Biomolecular corona on nanoparticles: a survey of recent literature and its implications in targeted drug delivery

Preservation of the soft protein corona in distinct flow allows identification of weakly bound proteins

Nanocarriers that are used for targeted drug delivery come in contact with biological liquids and subsequently proteins will adsorb to the nanocarriers' surface to form the so called 'protein corona'. The protein corona defines the biological identity and determines the biological response towards the nanocarriers in the body. To make nanomedicine safe and reliable it is required to get a better insight into this protein corona and, therefore, the adsorbed proteins have to be characterized. Currently, centrifugation is the common method to isolate the protein corona for further investigations. However, with this method it is only possible to investigate the strongly bound proteins, also referred to as 'hard protein corona'. Therefore, we want to introduce a new separation technique to separate nanoparticles including the soft protein corona containing also loosely bound proteins for further characterization. The used separation technique is the asymmetric flow field-flow fractionation (AF4). We were able to separate the nanoparticles with proteins forming the soft protein corona and were able to show that in our system only the hard protein corona directly influenced the cell uptake behavior.

STATEMENT OF SIGNIFICANCE

Currently, there is an ongoing debate whether only strongly bound proteins (hard corona) or also loosely bound proteins (soft corona) contribute to the biological identity of nanocarriers, because up to now isolation of the soft corona was not possible. Here, asymmetric flow field-flow fractionation was used to isolate nanoparticles with a preserved soft corona from the biological medium. This enabled the characterization of the soft corona composition and to evaluate its influence on cellular uptake. For our system we found that only the strongly bound proteins (hard corona) determined cell internalization. This method can now be used to evaluate the impact of the soft corona further and to characterize nanomaterials that cannot be separated from blood plasma by other means.

Dendritic PEG outer shells enhance serum stability of polymeric micelles

A higher surface density of poly(ethylene glycol) (PEG) on polymeric micelles enhances their stability in serum, leading to improved plasma circulation. To obtain fundamental, mechanistic understanding of the PEG effect associated with polymeric architecture/configuration, we have synthesized PEGylated dendron-based copolymers (PDCs) and linear block copolymers (LBCs) with similar molecular weights. These copolymers formed dendron (hyperbranched) and linear micelles, respectively, which were compared in terms of their stabilities in serum, micelle-serum protein interactions, and in vivo biodistributions. Overall, the dendron micelles exhibited a better serum stability (longer half-life) and thus a slower release profile than the linear micelles. Fluorescence quenching assays and molecular dynamics (MD) simulations revealed that the high serum stability of the dendron micelles can be attributed to reduced micelle-serum protein interactions, owing to their dendritic, dense PEG outer shell. These results provide an important design cue for various polymeric micelles and nanoparticles.

Regulatory T cell-targeted hybrid nanoparticles combined with immuno-checkpoint blockage for cancer immunotherapy

Immunosuppression in tumor microenvironments induced by regulatory T (Treg) cells is regarded a critical mechanism of tumor immune escape and poses a major impediment to cancer immunotherapy. In this study, we developed tLyp1 peptide-conjugated hybrid nanoparticles for targeting Treg cells in the tumor microenvironment. The tLyp1 peptide-modified hybrid nanoparticles presented good stability and effective targeting to Treg cells, and they enhanced the effect of imatinib in downregulating Treg cell suppression through inhibition of STAT3 and STAT5 phosphorylation. In addition, an in vivo study revealed high tumor accumulation of the hybrid nanoparticle. Specifically, prolonged survival rate, enhanced tumor inhibition, reduced intratumoral Treg cells, and elevated intratumoral CD8⁺ T cells against tumor were observed when combined with checkpoint-blockade by using anti-cytotoxic T-lymphocyte antigen-4 antibody. This study provided groundwork for a repertoire of nanoparticle-based drugs for targeting and modulating Treg cell function in the tumor microenvironment and for improving antitumor immunotherapy.

Investigation of adhesive interactions in the specific targeting of Triptorelin-conjugated PEG-coated magnetite nanoparticles to breast cancer cells

The understanding of adhesive interaction at the nanoscale between functionalized nanoparticles and biological cells is of great importance to develop effective theranostic nanocarriers for targeted cancer therapy. Here, we report a combination of experimental and computational approaches to evaluate the adhesion between Triptorelin (a Luteinizing Hormone-Releasing Hormone (LHRH) agonist)-conjugated poly-(ethylene glycol) (PEG)-coated magnetite nanoparticles (Triptorelin-MNPs) and breast cells. The adhesion forces between Triptorelin-MNPs and normal/cancerous breast cells are obtained using atomic force microscopy. The corresponding work of adhesion is then estimated using Johnson-Kendall-Roberts model. Our results demonstrate that Triptorelin-MNPs have a fourteen-fold greater work of adhesion to breast cancer cells than to normal breast cells. In addition, the work of adhesion between Triptorelin-MNPs and breast cancer cells is found to be three times more than that between unmodified MNPs and breast cancer cells. Hence, the experimental observation indicates that Triptorelin ligands facilitate the specific targeting of breast cancer cells. Furthermore, molecular dynamics simulations are performed to investigate the molecular origins of the adhesive interactions. The simulations reveal that the interactions between molecules (e.g. Triptorelin and PEG) and LHRH receptors are dominated by van der Waals energies, while the interactions of these molecules with cell membrane are dominated by electrostatic interactions. Moreover, both experimental and computational results reveal that PEG serves as an effective coating that enhances adhesive interactions to breast cancer cells that over-express LHRH receptors, while reduces the adhesion to normal breast cells. Our results highlight the potential to develop Triptorelin-MNPs into tumor-specific MRI contrast agents and drug carriers.

