Scavenger receptors mediate cellular uptake of polyvalent oligonucleotide-functionalized gold nanoparticles

Modulation of G protein-coupled adenosine receptors by strategically functionalized agonists and antagonists immobilized on gold nanoparticles

Gold nanoparticles (AuNPs) allow the tuning of pharmacokinetic and pharmacodynamic properties by active or passive targeting of drugs for cancer and other diseases. We have functionalized gold nanoparticles by tethering specific ligands, agonists and antagonists, of adenosine receptors (ARs) to the gold surface as models for cell surface interactions with G protein-coupled receptors (GPCRs). The AuNP conjugates with chain-extended AR ligands alone (PEGylated nucleosides and nonnucleosides, anchored to the Au via thioctic acid) were found to be insoluble in water due to hydrophobic entities in the ligand. Therefore, we added a second, biologically inactive pendant moiety to increase the water solubility, consisting of a PEGylated chain terminating in a carboxylic or phosphate group. The purity and stability of the immobilized biologically active ligand were examined by ultrafiltration and HPLC. Pharmacological receptor binding studies on these GPCR ligand-derivatized AuNPs (2-5 nm in diameter), performed using membranes of mammalian cells stably expressing human A1, A2A, and A3ARs, showed that the desired selectivity was retained with K(i) values (nanomolar) of A3AR agonist 21b and A2AAR antagonists 24 and 26a of 14 (A3), 34 (A2A), and 69 (A2A), respectively. The corresponding monomers displayed K i values of 37, 61, and 1,420 nM, respectively. In conclusion, we have synthesized stable, water-soluble AuNP derivatives of tethered A3 and A2AAR ligands that retain the biological properties of their monomeric ligands and are intended for therapeutic and imaging applications. This is the first prototypical application to gold carriers of small molecule (nonpeptide) GPCR ligands, which are under investigation for treatment of cancer and inflammatory diseases.

Nanobarcoding: detecting nanoparticles in biological samples using in situ polymerase chain reaction

BACKGROUND

Determination of the fate of nanoparticles (NPs) in a biological system, or NP biodistribution, is critical in evaluating an NP formulation for nanomedicine. Current methods to determine NP biodistribution are greatly inadequate, due to their limited detection thresholds. Herein, proof of concept of a novel method for improved NP detection based on in situ polymerase chain reaction (ISPCR), coined "nanobarcoding," is demonstrated.

METHODS

Nanobarcoded superparamagnetic iron oxide nanoparticles (NB-SPIONs) were characterized by dynamic light scattering, zeta potential, and hyperspectral imaging measurements. Cellular uptake of Cy5-labeled NB-SPIONs (Cy5-NB-SPIONs) was imaged by confocal microscopy. The feasibility of the nanobarcoding method was first validated by solution-phase PCR and "pseudo"-ISPCR before implementation in the model in vitro system of HeLa human cervical adenocarcinoma cells, a cell line commonly used for ISPCR-mediated detection of human papilloma virus (HPV).

RESULTS

Dynamic light-scattering measurements showed that NB conjugation stabilized SPION size in different dispersion media compared to that of its precursor, carboxylated SPIONs (COOH-SPIONs), while the zeta potential became more positive after NB conjugation. Hyperspectral imaging confirmed NB conjugation and showed that the NB completely covered the SPION surface. Solution-phase PCR and pseudo-ISPCR showed that the expected amplicons were exclusively generated from the NB-SPIONs in a dose-dependent manner. Although confocal microscopy revealed minimal cellular uptake of Cy5-NB-SPIONs at 50 nM over 24 hours in individual cells, ISPCR detected definitive NB-SPION signals inside HeLa cells over large sample areas.

CONCLUSION

Proof of concept of the nanobarcoding method has been demonstrated in in vitro systems, but the technique needs further development before its widespread use as a standardized assay.

