Effects of incorporated drugs on degradation of novel 2,2'-bis(2-oxazoline) linked poly(lactic acid) films

Earlier studies have indicated that the degradation rate of poly(lactic acid) (PDLLA) can be modified by using 2,2′-bis(2-oxazoline) as a chain extender in polymer synthesis to form a lactic acid-based poly(ester-amide) (PEA). In the present study, the effect of an incorporated drug on the degradation rate of the PEA was evaluated. The model drugs, neutral guaifenesin, acidic sodium salicylate (pK_a 3.0) and basic timolol (pK_a 9.2), were incorporated into solvent cast PDLLA and PEA films. The drug content in the films was 2% (w/w). The degradation studies were carried out in PBS (pH 7.4, 37 °C); the resulting decrease in molecular weight of polymers was determined by size exclusion chromatography and the weight loss of films was measured. In addition, the drug release from the films in PBS (pH 7.4, 37 °C) was studied. The model drugs were released from the PDLLA and PEA films in a biphasic or triphasic manner. The final fast release phase of the drugs from both PDLLA and PEA films started when the molecular weight (M_n) of the polymer had decreased close to 15,000 g/mol. The degradation rate of the PDLLA films was clearly enhanced by incorporated sodium salicylate or timolol. Whereas, the degradation rate of the PEA film was not enhanced by the incorporated drugs. The present results indicate that when compared to the PDLLA film, degradation rate of the PEA film in the presence of the drug is more predictable.     

Clonazepam release from core-shell type nanoparticles of poly(-caprolactone)/poly(ethylene glycol)/poly(-caprolactone) triblock copolymers

The triblock copolymer based on poly(-caprolactone) (PCL) as hydrophobic part and poly(ethylene glycol) (PEG) as hydrophilic one was synthesized and characterized. Core-shell type nanoparticles of poly(-caprolactone)/poly(ethylene glycol)/poly(-caprolactone) (CEC) block copolymer were prepared by a dialysis technique. According to the amphiphilic characters, CEC block copolymer can self-associate at certain concentration and their critical association concentration (CAC) was determined by fluorescence probe technique. CAC value of the CEC-2 block copolymer was evaluated as 0.0030 g/l. CAC values of CEC block copolymer decreased with the increase of PCL chain length, i.e. the shorter the PCL chain length, the higher the CAC values. From the observation of transmission electron microscopy (TEM), the morphologies of CEC-2 core-shell type nanoparticles were spherical shapes. Particle size of CEC-2 nanoparticles was 32.3±17.3 nm as a monomodal and narrow distribution. Particle size, drug loading, and drug release rate of CEC-2 nanoparticles were changed by the initial solvents and the molecular weight of CEC. The degradation behavior of CEC-2 nanoparticles was observed by ¹H NMR spectroscopy. It was suggested that clonazepam (CNZ) release kinetics were dominantly governed by diffusion mechanism.     

Modeling of drug release from biodegradable polymer blends

Numerous mathematical models that predict drug release from degradable systems have been reported. Most of these models cater only to single step, diffusion-controlled release while a few attempt to describe bi-phasic release. All these models, however, are only applicable to drug release from single (unblended) degradable polymer systems.In this paper, we propose and test novel models for drug (notably paclitaxel) release from films made of neat poly (ε-caprolactone) PCL, neat poly (dl-lactide-co-glycolide) PLGA and their blends. The model developed for neat PCL consists of two terms: initial burst and diffusional release. On the other hand, a more complex model proposed for tri-phasic release from neat PLGA consists of burst release, degradative (relaxation-induced) drug dissolution release and diffusional release.Finally, this very first model to predict release from blend of PLGA and PCL was developed based on a heuristic approach. Drug distribution between PCL-rich and PLGA-rich phases is dictated by partition coefficient, and the overall fraction of drug release is a summation of drug released from the two phases. The proposed models exhibited good prediction of the experimental data.     