STATEMENT OF SIGNIFICANCE

Systematic investigation of adhesive interactions between functionalized nanoparticles and cancer cells is of great importance in developing effective theranostic nanocarriers for targeted cancer therapy. Herein, we use a combination of atomic force microscopy technique and molecular dynamics simulations approach to explore the adhesive interactions at the nanoscale between Triptorelin-conjugated polyethylene glycol (PEG)-coated magnetite nanoparticles and normal/cancerous breast cells. This study characterizes and quantifies the work of adhesion, as well as adhesion forces, at the nanocarrier/cell interfaces, unravels the molecular origins of adhesive interactions and highlights the effectiveness of PEG coatings and Triptorelin ligands in the specific targeting of breast cancer cells. Our findings expand the fundamental understanding of nanoparticle/cell adhesion and provide guidelines for the design of more rational nanocarriers.

Machine learning provides predictive analysis into silver nanoparticle protein corona formation from physicochemical properties

Proteins encountered in biological and environmental systems bind to engineered nanomaterials (ENMs) to form a protein corona (PC) that alters the surface chemistry, reactivity, and fate of the ENMs. Complexities such as the diversity of the PC and variation with ENM properties and reaction conditions make the PC population difficult to predict. Here, we support the development of predictive models for PC populations by relating biophysicochemical characteristics of proteins, ENMs, and solution conditions to PC formation using random forest classification. The resulting model offers a predictive analysis into the population of PC proteins in Ag ENM systems of various ENM size and surface coatings. With an area under the receiver operating characteristic curve of 0.83 and F1-score of 0.81, a model with strong performance has been constructed based upon experimental data. The weighted contribution of each variable provides recommendations for mechanistic models based upon protein enrichment classification results. Protein biophysical properties such as pI and weight are weighted heavily. Yet, ENM size, surface charge, and solution ionic strength also proved essential to an accurate model. The model can be readily modified and applied to other ENM PC populations. The model presented here represents the first step toward robust predictions of PC fingerprints.

The Protein Corona of PEGylated PGMA-Based Nanoparticles is Preferentially Enriched with Specific Serum Proteins of Varied Biological Function

The composition of the protein corona formed on poly(ethylene glycol)-functionalized (PEGylated) poly(glycidyl methacrylate) (PGMA) nanoparticles (NPs) was qualitatively and quantitatively compared to the protein corona on non-PEGylated PGMA NPs. Despite the reputation of PEGylated NPs for stealth functionality, we demonstrate the preferential enrichment of specific serum proteins of varied biological function in the protein corona on PEGylated NPs when compared to non-PEGylated NPs. Additionally, we suggest that the base material of polymeric NPs plays a role in the preferential enrichment of select serum proteins to the hard corona.

The species origin of the serum in the culture medium influences the in vitro toxicity of silica nanoparticles to HepG2 cells

The formation of a protein corona around nanoparticles can influence their toxicity, triggering cellular responses that may be totally different from those elicited by pristine nanoparticles. The main objective of this study was to investigate whether the species origin of the serum proteins forming the corona influences the in vitro toxicity assessment of silica nanoparticles. Coronas were preformed around nanoparticles before cell exposures by incubation in fetal bovine (FBS) or human (HS) serum. The compositions of these protein coronas were assessed by nano-LC MS/MS. The effects of these protein-coated nanoparticles on HepG2 cells were monitored using real-time cell impedance technology. The nanoparticle coronas formed in human or fetal bovine serum comprised many homologous proteins. Using human compared with fetal bovine serum, nanoparticle toxicity in HepG2 cells decreased by 4-fold and 1.5-fold, when used at 50 and 10μg/mL, respectively. It is likely that "markers of self" are present in the serum and are recognized by human cell receptors. Preforming a corona with human serum seems to be more appropriate for in vitro toxicity testing of potential nanocarriers using human cells. In vitro cytotoxicity assays must reflect in vivo conditions as closely as possible to provide solid and useful results.

IgA and IgM protein primarily drive plasma corona-induced adhesion reduction of PLGA nanoparticles in human blood flow

The high abundance of immunoglobulins (Igs) in the plasma protein corona on poly(lactic-co-glycolic) acid (PLGA)-based vascular-targeted carriers (VTCs) has previously been shown to reduce their adhesion to activated endothelial cells (aECs) in human blood flow. However, the relative role of individual Ig classes (e.g., IgG, IgA, and IgM) in causing adhesion reduction remains largely unknown. Here, we characterized the influence of specific Ig classes in prescribing the binding efficiency of PLGA nano-sized VTCs in blood flow. Specifically, we evaluated the flow adhesion to aECs of PLGA VTCs with systematic depletion of various Igs in their corona. Adhesion reduction was largely eliminated for PLGA VTCs when all Igs were removed from the corona. Furthermore, re-addition of IgA or IgM to the Igs-depleted corona reinstated the low adhesion of PLGA VTCs, as evidenced by ∼40-70% reduction relative to particles with an Igs-deficient corona. However, re-addition of a high concentration of IgG to the Igs-depleted corona did not cause significant adhesion reduction. Overall, the presented results reveal that PLGA VTC adhesion reduction in blood flows is primarily driven by high adsorption of IgA and IgM in the particle corona. Pre-coating of albumin on PLGA VTCs mitigated the extent of adhesion reduction in plasma for some donors but was largely ineffective in general. Overall, this work may shed light into effective control of protein corona composition, thereby enhancing VTC functionality in vivo for eventual clinical use.

