Ligand Density and Nanoparticle Clustering Cooperate in the Multivalent Amplification of Epidermal Growth Factor Receptor Activation

Ligand Separation on Nanoconstructs Affects Targeting Selectivity to Protein Dimers on Cell Membranes

This work demonstrates that targeting ligand density on nanoparticles can affect interactions between the nanoconstructs and cell membrane receptors. We discovered that when the separation between covalently grafted DNA aptamers on gold nanostars was comparable to the distance between binding sites on a receptor dimer (matched density; MD), nanoconstructs exhibited a higher selectivity for binding to the dimeric form of the protein. Single-particle dynamics of MD nanoconstructs showed slower rotational rates and larger translational footprints on cancer cells expressing more dimeric forms of receptors (dimer+) compared with cells having more monomeric forms (dimer-). In contrast, nanoconstructs with either increased (nonmatched density; NDlow) or decreased ligand spacing (NDhigh) had minimal changes in dynamics on either dimer+ or dimer- cells. Real-time, single-particle analyses can reveal the importance of nanoconstruct ligand density for the selective targeting of membrane receptors in live cells.

Ectoenzymes as promising cell identification structures for the high avidity targeting of polymeric nanoparticles

Pharmacotherapy is often limited by undesired side effects while insufficient drug reaches the site of action. Active-targeted nanotherapy should provide a solution for this problem, by using ligands in the nanoparticle corona for the identification of receptors on the target-cell surface. However, since receptor binding is directly associated with pharmacological responses, today's targeting concepts must be critically evaluated. We hypothesized that addressing ectoenzymes would help to overcome this problem, but it was not clear if particles would show sufficiently high avidity to provide us with a viable alternative to classical ligand-receptor concepts. We scrutinized this aspect by immobilizing the highly selective angiotensin-converting enzyme 2 (ACE2) inhibitor MLN-4760 in the corona of block-copolymer nanoparticles and investigated enzyme binding via microscale thermophoresis and flow cytometry. Excellent avidities with Kd values as low as 243 pM for soluble ACE2 and 306 pM for ACE2-positive cells were obtained. In addition, the inhibitory activity had an IC50 value of 2.88 nM. Reliable target cell identification could be proven in coculture experiments. High avidity is the basis for minimizing material loss to off-target sites and paves the way for a paradigm shift in nanoparticle targeting which does not trigger unintended side effects following target cell identification.

Controlled spatial characteristics of ligands on nanoparticles: Determinant of cellular functions

Interactions of various ligands and receptors have been extensively investigated because they regulate a series of signal transduction leading to various functional cellular outcomes. The receptors on cell membrane recognize their specific ligands, resulting in specific binding between ligands and receptors. Accumulating evidence reveals that the receptors recognize the difference on the spatial characteristics of ligands as well as the types of ligands. Thus, control on spatial characteristics of multiple ligands presented on therapeutic nanoparticles is believed to impact the cellular functions. Specifically, the localized and multivalent distribution of ligands on nanoparticles can induce receptor oligomerization and receptor clustering, controlling intensity or direction of signal transduction cascades. Here, we will introduce recent studies on the use of material-based nanotechnology to control spatial characteristics of ligands and their effect on cellular functions. These therapeutic nanoparticles with controlled spatial characteristics of ligands may be a promising strategy for maximized therapeutic outcome.

In situ decrypting plasmonic nanoparticle size-controlled phosphorylation of epidermal growth factor receptor in living cells

Recently, interaction between epidermal growth factor receptor (EGFR) and EGFR-targeted nanoprobes is a hot topic. Here, we use dark field microscope (DFM) observe different aggregations of EGFR-targeted nanoprobes in diverticulum. Different aggregation states are related to phosphorylation of EGFR. EGFR phosphorylation can be adjusted by gold nanoparticles (GNPs) size.

