Dynamics of receptor-mediated nanoparticle internalization into endothelial cells

Effects of receptor properties on particle internalization through receptor-mediated endocytosis

Receptor-mediated endocytosis (RME) is a highly complex process carried out by bioparticles, such as viruses and drug carriers, to enter cells. The discovery of both clathrin-dependent and clathrin-free pathways makes the RME process even more intriguing. Numerical models have been developed to facilitate the exploration of the process. However, the impacts of the receptor properties on RME have been less studied partially due to the oversimplifications of the receptor models. In this paper, we implement a stochastic model to systematically investigate the effects of mechanical (receptor flexure), geometrical (receptor length) and biochemical (ligand-receptor cutoff) properties of receptors, on RME with and without the existence of clathrin. Our simulation results show that the receptor's flexural rigidity plays an important role in RME with clathrin. There is a threshold beyond which particle internalization will not occur. Without clathrin, it is very difficult to achieve complete endocytosis with ligand-receptor interactions alone. A shorter receptor length and longer ligand-receptor reaction cutoff promote the formation of ligand-receptor bonds and facilitate particle internalization. Complete internalization can only be obtained with an extremely short receptor length and long reaction cutoff. Therefore, there are most likely some additional mechanisms to drive the membrane deformation in clathrin-free RME. Our results yield important fundamental insights into RME and provide crucial guidance when correlating the simulation results with experimental observations.

Breaking the selectivity-uptake trade-off of photoimmunoconjugates with nanoliposomal irinotecan for synergistic multi-tier cancer targeting

BACKGROUND

Photoimmunotherapy involves targeted delivery of photosensitizers via an antibody conjugate (i.e., photoimmunoconjugate, PIC) followed by light activation for selective tumor killing. The trade-off between PIC selectivity and PIC uptake is a major drawback limiting the efficacy of photoimmunotherapy. Despite ample evidence showing that photoimmunotherapy is most effective when combined with chemotherapy, the design of nanocarriers to co-deliver PICs and chemotherapy drugs remains an unmet need. To overcome these challenges, we developed a novel photoimmunoconjugate-nanoliposome (PIC-Nal) comprising of three clinically used agents: anti-epidermal growth factor receptor (anti-EGFR) monoclonal antibody cetuximab (Cet), benzoporphyrin derivative (BPD) photosensitizer, and irinotecan (IRI) chemotherapy.

RESULTS

The BPD photosensitizers were first tethered to Cet at a molar ratio of 6:1 using carbodiimide chemistry to form PICs. Conjugation of PICs onto nanoliposome irinotecan (Nal-IRI) was facilitated by copper-free click chemistry, which resulted in monodispersed PIC-Nal-IRI with an average size of 158.8 ± 15.6 nm. PIC-Nal-IRI is highly selective against EGFR-overexpressing epithelial ovarian cancer cells with 2- to 6-fold less accumulation in low EGFR expressing cells. Successful coupling of PIC onto Nal-IRI enhanced PIC uptake and photoimmunotherapy efficacy by up to 30% in OVCAR-5 cells. Furthermore, PIC-Nal-IRI synergistically reduced cancer viability via a unique three-way mechanism (i.e., EGFR downregulation, mitochondrial depolarization, and DNA damage).

CONCLUSION

It is increasingly evident that the most effective therapies for cancer will involve combination treatments that target multiple non-overlapping pathways while minimizing side effects. Nanotechnology combined with photochemistry provides a unique opportunity to simultaneously deliver and activate multiple drugs that target all major regions of a cancer cell-plasma membrane, cytoplasm, and nucleus. PIC-Nal-IRI offers a promising strategy to overcome the selectivity-uptake trade-off, improve photoimmunotherapy efficacy, and enable multi-tier cancer targeting. Controllable drug compartmentalization, easy surface modification, and high clinical relevance collectively make PIC-Nal-IRI extremely valuable and merits further investigations in living animals.

Nanoparticle transport phenomena in confined flows

Nanoparticles submerged in confined flow fields occur in several technological applications involving heat and mass transfer in nanoscale systems. Describing the transport with nanoparticles in confined flows poses additional challenges due to the coupling between the thermal effects and fluid forces. Here, we focus on the relevant literature related to Brownian motion, hydrodynamic interactions and transport associated with nanoparticles in confined flows. We review the literature on the several techniques that are based on the principles of non-equilibrium statistical mechanics and computational fluid dynamics in order to simultaneously preserve the fluctuation-dissipation relationship and the prevailing hydrodynamic correlations. Through a review of select examples, we discuss the treatments of the temporal dynamics from the colloidal scales to the molecular scales pertaining to nanoscale fluid dynamics and heat transfer. As evident from this review, there, indeed has been little progress made in regard to the accurate modeling of heat transport in nanofluids flowing in confined geometries such as tubes. Therefore the associated mechanisms with such processes remain unexplained. This review has revealed that the information available in open literature on the transport properties of nanofluids is often contradictory and confusing. It has been very difficult to draw definitive conclusions. The quality of work reported on this topic is non-uniform. A significant portion of this review pertains to the treatment of the fluid dynamic aspects of the nanoparticle transport problem. By simultaneously treating the energy transport in ways discussed in this review as related to momentum transport, the ultimate goal of understanding nanoscale heat transport in confined flows may be achieved.

