Biodegradable and injectable paclitaxel‐loaded poly(ester amide)s microspheres: Fabrication and characterization

Recent advances in the development of poly(ester amide)s-based carriers for drug delivery

Biodegradable and biocompatible biomaterials have several important applications in drug delivery. The biomaterial family known as poly(ester amide)s (PEAs) has garnered considerable interest because it exhibits the benefits of both polyester and polyamide, as well as production from readily available raw ingredients and sophisticated synthesis techniques. Specifically, α-amino acid-based PEAs (AA-PEAs) are promising carriers because of their structural flexibility, biocompatibility, and biodegradability. Herein, we summarize the latest applications of PEAs in drug delivery systems, including antitumor, gene therapy, and protein drugs, and discuss the prospects of drug delivery based on PEAs, which provides a reference for designing safe and efficient drug delivery carriers.

Progress in regulating inflammatory biomaterials for intervertebral disc regeneration

Intervertebral disc degeneration (IVDD) is rising worldwide and leading to significant health issues and financial strain for patients. Traditional treatments for IVDD can alleviate pain but do not reverse disease progression, and surgical removal of the damaged disc may be required for advanced disease. The inflammatory microenvironment is a key driver in the development of disc degeneration. Suitable anti-inflammatory substances are critical for controlling inflammation in IVDD. Several treatment options, including glucocorticoids, non-steroidal anti-inflammatory drugs, and biotherapy, are being studied for their potential to reduce inflammation. However, anti-inflammatories often have a short half-life when applied directly and are quickly excreted, thus limiting their therapeutic effects. Biomaterial-based platforms are being explored as anti-inflammation therapeutic strategies for IVDD treatment. This review introduces the pathophysiology of IVDD and discusses anti-inflammatory therapeutics and the components of these unique biomaterial platforms as comprehensive treatment systems. We discuss the strengths, shortcomings, and development prospects for various biomaterials platforms used to modulate the inflammatory microenvironment, thus providing guidance for future breakthroughs in IVDD treatment.

Recent Advances of Poly(ester amide)s-Based Biomaterials

Biodegradable and biocompatible biomaterials have offered much more opportunities from an engineering standpoint for treating diseases and maintaining health. Poly(ester amide)s (PEAs), as an outstanding family among such biomaterials, have risen overwhelmingly in the past decades. These synthetic polymers have easily and widely available raw materials and a diversity of synthetic approaches, which have attracted considerable attention. More importantly, combining the superiorities of polyamides and polyesters, PEAs have emerged with better functions. They could have improved biodegradability, biocompatibility, and cell-material interactions. The PEAs derived from α-amino acids even allow the introduction of pendant sites for further modification or functionalization. Meanwhile, it is gradually recognized that the chemical structures are closely related to the physiochemical and biological properties of PEAs so that their properties can be precisely controlled. PEAs therefore become significant materials in the biomedical fields. This review will attempt to summarize the recent progress in the development of PEAs with respect to the preparation materials and methods, structure-property relationships along with their latest biomedical accomplishments, especially for drug delivery and tissue engineering.

Intra-articular drug delivery systems for osteoarthritis therapy: shifting from sustained release to enhancing penetration into cartilage

Osteoarthritis (OA) is a progressive chronic inflammation that leads to cartilage degeneration. OA Patients are commonly given pharmacological treatment, but the available treatments are not sufficiently effective. The development of sustained-release drug delivery systems (DDSs) for OA may be an attractive strategy to prevent rapid drug clearance and improve the half-life of a drug at the joint cavity. Such delivery systems will improve the therapeutic effects of anti-inflammatory effects in the joint cavity. Whereas, for disease-modifying OA drugs (DMOADs) which target chondrocytes or act on mesenchymal stem cells (MSCs), the cartilage-permeable DDSs are required to maximize their efficacy. This review provides an overview of joint structure in healthy and pathological conditions, introduces the advances of the sustained-release DDSs and the permeable DDSs, and discusses the rational design of the permeable DDSs for OA treatment. We hope that the ideas generated in this review will promote the development of effective OA drugs in the future.

