Targeting receptor-mediated endocytotic pathways with nanoparticles: rationale and advances

Synthetic polynucleotides as endosomolytic agents and bioenergy sources

Nucleotides (NTs), such as adenosine triphosphate (ATP) and guanosine triphosphate (GTP), are signaling and bioenergy molecules to mediate a range of cellular pathways. We recently reported their significant endosomolytic activity. To evaluate whether polymeric NTs keep endosomolytic and bioenergetic functions of NTs in drug delivery and cell survival, NTs were polymerized by a coupling reaction to form polynucleotides (pNTs: pATP and pGTP) with their molecular weights around 500kDa. The cellular toxicity, indicated by IC50, of pNT was as low as that of corresponding monomeric NT. pNTs were degraded by an intracellular enzyme, alkaline phosphatase. Introduction of pNTs in a polycation-gene complex (polyplex) enhanced the extent of gene expression in cancerous, non-cancerous, and stem cells, up to 1500-fold higher than that of pNT-free polyplex. In addition, cells stored in a pATP solution resulted in a significantly higher survival rate (e.g., up to 20% increase) when exposed to low temperatures than pATP-free solution. The presence of pNT in polyplexes prevented the reduction of transfection efficiency induced by a low temperature. The findings in this study suggest that endosomolytic and bioenergetic pNTs serve as a non-toxic gene carrier component and protect cells from a cold shock or energy depletion.

Hyperthermia approaches for enhanced delivery of nanomedicines to solid tumors

Drug delivery to solid tumors has received much attention in order to reduce harmful side effects and improve the efficacy of treatment. Different strategies have been utilized with nanoparticle drug delivery systems, or nanomedicines, including passive and active targeting strategies, as well as the incorporation of stimuli sensitivity. Additionally, hyperthermia has been used in combination with such systems to further improve accumulation, localization, penetration, and subsequently efficacy. Localized hyperthermia within the solid tumor tissue can be applied through different mechanisms able to trigger vascular and cellular mechanisms for enhanced delivery of nanomedicines. This review covers the use of nanoparticles in drug delivery, the different methods for inducing localized hyperthermia, combination effects of hyperthermia, and successful strategies for improving the delivery of nanomedicines using hyperthermia.

In vivo pharmacokinetics, biodistribution and antitumor effect of paclitaxel-loaded micelles based on α-tocopherol succinate-modified chitosan

In our previous study, α-tocopherol succinate modified chitosan (CS-TOS) was synthesized and encapsulated paclitaxel (PTX) to form micelles. Preliminary study revealed that the CS-TOS was a potential micellar carrier for PTX. In this study, some further researches were done using Taxol formulation as the control to evaluate the micelle system deeply. In vitro cell experiments demonstrated that the cytotoxic effect of PTX-loaded CS-TOS micelles against MCF-7 cells was comparable with that of Taxol formulation, and the PTX-loaded micelles had excellent cellular uptake ability, which was in a time-dependent manner. The in vivo pharmacokinetic study in rats showed that the micelles prolonged the half-life and increased AUC of PTX than Taxol formulation. From biodistribution study, it was clear that for micelles, the drug concentrations in the liver and spleen were significantly higher than those of Taxol formulation, but much lower in the heart and kidney. Furthermore, the PTX-loaded micelles showed superior antitumor effect, but yielded less toxicity as indicated by the results of antitumor efficacy study and survival study in U14 tumor-bearing mice. These results suggested that CS-TOS micelles could be a potentially useful drug delivery system to improve the performance and safety of PTX.

Cellular uptake and intracellular trafficking of oligonucleotides

Oligonucleotides manifest much promise as potential therapeutic agents. However, understanding of how oligonucleotides function within living organisms is still rather limited. A major concern in this regard is the mechanisms of cellular uptake and intracellular trafficking of both 'free' oligonucleotides and oligonucleotides associated with various polymeric or nanocarrier delivery systems. Here we review basic aspects of the mechanisms of endocytosis and intracellular trafficking and how insights from these processes can be used to understand oligonucleotide delivery. In particular we discuss opportunities for escape of oligonucleotides from endomembrane compartments and describe recent studies using small molecules to enhance oligonucleotide effects.

Internalization, Trafficking, Intracellular Processing and Actions of Antibody-Drug Conjugates

PURPOSE

This review discusses the molecular mechanism involved in the targeting and delivery of antibody-drug conjugates (ADCs), the new class of biopharmaceuticals mainly designed for targeted cancer therapy.

METHODS

this review goes over major progress in preclinical and clinical studies of ADCs, in the past 5 years.

RESULTS

The pharmacokinetics and pharmacodynamics of ADCs involve multiple mechanisms, including internalization of ADCs by target cells, intracellular trafficking, release of conjugated drugs, and payload.

CONCLUSION

These mechanisms actually jointly determine the efficacy of ADCs. Therefore, the optimization of ADCs should take them as necessary rationales.

