Serum Protein Adsorption Enhances Active Leukemia Stem Cell Targeting of Mesoporous Silica Nanoparticles

Towards a simple in vitro surface chemistry pre-screening method for nanoparticles to be used for drug delivery to solid tumours

An efficient nanoparticulate drug carrier intended for chemotherapy based on intravenous administration must exhibit a long enough blood circulation time, a good penetrability into the tumour volume, as well as an efficient uptake by cancer cells. Limiting factors for the therapeutic outcome in vivo are recognition of the nanoparticles as foreign objects, which triggers nanoparticle uptake by defence organs rich in macrophages, e.g. liver and spleen, on the time-scale of accumulation and uptake in/by the tumour. However, the development of nanomedicine towards efficient nanoparticle-based delivery to solid tumours is hampered by the lack of simple, reproducible, cheap, and predictive means for early identification of promising nanoparticle formulations. The surface chemistry of nanoparticles is known to be the most important determinant for the biological fate of nanoparticles, as it influences the extent of serum protein adsorption, and also the relative composition of the protein corona. Here we preliminarily evaluate an extremely simple screening method for nanoparticle surface chemistry pre-optimization based on nanoparticle uptake in vitro by PC-3 cancer cells and THP-1 macrophages. Only when both selectivity for the cancer cells as well as the extent of nanoparticle uptake are taken into consideration do the in vitro results mirror literature results obtained for small animal models. Furthermore, although not investigated here, the screening method does also lend itself to the study of actively targeted nanoparticles.

Engineered Nano-Bio Interfaces for Stem Cell Therapy

Engineered nanomaterials (ENMs) with different topographies provide effective nano-bio interfaces for controlling the differentiation of stem cells. The interaction of stem cells with nanoscale topographies and chemical cues in their microenvironment at the nano-bio interface can guide their fate. The use of nanotopographical cues, in particular nanorods, nanopillars, nanogrooves, nanofibers, and nanopits, as well as biochemical forces mediated factors, including growth factors, cytokines, and extracellular matrix proteins, can significantly impact stem cell differentiation. These factors were seen as very effective in determining the proliferation and spreading of stem cells. The specific outgrowth of stem cells can be decided with size variation of topographic nanomaterial along with variation in matrix stiffness and surface structure like a special arrangement. The precision chemistry enabled controlled design, synthesis, and chemical composition of ENMs can regulate stem cell behaviors. The parameters of size such as aspect ratio, diameter, and pore size of nanotopographic structures are the main factors for specific termination of stem cells. Protein corona nanoparticles (NPs) have shown a powerful facet in stem cell therapy, where combining specific proteins could facilitate a certain stem cell differentiation and cellular proliferation. Nano-bio reactions implicate the interaction between biological entities and nanoparticles, which can be used to tailor the stem cells' culmination. The ion release can also be a parameter to enhance cellular proliferation and to commit the early differentiation of stem cells. Further research is needed to fully understand the mechanisms underlying the interactions between engineered nano-bio interfaces and stem cells and to develop optimized regenerative medicine and tissue engineering designs.

Straightforward adsorption-based formulation of mesoporous silia nanoparticles for drug delivery applications

Mesoporous silica nanoparticles (MSNs) have emerged as a very promising drug delivery platform. However, multi-step synthesis and surface functionalization protocols rise the hurdle for translation of this promising drug delivery platform to the clinic. Furthermore, surface functionalization aiming at enhancing the blood circulation time, typically through surface functionalization with poly(ethylene glycol) (PEG) (PEGylation), has repeatedly been shown to be detrimental for the drug loading levels that can be achieved. Here, we present results related to sequential adsorptive drug loading and adsorptive PEGylation, where the conditions can be chosen so that the drug desorption during PEGylation is minimized. At the heart of the approach is the high solubility of PEG both in water and in apolar solvents, which makes it possible to use a solvent for PEGylation in which the drug exhibits a low solubility, as demonstrated here for two model drugs, one being water soluble and the other not. Analysis of the influence of PEGylation on the extent of serum protein adsorption underline the promise of the approach, and the results also allow the adsorption mechanisms to be elaborated. Detailed analysis of the adsorption isotherms enables determination of the fractions of PEG residing on the outer particle surfaces in comparison to inside the mesopore systems, and also makes it possible to determine the PEG conformation on the outer particle surfaces. Both parameters are directly reflected in the extent of protein adsorption to the particles. Finally, the PEG coating is shown to be stable on time-scales compatible with intravenous drug administration, which is why we are convinced that the presented approach or modifications thereof will pave the way for faster translation of this drug delivery platform to the clinic.

