Poly(ethylene glycol) Corona Chain Length Controls End-Group-Dependent Cell Interactions of Dendron Micelles

Dendritic nanoparticles for immune modulation: a potential next-generation nanocarrier for cancer immunotherapy

Immune activation, whether occurring from direct immune checkpoint blockade or indirectly as a result of chemotherapy, is an approach that has drastically impacted the way we treat cancer. Utilizing patients' own immune systems for anti-tumor efficacy has been translated to robust immunotherapies; however, clinically significant successes have been achieved in only a subset of patient populations. Dendrimers and dendritic polymers have recently emerged as a potential nanocarrier platform that significantly improves the therapeutic efficacy of current and next-generation cancer immunotherapies. In this paper, we highlight the recent progress in developing dendritic polymer-based therapeutics with immune-modulating properties. Specifically, dendrimers, dendrimer hybrids, and dendronized copolymers have demonstrated promising results and are currently in pre-clinical development. Despite their early stage of development, these nanocarriers hold immense potential to make profound impact on cancer immunotherapy and combination therapy. This overview provides insights into the potential impact of dendrimers and dendron-based polymers, offering a preview of their potential utilities for various aspects of cancer treatment.

Exploring the impact of PEGylation on the cell-nanomicelle interactions by AFM-based single-molecule force spectroscopy and force tracing

PEGylation has been considered the gold standard method for the modification of various drug delivery systems since the last century. However, the impact of PEGylation on the dynamic interaction between drug carriers and cell membranes has not been quantitatively clarified. Herein, the cellular binding and receptor-mediated endocytosis of a model PEGylated polypeptide nanomicelle were systematically investigated at the single-particle level using AFM-based single-molecule force spectroscopy (SMFS) and force tracing. A self-assembled elastin-like polypeptide (ELP) nanomicelle, which is capable of cross-linking, gastrin-releasing peptide (GRP) modification, and PEGylation was prepared. The cross-linked ELP-based nanomicelles exhibited outstanding stability in a broad temperature range of 4-40 °C, which facilitate the drug loading, as well as our cell-nanomicelle study at the single particle level. The unbinding force between the cross-linked ELP-based nanomicelles and the GRP receptor (GRPR)-containing cell (PC-3) membranes was quantitatively measured by AFM-SMFS. It is found that the PEGylated GRP-displaying nanomicelles exhibit the highest unbinding force, indicating the enhanced specific binding effect of PEGylation. Furthermore, the receptor-mediated endocytosis of the cross-linked ELP-based nanomicelles was monitored with the help of force tracing based on AFM-SMFS. Our results show that PEGylation decreases the endocytic force, duration, and engulfment depth of the PEGylated GRP-displaying nanomicelles, but increases their endocytic velocity, which results from the elimination of non-specific interactions during endocytosis. These observations demonstrate the diverse and complex roles of PEGylation on the interaction of polypeptide nanomicelles to cell membranes and may shed light on the rational design of organic polymer-based drug delivery systems aiming for active and passive targeting strategies. STATEMENT OF SIGNIFICANCE: A self-assembled elastin-like polypeptide (ELP) nanomicelle, which can be easily cross-linked, gastrin-releasing peptide (GRP) modified, and PEGylated, is designed. The AFM-SMFS experiment shows that PEGylation can enhance specific binding of the nanomicelles to the receptors on cell membranes. The force tracing experiment indicates that PEGylation decreases the endocytic force as well as engulfment depth of the nanomicelles through the elimination of non-specific interactions. PEGylation can benefit the drug delivery systems aiming at active targeting, while might not be an ideal modification for drug carriers designed for passive targeting, whose cellular uptake mainly depends on non-specific interactions.

