Quantum dots for tracking cellular transport of lectin-functionalized nanoparticles

Transepithelial transport of nanoparticles in oral drug delivery: From the perspective of surface and holistic property modulation

Despite the promising prospects of nanoparticles in oral drug delivery, the process of oral administration involves a complex transportation pathway that includes cellular uptake, intracellular trafficking, and exocytosis by intestinal epithelial cells, which are necessary steps for nanoparticles to enter the bloodstream and exert therapeutic effects. Current researchers have identified several crucial factors that regulate the interaction between nanoparticles and intestinal epithelial cells, including surface properties such as ligand modification, surface charge, hydrophilicity/hydrophobicity, intestinal protein corona formation, as well as holistic properties like particle size, shape, and rigidity. Understanding these properties is essential for enhancing transepithelial transport efficiency and designing effective oral drug delivery systems. Therefore, this review provides a comprehensive overview of the surface and holistic properties that influence the transepithelial transport of nanoparticles, elucidating the underlying principles governing their impact on transepithelial transport. The review also outlines the chosen of parameters to be considered for the subsequent design of oral drug delivery systems.

Mechanisms of Nanoparticle Transport across Intestinal Tissue: An Oral Delivery Perspective

Oral drug administration has been a popular choice due to patient compliance and limited clinical resources. Orally delivered drugs must circumvent the harsh gastrointestinal (GI) environment to effectively enter the systemic circulation. The GI tract has a number of structural and physiological barriers that limit drug bioavailability including mucus, the tightly regulated epithelial layer, immune cells, and associated vasculature. Nanoparticles have been used to enhance oral bioavailability of drugs, as they can act as a shield to the harsh GI environment and prevent early degradation while also increasing uptake and transport of drugs across the intestinal epithelium. Evidence suggests that different nanoparticle formulations may be transported via different intracellular mechanisms to cross the intestinal epithelium. Despite the existence of a significant body of work on intestinal transport of nanoparticles, many key questions remain: What causes the poor bioavailability of the oral drugs? What factors contribute to the ability of a nanoparticle to cross different intestinal barriers? Do nanoparticle properties such as size and charge influence the type of endocytic pathways taken? In this Review, we summarize the different components of intestinal barriers and the types of nanoparticles developed for oral delivery. In particular, we focus on the various intracellular pathways used in nanoparticle internalization and nanoparticle or cargo translocation across the epithelium. Understanding the gut barrier, nanoparticle characteristics, and transport pathways may lead to the development of more therapeutically useful nanoparticles as drug carriers.

New Perspective on Natural Plant Protein-Based Nanocarriers for Bioactive Ingredients Delivery

The health effects of bioactive substances in the human body are affected by several factors, including food processing conditions, storage conditions, light and heat, among others. These factors greatly limit the stability and bioavailability of bioactive substances. These problems can be solved by a novel protein-based nanocarrier technology, which has the excellent potential to enhance solubility, bioavailability, and the controlled release of bioactive substances. In addition, plant protein has the advantages of economy, environmental protection, and high nutrition compared to animal protein. In this review, the preparation, characterization, and application of plant protein-based nanocarriers are summarized. The research deficiency and future prospects of plant protein nanocarriers are emphasized.

Strategies for Delivering Nanoparticles across Tumor Blood Vessels

Nanoparticle transport across tumor blood vessels is a key step in nanoparticle delivery to solid tumors. However, the specific pathways and mechanisms of this nanoparticle delivery process are not fully understood. Here, the biological and physical characteristics of the tumor vasculature and the tumor microenvironment are explored and how these features affect nanoparticle transport across tumor blood vessels is discussed. The biological and physical methods to deliver nanoparticles into tumors are reviewed and paracellular and transcellular nanoparticle transport pathways are explored. Understanding the underlying pathways and mechanisms of nanoparticle tumor delivery will inform the engineering of safer and more effective nanomedicines for clinical translation.