Natural Biopolymers as Smart Coating Materials of Mesoporous Silica Nanoparticles for Drug Delivery

In recent years, the functionalization of mesoporous silica nanoparticles (MSNs) with different types of responsive pore gatekeepers have shown great potential for the formulation of drug delivery systems (DDS) with minimal premature leakage and site-specific controlled release. New nanotechnological approaches have been developed with the objective of utilizing natural biopolymers as smart materials in drug delivery applications. Natural biopolymers are sensitive to various physicochemical and biological stimuli and are endowed with intrinsic biodegradability, biocompatibility, and low immunogenicity. Their use as biocompatible smart coatings has extensively been investigated in the last few years. This review summarizes the MSNs coating procedures with natural polysaccharides and protein-based biopolymers, focusing on their application as responsive materials to endogenous stimuli. Biopolymer-coated MSNs, which conjugate the nanocarrier features of mesoporous silica with the biocompatibility and controlled delivery provided by natural coatings, have shown promising therapeutic outcomes and the potential to emerge as valuable candidates for the selective treatment of various diseases.

Nanoparticle and Stem Cell Combination Therapy for the Management of Stroke

Stroke is currently one of the primary causes of morbidity and mortality worldwide. Unfortunately, the available treatments for stroke are still extremely limited. Indeed, stem cell (SC) therapy is a new option for the treatment of stroke that could significantly expand the therapeutic time window of stroke. Some proposed mechanisms for stroke-based SC therapy are the incorporation of SCs into the host brain to replace dead or damaged cells/tissues. Moreover, acute cell delivery can inhibit apoptosis and decrease lesion size, providing immunomudolatory and neuroprotection effects. However, several major SC problems related to SCs such as homing, viability, uncontrolled differentiation, and possible immune response, have limited SC therapy. A combination of SC therapy with nanoparticles (NPs) can be a solution to address these challenges. NPs have received considerable attention in regulating and controlling the behavior of SCs because of their unique physicochemical properties. By reviewing the pathophysiology of stroke and the therapeutic benefits of SCs and NPs, we hypothesize that combined therapy will offer a promising future in the field of stroke management. In this work, we discuss recent literature in SC research combined with NP-based strategies that may have a synergistic outcome after stroke incidence.

Exploiting recent trends for the synthesis and surface functionalization of mesoporous silica nanoparticles towards biomedical applications

Rapid progress in developing multifunctional nanocarriers for drug delivery has been observed in recent years. Inorganic mesoporous silica nanocarriers (MSNs), emerged as an ideal candidate for gene/drug delivery with distinctive morphological features. These ordered carriers of porous nature have gained unique attention due to their distinctive features. Moreover, transformation can be made to these nanocarriers in terms of pores size, pores volume, and particle size by altering specific parameters during synthesis. These ordered porous materials have earned special attention as a drug carrier for treating multiple diseases. Herein, we highlight the strategies employed in synthesizing and functionalizing these versatile nanocarriers. In addition, the various factors that influence their sizes and morphological features were also discussed. The article also summarizes the recent advancements and strategies for drug and gene delivery by rendering smarter MSNs by incorporating functional groups on their surfaces. Averting off-target effects through various capping strategies is a massive milestone for the induction of stimuli-responsive nanocarriers that brings out a great revolution in the biomedical field.

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MSNs serve as an ideal candidate for gene/drug delivery with unique and excellent attributes.

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MSNs surface can be functionalized using specific materials to impart unique structural features.

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Functionalization of MSNs with stimuli-responsive molecules can act as gatekeepers by responding to the desired stimulus after uncapping.

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These capping agents act as vital targeting agents in developing MSNs being employed in various biomedical applications.

Engineering mesoporous silica nanoparticles for drug delivery: where are we after two decades?

