Morphology and in vitro release kinetics of drug-loaded micelles based on well-defined PMPC–b–PBMA copolymer

Production of paclitaxel-loaded PEG-b-PLA micelles using PEG for drug loading and freeze-drying

A new approach named PEG-assist is introduced for the production of drug-loaded polymeric micelles. The method is based on the use of PEG as the non-selective solvent for PEG-b-PLA in the fabrication procedure. Both hydration temperature and PEG molecular weight are shown to have a significant effect on the encapsulation efficiency of PTX in PEG_4kDa-b-PLA_2kDa micelles. The optimal procedure for fabrication includes the use of PEG_1kDa as the solvent at 60 °C, cooling the mixture to 40 °C, hydration at 40 °C, freezing at -80 °C and freeze-drying at -35 °C, 15 Pa. No significant difference (p > 0.05) in PTX encapsulation, average particle size and polydispersity index is observed between the samples before freeze-drying and after reconstitution of the freeze-dried cake. The prepared PTX formulations are stable at room temperature for at least 8 h. Scaling the batch size to 25× leads to no significant change (p > 0.05) in PTX encapsulation, average particle size and polydispersity index. PEG-assist method is applicable to other drugs such as 17-AAG, and copolymers of varied molecular weights. The use of no organic solvent, simplicity, cost-effectiveness, and efficiency makes PEG-assist a very promising approach for large scale production of drug-loaded polymeric micelles.

Modeling Polyzwitterion-Based Drug Delivery Platforms: A Perspective of the Current State-of-the-Art and Beyond

Drug delivery platforms are anticipated to have biocompatible and bioinert surfaces. PEGylation of drug carriers is the most approved method since it improves water solubility and colloid stability and decreases the drug vehicles’ interactions with blood components. Although this approach extends their biocompatibility, biorecognition mechanisms prevent them from biodistribution and thus efficient drug transfer. Recent studies have shown (poly)zwitterions to be alternatives for PEG with superior biocompatibility. (Poly)zwitterions are super hydrophilic, mainly stimuli-responsive, easy to functionalize and they display an extremely low protein adsorption and long biodistribution time. These unique characteristics make them already promising candidates as drug delivery carriers. Furthermore, since they have highly dense charged groups with opposite signs, (poly)zwitterions are intensely hydrated under physiological conditions. This exceptional hydration potential makes them ideal for the design of therapeutic vehicles with antifouling capability, i.e., preventing undesired sorption of biologics from the human body in the drug delivery vehicle. Therefore, (poly)zwitterionic materials have been broadly applied in stimuli-responsive “intelligent” drug delivery systems as well as tumor-targeting carriers because of their excellent biocompatibility, low cytotoxicity, insignificant immunogenicity, high stability, and long circulation time. To tailor (poly)zwitterionic drug vehicles, an interpretation of the structural and stimuli-responsive behavior of this type of polymer is essential. To this end, a direct study of molecular-level interactions, orientations, configurations, and physicochemical properties of (poly)zwitterions is required, which can be achieved via molecular modeling, which has become an influential tool for discovering new materials and understanding diverse material phenomena. As the essential bridge between science and engineering, molecular simulations enable the fundamental understanding of the encapsulation and release behavior of intelligent drug-loaded (poly)zwitterion nanoparticles and can help us to systematically design their next generations. When combined with experiments, modeling can make quantitative predictions. This perspective article aims to illustrate key recent developments in (poly)zwitterion-based drug delivery systems. We summarize how to use predictive multiscale molecular modeling techniques to successfully boost the development of intelligent multifunctional (poly)zwitterions-based systems.

Targeting Cancer Cells Overexpressing Folate Receptors with New Terpolymer-Based Nanocapsules: Toward a Novel Targeted DNA Delivery System for Cancer Therapy

Chemotherapeutics represent the standard treatment for a wide range of cancers. However, these agents also affect healthy cells, thus leading to severe off-target effects. Given the non-selectivity of the commonly used drugs, any increase in the selective tumor tissue uptake would represent a significant improvement in cancer therapy. Recently, the use of gene therapy to completely remove the lesion and avoid the toxicity of chemotherapeutics has become a tendency in oncotherapy. Ideally, the genetic material must be safely transferred from the site of administration to the target cells, without involving healthy tissues. This can be achieved by encapsulating genes into non-viral carriers and modifying their surface with ligands with high selectivity and affinity for a relevant receptor on the target cells. Hence, in this work we evaluate the use of terpolymer-based nanocapsules for the targeted delivery of DNA toward cancer cells. The surface of the nanocapsules is decorated with folic acid to actively target the folate receptors overexpressed on a variety of cancer cells. The nanocapsules demonstrate a good ability of encapsulating and releasing DNA. Moreover, the presence of the targeting moieties on the surface of the nanocapsules favors cell uptake, opening up the possibility of more effective therapies.

