Monthly Archives: April 2013

mPEG-PCL for tissue engineering Scaffold

Article highlights the use of mPEG-PCL, similar to that available at www.polyscitech.com, as an injectable scaffold for tissue engineering and cell-growth.

“Methoxy poly(ethylene glycol)-poly(ε-caprolactone) (MPEG-PCL) diblock copolymers were prepared by ring-opening polymerization and their phase transition behavior characterized as a function of temperature. The MPEG–PCL solutions formed a sol at room temperature, and underwent sol-to-gel followed by gel-to-sol phase transitions as the temperature was increased. The temperature range over which the solutions were in a gel state could be extended simply by increasing the PCL chain length in the diblock copolymer. Scanning electron microscopy (SEM) images of MPEG–PCL solutions in the sol and gel states revealed near-regular and irregular porous structures, respectively. in vitro culture of rat bone marrow stromal cells (rBMSCs) on gel surfaces exhibited mostly round cells after 1 day of incubation. SEM images of the attached cells clearly showed the cell body and anchoring filopodia. Injection of room-temperature diblock copolymer solutions into Sprague-Dawley rats produced a gel at body temperature. In situ gelforming scaffolds in vivo were successfully fabricated by simple subcutaneous injection of MPEG–PCL diblock copolymer solutions. The gel implants retained their original shape for 4 weeks without in- flammation at the injection site. Gel implants removed after 4 weeks were found to be surrounded by a thin fibrous capsule consisting of fibroblasts and blood vessels cells. Hematoxylin and eosin (H&E) and von Kossa staining revealed bone formation in gel implants containing both rBMSCs and dexamethasone, with the degree of bone formation increasing markedly with increasing dexamethasone concentration. Thus, our results show that in situ gel scaffolds fabricated from MPEG–PCL diblock copolymer solutions containing dexamethasone enable multipotent rBMSCs to produce viable bone when injected into rats.”

M.S. Kim, Sun Kyung Kim, Soon Hee Kim, Hoon Hyun, Gilson Khang, and Hai Bang Lee. Tissue Engineering. October 2006, 12(10): 2863-2873. doi:10.1089/ten.2006.12.2863.

Diblock copolymer promotes phase inversion, creates multiple emulsion

A diblock copolymer [styrene and 2-(dimethylamino)ethylmethacrylate monomers (DMAEMA) (similar to PolySciTech’s AO19 and AO33)] was used to generate toluene-water emulsions that stayed stable for months. Reported in Advanced Materials, Emulsions Controlled by Stimuli-Responsive Polymers, http://onlinelibrary.wiley.com/doi/10.1002/adma.201204496/abstractMultiple

protein delivery nanoparticles

Recent paper highlights use of PEG-PLA for protein delivery. See full paper here http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3534295/

Abstract:
“To improve the pharmacokinetics and stability of recombinant human erythropoietin (rhEPO), rhEPO was successfully formulated into poly(ethylene glycol)–poly(d,l-lactide) (PEG–PLA) di-block copolymeric micelles at diameters ranging from 60 to 200 nm with narrow polydispersity indices (PDIs; PDI < 0.3) and trace amount of protein aggregation. The zeta potential of the spherical micelles was in the range of −3.78 to 4.65 mV and the highest encapsulation efficiency of rhEPO in the PEG–PLA micelles was about 80%. In vitro release profiles indicated that the stability of rhEPO in the micelles was improved significantly and only a trace amount of aggregate was found. Pharmacokinetic studies in rats showed highly enhanced plasma retention time of the rhEPO-loaded PEG-PLA micelles in comparison with the native rhEPO group. Increased hemoglobin concentrations were also found in the rat study. Native polyacrylamide gel electrophoresis results demonstrated that rhEPO was successfully encapsulated into the micelles, which was stable in phosphate buffered saline with different pHs and concentrations of NaCl. Therefore, PEG–PLA micelles can be a potential protein drug delivery system."

Review Article about polyesters nanoparticles

A recent review article has an excellent discussion about use of PLGA nanoparticles for drug delivery.  Full text here (http://www.ncbi.nlm.nih.gov/pmc/articles/PMC3582541/)

Concepts and practices used to develop functional PLGA-based nanoparticulate systems

Hongkee Sah,1,2 Laura A Thoma,2 Hari R Desu,2 Edel Sah,3 and  George C Wood2

Int J Nanomedicine. 2013; 8: 747–765.
Published online 2013 February 21. doi:  10.2147/IJN.S40579
Abstract:

