Gemcitabine-releasing polymeric films for covered self-expandable metallic stent in treatment of gastrointestinal cancer. Int J Pharm. 2012;427:276-283. [PMID: 22366483 DOI: 10.1016/j.ijpharm.2012.02.016]

Biliary stents for active materials and surface modification: Recent advances and future perspectives

Demand for biliary stents has expanded with the increasing incidence of biliary disease. The implantation of plastic or self-expandable metal stents can be an effective treatment for biliary strictures. However, these stents are nondegradable and prone to restenosis. Surgical removal or replacement of the nondegradable stents is necessary in cases of disease resolution or restenosis. To overcome these shortcomings, improvements were made to the materials and surfaces used for the stents. First, this paper reviews the advantages and limitations of nondegradable stents. Second, emphasis is placed on biodegradable polymer and biodegradable metal stents, along with functional coatings. This also encompasses tissue engineering & 3D-printed stents were highlighted. Finally, the future perspectives of biliary stents, including pro-epithelialization coatings, multifunctional coated stents, biodegradable shape memory stents, and 4D bioprinting, were discussed.

Preclinical evaluation of endoscopic placement of a steroid-eluting metal stent in an in vivo porcine benign biliary stricture model

Treatment of benign biliary strictures (BBS) using fully covered self-expandable metal stents (FCSEMS) has a high success rate, but recurrence can occur. Corticosteroids may be useful based on their anti-fibrotic and anti-inflammatory effects. We investigated the safety and efficacy of corticosteroid-eluting FCSEMS in an animal model. BBSs were created by radiofrequency ablation in 12 mini-pigs. Four weeks later, FCSEMS coated with 0 mg (control), 15 mg (steroid 1 × group), or 30 mg (steroid 2 × group) triamcinolone were inserted endoscopically. The in vitro drug release assay revealed that the optimal stent had 15 mg of triamcinolone and a hydrophilic membrane. No transmural necrosis or perforation occurred in any animal. Fibrous wall thickness tended to decrease macroscopically and microscopically in a triamcinolone dose-dependent manner (control vs. steroid 2 × group: 773.1 vs. 468.5 µm, P = 0.037). Thickness also decreased over time in the steroid 2 × group (3 days vs. 4 weeks: 907.9 vs. 468.5 µm, P = 0.025). Blood parameters tended to improve after stent insertion. In a porcine BBS model, steroid-eluting FCSEMS showed potential as a safe and effective treatment modality to reduce fibrotic tissue. Studies are required to confirm their safety and efficacy in humans with refractory BBS.

A review on biodegradable biliary stents: materials and future trends

Biliary stricture is defined as the reduction and narrowing of the bile duct lumen, which can be caused by many factors such as cancer and inflammation. Biliary stent placement can effectively alleviate benign and malignant biliary strictures. However, the commonly used plastic or metallic biliary stents are far from ideal and do not satisfy all clinical requirements，although several types of biodegradable biliary stents have been developed and used clinically. In this review, we summarized current development status of biodegradable stents with the emphasis on the stent materials. We also presented the future development trends based on the published literature.

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Summary of current development status of bioresorbable biliary stents with the emphasis on the stent materials.

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The future development trends based on the published literature.

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The advantages of bioresorbable biliary stents compared with metallic and plastic biliary stents.

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.

Gastro-retentive drug delivery systems: a recent update on clinical pertinence and drug delivery

Gastro-retentive drug delivery systems are some of the best technologies delivered through oral route. These mainly came into picture for their effective local action in the GI region, specifically for the drugs with narrow absorption window. In the recent decades, several technologies have evolved showing different mechanisms for retaining the drug in GI region for longer duration with increased bioavailability. Floatable, mucoadhesive, swelable, magnetic, nanofibrous, high-density, and expandable systems have been investigated extensively as the potential gastro-retentive strategies. The advances in the technologies studied, their clinical pertinence, and methods of drug delivery are described in this review with their immense future utilities. Their entry into the pharmaceutical market is a huge matter to look into as most of the studied strategies are facing problems and hence are underrated to overcome the clinical trials. Their success in the clinical trials are enormously required for gaining their access into the pharmaceutical market. Selection of the right technology for the right purpose through the right mechanism of action is to be done for obtaining the system with desired activity.

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.

Feasibility and efficacy evaluation of metallic biliary stents eluting gemcitabine and cisplatin for extrahepatic cholangiocarcinoma

BACKGROUND

Effective endoscopic management is fundamental for the treatment of extrahepatic cholangiocarcinoma (ECC). However, current biliary stents that are widely used in clinical practice showed no antitumor effect. Drug-eluting stents (DESs) may achieve a combination of local chemotherapy and biliary drainage to prolong stent patency and improve prognosis.