Quantum Dot Labelling of Tepary Bean (Phaseolus acutifolius) Lectins by Microfluidics

Lectins are bioactive proteins with the ability to recognize cell membrane carbohydrates in a specific way. Diverse plant lectins have shown diagnostic and therapeutic potential against cancer, and their cytotoxicity against transformed cells is mediated through the induction of apoptosis. Previous works have determined the cytotoxic activity of a Tepary bean (Phaseolus acutifolius) lectin fraction (TBLF) and its anti-tumorigenic effect on colon cancer. In this work, lectins from the TBLF were additionally purified by ionic-exchange chromatography. Two peaks with agglutination activity were obtained: one of them was named TBL-IE2 and showed a single protein band in two-dimensional electrophoresis; this one was thus selected for coupling to quantum dot (QD) nanoparticles by microfluidics (TBL-IE2-QD). The microfluidic method led to low sample usage, and resulted in homogeneous complexes, whose visualization was achieved using multiphoton and transmission electron microscopy. The average particle size (380 nm) and the average zeta potential (-18.51 mV) were determined. The cytotoxicity of the TBL-IE2 and TBL-IE2-QD was assayed on HT-29 colon cancer cells, showing no differences between them (p ≤ 0.05), where the LC50 values were 1.0 × 10-3 and 1.7 × 10-3 mg/mL, respectively. The microfluidic technique allowed control of the coupling between the QD and the protein, substantially improving the labelling process, providing a rapid and efficient method that enabled the traceability of lectins. Future studies will focus on the potential use of the QD-labelled lectin to recognize tumor tissues.

Single-Virus Tracking: From Imaging Methodologies to Virological Applications

Uncovering the mechanisms of virus infection and assembly is crucial for preventing the spread of viruses and treating viral disease. The technique of single-virus tracking (SVT), also known as single-virus tracing, allows one to follow individual viruses at different parts of their life cycle and thereby provides dynamic insights into fundamental processes of viruses occurring in live cells. SVT is typically based on fluorescence imaging and reveals insights into previously unreported infection mechanisms. In this review article, we provide the readers a broad overview of the SVT technique. We first summarize recent advances in SVT, from the choice of fluorescent labels and labeling strategies to imaging implementation and analytical methodologies. We then describe representative applications in detail to elucidate how SVT serves as a valuable tool in virological research. Finally, we present our perspectives regarding the future possibilities and challenges of SVT.

Targeted photodynamic therapy of breast cancer cells using lactose-phthalocyanine functionalized gold nanoparticles

Gold nanoparticles (AuNPs), which have been widely used for the delivery of photosensitizers for photodynamic therapy (PDT) of cancer, can be dispersed in aqueous solutions improving the delivery of the hydrophobic photosensitizer into the body. Furthermore, the large surface of AuNPs can be functionalized with a variety of ligands, including proteins, nucleic acids and carbohydrates, that allow selective targeting to cancer tissue. In this study, gold nanoparticles were functionalized with a mixed monolayer of a zinc phthalocyanine and a lactose derivative. For the first time, a carbohydrate was used with a dual purpose, as the stabilizing agent of the gold nanoparticles in aqueous solutions and as the targeting agent for breast cancer cells. The functionalization of the phthalocyanine-AuNPs with lactose led to the production of water-dispersible nanoparticles that are able to generate singlet oxygen and effect cell death upon irradiation. The targeting ability of lactose of the lactose-phthalocyanine functionalized AuNPs was studied in vitro towards the galectin-1 receptor on the surface of breast cancer cells. The targeting studies showed the exciting potential of lactose as a specific targeting agent for galactose-binding receptors overexpressed on breast cancer cells.

Application of semiconductor quantum dots in bioimaging and biosensing

In this review we present new concepts and recent progress in the application of semiconductor quantum dots (QD) as labels in two important areas of biology, bioimaging and biosensing.

