Hydrophilic polyester microspheres: effect of molecular weight and copolymer composition on release of BSA

Nanomedicines Bearing an Alkylating Cytostatic Drug from the Group of 1,3,5-Triazine Derivatives: Development and Characterization

Cancer is still one of the major diseases worldwide. The discovery of new drugs and the improvement of existing ones is one of the areas of priority in the fight against cancer. Dioxadet ([5-[[4,6-bis(aziridin-1-yl)-1,3,5-triazin-2-yl]amino]-2,2-dimethyl-1,3-dioxan-5-yl]methanol) represents one of the promising 1,3,5-triazine derivatives and has cytostatic activity towards ovarian cancer. In this study, we first report the development of dioxadet-bearing nanomedicines based on block-copolymers of poly(ethylene glycol) monomethyl ether (mPEG) and poly(D,L-lactic acid) (PLA)/poly(ε-caprolactone) (PCL) and then conduct an investigation into their characteristics and properties. The preparation of narrow-sized nanoparticles with a hydrodynamic diameter of 100−120 nm was optimized using a nanoprecipitation approach. Thoughtful optimization of the preparation of nanomedicines was carried out through adjustments to the polymer’s molecular weight, the pH of the aqueous medium used for nanoprecipitation, the initial drug amount in respect to the polymer, and polymer concentration in the organic phase. Under optimized conditions, spherical-shaped nanomedicines with a hydrodynamic diameter of up to 230 nm (PDI < 0.2) containing up to 592 ± 22 μg of dioxadet per mg of polymer nanoparticles were prepared. Study of the drug’s release in a model medium revealed the release up to 64% and 46% of the drug after 8 days for mPEG-b-PLA and mPEG-b-PCL, respectively. Deep analysis of the release mechanisms was carried out with the use of a number of mathematical models. The developed nanoparticles were non-toxic towards both normal (CHO-K1) and cancer (A2780 and SK-OV-3) ovarian cells. A cell cycle study revealed lesser toxicity of nanomedicines towards normal cells and increased toxicity towards cancer cells. The IC50 values determined for dioxadet nanoformulations were in the range of 0.47−4.98 μg/mL for cancer cells, which is close to the free drug’s efficacy (2.60−4.14 μg/mL). The highest cytotoxic effect was found for dioxadet loaded to mPEG-b-PCL nanoparticles.

Nanotechnology synergized immunoengineering for cancer

Novel strategies modulating the immune system yielded enhanced anticancer responses and improved cancer survival. Nevertheless, the success rate of immunotherapy in cancer treatment has been below expectation(s) due to unpredictable efficacy and off-target effects from systemic dosing of immunotherapeutic(s). As a result, there is an unmet clinical need for improving conventional immunotherapy. Nanotechnology offers several new strategies, multimodality, and multiplex biological targeting advantage to overcome many of these challenges. These efforts enable programming the pharmacodynamics, pharmacokinetics, and delivery of immunomodulatory agents/co-delivery of compounds to prime at the tumor sites for improved therapeutic benefits. This review provides an overview of the design and clinical principles of biomaterials driven nanotechnology and their potential use in personalized nanomedicines, vaccines, localized tumor modulation, and delivery strategies for cancer immunotherapy. In this review, we also summarize the latest highlights and recent advances in combinatorial therapies availed in the treatment of cold and complicated tumors. It also presents key steps and parameters implemented for clinical success. Finally, we analyse, discuss, and provide clinical perspectives on the integrated opportunities of nanotechnology and immunology to achieve synergistic and durable responses in cancer treatment.