The present review details a chronological description of the events that took place during the development of mesoporous materials, their different synthetic routes and their use as drug delivery systems. The outstanding textural properties of these materials quickly inspired their translation to the nanoscale dimension leading to mesoporous silica nanoparticles (MSNs). The different aspects of introducing pharmaceutical agents into the pores of these nanocarriers, together with their possible biodistribution and clearance routes, would be described here. The development of smart nanocarriers that are able to release a high local concentration of the therapeutic cargo on-demand after the application of certain stimuli would be reviewed here, together with their ability to deliver the therapeutic cargo to precise locations in the body. The huge progress in the design and development of MSNs for biomedical applications, including the potential treatment of different diseases, during the last 20 years will be collated here, together with the required work that still needs to be done to achieve the clinical translation of these materials. This review was conceived to stand out from past reports since it aims to tell the story of the development of mesoporous materials and their use as drug delivery systems by some of the story makers, who could be considered to be among the pioneers in this area.

Surface Functionalization of Silica Nanoparticles: Strategies to Optimize the Immune-Activating Profile of Carrier Platforms

Silica nanoparticles (SiNPs) are generally regarded as safe and may represent an attractive carrier platform for nanomedical applications when loaded with biopharmaceuticals. Surface functionalization by different chemistries may help to optimize protein loading and may further impact uptake into the targeted tissues or cells, however, it may also alter the immunologic profile of the carrier system. In order to circumvent side effects, novel carrier candidates need to be tested thoroughly, early in their development stage within the pharmaceutical innovation pipeline, for their potential to activate or modify the immune response. Previous studies have identified surface functionalization by different chemistries as providing a plethora of modifications for optimizing efficacy of biopharmaceutical (nano)carrier platforms while maintaining an acceptable safety profile. In this study, we synthesized SiNPs and chemically functionalized them to obtain different surface characteristics to allow their application as a carrier system for allergen-specific immunotherapy. In the present study, crude natural allergen extracts are used in combination with alum instead of well-defined active pharmaceutical ingredients (APIs), such as recombinant allergen, loaded onto (nano)carrier systems with immunologically inert and stable properties in suspension. This study was motivated by the hypothesis that comparing different charge states could allow tailoring of the binding capacity of the particulate carrier system, and hence the optimization of biopharmaceutical uptake while maintaining an acceptable safety profile, which was investigated by determining the maturation of human antigen-presenting cells (APCs). The functionalized nanoparticles were characterized for primary and hydrodynamic size, polydispersity index, zeta potential, endotoxin contamination. As potential candidates for allergen-specific immunotherapy, the differently functionalized SiNPs were non-covalently coupled with a highly purified, endotoxin-free recombinant preparation of the major birch pollen allergen Bet v 1 that functioned for further immunological testing. Binding efficiencies of allergen to SiNPs was controlled to determine uptake of API. For efficacy and safety assessment, we employed human monocyte-derived dendritic cells as model for APCs to detect possible differences in the particles’ APC maturation potential. Functionalization of SiNP did not affect the viability of APCs, however, the amount of API physisorbed onto the nanocarrier system, which induced enhanced uptake, mainly by macropinocytosis. We found slight differences in the maturation state of APCs for the differently functionalized SiNP–API conjugates qualifying surface functionalization as an effective instrument for optimizing the immune response towards SiNPs. This study further suggests that surface-functionalized SiNPs could be a suitable, immunologically inert vehicle for the efficient delivery of biopharmaceutical products, as evidenced here for allergen-specific immunotherapy.

The impact of protein corona on the biological behavior of targeting nanomedicines

For successful translation of targeting nanomedicines from bench to bedside, it is vital to address their most common drawbacks namely rapid clearance and off-target accumulation. These complications evidently originate from a phenomenon called "protein corona (PC) formation" around the surface of targeting nanoparticles (NPs) which happens once they encounter the bloodstream and interact with plasma proteins with high collision frequency. This phenomenon endows the targeting nanomedicines with a different biological behavior followed by an unexpected fate, which is usually very different from what we commonly observe in vitro. In addition to the inherent physiochemical properties of NPs, the targeting ligands could also remarkably dictate the amount and type of adsorbed PC. As very limited studies have focused their attention on this particular factor, the present review is tasked to discuss the best simulated environment and latest characterization techniques applied to PC analysis. The effect of PC on the biological behavior of targeting NPs engineered with different targeting moieties is further discussed. Ultimately, the recent progresses in manipulation of nano-bio interfaces to achieve the most favorite therapeutic outcome are highlighted.

