Nanoparticles Based on a Hydrophilic Polyester with a Sheddable PEG Coating for Protein Delivery

Hydrophobic Modification of Poly(γ-glutamic acid) by Grafting 4-Phenyl-butyl Side Groups for the Encapsulation and Release of Doxorubicin

The delivery of drugs is a great challenge, since most of active pharmaceutical ingredients developed today are hydrophobic and poorly water soluble. From this perspective, drug encapsulation on biodegradable and biocompatible polymers can surpass this problem. Poly(γ-glutamic acid) (PGGA), a bioedible and biocompatible polymer has been chosen for this purpose. Carboxylic side groups of PGGA have been partially esterified with 4-phenyl-butyl bromide, producing a series of aliphatic-aromatic ester derivatives with different hydrophilic-lipophilic balances. Using nanoprecipitation or emulsion/evaporation methods, these copolymers were self-assembled in a water solution, forming nanoparticles with average diameters between 89 and 374 nm and zeta potential values between -13.1 and -49.5 mV. The hydrophobic core containing 4-phenyl-butyl side groups was used for the encapsulation of an anticancer drug, such as Doxorubicin (DOX). The highest encapsulation efficiency was reached for a copolymer derived from PGGA, with a 46 mol% degree of esterification. Drug release studies carried out for 5 days at different pHs (4.2 and 7.4) indicated that DOX was released faster at pH 4.2, revealing the potential of these nanoparticles as chemotherapy agents.

Evaluation of paclitaxel-loaded polymeric nanoparticles in 3D tumor model: impact of tumor stroma on penetration and efficacy

Since tumor stroma poses as a barrier to achieve efficacy of nanomedicines, it is essential to evaluate nano-chemotherapeutics in stroma-mimicking 3D models that reliably predict their behavior regarding these hurdles limiting efficacy. In this study, we evaluated the effect of paclitaxel-loaded polymeric micelles (PTX-PMCs) and polymeric nanoparticles (PTX-PNPs) in a tumor stroma-mimicking 3D in vitro model. PTX-PMCs (77 nm) based on a amphiphilic block copolymer of mPEG-b-p(HPMAm-Bz) and PTX-PNPs (159 nm) based on poly(lactic-co-glycolic acid) were prepared, which had an encapsulation efficiency (EE%) of 81 ± 15% and 45 ± 8%, respectively. 3D homospheroids of mouse 4T1 breast cancer cells and heterospheroids of NIH3T3 fibroblasts and 4T1 (5:1 ratio) were prepared and characterized with high content two-photon microscopy and immunostaining. Data showed an induction of epithelial-mesenchymal transition (α-SMA) in both homo- and heterospheroids, while ECM (collagen) deposition only in heterospheroids. Two-photon imaging revealed that both fluorescently labeled PMCs and PNPs penetrated into the core of homospheroids and only PMCs penetrated into heterospheroids. Furthermore, PTX-PMCs, PTX-PNPs, and free PTX induced cytotoxicity in tumor cells and fibroblasts grown as monolayer, but these effects were substantially reduced in 3D models, in particular in heterospheroids. Gene expression analysis showed that heterospheroids had a significant increase of drug resistance markers (Bcl2, Abgc2) compared to 2D or 3D monocultures. Altogether, this study shows that the efficacy of nanotherapeutics is challenged by stroma-induced poor penetration and development of resistant phenotype. Therefore, this tumor stroma-mimicking 3D model can provide an excellent platform to study penetration and effects of nanotherapeutics before in vivo studies.

