The effects of ligand valency and density on the targeting ability of multivalent nanoparticles based on negatively charged chitosan nanoparticles

A high-throughput lysosome trafficking assay guides ligand selection and elucidates differences in CD22-targeted nanodelivery

Targeted nanoparticles offer potential to selectively deliver therapeutics to cells; however, their subcellular fate following endocytosis must be understood to properly design mechanisms of drug release. Here we describe a nanoparticle platform and associated cell-based assay to observe lysosome trafficking of targeted nanoparticles in live cells. The nanoparticle platform utilizes two fluorescent dyes loaded onto PEG-poly(glutamic acid) and PEG-poly(Lysine) block co-polymers that also comprise azide reactive handles on PEG termini to attach antibody-based targeting ligands. Fluorophores were selected to be pH-sensitive (pHrodo Red) or pH-insensitive (Alexafluor 488) to report when nanoparticles enter low pH lysosomes. Dye-labelled block co-polymers were further assembled into polyion complex micelle nanoparticles and crosslinked through amide bond formation to form stable nano-scaffolds for ligand attachment. Cell binding and lysosome trafficking was determined in live cells by fluorescence imaging in 96-well plates and quantification of red- and green-fluorescence signals over time. The platform and assay was validated for selection of optimal antibody-derived targeting ligands directed towards CD22 for nanoparticle delivery. Kinetic analysis of uptake and lysosome trafficking indicated differences between ligand types and the ligand with the highest lysosome trafficking efficiency translated into effective DNA delivery with nanoparticles bearing the optimal ligand.

Engineering the protein corona: Strategies, effects, and future directions in nanoparticle therapeutics

Nanoparticles (NPs) serve as versatile delivery systems for anticancer, antibacterial, and antioxidant agents. The manipulation of protein-NP interactions within biological systems is crucial to the application of NPs in drug delivery and cancer nanotherapeutics. The protein corona (PC) that forms on the surface of NPs is the interface between biomacromolecules and NPs and significantly influences their pharmacokinetics and pharmacodynamics. Upon encountering proteins, NPs undergo surface alterations that facilitate their clearance from circulation by the mononuclear phagocytic system (MPS). PC behavior depends largely on the biological microenvironment and the physicochemical properties of the NPs. This review describes various strategies employed to engineer PC compositions on NP surfaces. The effects of NP characteristics such as size, shape, surface modification and protein precoating on PC performance were explored. In addition, this study addresses these challenges and guides the future directions of this evolving field.

Improving Cancer Targeting: A Study on the Effect of Dual-Ligand Density on Targeting of Cells Having Differential Expression of Target Biomarkers

Silica nanoparticles with hyaluronic acid (HA) and folic acid (FA) were developed to study dual-ligand targeting of CD44 and folate receptors, respectively, in colon cancer. Characterization of particles with dynamic light scattering showed them to have hydrodynamic diameters of 147-271 nm with moderate polydispersity index (PDI) values. Surface modification of the particles was achieved by simultaneous reaction with HA and FA and results showed that ligand density on the surface increased with increasing concentrations in the reaction mixture. The nanoparticles showed minimal to no cytotoxicity with all formulations showing ≥ 90% cell viability at concentrations up to 100 µg/mL. Based on flow cytometry results, SW480 cell lines were positive for both receptors, the WI38 cell line was positive for CD44 receptor, and Caco2 was positive for the folate receptor. Cellular targeting studies demonstrated the potential of the targeted nanoparticles as promising candidates for delivery of therapeutic agents. The highest cellular targeting was achieved with particles synthesized using folate:surface amine (F:A) ratio of 9 for SW480 and Caco2 cells and at F:A = 0 for WI38 cells. The highest selectivity was achieved at F:A = 9 for both SW480:WI38 and SW480:Caco2 cells. Based on HA conjugation, the highest cellular targeting was achieved at H:A = 0.5-0.75 for SW480 cell, at H:A = 0.75 for WI38 cell and at H:A = 0.5 for Caco2 cells. The highest selectivity was achieved at H:A = 0 for both SW480:WI38 and SW480:Caco2 cells. These results demonstrated that the optimum ligand density on the nanoparticle for targeting is dependent on the levels of biomarker expression on the target cells. Ongoing studies will evaluate the therapeutic efficacy of these targeted nanoparticles using in vitro and in vivo cancer models.

