Development of folate-conjugated polypyrrole nanoparticles incorporated with nitrogen-doped carbon quantum dots for targeted bioimaging and photothermal therapy

PPy nanoparticles are widely employed as PTT agents, because of their exceptional near-infrared absorption properties. Nonetheless, the efficacy of PTT with PPy nanoparticles is hindered by a challenge, specifically, a lack of precise targeting. In this study, a PTT imaging agent was developed by combining NCQDs having bright green fluorescent properties with PPy nanoparticles along with the masking of folic acid to overcome the challenge of targeting. The synthesized PPy:NCQDs:FA nanocomposite, characterized by extraordinary photothermal property, was utilized for imaging of folate receptor positive (FA+) MCF-7 cancer cells through the emission of green fluorescence by NCQDs incorporated within the nanocomposite. Additionally, these nanoparticles demonstrated a good level of cell viability, exceeding 82 %, even at a concentration of 600 μg mL-1. Even the in vivo toxicity inspection of the nanocomposite exemplified no observed acute toxicity at experimental dosages of 1 and 3 mg per kg body weight. By subjecting MCF-7 cells, inoculated with 100 μg mL-1 of nanocomposite, to NIR laser irradiation for 5 min, a significant decline in cell viability was witnessed, establishing the photothermal therapeutic potency of the nanocomposite. The death of cancer cells induced by nanocomposite was verified through MTT assay, imaging of cells by NCQDs alone, with nanocomposite, and by live/dead cell Calcein AM/PI staining assay. Quantification of induced apoptosis post-laser treatment is conducted through staining with Annexin V-FITC/PI. These findings establish potential use of PPy:NCQDs:FA nanocomposite as versatile theranostic agents, capable of targeted bioimaging and treatment for cancer cells exhibiting folate receptors.

Porous Organic Polymer-Based Nanocomposites for Hypoxia Relieving and Enhanced Chemotherapy in Hepatocellular Carcinoma

Uncontrolled proliferation and altered metabolism of cancer cells result in an imbalance of nutrients and oxygen supply, and persuade hypoxia. Hypoxia, in turn, activates the transcription gene HIF-1α, which eventually upregulates the efflux transporter P-gp and induces multidrug resistance (MDR). Thus, hypoxia leads to the development of resistance to conventional therapies. Therefore, the fabrication of a nanoscale porous system enriched with upconversion nanoparticles to target cancer cells, evade hypoxia, and enhance anticancer therapy is the key goal of this article. Herein, upconversion nanoparticles are embedded in a nanoscale porous organic polymer (POP) and further conjugated with a targeting moiety and a catalase molecule. The nanoscale POP embedded in UCNPs is generated at room temperature. The targeting ligand, lactobionic acid, is attached after polymer coating, which effectively targets liver cancer cells. Then, catalase is grafted effectively to produce oxygen. Endogenously generated oxygen alleviates hypoxia in liver cancer cells. The drug- and catalase-loaded composite exhibit greater cytotoxicity in hypoxic liver cells than in normal cells by overcoming hypoxia and downregulating the hypoxia-inducible factors.

Targeted cancer treatment using folate-conjugated sponge-like ZIF-8 nanoparticles: a review

ZIF-8 (zeolitic imidazolate framework-8) is a potential drug delivery system because of its unique properties, which include a large surface area, a large pore capacity, a large loading capacity, and outstanding stability under physiological conditions. ZIF-8 nanoparticles may be readily functionalized with targeting ligands for the identification and absorption of particular cancer cells, enhancing the efficacy of chemotherapeutic medicines and reducing adverse effects. ZIF-8 is also pH-responsive, allowing medication release in the acidic milieu of cancer cells. Because of its tunable structure, it can be easily functionalized to design cancer-specific targeted medicines. The delivery of ZIF-8 to cancer cells can be facilitated by folic acid-conjugation. Hence, it can bind to overexpressed folate receptors on the surface of cancer cells, which holds the promise of reducing unwanted deliveries. As a result of its importance in cancer treatment, the folate-conjugated ZIF-8 was the major focus of this review.

Recent advances in metal-organic frameworks for stimuli-responsive drug delivery

After entering the human body, drugs for treating diseases, which are prone to delivery and release in an uncontrolled manner, are affected by various factors. Based on this, many researchers utilize various microenvironmental changes encountered during drug delivery to trigger drug release and have proposed stimuli-responsive drug delivery systems. In recent years, metal-organic frameworks (MOFs) have become promising stimuli-responsive agents to release the loaded therapeutic agents at the target site to achieve more precise drug delivery due to their high drug loading, excellent biocompatibility, and high stimuli-responsiveness. The MOF-based stimuli-responsive systems can respond to various stimuli under pathological conditions at the site of the lesion, releasing the loaded therapeutic agent in a controlled manner, and improving the accuracy and safety of drug delivery. Due to the changes in different physical and chemical factors in the pathological process of diseases, the construction of stimuli-responsive systems based on MOFs has become a new direction in drug delivery and controlled release. Based on the background of the rapidly increasing attention to MOFs applied in drug delivery, we aim to review various MOF-based stimuli-responsive drug delivery systems and their response mechanisms to various stimuli. In addition, the current challenges and future perspectives of MOF-based stimuli-responsive drug delivery systems are also discussed in this review.