Short Preirradiation of TiO2 Nanoparticles Increases Cytotoxicity on Human Lung Coculture System

Anatase titanium dioxide nanoparticles (TiO₂ NPs) are used in a large range of industrial applications mainly due to their photocatalytic properties. Before entering the lung, virtually all TiO₂ NPs are exposed to some UV light, and lung toxicity of TiO₂ NPs might be influenced by photoexcitation that is known to alter TiO₂ surface properties. Although the TiO₂ NPs toxicity has been extensively investigated, limited data are available regarding the toxicity of TiO₂ NPs that have been pre-exposed to UV light, and their impact on humans remains unknown. In this study, five types of TiO₂NPs with tailored physicochemical features were characterized and irradiated by UV for 30 min. Following irradiation, cytotoxicity, pro-inflammatory response, and oxidative stress on a human lung coculture system (A549 epithelial cells and macrophages differentiated from THP-1 cells) were assessed. The surface charge of all samples was less negative after UV irradiation of TiO₂ NPs, and the average aggregate size was slightly increased. A higher cytotoxic effect was observed for preirradiated TiO₂ NPs compared to nonirradiated samples. Preirradiation of TiO₂ NPs had no significant impact on the pro-inflammatory response and oxidative stress as shown by a similar production of IL-8, TNF-α, and reactive oxygen species.

On the importance of the linking chemistry for the PEGylation of mesoporous silica nanoparticles

The typical method for minimizing serum protein adsorption in biological settings and prolonging blood circulation time of nanoparticles, is to anchor hydrophilic polymers (e.g., poly(ethylene glycol), PEG) on the particle surface, which is most often done by covalent attachment (PEGylation). Herein, different PEGylation methods were realised and compared to functionalize mesoporous silica nanoparticles (MSNs). First, reactive groups were installed using post-grafting procedures with different functional silanes. Further, PEGs carrying a functional group and having different chain lengths and termini, were used. The grafting efficacy as well as the structural and physicochemical characteristics of the resulting particles were determined. Finally, the serum protein adsorption behaviour of these functionalized particles was investigated using thermogravimetric analysis. The type of selected coupling method was shown to strongly influence the grafting efficiency as well as the resulting protein adsorption. The results highlight the importance of the right choice of the linking chemistry when aiming at surface functionalization of nanoparticles.

Insights into Characterization Methods and Biomedical Applications of Nanoparticle-Protein Corona

Nanoparticles (NPs) exposed to a biological milieu will strongly interact with proteins, forming "coronas" on the surfaces of the NPs. The protein coronas (PCs) affect the properties of the NPs and provide a new biological identity to the particles in the biological environment. The characterization of NP-PC complexes has attracted enormous research attention, owing to the crucial effects of the properties of an NP-PC on its interactions with living systems, as well as the diverse applications of NP-PC complexes. The analysis of NP-PC complexes without a well-considered approach will inevitably lead to misunderstandings and inappropriate applications of NPs. This review introduces methods for the characterization of NP-PC complexes and investigates their recent applications in biomedicine. Furthermore, the review evaluates these characterization methods based on comprehensive critical views and provides future perspectives regarding the applications of NP-PC complexes.

Response of pH-Sensitive Doxorubicin Nanoparticles on Complex Tumor Microenvironments by Tailoring Multiple Physicochemical Properties