Multivalent Binding of a Ligand-Coated Particle: Role of Shape, Size, and Ligand Heterogeneity

We utilize a multiscale modeling framework to study the effect of shape, size, and ligand composition on the efficacy of binding of a ligand-coated particle to a substrate functionalized with the target receptors. First, we show how molecular dynamics along with steered molecular dynamics calculations can be used to accurately parameterize the molecular-binding free energy and the effective spring constant for a receptor-ligand pair. We demonstrate this for two ligands that bind to the α₅β₁-domain of integrin. Next, we show how these effective potentials can be used to build computational models at the meso- and continuum-scales. These models incorporate the molecular nature of the receptor-ligand interactions and yet provide an inexpensive route to study the multivalent interaction of receptors and ligands through the construction of Bell potentials customized to the molecular identities. We quantify the binding efficacy of the ligand-coated-particle in terms of its multivalency, binding free-energy landscape, and the losses in the configurational entropies. We show that 1) the binding avidity for particle sizes less than 350 nm is set by the competition between the enthalpic and entropic contributions, whereas that for sizes above 350 nm is dominated by the enthalpy of binding; 2) anisotropic particles display higher levels of multivalent binding compared to those of spherical particles; and 3) variations in ligand composition can alter binding avidity without altering the average multivalency. The methods and results presented here have wide applications in the rational design of functionalized carriers and also in understanding cell adhesion.

Stiffness can mediate balance between hydrodynamic forces and avidity to impact the targeting of flexible polymeric nanoparticles in flow

We report computational investigations of deformable polymeric nanoparticles (NPs) under colloidal suspension flow and adhesive environment. We employ a coarse-grained model for the polymeric NP and perform Brownian dynamics (BD) simulations with hydrodynamic interactions and in the presence of wall-confinement, particulate margination, and wall-adhesion for obtaining NP microstructure, shape, and anisotropic and inhomogeneous transport properties for different NP stiffness. These microscopic properties are utilized in solving the Fokker-Planck equation to obtain the spatial distribution of NP subject to shear, margination due to colloidal microparticles, and confinement due to a vessel wall. Comparing our computational results for the amount of NP margination to the near-wall adhesion regime with those of our binding experiments in cell culture under shear, we found quantitative agreement on shear-enhanced binding, the effect of particulate volume fraction, and the effect of NP stiffness. For the experimentally realized polymeric NP, our model predicts that the shear and volume fraction mediated enhancement in targeting has a hydrodynamic transport origin and is not due to a multivalent binding effect. However, for ultrasoft polymeric NPs, our model predicts a substantial increase in targeting due to multivalent binding. Our results are also in general agreement with experiments of tissue targeting measurements in vivo in mice, however, one needs to exercise caution in extending the modeling treatment to in vivo conditions owing to model approximations. The reported combined computational approach and results are expected to enable fine-tuning of design and optimization of flexible NP in targeted drug delivery applications.

Urban particulate matter induces the expression of receptors for early and late adhesion molecules on human monocytes

Exposure to urban particulate matter (PM) is correlated with increases in the emergence of health services due to adverse events and deaths and is mainly related to cardiorespiratory complications. The translocation of particles from the lung into circulation has been proposed as a factor that may trigger systemic effects. Monocytes may be exposed to PM, and if the monocytes are activated, then they are likely to adhere to endothelial cells in a distant organ due to the expression of receptors for adhesion molecules. In the present study, we evaluated the expression of receptors for adhesion molecules (sLe^x, PSGL-1, LFA-1, VLA-4 and α_Vβ₃) in monocytes (U937 cells) exposed for 3 or 18 h to PM₁₀ (0.001, 0.003, 0.010, 0.030, 0.300, 3 or 30 µg/mL). Exposed cells were co-cultured with human endothelial cells that were naive or previously exposed to the same particles. When U937 cells were exposed to PM₁₀, similar levels of expression for early and late receptors for adhesion molecules were observed from 30 ng/mL as those induced by TNF-α. Cells exposed to particles at concentrations above 30 ng/mL were more adhesive to naive or exposed human endothelial cells. Taken together, our results suggest that it is plausible that activated monocytes may play a role in systemic effects induced by PM₁₀ due to the size distribution of the particles and the concentrations required to trigger the expression of receptors for adhesion molecules in monocytes.