Significantly enhanced bioavailability of niclosamide through submicron lipid emulsions with or without PEG-lipid: a comparative study

Niclosamide (NL) has demonstrated its great potential in fighting against leukaemia recently. However, either oral or systemic delivery of NL is challenged by its insoluble nature. Here, we developed two different NL-loaded submicron lipid emulsions (NL-SLEs) and compared their suitability in bioavailability enhancement. Conventional and PEGylated NL-SLEs (NL-CSLEs and NL-PSLEs) were prepared by melt dispersion/high pressure homogenisation technique. They were about 307.8 and 162.2 nm in particle size, respectively, and both of them possessed satisfactory stability and drug load (>9.0%). After oral administration, significantly enhanced bioavailability was achieved through NL-CSLEs and NL-PSLEs (441.11 and 463.55% relative to the reference). Apart from global size, NL-CSLEs and NL-PSLEs exhibited similar attributes in release, lipolysis, mucin binding, etc. Taken together, SLEs with or without PEG-lipid have shown to be promising for oral delivery of NL. PEG-lipid could significantly reduce the particle size of SLEs. But, macromolecular PEG-lipid was required to effectively stealth the lipid carriers.

Learning from biology: synthetic lipoproteins for drug delivery

Synthetic lipoproteins represent a relevant tool for targeted delivery of biological/chemical agents (chemotherapeutics, siRNAs, photosensitizers, and imaging contrast agents) into various cell types. These nanoparticles offer a number of advantages for drugs delivery over their native counterparts while retaining their natural characteristics and biological functions. Their ultra-small size (<30 nm), high biocompatibility, favorable circulation half-life, and natural ability to bind specific lipoprotein receptors, i.e., low-density lipoprotein receptor (LDLR) and Scavenger receptor class B member 1 (SRB1) that are found in a number of pathological conditions (e.g., cancer, atherosclerosis), make them superior delivery strategies when compared with other nanoparticle systems. We review the various approaches that have been developed for the generation of synthetic lipoproteins and their respective applications in vitro and in vivo. More specifically, we summarize the approaches employed to address the limitation on use of reconstituted lipoproteins by means of natural or recombinant apolipoproteins, as well as apolipoprotein mimetic molecules. Finally, we provide an overview of the advantages and disadvantages of these approaches and discuss future perspectives for clinical translation of these nanoparticles.

Aptamer-conjugated polymeric nanoparticles for the detection of cancer cells through "turn-on" retro-self-quenched fluorescence

We have developed a simple, sensitive, and rapid fluorescence assay for the detection of cancer cells, based on "turn-on" retro-self-quenched fluorescence inside the cells. 1,3-Phenylenediamine resin (DAR) nanoparticles (NPs) containing rhodamine 6G (R6G) are conjugated with aptamer (apt) sgc8c to prepare sgc8c-R6GDAR NPs, while that containing rhodamine 101 (R101) are conjugated with TD05 for the preparation of TD05-R101DAR NPs. The sgc8c-R6GDAR and TD05-R101DAR NPs separately recognize CCRF-CEM and Ramos cells. The fluorescence intensities of the two apt-DAR NPs are both weak due to self-quenching, but they increase inside the cells as a result of release of the fluorophores from the apt-DAR NPs. The apt-DAR NPs' structure becomes less compact at low pH value, leading to the release of the fluorophores. The sgc8c-R6GDAR and TD05-R101DAR NPs allow detection of as low as 44 CCRF-CEM cells and 79 Ramos cells mL(-1), respectively, using a commercial reader within 10 min. Practicality of the two probes have been validated by the quantitation and identification of CCRF-CEM and Ramos cells spiked in blood samples through conventional fluorescence and flow cytometry analysis, with advantages of sensitivity, selectivity, and rapidity.

Dual-responsive mPEG-PLGA-PGlu hybrid-core nanoparticles with a high drug loading to reverse the multidrug resistance of breast cancer: an in vitro and in vivo evaluation

In this study, monomethoxy (polyethylene glycol)-b-P (d,l-lactic-co-glycolic acid)-b-P (l-glutamic acid) (mPEG-PLGA-PGlu) nanoparticles with the ability to rapidly respond to the endolysosomal pH and hydrolase were prepared and the pH-sensitivity was tuned by adjusting the length of the PGlu segment. The mPEG5k-PLGA20k-PGlu (60) nanoparticles were specifically responsive to an endosomal pH of 5.0-6.0 due to the configuration transition of the PGlu segment and rapidly initiated chemical degradation after incubation with proteinase k for 10 min. Doxorubicin hydrochloride (DOX), used as a model drug, was easily encapsulated into nanoparticles and the DOX-loaded nanoparticles (DOX-NPs) exhibited a pH-dependent and enzyme-sensitive release profile in vitro. The dual sensitivity enabled the rapid escape of DOX-loaded nanoparticles from the endolysosomal system to target cellular nuclei, which resulted in increased cell toxicity against MCF/ADR resistant breast cancer cells and a higher cellular uptake than free DOX. In Vivo Imaging studies indicated that the nanoparticles could continuously accumulate in the tumor tissues through EPR effects and Ex vivo Imaging biodistribution studies indicated that DOX-NPs increased drug penetration into tumors compared with normal tissues. The in vivo antitumor activity demonstrated that DOX-loaded NPs had less body loss and a significant regression of tumor growth, indicating the increased anti-tumor efficacy and lower systemic toxicity. Therefore, this dual sensitive nanoparticle system may be a potential nanocarrier to overcome the multidrug resistance exhibited by breast cancer.