Antibody-linked spherical nucleic acids for cellular targeting

Spherical nucleic acid (SNA) constructs are promising new single entity gene regulation materials capable of both cellular transfection and gene knockdown, but thus far are promiscuous structures, exhibiting excellent genetic but little cellular selectivity. In this communication, we describe a strategy to impart targeting capabilities to these constructs through noncovalent functionalization with a complementary antibody-DNA conjugate. As a proof-of-concept, we designed HER2-targeting SNAs and demonstrated that such structures exhibit cell type selectivity in terms of their uptake, and significantly greater gene knockdown in cells overexpressing the target antigen as compared to the analogous antibody-free and off-target materials.

X-ray imaging of tumor growth in live mice by detecting gold-nanoparticle-loaded cells

We show that sufficient concentrations of gold nanoparticles produced by an original synthesis method in EMT-6 and CT-26 cancer cells make it possible to detect the presence, necrosis and proliferation of such cells after inoculation in live mice. We first demonstrated that the nanoparticles do not interfere with the proliferation process. Then, we observed significant differences in the tumor evolution and the angiogenesis process after shallow and deep inoculation. A direct comparison with pathology optical images illustrates the effectiveness of this approach.

Scavenger receptor mediated endocytosis of silver nanoparticles into J774A.1 macrophages is heterogeneous

We investigated the scavenger receptor mediated uptake and subsequent intracellular spatial distribution and clustering of 57.7 ± 6.9 nm diameter silver nanoparticles (zeta-potential = -28.4 mV) in the murine macrophage cell line J774A.1 through colorimetric imaging. The NPs exhibited an overall red-shift of the plasmon resonance wavelength in the cell ensemble as function of time and concentration, indicative of intracellular NP agglomeration. A detailed analysis of the NP clustering in individual cells revealed a strong phenotypic variability in the intracellular NP organization on the single cell level. Throughout the observation time of 24h cells containing non- or low-agglomerated NPs with a characteristic blue color coexisted with cells containing NPs with varying degrees of agglomeration, as evinced by distinct spectral shifts of their resonance wavelengths. Pharmacological inhibition studies indicated that the observed differences in intracellular NP organization resulted from coexisting actin- and clathrin-dependent endocytosis mechanisms in the macrophage population. Correlation of intracellular NP clustering with macrophage maturity marker (F4/80, CD14) expression revealed that differentiated J774A.1 cells preferentially contained compact NP agglomerates, whereas monocyte-like macrophages contained non-agglomerated NPs.

Exocytosis of peptide functionalized gold nanoparticles in endothelial cells

We present the exocytosis profile of two types of peptide-coated nanoparticles, which have similar charge and size but different functionality. While one kind of particles appears to progressively exocytose, the other one has a more complex profile, suggesting that some of the particles are re-uptaken by the cells. Both types of particles retain their colloidal stability after exocytosis.

Effects of the presence or absence of a protein corona on silica nanoparticle uptake and impact on cells

Nanoparticles enter cells through active processes, thanks to their capability of interacting with the cellular machinery. The protein layer (corona) that forms on their surface once nanoparticles are in contact with biological fluids, such as the cell serum, mediates the interactions with cells in situ. As a consequence of this, here we show that the same nanomaterial can lead to very different biological outcomes, when exposed to cells in the presence or absence of a preformed corona. In particular, silica nanoparticles exposed to cells in the absence of serum have a stronger adhesion to the cell membrane and higher internalization efficiency, in comparison to what is observed in medium containing serum, when a preformed corona is present on their surface. The different exposure conditions not only affect the uptake levels but also result in differences in the intracellular nanoparticle location and impact on cells. Interestingly, we also show that after only one hour of exposure, a corona of very different nature forms on the nanoparticles exposed to cells in the absence of serum. Evidence suggests that these different outcomes can all be connected to the different adhesion and surface properties in the two conditions.