A pH-responsive bi-MIL-88B MOF coated with folic acid-conjugated chitosan as a promising nanocarrier for targeted drug delivery of 5-Fluorouracil

Cancer has remained one of the leading causes of death worldwide, with a lack of effective treatment. The intrinsic shortcomings of conventional therapeutics regarding tumor specificity and non-specific toxicity prompt us to look for alternative therapeutics to mitigate these limitations. In this regard, we developed multifunctional bimetallic (FeCo) bi-MIL-88B-FC MOFs modified with folic acid-conjugated chitosan (FC) as drug delivery systems (DDS) for targeted delivery of 5-Fluorouracil (5-FU). The bi-MIL-88B nanocarriers were characterized through various techniques, including powder X-ray diffraction, scanning electron microscopy, energy-dispersive X-ray, thermogravimetric analysis, and Fourier transform infrared spectroscopy. Interestingly, 5-FU@bi-MIL-88B-FC showed slower release of 5-FU due to a gated effect phenomenon endowed by FC surface coating compared to un-modified 5-FU@bi-MIL-88B. The pH-responsive drug release was observed, with 58% of the loaded 5-FU released in cancer cells mimicking pH (5.2) compared to only 24.9% released under physiological pH (5.4). The in vitro cytotoxicity and cellular internalization experiments revealed the superiority of 5-FU@bi-MIL-88B-FC as a highly potent targeted DDS against folate receptor (FR) positive SW480 cancer cells. Moreover, due to the presence of Fe and Co in the structure, bi-MIL-88B exhibited peroxidase-like activity for chemodynamic therapy. Based on the results, 5-FU@bi-MIL-88B-FC could serve as promising candidate for smart DDS by sustained drug release and selective targeting.

Nanocarrier design–function relationship: The prodigious role of properties in regulating biocompatibility for drug delivery applications

The concept of drug delivery systems as a magic bullet for the delivery of bioactive compounds has emerged as a promising approach in the treatment of different diseases with significant advantages over the limitations of traditional methods. While nanocarrier-based drug delivery systems are the main advocates of drug uptake because they offer several advantages including reduced non-specific biodistribution, improved accumulation, and enhanced therapeutic efficiency; their safety and biocompatibility within cellular/tissue systems are therefore important for achieving the desired effect. The underlying power of "design-interplay chemistry" in modulating the properties and biocompatibility at the nanoscale level will direct the interaction with their immediate surrounding. Apart from improving the existing nanoparticle physicochemical properties, the balancing of the hosts' blood components interaction holds the prospect of conferring newer functions altogether. So far, this concept has been remarkable in achieving many fascinating feats in addressing many challenges in nanomedicine such as immune responses, inflammation, biospecific targeting and treatment, and so on. This review, therefore, provides a diverse account of the recent advances in the fabrication of biocompatible nano-drug delivery platforms for chemotherapeutic applications, as well as combination therapy, theragnostic, and other diseases that are of interest to scientists in the pharmaceutical industries. Thus, careful consideration of the "property of choice" would be an ideal way to realize specific functions from a set of delivery platforms. Looking ahead, there is an enormous prospect for nanoparticle properties in regulating biocompatibility.

Synthesis of Biocompatible Nanoporous ZIF-8-Gum Arabic as a New Carrier for the Targeted Delivery of Curcumin