GSK3787-Loaded Poly(Ester Amide) Particles for Intra-Articular Drug Delivery

Osteoarthritis (OA) is a debilitating joint disorder affecting more than 240 million people. There is no disease modifying therapeutic, and drugs that are used to alleviate OA symptoms result in side effects. Recent research indicates that inhibition of peroxisome proliferator-activated receptor δ (PPARδ) in cartilage may attenuate the development or progression of OA. PPARδ antagonists such as GSK3787 exist, but would benefit from delivery to joints to avoid side effects. Described here is the loading of GSK3787 into poly(ester amide) (PEA) particles. The particles contained 8 wt.% drug and had mean diameters of about 600 nm. Differential scanning calorimetry indicated the drug was in crystalline domains in the particles. Atomic force microscopy was used to measure the Young's moduli of individual particles as 2.8 MPa. In vitro drug release studies showed 11% GSK3787 was released over 30 days. Studies in immature murine articular cartilage (IMAC) cells indicated low toxicity from the drug, empty particles, and drug-loaded particles and that the particles were not taken up by the cells. Ex vivo studies on murine joints showed that the particles could be injected into the joint space and resided there for at least 7 days. Overall, these results indicate that GSK3787-loaded PEA particles warrant further investigation as a delivery system for potential OA therapy.

Lipase-catalysed polycondensation of levulinic acid derived diol-diamide monomers: access to new poly(ester-co-amide)s

A new family of biobased poly(ester-co-amide)s is reported from the enzymatic polycondensation of a library of levulinic acid derived diol-diamide monomers with diesters.

Poly(ester amide) particles for controlled delivery of celecoxib

Many potential pharmacological treatments for osteoarthritis can result in undesirable side effects due to the systemic administration of drugs, making the direct delivery of drugs to joints an attractive alternative. Poly(ester amide)s (PEAs) have been shown to exhibit promising properties for the development of particle-based intra-articular delivery vehicles. However, a limited range of PEA structures has been investigated. In this study, we prepared and characterized the properties of two different PEA particles composed of l-phenylalanine, sebacic acid, and either 1,4-butanediol or 1,8-octanediol (PBSe and POSe, respectively). The anti-inflammatory drug celecoxib (CXB) was encapsulated into the particles. Despite minor structural differences, PBSe and POSe exhibited different thermal and mechanical properties, and encapsulation of CXB influenced these properties. PBSe-CXB particles provided a slower release of drug in vitro relative to POSe-CXB. Toxicity studies showed that particles without drug exhibited low toxicity to ATDC5 and C2C12 cells, while the PBSe-CXB particles exhibited concentration-dependent toxicity. Host response to the particles was evaluated in an ovine model. No adverse effects were observed following intra-articular injection and it was observed that the particles diffused into the surrounding tissues. This work shows the importance of structural tuning in PEA delivery vehicles and demonstrates their potential for further development. © 2019 Wiley Periodicals, Inc. J Biomed Mater Res Part A: 107A: 1235-1243, 2019.

Fast Degradable Polycaprolactone for Drug Delivery

Polycaprolactone (PCL) was reported a long time ago; however, its biomedical applications has not been extensively investigated in comparison with poly(lactide- co-glycolide) (PLGA) due to its too slow degradation profile. Here, we are reporting an oxalate-connected oligocaprolactone multiblock copolymer (PCL-OX) as a fast degradable PCL while maintaining its crystalline properties and low melting point of PCL. The in vivo application of the paclitaxel-loaded PCL-OX microspheres provided a steady plasma drug concentration of 6-9 μg/mL over 28 days, similar to that of the PLGA microspheres. Both PCL and PLGA microspheres were completely cleared two months after in vivo implantation. The PCL-OX microspheres showed a similar tissue compatibility to that of PLGA microspheres in the subcutaneous layer of rats. These findings suggest that PCL-OX is a useful biomaterial that solves the slow degradation problems of PCL and, thus, may find uses in other biomedical applications as an alternative to PLGA.