In vivo reprogramming of immune cells: Technologies for induction of antigen-specific tolerance

Technologies that induce antigen-specific immune tolerance by mimicking naturally occurring mechanisms have the potential to revolutionize the treatment of many immune-mediated pathologies such as autoimmunity, allograft rejection, and allergy. The immune system intrinsically has central and peripheral tolerance pathways for eliminating or modulating antigen-specific responses, which are being exploited through emerging technologies. Antigen-specific tolerogenic responses have been achieved through the functional reprogramming of antigen-presenting cells or lymphocytes. Alternatively, immune privileged sites have been mimicked using biomaterial scaffolds to locally suppress immune responses and promote long-term allograft survival. This review describes natural mechanisms of peripheral tolerance induction and the various technologies being developed to achieve antigen-specific immune tolerance in vivo. As currently approved therapies are non-specific and carry significant associated risks, these therapies offer significant progress towards replacing systemic immune suppression with antigen-specific therapies to curb aberrant immune responses.

Protein Corona Analysis of Silver Nanoparticles Exposed to Fish Plasma

Nanoparticles (NPs) in contact with biological fluids experience changes in surface chemistry that can impact their biodistribution and downstream physiological impact. One such change involves the formation of a protein corona (PC) on the surface of NPs. Here we present a foundational study on PC formation following the incubation of polyvinylpyrrolidone-coated AgNPs (PVP-AgNPs, 50 nm) in the plasma of smallmouth bass (Micropterus dolomieu). PC formation increases with exposure time and is also affected by gender, with AgNPs incubated in male plasma having slightly thinner PCs and less negative zeta potentials than those incubated in female plasma. Proteomic analysis also revealed gender-specific differences in PC composition: in particular, egg-specific proteins (vitellogenin (VTG) and zona pellucida (ZP) were identified only in PCs derived from female plasma, raising the possibility of their roles in AgNP-related reproductive toxicity by promoting their accumulation in developing oocytes.

Technetium-99m radiolabeled paclitaxel as an imaging probe for breast cancer in vivo

The high incidence and mortality of breast cancer supports efforts to develop innovative imaging probes to effectively diagnose, evaluate the extent of the tumor, and predict the efficacy of tumor treatments while concurrently and selectively delivering anticancer agents to the cancer tissue. In the present study we described the preparation of technetium-99m (99mTc)-labeled paclitaxel (PTX) and evaluated its feasibility as a radiotracer for breast tumors (4T1) in BALB/c mice. Thin Layer Chromatography (TLC) was used to determine the radiochemical purity and in vitro stability of 99mTc-PTX. PTX micelles showed a unimodal distribution with mean diameter of 13.46±0.06nm. High radiochemical purity (95.8±0.3%) and in vitro stability (over than 95%), up to 24h, were observed. Blood circulation time of 99mTc-PTX was determined in healthy BALB/c mice. 99mTc-PTX decays in a one-phase manner with a half-life of 464.3 minutes. Scintigraphic images and biodistribution were evaluated at 4, 8 and 24h after administration of 99mTc-PTX in 4T1 tumor-bearing mice. The data showed a significant uptake in the liver, spleen and kidneys, due to the importance of these routes for excretion. Moreover, high tumor uptake was achieved, indicated by high tumor-to-muscle ratios. These findings indicate the usefulness of 99mTc-PTX as a radiotracer to identify 4T1 tumor in animal models. In addition, 99mTc-PTX might be used to follow-up treatment protocols in research, being able to provide information about tumor progression after therapy.

Surface chemistry of gold nanoparticles determines the biocorona composition impacting cellular uptake, toxicity and gene expression profiles in human endothelial cells

This study investigated the role of nanoparticle size and surface chemistry on biocorona composition and its effect on uptake, toxicity and cellular responses in human umbilical vein endothelial cells (HUVEC), employing 40 and 80 nm gold nanoparticles (AuNP) with branched polyethyleneimine (BPEI), lipoic acid (LA) and polyethylene glycol (PEG) coatings. Proteomic analysis identified 59 hard corona proteins among the various AuNP, revealing largely surface chemistry-dependent signature adsorbomes exhibiting human serum albumin (HSA) abundance. Size distribution analysis revealed the relative instability and aggregation inducing potential of bare and corona-bound BPEI-AuNP, over LA- and PEG-AuNP. Circular dichroism analysis showed surface chemistry-dependent conformational changes of proteins binding to AuNP. Time-dependent uptake of bare, plasma corona (PC) and HSA corona-bound AuNP (HSA-AuNP) showed significant reduction in uptake with PC formation. Cell viability studies demonstrated dose-dependent toxicity of BPEI-AuNP. Transcriptional profiling studies revealed 126 genes, from 13 biological pathways, to be differentially regulated by 40 nm bare and PC-bound BPEI-AuNP (PC-BPEI-AuNP). Furthermore, PC formation relieved the toxicity of cationic BPEI-AuNP by modulating expression of genes involved in DNA damage and repair, heat shock response, mitochondrial energy metabolism, oxidative stress and antioxidant response, and ER stress and unfolded protein response cascades, which were aberrantly expressed in bare BPEI-AuNP-treated cells. NP surface chemistry is shown to play the dominant role over size in determining the biocorona composition, which in turn modulates cell uptake, and biological responses, consequently defining the potential safety and efficacy of nanoformulations.

