Photoreactivity of Metal-Organic Frameworks in Aqueous Solutions: Metal Dependence of Reactive Oxygen Species Production

Promising applications of metal-organic frameworks (MOFs) in various fields have raised concern over their environmental fate and safety upon inevitable discharge into aqueous environments. Currently, no information regarding the transformation processes of MOFs is available. Due to the presence of repetitive π-bond structure and semiconductive property, photochemical transformations are an important fate process that affects the performance of MOFs in practical applications. In the current study, the generation of reactive oxygen species (ROS) in isoreticular MIL-53s was studied. Scavengers were employed to probe the production of (1)O2, O2(•-), and •OH, respectively. In general, MIL-53(Cr) and MIL-53(Fe) are dominated by type I and II photosensitization reactions, respectively, and MIL-53(Al) appears to be less photoreactive. The generation of ROS in MIL-53(Fe) may be underestimated due to dismutation. Further investigation of MIL-53(Fe) encapsulated diclofenac transformation revealed that diclofenac can be easily transformed by MIL-53(Fe) generated ROS. However, the cytotoxicity results implied that the ROS generated from MIL-53s have little effect on the viability of the human hepatocyte (HepG2) cell line. These results suggest that the photogeneration of ROS by MOFs may be metal-node dependent, and the application of MIL-53s as drug carriers needs to be carefully considered due to their high photoreactivity.

Antineoplastic busulfan encapsulated in a metal organic framework nanocarrier: first in vivo results

Nanoparticles of a mesoporous iron(iii) trimesate MIL-100 nanocarrier encapsulating high amounts of the challenging antineoplastic busulfan were administered to rats and compared with the commercial Busilvex®.

Biocompatible polymer–metal–organic framework composite patches for cutaneous administration of cosmetic molecules

Caffeine-containing polymer–nanoMOF patches as promising cutaneous formulations.

A multifunctional metal-organic framework based tumor targeting drug delivery system for cancer therapy

Drug delivery systems (DDSs) with biocompatibility and precise drug delivery are eagerly needed to overcome the paradox in chemotherapy that high drug doses are required to compensate for the poor biodistribution of drugs with frequent dose-related side effects. In this work, we reported a metal-organic framework (MOF) based tumor targeting DDS developed by a one-pot, and organic solvent-free "green" post-synthetic surface modification procedure, starting from the nanoscale MOF MIL-101. Owing to the multifunctional surface coating, premature drug release from this DDS was prevented. Due to the pH responsive benzoic imine bond and the redox responsive disulfide bond at the modified surface, this DDS exhibited tumor acid environment enhanced cellular uptake and intracellular reducing environment triggered drug release. In vitro and in vivo results showed that DOX loaded into this DDS exhibited effective cancer cell inhibition with much reduced side effects.

Heparin-engineered mesoporous iron metal-organic framework nanoparticles: toward stealth drug nanocarriers

The specific modification of the outer surface of the promising porous metal-organic framework nanocarriers (nanoMOFs) preserving their characteristic porosity is still a major challenge. Here a simple, fast, and biofriendly method for the external functionalization of the benchmarked mesoporous iron(III) trimesate nanoparticles MIL-100(Fe) with heparin, a biopolymer associated with longer-blood circulation times is reported. First, the coated nanoparticles showed intact crystalline structure and porosity with improved colloidal stability under simulated physiological conditions, preserving in addition its encapsulation and controlled release capacities. The effect of the heparin coating on the nanoMOF interactions with the biological environment is evaluated through cell uptake, cytotoxicity, oxidative stress, cytokine production, complement activation, and protein adsorption analysis. These results confirmed that the heparin coating endowed the nanoMOFs with improved biological properties, such as reduced cell recognition, lack of complement activation, and reactive oxygen species production. Overall, the ability to coat the surface of the nanoMOFs using a simple and straight-forward approach could be taken as a way to enhance the versatility and, thus, the potential of porous MOF nanoparticles in biomedicine.