The synthesis of biocompatible nanoporous zeolitic imidazolate framework-8 (ZIF-8) was performed in the presence of gum arabic (GA), curcumin (CCM), and folic acid (FA) as a template for the biomineralization process, a natural anticancer component, and a targeting agent, respectively. The synthesis of ZIF-8-GA-CCM-FA was completed in a single step at room temperature in aqueous media with a minimum amount of ethanol at a linker/metal molar ratio of 10. FA was dissolved by the alkaline medium produced by a 2-methyl imidazolium (HmIm) linker without using any toxic organic solvent or additional conjugation agents. The FA-modified carrier can target the folate receptors on Hela cells. To the best of our knowledge, this is the first report about the one-pot encapsulation of CCM and FA in a biocompatible ZIF-8-GA framework in a green solvent. This method enables high CCM loading in the ZIF-8-GA framework structure (ca. 90%) at a short time of 15 min. The effect of CCM concentration was investigated on the size, morphology, and crystallinity of the synthesized structures. The products were characterized with field emission scanning electron microscopy, Brunauer-Emmett-Teller surface area analysis, X-ray diffraction, Fourier transform infrared, and UV-vis spectroscopy techniques. The release rate of CCM from ZIF-8-GA-CCM-FA was studied at different pH values. In vitro drug release of CCM was higher in the acidic medium (pH 5.5, 6.5) compared to physiological pH (7.4). The cytotoxicity of ZIF-8-GA, ZIF-8-GA-CCM, and ZIF-8-GA-CCM-FA structures was evaluated by the standard 3-(4,5 dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay on the three cell lines (fibroblast (normal cell), Hela (FR-positive), and A549 (FR-negative). These results suggested that the ZIF-8-GA-CCM-FA framework can have a promising effect on the targeted treatment of cancer cells.

Review on Metal-Organic Framework Classification, Synthetic Approaches, and Influencing Factors: Applications in Energy, Drug Delivery, and Wastewater Treatment

Metal ions or clusters that have been bonded with organic linkers to create one- or more-dimensional structures are referred to as metal-organic frameworks (MOFs). Reticular synthesis also forms MOFs with properly designated components that can result in crystals with high porosities and great chemical and thermal stability. Due to the wider surface area, huge pore size, crystalline nature, and tunability, numerous MOFs have been shown to be potential candidates in various fields like gas storage and delivery, energy storage, catalysis, and chemical/biosensing. This study provides a quick overview of the current MOF synthesis techniques in order to familiarize newcomers in the chemical sciences field with the fast-growing MOF research. Beginning with the classification and nomenclature of MOFs, synthesis approaches of MOFs have been demonstrated. We also emphasize the potential applications of MOFs in numerous fields such as gas storage, drug delivery, rechargeable batteries, supercapacitors, and separation membranes. Lastly, the future scope is discussed along with prospective opportunities for the synthesis and application of nano-MOFs, which will help promote their uses in multidisciplinary research.

Application of MOF-based nanotherapeutics in light-mediated cancer diagnosis and therapy

Light-mediated nanotherapeutics have recently emerged as promising strategies to precisely control the activation of therapeutic reagents and imaging probe both in vitro and in vivo, largely ascribed to their unique properties, including minimally invasive capabilities and high spatiotemporal resolution. Nanoscale metal-organic frameworks (NMOFs), a new family of hybrid materials consisting of metal attachment sites and bridging ligands, have been explored as a new platform for enhanced cancer diagnosis and therapy due to their tunable size, modifiable surface, good biocompatibility, high agent loading and, most significantly, their ability to be preferentially deposited in tumors through enhanced permeability and retention (EPR). Especially the light-driven NMOF-based therapeutic platform, which not only allow for increased laser penetration depth and enhanced targeting, but also enable imaging-guided or combined treatments. This review provides up-to-date developments of NMOF-based therapeutic platforms for cancer treatment with emphasis on light-triggered therapeutic strategies and introduces their advances in cancer diagnosis and therapy in recent years.

Programmable Drug Release from a Dual-Stimuli Responsive Magnetic Metal-Organic Framework

Along with the increasing incidence of cancer and drawbacks of traditional drug delivery systems (DDSs), developing novel nanocarriers for sustained targeted-drug release has become urgent. In this regard, metal-organic frameworks (MOFs) have emerged as potential candidates due to their structural flexibility, defined porosity, lower toxicity, and biodegradability. Herein, a FeMn-based ferromagnetic MOF was synthesized from a preassembled Fe₂Mn(μ₃-O) cluster. The introduction of the Mn provided the ferromagnetic character to FeMn-MIL-88B. 5-Fluoruracil (5-FU) was encapsulated as a model drug in the MOFs, and its pH and H₂S dual-stimuli responsive controlled release was realized. FeMn-MIL-88B presented a higher 5-FU loading capacity of 43.8 wt % and rapid drug release behavior in a tumor microenvironment (TME) simulated medium. The carriers can rapidly release loaded drug of 70% and 26% in PBS solution (pH = 5.4) and NaHS solution (500 μM) within 24 h. The application of mathematical release models indicated 5-FU release from carriers can be precisely fitted to the first-order, second-order, and Higuchi models of release. Moreover, the cytotoxicity profile of the carrier against human embryonic kidney cells (HEK293T) suggests no adverse effects up to 100 μg/mL. The lesser toxic effect on cell viability can be attributed to the low toxicity values [LD₅₀ (Fe) = 30 g·kg^-1, (Mn) = 1.5 g·kg^-1, and (terephthalic acid) = 5 g·kg^-1] of the MOFs structural components. Together with dual-stimuli responsiveness, ferromagnetic nature, and low toxicity, FeMn-MIL-88B MOFs can emerge as promising carriers for drug delivery applications.

