Catheter-based drug delivery for restenosis

Nanomedicine approaches in vascular disease: a review

Nanomedicine approaches have revolutionized the treatment of cancer and vascular diseases, where the limitations of rapid nonspecific clearance, poor biodistribution and harmful side effects associated with direct systemic drug administration can be overcome by packaging the agents within sterically stabilized, long-circulating nanovehicles that can be further surface-modified with ligands to actively target cellular/molecular components of the disease. With significant advancements in genetics, proteomics, cellular and molecular biology and biomaterials engineering, the nanomedicine strategies have become progressively refined regarding the modulation of surface and bulk chemistry of the nanovehicles, control of drug release kinetics, manipulation of nanoconstruct geometry and integration of multiple functionalities on single nanoplatforms. The current review aims to capture the various nanomedicine approaches directed specifically toward vascular diseases during the past two decades. Analysis of the promises and limitations of these approaches will help identify and optimize vascular nanomedicine systems to enhance their efficacy and clinical translation in the future.

FROM THE CLINICAL EDITOR

Nanomedicine-based approaches have had a major impact on the treatment and diagnosis of malignancies and vascular diseases. This review discusses various nanomedicine approaches directed specifically toward vascular diseases during the past two decades, highlighting their advantages, limitations and offering new perspectives on future applications.

Streptokinase loading in liposomes for vascular targeted nanomedicine applications: encapsulation efficiency and effects of processing

Vascular diseases leading to thrombo-occlusion are the leading cause of morbidity and mortality worldwide. Revascularization and restoration of antegrade blood flow is critical for tissue survival and patient health. In this aspect, systemic administration of thrombolytics (e.g., streptokinase) to dissolve occlusive thrombi is a clinically established strategy. However, this strategy typically necessitates the administration of large doses, leading to a high incidence of hemorrhagic complications due to systemic side effects. To minimize this risk, liposomes specifically targeted to the site of thrombo-occlusion have been bioengineered by exploiting ligand-receptor relationships pertinent to thrombus-associated cell phenotypes. This study focuses on encapsulating streptokinase within these liposomes, specifically regarding the effect of liposome processing conditions on streptokinase encapsulation and activity. Theoretical calculations of encapsulation capacity agreed well with that reported in the literature. The experimental encapsulation efficiency values are 45.9 ± 34.0% (n = 9 ± SD) and 21.6 ± 30.0% (n = 6 ± SD), using two different methods. The liposome processing conditions are found to decrease streptokinase activity; however, over 30% remain active after processing, maintaining enough activity to be therapeutic especially when protected inside a vehicle targeted to the site of thrombo-occlusion. The insight gained from the research reported here would enable refining the design and the processing conditions of liposomal formulations of fibrinolytics to yield reduced variability in encapsulation efficiency and streptokinase activity. The design of a thrombus-targeted 'stealth' liposome reported earlier and the current findings of fibrinolytics' encapsulation and activity in such liposomes can be efficiently integrated to develop an efficient strategy for vascular nanomedicine.

Production and in vitro characterization of lisinopril-loaded nanoparticles for the treatment of restenosis in stented coronary arteries

Lisinopril, an angiotensin converting enzyme (ACE) inhibitor drug, was encapsulated in poly(lactide-co-glicolide) (PLGA) nanoparticles (NP) for site-specific delivery by catheters in prevention of restenosis. NP were prepared by emulsification-diffusion method. The PLGA type, stabilizing agent type and its concentration were studied as process variables. The z-average particle size varied between 265-412 nm. The highest zeta potential was seen in NP prepared with Pluronic F-68. None of the studied variables or their interactions had a significant effect on the particle size while all had main effect on the zeta potential. The highest entrapment efficiency was 93% and all studied variables and their interactions except PLGA type and its interaction with the stabilizer type had significant effects on the loading. Baker-Lonsdale model was the most appropriate model for release of lisinopril from NP. Five per cent PLGA 75:25 and 5% Pluronic F-68 showed promising results for 21 days release of lisinopril as an anti-restenotic agent.