Coordination-Induced Multivalent Self-Assembling Catalysts for Spectral Sensing Zn2+ with High Selectivity and Sensitivity

The introduction of signal amplification to molecular spectral sensing systems is an intriguing topic in supramolecular analytical chemistry. In this study, click chemistry was used to generate a triazole moiety to bridge with a long hydrophobic alkyl chain (C_n) and another short alkyl chain (C_m) bearing a 1,4,7-triazacyclonane (TACN) group for efficiently generating a self-assembling multivalent catalyst, C_n-triazole-C_m-TACN·Zn²⁺ (n and m represent the carbon numbers of both alkyl chains, respectively; n = 16, 18, and 20; m = 2 and 6), to catalyze the hydrolysis of 2-hydroxypropyl-4-nitrophenyl phosphate (HPNPP) when Zn²⁺ was added. The triazole moiety introduced adjacent to the TACN group plays an important role in improving the selectivity of Zn²⁺ because the triazole moiety can participate in the coordination interaction between the Zn²⁺ and neighboring TACN group. The supplementary triazole complexing increases the space requirement for coordinated metal ions. This catalytic sensing system also shows high sensitivity, with a favorable limit of detection down to 350 nM, even if only UV-vis absorption spectra rather than more sensitive fluorescence techniques were used for signaling, and can be used to determine the concentration of Zn²⁺ in tap water, which demonstrates the practical application feasibility.

Multivalent dipeptidyl peptidase IV fragment-nanogold complex inhibits cancer metastasis by blocking pericellular fibronectin

Inhibition of cancer metastasis is a fundamental challenge in cancer treatment. We have previously shown that metastasis of cancer cells in the lung is critically promoted by the interaction between the superficial dipeptidyl peptidase IV (DPP IV) expressed on lung endothelial cells and the pericellular polymeric fibronectin (polyFN) of circulating cancer cells. In the present study, we aimed to search for DPP IV fragments with high avidity to polyFN and develop FN-targeted gold nanoparticles (AuNPs) conjugated with DPP IV fragments for treating cancer metastasis. We first identified a DPP IV fragment encompassing amino acids 29-130 of DPP IV, designated DP4A, which contained FN-binding sites and could specifically bind to FN immobilized on gelatin agarose beads. Furthermore, we conjugated maltose binding protein (MBP)-fused DP4A proteins to AuNPs for fabricating a DP4A-AuNP complex and evaluated its FN-targeted activity in vitro and anti-metastatic efficacy in vivo. Our results show that DP4A-AuNP exhibited higher binding avidity to polyFN than DP4A by 9 folds. Furthermore, DP4A-AuNP was more potent than DP4A in inhibiting DPP IV binding to polyFN. In terms of polyFN-targeted effect, DP4A-AuNP interacted with FN-overexpressing cancer cells and was endocytosed into cells 10 to 100 times more efficiently than untargeted MBP-AuNP or PEG-AuNP with no noticeable cytotoxicity. Furthermore, DP4A-AuNP was superior to DP4A in competitive inhibition of cancer cell adhesion to DPP IV. Confocal microscopy analysis revealed that binding of DP4A-AuNP to pericellular FN induced FN clustering without altering its surface expression on cancer cells. Notably, intravenous treatment with DP4A-AuNP significantly reduced metastatic lung tumor nodules and prolonged the survival in the experimental metastatic 4T1 tumor model. Collectively, our findings suggest that the DP4A-AuNP complex with potent FN-targeted effects may have therapeutic potential for prevention and treatment of tumor metastasis to the lung.

Spatially Reprogramed Receptor Organization to Switch Cell Behavior Using a DNA Origami-Templated Aptamer Nanoarray

Receptor oligomerization is a highly complex molecular process that modulates divergent cell signaling. However, there is a lack of molecular tools for systematically interrogating how receptor oligomerization governs the signaling response. Here, we developed a DNA origami-templated aptamer nanoarray (DOTA) that enables precise programming of the oligomerization of receptor tyrosine kinases (RTK) with defined valency, distribution, and stoichiometry at the ligand-receptor interface. The DOTA allows for advanced receptor manipulations by arraying either monomeric aptamer ligands (mALs) that oligamerize receptor monomers to elicit artificial signaling or dimeric aptamer ligands (dALs) that preorganize the receptor dimer to recapitulate natural activation. We demonstrated that the multivalency and nanoscale spacing of receptor oligomerization coordinately influence the activation level of receptor tyrosine kinase signaling. Furthermore, we illustrated that DOTA-modulated receptor oligomerization could function as a signaling switch to promote the transition from epithelia to mesenchymal-like cells, demonstrating robust control over cellular behaviors. Together, we present a versatile all-in-one DNA nanoplatform for the systematical investigation and regulation of receptor-mediated cellular response.