Dendritic-Linear Copolymer and Dendron Lipid Nanoparticles for Drug and Gene Delivery

Polymers constitute a diverse class of macromolecules that have demonstrated their unique advantages to be utilized for drug or gene delivery applications. In particular, polymers with a highly ordered, hyperbranched structure─"dendrons"─offer significant benefits to the design of such nanomedicines. The incorporation of dendrons into block copolymer micelles can endow various unique properties that are not typically observed from linear polymer counterparts. Specifically, the dendritic structure induces the conical shape of unimers that form micelles, thereby improving the thermodynamic stability and achieving a low critical micelle concentration (CMC). Furthermore, through a high density of highly ordered functional groups, dendrons can enhance gene complexation, drug loading, and stimuli-responsive behavior. In addition, outward-branching dendrons can support a high density of nonfouling polymers, such as poly(ethylene glycol), for serum stability and variable densities of multifunctional groups for multivalent cellular targeting and interactions. In this paper, we review the design considerations for dendron-lipid nanoparticles and dendron micelles formed from amphiphilic block copolymers intended for gene transfection and cancer drug delivery applications. These technologies are early in preclinical development and, as with other nanomedicines, face many obstacles on the way to clinical adoption. Nevertheless, the utility of dendron micelles for drug delivery remains relatively underexplored, and we believe there are significant and dramatic advancements to be made in tumor targeting with these platforms.

Bimodal liquid biopsy for cancer immunotherapy based on peptide engineering and nanoscale analysis

Despite its high potential, PD-L1 expressed by tumors has not been successfully utilized as a biomarker for estimating treatment responses to immunotherapy. Circulating tumor cells (CTCs) and tumor-derived exosomes that express PD-L1 can potentially be used as biomarkers; however, currently available assays lack clinically significant sensitivity and specificity. Here, a novel peptide-based capture surface is developed to effectively isolate PD-L1-expressing CTCs and exosomes from human blood. For the effective targeting of PD-L1, this study integrates peptide engineering strategies to enhance the binding strength and specificity of a β-hairpin peptide derived from PD-1 (pPD-1). Specifically, this study examines the effect of poly(ethylene glycol) spacers, the secondary peptide structure, and modification of peptide sequences (e.g., removal of biologically redundant amino acid residues) on capture efficiency. The optimized pPD-1 configuration captures PD-L1-expressing tumor cells and tumor-derived exosomes with 1.5-fold (p = 0.016) and 1.2-fold (p = 0.037) higher efficiencies, respectively, than their whole antibody counterpart (aPD-L1). This enhanced efficiency is translated into more clinically significant detection of CTCs (1.9-fold increase; p = 0.035) and exosomes (1.5-fold increase; p = 0.047) from patients' baseline samples, demonstrating stronger correlation with patients' treatment responses. Additionally, we confirmed that the clinical accuracy of our system can be further improved by co-analyzing the two biomarkers (bimodal CTC/exosome analysis). These data demonstrate that pPD-1-based capture is a promising approach for capturing PD-L1-expressing CTCs and exosomes, which can be used as a reliable biomarker for cancer immunotherapy.

Dendrimers for cancer immunotherapy: Avidity-based drug delivery vehicles for effective anti-tumor immune response

Cancer immunotherapy, or the utilization of a patient's own immune system to treat cancer, has shifted the paradigm of cancer treatment. Despite meaningful responses being observed in multiple studies, currently available immunotherapy platforms have only proven effective to a small subset of patients. To address this, nanoparticles have been utilized as a novel carrier for immunotherapeutic drugs, achieving robust anti-tumor effects with increased adaptive and durable responses. Specifically, dendrimer nanoparticles have attracted a great deal of scientific interest due to their versatility in various therapeutic applications, resulting from their unique physicochemical properties and chemically well-defined architecture. This review offers a comprehensive overview of dendrimer-based immunotherapy technologies, including their formulations, biological functionalities, and therapeutic applications. Common formulations include: (1) modulators of cytokine secretion of immune cells (adjuvants); (2) facilitators of the recognition of tumorous antigens (vaccines); (3) stimulators of immune effectors to selectively attack cells expressing specific antigens (antibodies); and (4) inhibitors of immune-suppressive responses (immune checkpoint inhibitors). On-going works and prospects of dendrimer-based immunotherapies are also discussed. Overall, this review provides a critical overview on rapidly growing dendrimer-based immunotherapy technologies and serves as a guideline for researchers and clinicians who are interested in this field. This article is categorized under: Nanotechnology Approaches to Biology > Nanoscale Systems in Biology Therapeutic Approaches and Drug Discovery > Nanomedicine for Oncologic Disease Therapeutic Approaches and Drug Discovery > Emerging Technologies.