Elucidating the in vivo fate of nanocrystals using a physiologically based pharmacokinetic model: a case study with the anticancer agent SNX-2112

Introduction

SNX-2112 is a promising anticancer agent but has poor solubility in both water and oil. In the study reported here, we aimed to develop a nanocrystal formulation for SNX-2112 and to determine the pharmacokinetic behaviors of the prepared nanocrystals.

Methods

Nanocrystals of SNX-2112 were prepared using the wet-media milling technique and characterized by particle size, differential scanning calorimetry, drug release, etc. Physiologically based pharmacokinetic (PBPK) modeling was undertaken to evaluate the drug’s disposition in rats following administration of drug cosolvent or nanocrystals.

Results

The optimized SNX-2112 nanocrystals (with poloxamer 188 as the stabilizer) were 203 nm in size with a zeta potential of −11.6 mV. In addition, the nanocrystals showed a comparable release profile to the control (drug cosolvent). Further, the rat PBPK model incorporating the parameters of particulate uptake (into the liver and spleen) and of in vivo drug release was well fitted to the experimental data following administration of the drug nanocrystals. The results reveal that the nanocrystals rapidly released drug molecules in vivo, accounting for their cosolvent-like pharmacokinetic behaviors. Due to particulate uptake, drug accumulation in the liver and spleen was significant at the initial time points (within 1 hour).

Conclusion

The nanocrystals should be a good choice for the systemic delivery of the poorly soluble drug SNX-2112. Also, our study contributes to an improved understanding of the in vivo fate of nanocrystals.

Parameters and characteristics governing cellular internalization and trans-barrier trafficking of nanostructures

Cellular internalization and trans-barrier transport of nanoparticles can be manipulated on the basis of the physicochemical and mechanical characteristics of nanoparticles. Research has shown that these factors significantly influence the uptake of nanoparticles. Dictating these characteristics allows for the control of the rate and extent of cellular uptake, as well as delivering the drug-loaded nanosystem intra-cellularly, which is imperative for drugs that require a specific cellular level to exert their effects. Additionally, physicochemical characteristics of the nanoparticles should be optimal for the nanosystem to bypass the natural restricting phenomena of the body and act therapeutically at the targeted site. The factors at the focal point of emerging smart nanomedicines include nanoparticle size, surface charge, shape, hydrophobicity, surface chemistry, and even protein and ligand conjugates. Hence, this review discusses the mechanism of internalization of nanoparticles and ideal nanoparticle characteristics that allow them to evade the biological barriers in order to achieve optimal cellular uptake in different organ systems. Identifying these parameters assists with the progression of nanomedicine as an outstanding vector of pharmaceuticals.

Experimental and theoretical investigations in stimuli responsive dendrimer-based assemblies

Stimuli-responsive macromolecular assemblies are of great interest in drug delivery applications, as it holds the promise to keep the drug molecules sequestered under one set of conditions and release them under another. The former set of conditions could represent circulation, while the latter could represent a disease location. Over the past two decades, sizeable contributions to this field have come from dendrimers, which along with their monodispersity, provide great scope for structural modifications at the molecular level. In this paper, we briefly discuss the various synthetic strategies that have been developed so far to obtain a range of functional dendrimers. We then discuss the design strategies utilized to introduce stimuli responsive elements within the dendritic architecture. The stimuli itself are broadly classified into two categories, viz. extrinsic and intrinsic. Extrinsic stimuli are externally induced such as temperature and light variations, while intrinsic stimuli involve physiological aberrations such as variations in pH, redox conditions, proteins and enzyme concentrations in pathological tissues. Furthermore, the unique support from molecular dynamics (MD) simulations has been highlighted. MD simulations have helped back many of the observations made from assembly formation properties to rationalized the mechanism of drug release and this has been illustrated with discussions on G4 PPI (Poly propylene imine) dendrimers and biaryl facially amphiphilic dendrimers. The synergy that exists between experimental and theoretical studies open new avenues for the use of dendrimers as versatile drug delivery systems.

Controlled Drug Release from Pharmaceutical Nanocarriers

Nanocarriers providing spatiotemporal control of drug release contribute to reducing toxicity and improving therapeutic efficacy of a drug. On the other hand, nanocarriers face unique challenges in controlling drug release kinetics, due to the large surface area per volume ratio and the short diffusion distance. To develop nanocarriers with desirable release kinetics for target applications, it is important to understand the mechanisms by which a carrier retains and releases a drug, the effects of composition and morphology of the carrier on the drug release kinetics, and current techniques for preparation and modification of nanocarriers. This review provides an overview of drug release mechanisms and various nanocarriers with a specific emphasis on approaches to control the drug release kinetics.

