Local Delivery of Antiproliferative Agents via Stents

4-Methylumbelliferone-Functionalized Polyphosphazene and Its Assembly into Biocompatible Fluorinated Nanocoatings with Selective Antiproliferative Activity

Advanced multifunctional biomaterials are increasingly relying on clinically dictated patterns of selectivity against various biological targets. Integration of these frequently conflicting features into a single material surface may be best achieved by combining various complementary methodologies. Herein, a drug with a broad spectrum of activity, i.e., 4-methylumbelliferone (4-MU), is synthetically multimerized into water-soluble anionic macromolecules with the polyphosphazene backbone. The polymer structure, composition, and solution behavior are studied by ¹H and ³¹P NMR spectroscopy, size-exclusion chromatography, dynamic light scattering, and UV and fluorescence spectrophotometry. To take advantage of the clinically proven hemocompatibility of fluorophosphazene surfaces, the drug-bearing macromolecule was then nanoassembled onto the surface of selected substrates in an aqueous solution with fluorinated polyphosphazene of the opposite charge using the layer-by-layer (LbL) technique. Nanostructured 4-MU-functionalized fluoro-coatings exhibited a strong antiproliferative effect on vascular smooth muscle cells (VSMCs) and fibroblasts with no cytotoxicity against endothelial cells. This selectivity pattern potentially provides the opportunity for highly desirable fast tissue healing while preventing the overgrowth of VSMCs and fibrosis. Taken together with the established in vitro hemocompatibility and anticoagulant activity, 4-MU-functionalized fluoro-coatings demonstrate potential for applications as restenosis-resistant coronary stents and artificial joints.

Pharmaceutical Development of 5-Fluorouracil-Eluting Stents for the Potential Treatment of Gastrointestinal Cancers and Related Obstructions

BACKGROUND

Drug-eluting gastrointestinal (GI) stents are emerging as promising platforms for the treatment of GI cancers and provide the combined advantages of mechanical support to prevent lumen occlusion and as a reservoir for localized drug delivery to tumors. Therefore, in this work we present a detailed quality assurance study of 5-fluorouracil (5FU) drug-eluting stents (DESs) as potential candidates for the treatment of obstructive GI cancers.

METHODS

The 5FU DESs were fabricated via a simple two-step sequential dip-coating process of commercial GI self-expanding nitinol stents with a 5FU-loaded polyurethane basecoat and a drug-free protective poly(ethylene-co-vinyl acetate) topcoat. The drug loading, content uniformity and drug stability were determined using a validated high-performance liquid chromatography (HPLC) method, which is also recommended in the United States Pharmacopeia. In vitro drug release studies were performed in phosphate buffered saline to determine the drug releasing properties of the two 5FU-loaded stents. Gas chromatography (GC) and HPLC were employed to determine total residual tetrahydrofuran and N,N-dimethylformamide in the stents remaining from the manufacturing process. Sterilization of the stents was performed using gamma radiation and stability testing was carried out for 3 months.

RESULTS

The drug loading analysis revealed excellent uniformity in the distribution of 5FU between and within individual stents. Determination of drug stability in the biorelevant release media confirmed that 5FU remains stable over 100 d. In vitro drug release studies from the stents revealed sustained release of 5FU across two different time scales (161 and 30 d), and mathematical modeling of drug release profiles revealed a diffusion-controlled mechanism for the sustained 5FU release. GC and HPLC analysis revealed that the daily residual solvent leached from the stents was below the United States (US) Food and Drug Administration (FDA) guidelines, and therefore, unlikely to cause localized/systemic toxicities. Sterilization of the stents with gamma radiation and accelerated stability tests over a period of 3 months revealed no significant effect on the stability or in vitro release of 5FU.

CONCLUSION

Our results demonstrate that the 5FU DESs meet relevant quality standards and display favourable drug release characteristics for the potential treatment of GI cancers and related obstructions.

