Degradation and adhesive/cohesive strengths of a reservoir-based drug eluting stent.

This paper presents the results of loss of mechanical strengths due to the degradation that occurs in a model reservoir-based coronary stent, the NEVO(™) Sirolimus-eluting Stent (NEVO(™) SES). The adhesion of the formulation to the reservoir and cohesion within the formulation in the time course of hydrolysis were determined using a micro-testing system that was developed specifically for the measurements of the adhesive and cohesive strengths of suspended polymeric films. The strengths were measured after hydration, during degradation with gentle agitation, as well as degradation with pulsatile mechanical loading. The morphology and molecular weight changes in the time course of NEVO(™) SES formulation degradation were also studied using Scanning Electron Microscopy (SEM) and Gel Permeation Chromatography (GPC) techniques. Morphological changes, such as pore formation, lagged behind the decrease in the molecular weight of the formulation. In contrast, the adhesion/cohesion strengths showed that the mechanical integrity of the stents dropped significantly within a few hours of hydration, before reaching a plateau. Despite the significant molecular weight decrease and morphological changes, the plateau mechanical strengths reached were essentially the same during degradation, under both, mechanically unloaded and loaded conditions.

Adhesion and cohesion in structures containing suspended microscopic polymeric films.

This paper presents a novel technique for the characterization of adhesion and cohesion in suspended micro-scale polymeric films. The technique involves push-out testing with probes that are fabricated using focused ion beam techniques. The underlying stresses associated with different probe tip sizes were computed using a finite element model. The critical force for failure of the film substrate interface is used to evaluate adhesion, while the critical force for penetration of the film determines cohesion. When testing a standard material, polycarbonate, a shear strength of approximately 70 MPa was calculated using the Mohr-Coulomb theory. This value was shown to be in agreement with the results in the literature. The technique was also applied to the measurement of adhesion and cohesion in a model drug-eluting stent (the Nevo™ Sirolimus Eluting Coronary Stent) containing suspended microscopic polymeric films in metallic Co-Cr alloy reservoirs. The cohesive strength of the formulation was found to be comparable with that of plastics such as those produced by reaction injection molding and high-density polyethylene.

Quantitative spatial distribution of sirolimus and polymers in drug-eluting stents using confocal Raman microscopy.

Raman spectroscopy was used to differentiate each component found in the CYPHER Sirolimus-eluting Coronary Stent. The unique spectral features identified for each component were then used to develop three separate calibration curves to describe the solid phase distribution found on drug-polymer coated stents. The calibration curves were obtained by analyzing confocal Raman spectral depth profiles from a set of 16 unique formulations of drug-polymer coatings sprayed onto stents and planar substrates. The sirolimus model was linear from 0 to 100 wt % of drug. The individual polymer calibration curves for poly(ethylene-co-vinyl acetate) [PEVA] and poly(n-butyl methacrylate) [PBMA] were also linear from 0 to 100 wt %. The calibration curves were tested on three independent drug-polymer coated stents. The sirolimus calibration predicted the drug content within 1 wt % of the laboratory assay value. The polymer calibrations predicted the content within 7 wt % of the formulation solution content. Attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectra from five formulations confirmed a linear response to changes in sirolimus and polymer content.

Stent-based delivery of sirolimus reduces neointimal formation in a porcine coronary model.

BACKGROUND: The purpose of this study was to determine the efficacy of stent-based delivery of sirolimus (SRL) alone or in combination with dexamethasone (DEX) to reduce in-stent neointimal hyperplasia. SRL is a potent immunosuppressive agent that inhibits SMC proliferation by blocking cell cycle progression. METHODS AND RESULTS: Stents were coated with a nonerodable polymer containing 185 microgram SRL, 350 microgram DEX, or 185 microgram SRL and 350 microgram DEX. Polymer biocompatibility studies in the porcine and canine models showed acceptable tissue response at 60 days. Forty-seven stents (metal, n=13; SRL, n=13; DEX, n=13; SRL and DEX, n=8) were implanted in the coronary arteries of 16 pigs. The tissue level of SRL was 97+/-13 ng/artery, with a stent content of 71+/-10 microgram at 3 days. At 7 days, proliferating cell nuclear antigen and retinoblastoma protein expression were reduced 60% and 50%, respectively, by the SRL stents. After 28 days, the mean neointimal area was 2.47+/-1.04 mm(2) for the SRL alone and 2.42+/-1.04 mm(2) for the combination of SRL and DEX compared with the metal (5.06+/-1.88 mm(2), P<0.0001) or DEX-coated stents (4.31+/-3.21 mm(2), P<0.001), resulting in a 50% reduction of percent in-stent stenosis. CONCLUSIONS: Stent-based delivery of SRL via a nonerodable polymer matrix is feasible and effectively reduces in-stent neointimal hyperplasia by inhibiting cellular proliferation.