Efficient nuclear drug translocation and improved drug efficacy mediated by acidity-responsive boronate-linked dextran/cholesterol nanoassembly

The present study reported a lysosome-acidity-targeting bio-responsive nanovehicle self-assembled from dextran (Dex) and phenylboronic acid modified cholesterol (Chol-PBA), aiming at the nucleus-tropic drug delivery. The prominent advantage of this assembled nanoconstruction arose from its susceptibility to acidity-labile dissociation concurrently accompanied with the fast liberation of encapsulated drugs, leading to efficient nuclear drug translocation and consequently favorable drug efficacy. By elaborately exploiting NH4Cl pretreatment to interfere with the cellular endosomal acidification progression, this study clearly evidenced at a cellular level the strong lysosomal-acidity dependency of nuclear drug uptake efficiency, which was shown to be the main factor influencing the drug efficacy. The boronate-linked nanoassembly displayed nearly no cytotoxicity and can remain structural stability under the simulated physiological conditions including 10% serum and the normal blood sugar concentration. The cellular exposure to cholesterol was found to bate the cellular uptake of nanoassembly in a dose-dependent manner, suggesting a cholesterol-associated mechanism of the intracellular internalization. The in vivo antitumor assessment in xenograft mouse models revealed the significant superiority of DOX-loaded Dex/Chol-PBA nanoassembly over the controls including free DOX and the DOX-loaded non-sensitive Dex-Chol, as reflected by the more effective tumor-growth inhibition and the better systematic safety. In terms of the convenient preparation, sensitive response to lysosomal acidity and efficient nuclear drug translocation, Dex/Chol-PBA nanoassembly derived from natural materials shows promising potentials as the nanovehicle for nucleus-tropic drug delivery especially for antitumor agents. More attractively, this study offers a deeper insight into the mechanism concerning the contribution of acidity-responsive delivery to the enhanced chemotherapy performance.

Particle-based optical sensing of intracellular ions at the example of calcium - what are the experimental pitfalls?

Colloidal particles with fluorescence read-out are commonly used as sensors for the quantitative determination of ions. Calcium, for example, is a biologically highly relevant ion in signaling, and thus knowledge of its spatio-temporal distribution inside cells would offer important experimental data. However, the use of particle-based intracellular sensors for ion detection is not straightforward. Important associated problems involve delivery and intracellular location of particle-based fluorophores, crosstalk of the fluorescence read-out with pH, and spectral overlap of the emission spectra of different fluorophores. These potential problems are outlined and discussed here with selected experimental examples. Potential solutions are discussed and form a guideline for particle-based intracellular imaging of ions.

High-throughput screening identifies small molecules that enhance the pharmacological effects of oligonucleotides

The therapeutic use of antisense and siRNA oligonucleotides has been constrained by the limited ability of these membrane-impermeable molecules to reach their intracellular sites of action. We sought to address this problem using small organic molecules to enhance the effects of oligonucleotides by modulating their intracellular trafficking and release from endosomes. A high-throughput screen of multiple small molecule libraries yielded several hits that markedly potentiated the actions of splice switching oligonucleotides in cell culture. These compounds also enhanced the effects of antisense and siRNA oligonucleotides. The hit compounds preferentially caused release of fluorescent oligonucleotides from late endosomes rather than other intracellular compartments. Studies in a transgenic mouse model indicated that these compounds could enhance the in vivo effects of a splice-switching oligonucleotide without causing significant toxicity. These observations suggest that selected small molecule enhancers may eventually be of value in oligonucleotide-based therapeutics.

Target specific delivery of anticancer drug in silk fibroin based 3D distribution model of bone-breast cancer cells

To avoid the indiscriminating action of anticancer drugs, the cancer cell specific targeting of drug molecule becomes a preferred choice for the treatment. The successful screening of the drug molecules in 2D culture system requires further validation. The failure of target specific drug in animal model raises the issue of creating a platform in between the in vitro (2D) and in vivo animal testing. The metastatic breast cancer cells migrate and settle at different sites such as bone tissue. This work evaluates the in vitro 3D model of the breast cancer and bone cells to understand the cellular interactions in the presence of a targeted anticancer drug delivery system. The silk fibroin based cytocompatible 3D scaffold is used as in vitro 3D distribution model. Human breast adenocarcinoma and osteoblast like cells are cocultured to evaluate the efficiency of doxorubicin loaded folic acid conjugated silk fibroin nanoparticle as drug delivery system. Decreasing population of the cancer cells, which lower the levels of vascular endothelial growth factors, glucose consumption, and lactate production are observed in the drug treated coculture constructs. The drug treated constructs do not show any major impact on bone mineralization. The diminished expression of osteogenic markers such as osteocalcein and alkaline phosphatase are recorded. The result indicates that this type of silk based 3D in vitro coculture model may be utilized as a bridge between the traditional 2D and animal model system to evaluate the new drug molecule (s) or to reassay the known drug molecules or to develop target specific drug in cancer research.

Nanoparticle-based technologies for retinal gene therapy

For patients with hereditary retinal diseases, retinal gene therapy offers significant promise for the prevention of retinal degeneration. While adeno-associated virus (AAV)-based systems remain the most popular gene delivery method due to their high efficiency and successful clinical results, other delivery systems, such as non-viral nanoparticles (NPs) are being developed as additional therapeutic options. NP technologies come in several categories (e.g., polymer, liposomes, peptide compacted DNA), several of which have been tested in mouse models of retinal disease. Here, we discuss the key biochemical features of the different NPs that influence how they are internalized into cells, escape from endosomes, and are delivered into the nucleus. We review the primary mechanism of NP uptake by retinal cells and highlight various NPs that have been successfully used for in vivo gene delivery to the retina and RPE. Finally, we consider the various strategies that can be implemented in the plasmid DNA to generate persistent, high levels of gene expression.

Enhanced efficacy of chemotherapeutic drugs against colorectal cancer using ligand-decorated self-breakable agents

Targeting self-breakable micelles could facilitate Caco2 cancer cells in acidic tumor microenvironment to take up SN38 which the micelle loaded with and trigger drug release in cancer cells, resulting in enhanced drug efficacy.