Nanoparticle surface charge mediates the cellular receptors used by protein-nanoparticle complexes

Nanoparticles are increasingly important for biological applications ranging from drug delivery to cellular imaging. In the course of these applications, nanoparticles are exposed to a complex environment of extracellular proteins that can be adsorbed onto the surface of the nanoparticle, altering nanoparticle-cell interactions. We have investigated how proteins found in blood serum affect the binding of nanoparticles to the surface of cells. Using fluorescence microscopy, we find that the cellular binding of cationic nanoparticles is enhanced by the presence of serum proteins, while the binding of anionic nanoparticles is inhibited. We have determined that this difference in cellular binding is due to the use of distinct cellular receptors. Competition assays, quantified with flow cytometry, show that the protein-nanoparticle complex formed from the cationic nanoparticles binds to scavenger receptors on the cell surface. Interestingly, the protein-nanoparticle complex formed from anionic nanoparticles binds to native protein receptors. As nanoparticles become increasingly important for in vivo applications, we expect these results will inform the design of nanoparticles with improved cellular binding.

Hollow spherical nucleic acids for intracellular gene regulation based upon biocompatible silica shells

Cellular transfection of nucleic acids is necessary for regulating gene expression through antisense or RNAi pathways. The development of spherical nucleic acids (SNAs, originally gold nanoparticles functionalized with synthetic oligonucleotides) has resulted in a powerful set of constructs that are able to efficiently transfect cells and regulate gene expression without the use of auxiliary cationic cocarriers. The gold core in such structures is primarily used as a template to arrange the nucleic acids into a densely packed and highly oriented form. In this work, we have developed methodology for coating the gold particle with a shell of silica, modifying the silica with a layer of oligonucleotides, and subsequently oxidatively dissolving the gold core with I(2). The resulting hollow silica-based SNAs exhibit cooperative binding behavior with respect to complementary oligonucleotides and cellular uptake properties comparable to their gold-core SNA counterparts. Importantly, they exhibit no cytotoxicity and have been used to effectively silence the eGFP gene in mouse endothelial cells through an antisense approach.

Topical delivery of siRNA-based spherical nucleic acid nanoparticle conjugates for gene regulation

Topical application of nucleic acids offers many potential therapeutic advantages for suppressing genes in the skin, and potentially for systemic gene delivery. However, the epidermal barrier typically precludes entry of gene-suppressing therapy unless the barrier is disrupted. We now show that spherical nucleic acid nanoparticle conjugates (SNA-NCs), gold cores surrounded by a dense shell of highly oriented, covalently immobilized siRNA, freely penetrate almost 100% of keratinocytes in vitro, mouse skin, and human epidermis within hours after application. Significantly, these structures can be delivered in a commercial moisturizer or phosphate-buffered saline, and do not require barrier disruption or transfection agents, such as liposomes, peptides, or viruses. SNA-NCs targeting epidermal growth factor receptor (EGFR), an important gene for epidermal homeostasis, are > 100-fold more potent and suppress longer than siRNA delivered with commercial lipid agents in cultured keratinocytes. Topical delivery of 1.5 uM EGFR siRNA (50 nM SNA-NCs) for 3 wk to hairless mouse skin almost completely abolishes EGFR expression, suppresses downstream ERK phosphorylation, and reduces epidermal thickness by almost 40%. Similarly, EGFR mRNA in human skin equivalents is reduced by 52% after 60 h of treatment with 25 nM EGFR SNA-NCs. Treated skin shows no clinical or histological evidence of toxicity. No cytokine activation in mouse blood or tissue samples is observed, and after 3 wk of topical skin treatment, the SNA structures are virtually undetectable in internal organs. SNA conjugates may be promising agents for personalized, topically delivered gene therapy of cutaneous tumors, skin inflammation, and dominant negative genetic skin disorders.

Surface functionalization of nanoparticles for nanomedicine

Control of interactions between nanoparticles and biosystems is essential for the effective utilization of these materials in biomedicine. A wide variety of nanoparticle surface structures have been developed for imaging, sensing, and delivery applications. In this research Highlight, we will emphasize advances in tailoring nanoparticle interfaces for implementation in nanomedicine.