Optimized preparation of vinpocetine micelles and in vivo evaluation of its pharmacokinetics in rats

This study aimed to develop a novel monomethoxy poly(ethylene glycol)-b-poly(D, L-lactide) (mPEG₅₀₀₀-PLA_10 000) micelle drug delivery system to improve vinpocetine's (VP) dissolution and sustain VP concentrations in plasma. Three micelle fabrication methods were examined to maximize VP loading, followed by structurally characterization and investigation in vitro release and in vivo pharmacokinetics in Sprague-Dawley rats. The thin-film hydration is the most appropriate method of the three methods because of its high loading content. The loaded micelles exhibited a sustained release behavior up to 48 h. Following intraperitoneal administration (9 mg/kg), VP loaded micelles provided significantly higher (335%) AUC (area under concentration-time) compared to VP injection. And also increased the mean residence time [MRT_(0-t)] and elimination half-life (t_1/2z). There were obviously two peaks at 2 h and 9 h in VP loaded micelles concentration-time profile. In summary, these data demonstrated that poly mPEG-PLA micelles can efficiently sustain VP concentrations in plasma for 36 h, thus apprehending polymeric micelles suitability as poor aqueous solubility drug carriers.

Effects of processing parameters on the properties of amphiphilic block copolymer micelles prepared by supercritical carbon dioxide evaporation method

The operation parameters for the supercritical carbon dioxide (ScCO2) evaporation method greatly affect the properties of the prepared drug-loaded micelles. In this study, the effects of those key parameters on the drug-loading content (LC) and drug entrapment efficiency (EE) are discussed. It is observed that EE and LC of the micelles are slightly increased with the enhancing temperature and the copolymer molecular ratio of hydrophilic/hydrophobic segment, while decreased with the enhancing ScCO2 evaporation rate. The pressure and volume ratio of ScCO2 to H2O are observed the optimum condition. In addition, the verification experiment is carried out under the obtained optimizing parameters. The prepared micelles exhibit relatively regular spherical shape and narrow size distribution with the EE and LC value of 70.7% and 14.1%, respectively.

GSH-responsive polymeric micelles based on the thio–ene reaction for controlled drug release

A glutathione (GSH) responsive drug carrier is prepared that relies on the thio–ene reaction of olefinic bonds and GSH.

New acrylate terpolymer-based nanoparticles for the release of nucleic acid: a preliminary study

PURPOSE

Nano-drug delivery systems based on polymeric biomaterials have received considerable interest as drug delivery vehicles. In this work, radical polymerization was carried out in order to obtain nanoparticles based on a new acrylate terpolymer (PBMA-(PEG)MEMA-PDMAEMA).

METHODS

Nanoparticles were developed in the form both of nanospheres and nanocapsules, an innovative kind of hollow nanoparticles with a great potential because of their low effective density and high specific surface area. The ability of the nanoparticles to load and then release a nucleic acid (DNA) to be used in cancer treatment was also investigated.

RESULTS

Scanning electron microscopy analysis showed a spherical shape, nanometric dimensions, and a homogeneous distribution of the nanoparticles, also confirmed by dynamic light scattering measurements. Fourier-transform infrared spectroscopy chemical imaging analysis carried out on the nanocapsules before and after removal of the core demonstrated the presence of the cavity. High-performance liquid chromatography analysis confirmed good encapsulation efficiency of DNA both for nanospheres and nanocapsules. Drug release tests showed controlled release kinetics for both the systems with a high release of DNA in the first hours. In vitro MTT assay showed that the particles do not have cytotoxic effects on the cells.

CONCLUSIONS

The preliminary investigation showed that the terpolymer-based nanoparticles developed in this study could be good candidates to be used as innovative and versatile gene delivery systems.