Lipid Membrane-Wrapped Zeolitic Imidazolate Framework-8 for Synergistic Chemotherapy and Photothermal Therapy to Target Prostate Cancer

Endocrine therapy is often used for advanced prostate cancer. However, with cancer progress, prostate cancer gradually resistant to hormone which lead to serious threatens to life of patients. Herein, a multifunctional synergistic core–shell nanoplatform is reported for improving the therapeutic effect of chemotherapy for advanced or metastatic prostate cancer, and reducing the risk of leakage of chemotherapy drugs. Particularly, Zeolitic imidazolate framework-8 (ZIF-8) is chosen as inner core to load doxorubicin, and the of liposomes which are embedded with IR780 iodide are used as outer shell, and further modified with target ligand that binds to luteinizing hormone releasing hormone receptor. The prepared nanocarrier exhibit satisfactory photothermal effect under near infrared laser irradiation, and the temperature increases to 60.8 °C within 6 min. Meanwhile, the elevated temperature accelerates the degradation of lipid shell, releasing ZIF-8 core to acidic microenvironment of tumor, and resulting in the release of doxorubicin. Moreover, in vivo and in vitro studies have shown the ZIF-D@ALIP core–shell nanoparticles can achieve targeted drug delivery, pH and NIR dual stimuli-responsive drug release, as well as chemotherapy and photothermal therapy synergistically on the tumor site. In addition, the problem of premature leakage and changes in the physicochemical properties of anticancer drugs are avoided under the protection of the outer shell structure. Therefore, the core–shell nanostructure proposes a new lipid membrane coating strategy to promote the effective targeting of prostate cancer cells or tissues and provides some insights in clinical treatment for advanced prostate cancer.

Dissolution and Biological Assessment of Cancer-Targeting Nano-ZIF-8 in Zebrafish Embryos

Cancer-targeting nanotherapeutics offer promising opportunities for selective delivery of cytotoxic chemotherapeutics to cancer cells. However, the understanding of dissolution behavior and safety profiles of such nanotherapeutics is scarce. In this study, we report the dissolution profile of a cancer-targeting nanotherapeutic, gemcitabine (GEM) encapsulated within RGD-functionalized zeolitic imidazolate framework-8 (GEM⊂RGD@nZIF-8), in dissolution media having pH = 6.0 and 7.4. GEM⊂RGD@nZIF-8 was not only responsive in acidic media (pH = 6.0) but also able to sustain the dissolution rate (57.6%) after 48 h compared to non-targeting nanotherapeutic GEM⊂nZIF-8 (76%). This was reflected by the f₂ value of 36.1, which indicated a difference in the dissolution behaviors of GEM⊂RGD@nZIF-8 and GEM⊂nZIF-8 in acidic media compared to those in neutral media (pH = 7.4). A dissolution kinetic study showed that the GEM release mechanism from GEM⊂RGD@nZIF-8 followed the Higuchi model. In comparison to a non-targeting nanotherapeutic, the cancer-targeting nanotherapeutic exhibited an enhanced permeability rate in healthy zebrafish embryos but did not induce lethality to 50% of the embryos (LC₅₀ > 250 μg mL^-1) with significantly improved survivability (75%) after 96 h of incubation. Monitoring malformation showed minimal adverse effects with only 8.3% of edema at 62.5 μg mL^-1. This study indicates that cancer-targeting GEM⊂RGD@nZIF, with its pH-responsive behavior for sustaining chemotherapeutic dissolution in a physiologically relevant environment and its non-toxicity toward the healthy embryos within the tested concentrations, has considerable potential for use in cancer treatment.

Metal-Organic Frameworks for Bioimaging: Strategies and Challenges

Metal-organic frameworks (MOFs), composited with metal ions and organic linkers, have become promising candidates in the biomedical field own to their unique properties, such as high surface area, pore-volume, tunable pore size, and versatile functionalities. In this review, we introduce and summarize the synthesis and characterization methods of MOFs, and their bioimaging applications, including optical bioimaging, magnetic resonance imaging (MRI), computed tomography (CT), and multi-mode. Furthermore, their bioimaging strategies, remaining challenges and future directions are discussed and proposed. This review provides valuable references for the designing of molecular bioimaging probes based on MOFs.