Dissecting the Factors Affecting the Fluorescence Stability of Quantum Dots in Live Cells

Labeling and imaging of live cells with quantum dots (QDs) has attracted great attention in the biomedical field over the past two decades. Maintenance of the fluorescence of QDs in a biological environment is crucial for performing long-term cell tracking to investigate the proliferation and functional evolution of cells. The cell-penetrating peptide transactivator of transcription (TAT) is a well-studied peptide to efficiently enhance the transmembrane delivery. Here, we used TAT peptide-conjugated QDs (TAT-QDs) as a model system to examine the fluorescence stability of QDs in live cells. By confocal microscopy, we found that TAT-QDs were internalized into cells by endocytosis, and transported into the cytoplasm via the mitochondria, Golgi apparatus, and lysosomes. More importantly, the fluorescence of TAT-QDs in live cells was decreased mainly by cell proliferation, and the low pH value in the lysosomes could also lower the fluorescence intensity of intracellular QDs. Quantitative analysis of the amount of QDs in the extracellular region and whole cells indicated that the exocytosis was not the primary cause of fluorescence decay of intracellular QDs. This work facilitates a better understanding of the fluorescence stability of QDs for cell imaging and long-term tracking in live cells. Also, it provides insights into the utility of TAT for transmembrane transportation, and the preparation and modification of QDs for cell imaging and tracking.

Nanoformulated alpha-mangostin ameliorates Alzheimer's disease neuropathology by elevating LDLR expression and accelerating amyloid-beta clearance

Alzheimer's disease (AD), the most common form of dementia, is now representing one of the largest global healthcare challenges. However, an effective therapy is still lacking. Accumulation of amyloid-beta (Aβ) in the brain is supposed to trigger pathogenic cascades that eventually lead to AD. Therefore, Aβ clearance strategy is being actively pursued as a promising disease modifying therapy. Here, we found that α-mangostin (α-M), a polyphenolic xanthone derivative from mangosteen, up-regulated low density lipoprotein receptor (LDLR) expression in microglia and liver cells, and efficiently facilitated Aβ clearance. However, the in vivo application of α-M is limited due to its hydrophobic nature, poor aqueous solubility and stability, and thus low bioavailability and accumulation in the target organs. To overcome this limitation, α-M was encapsulated into the core of poly(ethylene glycol)-poly(l-lactide) (PEG-PLA) nanoparticles [NP(α-M)]. Such nanoencapsulation improved the biodistribution of α-M in both the brain and liver, enhanced the brain clearance of (125)I-radiolabeled Aβ1-42 in an LDLR-dependent manner, reduced Aβ deposition, attenuated neuroinflammatory responses, ameliorated neurologic changes and reversed behavioral deficits in AD model mice. These findings justified the concept that polyphenol-mediated modulation of LDLR expression might serve as a safe and efficient disease-modifying therapy for AD by accelerating Aβ clearance. It also demonstrated the powerful capacity of nanotechnology in modulating the biodistribution behavior of drug to improve its therapeutic efficacy in AD.

Nanoparticle-assisted optical tethering of endosomes reveals the cooperative function of dyneins in retrograde axonal transport

Dynein-dependent transport of organelles from the axon terminals to the cell bodies is essential to the survival and function of neurons. However, quantitative knowledge of dyneins on axonal organelles and their collective function during this long-distance transport is lacking because current technologies to do such measurements are not applicable to neurons. Here, we report a new method termed nanoparticle-assisted optical tethering of endosomes (NOTE) that made it possible to study the cooperative mechanics of dyneins on retrograde axonal endosomes in live neurons. In this method, the opposing force from an elastic tether causes the endosomes to gradually stall under load and detach with a recoil velocity proportional to the dynein forces. These recoil velocities reveal that the axonal endosomes, despite their small size, can recruit up to 7 dyneins that function as independent mechanical units stochastically sharing load, which is vital for robust retrograde axonal transport. This study shows that NOTE, which relies on controlled generation of reactive oxygen species, is a viable method to manipulate small cellular cargos that are beyond the reach of current technology.

Studies of Highly-Ordered Heterodiantennary Mannose/Glucose-Functionalized Polymers and Concanavalin A Protein Interactions Using Isothermal Titration Calorimetry