Biomimetic Human Serum Albumin Nanoparticle for Efficiently Targeting Therapy to Metastatic Breast Cancers

Triple-negative breast cancers (TNBCs), devoid of hormone receptors and human epidermal growth-factor receptor-2/Neu expression, bring about poor prognosis and induce a high rate of systematic metastases. The ineffectiveness of current therapies on TNBCs could be attributed to the lack of efficient targeted therapy. Paclitaxel (PTX) is considered one of first-line chemotherapeutics for TNBC treatment but, due to its low aqueous solubility and nonspecific accumulation, results in poor antitumor efficacy. The present study is aimed at enhancing the chemotherapeutic potency of PTX by improving the stability and targeting efficiency of PTX-loaded nanoparticulate drug carriers. Here, PTX was incorporated in nontoxic and endogenous material, human serum albumin (HSA), via an innovative disulfide reduction method to construct HSA-based PTX nanoparticle (HSA-PTX NP) to not only realize redox-responsive drug release but also improve in vivo stability. Besides, W peptide was selected as a target ligand to be conjugated with HSA-PTX NP for endowing active targeting ability. The resulting Wpep-HSA-PTX NP possessed a spherical structure (118 nm), 9.87% drug-loading content, and 86.3% entrapment efficiency. An in vitro drug release test showed that PTX release from Wpep-HSA-PTX NP was of a redox-responsive manner. Furthermore, cellular uptake of Wpep-HSA-PTX NP was significantly enhanced, exhibiting the improved antiproliferation and antitube formation effects of PTX in vitro. In comparison with those commercial formulations and conventional HSA NP, Wpep-HSA-PTX NP exhibited better pharmacokinetic behaviors and tumor homing characteristics. The antitumor efficacy of Wpep-HSA-PTX NP was further confirmed by the strong pro-apoptotic effect and reduced tumor burden. In a word, this evidence highlighted the proof of concept for Wpep-HSA NP as a promising conqueror to the ineffectiveness of TNBC therapy.

Synthesis, characterization and radiolabeling of polymeric nano-micelles as a platform for tumor delivering

The use of nanoparticles for diagnostic approaches leads to higher accumulation in the targeting tissue promoting a better signal-to-noise ratio and consequently, early tumor detection through scintigraphic techniques. Such approaches have inherent advantages, including the possibility of association with a variety of gamma-emitting radionuclides available, among them, Tecnethium-99m (^99mTc). ^99mTc is readily conjugated with nanoparticles using chelating agents, such as diethylenetriaminepentaacetic acid (DTPA). Leveraging this approach, we synthesized polymeric micelles (PM) consisting of 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-N-[methoxy(polyethyleneglycol)-2000] (DSPE-mPEG₂₀₀₀) functionalized with DTPA for radiolabeling with ^99mTc. Micelles made up of DSPE-mPEG₂₀₀₀ and DSPE-PEG₂₀₀₀-DTPA had a mean diameter of  ∼10nm, as measured by DLS and SAXS techniques, and a zeta potential of -2.7±1.1mV. Radiolabeled micelles exhibited high radiochemical yields and stability. In vivo assays indicated long blood circulation time (456.3min). High uptake in liver, spleen and kidneys was observed in the biodistribution and imaging studies on healthy and tumor-bearing mice. In addition, a high tumor-to-muscle ratio was detected, which increased over time, showing accumulation of the PM in the tumor region. These findings indicate that this system is a promising platform for simultaneous delivery of therapeutic agents and diagnostic probes.

The timeline of corona formation around silica nanocarriers highlights the role of the protein interactome

Magnetic mesoporous silica nanoparticles (M-MSNs) represent promising targeting tools for theranostics. Engineering the interaction of nanoparticles (NPs) with biological systems requires an understanding of protein corona formation around the nanoparticles as this drives the biological fate of nanocarriers. We investigated the behavior of proteins in contact with M-MSNs by high-throughput comparative proteomics, using human and bovine sera as biological fluids, in order to assess the adsorption dynamics of proteins in these media. Using system biology tools, and especially protein-protein interaction databases, we demonstrated how the protein network builds up within the corona over the course of the experiment. Based on these results, we introduce and discuss the role of the "corona interactome" as an important factor influencing protein corona evolution. The concept of the "corona interactome" is an original methodology which could be generalized to all NP candidates. Based on this, pre-coating nanocarriers with specific proteins presenting minimal interactions with opsonins might provide them with properties such as stealth.