Magnetic nanoparticles in primary neural cell cultures are mainly taken up by microglia

Background

Magnetic nanoparticles (MNPs) offer a large range of applications in life sciences. Applications in neurosciences are one focus of interest. Unfortunately, not all groups have access to nanoparticles or the possibility to develop and produce them for their applications. Hence, they have to focus on commercially available particles. Little is known about the uptake of nanoparticles in primary cells. Previously studies mostly reported cellular uptake in cell lines. Here we present a systematic study on the uptake of magnetic nanoparticles (MNPs) by primary cells of the nervous system.

Results

We assessed the internalization in different cell types with confocal and electron microscopy. The analysis confirmed the uptake of MNPs in the cells, probably with endocytotic mechanisms. Furthermore, we compared the uptake in PC12 cells, a rat pheochromocytoma cell line, which is often used as a neuronal cell model, with primary neuronal cells. It was found that the percentage of PC12 cells loaded with MNPs was significantly higher than for neurons. Uptake studies in primary mixed neuronal/glial cultures revealed predominant uptake of MNPs by microglia and an increase in their number. The number of astroglia and oligodendroglia which incorporated MNPs was lower and stable. Primary mixed Schwann cell/fibroblast cultures showed similar MNP uptake of both cell types, but the Schwann cell number decreased after MNP incubation. Organotypic co-cultures of spinal cord slices and peripheral nerve grafts resembled the results of the dispersed primary cell cultures.

Conclusions

The commercial MNPs used activated microglial phagocytosis in both disperse and organotypic culture systems. It can be assumed that in vivo application would induce immune system reactivity, too. Because of this, their usefulness for in vivo neuroscientific implementations can be questioned. Future studies will need to overcome this issue with the use of cell-specific targeting strategies. Additionally, we found that PC12 cells took up significantly more MNPs than primary neurons. This difference indicates that PC12 cells are not a suitable model for natural neuronal uptake of nanoparticles and qualify previous results in PC12 cells.

Nanoparticles act as protein carriers during cellular internalization

Two-colour fluorescence microscopy was used to track the cellular internalization of nanoparticles exposed to extracellular serum proteins. Single particle tracking revealed that nanoparticles and serum proteins are internalized and transported through the cell as a single complex. This study demonstrates the importance of nanoparticle-protein interactions in cellular applications.

Rolling circle amplification-templated DNA nanotubes show increased stability and cell penetration ability

DNA nanotubes hold promise as scaffolds for protein organization, as templates of nanowires and photonic systems, and as drug delivery vehicles. We present a new DNA-economic strategy for the construction of DNA nanotubes with a backbone produced by rolling circle amplification (RCA), which results in increased stability and templated length. These nanotubes are more resistant to nuclease degradation, capable of entering human cervical cancer (HeLa) cells with significantly increased uptake over double-stranded DNA, and are amenable to encapsulation and release behavior. As such, they represent a potentially unique platform for the development of cell probes, drug delivery, and imaging tools.

Multiplexed nanoflares: mRNA detection in live cells

We report the development of the multiplexed nanoflare, a nanoparticle agent that is capable of simultaneously detecting two distinct mRNA targets inside a living cell. These probes are spherical nucleic acid (SNA) gold nanoparticle (Au NP) conjugates consisting of densely packed and highly oriented oligonucleotide sequences, many of which are hybridized to a reporter with a distinct fluorophore label and each complementary to its corresponding mRNA target. When multiplexed nanoflares are exposed to their targets, they provide a sequence specific signal in both extra- and intracellular environments. Importantly, one of the targets can be used as an internal control, improving detection by accounting for cell-to-cell variations in nanoparticle uptake and background. Compared to single-component nanoflares, these structures allow one to determine more precisely relative mRNA levels in individual cells, improving cell sorting and quantification.