Preparations of the highly ordered monoantennary, homofunctional diantennary, and heterofunctional diantennary neoglycopolymers of α-d-mannose and β-d-glucose residues were achieved via ring-opening metathesis polymerization. Isothermal titration calorimetry measurements of these synthetic neoglycopolymers with Concanavalin A (Con A), revealed that heterofunctional diantennary architectures bearing both α-mannose and nonbinding β-glucose units, poly(Man-Glc), binds to Con A (Ka = 16.1 × 10(6) M(-1)) comparably to homofunctional diantennary neoglycopolymer (Ka = 30 × 10(6) M(-1)) bearing only α-mannose unit, poly(Man-Man). In addition, poly(Man-Glc) neoglycopolymer shows a nearly 5-fold increasing in binding affinity compared to monoantennary neoglycopolymer, poly(Man). Although the exact mechanism for the high binding affinity of poly(Man-Glc) to Con A is unclear, we hypothesize that the α-mannose bound to Con A might facilitate interaction of β-glucose with the extended binding site of Con A due to the close proximity of β-glucose to α-mannose residues in the designed polymerizable scaffold.

Enhancing Glioblastoma-Specific Penetration by Functionalization of Nanoparticles with an Iron-Mimic Peptide Targeting Transferrin/Transferrin Receptor Complex

Treatment of glioblastoma (GBM) remains to be the most formidable challenge because of the hindrance of the blood-brain barrier (BBB) along with the poor drug penetration into the glioma parenchyma. Nanoparticulate drug delivery systems (DDS) utilizing transferrin (Tf) as the targeting ligand to target the glioma-associated transferrin receptor (TfR) had met the problem of loss of specificity in biological environment due to the high level of endogenous Tf. Here we conjugated CRT peptide, an iron-mimicry moiety targeting the whole complex of Tf/TfR, to poly(ethylene glycol)-poly(l-lactic-co-glycolic acid) nanoparticles (CRT-NP), to open a new route to overcome such obstacle. High cellular associations, advanced transport ability through the BBB model, and penetration in 3-dimensional C6 glioma spheroids in vitro had preliminarily proved the advantages of CRT-NP over Tf-nanoparticle conjugates (Tf-NP). Compared with Tf-NP, NP, and Taxol, paclitaxel-loaded CRT-NP (CRT-NP-PTX) displayed a superior antiproliferation effect on C6 glioma cells and stronger inhibitory effect on glioma spheroids. Favored pharmacokinetics behavior and enhanced accumulation in glioma foci was observed, together with a much deeper distribution pattern in glioma parenchyma compared with unmodified nanoparticles and Tf-NP. Eventually, mice treated with CRT-NP-PTX showed a remarkably prolonged median survival compared to those treated with Taxol, NP, or Tf-NP. In conclusion, the modification of CRT to nanoparticles holds great promise for enhancement of antiglioma therapy.

Quantum dots: bright and versatile in vitro and in vivo fluorescence imaging biosensors

Colourful cells and tissues: semiconductor quantum dots and their versatile applications in multiplexed bioimaging research.

Antitumor effect of iRGD-modified liposomes containing conjugated linoleic acid-paclitaxel (CLA-PTX) on B16-F10 melanoma

In the present study, we prepared a novel delivery system of iRGD (CRGDK/RGPD/EC)-modified sterically stabilized liposomes (SSLs) containing conjugated linoleic acid–paclitaxel (CLA-PTX). The anti-tumor effect of iRGD-SSL-CLA-PTX was investigated on B16-F10 melanoma in vitro and in vivo. The in vitro targeting effect of iRGD-modified SSLs was investigated in a real-time confocal microscopic analysis experiment. An endocytosis-inhibition assay was used to evaluate the endocytosis pathways of the iRGD-modified SSLs. In addition, the in vitro cellular uptake and in vitro cytotoxicity of iRGD-SSL-CLA-PTX were evaluated in B16-F10 melanoma cells. In vivo biodistribution and in vivo antitumor effects of iRGD-SSL-CLA-PTX were investigated in B16-F10 tumor-bearing mice. The induction of apoptosis by iRGD-SSL-CLA-PTX was evaluated in tumor-tissue sections. Real-time confocal microscopic analysis results indicated that the iRGD-modified SSLs internalized into B16-F10 cells faster than SSLs. The identified endocytosis pathway of iRGD-modified SSLs indicated that energy- and lipid raft-mediated endocytosis played a key role in the liposomes’ cellular uptake. The results of the cellular uptake experiment indicated that the increased cellular uptake of CLA-PTX in the iRGD-SSL-CLA-PTX-treated group was 1.9-, 2.4-, or 2.1-fold compared with that in the CLA-PTX group after a 2-, 4-, or 6-hour incubation, respectively. In the biodistribution test, the CLA-PTX level in tumor tissues from iRGD-SSL-CLA-PTX-treated mice at 1 hour (1.84±0.17 μg/g) and 4 hours (1.17±0.28 μg/g) was 2.3- and 2.0-fold higher than that of CLA-PTX solution at 1 hour (0.79±0.06 μg/g) and 4 hours (0.58±0.04 μg/g). The value of the area under the curve for the first 24 hours in the tumors of iRGD-SSL-CLA-PTX-treated mice was significantly higher than that in the SSL-CLA-PTX and CLA-PTX solution-treated groups (P<0.01). The in vivo antitumor results indicated that iRGD-SSL-CLA-PTX significantly inhibited the growth of B16-F10 tumors compared with the SSL-CLA-PTX or CLA-PTX solution-treatment groups (P<0.01). The results of tumor-cell apoptosis showed that tumors from the iRGD-SSL-CLA-PTX-treated group exhibited more advanced cell apoptosis compared with the control, CLA-PTX solution-, and SSL-CLA-PTX-treated groups. In conclusion, the antitumor effect of iRGD-SSL-CLA-PTX was confirmed on B16-F10 melanoma in vitro and in vivo.