Multivalent Ligand-Nanoparticle Conjugates Amplify Reactive Oxygen Species Second Messenger Generation and Enhance Epidermal Growth Factor Receptor Phosphorylation

The epidermal growth factor (EGF) receptor (EGFR) is heterogeneously distributed on the cellular surface and enriched in clusters with diameters of tens of nanometers. Multivalent presentation of EGF ligand on nanoparticles (NPs) provides an approach for controlling and amplifying the local activation of EGFR in these clusters. Reactive oxygen species (ROS) have been indicated to play a role in the regulation of EGFR activation as second messengers, but the effect of nanoconjugation on EGF-mediated ROS formation and ROS-induced EGFR activation is not well established. The goal of this manuscript is to characterize the multivalent enhancement of EGF-induced ROS formation and to test its effect on EGFR phosphorylation in breast cancer cell models using gold (Au) NPs with a diameter of 81 ± 1 nm functionalized with two different EGF ligand densities (12 ± 7 EGF/NP (NP-EGF12) and 87 ± 6 EGF/NP (NP-EGF87)). In the EGFR overexpressing cell lines MDA-MB-231 and MDA-MB-468, NP-EGF87 achieved a measurable multivalent enhancement of ROS that peaked at concentrations c ROSmax ≤ 25 pM and that were EGFR and nicotinamide adenine dinucleotide phosphate oxidase (NOX) dependent. NP-EGF12 failed to generate comparable ROS levels as NP-EGF87 in the investigated NP input concentration range (0-100 pM). In cells with nearly identical numbers of bound NP-EGF87 and NP-EGF12, the ROS levels for NP-EGF87 were systematically higher, indicating that the multivalent enhancement is exclusively related not only to avidity but also to a stronger stimulation per NP. Importantly, the increase in EGF-induced ROS formation associated with EGF nanoconjugation at c ROSmax resulted in a measurable gain in EGFR phosphorylation, confirming that ROS generation contributes to the multivalent enhancement of EGFR activation in response to NP-EGF87.

The interactions between DNA nanostructures and cells: A critical overview from a cell biology perspective

DNA nanotechnology has yielded remarkable advances in  composite materials with diverse applications in biomedicine. The specificity and predictability of building 3D structures at the nanometer scale make DNA nanotechnology a promising tool for uses in biosensing, drug delivery, cell modulation, and bioimaging. However, for successful translation of DNA nanostructures to real-world applications, it is crucial to understand how they interact with living cells, and the consequences of such interactions. In this review, we summarize the current state of knowledge on the interactions of DNA nanostructures with cells. We identify key challenges, from a cell biology perspective, that influence progress towards the clinical translation of DNA nanostructures. We close by providing an outlook on what questions must be addressed to accelerate the clinical translation of DNA nanostructures. STATEMENT OF SIGNIFICANCE: Self-assembled DNA nanostructures (DNs) offers unique opportunities to overcome persistent challenges in the nanobiotechnology field. However, the interactions between engineered DNs and living cells are still not well defined. Critical systematization of current cellular models and biological responses triggered by DNs is a crucial foundation for the successful clinical translation of DNA nanostructures. Moreover, such an analysis will identify the pitfalls and challenges that are present in the field, and provide a basis for overcoming those challenges.

Lipid Phase Separation in Vesicles Enhances TRAIL-Mediated Cytotoxicity

Ligand spatial presentation and density play important roles in signaling pathways mediated by cell receptors and are critical parameters when designing protein-conjugated therapeutic nanoparticles. Here, we harness lipid phase separation to spatially control the protein presentation on lipid vesicles. We use this system to improve the cytotoxicity of TNF-related apoptosis inducing ligand (TRAIL), a therapeutic anticancer protein. Vesicles with phase-separated TRAIL presentation induce more cell death in Jurkat cancer cells than vesicles with uniformly presented TRAIL, and cytotoxicity is dependent on TRAIL density. We assess this relationship in other cancer cell lines and demonstrate that phase-separated vesicles with TRAIL only enhance cytotoxicity through one TRAIL receptor, DR5, while another TRAIL receptor, DR4, is less sensitive to TRAIL density. This work demonstrates a rapid and accessible method to control protein conjugation and density on vesicles that can be adopted to other nanoparticle systems to improve receptor signaling by nanoparticles.