Interactions of human endothelial cells with gold nanoparticles of different morphologies

The interactions between noncancerous, primary endothelial cells and gold nanoparticles with different morphologies but the same ligand capping are investigated. The endothelial cells are incubated with gold nanospheres, nanorods, hollow gold spheres, and core/shell silica/gold nanocrystals, which are coated with monocarboxy (1-mercaptoundec-11-yl) hexaethylene glycol (OEG). Cell viability studies show that all types of gold particles are noncytotoxic. The number of particles taken up by the cells is estimated using inductively coupled plasma (ICP), and are found to differ depending on particle morphology. The above results are discussed with respect to heating efficiency. Using experimental data reported earlier and theoretical model calculations which take into account the physical properties and distribution of particles in the cellular microenvironment, it is found that collective heating effects of several cells loaded with nanoparticles must be included to explain the observed viability of the endothelial cells.

Scavenger receptor-mediated uptake of cell-penetrating peptide nanocomplexes with oligonucleotides

Cell-penetrating peptides (CPPs) are short cationic peptides that penetrate cells by interacting with the negatively charged plasma membrane; however, the detailed uptake mechanism is not clear. In contrary to the conventional mode of action of CPPs, we show here that a CPP, PepFect14 (PF14), forms negatively charged nanocomplexes with oligonucleotides and their uptake is mediated by class-A scavenger receptors (SCARAs). Specific inhibitory ligands of SCARAs, such as fucoidin, polyinosinic acid, and dextran sulfate, totally inhibit the activity of PF14-oligonucleotide nanocomplexes in the HeLa pLuc705 splice-correction cell model, while nonspecific, chemically related molecules do not. Furthermore, RNA interference (RNAi) knockdown of SCARA subtypes (SCARA3 and SCARA5) that are expressed in this cell line led to a significant reduction of the activity to <50%. In line with this, immunostaining shows prevalent colocalization of the nanocomplexes with the receptors, and electron microscopy images show no binding or internalization of the nanocomplexes in the presence of the inhibitory ligands. Interestingly, naked oligonucleotides also colocalize with SCARAs when used at high concentrations. These results demonstrate the involvement of SCARA3 and SCARA5 in the uptake of PF14-oligonucleotide nanocomplexes and suggest for the first time that some CPP-based systems function through scavenger receptors, which could yield novel possibilities to understand and improve the transfection by CPPs.

Gold nanoparticles in biomedical applications: recent advances and perspectives

Gold nanoparticles (GNPs) with controlled geometrical, optical, and surface chemical properties are the subject of intensive studies and applications in biology and medicine. To date, the ever increasing diversity of published examples has included genomics and biosensorics, immunoassays and clinical chemistry, photothermolysis of cancer cells and tumors, targeted delivery of drugs and antigens, and optical bioimaging of cells and tissues with state-of-the-art nanophotonic detection systems. This critical review is focused on the application of GNP conjugates to biomedical diagnostics and analytics, photothermal and photodynamic therapies, and delivery of target molecules. Distinct from other published reviews, we present a summary of the immunological properties of GNPs. For each of the above topics, the basic principles, recent advances, and current challenges are discussed (508 references).

Nucleic acid-gold nanoparticle conjugates as mimics of microRNA

Novel conjugates of gold nanoparticles (13±1nm) functionalized with synthetic microRNAs can enter cells without the aid of cationic co-carriers and mimic the function of endogenous microRNAs. These conjugates can regulate multiple proteins through interactions with 3′ untranslated region of the target mRNA and control cell behavior. The conjugates are a promising new tool for studying miRNA function and new candidates for miRNA replacement therapies.

Inhibiting metastasis of breast cancer cells in vitro using gold nanorod-siRNA delivery system