Prolonged inhibition of inflammation in osteoarthritis by triamcinolone acetonide released from a polyester amide microsphere platform

Controlled biomaterial-based corticosteroid release might circumvent multiple injections and the accompanying risks, such as hormone imbalance and muscle weakness, in osteoarthritic (OA) patients. For this purpose, microspheres were prepared from an amino acid-based polyester amide (PEA) platform and loaded with triamcinolone acetonide (TAA). TAA loaded microspheres were shown to release TAA for over 60days in PBS. Furthermore, the bioactivity lasted at least 28days, demonstrated by a 80-95% inhibition of PGE₂ production using TNFα-stimulated chondrocyte culture, indicating inhibition of inflammation. Microspheres loaded with the near infrared marker NIR780-iodide injected in healthy rat joints or joints with mild collagenase-induced OA showed retention of the microspheres up till 70days after injection. After intra-articular injection of TAA-loaded microspheres, TAA was detectable in the serum until day seven. Synovial inflammation was significantly lower in OA joints injected with TAA-loaded microspheres based on histological Krenn scores. Injection of TAA-loaded nor empty microspheres had no effect on cartilage integrity as determined by Mankin scoring. In conclusion, the PEA platform shows safety and efficacy upon intra-articular injection, and its extended degradation and release profiles compared to the currently used PLGA platforms may render it a good alternative. Even though further in vivo studies may need to address dosing and readout parameters such as pain, no effect on cartilage pathology was found and inflammation was effectively lowered in OA joints.

Delivering therapeutics in peripheral artery disease: challenges and future perspectives

Targeted and sustained delivery of biologicals to improve neovascularization has been focused on stimulation angiogenesis. The formation of collaterals however is hemodynamically much more efficient, but as a target of therapy has been under-utilized. Although there is good understanding of the molecular processes involving collateral formation and there are interesting drugable candidates, the need for targeting and sustained delivery is still an obstacle towards safe and effective treatment. Molecular targeting with nanoparticles of liposomes is promising and so are peri-vascularly delivered polymer-based protein reservoirs. These developments will lead to future arteriogenesis strategies that are adjunct to current revascularization.

Poly(ester amide)s with pendant azobenzenes: multi-responsive self-immolative moieties for modulating polymer assemblies

Polymer nanoassemblies containing pendant azobenzenes in their cores were prepared. Light-induced trans–cis isomerization of the azobenzenes increased the polarity of the assembly core, while reduction led to assembly degradation.

Safety of intradiscal injection and biocompatibility of polyester amide microspheres in a canine model predisposed to intervertebral disc degeneration

Repair of degenerated intervertebral discs (IVD) might be established via intradiscal delivery of biologic therapies. Polyester amide polymers (PEA) were evaluated for in vitro cytotoxicity and in vivo biocompatibility, and thereafter intradiscal application of PEA microspheres (PEAMs) in a canine model predisposed to IVD degeneration at long-term (6 months) follow-up. PEA extracts did not induce cytotoxicity in mouse fibroblast cells (microscopy and XTT assay), while a slight foreign body reaction was demonstrated by histopathology after intramuscular implantation in rabbits. Intradiscal injection of a volume of 40 µL through 26 and 27G needles induced no degenerative changes in acanine model susceptible to IVD disease. Although sham-injected IVDs showed increased CAV1 expression compared with noninjected IVDs, which may indicate increased cell senescence, these findings were not supported by immunohistochemistry, biomolecular analysis of genes related to apoptosis, biochemical and histopathological results. PEAM-injected IVDs showed significantly higher BAX/BCL2 ratio vs sham-injected IVDs suggestive of an anti-apoptotic effect of the PEAMs. These findings were not supported by other analyses (clinical signs, disc height index, T2 values, biomolecular and biochemical analyses, and IVD histopathology). PEAs showed a good cytocompatibility and biocompatibility. PEAMs are considered safe sustained release systems for intradiscal delivery of biological treatments. © 2016 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 105B: 707-714, 2017.