EGFR Ligand Clustering on E2 Bionanoparticles for Targeted Delivery of Chemotherapeutics to Breast Cancer Cells

Naturally occurring protein nanocages are promising drug carriers because of their uniform size and biocompatibility. Engineering efforts have enhanced the delivery properties of nanocages, but cell specificity and high drug loading remain major challenges. Herein, we fused the SpyTag peptide to the surface of engineered E2 nanocages to enable tunable nanocage decoration and effective E2 cell targeting using a variety of SpyCatcher (SC) fusion proteins. Additionally, the core of the E2 nanocage incorporated four phenylalanine mutations previously shown to allow hydrophobic loading of doxorubicin and pH-responsive release in acidic environments. We functionalized the surface of the nanocage with a highly cell-specific epidermal growth factor receptor (EGFR)-targeting protein conjugate, 4GE11-mCherry-SC, developed previously in our laboratories by employing unnatural amino acid (UAA) protein engineering chemistries. Herein, we demonstrated the benefits of this engineered protein nanocage construct for efficient drug loading, with a straightforward method for removal of the unloaded drug through elastin-like polypeptide-mediated inverse transition cycling. Additionally, we demonstrated approximately 3-fold higher doxorubicin internalization in inflammatory breast cancer cells compared to healthy breast epithelial cells, leading to targeted cell death at concentrations below the IC50 of free doxorubicin. Collectively, these results demonstrated the versatility of our UAA-based EGFR-targeting protein construct to deliver a variety of cargoes efficiently, including engineered E2 nanocages capable of site-specific functionalization and doxorubicin loading.

Ultrasmall Luminescent Metal Nanoparticles: Surface Engineering Strategies for Biological Targeting and Imaging

In the past decade, ultrasmall luminescent metal nanoparticles (ULMNPs, d < 3 nm) have achieved rapid progress in addressing many challenges in the healthcare field because of their excellent physicochemical properties and biological behaviors. With the sharp shrinking size of large plasmonic metal nanoparticles (PMNPs), the contributions from the surface characteristics increase significantly, which brings both opportunities and challenges in the application-driven surface engineering of ULMNPs toward advanced biological applications. Here, the systematic advancements in the biological applications of ULMNPs from bioimaging to theranostics are summarized with emphasis on the versatile surface engineering strategies in the regulation of biological targeting and imaging performance. The efforts in the surface functionalization strategies of ULMNPs for enhanced disease targeting abilities are first discussed. Thereafter, self-assembly strategies of ULMNPs for fabricating multifunctional nanostructures for multimodal imaging and nanomedicine are discussed. Further, surface engineering strategies of ratiometric ULMNPs to enhance the imaging stability to address the imaging challenges in complicated bioenvironments are summarized. Finally, the phototoxicity of ULMNPs and future perspectives are also reviewed, which are expected to provide a fundamental understanding of the physicochemical properties and biological behaviors of ULMNPs to accelerate their future clinical applications in healthcare.

Plasmonic Imaging of Dynamic Interactions between Membrane Receptor Clusters beyond the Diffraction Limit in Live Cells

As a general mechanism, ligand-induced receptor clustering on cell membrane plays determinative roles in pattern recognition and transmembrane signaling. Nevertheless, probing the dynamic characteristics for the complicated interactions between receptor clusters remains difficult because of the lack of strategy for receptor cluster labeling and long-term monitoring in live cells. Herein, we proposed a data-mining-integrated plasmon coupling microscopy to study the dynamic cluster-cluster interactions on cell surface. The receptor clusters were activated and labeled with multivalent plasmonic nanoprobes, which enables the real-time monitoring of individual receptor clusters and the measurement of cluster-cluster interactions from the analysis of plasmonic coupling for the nanoprobe pairs beyond the diffraction limit. Using this method, we found that the protease-activated receptor 1 (PAR1) clusters would experience an initial contact and then form a weakly bound cluster-cluster complex, followed by cluster fusion to generate large-sized signaling complexes. The underlying state transitions for the cluster-cluster fusion process were uncovered using a data-mining technique named the K-means-based hidden Markov model with the scattering intensity of coupled nanoprobe pairs as observations. All of the findings from single-particle analysis and bulk measurements suggested that the allosteric inhibitors could suppress the dynamic transitions from the weakly bound cluster-cluster complexes to fused signaling complexes, leading to the subsequent downregulation of intracellular calcium signaling pathways. We believe that this strategy is promising for imaging and monitoring receptor clustering as well as protein phase separation on the cell surface in various biological and physiological processes.