“The functionality of bare polylactide-co-glycolide (PLGA) nanoparticles is limited to drug depot or drug solubilization in their hard cores. They have inherent weaknesses as a drug-delivery system. For instance, when administered intravenously, the nanoparticles undergo rapid clearance from systemic circulation before reaching the site of action. Furthermore, plain PLGA nanoparticles cannot distinguish between different cell types. Recent research shows that surface functionalization of nanoparticles and development of new nanoparticulate dosage forms help overcome these delivery challenges and improve in vivo performance. Immense research efforts have propelled the development of diverse functional PLGA-based nanoparticulate delivery systems. Representative examples include PEGylated micelles/nanoparticles (PEG, polyethylene glycol), polyplexes, polymersomes, core-shell–type lipid-PLGA hybrids, cell-PLGA hybrids, receptor-specific ligand-PLGA conjugates, and theranostics. Each PLGA-based nanoparticulate dosage form has specific features that distinguish it from other nanoparticulate systems. This review focuses on fundamental concepts and practices that are used in the development of various functional nanoparticulate dosage forms. We describe how the attributes of these functional nanoparticulate forms might contribute to achievement of desired therapeutic effects that are not attainable using conventional therapies. Functional PLGA-based nanoparticulate systems are expected to deliver chemotherapeutic, diagnostic, and imaging agents in a highly selective and effective manner.”

Clinically used block copolymers? (PSTB-01104A)

One common question is are there any block copolymers clinically used for drug delivery. There is currently a product Genexol-PM which is a PEG-PLA polymer used as a drug delivery system for paclitaxel in Korea. Below is one of the clinical studies which lead to its approval for this usage.

“ABSTRACT

Purpose: The rationale for developing an alternative paclitaxel formulation concerns Cremophor EL-related side effects, and a novel paclitaxel delivery system might augment its therapeutic efficacy. Genexol-PM is a polymeric micelle formulated paclitaxel free of Cremophor EL. A phase I study was performed to determine the maximum tolerated dosage, dose-limiting toxicities, and the pharmacokinetic profile of Genexol-PM in patients with advanced, refractory malignancies.

Experimental Design: Twenty-one patients were entered into the study. Genexol-PM was i.v. administered over 3 h every 3 weeks without premedication. The Genexol-PM dose was escalated from 135 mg/m2 to 390 mg/m2. Results: All of the patients were evaluable for toxicity and response. Acute hypersensitivity reactions were not observed.

Neuropathy and myalgia were the most common toxicities. During cycle 1, grade 3 myalgia occurred in 1 patient at 230 and 300 mg/m2, respectively. At 390 mg/m2, 2 of 3 patients developed grade 4 neutropenia or grade 3 polyneuropathy. Therefore, the maximum tolerated dosage was determined to be 390 mg/m2. There were 3 partial responses (14%) among the 21 patients. Of the 3 responders, 2 were refractory to prior taxane therapy. The paclitaxel area under the curve from time 0 to infinity and peak or maximum paclitaxel concentration seemed to increase with escalating dose, except at 230 mg/m2, which suggests that Genexol-PM has linear pharmacokinetics.

Conclusion: The main dose-limiting toxicities were neuropathy, myalgia, and neutropenia, and the recommended dosage for a phase II study is 300 mg/m2. Genexol-PM is believed to be superior to conventional paclitaxel in terms of the obviation of premedication and the delivery of higher paclitaxel doses without additional toxicity. ”

T.-Y. Kim, D.-W. Kim, J.-Y. Chung, S.G. Shin, S.-C. Kim, D.S. Heo, N.K. Kim, Y.-J. Bang, Phase I and Pharmacokinetic Study of Genexol-PM, a Cremophor-Free, Polymeric Micelle-Formulated Paclitaxel, in Patients with Advanced Malignancies Clin Cancer Res (2004). (link to full-text http://clincancerres.aacrjournals.org/content/10/11/3708.full.pdf+html)

PLGA-PEG-PLGA triblock thermogel (PSTB01101A)

The below study highlights the capabilities for PLGA-PEG-PLGA to be used for drug delivery thermogel.