Hierarchically Multivalent Peptide-Nanoparticle Architectures: A Systematic Approach to Engineer Surface Adhesion

The multivalent binding effect has been the subject of extensive studies to modulate adhesion behaviors of various biological and engineered systems. However, precise control over the strong avidity-based binding remains a significant challenge. Here, a set of engineering strategies are developed and tested to systematically enhance the multivalent binding of peptides in a stepwise manner. Poly(amidoamine) (PAMAM) dendrimers are employed to increase local peptide densities on a substrate, resulting in hierarchically multivalent architectures (HMAs) that display multivalent dendrimer-peptide conjugates (DPCs) with various configurations. To control binding behaviors, effects of the three major components of the HMAs are investigated: i) poly(ethylene glycol) (PEG) linkers as spacers between conjugated peptides; ii) multiple peptides on the DPCs; and iii) various surface arrangements of HMAs (i.e., a mixture of DPCs each containing different peptides vs DPCs cofunctionalized with multiple peptides). The optimized HMA configuration enables significantly enhanced target cell binding with high selectivity compared to the control surfaces directly conjugated with peptides. The engineering approaches presented herein can be applied individually or in combination, providing guidelines for the effective utilization of biomolecular multivalent interactions using DPC-based HMAs.

Modular amphiphilic poly(aryl ether)-based supramolecular nanomicelles: an efficient endocytic drug carrier

A rationally designed amphiphilic poly(aryl ether)-based dendrimer self-assembles into nanomicelles and exhibits tunable morphology upon varying the hydrophilic chain length. The 30 nm-sized dendrimer nanomicelles successfully entrapped Doxorubicin, demonstrated the sustained release of Doxorubicin and can successfully penetrate cancer cells through caveolae-dependent endocytosis, compared to the free drug.

Size-Dependent Drug Loading, Gene Complexation, Cell Uptake, and Transfection of a Novel Dendron-Lipid Nanoparticle for Drug/Gene Co-delivery

Dendron micelles have shown promising results as a multifunctional delivery system, owing to their unique molecular architecture. Herein, we have prepared a novel poly(amidoamine) (PAMAM) dendron-lipid hybrid nanoparticle (DLNP) as a nanocarrier for drug/gene co-delivery and examined how the dendron generation of DLNPs impacts their cargo-carrying capabilities. DLNPs, formed by a thin-layer hydration method, were internally loaded with chemo-drugs and externally complexed with plasmids. Compared to generation 2 dendron DLNP (D2LNPs), D3LNPs demonstrated a higher drug encapsulation efficiency (31% vs 87%) and better gene complexation (minimal N/P ratio of 20:1 vs 5:1 for complexation) due to their smaller micellar aggregation number and higher charge density, respectively. Furthermore, D3LNPs were able to avoid endocytosis and subsequent lysosomal degradation and demonstrated a higher cellular uptake than D2LNPs. As a result, D3LNPs exhibited significantly enhanced antitumor and gene transfection efficacy in comparison to D2LNPs. These findings provide design cues for engineering multifunctional dendron-based nanotherapeutic systems for effective combination cancer treatment.