Targeted Delivery of 5-fluorouracil with Monoclonal Antibody Modified Bovine Serum Albumin Nanoparticles

Herein, 1F2, an anti-HER2 monoclonal antibody (mAb), was covalently coupled to the surface of 5-Fluorouracil (5-FU) loaded bovine serum albumin (BSA) nanoparticles. Concerning two different crosslinkers for conjugation of 1F2, Maleimide-poly (ethylene glycol)-Succinimidyl carbonate (Mal-PEG5000-NHS) was selected due to its higher conjugation efficiency (23 ± 4%) obtained in comparison to N-succinimidyl 3-(2-Pyridyl Dithio) Propionate (SPDP) (8 ± 2%). A slight increase in the average particle size with a negligible prolongation of the 5-FU release was observed after 1F2 coupling. The 1F2-coupled 5-FU-loaded BSA nanoparticles interacted with nearly all HER2 receptors available on the surface of HER2-positive SKBR3 cells. No cellular uptake was observed for HER2-negative MCF7 cells. Physicochemical and biological properties of the mAb-modified nanoparticles did not significantly alter after three months of storage at room temperature. The in-vitro cytotoxicity evaluation by MTT assay, demonstrated lower SKBR3 viability (50.7 ± 9 %) after 5 hours contact with 1F2-coupled 5-FU-loaded BSA nanoparticles in comparison with the other control systems due to their cell attachment and internalization after washing. In addition, no significant toxicity was observed on MCF7 cells. This novel system can efficiently be employed for targeted delivery of 5-FU to HER2-positive cancerous cells.

Critical particle sizes for the engulfment of nanoparticles by membranes and vesicles with bilayer asymmetry

The adhesion and engulfment of nanoparticles by biomembranes is essential for many processes such as biomedical imaging, drug delivery, nanotoxicity, and viral infection. Many studies have shown that both surface chemistry, which determines the adhesive strength of the membrane-particle interactions, and particle size represent key parameters for these processes. Here, we show that the asymmetry between the two leaflets of a bilayer membrane provides another key parameter for the engulfment of nanoparticles. The asymmetric membrane prefers to curve in a certain manner as quantitatively described by its spontaneous curvature. We derive two general relationships between particle size, adhesive strength, and spontaneous curvature that determine the instabilities of (i) the nonadhering or free state and (ii) the completely engulfed state of the particle. For model membranes such as lipid or polymer bilayers with a uniform composition, the two relationships lead to two critical particle sizes that determine four distinct engulfment regimes, both for the endocytic and for the exocytic engulfment process. For strong adhesion, the critical particle sizes are on the order of 10 nm, while they are on the order of 1000 nm for weak or ultraweak adhesion. Our theoretical results are therefore accessible to both experimental studies and computer simulations of model membranes. In order to address the more complex process of receptor-mediated endocytosis, we take the adhesion-induced segregation of membrane components into account and consider bound and unbound membrane segments that differ in their spontaneous curvatures. To model protein coats as formed during clathrin-dependent endocytosis, we focus on the case in which the bound membrane segments have a large spontaneous curvature compared to the unbound ones. We derive explicit expressions for the engulfment rate and the uptake of nanoparticles, which both depend on the particle size in a nonmonotonic manner, and provide a quantitative fit to experimental data for clathrin-dependent endocytosis of gold nanoparticles.

Simultaneous delivery of therapeutic antagomirs with paclitaxel for the management of metastatic tumors by a pH-responsive anti-microbial peptide-mediated liposomal delivery system

The roles of microRNAs (miRNAs) in the regulation of metastasis have been widely recognized in the recent years. Mir-10b antagomir (antagomir-10b) was shown to impede metastasis through the down-regulation of mir-10b; however, it could not stunt the growth of primary tumors. In this study we showed that the co-delivery of antagomir-10b with paclitaxel (PTX) by a novel liposomal delivery system modified with an anti-microbial peptide [D]-H6L9 (D-Lip) could significantly both hinder the migration of 4T1 cells and induce evident cellular apoptosis and cell death in the meantime. The histidines in the sequence of [D]-H6L9 allowed the peptide to get protonated under pH5.0 (mimicking the lysosome/endosome environment), and strong membrane lytic effect could thus be activated, leading to the escape of liposomes from the lysosomes and the decrease of of mir-10b expression. The in vivo and ex vivo fluorescence imaging showed that D-Lip could reach 4T1 tumors efficaciously. Incorporation of PTX did not influence the antagomir-10b delivery effect of D-Lip; for the in vivo tumor inhibition assay, compared with all the other groups, the combination of antagomir-10b and PTX delivered by D-Lip could prominently delay the growth of 4T1 tumors and reduce the lung metastases at the same time, and the expression of Hoxd10 in tumors was also significantly up-regulated. Taken together, these results demonstrated that D-Lip could act as a sufficient tool in co-delivering antagomir-10b and PTX.

Micro- and nanotechnologies for intracellular delivery

The majority of drugs and biomolecules need to be delivered into cells to be effective. However, the cell membranes, a biological barrier, strictly resist drugs or biomolecules entering cells, resulting in significantly reduced intracellular delivery efficiency. To overcome this barrier, a variety of intracellular delivery approaches including chemical and physical ways have been developed in recent years. In this review, the focus is on summarizing the nanomaterial routes involved in making use of a collection of receptors for the targeted delivery of drugs and biomolecules and the physical ways of applying micro- and nanotechnologies for high-throughput intracellular delivery.