Stochastic simulations of nanoparticle internalization through transferrin receptor dependent clathrin-mediated endocytosis

BACKGROUND

Receptor dependent clathrin-mediated endocytosis (CME) is one of the most important endocytic pathways for the internalization of bioparticles into cells. During CME, the ligand-receptor interactions, development of clathrin-coated pit (CCP) and membrane evolution all act together to drive the internalization of bioparticles. In this work, we develop a stochastic computational model to investigate the CME based on the Metropolis Monte Carlo simulations.

METHODS

The model is based on the combination of a stochastic particle binding model with a membrane model. The energetic costs of membrane bending, CCP formation and ligand-receptor interactions are systematically linked together.

RESULTS

We implement our model to investigate the effects of particle size, ligand density and membrane stiffness on the overall process of CME from the drug delivery perspectives. Consistent with some experiments, our results show that the intermediate particle size and ligand density favor the particle internalization. Moreover, our results show that it is easier for a particle to enter a cell with softer membrane.

CONCLUSIONS

The model presented here is able to provide mechanistic insights into CME and can be readily modified to include other important factors, such as actins. The predictions from the model will aid in the therapeutic design of intracellular/transcellular drug delivery and antiviral interventions.

The Multifaceted Uses and Therapeutic Advantages of Nanoparticles for Atherosclerosis Research

Nanoparticles are uniquely suited for the study and development of potential therapies against atherosclerosis by virtue of their size, fine-tunable properties, and ability to incorporate therapies and/or imaging modalities. Furthermore, nanoparticles can be specifically targeted to the atherosclerotic plaque, evading off-target effects and/or associated cytotoxicity. There has been a wealth of knowledge available concerning the use of nanotechnologies in cardiovascular disease and atherosclerosis, in particular in animal models, but with a major focus on imaging agents. In fact, roughly 60% of articles from an initial search for this review included examples of imaging applications of nanoparticles. Thus, this review focuses on experimental therapy interventions applied to and observed in animal models. Particular emphasis is placed on how nanoparticle materials and properties allow researchers to learn a great deal about atherosclerosis. The objective of this review was to provide an update for nanoparticle use in imaging and drug delivery studies and to illustrate how nanoparticles can be used for sensing and modelling, for studying fundamental biological mechanisms, and for the delivery of biotherapeutics such as proteins, peptides, nucleic acids, and even cells all with the goal of attenuating atherosclerosis. Furthermore, the various atherosclerosis processes targeted mainly for imaging studies have been summarized in the hopes of inspiring new and exciting targeted therapeutic and/or imaging strategies.

Bio-nano interface and environment: A critical review

The bio-nano interface is the boundary where engineered nanomaterials (ENMs) meet the biological system, exerting the biological function for which they have been designed or inducing adverse effects on other cells or organisms when they reach nontarget scenarios (i.e., the natural environment). Research has been performed to determine the fate, transport, and toxic properties of ENMs, but much of it is focused on pristine or so-called as-manufactured ENMs, or else modifications of the materials were not assessed. We review the most recent progress regarding the bio-nano interface and the transformations that ENMs undergo in the environment, paying special attention to the adsorption of environmental biomolecules on the surface of ENMs. Whereas the protein corona has received considerable attention in the fields of biomedics and human toxicology, its environmental analogue (the eco-corona) has been much less studied. A section dedicated to the analytical methods for studying and characterizing the eco-corona is also presented. We conclude by presenting and discussing the key problems and knowledge gaps that need to be resolved in the near future regarding the bio-nano interface and the eco-corona. Environ Toxicol Chem 2017;36:3181-3193. © 2017 SETAC.

Multivalent ligand-receptor-mediated interaction of small filled vesicles with a cellular membrane

The ligand-receptor-mediated contacts of small sub-100-nm-sized lipid vesicles (or nanoparticles) with the cellular membrane are of interest in the contexts of cell-to-cell communication, endocytosis of membrane-coated virions, and drug (RNA) delivery. In all these cases, the interior of vesicles is filled by biologically relevant content. Despite the diversity of such systems, the corresponding ligand-receptor interaction possesses universal features. One of them is that the vesicle-membrane contacts can be accompanied by the redistribution of ligands and receptors between the contact and contact-free regions. In particular, the concentrations of ligands and receptors may become appreciably higher in the contact regions and their composition may there be different compared to that in the suspended state in the solution. A statistical model presented herein describes the corresponding distribution of various ligands and receptors and allows one to calculate the related change of the free energy with variation of the vesicle-engulfment extent. The results obtained are used to clarify the necessary conditions for the vesicle-assisted pathway of drug delivery.