Regulation of the Ocular Cell/Tissue Response by Implantable Biomaterials and Drug Delivery Systems

Therapeutic advancements in the treatment of various ocular diseases is often linked to the development of efficient drug delivery systems (DDSs), which would allow a sustained release while maintaining therapeutic drug levels in the target tissues. In this way, ocular tissue/cell response can be properly modulated and designed in order to produce a therapeutic effect. An ideal ocular DDS should encapsulate and release the appropriate drug concentration to the target tissue (therapeutic but non-toxic level) while preserving drug functionality. Furthermore, a constant release is usually preferred, keeping the initial burst to a minimum. Different materials are used, modified, and combined in order to achieve a sustained drug release in both the anterior and posterior segments of the eye. After giving a picture of the different strategies adopted for ocular drug release, this review article provides an overview of the biomaterials that are used as drug carriers in the eye, including micro- and nanospheres, liposomes, hydrogels, and multi-material implants; the advantages and limitations of these DDSs are discussed in reference to the major ocular applications.

Sustained Release of Vascular Endothelial Growth Factor from Poly(ε-caprolactone-PEG-ε-caprolactone)-b-Poly(l-lactide) Multiblock Copolymer Microspheres

Vascular endothelial growth factor (VEGF) is the major regulating factor for the formation of new blood vessels, also known as angiogenesis. VEGF is often incorporated in synthetic scaffolds to promote vascularization and to enhance the survival of cells that have been seeded in these devices. Such applications require sustained local delivery of VEGF of around 4 weeks for stable blood vessel formation. Most delivery systems for VEGF only provide short-term release for a couple of days, followed by a release phase with very low VEGF release. We now have developed VEGF-loaded polymeric microspheres that provide sustained release of bioactive VEGF for 4 weeks. Blends of two swellable poly(ε-caprolactone)-poly(ethylene glycol)-poly(ε-caprolactone)-b-poly(l-lactide) ([PCL-PEG-PCL]-b-[PLLA])-based multiblock copolymers with different PEG content and PEG molecular weight were used to prepare the microspheres. Loading of the microspheres was established by a solvent evaporation-based membrane emulsification method. The resulting VEGF-loaded microspheres had average sizes of 40-50 μm and a narrow size distribution. Optimized formulations of a 50:50 blend of the two multiblock copolymers had an average VEGF loading of 0.79 ± 0.09%, representing a high average VEGF loading efficiency of 78 ± 16%. These microspheres released VEGF continuously over 4 weeks in phosphate-buffered saline pH 7.4 at 37 °C. This release profile was preserved after repeated and long-term storage at -20 °C for up to 9 months, thereby demonstrating excellent storage stability. VEGF release was governed by diffusion through the water-filled polymer matrix, depending on PEG molecular weight and PEG content of the polymers. The bioactivity of the released VEGF was retained within the experimental error in the 4-week release window, as demonstrated using a human umbilical vein endothelial cells proliferation assay. Thus, the microspheres prepared in this study are suitable for embedment in polymeric scaffolds with the aim of promoting their functional vascularization.

Nanomedicine and macroscale materials in immuno-oncology

Immunotherapy is revolutionizing the treatment of cancer. It can achieve unprecedented responses in advanced-stage patients, including complete cures and long-term survival. However, immunotherapy also has limitations, such as its relatively low response rates and the development of severe side effects. These drawbacks are gradually being overcome by improving our understanding of the immune system, as well as by establishing combination regimens in which immunotherapy is combined with other treatment modalities. In addition to this, in recent years, progress made in chemistry, nanotechnology and materials science has started to impact immuno-oncology, resulting in more effective and less toxic immunotherapy interventions. In this context, multiple different nanomedicine formulations and macroscale materials have been shown to be able to boost anti-cancer immunity and the efficacy of immunomodulatory drugs. We here review nanotechnological and materials chemistry efforts related to endogenous and exogenous vaccination, to the engineering of antigen-presenting cells and T cells, and to the modulation of the tumor microenvironment. We also discuss limitations, current trends and future directions. Together, the insights provided and the evidence obtained indicate that there is a bright future ahead for engineering nanomedicines and macroscale materials for immuno-oncology applications.