Multivalent effect of peptide functionalized polymeric nanoparticles towards selective prostate cancer targeting

The concept of selective tumor targeting using nanomedicines has been around for decades; however, no targeted nanoparticle has yet reached the clinic. A key bottleneck is the non-selectivity of targeted nanomedicines in vivo, which is attributed to the lack of characterization of their surface properties, especially the ligand number, thereby calling for robust techniques that allow quantifiable outcomes for an optimal design. Multivalent interactions comprise multiple copies of ligands attached to scaffolds, allowing simultaneous binding to receptors, and they play an important role in targeting. As such, 'multivalent' nanoparticles facilitate simultaneous interaction of weak surface ligands with multiple target receptors resulting in higher avidity and enhanced cell selectivity. Therefore, the study of weak binding ligands for membrane-exposed biomarkers is crucial for the successful development of targeted nanomedicines. Here we carried out a study of a cell targeting peptide known as WQP having weak binding affinity for prostate specific membrane antigen, a known prostate cancer biomarker. We evaluated the effect of its multivalent targeting using polymeric NPs over its monomeric form on the cellular uptake in different prostate cancer cell lines. We developed a method of specific enzymatic digestion to quantify the number of WQPs on NPs having different surface valencies and observed that increasing valencies resulted in a higher cellular uptake of WQP-NPs over the peptide alone. We also found that WQP-NPs showed higher uptake in PSMA over-expressing cells, attributed to a stronger avidity for selective PSMA targeting. This kind of strategy can be useful for improving the binding affinity of a weak ligand as a means for selective tumor targeting.

Tuning Design Parameters of ICAM-1-Targeted 3DNA Nanocarriers to Optimize Pulmonary Targeting Depending on Drug Type

3DNA holds promise as a carrier for drugs that can be intercalated into its core or linked to surface arms. Coupling 3DNA to an antibody targeting intercellular adhesion molecule 1 (ICAM-1) results in high lung-specific biodistributions in vivo. While the role of individual parameters on ICAM-1 targeting has been studied for other nanocarriers, it has never been examined for 3DNA or in a manner capable of revealing the hierarchic interplay among said parameters. In this study, we used 2-layer vs. 4-layer anti-ICAM 3DNA and radiotracing to examine biodistribution in mice. We found that, below saturating conditions and within the ranges tested, the density of targeting antibodies on 3DNA is the most relevant parameter driving lung targeting over liver clearance, compared to the number of antibodies per carrier, total antibody dose, 3DNA dose, 3DNA size, or the administered concentration, which influenced the dose in organs but not the lung specific-over-liver clearance ratio. Data predicts that lung-specific delivery of intercalating (core loaded) drugs can be tuned using this biodistribution pattern, while that of arm-linked (surface loaded) drugs requires a careful parametric balance because increasing anti-ICAM density reduces the number of 3DNA arms available for drug loading.

Bioinspired and Biomimetic Nanomedicines for Targeted Cancer Therapy

Undesirable side effects and multidrug resistance are the major obstacles in conventional chemotherapy towards cancers. Nanomedicines provide alternative strategies for tumor-targeted therapy due to their inherent properties, such as nanoscale size and tunable surface features. However, the applications of nanomedicines are hampered in vivo due to intrinsic disadvantages, such as poor abilities to cross biological barriers and unexpected off-target effects. Fortunately, biomimetic nanomedicines are emerging as promising therapeutics to maximize anti-tumor efficacy with minimal adverse effects due to their good biocompatibility and high accumulation abilities. These bioengineered agents incorporate both the physicochemical properties of diverse functional materials and the advantages of biological materials to achieve desired purposes, such as prolonged circulation time, specific targeting of tumor cells, and immune modulation. Among biological materials, mammalian cells (such as red blood cells, macrophages, monocytes, and neutrophils) and pathogens (such as viruses, bacteria, and fungi) are the functional components most often used to confer synthetic nanoparticles with the complex functionalities necessary for effective nano-biointeractions. In this review, we focus on recent advances in the development of bioinspired and biomimetic nanomedicines (such as mammalian cell-based drug delivery systems and pathogen-based nanoparticles) for targeted cancer therapy. We also discuss the biological influences and limitations of synthetic materials on the therapeutic effects and targeted efficacies of various nanomedicines.