Nanoparticles for oral delivery: targeted nanoparticles with peptidic ligands for oral protein delivery

As the field of biotechnology has advanced, oral protein delivery has also made significant progress. Oral delivery is the most common method of drug administration with high levels of patient acceptance. Despite the preference of oral delivery, administration of therapeutic proteins has been extremely difficult. Increasing the bioavailability of oral protein drugs to the therapeutically acceptable level is still a challenging goal. Poor membrane permeability, high molecular weight, and enzymatic degradation of protein drugs have remained unsolved issues. Among diverse strategies, nanotechnology has provided a glimpse of hope in oral delivery of protein drugs. Nanoparticles have advantages, such as small size, high surface area, and modification using functional groups for high capacity or selectivity. Nanoparticles with peptidic ligands are especially worthy of notice because they can be used for specific targeting in the gastrointestinal (GI) tract. This article reviews the transport mechanism of the GI tract, barriers to protein absorption, current status and limitations of nanotechnology for oral protein delivery system.

Temporal techniques: dynamic tracking of nanomaterials in live cells

Temporal analytical techniques to track nanoparticles in live cell would provide rich information to well understand the biologic properties of nanoparticles in molecular level. Significant advances in fluorescence microscopy techniques with high temporal and spatial resolution allow single nanoparticles to label biomolecules, ions, and microstructures in live cells, which will address many fundamental questions in cell biology. This review highlights the real time tracking techniques for monitoring the movement of nanomaterials such as carbon nanotubes (CNTs), quantum dots (QDs), metal clusters, upconver-sional nanomaterials, and polystyrene (PS) nanoparticles etc. in live cells. The biological properties of nanoparticles in live cells are also briefly summarized according to fluorescence microscopy studies.

Glycopolymer probes of signal transduction

Glycans are key participants in biological processes ranging from reproduction to cellular communication to infection. Revealing glycan roles and the underlying molecular mechanisms by which glycans manifest their function requires access to glycan derivatives that vary systematically. To this end, glycopolymers (polymers bearing pendant carbohydrates) have emerged as valuable glycan analogs. Because glycopolymers can readily be synthesized, their overall shape can be varied, and they can be altered systematically to dissect the structural features that underpin their activities. This review provides examples in which glycopolymers have been used to effect carbohydrate-mediated signal transduction. Our objective is to illustrate how these powerful tools can reveal the molecular mechanisms that underlie carbohydrate-mediated signal transduction.