Insight into nanoparticle cellular uptake and intracellular targeting

Collaborative efforts from the fields of biology, materials science, and engineering are leading to exciting progress in the development of nanomedicines. Since the targets of many therapeutic agents are localized in subcellular compartments, modulation of nanoparticle-cell interactions for efficient cellular uptake through the plasma membrane and the development of nanomedicines for precise delivery to subcellular compartments remain formidable challenges. Cellular internalization routes determine the post-internalization fate and intracellular localization of nanoparticles. This review highlights the cellular uptake routes most relevant to the field of non-targeted nanomedicine and presents an account of ligand-targeted nanoparticles for receptor-mediated cellular internalization as a strategy for modulating the cellular uptake of nanoparticles. Ligand-targeted nanoparticles have been the main impetus behind the progress of nanomedicines towards the clinic. This strategy has already resulted in remarkable progress towards effective oral delivery of nanomedicines that can overcome the intestinal epithelial barrier. A detailed overview of the recent developments in subcellular targeting as a novel platform for next-generation organelle-specific nanomedicines is also provided. Each section of the review includes prospects, potential, and concrete expectations from the field of targeted nanomedicines and strategies to meet those expectations.

Identification of multiple cellular uptake pathways of polystyrene nanoparticles and factors affecting the uptake: relevance for drug delivery systems

Nanoparticles may address challenges by human diseases through improving diagnosis, vaccination and treatment. The uptake mechanism regulates the type of threat a particle poses on the host cells and how a cell responds to it. Hence, understanding the uptake mechanisms and cellular interactions of nanoparticles at the cellular and subcellular level is a prerequisite for their effective biomedical applications. The present study shows the uptake mechanisms of polystyrene nanoparticles and factors affecting their uptake in bone marrow-derived macrophages, 293T kidney epithelial cells and L929 fibroblasts. Labeling with the endocytic marker FM4-64 and transmission electron microscopy studies show that the nanoparticles were internalized rapidly via endocytosis and accumulated in intracellular vesicles. Soon after their internalizations, nanoparticles trafficked to organelles with acidic pH. Analysis of the ultrastructural morphology of the plasma membrane invaginations or extravasations provides clear evidence for the involvement of several uptake routes in parallel to internalize a given type of nanoparticles by mammalian cells, highlighting the complexity of the nanoparticle-cell interactions. Blocking the specific endocytic pathways by different pharmacological inhibitors shows similar outcomes. The potential to take up nanoparticles varies highly among different cell types in a particle sizes-, time- and energy-dependent manner. Furthermore, infection and the activation status of bone marrow-derived macrophages significantly affect the uptake potential of the cells, indicating the need to understand the diseases' pathogenesis to establish effective and rational drug-delivery systems. This study enhances our understanding of the application of nanotechnology in biomedical sciences.

Relating surface-enhanced Raman scattering signals of cells to gold nanoparticle aggregation as determined by LA-ICP-MS micromapping

The cellular response to nanoparticle exposure is essential in various contexts, especially in nanotoxicity and nanomedicine. Here, 14-nm gold nanoparticles in 3T3 fibroblast cells are investigated in a series of pulse-chase experiments with a 30-min incubation pulse and chase times ranging from 15 min to 48 h. The gold nanoparticles and their aggregates are quantified inside the cellular ultrastructure by laser ablation inductively coupled plasma mass spectrometry micromapping and evaluated regarding the surface-enhanced Raman scattering (SERS) signals. In this way, both information about their localization at the micrometre scale and their molecular nanoenvironment, respectively, is obtained and can be related. Thus, the nanoparticle pathway from endocytotic uptake, intracellular processing, to cell division can be followed. It is shown that the ability of the intracellular nanoparticles and their accumulations and aggregates to support high SERS signals is neither directly related to nanoparticle amount nor to high local nanoparticle densities. The SERS data indicate that aggregate geometry and interparticle distances in the cell must change in the course of endosomal maturation and play a critical role for a specific gold nanoparticle type in order to act as efficient SERS nanoprobe. This finding is supported by TEM images, showing only a minor portion of aggregates that present small interparticle spacing. The SERS spectra obtained after different chase times show a changing composition and/or structure of the biomolecule corona of the gold nanoparticles as a consequence of endosomal processing.

Engineered drug-protein nanoparticle complexes for folate receptor targeting

Nanomaterials that are used in therapeutic applications need a high degree of uniformity and functionality which can be difficult to attain. One strategy for fabrication is to utilize the biological precision afforded by recombinant synthesis. Through protein engineering, we have produced ~27-nm dodecahedral protein nanoparticles using the thermostable E2 subunit of pyruvate dehydrogenase as a scaffold and added optical imaging, drug delivery, and tumor targeting capabilities. Cysteines in the internal cavity of the engineered caged protein scaffold (E2 variant D381C) were conjugated with maleimide-bearing Alexa Fluor 532 (AF532) and doxorubicin (DOX). The external surface was functionalized with polyethylene glycol (PEG) alone or with the tumor-targeting ligand folic acid (FA) through a PEG linker. The resulting bi-functional nanoparticles remained intact and correctly assembled. The uptake of FA-displaying nanoparticles (D381C-AF532-PEG-FA) by cells overexpressing the folate receptor was approximately six times greater than of non-targeting nanoparticles (D381C-AF532-PEG) and was confirmed to be FA-specific. Nanoparticles containing DOX were all cytotoxic in the low micromolar range. To our knowledge, this work is the first time that acid-labile drug release and folate receptor targeting have been simultaneously integrated onto recombinant protein nanoparticles, and it demonstrates the potential of using biofabrication strategies to generate functional nanomaterials.