Development and In Vitro Evaluation of 5-Fluorouracil-Eluting Stents for the Treatment of Colorectal Cancer and Cancer-Related Obstruction

Self-expanding metal stents (SEMSs) are currently the gold standard for the localised management of malignant gastrointestinal (GI) stenosis and/or obstructions. Despite encouraging clinical success, in-stent restenosis caused by tumour growth is a significant challenge. Incorporating chemotherapeutic drugs into GI stents is an emerging strategy to provide localised and sustained release of drugs to intestinal malignant tissues to prevent tumour growth. Therefore, the aim of this work was to develop and evaluate a local GI stent-based delivery system that provides a controlled release of 5-fluorouracil (5FU) over a course of several weeks to months, for the treatment of colorectal cancer and cancer-related stenosis/obstructions. The 5FU-loaded GI stents were fabricated via sequential dip-coating of commercial GI stents with a drug-loaded polyurethane (PU) basecoat and a drug-free poly(ethylene-co-vinyl acetate) (PEVA) topcoat. For comparison, two types of commercial stents were investigated, including bare and silicone (Si) membrane-covered stents. The physicochemical properties of the 5FU-loaded stents were evaluated using photoacoustic Fourier-transform infrared (PA-FTIR) spectroscopy, X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and thermal analysis. In vitro release studies in biological medium revealed that the 5FU-loaded stents provided a sustained release of drug over the period studied (18 d), and cell viability, cell cycle distribution and apoptosis assays showed that the released 5FU had comparable anticancer activity against human colon cancer cells (HCT-116) to pure 5FU. This study demonstrates that dip-coating is a facile and reliable approach for fabricating drug-eluting stents (DESs) that are promising candidates for the treatment of GI obstructions and/or restenosis.

Influence of Polymer Composition on the Controlled Release of Docetaxel: A Comparison of Non-Degradable Polymer Films for Oesophageal Drug-Eluting Stents

Following the huge clinical success of drug-eluting vascular stents, there is a significant interest in the development of drug-eluting stents for other applications, such as the treatment of gastrointestinal (GI) cancers. Central to this process is understanding how particular drugs are released from stent coatings, which to a large extent is controlled by drug-polymer interactions. Therefore, in this study we investigated the release of docetaxel (DTX) from a selection of non-degradable polymer films. DTX-polymer films were prepared at various loadings (1, 5 and 10% w/w) using three commercially available polymers including poly(dimethylsiloxane) (PSi), poly (ethylene-co-vinyl acetate) (PEVA) and Chronosil polyurethane (PU). The formulations were characterised using different techniques such as photoacoustic Fourier-transform infrared (PA-FTIR) spectrophotometry, X-ray diffraction (XRD) and differential scanning calorimetry (DSC). The effect of DTX on the mechanical properties of the films, in-vitro release, and degradation tests were also assessed. For all polymers and DTX loadings, the drug was found to disperse homogenously without crystallisation within the polymer matrix. While no specific interactions were observed between DTX and PSi or PEVA, hydrogen-bonding appeared to be present between DTX and PU, which resulted in a concentration-dependent decrease in the Young’s moduli of the films due to disruption of inter-polymeric molecular interactions. In addition, the DTX-PU interactions were found to modulate drug release, providing near-linear release over 30 days, which was accompanied by a significant reduction in degradation products. The results indicate that DTX-loaded PU films are excellent candidates for drug-eluting stents for the treatment of oesophageal cancer.

Three-dimensional printed 5-fluorouracil eluting polyurethane stents for the treatment of oesophageal cancers

3D printing is introduced as rapid and facile approach to prepare personalized drug-eluting stents for the treatment of oesophageal cancers.

Gemcitabine-incorporated polyurethane films for controlled release of an anticancer drug

Background

Local delivery of anti-cancer drugs through a stent is a very promising and anticipated treatment modality for patients who have obstructions in their gastrointestinal tract with malignant tumors. Anticancer drug release via stents, however, needs to be optimized with respect to drug delivery behavior for the stents to be effective for prolonged containment of tumor proliferation and stent re-obstruction. Local stent-based drug delivery has been tested using an effective anti-cancer drug, gemcitabine, but the release from the stent-coated polyurethane films is often too fast and the drug is depleted from the coated film virtually in a day.

Methods

To moderate the drug release from a polyurethane film, a gemcitabine-incorporated polyurethane film was enveloped with a pure polyurethane film, with no drug loading, and with a silicone film by solution casting after activation of the silicone film surface with plasma treatment.