Preparation and in vitro characterization of paclitaxel-loaded pH-responsive polymeric micelles based on poly(2-ethyl-2-oxazoline)-vitamin E succinate

To ensure the delivery of antitumor drugs to tumor site and quick release in tumor cells, we designed and prepared pH-sensitive polymeric micelles by combining cationic ring-opening polymerization of 2-ethyl-2-oxazoline (EOz) with vitamin Esuccinate (VES), and then encapsulating paclitaxel (PTX) into the micelles self-assembled by poly(2-ethyl-2-oxazoline)-vitamin E succinate (PEOz-VES). The structure of the synthesized PEOz-VES was confirmed by ¹H NMR spectrum, and the molecular weight measured by GPC was 1212 g/mol. The pK_a of PEOz-VES with a low critical micelle concentration of (5.84±0.02) mg/L was determined to be 6.01. The PTX-loaded PEOz-VES polymeric micelles prepared by film hydration method were characterized to have a nanoscaled size of about 30 nm in diameter, a positive Zeta potential of 4.86 mV and uniform spherical morphology by TEM observation. The drug loading content and encapsulation efficiency were (2.63±0.16)% and (84.1±3.38)%, respectively. The in vitro release behavior of PTX from PEOz-VES micelles in PBS displayed pH-dependent pattern and was gradually accelerated with decrease of pH value, implying that the micelles could distinguish endo/lysosomal pH and tumor extracellular pH from physiological pH by accelerating drug release. Therefore, the designed PEOz-VES micelles might have significant promise for anti-cancer drug delivery.     

Synthesis of redox derivatives of lysine and related peptides containing phenothiazine or tris(2,2′-bipyridine)ruthenium(II)

Boc-l -Lysine derivatives and lysine-containing peptides bearing the electron donor 10H-phenothiazine (PTZ) or the redox chromophore tris(2,2′-bipyridine)ruthenium(II) dication ([Rub₃,]^2H, where b is 2,2-bipyridine) have been synthesized and characterized. SeO₂ oxidation (53% yield) of 4,4′-dimethyl-2,2′-bipyridine, Ag_2:O oxidation (85% yield) of the monoaldehyde, complexation (96% yield) of 4′-methyl-2,2′-bipyridine-4-carboxylic acid (m-OH) with Rub₂Cl_2:. activation (81% yield) of the acid [Rub₂m-OH]²⁺ (PF₆^?)₂, and condensation (83% yield) of the succinimido ester [Rub₂m-OSu]²⁺ (PF₆^?)₂ with Boc-Lys furnished the protected redox-chromophore module [Boc-Lys(Rub₂m)-OH]²⁺(PF₆^?)₂ in 29% overall yield over five steps. The first two steps constitute the first practical synthesis of the monocarboxylic acid m-OH (45% overall yield). Also prepared were m-OSu, Boc-Lys(m)-OH, Boc-Lys(m)-OCH₃, and [Rub₂m-NHCH₃]²⁺ (PF₆^?)_2:. Activation (91% yield) of 3-(10H-phenothiazine-10)propanoic acid (PTZpn-OH) and condensation (92% yield) of the succinimido ester PTZpn-OSu with Boc-Lys furnished the protected electron-donor module Boc-Lys(PTZpn)-OH (84% overall yield). The latter was used in solid-phase syntheses of two redox tripeptides. CH₃CO-Ala-Lys(PTZpn)-Ala-OH and [Rub₂m-Ala-Lys(PTZpn)-Ala-OH]² (PF₆^?)₂. The electrochemical properties of these redox amino acids and peptides were similar to those of PTZpn-OH, [Rub₂ m-OH]2⁺(PF₆)₂. or [Rub₂ m-NHCH₃]²⁺ (PF₆^?)₂. Lys(PTZpn). [Lys(Rub₂m)]²⁺ (PF₆)_2:. and other redox modules may be useful for engineering light-harvesting proteins, photovoltaic cells, and other molecular electronic devices.     

