Synthetic biodegradable polyesters for implantable controlled-release devices

INTRODUCTION

: Implantable devices can be designed to release drugs to localized regions of tissue at sustained and reliable rates. Advances in polymer engineering have led to the design and development of drug-loaded implants with predictable, desirable release profiles. Biodegradable polyesters exhibit chemical, physical, and biological properties suitable for developing implants for pain management, cancer therapy, contraception, antiviral therapy, and other applications.

AREAS COVERED

: This article reviews the use of biodegradable polyesters for drug-loaded implants by discussing the properties of commonly used polymers, techniques for implant formulation and manufacturing, mechanisms of drug release, and clinical applications of implants as drug delivery devices.

EXPERT OPINION

: Drug delivery implants are unique systems for safe and sustained drug release, providing high bioavailability and low toxicity. Depending on the implant design and tissue site of deployment, implants can offer either localized or systemic drug release. Due to the long history of use of degradable polyesters in medical devices, polyester-based implants represent an important class of controlled release technologies. Further, polyester-based implants are the largest category of drug delivery implants to reach the point of testing in humans or approval for human use.

Local drug delivery systems for inflammatory diseases: Status quo, challenges, and opportunities

Inflammation that is not resolved in due course becomes a chronic disease. The treatment of chronic inflammatory diseases involves a long-term use of anti-inflammatory drugs such as corticosteroids and nonsteroidal anti-inflammatory drugs, often accompanied by dose-dependent side effects. Local drug delivery systems have been widely explored to reduce their off-target side effects and the medication frequency, with several products making to the market or in development over the years. However, numerous challenges remain, and drug delivery technology is underutilized in some applications. This review showcases local drug delivery systems in different inflammatory diseases, including the targets well-known to drug delivery scientists (e.g., joints, eyes, and teeth) and other applications with untapped opportunities (e.g., sinus, bladder, and colon). In each section, we start with a brief description of the disease and commonly used therapy, introduce local drug delivery systems currently on the market or in the development stage, focusing on polymeric systems, and discuss the remaining challenges and opportunities in future product development.

Drug eluting implants in pharmaceutical development and clinical practice

Introduction: Drug eluting implants offer patient convenience and improved compliance through less frequent dosing, eliminating repeated, painful injections and providing localized, site specific delivery with applications in contraception, ophthalmology, and oncology.Areas covered: This review provides an overview of available implant products, design approaches, biodegradable and non-biodegradable polymeric materials, and fabrication techniques with a focus on commercial applications and industrial drug product development. Developing trends in the field, including expanded availability of suitable excipients, development of novel materials, scaled down manufacturing process, and a wider understanding of the implant development process are discussed and point to opportunities for differentiated drug eluting implant products.Expert opinion: In the future, long-acting implants will be important clinical tools for prophylaxis and treatment of global health challenges, especially for infectious diseases, to reduce the cost and difficulty of treating chronic indications, and to prolong local delivery in difficult to administer parts of the body. These products will help improve patient safety, adherence, and comfort.

Kinetics of Phenotypic and Functional Changes in Mouse Models of Sponge Implants: Rational Selection to Optimize Protocols for Specific Biomolecules Screening Purposes

The sponge implant has been applied as an important in vivo model for the study of inflammatory processes as it induces the migration, proliferation, and accumulation of inflammatory cells, angiogenesis, and extracellular matrix deposition in its trabeculae. The characterization of immune events in sponge implants would be useful in identifying the immunological events that could support the selection of an appropriate experimental model (mouse strain) and time post-implant analysis in optimized protocols for novel applications of this model such as in biomolecules screening. Here, the changes in histological/morphometric, immunophenotypic and functional features of infiltrating leukocytes (LEU) were assessed in sponge implants for Swiss, BALB/c, and C57BL/6 mice. A gradual increase of fibrovascular stroma and a progressive decrease in LEU infiltration, mainly composed of polymorphonuclear cells with progressive shift toward mononuclear cells at late time-points were observed over time. Usually, Swiss mice presented a more prominent immune response with late mixed pattern (pro-inflammatory/anti-inflammatory: IL-2/IFN-γ/IL-4/IL-10/IL-17) of cytokine production. While BALB/c mice showed an early activation of the innate response with a controlled cytokine profile (low inflammatory potential), C57BL/6 mice presented a typical early pro-inflammatory (IL-6/TNF/IFN-γ) response with persistent neutrophilic involvement. A rational selection of the ideal time-point/mouse-lineage would avoid bias or tendentious results. Criteria such as low number of increased biomarkers, no recruitment of cytotoxic response, minor cytokine production, and lower biomarker connectivity (described as biomarker signature analysis and network analysis) guided the choice of the best time-point for each model (Day5/Swiss; Day7/BALB/c; Day6/C57BL/6) with wide application for screening purposes, such as identification of therapeutic biomolecules, selection of antigens/adjuvants, and follow-up of innate and adaptive immune response to vaccines candidates.