Results

The pure polyurethane barrier film was effective; the interface of the two were indistinguishable on scanning electron microscopy, and the initial burst, i.e., the cumulative release in a day, decreased from 90 to 26%. The silicone film barrier, on the other hand, was defective as voids were seen using a scanning electron microscope, and micro-separation of the two layers was observed after the film was immersed in phosphate-buffered saline for 1 day during the in vitro drug release study.

Conclusions

Enveloping a gemcitabine-releasing polyurethane film with a homo-polymer barrier film was quite effective for moderating the initial burst of gemcitabine, thus, prolonging the release time of the drug. Enveloping the polyurethane film with a silicone film was also possible after plasma treatment of the silicone film surface, but the two films eventually separated in the aqueous environment. More studies are needed to tune the drug release behavior of gemcitabine from the stent covering film before attempting a clinical application of an anti-cancer drug releasing stent.

Enzyme Prodrug Therapy Engineered into Electrospun Fibers with Embedded Liposomes for Controlled, Localized Synthesis of Therapeutics

Enzyme prodrug therapy (EPT) enables localized conversion of inert prodrugs to active drugs by enzymes. Performance of EPT necessitates that the enzyme remains active throughout the time frame of the envisioned therapeutic application. β-glucuronidase is an enzyme with historically validated performance in EPT, however it retains its activity in biomaterials for an insufficiently long period of time, typically not exceeding 7 d. Herein, the encapsulation of β-glucuronidase in liposomal subcompartments within poly(vinyl alcohol) electrospun fibers is reported, leading to the assembly of biocatalytically active materials with activity of the enzyme sustained over at least seven weeks. It is further shown that liposomes provide the highly beneficial stabilization of the enzyme when incubated in cell culture media. The assembled biocatalytic materials successfully produce antiproliferative drugs (SN-38) using externally administered prodrugs (SN-38-glucuronide) and effectively suppress cell proliferation, with envisioned utility in the design of cardiovascular grafts.

Synthesis and characterization of cycloaliphatic hydrophilic polyurethanes, modified with l-ascorbic acid, as materials for soft tissue regeneration

In this paper we described synthesis and characteristic of obtained hydrophilic polyurethanes (PURs) modified with ascorbic acid (commonly known as vitamin C). Such materials may find an application in the biomedical field, for example in the regenerative medicine of soft tissues, according to ascorbic acid wide influence on tissue regeneration Flora (2009), Szymańska-Pasternak et al. (2011), Taikarimi and Ibrahim (2011), Myrvik and Volk (1954), Li et al. (2001), Cursino et al. (2005) . Hydrophilic PURs were obtained with the use of amorphous α,ω-dihydroxy(ethylene-butylene adipate) (dHEBA) polyol, 1,4-butanediol (BDO) chain extender and aliphatic 4,4'-methylenebis(cyclohexyl isocyanate) (HMDI). HMDI was chosen as a nontoxic diisocyanate, suitable for biomedical PUR synthesis. Modification with l-ascorbic acid (AA) was performed to improve obtained PUR materials biocompatibility. Chemical structure of obtained PURs was provided and confirmed by Fourier transform infrared spectroscopy (FTIR) and Proton nuclear magnetic resonance spectroscopy (¹HNMR). Differential scanning calorimetry (DSC) was used to indicate the influence of ascorbic acid modification on such parameters as glass transition temperature, melting temperature and melting enthalpies of obtained materials. To determine how these materials may potentially behave, after implementation in tissue, degradation behavior of obtained PURs in various chemical environments, which were represented by canola oil, saline solution, distilled water and phosphate buffered saline (PBS) was estimated. The influence of AA on hydrophilic-hydrophobic character of obtained PURs was established by contact angle study. This experiment revealed that ascorbic acid significantly improves hydrophilicity of obtained PUR materials and the same cause that they are more suitable candidates for biomedical applications. Good hemocompatibility characteristic of studied PUR materials was confirmed by the hemocompatibility test with human blood. Microbiological tests were carried out to indicate the microbiological sensitivity of obtained PURs. Results of performed studies showed that obtained AA-modified PUR materials may find an application in soft tissue regeneration.