Preparation,characterization, and in vitro/vivo evaluation of dexamethasone/poly(ε-caprolactone)-based electrode coatings for cochlear implants

With dexamethasone as the model drug and polycaprolactone (PCL) as the carrier material, a drug delivery coating for cochlear electrodes was prepared, to control cochlear fibrosis caused by cochlear implantation. A dexamethasone/poly (ε-caprolactone)-based electrode coating was prepared using the impregnation coating method. Preparation parameters were optimized, yielding 1 impregnation instance, impregnation time of 10 s, and PCL concentration of 10%. The coating was characterized in vitro using scanning electron microscopy, a universal machine, high-performance liquid chromatography, and CCK-8. The surface was porous and uniformly thick (average thickness, 48.67 µm)—with good flexibility, long-term slow drug release, and optimal drug concentration—and was biologically safe. The experimental results show that PCL is an ideal controlled-release material for dexamethasone as a drug carrier coating for cochlear implants.     

Drug release from thermo-responsive self-assembled polymeric micelles composed of cholic acid and poly(N-isopropylacrylamide)

Cholic acid, conjugated with amine-terminated poly(N-isopropylacrylamide) (abbreviated as CA/ATPNIPAAm), was synthesized by a N, N'-dicyclohexyl carbodiimide (DCC)-mediated coupling reaction. Self-assembled CA/ATPNIPAAm micelles were prepared by a diafiltration method in aqueous media. The CA/ATPNIPAAm micelles exhibited a lower critical solution temperature (LCST) at 31.5 degrees C. Micelle sizes measured by photon correlation spectroscopy (PCS) were approximately 31.6+/-5.8 nm. The CA/ATPNIPAAm micelles were spherical and their thermal size transition was observed by transmission electron microscope (TEM). A fluorescence probe technique was used for determining the micelle formation behavior of CA/ATPNIPAAm in aqueous solutions using pyrene as a hydrophobic probe. The critical micelle concentration (CMC) was evaluated as 8.9 x 10(-2) g/L. A drug release study was performed using indomethacin (IN) as a hydrophobic model drug. The release kinetics of IN from the CA/ATPNIPAAm micelles revealed a thermo-sensitivity by the unique character of poly(N-isopropylacrylamide) i.e. the release rate was higher at 25 degrees C than at 37 degrees C.     

Synthesis of a novel biodegradable poly(ester amine) (PEAs) copolymer based on low-molecular-weight polyethyleneimine for gene delivery

In this paper, a novel biodegradable poly(ester amine) (PEA) copolymer was successfully prepared from low-molecular-weight polyethyleneimine (PEI, Mn = 1800) and poly(-caprolactone)–Pluronic–poly(-caprolactone) (PCFC) copolymers. According to the results of agarose gel electrophoresis, particle sizes and zeta potential measurement and transfection efficiency, these PEA copolymers showed great ability to condense plasmid DNA effectively into nano-complexes with small particle size (≤200 nm) and moderate zeta potential (≥12 mV) at proper polymeric carrier/DNA weight ratio. Compared with low-molecular-PEI (Mn = 1800), the obtained PEAs exhibited higher transfection efficiency as well as lower cytotoxicity. These results indicated that such PEAs might have great potential application in gene delivery system.     

Injectable and biodegradable poly(organophosphazene) hydrogel as a delivery system of docetaxel for cancer treatment

Abstract

Although docetaxel (DTX) is an advanced taxoid, further augmentation of its properties is still required, such as improvement in its low aqueous solubility. Herein, we report the development of biodegradable/injectable poly(organophosphazene) (PPZ) hydrogels for the delivery of DTX without the use of organic solvents. An aqueous solution of PPZ containing α-amino-ω-methoxy-poly(ethylene glycol) (AMPEG) 750 instead of AMPEG 550 was prepared, thereby increasing the erosion capacity of the hydrogel by judicious balance of the hydrophobic/hydrophilic moieties. The safety of the hydrogel was demonstrated using a biocompatibility test. The PPZ aqueous solution (8?wt%) containing DTX exhibited a thermosensitive sol–gel–sol transition that was independent of the concentration of DTX (1–3?mg/mL). The in vitro release study indicated that the dominant release mechanism was either erosion or diffusion/erosion-controlled release depending on the DTX content of the hydrogel. The in vivo anticancer effect of the intratumorally injected PPZ system in human gastric cancer cell-xenografted mice was evaluated, which demonstrated a significantly (p?<?0.01) enhanced effect of the DTX-PPZ hydrogel system compared to the control (DTX solution, i.v.). In conclusion, the PPZ hydrogel may be a promising candidate for DTX delivery, affecting a decrease in the size of tumors with little toxicity prior to exeresis.     