Quantifying and controlling bond multivalency for advanced nanoparticle targeting to cells

Nanoparticles have drawn intense interest as delivery agents for diagnosing and treating various cancers. Much of the early success was driven by passive targeting mechanisms such as the enhanced permeability and retention (EPR) effect, but this has failed to lead to the expected clinical successes. Active targeting involves binding interactions between the nanoparticle and cancer cells, which promotes tumor cell-specific accumulation and internalization. Furthermore, nanoparticles are large enough to facilitate multiple bond formation, which can improve adhesive properties substantially in comparison to the single bond case. While multivalent binding is universally believed to be an attribute of nanoparticles, it is a complex process that is still poorly understood and difficult to control. In this review, we will first discuss experimental studies that have elucidated roles for parameters such as nanoparticle size and shape, targeting ligand and target receptor densities, and monovalent binding kinetics on multivalent nanoparticle adhesion efficiency and cellular internalization. Although such experimental studies are very insightful, information is limited and confounded by numerous differences across experimental systems. Thus, we focus the second part of the review on theoretical aspects of binding, including kinetics, biomechanics, and transport physics. Finally, we discuss various computational and simulation studies of nanoparticle adhesion, including advanced treatments that compare directly to experimental results. Future work will ideally continue to combine experimental data and advanced computational studies to extend our knowledge of multivalent adhesion, as well as design the most powerful nanoparticle-based agents to treat cancer.

Versatile Mitogenic and Differentiation-Inducible Layer Formation by Underwater Adhesive Polypeptides

Artificial materials have no biological functions, but they are important for medical devices such as artificial organs and matrices for regenerative medicine. In this study, mitogenic and differentiation-inducible materials are devised via the simple coating of polypeptides, which contain the sequence of epidermal growth factor or insulin-like growth factor with a key amino acid (3,4-dihydroxyphenylalanine) of underwater adhesive proteins. The adhesive polypeptides prepared via solid-phase synthesis form layers on various substrates involving organic and inorganic materials to provide biological surfaces. Through the direct activation of cognate receptors on interactive surfaces, the materials enable increased cell growth and differentiation compared to that achieved by soluble growth factors. This superior growth and differentiation are attributed to the long-lasting signal transduction (triggered by the bound growth factors), which do not cause receptor internalization and subsequent downregulation.

Determinants of Ligand-Functionalized DNA Nanostructure-Cell Interactions

Synthesis of ligand-functionalized nanomaterials with control over size, shape, and ligand orientation facilitates the design of targeted nanomedicines for therapeutic purposes. DNA nanotechnology has emerged as a powerful tool to rationally construct two- and three-dimensional nanostructures, enabling site-specific incorporation of protein ligands with control over stoichiometry and orientation. To efficiently target cell surface receptors, exploration of the parameters that modulate cellular accessibility of these nanostructures is essential. In this study, we systematically investigate tunable design parameters of antibody-functionalized DNA nanostructures binding to therapeutically relevant receptors, including the programmed cell death protein 1, the epidermal growth factor receptor, and the human epidermal growth factor receptor 2. We show that, although the native affinity of antibody-functionalized DNA nanostructures remains unaltered, the absolute number of bound surface receptors is lower compared to soluble antibodies due to receptor accessibility by the nanostructure. We explore structural determinants of this phenomenon to improve efficiency, revealing that receptor binding is mainly governed by nanostructure size and DNA handle location. The obtained results provide key insights in the ability of ligand-functionalized DNA nanostructures to bind surface receptors and yields design rules for optimal cellular targeting.