Nanoprecipitation of polymeric nanoparticle micelles based on 2-methacryloyloxyethyl phosphorylcholine (MPC) with 2-(diisopropylamino)ethyl methacrylate (DPA), for intracellular delivery applications

Biodistribution of nanoparticle-based intracellular delivery systems is mediated primarily by particle size and physicochemical properties. As such, overcoming the rapid removal of these by the reticuloendothelial system remains a significant challenge. To date, a number of copolymer nanoparticle systems based on 2-methacryloyloxyethyl phosphorylcholine (MPC) with 2-(diisopropylamino)ethyl methacrylate (DPA), displaying biomimetic and pH responsive properties, have been published, however these have been predominately polymersome based, whilst micelle systems have remained relatively unexplored. This study utilised nanoprecipitation to investigate the effects of solvent and buffer choice upon micelle size and polydispersity, and found using methanol produced monodisperse micelles of circa 70 nm diameter, whilst ethanol produced polydisperse systems with nanoparticles of circa 128 nm diameter. The choice of aqueous buffer, dialysis of the systems, extended storage, and exposure to a wide temperature range (5-70 °C) had no significant effect on micelle size, and the systems were highly resistant to dilution, indicating excellent colloidal stability. Optimisation of the nanoprecipitation process, post precipitation, was investigated, and model drugs successfully loaded whilst maintaining system stability. Subsequent in vitro studies suggested that the micelles were of negligible cellular toxicity, and an apparent cellular uptake was observed via confocal laser scanning microscopy. This paper presents the first report of an optimised nanoprecipitation methodology for the formation of MPC-DPA nanoparticle micelles, and in doing so achieved monodisperse systems with the size and physicochemical characteristics seen as desirable for long circulating therapeutic delivery vehicles.

Chain length dependence of non-surface activity and micellization behavior of cationic amphiphilic diblock copolymers

The cationic and anionic amphiphilic diblock copolymers with a critical chain length and block ratio do not adsorb at the air/water interface but form micelles in solution, which is a phenomenon called "non-surface activity". This is primarily due to the high charge density of the block copolymer, which creates a strong image charge effect at the air/water interface preventing adsorption. Very stable micelle formation in bulk solution could also play an important role in the non-surface activity. To further confirm these unique properties, we studied the adsorption and micellization behavior of cationic amphiphilic diblock copolymers of poly(n-butyl acrylate)-b-poly(3-(methacryloyloxy)ethyl)trimethylammonium chloride) (PBA-b-PDMC) with different molecular weights of hydrophobic blocks but with the same ionic block length. These block copolymers were successfully prepared via consecutive reversible addition-fragmentation chain transfer (RAFT) polymerization. The block copolymer with the shortest hydrophobic block length was surface-active; the solution showed surface tension reduction and foam formation. However, above the critical block ratio, the surface tension of the solution did not decrease with increasing polymer concentration, and there was no foam formation, indicating lack of surface activity. After addition of 0.1 M NaCl, stable foam formation and slight reduction of surface tension were observed, which is reminiscent of the electrostatic nature of the non-surface activity. Fluorescence and dynamic and static light scattering measurements showed that the copolymer with the shortest hydrophobic block did not form micelles, while the block copolymers formed spherical micelles having radii of 25-30 nm. These observations indicate that micelle formation is also important for non-surface activity. Upon addition of NaCl, cmc did not decrease but rather increased as observed for non-surface-active block copolymers previously studied. The micelles formed were very stable, and their size decreased by only ∼5 nm after addition of 0.1 M NaCl.

Disulfide cross-linked phosphorylcholine micelles for triggered release of camptothecin

A series of block copolymers based on 2-methacryloyloxyethyl phosphorylcholine (MPC) were synthesized by reversible addition-fragmentation chain transfer (RAFT) polymerization. Incorporation of dihydrolipoic acid (DHLA) into the hydrophobic block led to formation of block copolymer micelles in water. The micelles were between 15 and 30 nm in diameter, as characterized by dynamic light scattering (DLS), with some size control achieved by adjusting the hydrophobic/hydrophilic balance. Cross-linked micelles were prepared by disulfide formation, and observed to be stable in solution for weeks. The micelles proved amenable to disassembly when treated with a reducing agent, such as dithiothreitol (DTT), and represent a potential delivery platform for chemotherapeutic agents. As a proof-of-concept, camptothecin (CPT) was conjugated to the polymer scaffold through a disulfide linkage, and release of the drug from the micelle was monitored by fluorescence spectroscopy. These CPT-loaded prodrug micelles showed a reduction in release rate compared to physically encapsulated CPT. The use of disulfide conjugation facilitated drug release under reducing conditions, with a half-life (t1/2) of 5.5 h in the presence of 3 mM DTT, compared to 28 h in PBS. The toxicity of the micellar prodrugs was evaluated in cell culture against human breast (MCF7) and colorectal (COLO205) cancer cell lines.