Developments in Treatment Methodologies Using Dendrimers for Infectious Diseases

Dendrimers comprise a specific group of macromolecules, which combine structural properties of both single molecules and long expanded polymers. The three-dimensional form of dendrimers and the extensive possibilities for use of additional substrates for their construction creates a multivalent potential and a wide possibility for medical, diagnostic and environmental purposes. Depending on their composition and structure, dendrimers have been of interest in many fields of science, ranging from chemistry, biotechnology to biochemical applications. These compounds have found wide application from the production of catalysts for their use as antibacterial, antifungal and antiviral agents. Of particular interest are peptide dendrimers as a medium for transport of therapeutic substances: synthetic vaccines against parasites, bacteria and viruses, contrast agents used in MRI, antibodies and genetic material. This review focuses on the description of the current classes of dendrimers, the methodology for their synthesis and briefly drawbacks of their properties and their use as potential therapies against infectious diseases.

Computational screening of nanoparticles coupling to Aβ40 peptides and fibrils

Blocking the formation, growth, and breaking of amyloid fibrils by synthetic nanosystems could provide a treatment of neurodegenerative diseases. With this in mind, here atomistic molecular dynamics simulations are used to screen for nanoparticles (NPs), covered with different mixtures of ligands, including positively and negatively charged ligands, Aβ40-cut-peptide, and synthetic inhibitor ligands, in their selective coupling to Aβ40 peptides and their fibrils. The simulations reveal that only Aβ40-cut-peptide-covered NPs have strong and selective coupling to Aβ40 monomers. On the other hand, positive, positive-neutral, Janus, and peptide NPs couple to the beta sheet surfaces of Aβ40 fibrils and only the negative-neutral NPs couple to the fibril tips.

Novel Oxygen-Deficient Zirconia (ZrO2-x) for Fluorescence/Photoacoustic Imaging-Guided Photothermal/Photodynamic Therapy for Cancer

Theranostic nanoplatforms that integrate therapy and diagnosis in a single composite have become increasingly attractive in the field of precise and efficient tumor treatment. Herein, a novel oxygen-deficient zirconia (ZrO_2-x) nanosystem based on the conjugation of thiol-polyethylene glycol-amine (SH-PEG-NH₂) and chlorin e6 (Ce6) was elaborately designed and established for efficacious photothermal/photodynamic therapy (PTT/PDT) and fluorescence/photoacoustic (FL/PA) bimodal imaging for the first time. The crystalline-disordered, PEGylated ZrO_2-x nanoparticles (ZP NPs) displayed strong optical absorption in the near-infrared (NIR) window and were featured with significant photothermal conversion capacity. The ZP NPs were further covalently conjugated with Ce6 to form ZrO_2-x@PEG/Ce6 (ZPC) NPs, which displayed a long circulatory half-life, efficient tumor accumulation, and outstanding FL/PA imaging performance. Moreover, the nanocomposites effectively generated cytotoxic intracellular reactive oxygen species (ROS) responsive to laser activation. Both cell studies and animal experiments explicitly demonstrated that ZPC NPs mediated remarkable tumor ablation with minimal systemic toxicity thanks to their tumor-specific PTT/PDT effect. Collectively, these findings may open up new avenues to broaden the application of oxygen-deficient ZrO_2-x nanostructures as high-performance photothermal agents in tumor theranostics through rational design and accurate control of their physiochemical properties.

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.

The Effect of Molecular Structure on Cytotoxicity and Antitumor Activity of PEGylated Nanomedicines

Fundamental studies on the cellular uptake and drug release of PEGylated nanomedicines are beneficial to understand their fate in vivo and construct ideal nanoparticle formulations. In this work, the detailed metabolic process of PEGylated doxorubicin (Dox) nanomedicines were investigated via confocal laser scanning microscopy (CLSM), flow cytometry (FCM), cytotoxicity test, fluorescence imaging in vivo (FLIV) and liquid chromatography tandem mass spectrometry (LC-MS/MS). Among them, only LC-MS/MS could accurately determine the content of PEGylated Dox and Dox in vitro and in vivo. To the best of our knowledge, this was the first time the PEGylated Dox and released Dox were simultaneously quantified. The interplay of molecular structures, cellular uptake, drug release, and antitumor effect was well characterized. PEG with high molecular weight impeded the cellular uptake of nanoparticles, and the acid-labile hydrazone bond between Dox and PEG promoted Dox release significantly. Cellular uptake and drug release play decisive roles in cytotoxicity and antitumor effect, as evidenced by LC-MS/MS. We emphasized that LC-MS/MS would be a practicable method to quantify PEGylated drugs without complex tags, which could be more in-depth to understand the interaction between PEGylated nanomedicines and their antitumor efficacy.