Folic acid modified UiO-66 nano drug carrier for combination therapy

The drug delivery system which called RB-Drug@UiO-66-FA can release anticancer drugs slowly in an acidic environment, and generate 1O2 under light exposure, achieving the effect of chemotherapy–photodynamic therapy.

Heterostructures Made of Upconversion Nanoparticles and Metal-Organic Frameworks for Biomedical Applications

Heterostructure nanoparticles (NPs), constructed by two single-component NPs with distinct nature and multifunctional properties, have attracted intensive interest in the past few years. Among them, heterostructures made of upconversion NPs (UCNPs) and metal-organic frameworks (MOFs) can not only integrate the advantageous characteristics (e.g., porosity, structural regularity) of MOFs with unique upconverted optical features of UCNPs, but also induce cooperative properties not observed either for single component due to their special optical or electronic communications. Recently, diverse UCNP-MOF heterostructures are designed and synthesized via different strategies and have demonstrated appealing potential for applications in biosensing and imaging, drug delivery, and photodynamic therapy (PDT). In this review, the synthesis strategies of UCNP-MOF heterostructures are first summarized, then the authors focus mainly on discussion of their biomedical applications, particularly as PDT agents for cancer treatment. Finally, the authors briefly outlook the current challenges and future perspectives of UCNP-MOF hybrid nanocomposites. The authors believe that this review will provide comprehensive understanding and inspirations toward recent advances of UCNP-MOF heterostructures.

Zinc-Based Metal-Organic Frameworks in Drug Delivery, Cell Imaging, and Sensing

The design and structural frameworks for targeted drug delivery of medicinal compounds and improved cell imaging have been developed with several advantages. However, metal-organic frameworks (MOFs) are supplemented tremendously for medical uses with efficient efficacy. These MOFs are considered as an absolutely new class of porous materials, extensively used in drug delivery systems, cell imaging, and detecting the analytes, especially for cancer biomarkers, due to their excellent biocompatibility, easy functionalization, high storage capacity, and excellent biodegradability. While Zn-metal centers in MOFs have been found by enhanced efficient detection and improved drug delivery, these Zn-based MOFs have appeared to be safe as elucidated by different cytotoxicity assays for targeted drug delivery. On the other hand, the MOF-based heterogeneous catalyst is durable and can regenerate multiple times without losing activity. Therefore, as functional carriers for drug delivery, cell imaging, and chemosensory, MOFs' chemical composition and flexible porous structure allowed engineering to improve their medical formulation and functionality. This review summarizes the methodology for fabricating ultrasensitive and selective Zn-MOF-based sensors, as well as their application in early cancer diagnosis and therapy. This review also offers a systematic approach to understanding the development of MOFs as efficient drug carriers and provides new insights on their applications and limitations in utility with possible solutions.

Metal-Organic Frameworks (MOFs) for Cancer Therapy

MOFs exhibit inherent extraordinary features for diverse applications ranging from catalysis, storage, and optics to chemosensory and biomedical science and technology. Several procedures including solvothermal, hydrothermal, mechanochemical, electrochemical, and ultrasound techniques have been used to synthesize MOFs with tailored features. A continued attempt has also been directed towards functionalizing MOFs via "post-synthetic modification" mainly by changing linkers (by altering the type, length, functionality, and charge of the linkers) or node components within the MOF framework. Additionally, efforts are aimed towards manipulating the size and morphology of crystallite domains in the MOFs, which are aimed at enlarging their applications window. Today's knowledge of artificial intelligence and machine learning has opened new pathways to elaborate multiple nanoporous complex MOFs and nano-MOFs (NMOFs) for advanced theranostic, clinical, imaging, and diagnostic purposes. Successful accumulation of a photosensitizer in cancerous cells was a significant step in cancer therapy. The application of MOFs as advanced materials and systems for cancer therapy is the main scope beyond this perspective. Some challenging aspects and promising features in MOF-based cancer diagnosis and cancer therapy have also been discussed.

Peptide-Mediated Synthesis of Zeolitic Imidazolate Framework-8: Effect of Molecular Hydrophobicity, Charge Number and Charge Location

Three amphiphilic peptides with varied molecular hydrophobicity, charge number and charge location have been designed as regulators to modulate the crystal growth of zeolitic imidazolate framework-8 (ZIF-8). All three peptides can interact with ZIF-8 to inhibit {100} facet growth and produce truncated cubic crystals. The peptide's molecular hydrophobicity plays a dominant role in defining the final morphology and size of the ZIF-8 crystals. The peptides with less charge and higher hydrophobicity can promote nuclei formation and crystal growth to give smaller ZIF-8 crystals. However, the charge located in the center of the molecular hydrophobic region has little effect on the crystal nucleation and growth due to the shielding of its charge by molecular aggregation. The study provides insights into the effect of molecular charge and hydrophobicity on ZIF-8 crystal growth and is helpful for guiding the molecular design for regulating the synthesis of metal-organic framework materials.