Effect of anticoagulants on the protein corona-induced reduced drug carrier adhesion efficiency in human blood flow

Plasma proteins rapidly coat the surfaces of particulate drug carriers to form a protein corona upon their injection into the bloodstream. The high presence of immunoglobulins in the corona formed on poly(lactic-co-glycolic acid) (PLGA) vascular-targeted carrier (VTC) surfaces was recently shown to negatively impact their adhesion to activated endothelial cells (aECs) in vitro. Here, we characterized the influence of anticoagulants, or their absence, on the binding efficiency of VTCs of various materials via modulation of their protein corona. Specifically, we evaluated the adhesion of PLGA, poly(lactic acid) (PLA), polycaprolactone (PCL), silica, and polystyrene VTCs to aECs in heparinized, citrated, and non-anticoagulated (serum and whole) blood flows relative to buffer control. Particle adhesion is substantially reduced in non-anticoagulated blood flows regardless of the material type while only moderate to minimal reduction is observed for VTCs in anticoagulant-containing blood flow depending on the anticoagulant and material type. The substantial reduction in VTC adhesion in blood flows was linked to a high presence of immunoglobulin-sized proteins in the VTC corona via SDS-PAGE analysis. Of all the materials evaluated, PLGA was the most sensitive to plasma protein effects while PCL was the most resistant, suggesting particle hydrophobicity is a critical component of the observed negative plasma protein effects. Overall, this work demonstrates that anticoagulant positively alters the effect of plasma proteins in prescribing VTC adhesion to aECs in human blood flow, which has implication in the use of in vitro blood flow assays for functional evaluation of VTCs for in vivo use.

STATEMENT OF SIGNIFICANCE

This study addresses the impact of anticoagulant on altering the extent of the previously observed protein corona-induced adhesion reduction of vascular-targeted drug carriers in human blood flows. Specifically, serum blood flow (no anticoagulant) magnifies the negative effect of the plasma protein corona on drug carrier adhesion relative to citrated or heparinized blood flows. Overall, the results from this work suggest that serum better predicts targeted drug carrier adhesion efficiency in vivo compared to anticoagulant containing plasma. Furthermore, this study offers critical insight into the importance of how the choice of anticoagulant can greatly affect drug delivery-related processes in vitro.

An antigen-encapsulating nanoparticle platform for TH1/17 immune tolerance therapy

Tolerogenic nanoparticles (NPs) are rapidly being developed as specific immunotherapies to treat autoimmune disease. However, many NP-based therapies conjugate antigen (Ag) directly to the NP posing safety concerns due to antibody binding or require the co-delivery of immunosuppressants to induce tolerance. Here, we developed Ag encapsulated NPs comprised of poly(lactide-co-glycolide) [PLG(Ag)] and investigated the mechanism of action for Ag-specific tolerance induction in an autoimmune model of T helper type 1/17 dysfunction - relapse-remitting experimental autoimmune encephalomyelitis (R-EAE). PLG(Ag) completely abrogated disease induction in an organ specific manner, where the spleen was dispensable for tolerance induction. PLG(Ag) delivered intravenously distributed to the liver, associated with macrophages, and recruited Ag-specific T cells. Furthermore, programmed death ligand 1 (PD-L1) was increased on Ag presenting cells and PD-1 blockade lessened tolerance induction. The robust promotion of tolerance by PLG(Ag) without co-delivery of immunosuppressive drugs, suggests that these NPs effectively deliver antigen to endogenous tolerogenic pathways.

Probing the Interaction between Nanoparticles and Lipid Membranes by Quartz Crystal Microbalance with Dissipation Monitoring

There is increasing interest in using quartz crystal microbalance with dissipation monitoring (QCM-D) to investigate the interaction of nanoparticles (NPs) with model surfaces. The high sensitivity, ease of use and the ability to monitor interactions in real-time has made it a popular technique for colloid chemists, biologists, bioengineers, and biophysicists. QCM-D has been recently used to probe the interaction of NPs with supported lipid bilayers (SLBs) as model cell membranes. The interaction of NPs with SLBs is highly influenced by the quality of the lipid bilayers. Unlike many surface sensitive techniques, by using QCM-D, the quality of SLBs can be assessed in real-time, hence QCM-D studies on SLB-NP interactions are less prone to the artifacts arising from bilayers that are not well formed. The ease of use and commercial availability of a wide range of sensor surfaces also have made QCM-D a versatile tool for studying NP interactions with lipid bilayers. In this review, we summarize the state-of-the-art on QCM-D based techniques for probing the interactions of NPs with lipid bilayers.

Coating nanoparticles with tunable surfactants facilitates control over the protein corona

Nanoparticles with long blood circulation time are a prerequisite for targeted drug delivery. To make the nanoparticles invisible for phagocytizing cells, functional moieties on the particle surface are believed to be necessary to attract specific so-called 'stealth' proteins forming a protein 'corona'. Currently, covalent attachment of those moieties represents the only way to achieve that attraction. However, that approach requires a high synthetic effort and is difficult to control. Therefore, we present the coating of model nanoparticles with biodegradable polymeric surfactants as an alternative method. The thermodynamic parameters of the coating process can be tuned by adjusting the surfactants' block lengths and hydrophilicity. Consequently, the unspecific protein adsorption and aggregation tendency of the particles can be controlled, and stealth proteins inhibiting cell uptake are enriched on their surface. This non-covalent approach could be applied to any particle type and thus facilitates tuning the protein corona and its biological impact.