Preparation, Characterization, and Biological Evaluation of a Hydrophilic Peptide Loaded on PEG-PLGA Nanoparticles

The encapsulation of peptides and proteins in nanosystems has been extensively investigated for masking unfavorable biopharmaceutical properties, including short half-life and poor permeation through biological membranes. Therefore, the aim of this work was to encapsulate a small antimicrobial hydrophilic peptide (H-Ser-Pro-Trp-Thr-NH2, FS10) in PEG-PLGA (polyethylene glycol-poly lactic acid-co-glycolic acid) nanoparticles (Nps) and thereby overcome the common limitations of hydrophilic drugs, which because they facilitate water absorption suffer from rapid degradation. FS10 is structurally related to the well-known RNAIII inhibiting peptide (RIP) and inhibits S. aureus biofilm formation. Various parameters, including different method (double emulsion and nanoprecipitation), pH of the aqueous phase and polymeric composition, were investigated to load FS10 into PEG-PLGA nanoparticles. The combination of different strategies resulted in an encapsulation efficiency of around 25% for both the double emulsion and the nanoprecipitation method. It was found that the most influential parameters were the pH—which tailors the peptides charge—and the polymeric composition. FS10-PEG-PLGA nanoparticles, obtained under optimized parameters, showed size lower than 180 nm with zeta potential values ranging from −11 to −21 mV. In vitro release studies showed that the Nps had an initial burst release of 48−63%, followed by a continuous drug release up to 21 h, probably caused by the porous character of the Nps. Furthermore, transmission electron microscopy (TEM) analysis revealed particles with a spherical morphology and size of around 100 nm. Antimicrobial assay showed that the minimum inhibitory concentration (MIC) of the FS10-loaded Nps, against S. aureus strains, was lower (>128 µg/mL) than that of the free FS10 (>256 µg/mL). The main goal of this work was to develop polymeric drug delivery systems aiming at protecting the peptide from a fast degradation, thus improving its accumulation in the target site and increasing the drug-bacterial membrane interactions.

Preparation of BMP-2 loaded MPEG-PCL microspheres and evaluation of their bone repair properties

Autologous or allogeneic bone grafts are common methods to treat bone defects. Bone tissue engineering combining carrier material with the active factor can induce a generation of new bone at the bone defect site. However, its clinical application is restricted by the limited donors, the high morbidity at the donor site, the low activity in vivo, and dose-independent adverse effect. To overcome the limitations of traditional therapies, it is urgent to find and develop a repair material that can replace natural bones. Hence, we designed and prepared suitable MPEG-PCL microspheres loaded bone morphogenetic protein-2 (BMP-2/MPEG-PCL-MS) to effectively solve the problem mentioned above, prolong its reaction time at the targeted site, and avoid the pain of patients caused by frequent administration. The physicochemical properties and in vitro release behaviors were good. The microspheres showed high biocompatibility and strongly induced osteogenesis in vivo. BMP-2/MPEG-PCL-MS has been proven to exert sustained-release in vivo and maintain the inherent BMP-2 activity. They can be directly injected into the bone defect site, or implanted to a large bone defect site together with stent material to exert therapeutic effects. Hence, this smart drug delivery system has promising potential for clinical applications and provides a well-controlled design for combination of tissue engineering and pharmaceutics for further exploration.

Endothelial Cell Targeting by cRGD-Functionalized Polymeric Nanoparticles under Static and Flow Conditions

Since α_vβ₃ integrin is a key component of angiogenesis in health and disease, Arg-Gly-Asp (RGD) peptide-functionalized nanocarriers have been investigated as vehicles for targeted delivery of drugs to the α_vβ₃ integrin-overexpressing neovasculature of tumors. In this work, PEGylated nanoparticles (NPs) based on poly(lactic-co-glycolic acid) (PLGA) functionalized with cyclic-RGD (cRGD), were evaluated as nanocarriers for the targeting of angiogenic endothelium. For this purpose, NPs (~300 nm) functionalized with cRGD with different surface densities were prepared by maleimide-thiol chemistry and their interactions with human umbilical vein endothelial cells (HUVECs) were evaluated under different conditions using flow cytometry and microscopy. The cell association of cRGD-NPs under static conditions was time-, concentration- and cRGD density-dependent. The interactions between HUVECs and cRGD-NPs dispersed in cell culture medium under flow conditions were also time- and cRGD density-dependent. When washed red blood cells (RBCs) were added to the medium, a 3 to 8-fold increase in NPs association to HUVECs was observed. Moreover, experiments conducted under flow in the presence of RBC at physiologic hematocrit and shear rate, are a step forward in the prediction of in vivo cell–particle association. This approach has the potential to assist development and high-throughput screening of new endothelium-targeted nanocarriers.