Epidermal Growth Factor-gold Nanoparticle Conjugates-induced Cellular Responses: Effect of Interfacial Parameters between Cell and Nanoparticle

The original activity of epidermal growth factor (EGF) is to promote cell growth or block their apoptosis. However, its activity changes to proapoptotic, completely opposite to the original one, upon conjugation to nanoparticles. We have recently identified that this unique activity conversion was mediated by the confinement of EGF receptor (EGFR) within membrane rafts and signal condensation therein. In this study, we investigated the effect of interfacial parameters between the EGF molecule immobilized at the nanoparticle surface and the cell-surface membrane receptors and analyzed how their interactions were transduced to downstream signaling leading to apoptotic responses. We also studied the cell-type selective apoptotic responses and compared them with EGFR expression level to demonstrate the potential of the nanoparticle conjugate as a new type of anti-cancer drug activating EGFR rather than conventional blocking approaches.

Machine-Learning-Based Approach to Decode the Influence of Nanomaterial Properties on Their Interaction with Cells

In an in vitro nanotoxicity system, cell-nanoparticle (NP) interaction leads to the surface adsorption, uptake, and changes into nuclei/cell phenotype and chemistry, as an indicator of oxidative stress, genotoxicity, and carcinogenicity. Different types of nanomaterials and their chemical composition or "corona" have been widely studied in context with nanotoxicology. However, rare reports are available, which delineate the details of the cell shape index (CSI) and nuclear area factors (NAFs) as a descriptor of the type of nanomaterials. In this paper, we propose a machine-learning-based graph modeling and correlation-establishing approach using tight junction protein ZO-1-mediated alteration in the cell/nuclei phenotype to quantify and propose it as indices of cell-NP interactions. We believe that the phenotypic variation (CSI and NAF) in the epithelial cell is governed by the physicochemical descriptors (e.g., shape, size, zeta potential, concentration, diffusion coefficients, polydispersity, and so on) of the different classes of nanomaterials, which critically determines the intracellular uptake or cell membrane interactions when exposed to the epithelial cells at sub-lethal concentrations. The intrinsic and extrinsic physicochemical properties of the representative nanomaterials (NMs) were measured using optical (dynamic light scattering, NP tracking analysis) methods to create a set of nanodescriptors contributing to cell-NM interactions via phenotype adjustments. We used correlation function as a machine-learning algorithm to successfully predict cell and nuclei shapes and polarity functions as phenotypic markers for five different classes of nanomaterials studied herein this report. The CSI and NAF as nanodescriptors can be used as intuitive cell phenotypic parameters to define the safety of nanomaterials extensively used in consumer products and nanomedicine.

Mechanisms of Action of EGFR Tyrosine Kinase Receptor Incorporated in Extracellular Vesicles

EGFR and some of the cognate ligands extensively traffic in extracellular vesicles (EVs) from different biogenesis pathways. EGFR belongs to a family of four homologous tyrosine kinase receptors (TKRs). This family are one of the major drivers of cancer and is involved in several of the most frequent malignancies such as non-small cell lung cancer, breast cancer, colorectal cancer and ovarian cancer. The carrier EVs exert crucial biological effects on recipient cells, impacting immunity, pre-metastatic niche preparation, angiogenesis, cancer cell stemness and horizontal oncogene transfer. While EV-mediated EGFR signalling is important to EGFR-driven cancers, little is known about the precise mechanisms by which TKRs incorporated in EVs play their biological role, their stoichiometry and associations to other proteins relevant to cancer pathology and EV biogenesis, and their means of incorporation in the target cell. In addition, it remains unclear whether different subtypes of EVs incorporate different complexes of TKRs with specific functions. A raft of high spatial and temporal resolution methods is emerging that could solve these and other questions regarding the activity of EGFR and its ligands in EVs. More importantly, methods are emerging to block or mitigate EV activity to suppress cancer progression and drug resistance. By highlighting key findings and areas that remain obscure at the intersection of EGFR signalling and EV action, we hope to cross-fertilise the two fields and speed up the application of novel techniques and paradigms to both.

Principles and Applications of Biological Membrane Organization

Many critical biological events, including biochemical signaling, membrane traffic, and cell motility, originate at membrane surfaces. Each such event requires that members of a specific group of proteins and lipids rapidly assemble together at a specific site on the membrane surface. Understanding the biophysical mechanisms that stabilize these assemblies is critical to decoding and controlling cellular functions. In this article, we review progress toward a quantitative biophysical understanding of the mechanisms that drive membrane heterogeneity and organization. We begin from a physical perspective, reviewing the fundamental principles and key experimental evidence behind each proposed mechanism. We then shift to a biological perspective, presenting key examples of the role of heterogeneity in biology and asking which physical mechanisms may be responsible. We close with an applied perspective, noting that membrane heterogeneity provides a novel therapeutic target that is being exploited by a growing number of studies at the interface of biology, physics, and engineering.

