Novel thermosensitive polymeric micelles for docetaxel delivery

The effects of mixed MPEG-PLA/Pluronic copolymer micelles on the bioavailability and multidrug resistance of docetaxel

A mixed micelle that comprised of MPEG-PLA (MPP) and Pluronic copolymers was developed for enhanced bioavailability and to overcome multidrug resistance of docetaxel in cancer therapy. The mixed micelles that sufficiently solubilized docetaxel were evaluated for the effect of Pluronic copolymers weight ratio on the mixed micelles with respect to drug loading and drug release. In vitro, cell viability and cytotoxicity studies in KB and KBv cells revealed that the mixed micellar formulations were more potent than the commercial docetaxel formulation (Taxotere). In vivo pharmacokinetics study in rats showed that the mixed micelles significantly enhanced the bioavailability of docetaxel (3.6 fold) than Taxotere. Moreover, antitumor activity assessed in KBv cancer xenograft BALB/C nude mice models showed that the mixed micelles significantly reduced the tumor size than the control (Taxotere). Clear differences in the intracellular uptake of docetaxel between MPP and mixed micelles were observed using confocal laser scanning microscopy. This study presents not only a new micelle structure for a diblock-triblock copolymer system, but also a method for enhanced bioavailability of docetaxel and to overcome some of the limitations on its multidrug resistance in cancer therapy.

Reduced matrix viscosity in DNA sequencing by CE and microchip electrophoresis using a novel thermo-responsive copolymer

High viscosity is an inherent problem of sequencing matrices made of hydrophilic polymers. This problem is amplified in separations using microchips where the channels are even smaller. A novel thermal-associating graft copolymer, using linear polyacrylamide (LPA) as the backbone and poly(propylene oxide) (PPO) as the graft side chain was synthesized. The injection problem could be resolved by introducing PPO side chains that can be assembled by using temperature changes but without an obvious detrimental effect on the sieving ability of the LPA. Viscosity measurement showed that these LPA-g-PPO copolymers had a transition temperature of approximately 40 degrees C, above which a significant increase in viscosity was observed. The sequencing performance depended on the thermal association properties of PPO and related parameters. Without optimization, a read length of 1000 bases with a single base resolution of 0.3 was achieved within an hour on an ABI 310 analyzer, using 1.8 wt% LPA-g-PPO (1.8 MDa, PPO, 0.2%). This novel thermal reversible copolymer solution can be a promising candidate as a viable matrix for DNA sequencing in CE, and even more so in microchip electrophoresis.

In vivo anti-tumor efficacy of docetaxel-loaded thermally responsive nanohydrogel

Thermally responsive poly(N-isopropylacrylamide-co-acrylamide) (P(NIPA-co-AAm)) nanohydrogel (NHG) with a diameter of about 50 nm and a lower critical solution temperature (LCST) of about 40 degrees C was synthesized by a previously reported precipitation polymerization method. The physical properties including LCST, diameter and morphology were characterized. Four hydrophobic model drugs (5-fluorouracil (5-FU), fluorescein, docetaxel (DTX) and near-infrared dye-12 (NIRD-12)) with different hydrophilicities were respectively entrapped into the nanoparticles and their in vitro release kinetics from NHG was investigated. DTX was ultimately chosen as the goal anti-tumor drug and optimally entrapped into NHG with a drug loading content (DLC) of 7.38% and encapsulation efficiency (EE) of 73.8%. An in vitro drug release test indicated that DTX-loaded NHG had zero-order release kinetics at 43 degrees C. The respective anti-tumor efficacy of DTX-loaded NHG with or without hyperthermia on tumor tissue was evaluated in Kunming mice-bearing S180 sarcoma. The inhibition rates of DTX-loaded NHG with or without hyperthermia were 78.15% and 48.78%, respectively. DTX-loaded NHG also showed much lower toxicity during the therapeutic procedure. Results indicated that this kind of thermally responsive, drug-loaded NHG could be used as a promising strategy for tumor therapy with the help of local hyperthermia treatment.

