Enthalpy-driven micellization of oligocarbonate-fluorene end-functionalized Poly(ethylene glycol)☆

A fluorescent pyrene probe method was applied to measure the critical micelle concentration (CMC) of oligocarbonate-fluorene end-functionalized poly(ethylene glycol) (FmE445Fm) triblock copolymers in water. The CMC decreases with lower temperature and higher values of the hydrophobic block length, m. When analyzed by a closed-assembly micelle model, the estimated energetic parameters find a negative ΔH°mic and small positive ΔS°mic suggestive of enthalpy-driven micellization, which differs from entropy-driven oxyethylene/oxybutylene triblock copolymers and octaethylene glycol-n-alkyl ethers. The enthalpy-driven micellization of FmE445Fm may result from the limited hydration of individual hydrophobic F blocks that leads to few hydrogen-bonded waters released during F block association. The π-π stacking oligocarbonate-fluorene system also observed enthalpy-entropy compensation when compared to a series of published data on diblock and triblock copolymer systems. An anomalously low partition equilibrium constant for m = 15.3 implies a tightly-packed core that excludes pyrene intercalation into the fluorene core. This is discussed along with the possible limited applicability to estimate the CMC and potential model drug molecule insertions into the intercalated micelle core.

Preparation and characterization of methoxy poly(ethylene glycol)/poly(ε-caprolactone) amphiphilic block copolymeric nanospheres for tumor-specific folate-mediated targeting of anticancer drugs

Biodegradable methoxy poly(ethylene glycol)/poly(-caprolactone) (MPEG/PCL) amphiphilic block copolymer nanospheres coupled to folic acid have been designed to target a folate-binding protein that is overexpressed on the surface of many tumoral cells. For this purpose, hydroxy groups terminated on the MPEG/PCL copolymer were converted into primary amino groups, which were used to conjugate with the carboxylic group of folic acid. Nanospheres were prepared by the formation of micelles of the copolymer with or without the anticancer agent paclitaxel. Folate-mediated MPEG/PCL nanospheres were compared with hydroxyl- and amino-terminated nanospheres in terms of their size, surface characteristics, and drug-loading efficiency. Regardless of the type of terminal group, the MPEG/PCL nanospheres showed a narrow size distribution with an average diameter <80 nm without paclitaxel, and an average diameter of 115 nm when loaded with the drug. The results from zeta potential and X-ray photoelectron spectroscopy measurements revealed that the folate molecules were partially exposed, and were expressed on the surface of the nanospheres allowing folate receptor recognition. In in vitro, cytotoxicity tests, the nanospheres loaded with paclitaxel showed a higher cell viability than in cases where paclitaxel was absent. Thus, folate-mediated nanospheres composed of MPEG and PCL are potentially new drug carriers for tumor cell-selective targeting treatments.

Indomethacin-loaded methoxy poly(ethylene glycol)/ poly(epsilon-caprolactone) diblock copolymeric nanosphere: pharmacokinetic characteristics of indomethacin in the normal Sprague-Dawley rats

We prepared the drug-loaded polymeric nanospheres composed of the methoxy poly(ethylene glycol) (MePEG) and poly(epsilon-caprolactone) (PCL) that showed a narrow size distribution and average diameter of less than 200 nm. We could obtain the nanosphere having a relatively high drug-loading efficiency of about 42% when the feed weight ratio of indomethacin (IMC) to polymer was 1:1. To investigate the IMC pharmacokinetics in the IMC-loaded MePEG/PCL nanosphere (DMEP70) using the rats as animal model, we analyzed the IMC concentration in plasma with HPLC after i.v. bolus administered at a dose of 10 mg/kg in free IMC (control) and IMC-loaded MePEG/PCL nanosphere (DMEP70) groups via tail vein. Pharmacokinetics parameters (mean +/- s.d.) such as the mean residence time (MRT, h), the steady-state volume of distribution (Vdss, l), the terminal half-time (t 1/2, h) and the plasma clearance (CL, l/h) of IMC in each groups (control vs. DMEP70) were determined; MRT (16.97 +/- 4.83 vs. 28.69 +/- 11.28, p < 0.01); Vdss (14.26 +/- 4.86 vs. 20.37 +/- 12.04, p < 0.05); t 1/2 (15.12 +/- 4.77 vs. 23.1 +/- 8.24, p < 0.01); CL (0.84 +/- 0.27 vs. 0.71 +/- 0.41). From these results, we could concluded that MEP70 has a significant potential for sustained release and the enhancement of circulation time of loaded drug by prolonging terminal half-life, increasing MRT and Vdss of IMC. Therefore, The MePEG/PCL block copolymeric nanosphere system is being considered as promising biodegradable and biocompatible drug carrier vehicles for parentral use and may be useful as sustained release injectable delivery systems for hydrophobic drugs.