Apoptosis-inducing peptide loaded in PLGA nanoparticles induces anti-tumor effects in vivo

Induction of apoptosis in tumor cells specifically within the complex tumor microenvironment is highly desirable to kill them efficiently and to enhance the effects of chemotherapy. Second mitochondria-derived activator of caspase (Smac) is a key pro-apoptotic pathway which can be activated with a Smac mimetic peptide. However, in vivo application of peptides is hampered by several limitations such as poor pharmacokinetics, rapid elimination, enzymatic degradation, and insufficient intracellular delivery. In this study, we developed a nanosystem to deliver a Smac peptide to tumor by passive targeting. We first synthesized a chimeric peptide that consists of the 8-mer Smac peptide and a 14-mer cell penetrating peptide (CPP) and then encapsulated the Smac-CPP into polymeric nanoparticles (Smac-CPP-NPs). In vitro, Smac-CPP-NPs were rapidly internalized by 4T1 mammary tumor cells and subsequently released Smac-CPP into the cells, as shown with fluorescence microscopy. Furthermore, Smac-CPP-NPs induced apoptosis in tumor cells, as confirmed with cell viability and caspase 3/7 assays. Interestingly, combination of Smac-CPP-NPs with doxorubicin (dox), a clinically used cytostatic drug, showed combined effects in vitro in 4T1 cells. The effect was significantly better than that of SMAC-CPP-NPs alone as well as empty nanoparticles and dox. In vivo, co-treatment with Smac-CPP-NPs and free dox reduced the tumor growth to 85%. Furthermore, the combination of Smac-CPP-NPs and free dox showed reduced proliferating tumor cells (Ki-67 staining) and increased apoptotic cells (cleaved caspase-3 staining) in tumors. In conclusion, the present study demonstrates that the intracellular delivery of Smac-mimetic peptide using nanoparticle system can be an interesting strategy to attenuate the tumor growth and to potentiate the therapeutic efficacy of chemotherapy in vivo.

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.

Selective Cytotoxicity to HER2 Positive Breast Cancer Cells by Saporin-Loaded Nanobody-Targeted Polymeric Nanoparticles in Combination with Photochemical Internalization

In cancer treatment, polymeric nanoparticles (NPs) can serve as a vehicle for the delivery of cytotoxic proteins that have intracellular targets but that lack well-defined mechanisms for cellular internalization, such as saporin. In this work, we have prepared PEGylated poly(lactic acid- co-glycolic acid- co-hydroxymethyl glycolic acid) (PLGHMGA) NPs for the selective delivery of saporin in the cytosol of HER2 positive cancer cells. This selective uptake was achieved by decorating the surface of the NPs with the 11A4 nanobody that is specific for the HER2 receptor. Confocal microscopy observations showed rapid and extensive uptake of the targeted NPs (11A4-NPs) by HER2 positive cells (SkBr3) but not by HER2 negative cells (MDA-MB-231). This selective uptake was blocked upon preincubation of the cells with an excess of nanobody. Nontargeted NPs (Cys-NPs) were not taken up by either type of cells. Importantly, a dose-dependent cytotoxic effect was only observed on SkBr3 cells when these were treated with saporin-loaded 11A4-NPs in combination with photochemical internalization (PCI), a technique that uses a photosensitizer and local light exposure to facilitate endosomal escape of entrapped nanocarriers and biomolecules. The combined use of saporin-loaded 11A4-NPs and PCI strongly inhibited cell proliferation and decreased cell viability through induction of apoptosis. Also the cytotoxic effect could be reduced by an excess of nanobody, reinforcing the selectivity of this system. These results suggest that the combination of the targeting nanobody on the NPs with PCI are effective means to achieve selective uptake and cytotoxicity of saporin-loaded NPs.