AIM

To develop novel DESs coated with gemcitabine (GEM) and cisplatin (CIS)-coloaded nanofilms that can maintain the continuous and long-term release of antitumor agents in the bile duct to inhibit tumor growth and reduce systemic toxicity.

METHODS

Stents coated with different drug-eluting components were prepared by the mixed electrospinning method, with poly-L-lactide-caprolactone (PLCL) as the drug-loaded nanofiber membrane and GEM and/or CIS as the antitumor agents. Four different DESs were manufactured with four drug-loading ratios (5%, 10%, 15%, and 20%), including bare-loaded (PLCL-0), single-drug-loaded (PLCL-GEM and PLCL-CIS), and dual-drug-loaded (PLCL-GC) stents. The drug release property, antitumor activity, and biocompatibility were evaluated in vitro and in vivo to confirm the feasibility and efficacy of this novel DES for ECC.

RESULTS

The in vitro drug release study showed the stable, continuous release of both GEM and CIS, which was sustained for over 30 d without an obvious initial burst, and a higher drug-loaded content induced a lower release rate. The drug-loading ratio of 10% was used for further experiments due to its ideal inhibitory efficiency and relatively low toxicity. All drug-loaded nanofilms effectively inhibited the growth of EGI-1 cells in vitro and the tumor xenografts of nude mice in vivo; in addition, the dual-loaded nanofilm (PLCL-GC) had a significantly better effect than the single-drug-loaded nanofilms (P < 0.05). No significant differences in the serological analysis (P > 0.05) or histopathological changes were observed between the single-loaded and drug-loaded nanofilms after stent placement in the normal porcine biliary tract.

CONCLUSION

This novel PLCL-GEM and CIS-eluting stent maintains continuous, stable drug release locally and inhibits tumor growth effectively in vitro and in vivo. It can also be used safely in normal porcine bile ducts. We anticipate that it might be considered an alternative strategy for the palliative therapy of ECC patients.

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.

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.

A novel low molecular weight nanocomposite hydrogel formulation for intra-tumoural delivery of anti-cancer drugs

Herein, an injectable formulation composed of a low molecular weight gelator (LMWG) based hydrogel and drug-loaded polymeric nanocapsules (NCs) is described. The NCs, made of hyaluronic acid and polyglutamic acid and loaded with C14-Gemcitabine (GEM C14), showed a size of 40 and 80 nm and a encapsulation efficiency >90%. These NCs exhibited a capacity to control the release of the encapsulated drug for >1 month. GEM C14-loaded NCs showed activity against various cancer cell lines in vitro; cell growth inhibition by 50% (GI₅₀) values of 15 ± 6, 10 ± 9, 13 ± 3 and 410 ± 463 nM were obtained in HCT 116, MIA PaCa-2, Panc-1 and Panc-1 GEM resistant cell lines respectively. Nanocomposite hydrogels were prepared using the LMWG - N4-octanoyl-2'-deoxycytidine and loaded for the first time with polymeric NCs. 2% and 4% w/v nanocapsule concentrations as compared to 8% w/v NC concentrations with 2% and 3% w/v gelator concentrations gave mechanically stronger gels as determined by oscillatory rheology. Most importantly, the nanocomposite formulation reformed instantly into a gel after injection through a needle. Based on these properties, the nanocomposite gel formulation has potential for the intratumoural delivery of anticancer drugs.

A Review of Self-Expanding Esophageal Stents for the Palliation Therapy of Inoperable Esophageal Malignancies

Esophageal cancer is a very deadly disease, killing more than 15,000 people in the United States annually. Almost 400,000 new cases happen in the worldwide every year. More than 50% esophageal cancer patients are diagnosed at an advanced stage when they need an esophageal stent to open the blocked esophagus for feeding and drinking. Esophageal stents have evolved in stages over the years. Current clinically used stents commonly include stainless steel or nitinol self-expandable metallic stent (SEMS) and self-expandable plastic stent (SEPS). There are many choices of different types of stents and sizes, with fierce competition among manufacturers. However, current stent technology, whether uncovered, partially covered, fully covered SEMS or SEPS, has their own advantages to solve the dysphagia, stricture, and fistula problems, but they also cause some clinical complications. The ideal stent remains elusive. New 3D printing technique may bring new promising potential to manufacturing personalized esophageal stents. Drug-eluting stents could be the new avenue to do more than just pry open a stricture or cover a defect in the esophageal lumen, a possibility of proving local anticancer therapy simultaneously. Additionally, the lack of esophageal cancer animal models also hinders the progress of stent development. This paper reviews these topics for a comprehensive understanding of this field. In a conclusion, the ultimate goal of the future esophageal stent would have multifunction to treat the underlying conditions and restore esophageal function to near normal.