Surface Ligand Valency and Immunoliposome Binding: when More Is Not Always Better

PURPOSE

Nano-drug delivery systems are designed to contain surface ligands including antibodies for "active targeting". The number of ligands on each nanoparticle, known as the valency, is considered a critical determinant of the "targeting" property. We sought to understand the correlation between valency and binding properties using antibody conjugated liposomes, i.e. immunoliposomes (ILs), as the model.

METHODS

Anti-CD3 Fab containing a terminal cysteine residue were conjugated to DSPE-PEG-maleimide and incubated with preformed liposomes at 60°C. The un-incorporated antibodies were removed and the obtained ILs were characterized to contain in average 2-22 copies of anti-CD3 Fabs per liposome. The Biolayer Interferometry (BLI) probe surface was coated with various densities of CD3 epsilon&delta heterodimer (CD3D/E) to imitate different CD3 expression levels on target cells. The inference wavelength shifts upon anti-CD3 liposome binding were monitored and analyzed.

RESULTS

The data indicated ILs may bind either monovalently or multivalently, determined mainly by the surface ligand density rather than the ILs antibody valency. The ILs valency indeed correlated with the dissociation rate constant (K_off), but not with the association rate constant (K_on). Their binding capabilities also did not necessarily increase with the surface anti-CD3 valency.

CONCLUSION

We proposed a model for understanding the binding properties of ILs with different ligand valencies. The binding mode may change when the targeted surfaces had different antigen densities. The model should be important for the designing and optimization of active targeting drug delivery systems to fit different applications.

Voltage-dependent potassium channel Kv4.2 alleviates the ischemic stroke impairments through activating neurogenesis

As well as their ion transportation function, the voltage-dependent potassium channels could act as the cell signal inducer in a variety of pathogenic processes. However, their roles in neurogenesis after stroke insults have not been clearly illustrated. In our preliminary study, the expressions of voltage-dependent potassium channels Kv4.2 was significantly decreased after stroke in cortex, striatum and hippocampus by real-time quantitative PCR assay. To underlie the neuroprotection of Kv4.2 in stroke rehabilitation, recombinant plasmids encoding the cDNAs of mouse Kv4.2 was constructed. Behavioral tests showed that the increased Kv4.2 could be beneficial to the recovery of the sensory, the motor functions and the cognitive deficits after stroke. Temozolomide (TMZ), an inhibitor of neurogenesis, could partially abolish the mentioned protections of Kv4.2. The immunocytochemical staining showed that Kv4.2 could promote the proliferations of neural stem cells and induce the neural stem cells to differentiate into neurons in vitro and in vivo. And Kv4.2 could up-regulate the expressions of ERK1/2, p-ERK1/2, p-STAT3, NGF, p-TrkA, and BDNF, CAMKII and the concentration of intracellular Ca²⁺. Namely, we concluded that Kv4.2 promoted neurogenesis through ERK1/2/STAT3, NGF/TrkA, Ca²⁺/CAMKII signal pathways and rescued the ischemic impairments. Kv4.2 might be a potential drug target for ischemic stroke intervention.

Strategies and challenges to improve the performance of tumor-associated active targeting

Over the past decade, nanoparticle-based drug delivery systems have been extensively explored. However, the average tumour enrichment ratio of passive targeting systems corresponds to only 0.7% due to the nonspecific uptake by normal organs and poor selective retention in tumours. The therapeutic specificity and efficacy of nano-medicine can be enhanced by equipping it with active targeting ligands, although it is not possible to ignore the recognition and clearance of the reticuloendothelial system (RES) caused by targeting ligands. Given the complexity of the systemic circulation environment, it is necessary to carefully consider the hydrophobicity, immunogenicity, and electrical property of targeting ligands. Thus, for an active targeting system, the targeting ligands should be shielded in blood circulation and de-shielded in the tumour region for enhanced tumour accumulation. In this study, strategies for improving the performance of active targeting ligands are introduced. The strategies include irreversible shielding, reversible shielding, and methods of modulating the multivalent interactions between ligands and receptors. Furthermore, challenges and future developments in designing active ligand targeting systems are also discussed.