Cellular internalization, delivery efficiency, and therapeutic efficacy of nanoparticles vary according to the microenvironmental complexity for tumor types. Adjusting their physicochemical properties, such as surface properties and size, has significant potential for dealing with such complexities. Herein, we prepare four types of pH-sensitive doxorubicin nanoparticles (DOX-D1, DOX-D2, DOX-W1, and DOX-W2 Nano) using simply changing reaction medium or reactant ratio. DOX-D1 and DOX-D2 Nano exhibit similar surface characteristics (surface coating and targeting ligand content) and different size, while both DOX-W Nano examples present similar surface characteristics and size. And they can re-self-assemble into smaller particles in blood-mimic conditions and the order of size is as follows: DOX-D1> DOX-D2 ≈ DOX-W Nano, and DOX-W Nano has a higher targeting ligand content than DOX-D Nano. Thus, the bioactivities in vitro and tumor microenvironment responses of DOX-D1, DOX-D2, and DOX-W1 are further investigated due to their different physicochemical properties. DOX-W1 Nano exhibits a higher cellular uptake, a stronger antiproliferation than DOX-D1 and DOX-D2 Nano attributed to its smaller size, and a higher targeting moiety content. Despite the similar sizes of DOX-W1 and DOX-D2, DOX-D2 Nano shows a greater in vitro blood-brain barrier (BBB) permeability related to its surface coating. Interestingly, DOX-D1 with suitable size and surface property can efficiently bypass the BBB and deliver to an intracranial glioma; in comparison DOX-W1 Nano has excellent targeting efficiency in subcutaneous tumors (glioma and breast cancer). Accordingly, DOX-D1 Nano is preferential for the treatment of intracranial glioma while DOX-W1 Nano exhibits potent killing ability for subcutaneous tumors. Our work suggests tailoring multiple physicochemical properties of nanoparticles can play a significant role in addressing tumor microenvironment complexity.

Cytotoxicity-Related Bioeffects Induced by Nanoparticles: The Role of Surface Chemistry

Nanoparticles (NPs) are widely used in a variety of fields, including those related to consumer products, architecture, energy, and biomedicine. Once they enter the human body, NPs contact proteins in the blood and interact with cells in organs, which may induce cytotoxicity. Among the various factors of NP surface chemistry, surface charges, hydrophobicity levels and combinatorial decorations are found to play key roles inregulating typical cytotoxicity-related bioeffects, including protein binding, cellular uptake, oxidative stress, autophagy, inflammation, and apoptosis. In this review, we summarize the recent progress made in directing the levels and molecular pathways of these cytotoxicity-related effects by the purposeful design of NP surface charge, hydrophobicity, and combinatorial decorations.

Recent advances in the use of fluorescent nanoparticles for bioimaging

Rapid and recent progress in fluorescence microscopic techniques has allowed for routine discovery and viewing of biological structures and processes in unprecedented spatiotemporal resolution. In these imaging techniques, fluorescent nanoparticles (NPs) play important roles in the improvement of reporting systems. A short overview of recently developed fluorescent NPs used for advanced in vivo imaging will be discussed in this mini-review. The discussion begins with the contribution of fluorescence imaging in exploring the fate of NPs in biological systems. NP applications for in vivo imaging, including cell labeling, multimodal imaging and theranostic agents, are then discussed. Finally, despite all of the advancements in bioimaging, some unsolved challenges will be briefly discussed concerning future research directions.

Assembly of Multicomponent Nano-Bioconjugates Composed of Mesoporous Silica Nanoparticles, Proteins, and Gold Nanoparticles

The purpose of this work was the assembly of multicomponent nano-bioconjugates based on mesoporous silica nanoparticles (MSNs), proteins (bovine serum albumin, BSA, or lysozyme, LYZ), and gold nanoparticles (GNPs). These nano-bioconjugates may find applications in nanomedicine as theranostic devices. Indeed, MSNs can act as drug carriers, proteins stabilize MSNs within the bloodstream, or may have therapeutic or targeting functions. Finally, GNPs can either be used as contrast agents for imaging or for photothermal therapy. Here, amino-functionalized MSNs (MSN-NH2) were synthesized and characterized through various techniques (small angle X-rays scattering TEM, N2 adsorption/desorption isotherms, and thermogravimetric analysis (TGA)). BSA or lysozyme were then grafted on the external surface of MSN-NH2 to obtain MSN-BSA and MSN-LYZ bioconjugates, respectively. Protein immobilization on MSNs surface was confirmed by Fourier transform infrared spectroscopy, ζ-potential measurements, and TGA, which also allowed the estimation of protein loading. The MSN-protein samples were then dispersed in a GNP solution to obtain MSN-protein-GNPs nano-bioconjugates. Transmission electron microscopy (TEM) analysis showed the occurrence of GNPs on the MSN-protein surface, whereas almost no GNPs occurred in the protein-free control samples. Fluorescence and Raman spectroscopies suggested that proteins-GNP interactions involve tryptophan residues.