Tweaking dendrimers and dendritic nanoparticles for controlled nano-bio interactions: potential nanocarriers for improved cancer targeting

Nanoparticles have shown great promise in the treatment of cancer, with a demonstrated potential in targeted drug delivery. Among a myriad of nanocarriers that have been recently developed, dendrimers have attracted a great deal of scientific interests due to their unique chemical and structural properties that allow for precise engineering of their characteristics. Despite this, the clinical translation of dendrimers has been hindered due to their drawbacks, such as scale-up issues, rapid systemic elimination, inefficient tumor accumulation and limited drug loading. In order to overcome these limitations, a series of reengineered dendrimers have been recently introduced using various approaches, including: (i) modifications of structure and surfaces; (ii) integration with linear polymers and (iii) hybridization with other types of nanocarriers. Chemical modifications and surface engineering have tailored dendrimers to improve their pharmacokinetics and tissue permeation. Copolymerization of dendritic polymers with linear polymers has resulted in various amphiphilic copolymers with self-assembly capabilities and improved drug loading efficiencies. Hybridization with other nanocarriers integrates advantageous characteristics of both systems, which includes prolonged plasma circulation times and enhanced tumor targeting. This review provides a comprehensive summary of the newly emerging drug delivery systems that involve reengineering of dendrimers in an effort to precisely control their nano-bio interactions, mitigating their inherent weaknesses.

Tuning the Selectivity of Dendron Micelles Through Variations of the Poly(ethylene glycol) Corona

Engineering controllable cellular interactions into nanoscale drug delivery systems is key to enable their full potential. Here, using folic acid (FA) as a model targeting ligand and dendron micelles (DM) as a nanoparticle (NP) platform, we present a comprehensive experimental and modeling investigation of the structural properties of DMs that govern the formation of controllable, FA-mediated cellular interactions. Our experimental results demonstrate that a high level of control over the specific cell interactions of FA-targeted DMs can be achieved through modulation of the PEG corona length and the FA content. Using various molecular weight PEGs (0.6K, 1K, and 2K g/mol) and contents of dendron-FA conjugate incorporated into DMs (0, 5, 10, 25 wt %), the cell interactions of the targeted DMs could be controlled to exhibit minimal to >25-fold enhancement over nontargeted DMs. Molecular dynamics simulations indicated that structural characteristics, such as solvent accessible surface area of FA, local PEG density near FA, and FA mobility, account in part for the experimental differences in cellular interactions. The molecular structure that allows FA to depart from the surface of DMs to facilitate the initial cell surface binding was revealed to be the most important contributor for determining FA-mediated cellular interactions of DMs. The modular properties of DMs in controlling their specific cell interactions support the potential of DMs as a delivery platform and offer design cues for future development of targeted NPs.

Conjugation to Poly(amidoamine) Dendrimers and Pulmonary Delivery Reduce Cardiac Accumulation and Enhance Antitumor Activity of Doxorubicin in Lung Metastasis

Lung is one of the most common sites to which almost all other primary tumors metastasize. The major challenges in the chemotherapy of lung metastases include the low drug concentration found in the tumors and high systemic toxicity upon systemic administration. In this study, we combine local lung delivery and the use of nanocarrier-based systems for improving pharmacokinetics and biodistribution of the therapeutics to fight lung metastases. We investigate the impact of the conjugation of doxorubicin (DOX) to carboxyl-terminated poly(amidoamine) dendrimers (PAMAM) through a bond that allows for intracellular-triggered release, and the effect of pulmonary delivery of the dendrimer-DOX conjugate in decreasing tumor burden in a lung metastasis model. The results show a dramatic increase in efficacy of DOX treatment of the melanoma (B16-F10) lung metastasis mouse model upon pulmonary administration of the drug, as indicated by decreased tumor burden (lung weight) and increased survival rates of the animals (male C57BL/6) when compared to iv delivery. Conjugation of DOX further increased the therapeutic efficacy upon lung delivery as indicated by the smaller number of nodules observed in the lungs when compared to free DOX. These results are in agreement with the biodistribution characteristics of the DOX upon pulmonary delivery, which showed a longer lung accumulation/retention compared to iv administration. The distribution of DOX to the heart tissue is also significantly decreased upon pulmonary administration, and further decreased upon conjugation. The results show, therefore, that pulmonary administration of DOX combined to conjugation to PAMAM dendrimer through an intracellular labile bond is a potential strategy to enhance the therapeutic efficacy and decrease systemic toxicity of DOX.

Engineering nanoparticles to overcome barriers to immunotherapy

Advances in immunotherapy have led to the development of a variety of promising therapeutics, including small molecules, proteins and peptides, monoclonal antibodies, and cellular therapies. Despite this wealth of new therapeutics, the efficacy of immunotherapy has been limited by challenges in targeted delivery and controlled release, that is, spatial and temporal control on delivery. Particulate carriers, especially nanoparticles have been widely studied in drug delivery and vaccine research and are being increasingly investigated as vehicles to deliver immunotherapies. Nanoparticle-mediated drug delivery could provide several benefits, including control of biodistribution and transport kinetics, the potential for site-specific targeting, immunogenicity, tracking capability using medical imaging, and multitherapeutic loading. There are also a unique set of challenges, which include nonspecific uptake by phagocytic cells, off-target biodistribution, permeation through tissue (transport limitation), nonspecific immune-activation, and poor control over intracellular localization. This review highlights the importance of understanding the relationship between a nanoparticle's size, shape, charge, ligand density and elasticity to its vascular transport, biodistribution, cellular internalization, and immunogenicity. For the design of an effective immunotherapy, we highlight the importance of selecting a nanoparticle's physical characteristics (e.g., size, shape, elasticity) and its surface functionalization (e.g., chemical or polymer modifications, targeting or tissue-penetrating peptides) with consideration of its reactivity to the targeted microenvironment (e.g., targeted cell types, use of stimuli-sensitive biomaterials, immunogenicity). Applications of this rational nanoparticle design process in vaccine development and cancer immunotherapy are discussed.