Insights into maleimide-thiol conjugation chemistry: Conditions for efficient surface functionalization of nanoparticles for receptor targeting

Maleimide-thiol chemistry is widely used for the design and preparation of ligand-decorated drug delivery systems such as poly(lactide-co-glycolide) (PLGA) based nanoparticles (NPs). While many publications on nanocarriers functionalized exploiting this strategy are available in the literature, the conditions at which this reaction takes place vary among publications. This paper presents a comprehensive study on the conjugation of the peptide cRGDfK and the nanobody 11A4 (both containing a free thiol group) to maleimide functionalized PLGA NPs by means of the maleimide-thiol click reaction. The influence of different parameters, such as the nanoparticles preparation method and storage conditions as well as the molar ratio of maleimide to ligand used for conjugation, on the reaction efficiency has been evaluated. The NPs were prepared by a single or double emulsion method using different types and concentrations of surfactants and stored at 4 or 20 °C before reaction with the targeting moieties. Several maleimide to ligand molar ratios and different reaction times were studied and the conjugation efficiency was determined by quantification of the not-bound ligand by liquid chromatography. The kind of emulsion used to prepare the NPs as well as the type and concentration of surfactant used had no effect on the conjugation efficiency. Reaction between the maleimide groups present in the NPs and cRGDfK was optimal at a maleimide to thiol molar ratio of 2:1, reaching a conjugation efficiency of 84 ± 4% after 30 min at room temperature in 10 mM HEPES pH 7.0. For 11A4 nanobody the optimal reaction efficiency, 58 ± 12%, was achieved after 2 h of incubation at room temperature in PBS pH 7.4 using a 5:1 maleimide to protein molar ratio. Storage of the NPs at 4 °C for 7 days prior to their exposure to the ligands resulted in approximately 10% decrease in the reactivity of maleimide in contrast to storage at 20 °C which led to almost 40% of the maleimide being unreactive after the same storage time. Our findings demonstrate that optimization of this reaction, particularly in terms of reactant ratios, can represent a significant increase in the conjugation efficiency and prevent considerable waste of resources.

Multi-facet implications of PEGylated lysozyme stabilized-silver nanoclusters loaded recombinant PTEN cargo in cancer theranostics

Amalgamation of delivery and tracking of therapeutically relevant moieties on a single platform is made possible by the application of metal nanoclusters, an innovative class of luminescent nanomaterials. Metal nanoclusters, possessing molecule-like attributes, display extraordinary size and shape tunable properties befitting theranostic applications. Herein, we report successful assembly of therapeutically significant phosphatase protein PTEN and fluorescent lysozyme-stabilized silver nanoclusters to accomplish delivery and tracking of the protein. Down-regulation of PTEN perturbs the cellular networking leading to copious pathological conditions. The integration of purified recombinant PTEN with silver nanoclusters was evaluated by fluorescence spectroscopy study. A key feature of this study is the use of polyethylene glycol coating that allows fabrication of the assembly into spherical nanocomposites as characterized by transmission electron microscope along with retention of both optical functionality of the cluster and biological activity of the protein. Prior to cellular application, the functional integrity of PTEN in the composite was determined in vitro, by enzymatic assay employing para-nitrophenylphosphate as substrate. Cellular internalization of the cargo was studied by confocal microscopy and flow cytometry analysis. The efficacy of the payload on modulation of cellular signaling was assessed on cell lines that expressed PTEN differentially. PTEN null U-87 MG and PTEN expressing MCF7 cell lines displayed successful alteration of AKT and FAK signaling proteins culminating in cell cycle arrest and reduced wound healing capacity. A dose dependent reduction in cell proliferation of MCF7 cells was achieved. For U-87 MG, treatment with the payload resulted in chemosensitization toward anti-cancer drug erlotinib. Thus, PEG coated GST-PTEN loaded silver nanoclusters serves as a comprehensive system encompassing cellular imaging and protein delivery with potential biomedical implications.

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.