CXCL1 microspheres: a novel tool to stimulate arteriogenesis

CONTEXT

After arterial occlusion, diametrical growth of pre-existing natural bypasses around the obstruction, i.e. arteriogenesis, is the body's main coping mechanism. We have shown before that continuous infusion of chemokine (C-X-C motif) ligand 1 (CXCL1) promotes arteriogenesis in a rodent hind limb ischemia model.

OBJECTIVE

For clinical translation of these positive results, we developed a new administration strategy of local and sustained delivery. Here, we investigate the therapeutic potential of CXCL1 in a drug delivery system based on microspheres.

MATERIALS AND METHODS

We generated poly(ester amide) (PEA) microspheres loaded with CXCL1 and evaluated them in vitro for cellular toxicity and chemokine release characteristics. In vivo, murine femoral arteries were ligated and CXCL1 was administered either intra-arterially via osmopump or intramuscularly encapsulated in biodegradable microspheres. Perfusion recovery was measured with Laser-Doppler.

RESULTS

The developed microspheres were not cytotoxic and displayed a sustained chemokine release up to 28 d in vitro. The amount of released CXCL1 was 100-fold higher than levels in native ligated hind limb. Also, the CXCL1-loaded microspheres significantly enhanced perfusion recovery at day 7 after ligation compared with both saline and non-loaded conditions (55.4 ± 5.0% CXCL1-loaded microspheres versus 43.1 ± 4.5% non-loaded microspheres; n = 8-9; p < 0.05). On day 21 after ligation, the CXCL1-loaded microspheres performed even better than continuous CXCL1 administration (102.1 ± 4.4% CXCL1-loaded microspheres versus 85.7 ± 4.8% CXCL1 osmopump; n = 9; p < 0.05).

CONCLUSION

Our results demonstrate a proof of concept that sustained, local delivery of CXCL1 encapsulated in PEA microspheres provides a new tool to stimulate arteriogenesis in vivo.

A comparison of covalent and noncovalent strategies for paclitaxel release using poly(ester amide) graft copolymer micelles

Micelles formed from amphiphilic copolymers are promising for the delivery of drug molecules, potentially leading to enhanced properties and efficacies. Critical aspects of these systems include the use of biocompatible, biodegradable polymer backbones as well as the ability to control the incorporation of drugs and their release rates. In this work, a poly(ester amide)–poly(ethylene oxide) graft copolymer with paclitaxel conjugated via ester linkages was prepared and assembled into micelles. For comparison, micelles with physically encapsulated paclitaxel were also prepared. The release rates of these two systems were studied, and the micelles with covalently conjugated paclitaxel exhibited a prolonged release of the drug in comparison to the noncovalent system, which rapidly released the payload. In vitro studies suggested that the poly(ester amide)–poly(ethylene oxide) copolymers were nontoxic, whereas the toxicities of the drug-loaded micelles were dependent on their release rates. Overall, these systems are promising for further development as anticancer drug carriers.

Development and evaluation of a novel biodegradable sustained release microsphere formulation of paclitaxel intended to treat breast cancer

Objective:

The objective of this study was to develop a novel 1 month depot paclitaxel (PTX) microspheres that give a sustained and complete drug release.

Materials and Methods:

PTX loaded microspheres were prepared by o/w emulsion solvent evaporation technique using the blends of poly(lactic-co-glycolic acid) (PLGA) 75/25, polycaprolactone 14,000 and polycaprolactone 80,000. Fourier transform infrared spectroscopy was used to investigate drug excipient compatibility. Compatible blends were used to prepare F1-F6 microspheres, the process was characterised and the optimum formulation was selected based on the release. Optimised formulation was characterised for solid state of the drug using the differential scanning calorimetry (DSC) studies, surface morphology using the scanning electron microscopy (SEM), in vivo drug release, in vitro in vivo correlation (IVIVC) and anticancer activity. Anticancer activity of release medium was determined using the cell viability assay in Michigan Cancer Foundation (MCF-7) cell line.