Reducible Micelleplexes are Stable Systems for Anti-miRNA Delivery in Cerebrospinal Fluid

Glioblastoma multiforme (GBM) and other central nervous system (CNS) cancers have poor long-term prognosis, and there is a significant need for improved treatments. GBM initiation and progression are mediated, in part, by microRNA (miRNA), which are endogenous posttranscriptional gene regulators. Misregulation of miRNAs is a potential target for therapeutic intervention in GBM. In this work, a micelle-like nanoparticle delivery system based upon the block copolymer poly(ethylene glycol-b-lactide-b-arginine) was designed with and without a reducible linkage between the lactide and RNA-binding peptide, R15, to assess the ability of the micelle-like particles to disassemble. Using confocal live cell imaging, intracellular dissociation was pronounced for the reducible micelleplexes. This dissociation was also supported by higher efficiency in a dual luciferase assay specific for the miRNA of interest, miR-21. Notably, micelleplexes were found to have significantly better stability and higher anti-miRNA activity in cerebrospinal fluid than in human plasma, suggesting an advantage for applying micelleplexes to CNS diseases and in vivo CNS therapeutics. The reducible delivery system was determined to be a promising delivery platform for the treatment of CNS diseases with miRNA therapy.

Exploitation of nanoparticle–protein corona for emerging therapeutic and diagnostic applications

Exposure of nanoparticles (NPs) to biological fluids (e.g., plasma, interstitial fluid, and cytoplasm) leads to the absorption of proteins on the NP surface, forming a protein corona (PC) that drastically influences the NP physicochemical properties.

Effect of the protein corona on the colloidal stability and reactivity of LDH-based nanocarriers

The physicochemical properties of drug nanocarriers such as layered double hydroxides nanoparticles (LDH-NPs) determine their circulation times in biological media and their interaction with the targeted cells.

Differential Impact of Plasma Proteins on the Adhesion Efficiency of Vascular-Targeted Carriers (VTCs) in Blood of Common Laboratory Animals

Vascular-targeted carrier (VTC) interaction with human plasma is known to reduce targeted adhesion efficiency in vitro. However, the role of plasma proteins on the adhesion efficiency of VTCs in laboratory animals remains unknown. Here, in vitro blood flow assays are used to explore the effects of plasma from mouse, rabbit, and porcine on VTC adhesion. Porcine blood exhibited a strong negative plasma effect on VTC adhesion while no significant plasma effect was found with rabbit and mouse blood. A brush density poly(ethylene glycol) (PEG) on VTCs was effective at improving adhesion of microsized, but not nanosized, VTCs in porcine blood. Overall, the results suggest that porcine models, as opposed to mouse, can serve as better models in preclinical research for predicting the in vivo functionality of VTCs for use in humans. These considerations hold great importance for the design of various pharmaceutical products and development of reliable drug delivery systems.

Preparation of Core-Shell Hybrid Materials by Producing a Protein Corona Around Magnetic Nanoparticles

Nanoparticles experience increasing interest for a variety of medical and pharmaceutical applications. When exposing nanomaterials, e.g., magnetic iron oxide nanoparticles (MNP), to human blood, a protein corona consisting of various components is formed immediately. The composition of the corona as well as its amount bound to the particle surface is dependent on different factors, e.g., particle size and surface charge. The actual composition of the formed protein corona might be of major importance for cellular uptake of magnetic nanoparticles. The aim of the present study was to analyze the formation of the protein corona during in vitro serum incubation in dependency of incubation time and temperature. For this, MNP with different shells were incubated in fetal calf serum (FCS, serving as protein source) within a water bath for a defined time and at a defined temperature. Before and after incubation the particles were characterized by a variety of methods. It was found that immediately (seconds) after contact of MNP and FCS, a protein corona is formed on the surface of MNP. This formation led to an increase of particle size and a slight agglomeration of the particles, which was relatively constant during the first minutes of incubation. A longer incubation (from hours to days) resulted in a stronger agglomeration of the FCS incubated MNP. Quantitative analysis (gel electrophoresis) of serum-incubated particles revealed a relatively constant amount of bound proteins during the first minutes of serum incubation. After a longer incubation (>20 min), a considerably higher amount of surface proteins was determined for incubation temperatures below 40 °C. For incubation temperatures above 50 °C, the influence of time was less significant which might be attributed to denaturation of proteins during incubation. Overall, analysis of the molecular weight distribution of proteins found in the corona revealed a clear influence of incubation time and temperature on corona composition.

Nanoparticles as drug carriers: current issues with in vitro testing

Incorporation of nanotechnology in the field of drug delivery has created exciting opportunities for the purposeful design of nanocarriers with potentials such as targeted delivery or controlled release of the incorporated cargo, improvement of bioavailability and reduction of therapeutic side-effects. Prior to in vivo administration, nanocarriers should undergo a set of in vitro evaluation procedures to ensure their stability, safety, conformity and ability to fulfill the desired mission. In this paper, current issues with in vitro evaluation techniques used for nanocarrier characterization (assessment of particle size, surface charge, drug release and toxicity) will be discussed. Furthermore, sufficiency of in vitro evaluation procedures for the prediction of in vivo scenarios and the necessary considerations to improve the correlation between the two settings will be debated.

