Biodegradable poly(ɛ-caprolactone)–poly(ethylene glycol) copolymers as drug delivery system

Poly(?-caprolactone)–poly(ethylene glycol) (PCL–PEG) copolymers are important synthetic biomedical materials with amphiphilicity, controlled biodegradability, and great biocompatibility. They have great potential application in the fields of nanotechnology, tissue engineering, pharmaceutics, and medicinal chemistry. This review introduced several aspects of PCL–PEG copolymers, including synthetic chemistry, PCL–PEG micro/nanoparticles, PCL–PEG hydrogels, and physicochemical and toxicological properties.     

Concanavalin A-conjugated poly(ethylene glycol)–poly(lactic acid) nanoparticles for intranasal drug delivery to the cervical lymph nodes

Abstract

Concanavalin A (ConA)-conjugated poly(ethylene glycol)–poly(lactic acid) nanoparticles (ConA-NPs) were prepared for targeted drug delivery to the cervical lymph nodes after intranasal administration. ConA, a lectin specifically binding to α-mannose and α-glucose, was covalently conjugated on NPs without loss of its carbohydrates binding bioactivity. In vitro cellular uptake experiment demonstrated that NPs could be uptaken by Calu-3 cells in a time- and concentration-dependent manner, and conjugation of ConA on NPs could significantly increase the rate and amount of cellular uptake. ConA-NP showed no obvious toxicity to Calu-3 cells in vitro or to the nasal cilia of rats in vivo. Compared with NPs without ConA, ConA-NP is more effective in targeting drugs to the deep cervical lymph nodes, as evidenced by 1.36–2.52 times increase of targeting efficiency, demonstrating that ConA-NP is a potential carrier for targeted drug delivery to the cervical lymph nodes via nasal route.     

Formulation of highly soluble poly(ethylene glycol)‐peptide DNA condensates

Two poly(ethylene glycol) (PEG)‐peptides were synthesized and tested for their ability to bind to plasmid DNA and form soluble DNA condensates with reduced spontaneous gene expression. PEG‐vinyl sulfone or PEG‐orthopyridyl disulfide were reacted with the sulfhydryl of Cys‐Trp‐Lys₁₈ (CWK₁₈) resulting in the formation of nonreducible (PEG‐VS‐CWK₁₈) and reducible (PEG‐SS‐CWK₁₈) PEG‐ peptides. Both PEG‐peptides were prepared on a micromole scale, purified by RP‐HPLC in >80% yield, and characterized by 1H NMR and MALDI‐TOF. PEG‐peptides bound to plasmid DNA with an apparent affinity that was equivalent to alkylated (Alk)CWK₁₈, resulting in DNA condensates with a mean diameter of 80–90 nm and Z (zeta) potential of +10 mV. The particle size of PEG‐peptide DNA condensates was constant throughout the DNA concentration range of 0.05–2 mg/mL, indicating these to be approximately 20‐fold more soluble than AlkCWK₁₈ DNA condensates. The spontaneous gene transfer to HepG2 cells mediated by PEG‐VS‐CWK₁₈ DNA conden‐ sates was over two orders of magnitude lower than PEG‐SS‐CWK₁₈ DNA condensates and three orders of magnitude lower than AlkCWK₁₈ DNA condensates. PEG‐VS‐CWK₁₈ efficiently blocked in vitro gene transfer by reducing cell uptake. The results indicate that a high loading density of PEG on DNA is necessary to achieve highly soluble DNA condensates that reduce spontaneous in vitro gene transfer by blocking nonspecific uptake by HepG2 cells. These two properties are important for developing targeted gene delivery systems to be used in vivo.     

Nifedipine encapsulated core-shell type nanoparticles based on poly(γ-benzyl L-glutamate)/poly(ethylene glycol) diblock copolymers

The diblock copolymers based on PBLG and PEO (GE) were synthesized and characterized. Nanoparticles showed spherical shape from the observations of TEM and approved core-shell structure. Drug contents were increased with use of higher initial drug concentration and higher Mw of GE. Nifedipine (NFD) release rate was slower in longer PBLG chain length and higher NFD contents than short PBLG chain length and lower drug contents of NFD due to the hydrophobic interaction between PBLG domain and NFD.     