Sustained Intramural Retention and Regional Redistribution Following Local Vascular Delivery of Polylactic-Coglycolic Acid and Liposomal Nanoparticulate Formulations Containing Probucol.

BACKGROUND: Probucol reduces restenosis after angioplasty, provided oral administration is begun 1 month before the procedure. Local vascular delivery of a nonoparticulate formulation of probucol may obviate the need for drug loading by acutely raising arterial intramural concentration while providing sustained intramural retention. To test this hypothesis, we compared the retention and redistribution of (35)S-probucol encapsulated in either liposomal or polylactic-coglycolic acid (PLGA) nanoparticles after local vascular delivery. METHODS: Nanoparticles were delivered using a Crescendo microporous infusion catheter (Cordis, Warren, NJ) after balloon angioplasty of rabbit iliac arteries (n = 12-18 arteries per formulation per time point). Animals were euthanized on day 0, 3, or 7 after delivery. Iliac arteries, perivascular fat, and downstream tissues were harvested and the radioactivity disintegrations per minute was measured. Autoradiographic and confocal microscopic analyses of tissue sections were performed to evaluate intramural distribution of probucol. RESULTS: Immediately after delivery, radioactivity in the iliac arteries (log[dpm/mg], mean +/- SEM) was greater with PLGA (2.72 +/- 0.08) than with liposomal encapsulation (2.10 +/- 0.08, P = 0.001). Intramural retention of probucol was 23% at 7 days using liposomes and 10% using PLGA, corresponding to a probucol concentration of 0.1 ng/mg tissue for both formulations. By the third day after delivery, radioactivity in peri-iliac fat, femoral arteries, and hindlimb muscle increased by 88%, 29%, and 154%, respectively. Thereafter, radioactivity decreased to 56%, 43%, and 134% of initial dpm respectively, by day 7. CONCLUSIONS: although delivery efficiency was superior with PLGA encapsulation, intramural probucol concentrations were similar on day 7 using both formulations. Radial and axial redistribution of probucol was observed, indicating that this technique can be exploited to increase adjacent tissue delivery.

D-mannonolactam amidrazone. A new mannosidase inhibitor that also inhibits the endoplasmic reticulum or cytoplasmic alpha-mannosidase.

The amidrazone of D-mannonolactam (see compound 5, Fig. 1) was synthesized chemically as a mimic of the mannopyranosyl cation and tested as a potential inhibitor of mannosidases. In this study compound 5 is shown to be a more general mannosidase inhibitor than other currently known compounds and exhibits properties not previously observed with any other mannosidase inhibitors. Thus D-mannonolactam amidrazone not only inhibits the Golgi mannosidase I (IC50 = 4 microM) and mannosidase II (IC50 = 90-100 nM), but it is the first inhibitor that has been shown to be a potent inhibitor of the soluble or endoplasmic reticulum alpha-mannosidase (IC50 = 1 microM). This compound also inhibited the aryl-mannosidases regardless of anomeric configuration although it was much more effective on enzymes recognizing alpha-linked mannose, i.e. jack bean and mung bean alpha-mannosidases (IC50 = 400 nM) as compared with fungal beta-mannosidase (IC50 = 150 microM). Mannonoamidrazone was tested in animal cell cultures using influenza virus-infected Madin-Darby canine kidney cells as a model system, and was found to prevent almost completely the formation of complex types of N-linked oligosaccharides with the formation of about equal amounts of Man9(GlcNAc)2 and Man8(GlcNAc)2 structures. Thus D-mannonolactam amidrazone is a potent but broad spectrum mannosidase inhibitor whose structure and properties should provide valuable insight into the design of other useful glycosidase inhibitors.