Bombesin peptide conjugated gold nanocages internalize via clathrin mediated endocytosis

The nature of interaction and mechanism of internalization of receptor-avid peptide nanoparticles with cells is not yet completely understood. This article describes the cellular internalization mechanism and intracellular trafficking of peptide conjugated receptor targeted porous Gold nanocages (AuNCs) in cancer cells. We synthesized and characterized a library of AuNCs conjugated with bombesin (BBN) peptide. Evidence of selective affinity of AuNC-BBN toward gastrin releasing peptide receptors (GRPR) was obtained using radiolabeled competitive cell binding assay. Endocytic mechanism was investigated using cell inhibitor studies and monitored using optical and transmission electron microscopy (TEM). Results show AuNC-BBN uptake in PC3 cells is mediated by clathrin mediated endocytosis (CME). Indeed, in the presence of CME inhibitors, AuNC-BBN uptake in cells is reduced up to 84%. TEM images further confirm CME characteristic clathrin coated pits and lysosomal release of AuNCs. These results demonstrate that peptide ligands conjugated to the surface of nanoparticles maintain their target specificity. This bolsters the case for peptide robustness and its persisting functionality in intracellular vehicular delivery systems.

Targeted iron-oxide nanoparticle for photodynamic therapy and imaging of head and neck cancer

Photodynamic therapy (PDT) is a highly specific anticancer treatment modality for various cancers, particularly for recurrent cancers that no longer respond to conventional anticancer therapies. PDT has been under development for decades, but light-associated toxicity limits its clinical applications. To reduce the toxicity of PDT, we recently developed a targeted nanoparticle (NP) platform that combines a second-generation PDT drug, Pc 4, with a cancer targeting ligand, and iron oxide (IO) NPs. Carboxyl functionalized IO NPs were first conjugated with a fibronectin-mimetic peptide (Fmp), which binds integrin β1. Then the PDT drug Pc 4 was successfully encapsulated into the ligand-conjugated IO NPs to generate Fmp-IO-Pc 4. Our study indicated that both nontargeted IO-Pc 4 and targeted Fmp-IO-Pc 4 NPs accumulated in xenograft tumors with higher concentrations than nonformulated Pc 4. As expected, both IO-Pc 4 and Fmp-IO-Pc 4 reduced the size of HNSCC xenograft tumors more effectively than free Pc 4. Using a 10-fold lower dose of Pc 4 than that reported in the literature, the targeted Fmp-IO-Pc 4 NPs demonstrated significantly greater inhibition of tumor growth than nontargeted IO-Pc 4 NPs. These results suggest that the delivery of a PDT agent Pc 4 by IO NPs can enhance treatment efficacy and reduce PDT drug dose. The targeted IO-Pc 4 NPs have great potential to serve as both a magnetic resonance imaging (MRI) agent and PDT drug in the clinic.

Nucleotides as nontoxic endogenous endosomolytic agents in drug delivery

Nontoxic endogenous nucleotides such as adenosine triphosphate and guanosine triphosphate have secondary phosphate groups, causing proton-buffering capacity and/or hemolytic activity in endolysosomal pH ranges. Nucleotides co-delivered in single polymeric pDNA nanocarrier induce highly enhanced transfection efficiency with negligible cytotoxicity due to their endosomolytic functions.

Design of chitosan-based nanoformulations for efficient intracellular release of active compounds

The use of chitosan-based nanocarriers to transport active compounds gained an increasing attention in drug delivery. Intracellular delivery, with efficient intracellular release, become an important design considerations in chitosan based nanoformlations. Internal stimuli-responsive nanoformulations are designed to release active compounds after internalization based on certain internal stimuli like pH, redox potential and enzymes. Futhermore, nondestructive pathways may provide a nondigestive compartment for active compounds transport, which can protect the encapsulated agents from possible lysosomal degradation, thereby realizing release agents safely. This review gives a brief overview about the chitosan-based nanoformulations for efficient intracellular cargo release, including internal stimuli-responsive nanoformulations and nondestructive pathways based nanoformulations: design strategies and applications. The present problems and a possible future perspective related them are also discussed.