Stealth effect of biomolecular corona on nanoparticle uptake by immune cells

When injected in a biological milieu, a nanomaterial rapidly adsorbs biomolecules forming a biomolecular corona. The biomolecular corona changes the interfacial composition of a nanomaterial giving it a biological identity that determines the physiological response. Characterization of the biomolecular structure and composition has received increasing attention mostly due to its detrimental impact on the nanomaterial's metabolism in vivo. It is generally accepted that an opsonin-enriched biomolecular corona promotes immune system recognition and rapid clearance from circulation. Here we applied dynamic light scattering and nanoliquid chromatography tandem mass spectrometry to thoroughly characterize the biomolecular corona formed around lipid and silica nanoparticles (NPs). Incubation with human plasma resulted in the formation of NP-biomolecular coronas enriched with immunoglobulins, complement factors, and coagulation proteins that bind to surface receptors on immune cells and elicit phagocytosis. Conversely, we found that protein-coated NPs were protected from uptake by macrophage RAW 264.7 cells. This implies that the biomolecular corona formation provides a stealth effect on macrophage recognition. Our results suggest that correct prediction of the NP's fate in vivo will require more than just the knowledge of the biomolecular corona composition. Validation of efficient methods for mapping protein binding sites on the biomolecular corona of NPs is an urgent task for future research.

Surface plasmon resonance as a high throughput method to evaluate specific and non-specific binding of nanotherapeutics

Surface plasmon resonance (SPR) is a powerful analytical technique used to quantitatively examine the interactions between various biomolecules, such as proteins and nucleic acids. The technique has been particularly useful in screening and evaluating binding affinity of novel small molecule and biomolecule-derived therapeutics for various diseases and applications including lupus medications, thrombin inhibitors, HIV protease inhibitors, DNA gyrase inhibitors and many others. Recently, there has been increasing interest in nanotherapeutics (nanoRx), due to their unique properties and potential for controlled release of encapsulated drugs and structure-specific targeting to diseased tissues. NanoRx offer the potential to solve many drug delivery challenges by enabling, specific interactions between molecules on the surface of the nanoparticle and molecules in the diseased tissue, while minimizing off-target interactions toward non-diseased tissues. These properties are largely dependent upon careful control and balance of nanoRx interactions and binding properties with tissues in vivo. Given the great promise of nanoRx with regard to engineering specific molecular interactions, SPR can rapidly quantify small aliquots of nanoRx formulations for desired and undesired molecular interactions. Moving forward, we believe that utilization of SPR in the screening and design of nanoRx has the potential to greatly improve the development of targeted nanoRx formulations and eventually lead to improved therapeutic efficacy. In this review, we discuss (1) the fundamental principles of SPR and basic quantitative analysis of SPR data, (2) previous applications of SPR in the study of non-particulate therapeutics and nanoRx, and (3) future opportunities for the use of SPR in the evaluation of nanoRx.

Silver nanoparticle protein corona and toxicity: a mini-review

Silver nanoparticles are one of the most important materials in the nanotechnology industry. Additionally, the protein corona is emerging as a key entity at the nanobiointerface; thus, a comprehensive understanding of the interactions between proteins and silver nanoparticles is imperative. Therefore, literature reporting studies involving both single molecule protein coronas (i.e., bovine and human serum albumin, tubulin, ubiquitin and hyaluronic-binding protein) and complex protein coronas (i.e., fetal bovine serum and yeast extract proteins) were selected to demonstrate the effects of protein coronas on silver nanoparticle cytotoxicity and antimicrobial activity. There is evidence that distinct and differential protein components may yield a "protein corona signature" that is related to the size and/or surface curvature of the silver nanoparticles. Therefore, the formation of silver nanoparticle protein coronas together with the biological response to these coronas (i.e., oxidative stress, inflammation and cytotoxicity) as well as other cellular biophysicochemical mechanisms (i.e., endocytosis, biotransformation and biodistribution) will be important for nanomedicine and nanotoxicology. Researchers may benefit from the information contained herein to improve biotechnological applications of silver nanoparticles and to address related safety concerns. In summary, the main aim of this mini-review is to highlight the relationship between the formation of silver nanoparticle protein coronas and toxicity.

Charged group surface accessibility determines micelleplexes formation and cellular interaction

Micelleplexes are a class of nucleic acid carriers that have gained acceptance due to their size, stability, and ability to synergistically carry small molecules. MicroRNAs (miRNAs) are small non-coding RNA gene regulator that is consists of 19-22 nucleotides. Altered expression of miRNAs plays an important role in many human diseases. Using a model 22-nucleotide miRNA sequence, we investigated the interaction between charged groups on the micelle surface and miRNA. The model micelle system was formed from methoxy-poly(ethylene glycol)-b-poly(lactide) (mPEG-PLA) mixed with methoxy-poly(ethylene glycol)-b-poly(lactide)-b-oligoarginine (mPEG-PLA-Rx, x = 8 or 15). Surface properties of the micelles were varied by controlling the oligoarginine block length and conjugation density. Micelles were observed to have a core-shell conformation in the aqueous environment where the PLA block constituted the hydrophobic core, mPEG and oligoarginine formed a hydrophilic corona. Significantly different thermodynamic behaviors were observed during the interaction of single stranded miRNA with micelles of different surface properties, and the resulting micelleplexes mediated substantial cellular association. Depending upon the oligoarginine length and density, micelles exhibited miRNA loading capacity directly related to the presentation of charged groups on the surface. The effect of charged group accessibility of cationic micelle on micelleplex properties provides guidance on future miRNA delivery system design.