Development of a pH-sensitive functionalized metal organic framework: in vitro study for simultaneous delivery of doxorubicin and cyclophosphamide in breast cancer

Exploration of an efficient dual-drug based nanocarrier with high drug loading capacity, specific targeting properties, and long-term stability is highly desirable in cancer therapy. Metal-organic frameworks (MOFs) have proven to be a promising class of drug carriers due to their high porosity, crystalline properties with defined structure information, and their potential for further functionalization. To enhance the drug efficacy as well as to overcome the burst effect of drugs, here we synthesized a pH responsive folic acid (FA) and graphene oxide (GO) decorated zeolitical imidazolate frameworks-8 (GO-FA/ZIF-8), for targeted delivery of doxorubicin (DOX) and cyclophosphamide (CP), simultaneously. In this system, DOX molecules were encapsulated in the pores of ZIF-8 during in situ synthesis of ZIF-8 and CP molecules have been captured by the GO surface via hydrogen bonding and π-π interactions as well. Furthermore, the resulting pH-responsive nanocarrier (DOX@ZIF-8/GO-FA/CP) showed in vitro sustained release characteristics (76% of DOX and 80% of CP) by cleavage of chemical bonding and disruption of the MOFs structure under acidic condition (at pH 5.6). Moreover, DOX@ZIF-8/GO-FA/CP has synergistic cytotoxic effects as compared to the combination of both the drugs without ZIF-8/GO-FA when treating MCF-7 and MDA-MB-231 breast cancer cell lines (with a combination index of 0.29 and 0.75 for MCF-7 and MDA-MB-231 cell-lines, respectively). Hence this system can be applied as an effective platform for smart dual drug delivery in breast cancer treatment through its remarkable manageable multidrug release.

When metal-organic framework mediated smart drug delivery meets gastrointestinal cancers

Cancers of the gastrointestinal tract constitute one of the most common cancer types worldwide and a ∼58% increase in the global number of cases has been estimated by IARC for the next twenty years. Recent advances in drug delivery technologies have attracted scientific interest for developing and utilizing efficient therapeutic systems. The present review focuses on the use of nanoscale MOFs (Nano-MOFs) as carriers for drug delivery and imaging purposes. In pursuit of significant improvements to current gastrointestinal cancer chemotherapy regimens, systems that allow multiple concomitant therapeutic options (polytherapy) and controlled release are highly desirable. In this sense, MOF-based nanotherapeutics represent a significant step towards achieving this goal. Here, the current state-of-the-art of interdisciplinary research and novel developments into MOF-based gastrointestinal cancer therapy are highlighted and reviewed.

Metal-organic frameworks for advanced drug delivery

Metal-organic frameworks (MOFs), comprised of organic ligands and metal ions/metal clusters via coordinative bonds are highly porous, crystalline materials. Their tunable porosity, chemical composition, size and shape, and easy surface functionalization make this large family more and more popular for drug delivery. There is a growing interest over the last decades in the design of engineered MOFs with controlled sizes for a variety of biomedical applications. This article presents an overall review and perspectives of MOFs-based drug delivery systems (DDSs), starting with the MOFs classification adapted for DDSs based on the types of constituting metals and ligands. Then, the synthesis and characterization of MOFs for DDSs are developed, followed by the drug loading strategies, applications, biopharmaceutics and quality control. Importantly, a variety of representative applications of MOFs are detailed from a point of view of applications in pharmaceutics, diseases therapy and advanced DDSs. In particular, the biopharmaceutics and quality control of MOFs-based DDSs are summarized with critical issues to be addressed. Finally, challenges in MOFs development for DDSs are discussed, such as biostability, biosafety, biopharmaceutics and nomenclature.

A highly sensitive upconversion nanoparticles@zeolitic imidazolate frameworks fluorescent nanoprobe for gallic acid analysis

In this work, a core-shell structured upconversion nanoparticles@zeolitic imidazolate frameworks (ZIF-8) fluorescent nanoprobe (NaErF₄:Tm@SiO₂@ZIF-8) has been designed for the detection of gallic acid (GA). The mechanism is according to the 3, 3', 5, 5'-tetramethylbenzidine (TMB) can be oxidized to oxidized TMB (oxTMB) by Ag⁺. Under 980 nm laser excitation, NaErF₄:Tm@SiO₂@ZIF-8 can emit red light at 652 nm, which have a good overlap with the absorption spectra of oxTMB, resulting in the fluorescence quenching at 652 nm. Continually adding GA into the above solution, oxTMB will restore to TMB, and the fluorescence intensity at 652 nm gradually recovers, which can realize the detection towards GA. The linear detection range of GA is from 0 to 30 μM, and the limit of detection (LOD) of GA is 0.35 μM. The ZIF-8 can largely enhance the sensitivity of the nanoprobe, due to the physical absorption and the electrostatic attraction between ZIF-8 and the oxTMB. More importantly, this is the first time to realize the detection of GA with high sensitivity by using upconversion fluorescence. Besides, we have realized the analysis of GA in real samples, which certify the feasible of the nanoprobe in potential applications.