Lactoferrin-modified PEG-co-PCL nanoparticles for enhanced brain delivery of NAP peptide following intranasal administration

Development of effective non-invasive drug delivery systems is of great importance to the treatment of Alzheimer's diseases and has made great progress in recent years. In this work, lactoferrin (Lf), a natural iron binding protein, whose receptor is highly expressed in both respiratory epithelial cells and neurons is here utilized to facilitate the nose-to-brain drug delivery of neuroprotection peptides. The Lf-conjugated PEG-PCL nanoparticle (Lf-NP) was constructed via a maleimide-thiol reaction with the Lf conjugation confirmed by CBQCA Protein Quantitation and XPS analysis. Other important parameters such as particle size distribution, zeta potential and in vitro release of fluorescent probes were also characterized. Compared with unmodified nanoparticles (NP), Lf-NP exhibited a significantly enhanced cellular accumulation in 16HBE14o-cells through both caveolae-/clathrin-mediated endocytosis and direct translocation. Following intranasal administration, Lf-NP facilitated the brain distribution of the coumarin-6 incorporated with the AUC0-8h in rat cerebrum (with hippocampus removed), cerebellum, olfactory tract, olfactory bulb and hippocampus 1.36, 1.53, 1.70, 1.57 and 1.23 times higher than that of coumarin-6 carried by NP, respectively. Using a neuroprotective peptide - NAPVSIPQ (NAP) as the model drug, the neuroprotective and memory improvement effect of Lf-NP was observed even at lower dose than that of NP in a Morris water maze experiment, which was also confirmed by the evaluation of acetylcholinesterase, choline acetyltransferase activity and neuronal degeneration in the mice hippocampus. In conclusion, Lf-NP may serve as a promising nose-to-brain drug delivery carrier especially for peptides and proteins.

Lipid-based liquid crystalline nanoparticles as oral drug delivery vehicles for poorly water-soluble drugs: cellular interaction and in vivo absorption

Background

Lipid-based liquid crystalline nanoparticles (LCNPs) have attracted growing interest as novel drug-delivery systems for improving the bioavailability of both hydrophilic and hydrophobic drugs. However, their cellular interaction and in vivo behavior have not been fully developed and characterized.

Methods

In this study, self-assembled LCNPs prepared from soy phosphatidylcholine and glycerol dioleate were developed as a platform for oral delivery of paclitaxel. The particle size of empty LCNPs and paclitaxel-loaded LCNPs was around 80 nm. The phase behavior of the liquid crystalline matrix was characterized using crossed polarized light microscopy and small-angle X-ray scattering, and showed both reversed cubic and hexagonal phase in the liquid crystalline matrix. Transmission electron microscopy and cryofield emission scanning electron microscopy analysis revealed an inner winding water channel in LCNPs and a “ ball-like”/“hexagonal” morphology.

Results

Cellular uptake of LCNPs in Caco-2 cells was found to be concentration-dependent and time-dependent, with involvement of both clathrin and caveolae/lipid raft-mediated endocytosis. Under confocal laser scanning microscopy, soy phosphatidylcholine was observed to segregate from the internalized LCNPs and to fuse with the cell membrane. An in vivo pharmacokinetic study showed that the oral bioavailability of paclitaxel-loaded LCNPs (13.16%) was 2.1 times that of Taxol^® (the commercial formulation of paclitaxel, 6.39%).

Conclusion

The findings of this study suggest that this LCNP delivery system may be a promising candidate for improving the oral bioavailability of poorly water-soluble agents.

Photothermal imaging and measurement of protein shell stoichiometry of single HIV-1 Gag virus-like nanoparticles

Virus life stages often constitute a complex chain of events, difficult to track in vivo and in real-time. Challenges are associated with spatial and time limitations of current probes: most viruses are smaller than the diffraction limit of optical microscopes while the entire time scale of virus dynamics spans over 8 orders of magnitude. Thus, virus processes such as entry, disassembly, and egress have generally remained poorly understood. Here we discuss photothermal heterodyne imaging (PHI) as a possible alternative to fluorescence microscopy in the study of single virus-like nanoparticle (VNP) dynamics, with relevance in particular to virus uncoating. Being based on optical absorption rather than emission, PHI could potentially surpass some of the current limitations associated with fluorescent labels. As proof-of-principle, single VNPs self-assembled from 60 nm DNA-functionalized gold nanoparticles (DNA-Au NPs) encapsulated in a Gag protein shell of the human immunodeficiency virus (HIV-1) were imaged, and their photothermal response was compared with DNA-Au NPs. For the first time, the protein stoichiometry of a single virus-like particle was estimated by a method other than electron microscopy.