Electrochemical corrosion behavior of a non-vascular, bi-stent combination, surgical esophageal nitinol stent in phosphate-buffered saline solution

In the present work, the corrosion behavior of a bi-stent combination, which is the combination of an uncoated outer stent and silicone-coated body stent, was assessed by the use of electrochemical methods in phosphate-buffered saline at 37 °C. Although each stent comprising the bi-stent combination showed favorable corrosion properties, the bi-stent combination showed significant decreases in these corrosion properties. Corrosion was concentrated on the uncoated outer stent of the bi-stent combination. The cathodic reaction was activated on the outer stent of the bi-stent combination by the galvanic effect, and the hydrogen generated was detrimental to the surface film on the outer stent. In addition, hydrogen had a synergic effect with chloride and accelerated the corrosion reaction on the outer stent.

Stent-mediated gene and drug delivery for cardiovascular disease and cancer: A brief insight

This review concisely recapitulates the different existing modes of stent-mediated gene/drug delivery, their considerable advancement in clinical trials and a rationale for other merging new technologies such as nanotechnology and microRNA-based therapeutics, in addition to addressing the limitations in each of these perpetual stent platforms. Over the past decade, stent-mediated gene/drug delivery has materialized as a hopeful alternative for cardiovascular disease and cancer in contrast to routine conventional treatment modalities. Regardless of the phenomenal recent developments achieved by coronary interventions and cancer therapies that employ gene and drug-eluting stents, practical hurdles still remain a challenge. The present review highlights the limitations that each of the existing stent-based gene/drug delivery system encompasses and therefore provides a vision for the future with respect to discovering an ideal stent therapeutic platform that would circumvent all the practical hurdles witnessed with the existing technology. Further study of the improvisation of next-generation drug-eluting stents has helped to overcome the issue of restenosis to some extent. However, current stent formulations fall short of the anticipated clinically meaningful outcomes and there is an explicit need for more randomized trials aiming to further evaluate stent platforms in favour of enhanced safety and clinical value. Gene-eluting stents may hold promise in contributing new ideas for stent-based prevention of in-stent restenosis through genetic interventions by capitalizing on a wide variety of molecular targets. Therefore, the central consideration directs us toward finding an ideal stent therapeutic platform that would tackle all of the gaps in the existing technology.

A novel photodynamic therapy-based drug delivery system layered on a stent for treating cholangiocarcinoma

This study aimed to investigate the drug delivery efficacy and bio-effectiveness of a novel photodynamic therapy (PDT)-matrix drug delivery system for cholangiocarcinoma (CCA). Metallic stents were coated with polyurethane (PU) as the first layer. A 2-hydroxyethyl methacrylate (2-HEMA)/ethylene glycol dimethacrylate (EGDMA)/benzoyl peroxide (BPO) layer and a poly(ethylene-co-vinyl acetate) (PEVA)/poly(n-butyl methacrylate) (PBMA)/polyvinylpyrrolidone K30 (K30) layer containing various concentrations of Photofrin were then incorporated onto the stent as the second and third layers. After incubating the layered membranes with cultured CCA cell line, the release of Photofrin, cell viability, the intracellular uptake of Photofrin, reactive oxygen species (ROS) generation, and apoptosis were determined. Using a single-layer diffusion model, the maximum release of Photofrin from the 5 to 10% K30 formulas was 80 and 100%, respectively, after 24 h. When using the multiple-layer diffusion model, the released Photofrin showed an initial burst of the loading dose from the PEVA/PBMA/K30 layer. In the immobilized model, less than 5% of the Photofrin from the 2-HEMA/EGDMA/BPO layer was released over the 24-h period. Cell viability decreased linearly with increasing Photofrin concentrations, and ROS generation and apoptosis were shown to increase significantly with increasing Photofrin concentrations, until the concentration of Photofrin reached a saturation point of 1.5 μg/ml. This new, multiple-layered, PDT-based stent with dual-release mechanisms is a promising treatment for CCA and cancer-related ductal stenosis.