Polysorbate 80 coated poly (ɛ-caprolactone)-poly (ethylene glycol)-poly (ɛ-caprolactone) micelles for paclitaxel delivery

Physicochemical properties of two anhydrates (α-form and β-form) and three hydrates (hemihydrate, monohydrate and sesquihydrate) of sitafloxacin (STFX), a novel fluoroquinolone antibiotic, were investigated and correlated with the crystal structure of each crystalline form. STFX sesquihydrate showed larger weight change between 1% and 95% relative humidities (RHs) than other crystalline forms. In the crystal of sesquihydrate, STFX molecules form a channel structure where water molecules exist. Contrary to sesquihydrate, water molecules in a monohydrate are located in well-defined and isolated crystallographic sites. The β-form exhibited the worst photostability than any other forms under the irradiation of a D65 lamp. The intramolecular hydrogen bonding in the β-form caused a red shift on the solid-state UV spectrum by prolonging the conjugation system of the quinolone ring, resulting in greater absorption of photoenergy and consequent degradation. Solubility is also affected by the crystalline structure. Standard free energy of the formation of STFX molecule in each crystalline form and/or lattice energy binding STFX molecules to retain the crystal structure might cause a difference in solubility.     

Preparation of Tacrolimus loaded micelles based on poly(ɛ-caprolactone)-poly(ethylene glycol)-poly(ɛ-caprolactone)

Self-assembled polymeric micelles are widely applied in drug delivery system. In this study, Tacrolimus (FK506) loaded micelles were prepared based on biodegradable poly(?-caprolactone)-poly(ethylene glycol)-poly(?-caprolactone) (PCEC) copolymers. Micelles were prepared by self-assembly of triblock copolymer PCEC in distilled water triggered by its amphiphilic characteristics. Drug loading and encapsulation efficiency were determined by adjusting the weight ratio of FK506 and PCEC. The particle size distribution and variation of obtained micelles were determined using Malvern laser particle size analyzer, while the spherical geometry was observed on transmission electron microscope (TEM), and the crystallographic assays were fulfilled by X-ray diffractometer (XRD). Besides, in vitro release profile demonstrated a significant difference between rapid release of free Tacrolimus and much slower and sustained release of FK506 loaded micelles. These results suggested that we have successfully prepared Tacrolimus loaded micelles in an improved method which is safer and more efficient. The prepared micelles might be potential carriers for Tacrolimus delivery in immunosuppressive therapy.     

In vivo cancer imaging by poly(ethylene glycol)-b-poly(ɛ-caprolactone) micelles containing a near-infrared probe

Noninvasive near-infrared (NIR) fluorescence imaging is a promising technique for the intraoperative assessment of solid tumor removal. We incorporated a lipophilic NIR probe, 1,1′-dioctadecyltetramethyl indotricarbocyanine iodide (DiR), in poly(ethylene glycol)-b-poly(?-caprolactone) (PEG-b-PCL) micelles, resulting in DiR solubilization in water, occupying nanoscopic PEG-b-PCL micelles. DiR in a self-quenched or nonquenched state showed different kinetics of release from PEG-b-PCL micelles in vitro; however, both obtained high tumor delineation (tumor-to-muscle ratio of 30–43 from collected organs). These results suggest that PEG-b-PCL micelles with DiR are a promising nanosized imaging agent that will provide a basis for enhanced surgical guidance via NIR visualization of tumors.From the Clinical EditorIn this paper, noninvasive near-infrared fluorescence imaging coupled with specific lipophilic probes is discussed as a promising technique for intraoperative assessment of solid tumor removal, leading to optimized outcomes for in toto removal of tumors.     