Low molecular weight protamine-functionalized nanoparticles for drug delivery to the brain after intranasal administration

The development of new strategies for enhancing drug delivery to the brain is of great importance in diagnostics and therapeutics of central nervous diseases. Low-molecular-weight protamine (LMWP) as a cell-penetrating peptide possesses distinct advantages including high cell translocation potency, absence of toxicity of peptide itself, and the feasibility as an efficient carrier for delivering therapeutics. Therefore, it was hypothesized that brain delivery of nanoparticles conjugated with LMWP should be efficiently enhanced following intranasal administration. LMWP was functionalized to the surface of PEG-PLA nanoparticles (NP) via a maleimide-mediated covalent binding procedure. Important parameters such as particle size distribution, zeta potential and surface content were determined, which confirmed the conjugation of LMWP to the surface of nanoparticle. Using 16HBE14o- cells as the cell model, LMWP-NP was found to exhibit significantly enhanced cellular accumulation than that of unmodified NP via both lipid raft-mediated endocytosis and direct translocation processes without causing observable cytotoxic effects. Following intranasal administration of coumarin-6-loaded LMWP-NP, the AUC(0-8 h) of the fluorescent probe detected in the rat cerebrum, cerebellum, olfactory tract and olfactory bulb was found to be 2.03, 2.55, 2.68 and 2.82 folds, respectively, compared to that of coumarin carried by NP. Brain distribution analysis suggested LMWP-NP after intranasal administration could be delivered to the central nervous system along both the olfactory and trigeminal nerves pathways. The findings clearly indicated that the brain delivery of nanoparticles could be greatly facilitated by LMWP and the LMWP-functionalized nanoparticles appears as a effective and safe carrier for nose-to-brain drug delivery in potential diagnostic and therapeutic applications.

Aptamer-functionalized PEG-PLGA nanoparticles for enhanced anti-glioma drug delivery

Targeted delivery of therapeutic nanoparticles in a disease-specific manner represents a potentially powerful technology especially when treating infiltrative brain tumors such as gliomas. We developed a nanoparticulate drug delivery system decorated with AS1411 (Ap), a DNA aptamer specifically binding to nucleolin which was highly expressed in the plasma membrane of both cancer cells and endothelial cells in angiogenic blood vessels, as the targeting ligand to facilitate anti-glioma delivery of paclitaxel (PTX). Ap was conjugated to the surface of PEG-PLGA nanoparticles (NP) via an EDC/NHS technique. With the conjugation confirmed by Urea PAGE and XPS, the resulting Ap-PTX-NP was uniformly round with particle size at 156.0 ± 54.8 nm and zeta potential at -32.93 ± 3.1 mV. Ap-nucleolin interaction significantly enhanced cellular association of nanoparticles in C6 glioma cells, and increased the cytotoxicity of its payload. Prolonged circulation and enhanced PTX accumulation at the tumor site was achieved for Ap-PTX-NP, which eventually obtained significantly higher tumor inhibition on mice bearing C6 glioma xenografts and prolonged animal survival on rats bearing intracranial C6 gliomas when compared with PTX-NP and Taxol(®). The results of this contribution demonstrated the potential utility of AS1411-functionalized nanoparticles for a therapeutic application in the treatment of gliomas.

The mechanism of enhancement on oral absorption of paclitaxel by N-octyl-O-sulfate chitosan micelles