In Vitro and In Vivo Assessment of Docetaxel Formulation Developed for Esophageal Stents

Esophageal cancer (EC) mostly affects the elderly population and is frequently diagnosed at an advanced stage. Self-expanding metal stents (SEMS) are the most popular mode of palliation, but they are associated with reocclusion caused by tumor growth. To overcome this problem, docetaxel (DTX)-loaded polyurethane formulations were prepared for stent application. The films were evaluated against the cancer cell lines, OE-19 and OE-21, and normal esophageal cell line Het-1A. The DTX and the formulations were evaluated in vitro for the cytotoxicity and in vivo in nude mice. It was found that DTX and the formulations have a weak activity against the EC cell lines and an even weaker activity against Het-1A cell line. Preliminary in vivo studies showed skin toxicity in nude mice necessitating modification of the formulation. Reevaluation in a mouse xenograft model resulted in toxicity at high dose formulations while the low dose formulation exhibited modest advantage over commercial IV formulation; however, there was no significant difference between the commercial IV and blank formulation. DTX combination with an anti-cancer agent having complementary mode of action and non-overlapping toxicity could yield better outcome in future.

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.

Effect of polymer microstructure on the docetaxel release and stability of polyurethane formulation

PurSil®AL20 (PUS), a copolymer of 4,4'-dicyclohexylmethane diisocyanate (HMDI), 1,4-butane diol (BD), poly-tetramethylene oxide (PTMO) and poly-dimethyl siloxane (PDMS) was investigated for stability as a vehicle for Docetaxel (DTX) delivery through oesophageal drug eluting stent (DES). On exposure to stability test conditions, it was found that DTX release rate declined at 4 and 40 °C. In order to divulge reasons underlying this, changes in DTX solid state as well as PUS microstructure were followed. It was found that re-crystallization of DTX in PDMS rich regions was reducing the drug release at both 4 °C and 40 °C samples. So far microstructural features have not been correlated with stability and drug release, and in this study we found that at 40 °C increase in microstructural domain sizes and the inter-domain distances (from ∼85 Å to 129 Å) were responsible for hindering the DTX release in addition to DTX re-crystallization.

Drug eluting biliary stents to decrease stent failure rates: A review of the literature

Biliary stenting is clinically effective in relieving both malignant and non-malignant obstructions. However, there are high failure rates associated with tumor ingrowth and epithelial overgrowth as well as internally from biofilm development and subsequent clogging. Within the last decade, the use of prophylactic drug eluting stents as a means to reduce stent failure has been investigated. In this review we provide an overview of the current research on drug eluting biliary stents. While there is limited human trial data regarding the clinical benefit of drug eluting biliary stents in preventing stent obstruction, recent research suggests promise regarding their safety and potential efficacy.

Stents for colorectal obstruction: Past, present, and future

Since the development of uncovered self-expanding metal stents (SEMS) in the 1990s, endoscopic stents have evolved dramatically. Application of new materials and new designs has expanded the indications for enteral SEMS. At present, enteral stents are considered the first-line modality for palliative care, and numerous types of enteral stents are under development for extended clinical usage, beyond a merely palliative purpose. Herein, we will discuss the current status and the future development of lower enteral stents.

Engineering Stent Based Delivery System for Esophageal Cancer Using Docetaxel

Esophageal cancer patients are often diagnosed as "advanced" cases. These patients are subjected to palliative stenting using self-expanding metallic stents (SEMS) to maintain oral alimentation. Unfortunately, SEMS get reoccluded due to tumor growth, in and over the stent struts. To investigate potential solutions to this problem, docetaxel (DTX) delivery films were prepared using PurSil AL 20 (PUS), which can be used as a covering material for the SEMS. Drug-polymer miscibility and interactions were studied. Bilayer films were prepared by adhering the blank film to the DTX loaded film in order to maintain the unidirectional delivery to the esophagus. In vitro release and the local DTX delivery were studied using in vitro permeation experiments. It was found that DTX and PUS were physically and chemically compatible. The bilayer films exhibited sustained release (>30 days) and minimal DTX permeation through esophageal tissues in vitro. The rate-determining step for the DTX delivery was calculated. It was found that >0.9 fraction of rate control lies with the esophageal tissues, suggesting that DTX delivery can be sustained for longer periods compared to the in vitro release observed. Thus, the bilayer films can be developed as a localized sustained delivery system in combination with the stent.