Overcoming the protein corona in chitosan-based nanoparticles

Numerous properties of chitosan have led to its extensive use in the formulation of nanomaterials for drug delivery. However, the cationic surface of chitosan-based nanoparticles adsorbs proteins upon exposure to biological fluids, forming a phenomenon known as 'protein corona'. This causes several effects such as decreased bioavailability and limited in vivo clinical applications of chitosan nanoparticles. Understanding and overcoming the effects of protein adsorption on chitosan nanoparticles is key for drug delivery purposes. This review focuses on the strategies implemented to increase the stability of chitosan nanoparticles in the systemic circulation by averting the formation of protein corona and the limitations of PEGylation.

Advances in receptor modulation strategies for flexible, efficient, and enhanced antitumor efficacy

Tumor-sensitivity, effective transport, and precise delivery to tumor cells of nano drug delivery systems (NDDs) have been great challenges to cancer therapy in recent years. The conventional targeting approach involves actively installing the corresponding ligand on the nanocarriers, which is prone to recognize the antigen blasts overexpressed on the surface of tumor cells. However, there are some probable limitations for the active tumor-targeting systems in vivo as follows: a. the limited ligand amount of modifications; b. possible steric hindrance, which was likely to prevent ligand-receptor interaction during the delivery process. c. the restrained antigen saturation highly expressed on the cell membrane, will definitely decrease the specificity and often lead to "off-target" effects of NDDs; and d. water insolubility of nanocarriers due to excess of ligands modification. Obviously, any regulation of receptors on surface of tumor cells exerted an important influence on the delivery of targeting systems. Herein, receptor upregulation was mostly desired for enhancing targeted therapy from the cellular level. This technique with the amplification of receptors has the potential to enhance tumor sensitivity towards corresponding ligand-modified nanoparticles, and thereby increasing the effective therapeutic concentration as well as improving the efficacy of chemotherapy. The enhancement of positively expressed receptors on tumor cells and receptor-dependent therapeutic agents or NDDs with an assembled "self-promoting" effect contributes to increasing cell sensitivity to NPs, and will provide a basic platform for clinical therapeutic practice. In this review, we highlight the significance of modulating various receptors on different types of cancer cells for drug delivery and therapeutic benefits.

Relevant Physicochemical Methods to Functionalize, Purify, and Characterize Surface-Decorated Lipid-Based Nanocarriers

Surface functionalization of lipid-based nanocarriers (LBNCs) with targeting ligands has attracted huge interest in the field of nanomedicines for their ability to overcome some physiological barriers and their potential to deliver an active molecule to a specific target without causing damage to healthy tissues. The principal objective of this review is to summarize the present knowledge on LBNC decoration used for biomedical applications, with an emphasis on the ligands used, the functionalization approaches, and the purification methods after ligand corona formation. The most potent experimental techniques for the LBNC surface characterization are described. The potential of promising methods such as nuclear magnetic resonance spectroscopy and isothermal titration calorimetry to characterize ligand surface corona is also outlined.

Ligand Density Controls C-Type Lectin-Like Molecule-1 Receptor-Specific Uptake of Polymer Nanoparticles

The newest generation of drug delivery systems (DDSs) exploits ligands to mediate specific targeting of cells and/or tissues. However, studies investigating the link between ligand density and nanoparticle (NP) uptake are limited to a small number of ligand-receptor systems. C-type lectin-like molecule-1 (CLL1) is uniquely expressed on myeloid cells, which enables the development of receptors specifically targeting treat various diseases. This study aims to investigate how NPs with different CLL1 targeting peptide density impact cellular uptake. To this end, poly(styrene-alt-maleic anhydride)-b-poly(styrene) NPs are functionalized with cyclized CLL1 binding peptides (cCBP) ranging from 240 ± 12 to 31 000 ± 940 peptides per NP. Unexpectedly, the percentage of cells with internalized NPs is decreased for all cCBP-NP designs regardless of ligand density compared to unmodified NPs. Internalization through CLL1 receptor-mediated processes is further investigated without confounding the effects of NP size and surface charge. Interestingly, high density cCBP-NPs (>7000 cCBP per NP) uptake is dominated by CLL1 receptor-mediated processes while low density cCBP-NPs (≈200 cCBP per NP) and untargeted NP occurred through non-specific clathrin and caveolin-mediated endocytosis. Altogether, these studies show that ligand density and uptake mechanism should be carefully investigated for specific ligand-receptor systems for the design of targeted DDSs to achieve effective drug delivery.