A "green" strategy to construct non-covalent, stable and bioactive coatings on porous MOF nanoparticles

Nanoparticles made of metal-organic frameworks (nanoMOFs) attract a growing interest in gas storage, separation, catalysis, sensing and more recently, biomedicine. Achieving stable, versatile coatings on highly porous nanoMOFs without altering their ability to adsorb molecules of interest represents today a major challenge. Here we bring the proof of concept that the outer surface of porous nanoMOFs can be specifically functionalized in a rapid, biofriendly and non-covalent manner, leading to stable and versatile coatings. Cyclodextrin molecules bearing strong iron complexing groups (phosphates) were firmly anchored to the nanoMOFs' surface, within only a few minutes, simply by incubation with aqueous nanoMOF suspensions. The coating procedure did not affect the nanoMOF porosity, crystallinity, adsorption and release abilities. The stable cyclodextrin-based coating was further functionalized with: i) targeting moieties to increase the nanoMOF interaction with specific receptors and ii) poly(ethylene glycol) chains to escape the immune system. These results pave the way towards the design of surface-engineered nanoMOFs of interest for applications in the field of targeted drug delivery, catalysis, separation and sensing.

Aptamer-mediated up-conversion core/MOF shell nanocomposites for targeted drug delivery and cell imaging

Multifunctional nanocarriers for targeted bioimaging and drug delivery have attracted much attention in early diagnosis and therapy of cancer. In this work, we develop a novel aptamer-guided nanocarrier based on the mesoporous metal-organic framework (MOF) shell and up-conversion luminescent NaYF4:Yb(3+)/Er(3+) nanoparticles (UCNPs) core for the first time to achieve these goals. These UCNPs, chosen as optical labels in biological assays and medical imaging, could emit strong green emission under 980 nm laser. The MOF structure based on iron (III) carboxylate materials [MIL-100 (Fe)] possesses high porosity and non-toxicity, which is of great value as nanocarriers for drug storage/delivery. As a unique nanoplatform, the hybrid inorganic-organic drug delivery vehicles show great promising for simultaneous targeted labeling and therapy of cancer cells.

A biocompatible porous Mg-gallate metal–organic framework as an antioxidant carrier

The slow release of gallic acid from a biocompatible porous MOF lead to a strong antioxidant activity.

In vitro biocompatibility of mesoporous metal (III; Fe, Al, Cr) trimesate MOF nanocarriers

The high porosity and versatile composition of the benchmarked mesoporous metal (Fe, Al, Cr) trimesate metal–organic frameworks (MIL-100(Fe, Al, Cr)) make them very promising solids in different strategic industrial and societal domains (separation, catalysis, biomedicine, etc.).

Design of a versatile nanocomposite for ‘seeing’ drug release and action behavior

To design a new method for ‘seeing’ drug release and action behavior, we combined a rare-earth complex with a magnetic-core-coated phenyl mesoporous silica nanoparticles matrix, taking advantage of the drug coordination for real-time monitoring.

Synthesis, culture medium stability, and in vitro and in vivo zebrafish embryo toxicity of metal-organic framework nanoparticles

Metal-organic frameworks (MOFs) are among the most attractive porous materials available today. They have garnered much attention for their potential utility in many different areas such as gas storage, separation, catalysis, and biomedicine. However, very little is known about the possible health or environmental risks of these materials. Here, the results of toxicity studies on sixteen representative uncoated MOF nanoparticles (nanoMOFs), which were assessed for cytotoxicity to HepG2 and MCF7 cells in vitro, and for toxicity to zebrafish embryos in vivo, are reported. Interestingly, there is a strong correlation between their in vitro toxicity and their in vivo toxicity. NanoMOFs were ranked according to their respective in vivo toxicity (in terms of the amount and severity of phenotypic changes observed in the treated zebrafish embryos), which varied widely. Altogether these results show different levels of toxicity of these materials; however, leaching of solubilized metal ions plays a main role.

Synthesis of hierarchical iron hydrogen phosphate crystal as a robust peroxidase mimic for stable H₂O₂ detection

To develop a green, cost-efficient and robust peroxidase mimic, micro/nano hierarchical morphology (for ease of separation and reuse), relative chemically stable composition (for ease of storage) and stable crystal structure (for long-term stability) are highly desired. Herein, using phosphoric acid as a chelating ligand to control the release of iron ions, hierarchical iron(III) hydrogen phosphate hydrate crystals are successfully prepared by nanosheets formation and following self-assembling in a facile low-temperature hydrothermal process. They are first found to have peroxidase-like activity and showed higher affinity for H2O2 and lower affinity for 3,3',5,5'-tetramethylbenzidine compared with horseradish peroxidase. The affinity feature is used for quantitative detection of H2O2 and shows a wide linear detection range from 57.4 to 525.8 μM (R(2) = 0.994) with a low detection limit of 1 μM. Benefited from chemical stability of hierarchical iron(III) salt crystals, they own good reproducibility (relative standard deviation = 1.95% for 10 independent measurements), long-term stability (no activity loss after 10 cycles), and ease of recovery (by simple centrifugation). Because the method is easily accessible, iron hydrogen phosphate hierarchical crystals have great potential for practical use of H2O2 sensing and detection under harsh conditions.