Relationship between polarities of antibiotic and polymer matrix on nanoparticle formulations based on aliphatic polyesters

In the field of nanomedicine, nanoparticles are developed to target antibiotics to sites of bacterial infection thus enabling adequate drug exposure and decrease development of resistant bacteria. In the present study, we investigated the encapsulation of two antibiotics with different polarity into different PEGylated polymeric nanoparticles based on aliphatic polyesters, to obtain a better understanding of critical factors determining encapsulation and release. The nanoparticles were prepared from diblock copolymers comprising of a poly(ethylene glycol) block attached to an aliphatic polyester block of varying polarity: poly(lactic-co-glycolic acid) (mPEG-PLGA), poly(lactic-co-hydroxymethyl glycolic acid) (mPEG-PLHMGA) and poly(lactic-co-benzyloxymethyl glycolic acid) (mPEG-PLBMGA). Hydrophobic bedaquiline and hydrophilic vancomycin were encapsulated via single and double-emulsion solvent evaporation techniques, respectively. Encapsulation, degradation and release studies at physiological simulating conditions were performed. Drug polarity and preparation techniques influenced encapsulation efficiency into polymer nanoparticles, giving almost complete encapsulation of bedaquiline and approx. 30% for vancomycin independent of the polymer type. The nonpolar bedaquiline showed a predominantly diffusion-controlled release independent of polymer composition. However, polar vancomycin was released by a combination of diffusion and polymer degradation, which was significantly affected by polymer composition, the most hydrophilic polymer displaying the fastest release.

Branched polyesters: Preparative strategies and applications

In the last 20years, the availability of precision chemical tools (e.g. controlled/living polymerizations, 'click' reactions) has determined a step change in the complexity of both the macromolecular architecture and the chemical functionality of biodegradable polyesters. A major part in this evolution has been played by the possibilities that controlled macromolecular branching offers in terms of tailored physical/biological performance. This review paper aims to provide an updated overview of preparative techniques that derive hyperbranched, dendritic, comb, grafted polyesters through polycondensation or ring-opening polymerization mechanisms.

Extended ocular drug delivery systems for the anterior and posterior segments: biomaterial options and applications

INTRODUCTION

The development of new therapies for treating various eye conditions has led to a demand for extended release delivery systems, which would lessen the need for frequent application while still achieving therapeutic drug levels in the target tissues. Areas covered: Following an overview of the different ocular drug delivery modalities, this article surveys the biomaterials used to develop sustained release drug delivery systems. Microspheres, nanospheres, liposomes, hydrogels, and composite systems are discussed in terms of their primary materials. The advantages and disadvantages of each drug delivery system are discussed for various applications. Recommendations for modifications and strategies for improvements to these basic systems are also discussed. Expert opinion: An ideal sustained release drug delivery system should be able to encapsulate and deliver the necessary drug to the target tissues at a therapeutic level without any detriment to the drug. Drug encapsulation should be as high as possible to minimize loss and unless it is specifically desired, the initial burst of drug release should be kept to a minimum. By modifying various biomaterials, it is possible to achieve sustained drug delivery to both the anterior and posterior segments of the eye.

Release and pharmacokinetics of near-infrared labeled albumin from monodisperse poly(d,l-lactic-co-hydroxymethyl glycolic acid) microspheres after subcapsular renal injection