Biomedical and Pharmacological Uses of Fluorescein Isothiocyanate Chitosan-Based Nanocarriers

Chitosan-based nanocarriers (ChNCs) are considered suitable drug carriers due to their ability to encapsulate a variety of drugs and cross biological barriers to deliver the cargo to their target site. Fluorescein isothiocyanate-labeled chitosan-based NCs (FITC@ChNCs) are used extensively in biomedical and pharmacological applications. The main advantage of using FITC@ChNCs consists of the ability to track their fate both intra and extracellularly. This journey is strictly dependent on the physico-chemical properties of the carrier and the cell types under investigation. Other applications make use of fluorescent ChNCs in cell labeling for the detection of disorders in vivo and controlling of living cells in situ. This review describes the use of FITC@ChNCs in the various applications with a focus on understanding their usefulness in labeled drug-delivery systems.

Facile Fabrication of Nanoparticles with Dual-Targeting Ligands for Precise Hepatocellular Carcinoma Therapy In Vitro and In Vivo

Efficient hepatocellular carcinoma (HCC) therapy remains a significant challenge due to the unsatisfactory targeting efficiency of nanoparticles (NPs) with either a passive targeting or a single active targeting property. Although a dual-targeting mechanism-based strategy can promote the partial targeting efficiency, most of the reported NPs with dual-targeting properties generally suffer from sophisticated chemical design, multistep synthesis, and purification procedures, leading to batch-to-batch variation and difficulties in scalable production. To develop a facile yet efficient strategy toward dual-targeting ligand-functionalized NPs for precise HCC therapy and potential clinical translation, folic acid (FA) was readily introduced as a hydrophobic and targeting component to a hydrophilic macromolecular prodrug, galactosylated chitosan-5-fluorouracil acetic acid (GC-FU), to afford FA-GC-FU formulation that can self-assemble into NPs driven by the solubility variation of FA and GC-FU without the necessity of previously used physical cross-linking. The resulting nanoparticles of FA-GC-FU can target the overexpressed asialoglycoprotein receptors (ASGPRs) and folate receptors (FRs) on the surface of HCC cells, respectively, via the FA and lactobionic acid (LA) residues exposed on the surface of the NPs, leading to the maximized targeting efficiency of HCC and minimized nonspecific uptake by normal hepatocytes in vitro and in vivo. Therefore, this study not only developed a simple yet efficient strategy toward a facile fabrication of NPs with dual-targeting ligands but also presented a precise therapeutic platform for HCC with great potential for clinical translation.

Fine-tuning bispecific therapeutics

Bispecific therapeutics target two distinct antigens simultaneously and provide novel functionalities that are not attainable with single monospecific molecules or combinations of them. The unique potential of bispecific therapeutics is driving extensive efforts to discover synergistic dual targets, design molecular formats to integrate bispecific elements, and accelerate successful clinical translation. In particular, the past decade has witnessed a boom in the design and development of bispecific antibody formats with more than 100 collections to date. Despite the remarkable progress that has been made to expand the number of formats, qualitative fine-tuning of bispecific formats is needed to achieve optimal dual-target engagement based on understanding of the spatiotemporal interdependence of the two physically linked binding specificities and the complex target biology associated with bispecific approaches. This review provides insights into the design parameters - including affinity, valency, and geometry - that need to be considered at an early stage of development in order to take the best advantage of bispecific therapeutics.

Recent trends in protein and peptide-based biomaterials for advanced drug delivery

Engineering protein and peptide-based materials for drug delivery applications has gained momentum due to their biochemical and biophysical properties over synthetic materials, including biocompatibility, ease of synthesis and purification, tunability, scalability, and lack of toxicity. These biomolecules have been used to develop a host of drug delivery platforms, such as peptide- and protein-drug conjugates, injectable particles, and drug depots to deliver small molecule drugs, therapeutic proteins, and nucleic acids. In this review, we discuss progress in engineering the architecture and biological functions of peptide-based biomaterials -naturally derived, chemically synthesized and recombinant- with a focus on the molecular features that modulate their structure-function relationships for drug delivery.