Synthetic and bioinspired cage nanoparticles for drug delivery

Nanotechnology has the potential to revolutionize drug delivery, but still faces some limitations. One of the main issues regarding conventional nanoparticles is their poor drug-loading and their early burst release. Thus, to overcome these problems, researchers have taken advantage of the host–guest interactions that drive some assemblies to form cage molecules able to strongly entrap their cargo and design new nanocarriers called cage nanoparticles. These systems can be classified into two categories: bioinspired nanosystems such as virus-like particles, ferritin, small heat shock protein: and synthetic host–guest supramolecular systems that require engineering to actually form supramolecular nanoassemblies. This review will highlight the recent advances in cage nanoparticles for drug delivery with a particular focus on their biomedical applications.

Self-assembled nanoscale coordination polymers with trigger release properties for effective anticancer therapy

Nanoscale coordination polymers (NCPs) are self-assembled from metal ions and organic bridging ligands, and can overcome many drawbacks of existing drug delivery systems by virtue of tunable compositions, sizes, and shapes; high drug loadings; ease of surface modification; and intrinsic biodegradability. Here we report the self-assembly of zinc bisphosphonate NCPs that carry 48±3 wt% cisplatin prodrug and 45±5 wt% oxaliplatin prodrug. In vivo pharmacokinetic studies in mice show minimal uptake of pegylated NCPs by the mononuclear phagocyte system and excellent blood circulation half-lives of 16.4±2.9 and 12.0±3.9 h for the NCPs carrying cisplatin and oxaliplatin, respectively. In all tumor xenograft models evaluated, including CT26 colon cancer, H460 lung cancer, and AsPC-1 pancreatic cancer, pegylated NCPs show superior potency and efficacy compared to free drugs. As the first example of using NCPs as nanotherapeutics with enhanced antitumor activities, this study establishes NCPs as a promising drug delivery platform for cancer therapy.

Understanding the colloidal stability of the mesoporous MIL-100(Fe) nanoparticles in physiological media

The colloidal and chemical stability of nanoparticles of the nontoxic and biodegradable iron(III) trimesate MIL-100(Fe) nanocarrier have been evaluated in the presence of a series of simulated physiological fluids for intravenous and oral administration. MIL-100(Fe) nanoparticles exhibit an appropriate colloidal stability and biodegradability, mainly dependent on both the nature of their physicochemical surface and the media composition, being a priori compatible with their biomedical use.

Toxic effect of zinc nanoscale metal-organic frameworks on rat pheochromocytoma (PC12) cells in vitro

Metal-organic frameworks (MOFs) possess unique properties desirable for delivery of drugs and gaseous therapeutics, but their uncharacterized interactions with cells raise increasing concerns of their safety in such biomedical applications. We evaluated the adverse effects of zinc nanoscale MOFs on the cell morphology, cytoskeleton, cell viability and expression of neurotrophin signaling pathway-associated GAP-43 protein in rat pheochromocytoma PC12 cells. At the concentration of 25 μg/ml, zinc MOFs did not significantly affect morphology, viability and membrane integrity of the cells. But at higher concentrations (over 100 μg/ml), MOFs exhibited a time- and concentration-dependent cytotoxicity, indicating their entry into the cells via endocytosis where they release Zn(2+) into the cytosol to cause increased intracellular concentration of Zn(2+). We demonstrated that the toxicity of MOFs was associated with a disrupted cellular zinc homeostasis and down-regulation of GAP-43 protein, which might be the underlying mechanism for the improved differentiation in PC12 cells. These findings highlight the importance of cytotoxic evaluation of the MOFs before their biomedical application.