Subcapsular renal injection is a novel administration method for local delivery of therapeutics for the treatment of kidney related diseases. The aim of this study was to investigate the feasibility of polymeric microspheres for sustained release of protein therapeutics in the kidney and study the subsequent redistribution of the released protein. For this purpose, monodisperse poly(d,l-lactic-co-hydroxymethyl glycolic acid) (PLHMGA) microspheres (40 μm in diameter) loaded with near-infrared dye-labeled bovine serum albumin (NIR-BSA) were prepared by a membrane emulsification method. Rats were injected with either free NIR-BSA or with NIR-BSA loaded microspheres (NIR-BSA-ms) and the pharmacokinetics of the released NIR-BSA was studied for 3 weeks by ex vivo imaging of organs and blood. Quantitative release data were obtained from kidney homogenates and possible metabolism of the protein was investigated by SDS-PAGE analysis of the samples. The ex vivo images showed a rapid decrease of the NIR signal within 24h in kidneys injected with free NIR-BSA, while, importantly, the signal of the labeled protein was still visible at day 21 in kidneys injected with NIR-BSA-ms. SDS-PAGE analysis of the kidney homogenates showed that intact NIR-BSA was released from the microspheres. The locally released NIR-BSA drained to the systemic circulation and subsequently accumulated in the liver, where it was degraded and excreted renally. The in vivo release of NIR-BSA was calculated after extracting the protein from the remaining microspheres in kidney homogenates. The in vivo release rate was faster (89 ± 4% of the loading in 2 weeks) compared to the in vitro release of NIR-BSA (38 ± 1% in 2 weeks). In conclusion, PLHMGA microspheres injected under the kidney capsule provide a local depot from which a formulated protein is released over a prolonged time-period.

Polymeric microparticles for sustained and local delivery of antiCD40 and antiCTLA-4 in immunotherapy of cancer

This study investigated the feasibility of the use of polymeric microparticles for sustained and local delivery of immunomodulatory antibodies in immunotherapy of cancer. Local delivery of potent immunomodulatory antibodies avoids unwanted systemic side effects while retaining their anti-tumor effects. Microparticles based on poly(lactic-co-hydroxymethyl-glycolic acid) (pLHMGA) and loaded with two distinct types of immunomodulatory antibodies (CTLA-4 antibody blocking inhibitory receptors on T cells or CD40 agonistic antibody stimulating dendritic cells) were prepared by double emulsion solvent evaporation technique. The obtained particles had a diameter of 12-15 μm to avoid engulfment by phagocytes and were slightly porous as shown by SEM analysis. The loading efficiency of the antibodies in the microparticles was >85%. The in vitro release profile of antiCD40 and antiCTLA-4 from microparticles showed a burst release of about 20% followed by a sustained release of the content up to 80% of the loading in around 30 days. The therapeutic efficacy of the microparticulate formulations was studied in colon carcinoma tumor model (MC-38). Mice bearing subcutaneous MC-38 tumors were treated with the same dose of immunomodulatory antibodies formulated either in incomplete Freund's adjuvant (IFA) or in microparticles. The antibody-loaded microparticles showed comparable therapeutic efficacy to the IFA formulation with no local adverse effects. The biodegradable microparticles were fully resorbed in vivo and no remnants of inflammatory depots as observed with IFA were present in the cured mice. Moreover the microparticles exhibited lower antibody serum levels in comparison with IFA formulations which lowers the probability of systemic adverse effects. In conclusion, pLHMGA microparticles are excellent delivery systems in providing long-lasting and non-toxic antibody therapy for immunotherapy of cancer.

Near-infrared labeled, ovalbumin loaded polymeric nanoparticles based on a hydrophilic polyester as model vaccine: In vivo tracking and evaluation of antigen-specific CD8(+) T cell immune response

Particulate antigen delivery systems aimed at the induction of antigen-specific T cells form a promising approach in immunotherapy to replace pharmacokinetically unfavorable soluble antigen formulations. In this study, we developed a delivery system using the model protein antigen ovalbumin (OVA) encapsulated in nanoparticles based on the hydrophilic polyester poly(lactide-co-hydroxymethylglycolic acid) (pLHMGA). Spherical nanoparticles with size 300-400 nm were prepared and characterized and showed a strong ability to deliver antigen to dendritic cells for cross-presentation to antigen-specific T cells in vitro. Using near-infrared (NIR) fluorescent dyes covalently linked to both the nanoparticle and the encapsulated OVA antigen, we tracked the fate of this formulation in mice. We observed that the antigen and the nanoparticles are efficiently co-transported from the injection site to the draining lymph nodes, in a more gradual and durable manner than soluble OVA protein. OVA-loaded pLHMGA nanoparticles efficiently induced antigen cross-presentation to OVA-specific CD8+ T cells in the lymph nodes, superior to soluble OVA vaccination. Together, these data show the potential of pLHMGA nanoparticles as attractive antigen delivery vehicles.