Propranolol-Loaded Mesoporous Silica Nanoparticles for Treatment of Infantile Hemangiomas

Infantile hemangioma (IH) is one of the most common neoplasm of infancy. Although with the potential to involute slowly after proliferation, IH has several subsets that could develop severe complications and lead to functional impairment or permanent disfigurement. In the present study, a novel propranolol (PRN) delivery system is developed that encapsulated in mesoporous silica nanoparticles (MSN). The primary nanoparticles are further treated with polyvinyl alcohol (PVA) to form PVA-MSN-PRN nanoparticles. The encapsulation efficiency is 58.8% ± 7.2%, and nanoparticles could release PRN in a controlled-release way. It is discovered that PVA-MSN-PRN could significantly suppress hemangioma stem cell (Hemsc) proliferation, promote Hemsc apoptosis in vitro, and inhibit the growth of hemangiomain xenografts in vivo. A conclusion could be made that this novel nanodrug delivery system has high therapeutic efficacy, low cytotoxicity, low administration frequency, and provides an attractive strategy for efficient IH therapy.

A health concern regarding the protein corona, aggregation and disaggregation

Nanoparticle (NP)-protein complexes exhibit the "correct identity" of NP in biological media. Therefore, protein-NP interactions should be closely explored to understand and modulate the nature of NPs in medical implementations. This review focuses mainly on the physicochemical parameters such as dimension, surface chemistry, morphology of NPs, and influence of pH on the formation of protein corona and conformational changes of adsorbed proteins by different kinds of techniques. Also, the impact of protein corona on the colloidal stability of NPs is discussed. Uncontrolled protein attachment on NPs may bring unwanted impacts such as protein denaturation and aggregation. In contrast, controlled protein adsorption by optimal concentration, size, pH, and surface modification of NPs may result in potential implementation of NPs as therapeutic agents especially for disaggregation of amyloid fibrils. Also, the effect of NPs-protein corona on reducing the cytotoxicity and clinical implications such as drug delivery, cancer therapy, imaging and diagnosis will be discussed. Validated correlative physicochemical parameters for NP-protein corona formation frequently derived from protein corona fingerprints of NPs which are more valid than the parameters obtained only on the base of NP features. This review may provide useful information regarding the potency as well as the adverse effects of NPs to predict their behavior in vivo.

Advances in mesoporous silica nanoparticles for targeted stimuli-responsive drug delivery: an update

INTRODUCTION

Mesoporous silica nanoparticles (MSNs) are outstanding nanoplatforms for drug delivery. Herein, the most recent advances to turn MSN-based carriers into minimal side effect drug delivery agents are covered.

AREAS COVERED

This review summarizes the scientific advances dealing with MSNs for targeted and stimuli-responsive drug delivery since 2015. Delivery aspects to diseased tissues together with approaches to obtain smart MSNs able to respond to internal or external stimuli and their applications are here described. Special emphasis is done on the combination of two or more stimuli on the same nanoplatform and on combined drug therapy.

EXPERT OPINION

The use of MSNs in nanomedicine is a promising research field because they are outstanding platforms for treating different pathologies. This is possible thanks to their structural, chemical, physical and biological properties. However, there are certain issues that should be overcome to improve the suitability of MSNs for clinical applications. All materials must be properly characterized prior to their in vivo evaluation; furthermore, preclinical in vivo studies need to be standardized to demonstrate the MSNs clinical translation potential.

Influence of serum concentration and surface functionalization on the protein adsorption to mesoporous silica nanoparticles

A study of a protein corona on mesoporous silica nanoparticles (MSNs) at in vitro and in vivo relevant serum concentrations is presented. Three MSNs different in terms of mesoscopic pore arrangement, surface chemistry, and surface roughness were studied. After incubation in either 10% or 100% serum, the hard protein corona–particle complexes were collected and analyzed by DLS, zeta-potential, and TGA, and the corona proteins were analyzed with SDS-PAGE. A good correlation between SDS-PAGE and TG results in terms of total amounts of proteins adsorbed was established. The results demonstrated that more proteins, especially apolipoproteins, were associated with the particles at higher serum concentration regardless of surface chemistry and morphological differences. Also, the mean molecular weight of the adsorbed proteins was clearly lower under full serum conditions modeling in vivo conditions as compared to under dilute conditions modeling in vitro conditions, but functionalization of the MSNs by carboxylic acid functionalities reduced protein adsorption. The influence of the structural characteristics of the MSNs on the protein adsorption was minor.