Glucocorticoid-mediated effects on angiogenesis in solid tumors

Angiogenesis is essential in tumor development to maintain the oxygen and nutrient supply. Glucocorticoids have shown both direct and indirect angiostatic properties in various types of solid cancers. In most of the reported cases glucocorticoid-mediated actions involved suppression of multiple pro-angiogenic factors expression by cancer cells. The anti-angiogenic properties of glucocorticoids correlated with diminished tumor vasculature and reduced tumor growth in multiple in vivo studies. However, when glucocorticoid treatment is considered, possible adverse events should be taken into account. Additional research is needed to further test the use of these steroidal drugs in cancer therapy.

Sustained Release Drug Delivery Applications of Polyurethanes

Since their introduction over 50 years ago, polyurethanes have been applied to nearly every industry. This review describes applications of polyurethanes to the development of modified release drug delivery. Although drug delivery research leveraging polyurethanes has been ongoing for decades, there has been renewed and substantial interest in the field in recent years. The chemistry of polyurethanes and the mechanisms of drug release from sustained release dosage forms are briefly reviewed. Studies to assess the impact of intrinsic drug properties on release from polyurethane-based formulations are considered. The impact of hydrophilic water swelling polyurethanes on drug diffusivity and release rate is discussed. The role of pore formers in modulating drug release rate is examined. Finally, the value of assessing mechanical properties of the dosage form and approaches taken in the literature are described.

Regulation of angiogenesis through the efficient delivery of microRNAs into endothelial cells using polyamine-coated carbon nanotubes

MicroRNAs (miRNAs) directly regulate gene expression at a post-transcriptional level and represent an attractive therapeutic target for a wide range of diseases. Here, we report a novel strategy for delivering miRNAs to endothelial cells (ECs) to regulate angiogenesis, using polymer functionalized carbon nanotubes (CNTs). CNTs were coated with two different polymers, polyethyleneimine (PEI) or polyamidoamine dendrimer (PAMAM), followed by conjugation of miR-503 oligonucleotides as recognized regulators of angiogenesis. We demonstrated a reduced toxicity for both polymer-coated CNTs, compared with pristine CNTs or polymers alone. Moreover, polymer-coated CNT stabilized miR-503 oligonucleotides and allowed their efficient delivery to ECs. The functionality of PAMAM-CNT-miR-503 complexes was further demonstrated in ECs through regulation of target genes, cell proliferation and angiogenic sprouting and in a mouse model of angiogenesis. This comprehensive series of experiments demonstrates that the use of polyamine-functionalized CNTs to deliver miRNAs is a novel and effective means to regulate angiogenesis.

Multiple tissue response modifiers to promote angiogenesis and prevent the foreign body reaction around subcutaneous implants

Dexamethasone-releasing PLGA poly(lactic-co-glycolic acid) microsphere/PVA (polyvinyl alcohol) hydrogel composite coatings have been shown to prevent the foreign body reaction (FBR) to subcutaneous implants in small and large animal models. Such coatings were developed to extend the lifetime of implantable biosensors. However, long-term exposure of tissue to low levels of dexamethasone results in a reduction in blood vessel density due to the anti-angiogenic effect of dexamethasone. This mild effect, while not threatening to the subject's health, may interfere with analyte detection and the sensor response time over the long-term. The present work is focused on the development of coatings that deliver combinations of three tissue response modifiers (TRMs): dexamethasone, VEGF (vascular endothelial growth factor) and PDGF (platelet derived growth factor). Dexamethasone, VEGF and PDGF prevent the FBR, increase angiogenesis and promote blood vessel maturation (which increases blood flow), respectively. To minimize any potential interference among these three TRMs (for example, PDGF increases fibrosis), the relative doses of dexamethasone, VEGF and PDGF were adjusted. It was determined that: a) all three TRMs are required for maximum promotion of angiogenesis, blood vessel maturation and prevention of the FBR; b) VEGF has to be administered at higher doses than PDGF; c) an increase in dexamethasone dosing must be accompanied by a proportional increase in growth factor dosing; and d) modification of the TRM ratio can achieve a constant capillary density throughout the implantation period which is important for applications such as biosensors to maintain sensitivity and a stable sensor baseline. Moreover, an osmosis-driven process for encapsulation of proteins in PLGA microspheres that showed low burst release was developed.