Biophysically inspired model for functionalized nanocarrier adhesion to cell surface: roles of protein expression and mechanical factors

In order to achieve selective targeting of affinity-ligand coated nanoparticles to the target tissue, it is essential to understand the key mechanisms that govern their capture by the target cell. Next-generation pharmacokinetic (PK) models that systematically account for proteomic and mechanical factors can accelerate the design, validation and translation of targeted nanocarriers (NCs) in the clinic. Towards this objective, we have developed a computational model to delineate the roles played by target protein expression and mechanical factors of the target cell membrane in determining the avidity of functionalized NCs to live cells. Model results show quantitative agreement with in vivo experiments when specific and non-specific contributions to NC binding are taken into account. The specific contributions are accounted for through extensive simulations of multivalent receptor-ligand interactions, membrane mechanics and entropic factors such as membrane undulations and receptor translation. The computed NC avidity is strongly dependent on ligand density, receptor expression, bending mechanics of the target cell membrane, as well as entropic factors associated with the membrane and the receptor motion. Our computational model can predict the in vivo targeting levels of the intracellular adhesion molecule-1 (ICAM1)-coated NCs targeted to the lung, heart, kidney, liver and spleen of mouse, when the contributions due to endothelial capture are accounted for. The effect of other cells (such as monocytes, etc.) do not improve the model predictions at steady state. We demonstrate the predictive utility of our model by predicting partitioning coefficients of functionalized NCs in mice and human tissues and report the statistical accuracy of our model predictions under different scenarios.

E-selectin-targeting delivery of microRNAs by microparticles ameliorates endothelial inflammation and atherosclerosis

E-selectin is a surface marker of endothelial cell (EC) inflammation, one of the hallmarks of atherogenesis. Thus, we tested the hypothesis that delivery of microRNA (miR)-146a and miR-181b with an E-selectin-targeting multistage vector (ESTA-MSV) to inflamed endothelium covering atherosclerotic plaques inhibits atherosclerosis. Cy5-conjugated miR-146a and miR-181b were packaged in polyethylene glycol-polyethyleneimine (PEG/PEI) nanoparticles and loaded into ESTA-MSV microparticles. Both miRs were downregulated in tumor necrosis factor (TNF)-α-treated ECs. Transfection of TNF-α-treated mouse aortas and cultured ECs with miRs was more efficient with ESTA-MSV than with the PEG/PEI. Likewise, miR-146a/-181b packaged in ESTA-MSV efficiently suppressed the chemokines, CCL2, CCL5, CCL8, and CXCL9, and monocyte adhesion to ECs. Complementary in vivo tests were conducted in male apolipoprotein E-deficient mice fed a Western diet and injected intravenously with the particles prepared as above biweekly for 12 weeks. Treatment with miRs packaged in ESTA-MSV but not in PEG/PEI reduced atherosclerotic plaque size. Concurrently, vascular inflammation markers, including macrophages in aortic root lesions and chemokine expression in aortic tissues were reduced while the vascular smooth muscle cells and collagen increased in plaques from ESTA-MSV/miRs-treated vs. vehicle-treated mice. Our data supported our hypothesis that ESTA-MSV microparticle-mediated delivery of miR-146a/-181b ameliorates endothelial inflammation and atherosclerosis.

Bioimpacts of nanoparticle size: why it matters?

During the last two decades, applications of nanotechnology are delivered to benefit the human society. The fact is that various nanomaterials are able to be tailor made to achieve desired properties. In biomedical field, nanotechnology has created great excitements to advance both diagnosis and therapy areas – the field so-called nanomedicines in different forms of nanoparticles (NPs) and nanosystems (NSs). It is noteworthy to mention NPs/NSs do not act similarly in the biological milieu, in which their biological behaviors/ impacts varies with size, morphology, and physicochemical characteristics. On the other hand, nanomedicines impacts on biological systems seem to be influenced by its possible interaction(s) with different bioelements of cell membrane, in particular the endocytic pathway(s) by which NPs/NSs can be internalized and localized. This latter phenomenon is influenced by membrane viscoelastic property, polymerization/depolymerization of cytoskeletal system, and the particle specification itself. Among all other properties of NPs/NSs, as shown by various researchers, the size is an important parameter in the fate of the particle. Accordingly, in-depth efforts to unravel the size dependent effects of nanomedicins can provide insights to design and develop more efficacious NSs with greater benefits and lower side effects. This editorial aims to highlight some important aspects of size dependent impacts NPs/NSs.