Synthesis of fluorescent polyisoprene nanoparticles and their uptake into various cells

Quantifying fluorescent nanoparticle uptake in mammalian cells using a plate reader

In keeping with the rapid expansion of nanoparticle applications, various tools are required to investigate how nanoparticles interact with biological entities. Many assays have been developed to measure the cellular uptake of nanoparticles, but so far most of the methods are laborious and often non-quantitative. Here we developed an easily accessible and robust quantitative measurement method of the level of cellular uptake of fluorescently labeled nanoparticles using a plate reader. In the experimental design, potential issues that could lead to measurement variation were identified and addressed. For example, the variation in fluorescence intensity of samples due to differences in cell number was normalized to optical density, which is a physical value corresponding to the cell number. Number of washings and sample handling temperature were optimized to minimize the interference by residual nanoparticles and possible efflux of nanoparticles from cells, respectively. The developed assay was demonstrated with the lymphocyte cell line Jurkat to measure the cellular uptake of fluorescently labeled 50 nm polystyrene beads, and its applicability was further confirmed with the lung carcinoma cell line A549 and another lymphocyte cell line RPMI8226.

Enzymatic and Chemical Approaches for Post-Polymerization Modifications of Diene Rubbers: Current state and Perspectives

Diene rubbers are polymeric materials which present elastic properties and have double bonds in the macromolecular backbone after the polymerization process. Post-polymerization modifications of rubbers can be conducted by enzymatic or chemical methods. Enzymes are environmentally friendly catalysts and with the increasing demand for rubber waste management, biodegradation and biomodifications have become hot topics of research. Some rubbers are renewable materials and are a source of organic molecules, and biodegradation can be conducted to obtain either oligomers or monomers. On the other hand, chemical modifications of rubbers by click-chemistry are important strategies for the creation and combination of new materials. In a way to expand the scope of uses to other non-traditional applications, several and effective modifications can be conducted with diene rubbers. Two groups of efficient tools, enzymatic, and chemical modifications in diene rubbers, are summarized in this review. By analyzing stereochemical and reactivity aspects, the authors also point to some applications perspectives for biodegradation products and to rational modifications of diene rubbers by combining both methodologies.

Neural stem cells improve intracranial nanoparticle retention and tumor-selective distribution

AIM

The purpose of this work is to determine if tumor-tropic neural stem cells (NSCs) can improve the tumor-selective distribution and retention of nanoparticles (NPs) within invasive brain tumors.

MATERIALS & METHODS

Streptavidin-conjugated, polystyrene NPs are surface-coupled to biotinylated human NSCs. These NPs are large (798 nm), yet when conjugated to tropic cells, they are too large to passively diffuse through brain tissue or cross the blood-tumor barrier. NP distribution and retention was quantified 4 days after injections located either adjacent to an intracerebral glioma, in the contralateral hemisphere, or intravenously.

RESULTS & CONCLUSION

In all three in vivo injection paradigms, NSC-coupled NPs exhibited significantly improved tumor-selective distribution and retention over free-NP suspensions. These results provide proof-of-principle that NSCs can facilitate the tumor-selective distribution of NPs, a platform useful for improving intracranial drug delivery.

Absolute quantitation of sub-micrometer particles in cells by flow cytometry

Absolute quantitative measurements of nanoparticle (NP) uptake are a prerequisite to determine doses of NPs in pharmacological and toxicological studies. However, absolute quantitation is rarely reported, hindering the comparison between different studies. Here, a new flow cytometric approach is presented to analyze fluorescent NPs with a "standard" non-scanning flow cytometer and to quantify them inside cells. The mean fluorescence intensity of a single particle and the particle concentration (NPs per μL medium) are obtained. A routine for rapid quantitative counting of the endocytosed NPs in HeLa cells by flow cytometry (FC) is developed and validated by confocal laser scanning microscopy. As a proof-of-concept, the quantitative measurements show that the cellular uptake efficiency of negatively charged poly(methyl methacrylate) NPs is very low, that is, in the range of 10(-3) % of the added particle amount.