Computational studies of micellar and nanoparticle nanomedicines

The review highlights recent computational modeling of micellar and nanoparticle nanomedicines, which elucidates their functional roles in atomistic details.

Elucidating Surface Ligand-Dependent Kinetic Enhancement of Proteolytic Activity at Surface-Modified Quantum Dots

Combining biomolecules such as enzymes with nanoparticles has much to offer for creating next generation synergistically functional bionanomaterials. However, almost nothing is known about how these two disparate components interact at this critical biomolecular-materials interface to give rise to improved activity and emergent properties. Here we examine how the nanoparticle surface can influence and increase localized enzyme activity using a designer experimental system consisting of trypsin proteolysis acting on peptide-substrates displayed around semiconductor quantum dots (QDs). To minimize the complexity of analyzing this system, only the chemical nature of the QD surface functionalizing ligands were modified. This was accomplished by synthesizing a series of QD ligands that were either positively or negatively charged, zwitterionic, neutral, and with differing lengths. The QDs were then assembled with different ratios of dye-labeled peptide substrates and exposed to trypsin giving rise to progress curves that were monitored by Förster resonance energy transfer (FRET). The resulting trypsin activity profiles were analyzed in the context of detailed molecular dynamics simulations of key interactions occurring at this interface. Overall, we find that a combination of factors can give rise to a localized activity that was 35-fold higher than comparable freely diffusing enzyme-substrate interactions. Contributing factors include the peptide substrate being prominently displayed extending from the QD surface and not sterically hindered by the longer surface ligands in conjunction with the presence of electrostatic and other productive attractive forces between the enzyme and the QD surface. An intimate understanding of such critical interactions at this interface can produce a set of guidelines that will allow the rational design of next generation high-activity bionanocomposites and theranostics.

Radiolabelled Polymeric Materials for Imaging and Treatment of Cancer: Quo Vadis?

Owing to their tunable blood circulation time and suitable plasma stability, polymer-based nanomaterials hold a great potential for designing and utilising multifunctional nanocarriers for efficient imaging and effective treatment of cancer. When tagged with appropriate radionuclides, they may allow for specific detection (diagnosis) as well as the destruction of tumours (therapy) or even customization of materials, aiming to both diagnosis and therapy (theranostic approach). This review provides an overview of recent developments of radiolabelled polymeric nanomaterials (natural and synthetic polymers) for molecular imaging of cancer, specifically, applying nuclear techniques such as positron emission tomography (PET) and single-photon emission computed tomography (SPECT). Different approaches to radiolabel polymers are evaluated from the methodical radiochemical point of view. This includes new bifunctional chelating agents (BFCAs) for radiometals as well as novel labelling methods. Special emphasis is given to eligible strategies employed to evade the mononuclear phagocytic system (MPS) in view of efficient targeting. The discussion encompasses promising strategies currently employed as well as emerging possibilities in radionuclide-based cancer therapy. Key issues involved in the clinical translation of radiolabelled polymers and future scopes of this intriguing research field are also discussed.