Effect of recombinant human bone morphogenetic protein-2 and Ling Zhi-8 on osteogenesis: a comparative study using a rabbit sinus model

PURPOSE

This study evaluated the osteogenetic capability of Ling Zhi-8 (LZ-8; a protein purified from traditional Chinese medicine [lingzhi]) compared with recombinant human bone morphogenic protein-2 (rhBMP-2) in a standardized bony defect using a rabbit sinus model.

MATERIALS AND METHODS

Twelve male New Zealand white rabbits (18 to 24 weeks old, 3.3 to 3.8 kg) were included in the study. Implants of normal saline 0.1 mg, rhBMP-2 0.1 mg, and LZ-8 0.1 mg were each mixed with a uniform biodegradable polyurethane-based material (Nasopore). The implants were inserted in a standardized bony defect of the nasal bone created by a 2.5-mm trephine bur. The rabbits were sacrificed at 1, 2, 4, and 8 weeks postoperatively. Volume computerized tomographic and histomorphometric examinations were used to evaluate the quantity and quality of regenerated bone.

RESULTS

At postoperative week 4, radiography showed that the new bone volume was significantly larger in the rhBMP-2 group compared with the LZ-8 group (P = .041) and the control group (P = .015). Histomorphometrically, better wound healing of the rhBMP-2 group was found during the healing phase compared with the other 2 groups.

CONCLUSION

The biomaterial implants using rhBMP-2 and LZ-8 had good biocompatibility and osteogenetic capabilities in the rabbit sinus model. Bone healing in rhBMP-2-treated defects was excellent and showed a significant difference compared with LZ-8. However, LZ-8-treated defects also exhibited bone regeneration, and this traditional Chinese medicine may possess osteogenic potential. Further investigations of the mechanism and application of this protein in osteogenesis are needed.

Bevacizumab-loaded polyurethane subconjunctival implants: effects on experimental glaucoma filtration surgery

PURPOSE

Vascular endothelial growth factor (VEGF) may contribute to the scarring process resulting from glaucoma filtration surgery, since this cytokine may stimulate fibroblast proliferation. The aim of this study was to describe a new bevacizumab-loaded polyurethane implant (BPUI) and to evaluate its effectiveness as a new drug delivery system of anti-VEGF antibody in a rabbit model of glaucoma filtration surgery.

METHODS

An aqueous dispersion of polyurethane was obtained via the conventional process. Bevacizumab (1.5 mg) was then incorporated into the dispersion and was subsequently dried to form the polymeric films. Films with dimensions of 3×3×1 mm that either did (group BPUI, n=10) or did not contain bevacizumab (group PUI, n=10) were implanted in the subconjunctival space, at the surgical site in 1 eye of each rabbit. The in vitro bevacizumab release was evaluated using size-exclusion high-performance liquid chromatography (HPLC), and the in vivo effects of the drug were investigated in a rabbit experimental trabeculectomy model by examining the bleb characteristics and collagen accumulation, and by performing immunohistological analyses of VEGF expression.

RESULTS

HPLC showed that only 10% of the bevacizumab in the implants had been released by postoperative day 5. In vivo studies demonstrated that the drug had no adverse effects; however, no significant differences in either the bleb area score or the collagen deposit intensity between the group PUI and the group that BPUI were observed. Moreover, the group BPUI presented a significantly lower proportion of VEGF-expressing fibroblasts than group PUI (0.17±0.03 vs. 0.35±0.05 cells/field, P=0.005).

CONCLUSIONS

This study demonstrated that bevacizumab release from the BPUIs only occurred for a short time probably from the surface of the films. Nevertheless, they were well tolerated in rabbit eyes and reduced the number of VEGF-expressing fibroblasts.