Complex encounters: nanoparticles in whole blood and their uptake into different types of white blood cells

Aim: A whole blood assay for evaluating the uptake of nanoparticles into white blood cells in order to close the gap between basic studies in cell culture and pharmacokinetic studies in animals was developed. Materials & methods: After drawing peripheral blood into standard blood collection vials with different anticoagulants, amino- and carboxy-functionalized polymeric styrene nanoparticles were added and uptake was evaluated by flow cytometry. Results: By counterstaining surface markers of leukocytes (e.g., monocytes, neutrophil granulocytes, B or T lymphocytes), investigations of different cell types can be conducted in a single run by flow cytometry. The authors demonstrated that anticoagulation should be done with heparin, and not EDTA, in order to prevent hampering of uptake mechanisms. Conclusion: By using heparinized whole blood, the authors demonstrated differences and usefulness of this assay for screening cellular uptake as it should occur in the bloodstream. Nevertheless, animal studies are warranted for final assessment of the nanoparticles.

Original submitted 11 November 2011; Revised submitted 1 July 2012; Published online 31 August 2012

Suppressing unspecific cell uptake for targeted delivery using hydroxyethyl starch nanocapsules

Synthesizing nanocarriers with stealth properties and delivering a "payload" to the particular organ remains a big challenge but is the prime prerequisite for any in vivo application. As a nontoxic alternative to the modification by poly(ethylene glycol) PEG, we describe the synthesis of cross-linked hydroxyethyl starch (HES, M(w) 200,000 g/mol) nanocapsules with a size range of 170-300 nm, which do not show nonspecific uptake into cells. The specific uptake was shown by coupling a folic acid conjugate as a model targeting agent onto the surface of the nanocapsules, because folic acid has a high affinity to a variety of human carcinoma cell lines which overexpress the folate receptor on the cell surface. The covalent binding of the folic acid conjugate onto HES capsules was confirmed by FTIR and NMR spectroscopy. The coupling efficiency was determined using fluorescence spectroscopy. The specific cellular uptake of the HES nanocapsules after folic acid coupling into the folate-receptor presenting cells was studied by confocal laser scanning microscopy (CLSM) and flow cytometry.

Synthesis of polyester nanoparticles in miniemulsion obtained by radical ring-opening of BMDO and their potential as biodegradable drug carriers

5,6-Benzo-2-methylene-1,3-dioxepane (BMDO) is used to obtain degradable polymeric nanoparticles via a statistical free-radical copolymerization with MMA and styrene in direct miniemulsion. The nanoparticles are analyzed by means of IR, NMR, DLS, SEM, and TEM. They show excellent cellular uptake and drug delivery properties. The cellular uptake into HeLa cells of particles resulting from copolymerization of BMDO with styrene is drastically enhanced compared to pure polystyrene. As a model drug system, paclitaxel is incorporated in PBMDO particles and its release and the effect on HeLa cells is studied and compared to commercial drug formulations. It is found that a drug delivery system based on PBMDO shows an excellent pharmacological effect.

Enhancement of cellular uptake and antitumor efficiencies of micelles with phosphorylcholine

Internalization of drug delivery micelles into cancer cells is a crucial step for antitumor therapeutics. Novel amphiphilic star-shaped copolymers with zwitterionic phosphorylcholine (PC) block, 6-arm star poly(ε-caprolactone)-b-poly(2-methacryloyloxyethyl phosphorylcholine) (6sPCL-b-PMPC), have been developed for encapsulation of poorly water-soluble drugs and enhancement of their cellular uptake. The star-shaped copolymers were synthesized by a combination of ring-opening polymerization (ROP) and atom transfer radical polymerization (ATRP). The copolymers self-assembled to form spherical micelles with low critical micelle concentration (CMC). The sizes of the micelles range from 80 to 170 nm and increase 30 ≈ 80% after paclitaxel (PTX) loading. Labeled with fluorescein isothiocyanate (FITC), the micelles were confirmed by fluorescence microscopy to have been internalized efficiently by tumor cells. Direct visualization of the micelles within tumor cells by transmission electron microscopy (TEM) confirmed that the 6sPCL-b-PMPC micelles were more efficiently uptaken by tumor cells compared to PCL-b-PEG micelles. When incorporated with PTX, the 6sPCL-b-PMPC micelles show much higher cytotoxicity against Hela cells than PCL-b-PEG micelles, in response to the higher efficiency of cellular uptake.