Engineering the Orientation, Density, and Flexibility of Single-Domain Antibodies on Nanoparticles To Improve Cell Targeting

Nanoparticles targeted to specific cells have the potential to improve the delivery of therapeutics. The effectiveness of cell targeting can be significantly improved by optimizing how the targeting ligands are displayed on the nanoparticle surface. Crucial to optimizing the cell binding are the orientation, density, and flexibility of the targeting ligand on the nanoparticle surface. In this paper, we used an anti-EGFR single-domain antibody (sdAb or nanobody) to target fluorescent nanocrystals (Qdots) to epidermal growth factor receptor (EGFR)-positive cells. The sdAbs were expressed with a synthetic amino acid (azPhe), enabling site-specific conjugation to Qdots in an improved orientation. To optimize the targeting efficiency, we engineered the point of attachment (orientation), controlled the density of targeting groups on the surface of the Qdot, and optimized the length of the poly(ethylene glycol) linker used to couple the sdAb to the Qdot surface. By optimizing orientation, density, and flexibility, we improved cell targeting by more than an order of magnitude. This work highlights the importance of understanding the structure of the nanoparticle surface to achieve the optimal interactions with the intended receptors and how engineering the nanoparticle surface can significantly improve cell targeting.

Quantitative Study of the Interaction of Multivalent Ligand-Modified Nanoparticles with Breast Cancer Cells with Tunable Receptor Density

Multivalent nanoparticles that target a cell surface receptor that is overexpressed by cancer cells are a promising delivery system for cancer therapy. However, the impact of the receptor density and nanoparticle ligand valency on the cell uptake has not been studied in a system where both variables can be systematically tuned over a wide range. To address this lacuna, we report cell-uptake studies on a genetically engineered breast cancer cell line with tunable ErbB2 expression by a polypeptide micelle with tunable ligand valency. We examined the uptake of ErbB2-targeting micelles at 5 ligand densities and 11 receptor densities. We identified a matching pattern between receptors and ligands in which a receptor-to-ligand density ratio of 0.7-4.5 and a minimum of ∼1.6 bonds are required to initiate receptor-mediated endocytosis. Lower and upper limits of receptor density in the cell-uptake profile suggested a standard by which to categorize breast cancer patients as ErbB2-low, ErbB2-medium, and ErbB2-high, with each group expected to respond differently to multivalent therapeutic nanoparticles. At ErbB2-medium and ErbB2-high levels, increasing the ligand valency to 40-valent ErbB2-targeting peptides for a 20 nm radius nanoparticle accelerated the cell uptake, suggesting that the use of nanoparticles with high ligand valency for drug delivery will greatly benefit patients in these two groups. This study advances our understanding of how to rationally optimize nanotechnology for targeted drug delivery.

The presence of PEG on nanoparticles presenting the c[RGDfK]- and/or ATWLPPR peptides deeply affects the RTKs-AKT-GSK3β-eNOS signaling pathway and endothelial cells survival

Covering the surface of a nanoparticle with polyethylene glycol (PEG) is a common way to prevent non-specific interactions but how its presence impacts on the activity of targeting ligands is still poorly documented. We synthesized a set of 9 silica nanoparticles grafted with c[RGDfK]-, a peptide targeting integrin α_vß₃ (cRGD)_, and/or with ATWLPPR, an anti-neuropilin 1 peptide (ATW). We then added various PEGs, and studied NPs binding on primary endothelial cells, the downstream activated signaling pathways and the impact on apoptosis. Our results show that the presence of PEG2000 on cRGD/ATW nanoparticles moderately improves cell binding but induces a 6000 times augmentation of AKT-dependent cell response due to the recruitment of other Receptor Tyrosine Kinases. Augmenting the length of the spacer that separates the peptides from the silica (using PEG3000) mainly resulted in a loss of specificity. Finally, the PEG-mediated hyperactivation of AKT did not protect endothelial cell from dying in the absence of serum, while its moderate activation obtained without PEG did. Finally, PEGylation of cRGD/ATW-NPs can generate nanoparticles with potent capacities to activate the AKT-GSK3β-eNOS cascade and to affect the resistance of endothelial cells to apoptosis. Thus, the impact of PEGylation should be precisely considered in order to avoid the apparition of counter-productive biological responses.