Results:

Blend of PLGA with polycaprolactone (Mwt 14,000) at a ratio of 1:1 (F5) resulted in complete release of the drug in a time frame of 30 days. F5 was considered as the optimised formulation. Incomplete release of the drug resulted from other formulations. The surface of the optimised formulation was smooth and the drug changed its solid state upon fabrication. The formulation also resulted in 1-month drug release in vivo. The released drug from F5 demonstrated anticancer activity for 1-month. Cell viability was reduced drastically with the release medium from F5 formulation. A 100% IVIVC was obtained with F5 formulation suggesting the authenticity of in vitro release, in vivo release and the use of the formulation in breast cancer.

Conclusions:

From our study, it was concluded that with careful selection of different polymers and their combinations, PTX 1 month depot formulation with 100% drug release and that can be used in breast cancer was developed.

Block copolymer of poly(ester amide) and polyesters: synthesis, characterization, and in vitro cellular response

In order to expand the properties and applications of aliphatic absorbable polyesters, a new biodegradable block copolymer family, poly(ester amide)-b-poly(ε-caprolactone) (PEA-b-PCL), was synthesized and characterized. These copolymers were synthesized by first preparing l-phenylalanine-based poly(ester amide) macroinitiators (Phe-PEAs) with free amine end groups via a solution polycondensation. The amine-terminated Phe-PEA macroinitiators were then used to initiate the ring-opening polymerization of ε-caprolactone monomer to prepare the PEA-b-PCL copolymers. The molecular weight (MW) of PEA-b-PCLs can be well controlled by adjusting the Phe-PEA MW and weight ratio of ε-caprolactone to Phe-PEA, and ranged from 7 to 50kgmol(-1). The copolymers' structure and properties were characterized by various physicochemical methods, such as nuclear magnetic resonance, gel permeation chromatography and solubility testing. The in vitro enzymatic biodegradation tests were performed to evaluate the biodegradation rate of the copolymers. The results showed that the introduction of Phe-PEA to PCL did not significantly change the degradation rate of PCL. Biological studies were conducted to assess the polymer's biological properties, like supporting the cell attachment and proliferation, and inflammation response. The results showed that the bovine aortic endothelial cells had very good attachment and proliferation performance on PEA-b-PCL coating surface. TNF-α release profiles showed that PEA-b-PCL exhibited a muted J774 macrophage inflammatory response.

Solid lipid nanoparticles of paclitaxel strengthened by hydroxypropyl-β-cyclodextrin as an oral delivery system

The objective of this study was to evaluate the potential of surface-modified paclitaxel (PTX)-incorporated solid lipid nanoparticles with hydroxypropyl-β-cyclodextrin (smPSH). The smPSH released 89.70 ± 3.99% of its entrapped PTX within 24 h when placed in dissolution medium containing sodium lauryl sulfate. The cellular uptake of PTX from smPSH in Caco-2 cells was 5.3-fold increased compared to a PTX solution based on a Taxol formulation. Moreover, smPSH showed an increased cytotoxicity compared to PTX solution. In addition, AUC (5.43 µg•h/ml) and Cmax (1.44 µg/ml) of smPSH were higher than those (1.81 µg•h/ml and 0.73 µg/ml) of PTX solution. The drug concentration of smPSH (11.12 ± 4.45 ng/mg of lymph tissue) in lymph nodes was higher than that of the PTX solution (0.89 ± 0.75 ng/mg of lymph tissue), suggesting that more PTX was transported to the lymphatic vessels in the form of smPSH. In conclusion, smPSH have a potential as an alternative delivery system for oral administration of PTX.