Drug release from the enzyme-degradable and pH-sensitive hydrogel composed of glycidyl methacrylate dextran and poly(acrylic acid)

Hydrogels composed of glycidyl methacrylate dextran (GMD) and poly(acrylic acid, PAA) were prepared by UV irradiation method for colon-specific drug delivery. GMD was synthesized by coupling of glycidyl methacrylate to dextran in the presence of 4-(N,N-dimethylamino)pyridine. GMD was photo-polymerized by ammonium peroxydisulfate as initiating system in phosphate-buffered solution (0.1 M, pH 7.4). And then, acrylic acid monomer was added and subsequently heat-polymerized by 2,2'-azobisisobutyronitrile as an initiator. The hydrogels exhibited high swelling ratio (about 20) at 37 degrees C, and showed a pH-dependent swelling behavior. In addition, the swelling ratio of the hydrogel was remarkably enhanced to about 45 times in the presence of dextranase at pH 7.4. The swelling-deswelling behavior proceeded reversibly for the GMD/PAA hydrogels between pH 2 and pH 7.4. Release of 5-aminosalicylic acid from the GMD/PAA hydrogels was evaluated in simulated gastrointestinal pH fluids in the absence or presence of dextranase. We concluded that the hydrogels prepared could be used as a dual-sensitive drug carrier for sequential release in gastrointestinal tract.     

Comparison of endocrine-mediated effects of two bisphenol A related compounds, 2,2-bis(4-cyanatophyenyl)propane and 4,4'-cyclohexylidenebisphenol, based on subacute oral toxicity studies using rats

The purpose of this study was to compare endocrine-mediated effects of bisphenol A related compounds, 2,2-bis(4-cyanatophyenyl)propane and 4,4′-cyclohexylidenebisphenol with reference to OECD Test Guideline No. 407. Rats were orally gavaged with 0, 4, 20, and 100 mg/kg/day of 2,2-bis(4-cyanatophyenyl)propane, and 0, 30, 100, and 300 mg/kg/day of 4,4′-cyclohexylidenebisphenol for at least 28 days beginning at 8 weeks of age. Endocrine-mediated effects were not observed in rats given 2,2-bis(4-cyanatophyenyl)propane. Male accessory sex organ weights decreased in the 4,4′-cyclohexylidenebisphenol 300 mg/kg group and serum T4 values increased in all male groups treated with this compound. Our results suggest that endocrine-mediated changes caused by the present bisphenol related compound can be divided into estrogenic or thyroid hormonal effects, and estrogenic effects observed in the repeated-dose study were related to their estrogenic potency confirmed by uterotrophic assay.     

Folate-modified poly(2-ethyl-2-oxazoline) as hydrophilic corona in polymeric micelles for enhanced intracellular doxorubicin delivery

The transmembrane transport of drug loaded micelles to intracellular compartment is quite crucial for efficient drug delivery. In the current study, we investigated the cellular internalization and anticancer activity of doxorubicin loaded micelles with folate modified stealthy PEOz corona. Folate-decorated micelles incorporating doxorubicin were characterized for particle size, degree of folate decoration, drug loading content and encapsulation efficiency, morphology, and surface charge. The targeting capability and cell viability were assessed using HeLa, KB, A549 and MCF-7/ADR cell lines. In vitro study clearly illustrated the folate receptor (FR) mediated targeting of FA modified micelles to FR-positive human HeLa, KB and MCF-7/ADR cells, while specific delivery to FR-negative A549 cells was not apparently increased at the same experimental conditions. Cytotoxicity assay showed 60% and 58% decrease in IC₅₀ values for HeLa and KB cells, while only a slight decrease for A549 cells, following treatment with folate modified formulations. The enhanced intracellular delivery of FA modified micelles in MCF-7/ADR cells was also observed. In vivo antitumor tests revealed DOX entrapped FA-PEOz-PCL micelles effectively inhibited the tumor growth and reduced the toxicity to mice compared with free DOX. The current study showed that the targeted nano-vector improved cytotoxicity of DOX and suggested that this novel PEOz endowed stealthy micelle system held great promise in tumor targeted therapy.     