Functionalized (poly(ɛ-caprolactone))₂-poly(ethylene glycol) nanoparticles with grafting nicotinic acid as drug carriers

Nicotinic acid was grafted on (poly(?-caprolactone))₂-poly(ethylene glycol) copolymers that were used for the preparation of nanoparticles with the objectives to monitor particle size and to optimize the drug loading capacity as well as the release profile of the particles. Increasing amounts of grafting nicotinic acid increased the particle size as a result of an enhanced hydrophobicity of the copolymer. Ibuprofen and indomethacin with two different molecular characteristics were selected as model drugs to be bound to the nanoparticles. The presence of grafting nicotinic acid enhanced the loading capacity for both drugs compared to the nanoparticles without nicotinic acid. However, no correlation between amount of grafting nicotinic acid and loading capacity was observed. The release characteristic of both drugs was fitted to the Higuchi model indicating Fickian diffusion. The release characteristic of indomethacin mainly depended on the crystalline property of the copolymer whereas that of ibuprofen was additionally influenced by the hydrogen bonding between drug and grafted copolymer.     

Prednisolone-α-cyclodextrin-star poly(ethylene glycol) polypseudorotaxane with delayed pH-sensitivity as a targeted drug delivery system

The acylation of prednisolone 20-hydrazone with star poly(ethylene glycol) tetracarboxylic acid (M = 20,000) has been used to prepare the corresponding pH-sensitive conjugate. With α-cyclodextrin, this conjugate forms a polypseudorotaxane, which was characterised by means of (1)H NMR spectra, powder X-ray diffraction patterns and STM microscopy. The rate of acid-catalysed hydrolysis of the conjugate was studied under in vitro conditions in model media of hydrochloric acid solutions, phosphate and acetate buffers (pH 2-5.8). The acid-catalysed hydrolysis (at pH 2) of the polypseudorotaxane was ca 3.5 times slower than that of the original conjugate. After 1h in this medium, 86% of the covalently attached prednisolone remained unchanged. The prepared polypseudorotaxane represents a promising peroral transport system of prednisolone with a pH-sensitive linker with delayed acid-catalysed hydrolysis thanks to protection at the molecular level using α-cyclodextrin.     

Biological evaluation of Fe3O4–poly(l-lactide)–poly(ethylene glycol)–poly(l-lactide) magnetic microspheres prepared in supercritical CO2

The biocompatibility of Fe₃O₄–poly(l-lactide)–poly(ethylene glycol)–poly(l-lactide) magnetic microspheres (Fe₃O₄–PLLA–PEG–PLLA MMPs) prepared in a process of suspension-enhanced dispersion by supercritical CO₂ (SpEDS) was evaluated at various levels: cellular, molecular, and integrated. At the cellular level, the investigations of cytotoxicity and intracellular reactive oxygen species (ROS) generation indicate that the polymer-coated MMPs (2.0 mg/mL) had a higher toxicity than uncoated Fe₃O₄ nanoparticles, which led to about 20% loss of cell viability and an increase (0.2 fold) in ROS generation; the differences were not statistically significant (p > 0.05). However, an opposite phenomenon was observed in tests of hemolysis, which showed that the MMPs displayed the weakest hemolytic activity, namely only about 6% at the highest concentration (20 mg/mL). This phenomenon reveals that polymer-coated MMPs created less toxicity in red blood cells than uncoated Fe₃O₄ nanoparticles. At the molecular level, the MMPs were shown to be less genotoxic than Fe₃O₄ nanoparticles by measuring the micronucleus (MN) frequency in CHO-K1 cells. Furthermore, the mRNA expression of pro-inflammatory cytokines demonstrates that polymer-coated MMPs elicited a less intense secretion of pro-inflammatory cytokines than uncoated Fe₃O₄ nanoparticles. Acute toxicity tests of MMPs show quite a low toxicity, with an LD₅₀ > 1575.00 mg/kg. The evidence of low toxicity presented in the results indicates that the Fe₃O₄–PLLA–PEG–PLLA MMPs from the SpEDS process have great potential for use in biomedical applications.     

Poly(ethylene glycol)-poly(ε-caprolactone) Iodinated Nanocapsules as Contrast Agents for X-ray Imaging

Purpose

Synthesis and formulation of iodinated PCL-mPEG nanocapsules as new original blood pool contrast agents for computed tomography.

Methods

PCL-mPEG was synthesized and formulated following the emulsion–solvent diffusion process, in the form of iodinated nanocapsules. Physico-chemical characterization of such nano-materials was performed by DLS and transmission electron microscopy. A stability study of the nanocapsules suspension was followed-up to 3 month. Blood biocompatibility was performed. Finally, the nanocapsules suspension radiopacity was evaluated in vitro then in vivo in mice as micro-CT contrast agent.