Interaction Pathways between Plasma Membrane and Block Copolymer Micelles

In this work, the interactions between block copolymer micelles (BCMs) and plasma membranes were investigated by performing coarse-grained molecular dynamics (CGMD) simulations. Different binding strengths between the BCMs and the membranes were tested, and four interaction pathways were discovered: attachment, semiendocytosis, endocytosis, and fusion. Endocytosis was the most efficient way for the BCMs to be taken up, and fusion could lead to cytotoxicity. Unlike rigid particles, deformation of the BCMs strongly affected the interaction pathways. We examined the effects of changing the aggregation number of the BCMs (N_agg), the chain length of the polymer (N_b), and the chain stiffness of the hydrophobic block (k_a), and we learned that smaller N_agg and lower N_b could lead to weaker cellular uptake capacities, whereas larger N_agg and higher N_b gave rise to higher cytotoxicities. Moreover, a weaker chain stiffness of the hydrophobic block could be more favorable for obtaining BCMs with higher internalization efficacies and lower cytotoxicities. The results of these simulations could aid in the design of BCMs with desirable cellular internalization capacities and lower cytotoxicities. Such BCMs could be useful in drug-delivery systems.

One bioprobe: a fluorescent and AIE-active macromolecule; two targets: nucleolus and mitochondria with long term tracking

The novel macromolecule fluorescent probe TPPA–DBO was developed with highly specific nucleolus-targeting and long term cell tracking ability.

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.

Mixed Layers of Nonionic Dendritic Amphiphiles and DPPC at the Water Surface

Nonionic dendritic amphiphiles that self-assemble into defined supramolecular aggregates are useful for the efficient solubilization of active agents, for example, in drug delivery. We investigated a new class of dendritic amphiphiles based on a hydrophilic polyol dendron head connected to a two-chain hydrophobic block. In analogy to phospholipids, these molecules form well-organized layers in bulk (vesicles) or at the water surface (Langmuir monolayer). The actual study focuses on the phase behavior and microscopic structure of mixed Langmuir layers of theses dendritic amphiphiles with the well-known phospholipid DPPC. The combination of surface pressure area isotherms with X-ray grazing incident diffraction and Brewster angle microscopy gives us information on the phase behavior of the mixed monolayers and the orientation of the amphiphiles inside the condensed domains with molecular resolution. We could prove that the dendritic generation and, by this, the headgroup size of the amphiphilic molecules have a significant influence on their interaction with DPPC at the air-water interface. Thus, our findings are important for the understanding of mixed lipid membranes in general as well as for the preparation of artificial membranes and vesicles with adjustable properties, e.g., their drug delivery potential.

Nanoparticle stability in biologically relevant media: influence of polymer architecture

We have contrasted the behavior of nanoparticles formed by the self-assembly of polymers based on poly(ethylene glycol) (PEG) and poly(D,L-lactide), with linear, linear-dendritic and bottle-brush architectures in biologically relevant media. Polymer PEG content ranged between 14% and 46% w/w, and self-assembly was triggered by a rapid and large change in solvent quality inside a four-stream vortex mixer. We examined nanoparticle interaction with human serum albumin (HSA), and solute release in the presence of fetal bovine serum. Dynamic light scattering data showed that PEG surface brushes of all nanoparticles provided effective steric stabilization, thus limiting their interaction with human serum albumin. Calorimetric experiments revealed that nanoparticle-HSA interaction was relatively weak and enthalpically driven, whereas dynamic light scattering results of incubated nanoparticles showed the absence of larger aggregates for most of the polymers examined. Solute core partitioning was examined by the loss of Forster resonance energy transfer (FRET) from a core-loaded donor-acceptor pair. The rate and magnitude of FRET efficiency loss was strongly dependent on the polymer architecture, and was found to be lowest for the bottle-brush, attributed to its covalent nature. Collectively, these findings are expected to impact the molecular design of increasingly stable polymeric carriers for drug delivery applications.

Recent advances in targeted drug delivery approaches using dendritic polymers

Since they were first synthesized over 30 years ago, dendrimers have seen rapid translation into various biomedical applications. A number of reports have not only demonstrated their clinical utility, but also revealed novel design approaches and strategies based on the elucidation of underlying mechanisms governing their biological interactions. This review focuses on presenting the latest advances in dendrimer design, discussing the current mechanistic understandings, and highlighting recent developments and targeted approaches using dendrimers in drug/gene delivery.

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.