Labeling of mesenchymal stromal cells with iron oxide-poly(L-lactide) nanoparticles for magnetic resonance imaging: uptake, persistence, effects on cellular function and magnetic resonance imaging properties

Background aims. Mesenchymal stromal cells (MSC) are the focus of research in regenerative medicine aiming at the regulatory approval of these cells for specific indications. To cope with the regulatory requirements for somatic cell therapy, novel approaches that do not interfere with the natural behavior of the cells are necessary. In this context in vivo magnetic resonance imaging (MRI) of labeled MSC could be an appropriate tool. Cell labeling for MRI with a variety of different iron oxide preparations is frequently published. However, most publications lack a comprehensive assessment of the noninterference of the contrast agent with the functionality of the labeled MSC, which is a prerequisite for the validity of cell-tracking via MRI. Methods.We studied the effects of iron oxide-poly(L-lactide) nanoparticles in MSC with flow cytom-etry, transmission electron microscopy (TEM), confocal laser scanning microscopy (CLSM), Prussian blue staining, CyQuant® proliferation testing, colony-forming unit-fibroblast (CFU-F) assays, flow chamber adhesion testing, immuno-logic tests and differentiation tests. Furthermore iron-labeled MSC were studied by MRI in agarose phantoms and Wistar rats. Results. It could be demonstrated that MSC show rapid uptake of nanoparticles and long-lasting intracellular persistence in the endosomal compartment. Labeling of the MSC with these particles has no influence on viability, differentiation, clonogenicity, proliferation, adhesion, phenotype and immunosuppressive properties. They show excellent MRI properties in agarose phantoms and after subcutaneous implantation in rats over several weeks. Conclusions. These particles qualify for studying MSC homing and trafficking via MRI.

One-pot synthesis of pegylated fluorescent nanoparticles by RAFT miniemulsion polymerization using a phase inversion process

Water-soluble and fluorescent core-shell nanoparticles (FNP) are synthesized in a miniemulsion reversible addition-fragmentation transfer (RAFT) polymerization and are shown to respond to pH. The particles are obtained from a hydrophilic PEO-b-PAA macromolecular RAFT agent which is block-extended with styrene and a fluorescent BODIPY monomer. A miniemulsion is then formed with the residual hydrophobic monomers. After completion of the polymerization, FNP of ≈ 60 nm in diameter are obtained. The fluorescence of the BODIPY dye in the particles is found to remain (0.2 quantum yield). The particles can be precipitated in acidic pH and redispersed upon addition of base without loss of their integrity or noticeable rearrangement.

Miniemulsion polymerization as a versatile tool for the synthesis of functionalized polymers

The miniemulsion technique is a particular case in the family of heterophase polymerizations, which allows the formation of functionalized polymers by polymerization or modification of polymers in stable nanodroplets. We present here an overview of the different polymer syntheses within the miniemulsion droplets as reported in the literature, and of the current trends in the field.

Poly(ε-caprolactone)-block-poly(ethyl ethylene phosphate) micelles for brain-targeting drug delivery: in vitro and in vivo valuation

PURPOSE

The purpose of this work was to investigate the potential of poly(ε-caprolactone)-block-poly(ethyl ethylene phosphate) (PCL-PEEP) micelles for brain-targeting drug delivery.

METHOD

The coumarin-6-loaded PCL-PEEP micelles (CMs) were prepared and characterized. The cellular uptake of CMs was evaluated on in vitro model of brain-blood barrier (BBB), and the brain biodistribution of CMs in ICR mice was investigated.

RESULTS

PCL-PEEP could self-assemble into 20 nm micelles in water with the critical micelle concentration (CMC) 0.51 μg/ml and high coumarin-6 encapsulation efficiency (92.5 ± 0.7%), and the micelles were stable in 10% FBS with less than 25% leakage of incorporated coumarin-6 during 24 h incubation at 37°C. The cellular uptake of CMs by BBB model was significantly higher and more efficient than coumarin-6 solution (CS) at 50 ng/ml. Compared with CS, 2.6-fold of coumarin-6 was found in the brains of CM-treated mice, and C(max) of CMs was 4.74% of injected dose/g brain. The qualitative investigation on the brain distribution of CMs indicated that CMs were prone to accumulate in hippocampus and striatum.

CONCLUSION

These results suggest that PCL-PEEP micelles could be a promising brain-targeting drug delivery system with low toxicity.