Novel thermo-sensitive core-shell nanoparticles for targeted paclitaxel delivery

Novel thermo-sensitive nanoparticles self-assembled from poly(N,N-diethylacrylamide-co-acrylamide)-block-poly(gamma-benzyl L-glutamate) were designed for targeted drug delivery in localized hyperthermia. The lower critical solution temperature (LCST) of nanoparticles was adjusted to a level between physiological body temperature (37 degrees C) and that used in local hyperthermia (about 43 degrees C). The temperature-dependent performances of the core-shell nanoparticles were systemically studied by nuclear magnetic resonance (NMR), circular dichroism (CD), fluorescence spectroscopy, dynamic light scattering (DLS), and atom force microscopy (AFM). The mean diameter of the nanoparticles increased slightly from 110 to 129 nm when paclitaxel (PTX), a poorly water-soluble anti-tumor drug, was encapsulated. A stability study in bovine serum albumin (BSA) solution indicated that the PTX loaded nanoparticles may have a long circulation time under physiological environments as the LCST was above physiological body temperature and the shell remained hydrophilic at 37 degrees C. The PTX release profiles showed thermo-sensitive controlled behavior. The proliferation inhibiting activity of PTX loaded nanoparticles was evaluated against Hela cells in vitro, compared with Taxol (a formulation of paclitaxel dissolved in Cremophor EL and ethanol). The cytotoxicity of PTX loaded nanoparticles increased obviously when hyperthermia was performed. The nanoparticles synthesized here could be an ideal candidate for thermal triggered anti-tumor PTX delivery system.

The antitumor effect of novel docetaxel-loaded thermosensitive micelles

To further evaluate the novel docetaxel-loaded micelle based on the biodegradable thermosensitive copolymer poly(N-isopropylacrylamide-co-acrylamide)-b-poly(dl-lactide) that we had synthesized before, in this paper, we studied its in vitro cytotoxicity in three different tumor cell lines by standard MTT assays using different tumor cell lines, followed by studies of acute toxicity and the tumor distribution studies which were conducted in Kunming mice. Meanwhile, the in vivo antitumor efficacy as well as toxicity of the micelle was evaluated in C57BL/6 mice. According to our findings, the in vitro cytotoxicity of docetaxel-loaded micelles was lower than that of the conventional docetaxel formulation at 37 degrees C, while hyperthermia greatly enhanced the efficacy of drug-loaded micelles. The acute toxicity study showed reduced toxicity of docetaxel-loaded micelle compared to that of conventional docetaxel formulation. Moreover, docetaxel-loaded micelle enabled a prominent higher docetaxel concentration in tumor than conventional docetaxel formulation. Furthermore, a significantly higher antitumor efficacy was observed in mice treated with docetaxel-loaded micelles accompanied by hyperthermia; docetaxel-loaded micelles also caused less body weight loss of mice. This study demonstrates an increased antitumor efficacy and reduced toxicity of the novel docetaxel-loaded micelle and indicates its prospect of clinical applications.

Targeting therapy with docetaxel thermosensitive nano-micelles of human gastric cancer xenografts in nude mice

AIM: To study the curative effects of docetaxel thermosensitive nano-micelles on human gastric cancer xenografts in nude mice.

METHODS: Human gastric cancer cell line BGC-823 was implanted into 48 nude mice. Different drugs were injected through the caudal vein in eight groups after establishment of the experimental model. Permanent temperature of the tumor was taken in the thermotherapy group. Tumor growth was monitored once every other day. Dynamic viewing and determining the rate of tumor regression in terms of tumor weight and volume were used to evaluate therapeutic efficacy. The side effect was evaluated through surveying all the condition and the relative variation in mouse body weight.

RESULTS: Tumor growth speed in the docetaxel thermosensitive nano-micelle thermotherapy group was significantly slower than that in the other groups. Tumor volume and weight regression in the docetaxel thermosensitive nano-micelle thermotherapy group were 81.5% and 85.4%, respectively, which were markedly higher than those of the docetaxel thermosensitive nano-micelle group (32.2% and 37.5%) and the docetaxel injection group (49.2% and 58.0%) (both P < 0.05). The drug side effects and toxicity of docetaxel thermosensitive nano-micelle thermotherapy were significantly less than those in the other groups.

CONCLUSION: Docetaxel thermosensitive nano-micelles show good inhibition of tumor growth, which indicates a favorable potential in clinical application.

Thermo- and pH-responsive polymers in drug delivery

Stimuli-responsive polymers show a sharp change in properties upon a small or modest change in environmental condition, e.g. temperature, light, salt concentration or pH. This behaviour can be utilised for the preparation of so-called 'smart' drug delivery systems, which mimic biological response behaviour to a certain extent. The possible environmental conditions to use for this purpose are limited due to the biomedical setting of drug delivery as application. Different organs, tissues and cellular compartments may have large differences in pH, which makes the pH a suitable stimulus. Therefore the majority of examples, discussed in this paper, deal with pH-responsive drug delivery system. Thermo-responsive polymer is also covered to a large extent, as well as double-responsive system. The physico-chemical behaviour underlying the phase transition will be discussed in brief. Then selected examples of applications are described.