Lesion complexity determines arterial drug distribution after local drug delivery.

Though stents are deployed in diseased arteries drug distribution has only been quantified in intact, non-diseased vessels. We correlated steady-state arterial drug distribution with tissue ultrastructure and composition in abdominal aortae from atherosclerotic human autopsy specimens and rabbits with lesions induced by dietary manipulation and controlled injury. Paclitaxel, everolimus, and sirolimus depositions in the human aortae were maximal in the media and scaled inversely with lipid content. Net tissue paclitaxel and everolimus levels were indistinguishable in mildly injured rabbit arteries independent of diet. Yet, serial sectioning of cryopreserved arterial segments demonstrated a differential transmural deposition pattern that was amplified with disease and correlated with the expression of their intracellular targets, tubulin and FKBP-12. Tubulin distribution and paclitaxel binding increased with vascular injury and macrophage infiltration, and were reduced with lipid content. Sirolimus analogs and their specific binding target FKBP-12 were less sensitive to alterations of diet in mildly injured arteries, presumably reflecting a faster transient response of FKBP-12 to injury. The data demonstrate that disease-induced changes in the distribution of drug-binding proteins and interstitial lipid alter the distribution of these drugs, forcing one to consider how disease might affect the evaluation and efficacy of the local release of these and like compounds.

A novel drug-eluting stent coated with an integrin-binding cyclic Arg-Gly-Asp peptide inhibits neointimal hyperplasia by recruiting endothelial progenitor cells.

OBJECTIVES: Novel stents loaded with an integrin-binding cyclic Arg-Gly-Asp peptide (cRGD) were analyzed for their potential to limit coronary neointima formation and to accelerate endothelialization by attracting endothelial progenitor cells (EPCs). BACKGROUND: Re-endothelialization is important for healing after arterial injury. METHODS: Effects of cRGD on EPC number, recruitment in flow, and invasion were analyzed in vitro. A durable polymer coating containing 67 microg cRGD per stent was developed for Guidant Tetra stents. Twelve cRGD-loaded polymer, 12 unloaded polymer, and 12 bare metal stents were deployed in porcine coronary arteries. Quantification of cRGD in peri-stent tissue was established by high-performance liquid chromatography (HPLC) and mass spectrometry (MS). Histomorphometry and immunostaining were performed after 4 and 12 weeks. Recruitment of labeled porcine EPCs was assessed 7 days after intracoronary infusion. RESULTS: The cRGD clearly supported the outgrowth, recruitment, and migration of EPCs in vitro. At 4 weeks, there was no difference for mean neointimal area and percent area stenosis in the cRGD-loaded, polymer, or bare metal stent group. At 12 weeks, neointimal area (2.2 +/- 0.3 mm2) and percent area stenosis (33 +/- 5%) were significantly reduced compared with polymer stents (3.8 +/- 0.4 mm2, 54 +/- 6%; p = 0.010) or bare metal stents (3.8 +/- 0.3 mm2, 53 +/- 3%; p < 0.001). The HPLC/MS confirmed cRGD tissue levels of 1 to 3 mug/stent at 4 weeks, whereas cRGD was not detectable at 12 weeks. Staining for CD34 and scanning electron microscopy indicated enhanced endothelial coverage on cRGD-loaded stents at 4 weeks associated with a significant increase in the early recruitment of infused EPCs. CONCLUSIONS: Stent coating with cRGD may be useful for reducing in-stent restenosis by accelerating endothelialization.

Analysis of peptide affinity to major histocompatibility complex proteins for the two-step binding mechanism.

A novel approach to the analysis of an equilibrium two-step peptide-protein binding is developed and applied to the experimental data. The first step of the process is the release of an endogenous peptide from a binding groove and the second is the binding of an added peptide. The method developed enables us to determine consequently the maximum protein occupancy level (protein-binding capacity), the dissociation constant of an endogenous peptide, and the dissociation constant of a binding (antigenic) peptide. It is shown and confirmed by experimental data that the value of an equilibrium dissociation constant of a binding peptide could be much less than the experimental value of ED(50) (concentration of added peptide required to bind half of the protein), but not equal to that commonly assumed for major histocompatibility complex (MHC)-peptide binding. The model considered gives a clear understanding of why some peptides may be good binders to MHC protein in vitro, but do not exhibit anticipated activity on the cellular level and vice versa.