Results

In this study, the iodine concentration in nanocapsules suspension was about 70 mgI/mL. Besides, these nanocarriers appeared non-toxic, and stable in suspension. In vivo, i.v. administration of 10 μL/g of mouse body weight of theses nano-particles induced a vascular contrast enhancement of 168 HU and a half-life in blood of 4.2 +/? 0.5 h. Elimination route of these particles appears mainly performed by the liver, without sequestration in spleen and lymph nodes confirming their stealth properties.

Conclusions

This study proposes the first example of iodinated biodegradable polymeric blood pool contrast agent, able to induce an exploitable contrast enhancement. The main advantage of polymeric system compared to lipid ones, lies in their stability and handling, e.g. towards drying for storage.     

Paclitaxel-loaded polymeric micelles based on poly(ɛ-caprolactone)-poly(ethylene glycol)-poly(ɛ-caprolactone) triblock copolymers: in vitro and in vivo evaluation

The purpose of this study was to develop polymeric nanoscale drug-delivery system (nano-DDS) for paclitaxel (PTX) from poly(?-caprolactone)-poly(ethylene glycol)-poly(?-caprolactone) (PCL-PEG-PCL, PCEC) copolymers, intended to be intravenously administered, able to improve the therapeutic efficacy of the drug and devoid of the adverse effects of Cremophor EL. Both of the PTX-loaded polymeric micelles and polymersomes were successfully prepared from PCEC copolymers. The obtained PTX-loaded micelles exhibited core-shell morphology with satisfactory size (93 nm), and were favorable for intravenous injection. In vitro cytotoxicity demonstrated that the cytotoxic effect of PTX-loaded micelles was lower than that of Taxol (Bristol-Myers Squibb, Princeton, New Jersey). Pharmacokinetic results indicated that the PTX-loaded micelles had longer systemic circulation time and slower plasma elimination rate than those of Taxol. Furthermore, PTX-loaded micelles showed greater tumor growth-inhibition effect in vivo on EMT6 breast tumor, in comparison with Taxol. Therefore, the prepared polymeric micelles might be potential nano-DDS for PTX delivery in cancer chemotherapy.From the Clinical EditorIn this paper, a paclitaxel- loaded polymeric micelle system is demonstrated to provide optimized intravenous delivery method of this anti-cancer agent. While the study is early preclinical, this approach may have the potential to eventually be studied in clinical trials as well.     

Cholesterol–PEG comodified poly (N-butyl) cyanoacrylate nanoparticles for brain delivery: in vitro and in vivo evaluations

This study investigated cholesterol–polyethylene glycol (PEG) comodified poly (ethyleneglycol)-poly (lactide) nanoparticles (CLS-PEG NPs) as a novel, biodegradable brain drug delivery system and included an evaluation of its in vitro and in vivo properties. To this end, coumarin-6 (C6), a fluorescent probe, was encapsulated into CLS-PEG NPs by an emulsion polymerization method. We reported that the use of CLS-PEG NPs led to a sustained drug release in vitro. Additionally, cell viability experiments confirmed their safety. The uptake and transport of CLS-PEG NPs, by bEnd.3 cells (an immortalized mouse brain endothelial cell line), was significantly higher than that of a control C6 solution. An investigation of the uptake mechanisms of different NP formulations demonstrated that cholesterol modifications may be the primary way to improve the efficiency of cellular uptake, wherein macropinocytosis may be the most important endocytic pathway in this process. An investigation of the transport mechanisms of CLS-PEG NPs also implicated macropinocytosis, energy and cholesterol in bEnd.3 cells lines. Following an intravenous (IV) administration to rats, pharmacokinetic experiments indicated that C6-loaded CLS-PEG NPs achieved sustained release for up to 12?h. In addition, IV delivery of CLS-PEG NPs appeared to significantly improve the ability of C6 to pass through the blood–brain barrier: the concentration of C6 found in the brain increased nearly 14.2-fold when C6 CLS-PEG NPs were used rather than a C6 solution. These in vitro and in vivo results strongly suggest that CLS-PEG NPs are a promising drug delivery system for targeting the brain, with low toxicity.     