RNA-Eluting Surfaces for the Modulation of Gene Expression as A Novel Stent Concept

Presently, a new era of drug-eluting stents is continuing to improve late adverse effects such as thrombosis after coronary stent implantation in atherosclerotic vessels. The application of gene expression–modulating stents releasing specific small interfering RNAs (siRNAs) or messenger RNAs (mRNAs) to the vascular wall might have the potential to improve the regeneration of the vessel wall and to inhibit adverse effects as a new promising therapeutic strategy. Different poly (lactic-co-glycolic acid) (PLGA) resomers for their ability as an siRNA delivery carrier against intercellular adhesion molecule (ICAM)-1 with a depot effect were tested. Biodegradability, hemocompatibility, and high cell viability were found in all PLGAs. We generated PLGA coatings with incorporated siRNA that were able to transfect EA.hy926 and human vascular endothelial cells. Transfected EA.hy926 showed significant siICAM-1 knockdown. Furthermore, co-transfection of siRNA and enhanced green fluorescent protein (eGFP) mRNA led to the expression of eGFP as well as to the siRNA transfection. Using our PLGA and siRNA multilayers, we reached high transfection efficiencies in EA.hy926 cells until day six and long-lasting transfection until day 20. Our results indicate that siRNA and mRNA nanoparticles incorporated in PLGA films have the potential for the modulation of gene expression after stent implantation to achieve accelerated regeneration of endothelial cells and to reduce the risk of restenosis.

Gefitinib/gefitinib microspheres loaded polyurethane constructs as drug-eluting stent coating

One of the complications of bronchotracheal cancer is obstruction of the upper airways. Local tumor resection in combination with an airway stent can suppress intraluminal tumor (re)growth. We have investigated a novel drug-eluting stent coating for local release of the anticancer drug gefitinib. A polyurethane (PU) sandwich construct was prepared by a spray coating method in which gefitinib was embedded between a PU support layer of 200μm and a PU top layer of 50-200μm. Gefitinib was either embedded in the construct as small crystals or as gefitinib-loaded poly(lactic-co-glycolic acid) (PLGA) microspheres (MSP). The drug was incorporated in the PU constructs with high recovery (83-93%), and the spray coating procedure did not affect the morphologies of the embedded microspheres as demonstrated by scanning electron microscopy (SEM), confocal laser scanning microscopy and fluorescence microscopy analysis. PU constructs loaded with gefitinib crystals released the drug for 7-21days and showed diffusion based release kinetics. Importantly, directional release of the drug towards the top layer, which is supposed to face the tumor mass, was controlled by the thicknesses of the PU top layer. PU constructs loaded with gefitinib microspheres released the drug in a sustained manner for >6months indicating that drug release from the microspheres became the rate limiting step. In conclusion, the sandwich structure of drug-loaded PLGA microspheres in PU coating is a promising coating for airway stents that release anticancer drugs locally for a prolonged time.

Preparation of a Microporous Polyurethane Film with Negative Surface Charge for siRNA Delivery via Stent

Polyurethane (PU) and polyethylene glycol (PEG) were used to prepare a porous stent-covering material for the controlled delivery of small interfering RNA (siRNA). Microporous polymer films were prepared using a blend of polyurethane and water-soluble polyethylene glycol by the solution casting method; the PEG component was extracted in water to make the film microporous. This film was dipped in 2% poly(methyl methacrylate-co-methacrylic acid) solution to coat the polymer film with the anionic polyelectrolyte. The chemical components of the film surface were characterized by Fourier Transform Infrared (FTIR) spectroscopy and its structural morphology was examined by scanning electron microscopy (SEM). The effect of the negatively charged surface after attachment of a fluorescein isothiocyanate- (FITC-) labeled siRNA-polyethyleneimine complex onto the microporous polyurethane film and the controlled release of the complex from the film was investigated by fluorescence microscopy. Fluorescence microscopy showed the PU surface with intense fluorescence by the aggregates of the FITC-labeled-siRNA-PEI complex (measuring up to few microns in size); additionally, the negatively charged PU surface revealed broad and diffuse fluorescence. These results suggest that the construction of negatively charged microporous polyurethane films is feasible and could be applied for enhancing the efficiency of siRNA delivery via a stent-covering polyurethane film.