“Injectable biodegradable temperature-responsive poly(dl-lactide-co-glycolide-b-ethylene glycol-b-dl-lactide-co-glycolide) (PLGA-PEG-PLGA) triblock copolymers with dl-lactide/glycolide molar ratio ranging from 6/1 to 15/l were synthesized from monomers of dl-lactide, glycolide and polyethylene glycol and characterized by 1H NMR. The resulting copolymers are soluble in water to form free flowing fluid at room temperature but become hydrogels at body temperature. The hydrophobicity of the copolymer increased with the increasing of dl-lactide/glycolide molar ratio. In vitro dissolution studies with two different hydrophobic drugs (5-fluorouracil and indomethacin) were performed to study the effect of dl-lactide/glycolide molar ratio on drug release and to elucidate drug release mechanism. The release mechanism for hydrophilic 5-fluorouracil was diffusion-controlled, while hydrophobic indomethacin showed an biphasic profile comprising of an initial diffusion-controlled stage followed by the hydrogel erosion-dominated stage. The effect of dl-lactide/glycolide molar ratio on drug release seemed to be dependent on the drug release mechanism. It has less effect on the drug release during the diffusion-controlled stage, but significantly affected drug release during the hydrogel erosion-controlled stage. Compared with ReGel system, the synthesized copolymers showed a higher gelation temperature and longer period of drug release. The copolymers can solubilize the hydrophobic indomethacin and the solubility (13.7 mg/ml) was increased 3425-fold compared to that in water (4 [mu]g/ml, 25 °C). Two methods of physical mixing method and solvent evaporation method were used for drug solubilization and the latter method showed higher solubilization efficiency.”

M. Qiao, D. Chen, X. Ma, Y. Liu, Injectable biodegradable temperature-responsive PLGA-PEG-PLGA copolymers: Synthesis and effect of copolymer composition on the drug release from the copolymer-based hydrogels. International Journal of Pharmaceutics 294(1-2) (2005) 103-112. http://www.sciencedirect.com/science/article/B6T7W-4FM01FH-2/2/c45e29a956179c5b82a3c47701f8405f

PEG-(polyester) nanoparticles resistance to phagocytosis (PSTB01026C)

The below study highlights the capabilities for PEG-polyester to be used for drug delivery nanoparticles with a focus on how to prevent phagocytosis of the particles for long-term circulation.

“PEG content from 0.5 to 20 wt %, a PEG content between 2 and 5 wt % was determined as a threshold value for optimal protein resistance. When increasing the PEG content in the nanoparticles above 5 wt % no further reduction in protein adsorption was achieved. Phagocytosis by PMN studied using chemiluminescence and zeta potential data agreed well with these findings: the same PEG surface density threshold was found to ensure simultaneously efficient steric stabilization and to avoid the uptake by PMN cells. Supposing all the PEG chains migrate to the surface, this would correspond to a distance of about 1.5 nm between two terminally attached PEG chains in the covering ‘brush’. Particles from PEG5K-PLA45K, PEG5K-PLGA45K and PEG5K-PCL45K copolymers enabled to study the influence of the core on plasma protein adsorption, all other parameters (corona thickness and density) being kept constant. Adsorption patterns were in good qualitative agreement with each other. Only a few protein species were exclusively present just on one type of nanoparticle. However, the extent of proteins adsorbed differed in a large extent from one particle to another. In vivo studies could help elucidating the role of the type and amount of proteins adsorbed on the fate of the nanoparticles after intraveinous administration, as a function of the nature of their core. These results could be useful in the design of long circulating intravenously injectable biodegradable drug carriers endowed with protein resistant properties and low phagocytic uptake. ”

R. Gref, M. Lück, P. Quellec, M. Marchand, E. Dellacherie, S. Harnisch, T. Blunk, R.H. Müller, [`]Stealth’ corona-core nanoparticles surface modified by polyethylene glycol (PEG): influences of the corona (PEG chain length and surface density) and of the core composition on phagocytic uptake and plasma protein adsorption. Colloids and Surfaces B: Biointerfaces 18(3-4) (2000) 301-313. http://www.sciencedirect.com/science/article/B6TFS-40T9J4H-D/2/7f6343d21452368fcae44f7f1a2c

mPEG-PLGA nanoparticles

The below study highlights the capabilities for PEG-PLGA to be used for drug delivery nanoparticles.

“Injectable nanoparticulate carriers have important potential applications such as site-specific drug delivery or medical imaging. Conventional carriers, however, cannot generally be used because they are eliminated by the reticulo-endothelial system within seconds or minutes after intravenous injection. To address these limitations, monodisperse biodegradable nanospheres were developed from amphiphilic copolymers composed of two biocompatible blocks. The nanospheres exhibited dramatically increased blood circulation times and reduced liver accumulation in mice. Furthermore, they entrapped up to 45 percent by weight of the drug in the dense core in a one-step procedure and could be freeze-dried and easily redispersed without additives in aqueous solutions. ”

R. Gref, Y. Minamitake, M.T. Peracchia, V. Trubetskoy, V. Torchilin, R. Langer, Biodegradable long-circulating polymeric nanospheres. Science 263(5153) (1994) 1600-1603. http://www.sciencemag.org/cgi/content/abstract/263/5153/1600