The microclimate pH in poly(D,L-lactide-co-hydroxymethyl glycolide) microspheres during biodegradation

The microclimate pH (μpH) in biodegradable polymers, such as poly(D,L-lactic-co-glycolic acid) (PLGA) 50/50, commonly falls to deleterious acidic levels during biodegradation, resulting in instability of encapsulated acid-labile molecules. The μpH distribution in microspheres of a more hydrophilic polyester, poly(D,L-lactide-co-hydroxymethyl glycolide) (PLHMGA), was measured and compared to that in PLGA 50/50 of similar molecular weight and degradation time scales. pH mapping in the polymers was performed after incubation under physiological conditions by using a previously validated ratiometric method employing confocal laser scanning microscopy (CLSM). Confocal μpH maps revealed that PLHMGA microspheres, regardless of copolymer composition, developed a far less acidic μpH during 4 weeks of incubation compared with microspheres from PLGA. A pH-independent fluorescent probe marker of polymer matrix diffusion of μpH-controlling water-soluble acid degradation products, bodipy, was observed by CLSM to diffuse ~3-7 fold more rapidly in PLHMGA compared to PLGA microspheres, consistent with much more rapid release of acids observed from the hydrophilic polymer during bioerosion. Hence, PLHMGA microspheres are less susceptible to acidification during degradation as compared to similar PLGA formulations, and therefore, PLHMGA may be more suitable to deliver acid labile molecules such as proteins.

Controlled release of octreotide and assessment of peptide acylation from poly(D,L-lactide-co-hydroxymethyl glycolide) compared to PLGA microspheres

Purpose

To investigate the in vitro release of octreotide acetate, a somatostatin agonist, from microspheres based on a hydrophilic polyester, poly(D,L-lactide-co-hydroxymethyl glycolide) (PLHMGA).

Methods

Spherical and non-porous octreotide-loaded PLHMGA microspheres (12 to 16 μm) and loading efficiency of 60–70% were prepared by a solvent evaporation. Octreotide release profiles were compared with commercial PLGA formulation (Sandostatin LAR^®); possible peptide modification with lactic, glycolic and hydroxymethyl glycolic acid units was monitored.

Results

PLHMGA microspheres showed burst release (~20%) followed by sustained release for 20–60 days, depending on the hydrophilicity of the polymer. Percentage of released loaded peptide was high (70–90%); > 60% of released peptide was native octreotide. PLGA microspheres did not show peptide release for the first 10 days, after which it was released in a sustained manner over the next 90 days; > 75% of released peptides were acylated adducts.

Conclusions

PLHMGA microspheres are promising controlled systems for peptides with excellent control over release kinetics. Moreover, substantially less peptide modification occurred in PLHMGA than in PLGA microspheres.

Electronic Supplementary Material

The online version of this article (doi:10.1007/s11095-011-0517-3) contains supplementary material, which is available to authorized users.

Functional aliphatic polyesters for biomedical and pharmaceutical applications

Functional aliphatic polyesters are biodegradable polymers with many possibilities to tune physico-chemical characteristics such as hydrophilicity and degradation rate as compared to traditional polyesters (e.g. PLLA, PLGA and PCL), making the materials suitable for drug delivery or as scaffolds for tissue engineering. Lately, a large number of polyesters have been synthesized by homopolymerization of functionalized monomers or co-polymerization with other monomers mainly via ring-opening polymerization (ROP) of cyclic esters. This review presents the recent trends in the synthesis of these materials and their application for protein delivery and tissue engineering.