Comparison of 2,2-bis(bromomethyl)-1,3-propanediol induced genotoxicity in UROtsa cells and primary rat hepatocytes: Relevance of metabolism and oxidative stress

2,2-Bis(bromomethyl)-1,3-propanediol (BMP) is a brominated flame retardant used in urethane foams and polyester resins. In a two year dietary study, BMP caused neoplastic lesions at multiple sites including the urinary bladder of both rats and mice. However, liver was not a target tissue. We previously reported that BMP elicited oxidative DNA damage in a human uroepithelial cell line (UROtsa). The present in vitro study investigated the susceptibility of target (UROtsa cells) and non-target cells (primary rat hepatocytes) to BMP-induced genotoxicity. In contrast to hepatocytes, BMP exhibited greater genotoxic potential in UROtsa cells as evidenced by the concentration dependent increase in DNA strand breaks and DNA binding. Total content of intracellular GSH quantified in UROtsa cells (2.7 ± 1.0 nmol/mg protein) was 4 fold lower than that in hepatocytes (10.7 ± 0.3 nmol/mg protein). HPLC analysis indicated BMP was not metabolized and/or consumed in UROtsa cells at any of the concentrations tested (10–250 μM) but was extensively converted to a mono-glucuronide in hepatocytes. These results demonstrate that a target cell line such as UROtsa cells are more susceptible to BMP-induced DNA damage when compared to non-target cells. This increased susceptibility may relate to the deficiency of antioxidant and/or metabolic capabilities in UROtsa cells.     

Norfloxacin-Poly(l-Lysine Citramide Imide) Conjugates and Structure-dependence of the Drug Release

Norfloxacin (Nflx), an antibiotic which is active against some intracellular bacteria, was coupled to a polymeric carrier, namely poly(_l-lysine citramide) via a lysine or an ethylcarbamate spacer to obtain a macromolecular prodrug. The carrier, which derived from the two metabolites citric acid and _l-lysine, is known to be biocompatible and slowly degradable under slight acidic conditions. Conjugates were characterised by UV, ¹H and ¹³C NMR and SEC. The presence of Norfloxacin and the lysine type spacer caused chain aggregation, due to a probable physical cure. The release of Norfloxacin from these prodrugs and from a prodrug where Norfloxacin is bound to the carrier backbone without spacer arm was investigated comparatively in vitro. Conjugation via a carbamate-type linkage appeared as a method to achieve the release of Norfloxacin from a PLCA-type conjugate at neutral.     

Drug release from core-shell type nanoparticles of poly(DL-lactide-co-glycolide)-grafted dextran

This study prepared core-shell type nanoparticles of a poly(DL-lactide-co-glycolide) (PLGA) grafted-dextran. The synthesis of the PLGA-dextran conjugate was confirmed by Fourier transform-infrared (FT-IR) spectroscopy. The PLGA grafted-dextran was able to form nanoparticles in water by self-assembly and their particle size was 245.3?±?95.1?nm. From fluorescence probe study using pyrene as a hydrophobic probe, critical association concentration (CAC) values were determined from the fluorescence excitation spectra and were found to be 0.006?g?l^?1. Morphological observations using a scanning electron microscope (SEM) showed that the polymeric nanoparticles of the PLGA-dextran conjugate have uniformly spherical shapes. Their size and morphology provide them with acceptable properties for use as a drug-targeting carriers. Drug release from core-shell type nanoparticles was faster in the presence of dextranase, indicating that core-shell type nanoparticles of PLGA grafted-dextran can be used as an oral drug carriers.     