Role of Surface RGD Patterns on Protein Nanocages in Tumor Targeting Revealed Using Precise Discrete Models

The effectiveness of active targeting in cancer nanomedicine is becoming increasingly more debatable. Here, the role of the ligand functionalization patterns (number and distribution) on nanoparticle surfaces in tumor targeting is investigated using a 9 nm sized miniferritin protein nanocage, Dps modified with Arg-Gly-Asp (RGD) ligands whose functionalization patterns are precisely controlled. In vitro and in vivo experiments show that RGD modification endows Dps with tumor targeting capacity no matter what the surface pattern is. The tumor targeting of 2-ligand Dps, which is better than that of 1-ligand Dps, rivals or surpasses that of the 12- or 24-ligand Dps. The 12-ligand Dps with clustered RGD distribution shows 2.3 times the in vivo targeting efficiency of that with even distribution. The surface ligand pattern effects are correlated at least to receptor clustering and opsonization. This study provides insights into the understanding of the controversial findings on active tumor targeting in the literature and highlights the necessity of precise functionalization to achieve optimal active targeting in developing cancer nanomedicine.

Multivalent nanoparticles for personalized theranostics based on tumor receptor distribution behavior

It is acknowledged that the targeting ability of multivalent ligand-modified nanoparticles (MLNs) strongly depends on the ligand spatial presentation determined by ligand valency. However, the receptor overexpression level varies between different types or stages of tumors. Thus, it is essential to explore the influence of ligand valency on the targeting ability of MLNs to tumors with different levels of receptor overexpression. In this study, a dual-acting agent raltitrexed was used as a ligand to target the folate receptor (FR). Different copies of the raltitrexed-modified multivalent dendritic polyethyleneimine ligand cluster PRn (n = 2, 4, and 8) were conjugated onto magnetic nanoparticles to form multivalent magnetic NPs (MMNs) with different valences. The in vitro studies demonstrated that Fe-PR4 was the most effective valency in the treatment of high FR overexpressing KB cells with a decentralized receptor distribution, owing to the fact that Fe-PR2 was negative in statistical rebinding and Fe-PR8 could induce steric hindrance in the limited binding area. Instead, in moderate FR overexpressing HeLa cells with clustered receptor display, the extra ligands on Fe-PR8 would facilitate statistical rebinding more beneficially. Furthermore, in in vivo tumor inhibition and targeted magnetic resonance imaging (MRI) of KB tumors and another moderate FR expressing H22 tumor, similar results were obtained with the cell experiments. Overall, the optimizable treatment effect of Fe-PRn by modulating the ligand valency based on the overexpressing tumor receptor distribution behavior supports the potential of Fe-PRn as a nanomedicine for personalized theranostics.

Investigation of the Internal Chemical Composition of Chitosan-Based LbL Films by Depth-Profiling X-ray Photoelectron Spectroscopy (XPS) Analysis

Chitosan-based thin films were assembled using the layer-by-layer technique, and the axial composition was accessed using X-ray photoelectron spectroscopy with depth profiling. Chitosan (CHI) samples possessing different degrees of acetylation ([Formula: see text]) and molecular weight ([Formula: see text]) produced via the ultrasound-assisted deacetylation reaction were used in this study along with two different polyanions, namely, sodium polystyrenesulfonate (PSS) and carboxymethylcellulose (CMC). When chitosan, a positively charged polymer in aqueous acid medium, was combined with a strong polyanion (PSS), the total positive charge of chitosan, directly related to its [Formula: see text], was the key factor affecting the film formation. However, for CMC/CHI films, the pH of the medium and [Formula: see text] of chitosan strongly affected the film structure and composition. Consequently, the structure and the axial composition of chitosan-based films can be finely adjusted by choosing the polyanion and defining the chitosan to be used according to its DA and [Formula: see text] for the desired application, as demonstrated by the antibacterial tests.