Dong-Gon Kim

Suppression of post-angioplasty restenosis with an Akt1 siRNA-embedded coronary stent in a rabbit model.

Restenosis is the formation of blockages occurring at the site of angioplasty or stent placement. In order to avoid such blockages, the suppression of smooth muscle cells near the implanted stent is required. The Akt1 protein is known to be responsible for cellular proliferation, and specific inhibition of Akt1 gene expression results in the retardation of cell growth. To take advantage of these benefits, we developed a new delivery technique for Akt1 siRNA nanoparticles from a hyaluronic acid (HA)-coated stent surface. For this purpose, the disulfide cross-linked low molecular polyethyleneimine (PEI) (ssPEI) was used as a gene delivery carrier because disulfide bonds are stable in an oxidative extracellular environment but degrade rapidly in reductive intracellular environments. In this study, Akt1 siRNA showed efficient ionic interaction with the ssPEI carrier, which was confirmed by polyacrylamide gel electrophoresis. Akt1 siRNA/ssPEI nanoparticles (ASNs) were immobilized on the HA-coated stent surface and exhibited stable binding and localization, followed by time-dependent sustained release for intracellular uptake. Cellular viability on the nanoparticle-immobilized surface was assessed using A10 vascular smooth muscle cells, and the results revealed that immobilized ASNs exhibited negligible cytotoxicity against the adhering A10 cells. Transfection efficiency was quantified using a luciferase assay; the transgene expression of Akt1 suppression through the delivered Akt1 siRNA was measured using RT-PCR and western blot, demonstrating higher gene silencing efficiency when compared to other carriers. ASN coated on HA stents were deployed in the balloon-injured external iliac artery in rabbits in vivo. It was shown that the Akt1 released from the stent suppressed the growth of the smooth muscle at the peri-stent implantation area, resulting in the prevention of restenosis in the post-implantation phase.

Comparison of sirolimus loaded PLGA-PEG Co-polymer coronary stent and bare metal stent in a porcine coronary restenosis model

The aim of this study was to compare the effect of the sirolimus loaded PLGA-PEG co-polymer coronary stent with that of the bare metal stent in a porcine coronary restenosis model. Pigs were randomized into two groups (10 pigs, 10 coronary arteries in each group), in which either the sirolimus loaded PLGA-PEG copolymer stent (SPPS, n=10) or the bare metal stent (BMS, n=10) was implanted in the coronary arteries. Histopathologic analysis was performed at 28 days after stenting. There were no significant differences in the injury score, internal elastic lamina (IEL) area, and inflammation score between the two groups. There were significant differences in the lumen area (3.6±0.42 mm2 in the SPPS group vs. 2.5±0.89 mm2 in the BMS group, p<0.001), in the neointimal area (1.2±0.34 mm2 in the SPPS group vs. 2.5±0.99 mm2 in the BMS group, p<0.001), in the percent area stenosis (26.0±6.58% in the SPPS group vs. 48.6±16.95% in the BMS group, p<0.001) and in the fibrin score (1.2±0.41 in the SPPS group vs. 0.5±0.26 in the BMS group, p<0.001). These results demonstrate that SPPS had a superior effect on suppression of neointimal hyperplasia than BMS at one month after stenting in a porcine coronary restenosis model.

Synthesis of Dextran/Methoxy Poly(ethylene glycol) Block Copolymer

We synthesized a block copolymer composed of dextran and methoxy poly(ethylene glycol) (mPEG). To accomplish this, the end group of dextran was modified by reductive amination. The aminated dextran (Dextran-NH2) showed the intrinsic peaks of both dextran at 3~5.5 ppm and hexamethylene diamine at 1~2.6 ppm at 1H nuclear magnetic resonance (NMR) spectrum. The amino end group of dextran was conjugated with mPEG to make the block copolymer consisting of dextran/mPEG (abbreviated as DexPEG). The synthesized aminated dextran and DexPEG were characterized using 1H NMR and gel permeation chromatography (GPC). The molecular weight and conjugation yield were estimated by comparing the intensity ratio of the proton peaks of the glucose molecule (4.9 ppm and 3.3~4.0 ppm) to that of the ethylene group of mPEG (3.7 ppm). Abundant hydroxyl group in the dextran chain can be used as a source of bioactive agent conjugation.

Blood-compatible and biodegradable polymer-coated drug-eluting stent

A drug-eluting stent (DES) is a metal stent that has been coated with a drug known to suppress restenosis. To prepare a novel DES, a bare metal stent (BMS) was coated with sirolimus (SRL) in a blood-compatible, biodegradable polymer, poly lactic-glycolic acid, grafted with poly ethylene glycol (PLGA-PEG), by an ultrasonic spray method. The PLGA-PEG-coated DES was designed to control the drug release-rate by varying the PEG content in the polymer. The release behavior of SRL from the DES showed a burst-release pattern in 7 days and then sustained-release over 21 days. The amount of SRL released increased with increasing PEG content in the polymer up to 15%. The PLGA-PEG copolymer coated on the stent showed the potential to act as a bio-degradable drug reservoir. In an in vitro platelet adhesion test, the PLGA-PEG15-coated DES showed significantly reduced platelet deposition versus the BMS. The DES revealed anti-thrombotic activity and blood-compatibility presumably due to the increased hydrophilicity of the surface of the stent and the amount of SRL loading corresponding to the high PEG content in the polymer. In an animal study, the restenosis rate was reduced in the PLGA-PEG15-coated DES group (20.2±11.02%) versus the BMS group (44.2±12.11%). The PLGA-PEG15-coated DES inhibited smooth muscle cell (SMC) proliferation and prevented in-stent restenosis (ISR) in in vivo test. We successfully obtained the PLGA-PEG15-coated DES with smooth surface and sustained drug-release properties.