The microencapsulation of protein using a novel ternary blend based on poly(a-caprolactone)

Abstract

Microspheres with an entrapped protein were prepared from poly(e-caprolac-tone) (PCL), and a novel ternary blend, comprising of high and low molecular weight PCL in combination with poloxamer 181, a triblock copolymer of poly(ethylene oxide)-poly(propylene oxide)-poly(ethylene oxide). The inclusion of low molecular weight PCL served to enhance phase mixing by a reduction in the molecular weight of the polymeric components. Encapsulation of the protein, bovine serum albumin, was possible using a water-in-oil-in-water multiple emulsion solvent evaporation technique. Microspheres prepared from unblended PCL were irregular and porous in nature. The presence of surface imperfections and macroscopic pores was attributable to the high rate of crystallization of the PCL polymer from solution. The inclusion of poloxamer 181 into the matrix retarded the rate of crystallization of the PCL, thereby enhancing particulate sphericity and regularity. Manipulation of the process parameters of blended microspheres provided a means of controlling the particle size and the entrapment efficiency of the protein. The influence of variables such as protein to polymer ratio, internal phase volume and emulsifier concentration in both the internal and external aqueous phases, on the properties of the microspheres was investigated. A mean particle size ranging from 10 to 42 μm could be achieved by altering the internal phase volume of the primary emulsion, whilst a high protein entrapment (11% w/w) was possible with a protein to polymer ratio of 1:4. Native-PAGE analysis of the entrapped protein indicated a maintenance of bulk structural integrity.     

2-(2‘-Pyridyl)-ethyl-ester (Pet ester) derivatives of polyfunctional amino acids

The 2-(2′-pyridyl)-ethyl-esters (Pet-esters) of bi- and tri-functional amino acids are introduced as a semipermanent protecting group in peptide synthesis.     

Drug release behaviors of a pH sensitive semi-interpenetrating polymer network hydrogel composed of poly(vinyl alcohol) and star poly[2-(dimethylamino)ethyl methacrylate

A series of pH sensitive semi-interpenetrating polymer network (semi-IPN) structural hydrogels composed of poly(vinyl alcohol) (PVA) and 21-arm star poly[2-(dimethylamino)ethyl methacrylate] (star PDMAEMA) with different molecular weight were prepared. Riboflavin was used as a model drug to evaluate the drug loading capacities and drug release behaviors of the semi-IPN structural hydrogels. The molecular weight of the star PDMAEMA polymers was calculated by GPC, and the formation of semi-IPN structure was confirmed by FTIR and SEM. It was found that the molecular weight of star PDMAEMA has significant effect on the structure, swelling ratio and drug release behaviors of the semi-IPN hydrogel at different pH conditions. The results suggested that the PVA/star PDMAEMA-50,000 hydrogel exhibited highest swelling ratio and drug loading capacity. The pH-sensitive semi-IPN hydrogel based on star PDMAEMA could be a promising drug delivery system due to the controllable porous structure.     

Drug release mechanism of paclitaxel from a chitosan–lipid implant system: Effect of swelling, degradation and morphology

Localized and sustained delivery of anti-cancer agents to the tumor site has great potential for the treatment of solid tumors. A chitosan–egg phosphatidylcholine (chitosan–ePC) implant system containing PLA-b-PEG/PLA nanoparticles has been developed for the delivery of paclitaxel to treat ovarian cancer. Production of volumes of ascites fluid in the peritoneal cavity is a physical manifestation of ovarian cancer. In vitro release studies of paclitaxel from the implant were conducted in various fluids including human ascites fluid. A strong correlation (r² = 0.977) was found between the release of paclitaxel in ascites fluid and PBS containing lysozyme (pH 7.4) at 37 °C. The drug release mechanism for this system was proposed based on swelling, degradation and morphology data. In addition, in vitro release of paclitaxel was found to be a good indicator of the in vivo release profile (correlation between release rates: r² = 0.965). Release of paclitaxel was found to be sustained over a four-week period following implantation of the chitosan–ePC system into the peritoneal cavity of healthy Balb/C mice. Also, the concentrations of paclitaxel in both plasma and tissues (e.g. liver, kidney and small intestine) were found to be relatively constant.