Doxorubicin-Loaded MnO2@Zeolitic Imidazolate Framework-8 Nanoparticles as a Chemophotothermal System for Lung Cancer Therapy

Doxorubicin-loaded MnO₂@zeolitic imidazolate framework-8 (DOX/MnO₂@ZIF-8) nanoparticles, a smart multifunctional therapeutic platform, were prepared for the treatment of lung cancer. The morphology, structure, and redox and photothermal properties of MnO₂@ZIF-8 were characterized by the corresponding methods. The anticancer drug DOX released from the DOX/MnO₂@ZIF-8 nanoparticles was measured. The cell viability of Lewis lung cancer (LLC) cells treated with MnO₂@ZIF-8 or DOX/MnO₂@ZIF-8 nanoparticles was determined using the cell counting kit-8 (CCK-8) method. The cellular uptake of DOX/MnO₂@ZIF-8 nanoparticles into LLC cells was observed using a confocal laser scanning microscope. TUNEL staining was performed to evaluate the in vivo therapeutic efficacy of DOX/MnO₂@ZIF-8 nanoparticles. The results showed that the as-prepared MnO₂@ZIF-8 nanoparticles had an average particle size of 155.59 ± 13.61 nm and the DOX loading efficiency was 12 wt %. MnO₂@ZIF-8 could react with H₂O₂ to generate O₂ and showed a great photothermal conversion effect both in vitro and in vivo. Up to 82% of total DOX could be released from DOX/MnO₂@ZIF-8 nanoparticles at pH = 5.0. The CCK-8 assay showed that MnO₂@ZIF-8 had low cytotoxicity to LLC cells, while DOX/MnO₂@ZIF-8 can significantly reduce the cell viability. DOX/MnO₂@ZIF-8 can be accumulated in LLC cells over time. Compared with PBS and DOX/MnO₂@ZIF-8 groups, the mice in the DOX/MnO₂@ZIF-8 + NIR group had the most apoptotic cells and significantly reduced tumor volume. In conclusion, these findings suggest that the as-prepared MnO₂@ZIF-8 nanoparticles with synergetic therapeutic effects by photothermal therapy and improved tumor microenvironment and as a pH-responsive nanocarrier for delivering the nonspecific anticancer drug DOX might be applied in the treatment of lung cancer.

Delivery of oxaliplatin to colorectal cancer cells by folate-targeted UiO-66-NH2

Oxaliplatin is being used in different malignancies and several side effects are reported for patients taking Oxaliplatin, including peripheral neuropathy, nausea and vomiting, diarrhea, mouth sores, low blood counts, fatigue, loss of appetite, etc. Here we have developed a targeted anticancer drug delivery system based on folate-conjugated amine-functionalized UiO-66 for the delivery of oxaliplatin (OX). UiO-66-NH₂ (U) and UiO-66-NH₂-FA(FU) were pre-functionalized by the incorporation of folic acid (FA) into the structure via coordination of the carboxylate group of FA. The FTIR spectra of drug-loaded U and FU showed the presence of new carboxylic and aliphatic groups of OX and FA. Powder X-ray diffraction (PXRD) patterns were matched accordingly with the reference pattern and FESEM results showed semi-spherical particles (115-128 nm). The evaluated amounts of OX in U and FU were calculated 304.5 and 293 mg/g_, respectively. The initial burst release of OX was 15.7% per hour for U(OX) and 10.8% per hour for FU(OX). The final release plateau gives 62.9% and 52.3% for U(OX) and FU(OX). To evaluate the application of the prepared delivery platform, they were tested on colorectal cancer cells (CT-26) via MTT assay, cell migration assay, and spheroid model. IC₅₀ values obtained from MTT assay were 21.38, 95.50, and 18.20 μg/mL for OX, U(OX), and FU(OX), respectively. After three days of treatment, the CT26 spheroids at two doses of 500 and 50 μg/mL of U(OX) and FU(OX) showed volume reduction. Moreover, the oxidative behavior of the prepared systems within the cell was assessed by total thiol, malondialdehyde, and superoxide dismutase activity. The results showed that FU(OX) had higher efficacy in preventing the growth of CT-26 spheroid, and was more effective than oxaliplation in cell migration inhibition, and induced higher oxidative stress and apoptosis.