Breast cancer is the most common malignant disease in women, and it is not the primary tumor but its metastasis kills most patients with breast cancer. Anti-metastasis therapy based on RNA interference (RNAi) is emerging as one of promising strategies in tumor therapy. However, construction of an efficient delivery system for siRNA is still one of the major challenges. In this work, siRNA against protease-activated receptor-1 (PAR-1) which is a pivotal gene involved in tumor metastasis was conjugated to gold nanorods (AuNRs) via electrostatic interaction and delivered to highly metastatic human breast cancer cells. It was demonstrated that the siRNA oligos were successfully delivered into the cancer cells and mainly located in vesicle-like structures including lysosome. After transfected with the complex of AuNRs and PAR-1 siRNA (AuNRs@PAR-1 siRNA), expression of PAR-1 at both mRNA and protein levels were efficiently down regulated, as evidenced by quantitative real time PCR and flow cytometry analysis, respectively. Transwell migration assay confirmed the decrease in metastatic ability of the cancer cells. The silencing efficiency of the complex was in-between that of TurboFect and Lipofectamine, however, the cytotoxicity of the AuNRs was lower than that of the latter two. Taken together, AuNRs with PAR-1 siRNA are suited for RNAi based anti-metastasis therapy.

Duplex end breathing determines serum stability and intracellular potency of siRNA-Au NPs

Structural requirements of siRNA-functionalized gold nanoparticles (siRNA-Au NPs) for Dicer recognition and serum stability were studied. We show that the 3' overhang on the nucleic acids of these particles is preferentially recognized by Dicer but also makes the siRNA duplexes more susceptible to nonspecific serum degradation. Dicer and serum nucleases show lower preference for blunt duplexes as opposed to those with 3' overhangs. Importantly, gold nanoparticles functionalized with blunt duplexes with relatively less thermal breathing are up to 15 times more stable against serum degradation without compromising Dicer recognition. This increased stability leads to a 300% increase in cellular uptake of siRNA-Au NPs and improved gene knockdown.

Beauty is skin deep: a surface monolayer perspective on nanoparticle interactions with cells and bio-macromolecules

Surface recognition of biosystems is a critical component in the development of novel biosensors and delivery vehicles, and for the therapeutic regulation of biological processes. Monolayer-protected nanoparticles present a highly versatile scaffold for selective interaction with bio-macromolecules and cells. Through the engineering of the monolayer surface, nanoparticles can be tailored for surface recognition of biomolecules and cells. This review highlights recent progress in nanoparticle-bio-macromolecule/cellular interactions, emphasizing the effect of the surface monolayer structure on the interactions with proteins, DNA, and cell surfaces. The extension of these tailored interactions to hybrid nanomaterials, biosensing platforms, and delivery vehicles is also discussed.

Five years of siRNA delivery: spotlight on gold nanoparticles

Gold nanoparticles have become widely used in scientific research due to their unique physical and chemical properties. In the last several years their use as siRNA delivery agents has been investigated. Here, progress made using gold nanoparticles for siRNA delivery is described and the different strategies employed are compared.

Polyvalent nucleic acid nanostructures

Polyvalent oligonucleotide-nanoparticle conjugates possess several unique emergent properties, including enhanced cellular uptake, high antisense bioactivity, and nuclease resistance, which hypothetically originate from the dense packing and orientation of oligonucleotides on the surface of the nanoparticle. In this Communication, we describe a new class of polyvalent nucleic acid nanostructures (PNANs), which are comprised of only cross-linked and oriented nucleic acids. We demonstrate that these particles are capable of effecting high cellular uptake and gene regulation without the need of a cationic polymer co-carrier. The PNANs also exhibit cooperative binding behavior and nuclease resistance properties.

Gold nanoparticles in biology and medicine: recent advances and prospects

Functionalized gold nanoparticles with controlled geometrical and optical properties are the subject of intensive studies and biomedical applications, including genomics, biosensorics, immunoassays, clinical chemistry, laser phototherapy of cancer cells and tumors, the targeted delivery of drugs, DNA and antigens, optical bioimaging and the monitoring of cells and tissues with the use of state-of-the-art detection systems. This work will provide an overview of the recent advances and current challenges facing the biomedical application of gold nanoparticles of various sizes, shapes, and structures. The review is focused on the application of gold nanoparticle conjugates in biomedical diagnostics and analytics, photothermal and photodynamic therapies, as a carrier for delivering target molecules, and on the immunological and toxicological properties. Keeping in mind the huge volume and high speed of the data update rate, 2/3 of our reference list (certainly restricted to 250 Refs.) includes publications encompassing the past 5 years.