Amphiphilic and Hydrophilic Block Copolymers from Aliphatic N-Substituted 8-Membered Cyclic Carbonates: A Versatile Macromolecular Platform for Biomedical Applications

Introduction of hydrophilic components, particularly amines and zwitterions, onto a degradable polymer platform, while maintaining precise control over the polymer composition, has been a challenge. Recognizing the importance of these hydrophilic residues in multiple aspects of the nanobiomedicine field, herein, a straightforward synthetic route to access well-defined amphiphilic and hydrophilic degradable block copolymers from diethanolamine-derived functional eight-membered N-substituted aliphatic cyclic carbonates is reported. By this route, tertiary amine, secondary amine, and zwitterion residues can be incorporated across the polymer backbone. Demonstration of pH-responsiveness of these hydrophilic residues and their utility in the development of drug-delivery vehicles, catered for the specific requirements of respective model drugs (doxorubicin and diclofenac sodium salt) are shown. As hydrophilic components in degradable polymers play crucial roles in the biological interactions, these materials offers opportunities to expand the scope and applicability of aliphatic cyclic carbonates. Our approach to these functional polycarbonates will expand the range of biocompatible and biodegradable synthetic materials available for nanobiomedicine, including drug and gene delivery, antimicrobials, and hydrophilic polymers as poly(ethylene glycol) (PEG) alternatives.

Tumor stroma-containing 3D spheroid arrays: A tool to study nanoparticle penetration

Nanoparticle penetration through tumor tissue after extravasation is considered as a key issue for tumor distribution and therapeutic effects. Most tumors possess abundant stroma, a fibrotic tissue composed of cancer-associated fibroblasts (CAFs) and extracellular matrix (ECM), which acts as a barrier for nanoparticle penetration. There is however a lack of suitable in vitro systems to study the tumor stroma penetration of nanoparticles. In the present study, we developed and thoroughly characterized a 3D co-culture spheroidal array to mimic tumor stroma and investigated the penetration of silica and PLGA nanoparticles in these spheroids. First, we examined human breast tumor patient biopsies to characterize the content and organization of stroma and found a high expression of alpha-smooth muscle actin (α-SMA; 40% positive area) and collagen-1 (50% positive area). Next, we prepared homospheroids of 4T1 mouse breast cancer cells or 3T3 mouse fibroblasts alone as well as heterospheroids combining 3T3 and 4T1 cells in different ratios (1:1 and 5:1) using a microwell array platform. Confocal live imaging revealed that fibroblasts distributed and reorganized within 48h in heterospheroids. Furthermore, immunohistochemical staining and gene expression analysis showed a proportional increase of α-SMA and collagen in heterospheroids with higher fibroblast ratios attaining 35% and 45% positive area at 5:1 (3T3:4T1) ratio, in a good match with the clinical breast tumor stroma. Subsequently, we studied the penetration of high and low negatively charged fluorescent silica nanoparticles (30nm; red and 100 or 70nm; green; zeta potential: -40mV and -20mV) and as well as Cy5-conjugated pegylated PLGA nanoparticles (200nm, -7mV) in both homo- and heterospheroid models. Fluorescent microscopy on spheroid cryosections after incubation with silica nanoparticles showed that 4T1 homospheroids allowed a high penetration of about 75-80% within 24h, with higher penetration in case of the 30nm nanoparticles. In contrast, spheroids with increasing fibroblast amounts significantly inhibited NP penetration. Silica nanoparticles with a less negative zeta potential exhibited lesser penetration compared to highly negative charged nanoparticles. Subsequently, similar experiments were conducted using Cy5-conjugated pegylated PLGA nanoparticles and confocal laser scanning microscopy; an increased nanoparticle penetration was found in 4T1 homospheroids until 48h, but significantly lower penetration in heterospheroids. Furthermore, we also developed human homospheroids (MDA-MB-231 or Panc-1 tumor cells) and heterospheroids (MDA-MB-231/BJ-hTert and Panc-1/pancreatic stellate cells) and performed silica nanoparticle (30 and 100nm) penetration studies. As a result, heterospheroids had significantly a lesser penetration of the nanoparticles compared to homospheroids. In conclusion, our data demonstrate that tumor stroma acts as a strong barrier for nanoparticle penetration. The 30-nm nanoparticles with low zeta potential favor deeper penetration. Furthermore, the herein proposed 3D co-culture platform that mimics the tumor stroma, is ideally suited to systematically investigate the factors influencing the penetration characteristics of newly developed nanomedicines to allow the design of nanoparticles with optimal penetration characteristics.