Strategies in functional poly(ester amide) syntheses to study human coronary artery smooth muscle cell interactions

The design of new generation cardiovascular biomaterials focuses on biomimetic properties that are capable of eliciting specific cellular responses and directing new tissue formation. Synthetic poly(ester amide)s (PEAs) containing α-amino acid residues have the potential to elicit favorable cellular responses. Furthermore, they are biodegradable owing to the incorporation of naturally occurring amino acids. In this study, a family of PEAs was synthesized from selected α-amino acids using both solution and interfacial polymerization approaches to optimize their properties for vascular tissue engineering applications. By careful selection of the monomers and the polymerization approach, high-molecular-weight PEAs with low glass-transition temperatures were obtained. Human coronary artery smooth muscle cells (HCASMCs) cultured directly on bare PEA films attached and spread well up to 7 days of culture. Moreover, cell viability was significantly enhanced on all nonfunctional PEAs compared with tissue culture polystyrene controls. The trifluoroacetic acid salt of the lysine-containing functional PEAs was found to retard cell growth but still supported cell viability up to 5 days of culture. Immunostaining of HCASMCs revealed strong vinculin expression, suggesting that the HCASMCs initiated cellular processes for focal adhesion contacts with all PEA surfaces. Conversely, smooth muscle α-actin expression was not abundant on the PEA surfaces, suggesting a proliferative smooth muscle cell phenotype. Altogether, our results indicate that these PEAs are promising materials for vascular tissue engineering scaffolds.

Biodegradable functional poly(ester amide)s with pendant hydroxyl functional groups: synthesis, characterization, fabrication and in vitro cellular response

The synthesis of a new family of biodegradable α-amino acid poly(ester amide)s (AA-PEAs) with pendant benzyl ether groups and hydroxyl functional groups is reported. The synthetic strategy employs the ring opening reaction of O-benzyl-L-serine-N-carboxyanhydride with di-p-toluenesulfonic acid salts of bis-L-valine butane-1,4-diester, followed by solution polycondesation reactions with di-p-nitrophenyl sebacate in N,N-dimethylacetamide. Catalytic hydrogenation of the resulting benzyl ether protected AA-PEAs (PEA-Ser-Bzs) was performed to restore the hydroxyl functional groups in the functionalized AA-PEAs (PEA-Ser-OH). All resulting polymers were characterized by standard physico-chemical methods. The pendant hydroxyl groups in PEA-Ser-OH were used to fabricate AA-PEA-based gels via acrylation and photo-gelation. The cell-polymer interactions of PEA-Ser-Bz and PEA-Ser-OH were evaluated in terms of cell attachment and proliferation assay using bovine aortic endothelial cells (BAECs) as well as fibroblasts. The cell culture data indicated that the hydrophobic/hydrophilic characteristics (from contact angle data) of these AA-PEAs could significantly affect the interaction between BAECs and AA-PEA. This finding may provide additional possible applications for this new family of functionalized AA-PEA polymers.

Versatile Biodegradable Poly(ester amide)s Derived from α-Amino Acids for Vascular Tissue Engineering

Biodegradable poly(ester amide) (PEA) biomaterials derived from α-amino acids, diols, and diacids are promising materials for biomedical applications such as tissue engineering and drug delivery because of their optimized properties and susceptibility for either hydrolytic or enzymatic degradation. The objective of this work was to synthesize and characterize biodegradable PEAs based on the α-amino acids l-phenylalanine and l-methionine. Four different PEAs were prepared using 1,4-butanediol, 1,6-hexanediol, and sebacic acid by interfacial polymerization. High molecular weight PEAs with narrow polydispersity indices and excellent film-forming properties were obtained. The incubation of these PEAs in PBS and chymotrypsin indicated that the polymers are biodegradable. Human coronary artery smooth muscle cells were cultured on PEA films for 48 h and the results showed a well-spread morphology. Porous 3D scaffolds fabricated from these PEAs were found to have excellent porosities indicating the utility of these polymers for vascular tissue engineering.