In this work, protein adsorption on MSNs at in vitro (10%) and in vivo (100%) relevant serum concentrations was studied using three types of MSNs and their functional derivatives.

Biodistribution and Excretion of Intravenously Injected Mesoporous Silica Nanoparticles: Implications for Drug Delivery Efficiency and Safety

Mesoporous silica nanoparticles (MSNs) are currently attracting a high interest for use as drug carriers in vivo. To date only data on the biodistribution in small animals are available. As any nanoparticle system, the MSNs typically accumulate in the RES organs lung, liver, and spleen upon intravenous (i.v.) administration. However, the literature data are partly inconclusive, which can be connected to the wide variability of the experimental designs, differing for example in particle size and shape, mesopore size, and surface functionalization, as well as the animal models used, the amount administered, and the means for particle detection. The present review is an attempt to summarize the literature to date with main focus on the increasing number of studies related to quantitative full body distributions. Whenever possible, attempts are also made to discuss differences in experimental observations between studies. Finally, an outlook is given listing some open issues, and highlighting the need for more standardized experimental designs in order to allow for a faster identification of optimal particle characteristics for drug delivery applications of MSNs.

Targeting Somatostatin Receptors By Functionalized Mesoporous Silica Nanoparticles - Are We Striking Home?

The concept of delivering nanoformulations to desired tissues by means of targeting membrane receptors of high local abundance by ligands anchored to the nanocarrier has gained a lot of attention over the last decade. Currently, there is no unanimous opinion on whether surface functionalization of nanocarriers by targeting ligands translates into any real benefit in terms of pharmacokinetics or treatment outcomes. Having examined the published nanocarriers designed to engage with somatostatin receptors, we realized that in the majority of cases targetability claims were not supported by solid evidence of targeting ligand-targeted receptor coupling, which is the very crux of a targetability concept. Here, we present an approach to characterize targetability of mesoporous silica-based nanocarriers functionalized with ligands of somatostatin receptors. The targetability proof in our case comes from a functional assay based on a genetically-encoded cAMP probe, which allows for real-time capture of receptor activation in living cells, triggered by targeting ligands on nanoparticles. We elaborate on the development and validation of the assay, highlighting the power of proper functional tests in the characterization pipeline of targeted nanoformulations.

Evaluation of mesoporous silica nanoparticles for oral drug delivery - current status and perspective of MSNs drug carriers

The oral pathway is considered as the most common method for drug administration, although many drugs, especially the highly pH- and/or enzymatic biodegradable peptide drugs, are very difficult to formulate and achieve a good intestinal absorption. Efficient systematic absorption of an active substance, delivered via oral ingestion, is only achievable if the drug (1) is substantially present as a solution in the gastrointestinal tract, (2) is able to penetrate through the intestinal mucus, (3) overcomes the different gastrointestinal barriers, and (4) provides an effective therapeutic dose. Therefore, optimization of oral bioavailability of poorly-soluble drugs still remains a significant challenge for the pharmaceutical industry. Even though numerous conventional drug carriers have successfully solved some of the issues related to oral delivery of poorly-soluble drugs, only few of them met commercialization requirements. These drawbacks have led the scientific world to reconsider its approaches toward targeted drug delivery systems and researchers started looking for alternative vectorized carriers. In this area, nanoparticle-based materials have several significant advantages over free and non-formulated drugs. For example, nanosized porous silica carriers allow for more sustained and controlled drug release or improved oral bioavailability. Thus, in the present review, we will highlight the most important features of nanostructured silica drug carriers, such as particle size, particle shape, surface roughness or surface functionalization, and underline the key advantages of these nanosupports. In particular, this article will discuss recent progress and challenges in the area of mesoporous silica nanocarriers used for oral drug delivery. Additional emphasis will be set on the biological and chemical features of the gastrointestinal tract as well as currently tested nanoformulations and strategies to avoid drug degradation in the gastrointestinal environment.