the swollen state (at pH 7.0). Finally, as the cross-linking ratio of the copolymer increased, the swelling ratio of the hydrogels decreased at both pH 2.2 and 7.0.     

Synthesis and characterization of pH-sensitive glycopolymers for oral drug delivery systems

pH-sensitive hydrogels are suitable candidates for oral delivery of therapeutic peptides and proteins, due to their ability to respond to environmental pH changes. New pH-sensitive glycopolymers have been developed by free-radical photopolymerization of methacrylic acid and 2- methacryloxyethyl glucoside, using tetra(ethylene glycol) dimethacrylate as a cross-linking agent. To determine the suitability of these hydrogels as carriers for oral drug delivery devices, their swelling behavior was investigated as a function of the pH and copolymer compositions, and various structural parameters such as the number-average molecular weight between cross-links, M _c, the mesh size, ξ, and the cross-linking density, ρ _x, were calculated. The transition between the swollen and the collapsed states of these hydrogels was at a pH of 5. The swelling ratios of the hydrogels increased at pH values above 5. The mesh sizes of the hydrogels were between 18 and 35 Å in the collapsed state (at pH 2.2) and between 70 and 111 Å in the swollen state (at pH 7.0). Finally, as the cross-linking ratio of the copolymer increased, the swelling ratio of the hydrogels decreased at both pH 2.2 and 7.0.     

In vivo characteristics of low molecular weight copolymers composed of L-lactic acid and various DL-hydroxy acids as biodegradable carriers for drug delivery systems

Low molecular weight and amorphous copolyesters composed of 70 mol% L-lactic acid and 30 mol% DL-hydroxy acids such as DL-lactic acid, DL-alpha-hydroxy-n-butyric acid, DL-alpha-hydroxyisovaleric acid and DL-alpha-hydroxyisocaproic acid were synthesized by direct copolycondensation in the absence of catalysts, to evaluate their in vivo capabilities as biodegradable carriers for drug delivery systems. For this purpose, the copolyester was moulded into a small cylindrical specimen under melt-pressing technique and implanted subcutaneously in the back of male adult rats. The in vivo degradation pattern can be subdivided into three types: the formations of parabolic type (L-LA/DL-HBA copolymer), linear type (L-LA/DL-LA copolymer) and S type (L-LA/DL-HIVA and L-LA/DL-HICA copolymers). A luteinizing hormone-releasing hormone agonist, des-Gly10-(D-Leu6)-LH-RH ethylamide monoacetate (LH-RH agonist), was incorporated into the small cylinders of copolyester formulations, of which the strongest pharmacological influence was observed in a copoly(L-LA/DL-HICA) formulation system, resulting in the maintenance of effective pharmacological influence throughout an experimental period of 15 wk, at which the in vivo release rate of LH-RH agonist was held constant at approximately 45 micrograms/d.     

Core-shell nanospheres for oligonucleotide delivery. V: adsorption/release behavior of 'stealth' nanospheres

The adsorption/release behavior of oligodeoxynucleotides (ODNs) on new PEGylated core-shell polymethylmethacrylate nanospheres is described. The outer shell consists of alkyl chains containing quaternary ammonium groups and of poly(ethylene glycol) chains, both covalently bound to the inner core. Ion pair formation between negatively charged ODN phosphate groups and positively charged groups on the nanosphere surface is the main interaction mechanism. No cellular toxicity in HL60 cells is observed at nanosphere concentrations required for biologically active ODN delivery. These results indicate that these novel cationic polymeric nanoparticles are safe and represent promising vectors for oligonucleotide delivery.