Bioresorbable drug-eluting scaffolds for treatment of vascular disease

INTRODUCTION

Theoretical advantages of fully bioresorbable scaffold (BRS) stem from transient vessel support without rigid caging. Therefore, it could reduce long-term adverse events associated with the presence of foreign materials.

AREAS COVERED

This article will provide an overview of: drug-eluting BRS for various applications in the treatment of vascular disease; The mechanisms of active agent release from such scaffolds; currently available drug-eluting BRS and their future applications are also discussed.

EXPERT OPINION

The current BRS have been developed in order to achieve optimal vascular patency while providing long-term safety. The clinical efficacy and safety of BRS in coronary treatment have been reported as equal to that of the current metallic drug eluting stents in simple lesions. The application of BRS can potentially be expanded to other vascular beds. The research in bioengineering for the appropriate materials should not only focus on biocompatibility but also should be tailored according to the sites of implantation, which may require different strength and supporting period. The ultimate goal in this field is to develop a biocompatible device that provides equivalent and complementary therapy to other devices, and is able to disappear when the mechanical support and drug delivery are no longer required.

Surface Modification of Biodegradable Polymers towards Better Biocompatibility and Lower Thrombogenicity

Purpose

Drug-eluting stents (DES) based on permanent polymeric coating matrices have been introduced to overcome the in stent restenosis associated with bare metal stents (BMS). A further step was the development of DES with biodegradable polymeric coatings to address the risk of thrombosis associated with first-generation DES. In this study we evaluate the biocompatibility of biodegradable polymer materials for their potential use as coating matrices for DES or as materials for fully bioabsorbable vascular stents.

Materials and Methods

Five different polymers, poly(L-lactide) PLLA, poly(D,L-lactide) PDLLA, poly(L-lactide-co-glycolide) P(LLA-co-GA), poly(D,L-lactide-co-glycolide) P(DLLA-co-GA) and poly(L-lactide-co-ε-caprolactone), P(LLA-co-CL) were examined in vitro without and with surface modification. The surface modification of polymers was performed by means of wet-chemical (NaOH and ethylenediamine (EDA)) and plasma-chemical (O₂ and NH₃) processes. The biocompatibility studies were performed on three different cell types: immortalized mouse fibroblasts (cell line L929), human coronary artery endothelial cells (HCAEC) and human umbilical vein endothelial cells (HUVEC). The biocompatibility was examined quantitatively using in vitro cytotoxicity assay. Cells were investigated immunocytochemically for expression of specific markers, and morphology was visualized using confocal laser scanning (CLSM) and scanning electron (SEM) microscopy. Additionally, polymer surfaces were examined for their thrombogenicity using an established hemocompatibility test.

Results

Both endothelial cell types exhibited poor viability and adhesion on all five unmodified polymer surfaces. The biocompatibility of the polymers could be influenced positively by surface modifications. In particular, a reproducible effect was observed for NH₃-plasma treatment, which enhanced the cell viability, adhesion and morphology on all five polymeric surfaces.

Conclusion

Surface modification of polymers can provide a useful approach to enhance their biocompatibility. For clinical application, attempts should be made to stabilize the plasma modification and use it for coupling of biomolecules to accelerate the re-endothelialization of stent surfaces in vivo.

Polyurethane membrane with porous surface for controlled drug release in drug eluting stent

Background

Membrane covered drug eluting stents (DES) were prepared to prevent tumor ingrowth and to control drug release. Polyurethane (PU) is commonly used for DES coating material because of high tensile strength. The release of paclitaxel (PTX) may increase from porous PU membrane.

Results

Polyethylene glycol (PEG) was incorporated into PU membranes to form porous structure and control the release of hydrophobic anti-cancer drug such as PTX. The bare metal stents were coated with PEG incorporated PU and then, PEG was washed out to form porous structure. The crystallization of PTX was inhibited in porous PU membranes and the release of PTX from porous PU membranes was approximately 8.6% more extended over 19 days.

Conclusions

The enhanced release of PTX from porous PU membranes may increase the patency for the DES covering materials.