Surfactant-free microspheres of Poly(ε-caprolactone)/poly (ethylene glyco I )/poly(ε-caprolactone) triblock copolymers as a protein carrier

The aim of this study is to prepare biodegradable microspheres without the use of surfactants or emulsifiers for a novel sustained delivery carriers of protein drugs. A poly(epsilon-caprolactoney poly(ethylene glycol)/poly(epsilon-caprolactone) (CEC) triblock copolymer was synthesized by the ring-opening of epsilon-caprolactone with dihydroxy poly (ethylene glycol) to prepare surfactant-free microspheres. When dichloromethane (DCM) or ethyl formate (EF) was used as a solvent, the formation of microspheres did not occur. Although the microspheres could be formed prior to lyophilization under certain conditions, the morphology of microspheres was not maintained during the filtration and lyophilization process. Surfactant-free microspheres were only formed when ethyl acetate (EA) was used as the organic solvent and showed good spherical microspheres although the surfaces appeared irregular. The content of the protein in the microsphere was lower than expected, probably because of the presence of water channels and pores. The protein release kinetics showed a burst release until 2 days and after that sustained release pattern was showed. Therefore, these observations indicated that the formation of microsphere without the use of surfactant is feasible, and, this the improved process, the protein is readily incorporated in the microsphere.     

Evaluation of the polyethylene glycol–KF–water system in the context of purifying PEG–protein adducts

Covalent binding of PEG to proteins leads to conjugates widely investigated in several biotechnological processes. Their use as pharmaceuticals requires both careful purification and proper characterization. In this context, this paper examines the potentialities offered by hydrophobic interaction chromatography and compares aqueous potassium fluoride and ammonium sulfate as the eluents. Relative contribution of the various forces which dictate the chromatographic behaviour of PEG–protein adducts on Fractogel TSK–Butyl 650 is discussed.     

Body distribution and in situ evading of phagocytic uptake by macrophages of long-circulating poly （ethylene glycol） cyanoacrylate-co-nhexadecyl cyanoacrylate nanoparticles

AIM: To investigate the body distribution in mice of [14C]-labeled poly methoxyethyleneglycol cyanoacrylate-co-n-hexadecyl cyanoacrylate (PEG-PHDCA) nanoparticles and in situ evading of phagocytic uptake by mouse peritoneal macrophages. METHODS: PEG-PHDCA copolymers were synthesized by condensation of methoxypolyethylene glycol cyanoacetate with [14C]-hexadecyl-cyanoacetate. [14C]-nanoparticles were prepared using the nanoprecipitation/solvent diffusion method, while fluorescent nanoparticles were prepared by incorporating rhodamine B. In situ phagocytic uptake was evaluated by flow cytometry. Body distribution in mice was evaluated by determining radioactivity in tissues using a scintillation method. RESULTS: Phagocytic uptake by macrophages can be efficiently evaded by fluorescent PEG-PHDCA nanoparticles. After 48 h, 31% of the radioactivity of the stealth [14C]-PEG-PHDCA nanoparticles after iv injection was still found in blood, whereas non-stealth PHDCA nanoparticles were cleaned up from the bloodstream in a short time. The distribution of stealth PEG-PHDCA nanoparticles and non-stealth PHDCA nanoparticals in mice was poor in lung, kidney, and brain, and a little higher in hearts. Lymphatic accumulation was unusually high for both stealth and non-stealth nanoparticles, typical of lymphatic capture. The accumulation of stealth PEG-PHDCA nanoparticles in the spleen was 1.7 times as much as that of non-stealth PHDCA (P< 0.01). But the accumulation of stealth PEG-PHDCA nanoparticles in the liver was 0.8 times as much as that of non-stealth PHDCA (P< 0.05). CONCLUSION: PEGylation leads to long-circulation of nanoparticles in the bloodstream, and splenotropic accumulation opens up the potential for further development of spleen-targeted drug delivery.     