Mathematical modelling of NABD release from endoluminal gel paved stent

Coronary restenosis consists of the partial/total re-occlusion of the artery lumen following percutaneous transluminal angioplasty (PTCA). In order to match this pathology, PTCA is followed by the implantation of rigid scaffolds (stent or coated stent) aimed to contrast the most important mechanical (coronary wall elastic recoil and late remodelling) and biological (smooth muscle cells iper-proliferation) factors leading to restenosis. In the light of the clinical problems recently arisen about the use of traditional coated stents, this paper proposes a theoretical study to comprehend the release kinetics of novel anti-proliferative drugs, i.e. nucleic acid based drugs (NABD), complexed with the proper delivery agent (DA). The release of NABD-DA is supposed to occur from a double gel layer adhering to coronary wall and embedding the stent. The proposed mathematical model assumes that diffusion, convection and cellular internalisation/metabolism are the leading mechanisms ruling drug spreading in the coronary wall. In addition, stent void fraction, positioning (totally embedded or totally out of the coronary wall) and continuous or discontinuous character of the gel layer are other three important model parameters. In order to generalise the results, stent geometry is idealised as a series of not connected, equally spaced, rings positioned in the stented zone. In correspondence of stent strut, drug transport cannot occur. The most important outcomes of this study are that, in the usual void fraction range (0.7-0.9), stent presence does not sensibly affect NABD-DA release kinetics. In addition, whereas stent positioning in the continuous gel configuration (totally embedded or totally out of coronary wall) is not very important, in the discontinuous case, it becomes relevant. Finally, this study evidences that a proper mixture of NABD complexed with different (in dimensions and kind) DA can ensure an almost constant NABD coronary concentration for several months, as requested by clinical observations.

Locally delivered nanoencapsulated tyrphostin (AGL-2043) reduces neointima formation in balloon-injured rat carotid and stented porcine coronary arteries

Local delivery of antiproliferative drugs encapsulated in biodegradable nanoparticles (NP) has shown promise as an experimental strategy for preventing restenosis development. A novel PDGFRbeta-specific tyrphostin, AGL-2043, was formulated in polylactide-based nanoparticles and was administered intraluminally to the wall of balloon-injured rat carotid and stented pig coronary arteries. The disposition and elimination kinetics within the vessel wall, as well as the antirestenotic potential of the novel drug and delivery system, were evaluated. The efficacy and the local drug elimination kinetics were affected by the size of the NP and the drug-carrier binding mode. Despite similar arterial drug levels 90 min after delivery in rats, small NP were more efficacious in comparison to large NP (90 and 160 nm, respectively). AGL-2043 selectively inhibited vascular SMC in a dose-dependent manner. The antiproliferative effect of nanoencapsulated tyrphostin was considerably higher than that of surface-adsorbed drug. In the pig model, intramural delivery of AGL-2043 resulted in reduced in-stent neointima formation in the coronary arteries over control despite similar degrees of wall injury. The results of this study suggest that locally delivered tyrphostin AGL-2043 formulated in biodegradable NP may be applicable for antirestenotic therapy independent of stent design or type of injury.

Local drug delivery in restenosis injury: thermoresponsive co-polymers as potential drug delivery systems

The success of percutaneous transluminal coronary angioplasty in treatment of acute coronary syndromes has been compromised by the incidence of restenosis. The physical insult of balloon insertion can damage or remove the endothelial monolayer, thereby generating a prothrombotic surface. The resulting inappropriate response to injury can also lead to penetration of inflammatory cells, conversion of the underlying media to a synthetic phenotype, deposition of extracellular matrix, constrictive remodeling, and neointimal hyperplasia. While stent implantation at the time of balloon insertion has offset some of these events, inflammatory responses to the implanted biomaterial (stent) and intimal hyperplasia are still prominent features of the procedure, leading in 20-30% of cases to in-stent restenosis within a year. Systemic delivery of drugs designed to offset in-stent restenosis injury has been largely unsuccessful, which has led to the development of strategies for coating stents with drugs for local delivery. Drug-eluting stents constitute an innovative means of further reducing the incidence of restenosis injury and clinical trials have shown encouraging results. This review focuses on properties of a class of environment-sensitive hydrogels, the N-isopropylacrylamide-based thermoresponsive co-polymers, on their potential roles as stent coatings, on their demonstrated ability to incorporate and release drugs that modify vascular endothelial and smooth muscle cell functions, and on issues that still await clarification, prior to their adoption in a clinical setting.