Photochemical tissue penetration via photosensitizer for effective drug penetration in a non-vascular tumor

To improve the tissue penetration efficiency (PE%) of hydrophilic-drugs in non-vascular drug eluting stents (DES), we designed photochemical tissue penetration (PTP) invested DES (PTP-DES). The PTP technology was applied to the stent as a covering membrane to generate singlet oxygen. Singlet oxygen damages the epithelial layer, so the PE% of released drugs could be improved. To prepare the PTP-DES membrane, chlorin e6 (Ce6, photosensitizer) was incorporated in a gemcitabine (GEM) eluting polyurethane (PU) membrane (Ce6-GEM-PU). Ce6-GEM-PU has smooth surface that is ∼40 μm thick. The photoactivity of Ce6 was maintained for 2 weeks (in vitro GEM releasing period). In a separate cell culture system, both 1.5 folds higher PE% and an improved tumor cell growth inhibition effect were shown after light exposure. Additionally, in tissue penetration experimental system, 2 folds increased in the PE% of GEM was induced by laser exposure at 80 J/cm2. Additionally, improved PE% of hydrophilic molecules (Fluorescein and GEM) was confirmed in colon tumor bearing mice. Consequentially, tumor growth, when implanted with Ce6-GEM-PU, was effectively inhibited without significant side effects. Based on these results, we believe that the PTP-DES system has great potential for improving the therapeutic effect of conventional DES.

Polymeric photosensitizer-embedded self-expanding metal stent for repeatable endoscopic photodynamic therapy of cholangiocarcinoma

Photodynamic therapy (PDT) is a new therapeutic approach for the palliative treatment of malignant bile duct obstruction. In this study, we designed photosensitizer-embedded self-expanding nonvascular metal stent (PDT-stent) which allows repeatable photodynamic treatment of cholangiocarcinoma without systemic injection of photosensitizer. Polymeric photosensitizer (pullulan acetate-conjugated pheophorbide A; PPA) was incorporated in self-expanding nonvascular metal stent. Residence of PPA in the stent was estimated in buffer solution and subcutaneous implantation on mouse. Photodynamic activity of PDT-stent was evaluated through laserexposure on stent-layered tumor cell lines, HCT-116 tumor-xenograft mouse models and endoscopic intervention of PDT-stent on bile duct of mini pigs. Photo-fluorescence imaging of the PDT-stent demonstrated homogeneous embedding of polymeric Pheo-A (PPA) on stent membrane. PDT-stent sustained its photodynamic activities at least for 2 month. And which implies repeatable endoscopic PDT is possible after stent emplacement. The PDT-stent after light exposure successfully generated cytotoxic singlet oxygen in the surrounding tissues, inducing apoptotic degradation of tumor cells and regression of xenograft tumors on mouse models. Endoscopic biliary in-stent photodynamic treatments on minipigs also suggested the potential efficacy of PDT-stent on cholangiocarcinoma. In vivo and in vitro studies revealed our PDT-stent, allows repeatable endoscopic biliary PDT, has the potential for the combination therapy (stent plus PDT) of cholangiocarcinoma.

Prototype of biliary drug-eluting stent with photodynamic and chemotherapy using electrospinning

Background

The combination of biliary stent with photodynamic and chemotherapy seemed to be a beneficial palliative treatment of unresectable cholangiocarcinoma. However, by intravenous delivery to the target tumor the distribution of the drug had its limitations and caused serious side effect on non-target organs. Therefore, in this study, we are going to develop a localized eluting stent, named PDT-chemo stent, covered with gemcitabine (GEM) and hematoporphyrin (HP).

Methods

The prototype of PDT-chemo stent was made through electrospinning and electrospraying dual-processes with an electrical charge to cover the stent with a drug-storing membrane from polymer liquid. The design of prototype used PU as the material of the backing layer, and PCL/PEG blends in different molar ratio of 9:1 and of 1:4 were used in two drug-storing layers with GEM and HP loaded respectively.

Results

The optical microscopy revealed that the backing layer was formed in fine fibers from electrospinning, while drug-storing layers, attributed to the droplets from electrospraying process. The covered membrane, the morphology of which was observed by scanning electron microscopy (SEM), covered the stent surface homogeneously without crack appearances. The GEM had almost 100% of electrosprayed efficiency than 70% HP loaded on the covered membrane due to the different solubility of drug in PEG/PCL blends. Drug release study confirmed the two-phased drug release pattern by regulating in different molar ratio of PEG/PCL blends polymer.

Conclusions

The result proves that the PDT-chemo stent is composed of a first burst-releasing phase from HP and a later slow-releasing phase from GEM eluting. This two-phase of drug eluting stent may provide a new prospect of localized and controlled release treatment for cholangiocarcinoma disease.

Colonic stenting: a practical update

Colonic stenting is part of the UK service provision guidelines for colorectal cancer. However, there are issues about availability and expertise within the UK, and controversies remain regarding various clinical and technical aspects of the technique. Based on the current evidence, this article will provide a practical update on the indications, the clinical and technical considerations and the remaining unanswered questions regarding colonic stenting.