Biological evaluation of Fe₃O₄-poly(L-lactide)-poly(ethylene glycol)-poly(L-lactide) magnetic microspheres prepared in supercritical CO₂

Traditional gold mining, using metallic mercury (Hg(0)) to form gold amalgam, followed by burning to remove the Hg(0), is widely used in South America, Africa and Asia. The gold is sold to merchants who burn it again to eliminate remaining Hg(0). In Ecuador, 200 gold miners, 37 gold merchants and 72 referents were studied. The median Hg concentrations in urine (U-Hg) were 3.3 (range 0.23-170), 37 (3.2-420), and 1.6 (0.2-13)μg/g creatinine, respectively, and in whole blood (B-Hg) were 5.2, 30, and 5.0 μg/L, respectively. Biomarker concentrations among merchants were statistically significantly higher than among miners and referents; also the miners differed from the referents. Burning of gold amalgam among miners was intermittent; U-Hg decreased in the burning-free period. In computerized neuromotor examinations, B-Hg and U-Hg concentrations were associated with increases in the centre frequency of the tremor, as well as in reaction time and postural stability.Retention of Hg (B-Hg), and the elimination rate (U-Hg) appears to be modified by polymorphism in a gene of an enzyme in the glutathione synthesis (GCLM), but there were no significant genetic modifications for the associations between exposure and neurotoxicity.Thus, the gold merchants have a much higher exposure and risk than the miners, in whom the exposure varies over time. The metabolism of Hg is modified by genetic traits. The present exposure to Hg had limited neurotoxic effects.     

Does unintentional ingestion of ethylene glycol represent a serious risk?

The objective of this study was to evaluate data retrospectively on accidental ingestion of ethylene glycol (EG), based on calls to the Czech Toxicological Information Centre and from toxicological laboratories, in the years 2000-2004. All patients who ingested a known amount of EG and/or subjects with measured serum EG levels were included. A variety of clinical and laboratory parameters was collected. The medical records of 86 subjects, who had ingested from one to three swallows of EG, were analysed. The following findings emerged-metabolic acidosis (41%), vomiting (36%), nephrotoxicity (10%), and CNS depression (9%). In 15 children, the time interval between ingestion and hospitalisation was 1 hour or less. Ethanol was given to 12 children (four as first aid), and none developed hypoglycaemia. Of the 71 adults, 93% were treated with ethanol (19 as first aid). No side effects were documented. Seventeen patients received haemodialysis (HD). Two patients recovered without HD; their EG levels were higher than in the HD-treated patients. Unintentional EG ingestion usually involves ingestion of a small amount of EG, and was connected with mild signs of intoxication. Early therapy with ethanol alone appears sufficient in such cases, and represents no risk of adverse effects.     

Thermosensitive PEG–PCL–PEG (PECE) hydrogel as an in situ gelling system for ocular drug delivery of diclofenac sodium

Development of efficient ocular drug delivery systems was still a challenging task. The objective of this article was to develop a thermosensitive PEG–PCL–PEG (PECE) hydrogel and investigate its potential application for ocular drug delivery of diclofenac sodium (DIC). PECE block polymers were synthesized by coupling MPEG-PCL co-polymer using IPDI reagent, and then its sol–gel transition as a function with temperature was investigated by a rheometer. The results showed that 30% (w/v) PECE aqueous solution exhibited sol–gel transition at approximately 35?°C. In vitro release profiles showed the entrapped DIC was sustained release from PECE hydrogels up to 7 days and the initial drug loading greatly effect on release behavior of DIC from PECE hydrogels. MTT assay results indicated that no matter PECE or 0.1% (w/v) DIC-loaded PECE hydrogels were nontoxic to HCEC and L929 cells after 24?h culturing. In vivo eye irritation test showed that the instillation of either 30% (w/v) PECE hydrogels or 0.1% (w/v) DIC-loaded PECE hydrogels to rabbit eye did not result in eye irritation within 72?h. In vivo results showed that the AUC_0–48?h of 0.1% (w/v) DIC-loaded PECE hydrogels exhibited 1.6-fold increment as compared with that of commercial 0.1% (w/v) DIC eye drops, suggesting the better ophthalmic bioavailability could be obtained by the instillation of 0.1% (w/v) DIC-loaded PECE hydrogels.