Taxol-loaded block copolymer nanospheres composed of methoxy poly(ethylene glycol) and poly(epsilon-caprolactone) as novel anticancer drug carriers

We prepared the methoxy poly(ethylene glycol) (MePEG)/poly(epsilon-caprolactone) (PCL) amphiphilic block copolymeric nanospheres containing taxol which has promising anticancer activity. MePEG/PCL block copolymeric nanospheres (MEP50) showed a narrow size distribution and an average diameter of less than 100 nm. When the initial weight ratio of taxol to polymer was 0.5:1.0, we could obtain the nanospheres having a relatively high drug-loading of more than about 20%. The size of the MePEG/PCL nanospheres also increased according to the taxol loading. However, the nanospheres did not exhibit a significant change in the size distribution and also showed a size of less than 100 nm for even that with drug-loading content (DLC) of about 20%. From the 1H NMR analysis, we identified that the MePEG/PCL nanospheres prepared by dialysis procedure have core-shell structure consisting of the hydrophilic outer shell of MePEG and the hydrophobic inner core of PCL. We confirmed the low toxicity of MePEG/PCL nanospheres (MEP70) in the acute toxicity study using male ICR mice. In addition, considering the extremely lipophilic characteristics of taxol, this MePEG/PCL, nanosphere system with high taxol loading content and suspended properties in water could be useful for the delivery of taxol.

Preparation and characterization of biodegradable nanospheres composed of methoxy poly(ethylene glycol) and DL-lactide block copolymer as novel drug carriers

We synthesized amphiphilic diblock copolymer based on methoxy poly(ethylene glycol) (MePEG) and dl-lactide with different molar composition in bulk without catalyst. Using the resulting amphiphilic diblock copolymers, we prepared drug-loaded polymeric nanospheres by micelle formation through solution behavior of amphiphilic copolymer in selective solvents. The structure of MePEG/dl-lactide diblock copolymers was identified by IR, WAXD, GPC, 1H-NMR. The size of nanosphere measured by dynamic light scattering showed a narrow monodisperse size distribution and average diameter less than 200 nm. From the surface chemical composition of nanosphere by ESCA, the presence of MePEG chains on the nanosphere layers was confirmed. The critical micelle concentration of ML50 sample investigated by fluorescence spectroscopy was 1.44x10-7 mol/l which is lower than common low molecular weight surfactants. In addition, we could obtain nanospheres having a relatively high drug-loading of about 33.0% when the feed weight ratio of indomethacin to polymer was 1:1. In vitro release experiments of the indomethacin-loaded MePEG/dl-lactide nanospheres exhibited sustained release behavior without any burst effects. The results of cytotoxicity tests showed that the MePEG/dl-lactide nanospheres didn't induce any relevant cell damage.

Methoxy poly(ethylene glycol) and epsilon-caprolactone amphiphilic block copolymeric micelle containing indomethacin. II. Micelle formation and drug release behaviours

Amphiphilic diblock copolymer composed of methoxy poly(ethylene glycol) and epsilon-caprolactone (epsilon-CL) was prepared by polymerization of epsilon-CL initiated with MePEG. MePEG/epsilon-CL block copolymeric micelles containing indomethacin (IMC) were prepared by a dialysis method and evaluated as a novel drug carrier. The size of micelle formed was less than 200 nm, and the size distribution of the micelle showed a narrow and monodisperse unimodal pattern. Also, the micelles formed by a dialysis method exhibited spherical structures. The indomethacin content in nanospheres was about 42.2%, for those prepared using copolymer, having molecular weight of about 12,000 and polymer/IMC weight ratio of 1/1. A release rate of indomethacin from nanospheres was slow, and thus the release continued over 15 days. As the molecular weights of the copolymer and the amount of drug entrapped increased, the release rate decreased. These results indicated that the drug-loaded nanospheres could be useful as a novel drug carrier in injectable delivery systems for hydrophobic drugs.