The overall objective of the present investigation was to demonstrate the effect of N-octyl-O-sulfate chitosan (NOSC) micelles on enhancing the oral absorption of paclitaxel (PTX) in vivo and in vitro, and identify the mechanism of this action of NOSC. In vivo, the oral bioavailability of PTX loaded in NOSC micelles (PTX-M) was 6-fold improved in comparison with that of an orally dosed Taxol(®). In the Caco-2 uptake studies, NOSC micelles brought about a significantly higher amount of PTX accumulated in Caco-2 cells via both clathrin- and caveolae-mediated endocytosis, and NOSC had the effect on inhibiting PTX secreted by P-glycoprotein (P-gp), which was also proved by the studies on rhodamine 123 incorporated in NOSC micelles, fluorescence labeled micelles. The mechanism of NOSC on P-gp inhibition was demonstrated in connection with interfering the P-gp ATPase by NOSC rather than reducing the P-gp expression. Moreover, NOSC with the concentration approaching the critical micellar concentration (CMC) had the strongest effect on P-gp inhibition. In the Caco-2 transport studies, the presence of verapamil and NOSC both improved the transport of Taxol(®), which further certified the effect of NOSC on P-gp inhibition, and PTX-M enhanced the permeability of PTX compared with Taxol(®). The apparent permeability coefficient (Papp) of PTX-M decreased significantly at 4 °C in comparison with at 37 °C, which indicated a predominant active endocytic mechanism for the transport of PTX-M, a P-gp-independent way. Furthermore, the transcytosis of PTX-M was via clathrin-mediated rather than caveolae-mediated. In addition, the transepithelial electrical resistance (TEER) of Caco-2 cell monolayers had no significant change during the transport study, which pointed out that NOSC had no effect on opening the intercellular tight junctions. Based on the obtained results, it is suggested that NOSC micelles might be a potentially applicable tool for enhancing the oral absorption of P-gp substrates.

Morniga G: a plant lectin as an endocytic ligand for photosensitizer molecule targeting toward tumor-associated T/Tn antigens

Porphyrins are used as photosensitizer (PS) in photodynamic therapy in cancer treatment. Nevertheless, the development of photochemotherapy in oncology remains limited, because of the low selectivity of PSs. In order to allow PS targeting toward tumor-associated antigens, for the first time a white-light activatable porphyrin, [5-(4-(5-carboxy-1-butoxy)-phenyl)-10,15,20-tris(4-N-methyl)-pyridiniumyl)-porphyrin] (TrMPyP) was covalently linked to Morniga G (MorG), a galactose-specific binding plant lectin, known to recognize with high-affinity tumor-associated T/Tn antigen in cell-free systems. Firstly, using fluorescein-labeled MorG, the sugar-dependent binding and uptake of lectin by Tn-positive (Jurkat lymphoid leukemia) cells was demonstrated. Secondly, the TrMPyP-MorG conjugate was molecularly characterized. Cytometric and confocal microscopic analysis demonstrated that PS covalent linking to MorG preserved sugar-dependent specific binding and uptake of lectin by Jurkat leukemia lymphocytes. Thirdly, the conjugate (with a 1:1 PS:lectin ratio) that was bound and quickly (5 min) taken-up, induced greater than 90% cytotoxicity upon irradiation at 10 nm concentration, whereas the free PS was absolutely nontoxic. On the contrary, normal lymphocytes strongly resisted to the conjugate-mediated phototoxicity. Thus, owing to their binding and endocytosis capacities, plant lectins represent promising molecules for targeting of tumor glycan alteration and to enhance the efficiency of specific delivery of PSs to tumor cells.

Gateways for the intracellular access of nanocarriers: a review of receptor-mediated endocytosis mechanisms and of strategies in receptor targeting

IMPORTANCE OF THE FIELD

The last 10 years have seen a dramatic growth in understanding and controlling how complex, drug-loaded (nano)structures, as well as pathogens, or biopharmaceuticals can gather access to the cytoplasm, which is a key step to increasing the effectiveness of their action.

AREAS COVERED IN THIS REVIEW

The review offers an updated overview of the current knowledge of endocytic processes; furthermore, the cell surface receptors most commonly used in drug delivery are here discussed on the basis of their reported internalization mechanisms, with examples of their use as nanocarrier targets taken from the most recent scientific literature.

WHAT THE READER WILL GAIN

Knowledge of molecular biology details is increasingly necessary for a rational design of drug delivery systems. Here, the aim is to provide the reader with an attempt to link a mechanistic knowledge of endocytic mechanisms with the identification of appropriate targets (internalization receptors) for nanocarriers.

TAKE HOME MESSAGE

Much advance is still needed to create a complete and coherent biological picture of endocytosis, but current knowledge already allows individuation of a good number of targetable groups for a predetermined intracellular fate of nanocarriers.