Evaluation of a novel slow-release paclitaxel-eluting stent with a bioabsorbable polymeric surface coating.

OBJECTIVES: We sought to evaluate a new second-generation drug-eluting stent (DES), comprising a slow-release biodegradable polylactide coglycolide (PLGA) polymer and low-dose paclitaxel on a thin-strut cobalt chromium stent platform, in a clinically relevant animal model. BACKGROUND: Our previous work demonstrated subacute vascular toxicity and necrosis triggering late excess neointima in pig coronaries, with a moderate paclitaxel dose eluted from an erodible polymer. The use of slower-releasing absorbable polymers with lower doses of paclitaxel is expected to minimize such adverse outcomes. METHODS: Three types of stents were implanted in pig coronary arteries using quantitative coronary angiography to optimize stent apposition: bare-metal stents (BMS); absorbable, slow-release polymer-coated-only stents (POLY); and absorbable polymer-based paclitaxel-eluting stents (PACL). The dose density of paclitaxel was 0.15 microg/mm(2) with in vitro studies demonstrating a gradual elution over the course of 12 to 16 weeks. Animals underwent angiographic restudy and were terminated at 1 and 3 months for complete histopathologic and histomorphometric analyses. RESULTS: At 1 month, intimal thickness varied significantly according to stent type, with the lowest level for the PACL group compared with the BMS and POLY groups (0.06 +/- 0.02 mm vs. 0.17 +/- 0.07 mm, 0.17 +/- 0.08 mm, respectively, p < 0.001); histological percent area stenosis was 18 +/- 4% for PACL compared with 27 +/- 7% for BMS and 30 +/- 12% for POLY, respectively (p = 0.001). At 3 months, PACL showed similar neointimal thickness as BMS and POLY (0.09 +/- 0.05 mm vs. 0.13 +/- 0.10 mm and 0.11 +/- 0.03 mm respectively, p = 0.582). Histological percent area stenosis was 23 +/- 8% for PACL versus 23 +/- 11% for BMS and 23 +/- 2% for POLY, respectively (p = 1.000). CONCLUSIONS: This study shows favorable vascular compatibility and efficacy for a novel DES that elutes paclitaxel in porcine coronary arteries. These results support the notion that slowing the release rate and lowering the dose of paclitaxel favorably influences the vascular biological response to DES implant, decreasing early toxicity and promoting stable healing while still suppressing neointima formation.

Toxic vessel reaction to an absorbable polymer-based paclitaxel-eluting stent in pig coronary arteries.

OBJECTIVES: The goal of this study was to evaluate a new drug-eluting stent (DES) comprising a bioabsorbable polymer eluting a moderate dose of paclitaxel in a clinically relevant animal model. BACKGROUND: Although DES limit restenosis, adverse vascular pathologies and toxicities continue to be of major concern. Optimization of DES components, especially completely absorbable polymers, may reduce these toxicities. METHODS: Bare-metal (BM), absorbable polymer coating only (POLY), and polymer-based paclitaxel-eluting (PACL) stents were implanted in porcine coronary arteries using intravascular ultrasound (IVUS) to optimize stent apposition. The dose density of paclitaxel was 0.30-0.35 mcg/mm2, with in vitro elution studies demonstrating a gradual elution over 6-8 weeks. The animals were terminated at 1 week, 1 month and 3 months. Histopathologic and histomorphometric analyses were perform. RESULTS: The arteries with PACL showed extensive smooth muscle cell necrosis at 1 week and poor apposition of stent struts at 1 month (malapposition measured as gap width between strut and internal elastic lamina), with greater gap width compared to the BM and POLY groups (0.22 mm +/- 0.02 vs. 0.03 mm +/- 0.02 and 0.02 mm +/- 0.01, respectively; p < 0.001). At 3 months, the PACL group showed rebound neointimal thickness and histological percent stenosis compared to the BM group (0.48 mm +/- 0.14 vs. 0.07 mm +/- 0.02, respectively; p < 0.001 and 59% +/- 11 vs. 17% +/- 2, respectively; p < 0.001). CONCLUSIONS: Despite in vitro data showing slow, sustained release of paclitaxel from a bioabsorbable polymer, the porcine coronary artery model demonstrated a sequence of medial necrosis, stent malapposition and late neointimal thickening. Since the therapeutic window for paclitaxel may be narrower than currently inferred, thorough preclinical testing coupled with the polymer development process for stents eluting paclitaxel is needed.