Characterizing Large-Scale Receptor Clustering on the Single Cell Level: A Comparative Plasmon Coupling and Fluorescence Superresolution Microscopy Study

Spatial clustering of cell membrane receptors has been indicated to play a regulatory role in signal initiation, and the distribution of receptors on the cell surface may represent a potential biomarker. To realize its potential for diagnostic purposes, scalable assays capable of mapping spatial receptor heterogeneity with high throughput are needed. In this work, we use gold nanoparticle (NP) labels with an average diameter of 72.17 ± 2.16 nm as bright markers for large-scale epidermal growth factor receptor (EGFR) clustering in hyperspectral plasmon coupling microscopy and compare the obtained clustering maps with those obtained through fluorescence superresolution microscopy (direct stochastic optical reconstruction microscopy, dSTORM). Our dSTORM experiments reveal average EGFR cluster sizes of 172 ± 99 and 150 ± 90 nm for MDA-MB-468 and HeLa, respectively. The cluster sizes decrease after EGFR activation. Hyperspectral imaging of the NP labels shows that differences in the EGFR cluster sizes are accompanied by differences in the average separations between electromagnetically coupled NPs. Because of the distance dependence of plasmon coupling, changes in the average interparticle separation result in significant spectral shifts. For the experimental conditions investigated in this work, hyperspectral plasmon coupling microscopy of NP labels identified the same trends in large-scale EGFR clustering as dSTORM, but the NP imaging approach provided the information in a fraction of the time. Both dSTORM and hyperspectral plasmon coupling microscopy confirm the cortical actin network as one structural component that determines the average size of EGFR clusters.

Surface Coverage-Regulated Cellular Interaction of Ultrasmall Luminescent Gold Nanoparticles

Investigations for accurately controlling the interaction between functional nanoparticles (NPs) and living cells set a long-thought benefit in nanomedicine and disease diagnostics. Here, we reveal a surface coverage-dependent cellular interaction by comparing the membrane binding and uptake of three ultrasmall luminescent gold NPs (AuNPs) with different surface coverages. Lower surface coverage leads to fast cellular interaction and strong membrane binding but low cellular uptake, whereas high surface coverage induces slow cellular interaction and low membrane binding but major cellular uptake. The slight number increase of cell-penetrating peptide on the surface of AuNPs shows improved cellular interaction dynamics and internalization through direct cellular membrane penetration. Furthermore, the different intrinsic emissions resulted from the surface coverage variation, especially the pH-responsive dual emissions, make the AuNPs powerful optical probes for subcellular imaging and tracking. The findings advance the fundamental understanding of the cellular interaction mechanisms of ultrasmall AuNPs and provide a feasible strategy for the design of functional NPs with tunable cellular interaction by surface regulation.

Controlled Epidermal Growth Factor Receptor Ligand Display on Cancer Suicide Enzymes via Unnatural Amino Acid Engineering for Enhanced Intracellular Delivery in Breast Cancer Cells

Proteins are ideal candidates for disease treatment because of their high specificity and potency. Despite this potential, delivery of proteins remains a significant challenge due to the intrinsic size, charge, and stability of proteins. Attempts to overcome these challenges have most commonly relied on direct conjugation of polymers and peptides to proteins via reactive groups on naturally occurring residues. While such approaches have shown some success, they allow limited control of the spacing and number of moieties coupled to proteins, which can hinder bioactivity and delivery capabilities of the therapeutic. Here, we describe a strategy to site-specifically conjugate delivery moieties to therapeutic proteins through unnatural amino acid (UAA) incorporation, in order to explore the effect of epidermal growth factor receptor (EGFR)-targeted ligand valency and spacing on internalization of proteins in EGFR-overexpressing inflammatory breast cancer (IBC) cells. Our results demonstrate the ability to enhance targeted protein delivery by tuning a small number of EGFR ligands per protein and clustering these ligands to promote multivalent ligand-receptor interactions. Furthermore, the tailorability of this simple approach was demonstrated through IBC-targeted cell death via the delivery of yeast cytosine deaminase (yCD), a prodrug converting enzyme.