Exploring and exploiting dynamic noncovalent chemistry for effective surface modification of nanoscale metal-organic frameworks

Surface properties determine, to a great extent, the biologically relevant functions of various kinds of nanosized materials. Although the modification of the surface of traditional inorganic or polymeric nanoparticles can be routinely achieved through covalent or noncovalent manner or both, the surface modification of nanoscale metal-organic frameworks (nano-MOFs) is extremely challenging because of their rapid degradation in aqueous environments. In this work, we systematically studied the synergistic and dynamic noncovalent interactions between fluorescent probes and iron(III) carboxylate nano-MOFs (i.e., MIL-101-NH2 (Fe), one of the most prevalent MOFs used in drug delivery and imaging). We further examined the interplay between the surface binding of fluorescent probes and the degradation of MIL-101-NH2 (Fe) in aqueous medium. It was demonstrated that the surface binding of probes is not only of high affinity but also dynamic and nonsheddable, even during the degradation, a feature that is essentially different from the covalent conjugation. Subsequently, we developed a unique and straightforward strategy for the surface modification of MIL-101-NH2 (Fe) with polymer by exploiting the synergy of noncovalent interactions between functionalized copolymers and MIL-101-NH2 (Fe). We demonstrated that the binding of polymers onto MIL-101-NH2 (Fe) surface was very effective in aqueous solution and surprisingly nonsheddable during the process of degradation. Surface polymers can creep on the surface of MIL-101-NH2 (Fe), in a dynamic and real-time manner, to the new sites formed immediately after the degradation. In addition, the stability of MIL-101-NH2 (Fe) particles in aqueous environments can be improved to some extent by the surface polymer coating. The results presented herein constitute an important innovation for surface engineering of nano-MOFs, which would benefit the application of nano-MOFs as delivery systems in aqueous systems.

Metal-organic frameworks as sensory materials and imaging agents

Metal-organic frameworks (MOFs) are a class of hybrid materials self-assembled from organic bridging ligands and metal ion/cluster connecting points. The combination of a variety of organic linkers, metal ions/clusters, and structural motifs can lead to an infinite array of new materials with interesting properties for many applications. In this Forum Article, we discuss the design and applications of MOFs in chemical sensing and biological imaging. The first half of this article focuses on the development of MOFs as chemical sensors by highlighting how unique attributes of MOFs can be utilized to enhance sensitivity and selectivity. We also discuss some of the issues that need to be addressed in order to develop practically useful MOF sensors. The second half of this article focuses on the design and applications of nanoscale MOFs (NMOFs) as imaging contrast agents. NMOFs possess several interesting attributes, such as high cargo loading capacity, ease of postmodification, tunable size and shape, and intrinsic biodegradability, to make them excellent candidates as imaging contrast agents. We discuss the use of representative NMOFs in magnetic resonance imaging (MRI), X-ray computed tomography (CT), and optical imaging. Although still in their infancy, we believe that the compositional tunability and mild synthetic conditions of NMOF imaging agents should greatly facilitate their further development for clinical translation.

A “Ship in a Bottle” Strategy To Load a Hydrophilic Anticancer Drug in Porous Metal Organic Framework Nanoparticles: Efficient Encapsulation, Matrix Stabilization, and Photodelivery

An essential challenge in the development of nanosized metal organic framework (nanoMOF) materials in biomedicine is to develop a strategy to stabilize their supramolecular structure in biological media while being able to control drug encapsulation and release. We have developed a method to efficiently encapsulate topotecan (TPT, 1), an important cytotoxic drug, in biodegradable nanoMOFs. Once inside the pores, 1 monomers aggregate in a "ship in a bottle" fashion, thus filling practically all of the nanoMOFs' available free volume and stabilizing their crystalline supramolecular structures. Highly efficient results have been found with the human pancreatic cell line PANC1, in contrast with free 1. We also demonstrate that one- and two-photon light irradiation emerges as a highly promising strategy to promote stimuli-dependent 1 release from the nanoMOFs, hence opening new standpoints for further developments in triggered drug delivery.

Cytotoxicity of nanoscaled metal-organic frameworks

A series of fourteen porous Metal-Organic Frameworks (MOFs) with different compositions (Fe, Zn, and Zr; carboxylates or imidazolates) and structures have been successfully synthesised at the nanoscale and fully characterised by XRPD, FTIR, TGA, N₂ porosimetry, TEM, DLS and ζ-potential. Their toxicological assessment was performed using two different cell lines: human epithelial cells from foetal cervical carcinoma (HeLa) and murine macrophage cell line (J774). It appears that MOF nanoparticles (NPs) exhibit low cytotoxicity, comparable to those of other commercialised nanoparticulate systems, the less toxic being the Fe carboxylate and the more toxic being the zinc imidazolate NPs. The cytotoxicity values, higher in J774 cells than in HeLa cells, are mainly function of their composition and cell internalisation capacity. Finally, cell uptake of one of the most relevant Fe-MOF-NPs for drug vectorisation has been investigated by confocal microscopy studies, and indicates a faster kinetics of cell penetration within J774 compared to HeLa cells.