Non-surface activity and micellization behavior of cationic amphiphilic block copolymer synthesized by reversible addition-fragmentation chain transfer process

Cationic amphiphilic diblock copolymers of poly(n-butylacrylate)-b-poly(3-(methacryloylamino)propyl)trimethylammonium chloride) (PBA-b-PMAPTAC) with various hydrophobic and hydrophilic chain lengths were synthesized by a reversible addition-fragmentation chain transfer (RAFT) process. Their molecular characteristics such as surface activity/nonactivity were investigated by surface tension measurements and foam formation observation. Their micelle formation behavior and micelle structure were investigated by fluorescence probe technique, static and dynamic light scattering (SLS and DLS), etc., as a function of hydrophilic and hydrophobic chain lengths. The block copolymers were found to be non-surface active because the surface tension of the aqueous solutions did not change with increasing polymer concentration. Critical micelle concentration (cmc) of the polymers could be determined by fluorescence and SLS measurements, which means that these polymers form micelles in bulk solution, although they were non-surface active. Above the cmc, the large blue shift of the emission maximum of N-phenyl-1-naphthylamine (NPN) probe and the low micropolarity value of the pyrene probe in polymer solution indicate the core of the micelle is nonpolar in nature. Also, the high value of the relative intensity of the NPN probe and the fluorescence anisotropy of the 1,6-diphenyl-1,3,5-hexatriene (DPH) probe indicated that the core of the micelle is highly viscous in nature. DLS was used to measure the average hydrodynamic radii and size distribution of the copolymer micelles. The copolymer with the longest PBA block had the poorest water solubility and consequently formed micelles with larger size while having a lower cmc. The "non-surface activity" was confirmed for cationic amphiphilic diblock copolymers in addition to anionic ones studied previously, indicating the universality of non-surface activity nature.

Selection suitable solvents to prepare paclitaxel-loaded micelles by solvent evaporation method

Amphiphilic block copolymer micelle is one of the most important drug delivery systems to improve the water-solubility of lipophilic drugs. Blank micelles were prepared by solvent evaporation method in order to choose the suitable solvents for PBMA-b-PMPC (poly(n-butyl methacrylate)-b-poly(2-methacryloyloxyethyl phosphorylcholine)) copolymer micelles. The selected solvents, which include chloroform/ethanol mixture and ScCO(2), were used to prepare the paclitaxel-loaded micelles. The micelles with high drug encapsulation efficiency and drug-loading content showed both narrow size distribution and regularly spherical shape. In vitro drug release studies indicated that paclitaxel could be slowly and continuously released from the micelles. More than 50% incorporated drug was released within 132 h from the micelles prepared using ScCO(2) as solvent while only 20% was released at the same period from those prepared using chloroform/ethanol mixture. In addition, the environmentally-friendly solvent, ScCO(2), was used for the first time to prepare the paclitaxel-loaded micelles during the solvent evaporation process.

Advances in polymeric micelles for drug delivery and tumor targeting

A plethora of formulation techniques have been reported in the literature for targeting drugs to specific sites. Polymeric micelles (PMs) can be targeted to tumor sites by passive as well as active mechanisms. Some inherent properties of PMs, including size in the nanorange, stability in plasma, longevity in vivo, and pathological characteristics of tumor allow PMs to be targeted to the tumor site by a passive mechanism called the enhanced permeability and retention effect. PMs formed from an amphiphilic block copolymer are suitable for encapsulation of poorly water-soluble, hydrophobic anticancer drugs. Other characteristics of PMs such as separate functionality at the outer shell are useful for targeting the anticancer drug to tumor by active mechanisms. PMs can be conjugated with many ligands such as antibody fragments, epidermal growth factors, α(2)-glycoprotein, transferrin, and folate to target micelles to cancer cells. Application of heat or ultrasound are the alternative methods to enhance drug accumulation in tumoral cells. Targeting using micelles can also be directed toward tumor angiogenesis, which is a potentially promising target for anticancer drugs. PMs have been used for the delivery of many anticancer agents in preclinical and clinical studies. This review summarizes recently available information regarding targeting of anticancer drugs to the tumor site using PMs.

Living Radical Polymerization by the RAFT Process - A Second Update

This paper provides a second update to the review of reversible deactivation radical polymerization achieved with thiocarbonylthio compounds (ZC(=S)SR) by a mechanism of reversible addition–fragmentation chain transfer (RAFT) that was published in June 2005 (Aust. J. Chem. 2005, 58, 379–410). The first update was published in November 2006 (Aust. J. Chem. 2006, 59, 669–692). This review cites over 500 papers that appeared during the period mid-2006 to mid-2009 covering various aspects of RAFT polymerization ranging from reagent synthesis and properties, kinetics and mechanism of polymerization, novel polymer syntheses and a diverse range of applications. Significant developments have occurred, particularly in the areas of novel RAFT agents, techniques for end-group removal and transformation, the production of micro/nanoparticles and modified surfaces, and biopolymer conjugates both for therapeutic and diagnostic applications.