Multifunctional pH-sensitive polymeric nanoparticles for theranostics evaluated experimentally in cancer

A multifunctional pH-sensitive polymeric nanoparticle system was developed for simultaneous tumor magnetic resonance imaging (MRI) and therapy. The nanoparticles were self-assembled using the multi-block polymer poly(lactic acid)-poly(ethylene glycol)-poly(l-lysine)-diethylenetriamine pentaacetic acid (PLA-PEG-PLL-DTPA) and the pH-sensitive material poly(l-histidine)-poly(ethylene glycol)-biotin (PLH-PEG-biotin). The anti-hepatocellular carcinoma (HCC) drug sorafenib was encapsulated inside the nanoparticles. Gd ions were chelated to the DTPA groups which were distributed on the nanoparticle surface. Biotinylated vascular endothelial growth factor receptor (VEGFR) antibodies were linked to the surface biotin groups of nanoparticles through the avidin linker to form the target pH-sensitive theranostic nanoparticles (TPTN). TPTN exhibited spherical or ellipsoidal shapes, uniform particle size distribution (181.4 ± 3.4 nm), positive zeta potential (14.95 ± 0.60 mV), high encapsulation efficiency (95.02 ± 1.47%) and drug loading (2.38 ± 0.04%). The pH-sensitive sorafenib release from TPTN was observed under different pH values (47.81% at pH = 7.4 and 99.32% at pH = 5.0, respectively). In cell cytotoxicity studies, TPTN showed similar antitumor effect against HepG2 cells compared to solubilized sorafenib solution after pre-incubation in acid PBS (pH = 5.0) for 1 h in vitro (P > 0.05). In in vivo anti-tumor studies, TPTN showed significantly higher antitumor effect in H22 tumor (VEGFR overexpressed cell line) bearing mice compared to the solubilized sorafenib solution (oral or i.v. administration) group (P < 0.05). In the MRI test, the T1 relaxivity value of TPTN was 17.300 mM(-1) s(-1) which was 3.6 times higher than Magnevist® (r1 = 4.8 mM(-1) s(-1)). As a positive contrast agent, TPTN exhibited higher resolution and longer imaging time (more than 90 min) in the MRI diagnosis of tumor-bearing mice compared to Magnevist® (more than 60 min). Furthermore, histological examination of TBN (blank TPTN, without sorafenib loaded) showed no visible tissue toxicity compared to normal saline. Thus, TPTN possessed dual-loading drugs and imaging agents, active targeting and pH-triggered drug release properties in one platform with good biocompatibility. All of these results indicated that TPTN was a promising theranostic carrier which could be a platform for the development of novel multifunctional theranostic agents.

Tracking of magnetite labeled nanoparticles in the rat brain using MRI

This study was performed to explore the feasibility of tracing nanoparticles for drug transport in the healthy rat brain with a clinical MRI scanner. Phantom studies were performed to assess the R1 ( =  1/T1) relaxivity of different magnetically labeled nanoparticle (MLNP) formulations that were based on biodegradable human serum albumin and that were labeled with magnetite of different size. In vivo MRI measurements in 26 rats were done at 3T to study the effect and dynamics of MLNP uptake in the rat brain and body. In the brain, MLNPs induced T1 changes were quantitatively assessed by T1 relaxation time mapping in vivo and compared to post-mortem results from fluorescence imaging. Following intravenous injection of MLNPs, a visible MLNP uptake was seen in the liver and spleen while no visual effect was seen in the brain. However a histogram analysis of T1 changes in the brain demonstrated global and diffuse presence of MLNPs. The magnitude of these T1 changes scaled with post-mortem fluorescence intensity. This study demonstrates the feasibility of tracking even small amounts of magnetite labeled NPs with a sensitive histogram technique in the brain of a living rodent.

Targeted theranostic nanoparticles: receptor-mediated entry into cells, pH-induced signal generation and cytosolic delivery

Virus-like theranostic nanoparticles: virus-like poly(amino acid) nanoparticles are synthesized that can be internalized via receptor-mediated endocytosis, resulting in encapsulated pH-activatable fluorescence probes that can be turned on in acidic environments but otherwise remain undetectable. The encapsulated anticancer drugs are also released into cytosol by endosome disruption.

Functional transformations of bile acid transporters induced by high-affinity macromolecules

Apical sodium-dependent bile acid transporters (ASBT) are the intestinal transporters that form intermediate complexes with substrates and its conformational change drives the movement of substrates across the cell membrane. However, membrane-based intestinal transporters are confined to the transport of only small molecular substrates. Here, we propose a new strategy that uses high-affinity binding macromolecular substrates to functionally transform the membrane transporters so that they behave like receptors, ultimately allowing the apical-basal transport of bound macromolecules. Bile acid based macromolecular substrates were synthesized and allowed to interact with ASBT. ASBT/macromolecular substrate complexes were rapidly internalized in vesicles, localized in early endosomes, dissociated and escaped the vesicular transport while binding of cytoplasmic ileal bile acid binding proteins cause exocytosis of macromolecules and prevented entry into lysosomes. This newly found transformation process of ASBT suggests a new transport mechanism that could aid in further utilization of ASBT to mediate oral macromolecular drug delivery.

Cellular uptake and intracellular trafficking of oligonucleotides: implications for oligonucleotide pharmacology

One of the major constraints on the therapeutic use of oligonucleotides is inefficient delivery to their sites of action in the cytosol or nucleus. Recently it has become evident that the pathways of cellular uptake and intracellular trafficking of oligonucleotides can strongly influence their pharmacological actions. Here we provide background information on the basic processes of endocytosis and trafficking and then review recent literature on targeted delivery and subcellular trafficking of oligonucleotides in that context. A variety of approaches including molecular scale ligand-oligonucleotide conjugates, ligand-targeted nanocarriers, and the use of small molecules to enhance oligonucleotide effects are discussed.