Supramolecular magnetonanohybrids for multimodal targeted therapy of triple-negative breast cancer cells

Despite the undeniable advances in recent decades, cancer remains one of the deadliest diseases of the current millennium, where the triple-negative breast cancer (TNBC) is very aggressive, extremely metastatic, and resistant to conventional chemotherapy. The nanotheranostic approach focusing on targeting membrane receptors often expressed at abnormal levels by cancer cells can be a strategic weapon for fighting malignant tumors. Herein, we introduced a novel "all-in-one nanosoldier" made of colloidal hybrid nanostructures, which were designed for simultaneously targeting, imaging, and killing TNBC cells. These nanohybrids comprised four distinct components: (a) superparamagnetic iron oxide nanoparticles, as bi-functional nanomaterials for inducing ferroptosis via inorganic nanozyme-mediated catalysis and magnetotherapy by hyperthermia treatment; (b) carboxymethyl cellulose biopolymer, as a water-soluble capping macromolecule; (c) folic acid, as the membranotopic vector for targeting folate receptors; (d) and doxorubicin (DOX) drug for chemotherapy. The results demonstrated that this novel strategy was highly effective for targeting and killing TNBC cells in vitro, expressing high levels of folate membrane-receptors. The results evidenced that three integrated mechanisms triggered the deaths of the cancer cells in vitro: (a) ferroptosis, by magnetite nanoparticles inducing a Fenton-like reaction; (b) magneto-hyperthermia effect by generating heat under an alternate magnetic field; and (c) chemotherapy, through the DOX intracellular release causing DNA dysfunction. This "all-in-one nanosoldier" strategy offers a vast realm of prospective alternatives for attacking cancer cells, combining multimodal therapy and the delivery of therapeutic agents to diseased sites and preserving healthy cells, which is one of the most critical clinical challenges faced in fighting drug-resistant breast cancers.

Applications of nanoscale metal-organic frameworks as imaging agents in biology and medicine

Nanoscale metal-organic frameworks (NMOFs) are an interesting and unique class of hybrid porous materials constructed by the self-assembly of metal ions/clusters with organic linkers. The high storage capacities, facile synthesis, easy surface functionalization, diverse compositions and excellent biocompatibilities of NMOFs have made them promising agents for theranostic applications. By combination of a large variety of metal ions and organic ligands, and incorporation of desired molecular functionalities including imaging modalities and therapeutic molecules, diverse MOF structures with versatile functionalities can be obtained and utilized in biomedical imaging and drug delivery. In recent years, NMOFs have attracted great interest as imaging agents in optical imaging (OI), magnetic resonance imaging (MRI), computed tomography (CT), positron emission tomography (PET) and photoacoustic imaging (PAI). Furthermore, the significant porosity of MOFs allows them to be loaded with multiple imaging agents and therapeutics simultaneously and applied for multimodal imaging and therapy as a single entity. In this review, which is intended as an introduction to the use of MOFs in biomedical imaging for a reader entering the subject, we summarize the up-to-date progress of NMOFs as bioimaging agents, giving (i) a broad perspective of the varying imaging techniques that MOFs can enable, (ii) the different routes to manufacturing functionalised MOF nanoparticles and hybrids, and (iii) the integration of imaging with differing therapeutic techniques. The current challenges and perspectives of NMOFs for their further clinical translation are also highlighted and discussed.

NIR-triggered biodegradable MOF-coated upconversion nanoparticles for synergetic chemodynamic/photodynamic therapy with enhanced efficacy

The generation of reactive oxygen species (ROS) is often limited by the overexpression of glutathione (GSH) in the tumor microenvironment (TME) and the penetration depth of visible light.

A versatile and multifunctional metal-organic framework nanocomposite toward chemo-photodynamic therapy

Previously most of the applications of targeting components have been based on the enhanced permeability and retention effect achieved using folic acid, which consider the side effects of the targeting components to some extent. Herein, we report a new strategy to decorate the surface of MOFs using a pemetrexed (MTA) targeting molecule, affording a new drug delivery system of ALA@UIO-66-NH-FAM/MTA (ALA = 5-amino-levulinic acid and FAM = 5-carboxyfluorescein). The confocal microscopy and flow cytometry results showed that ALA@UIO-66-NH-FAM/MTA presented a better targeting effect compared to ALA@UIO-66-NH-FAM/FA (FA = folic acid) and indicated a gradually increasing tendency of the targeting effect with the increasing expression of folate receptors on the tumor cell cytomembrane. Furthermore, the cytotoxicity experiment indicates that the combination of chemotherapy and photodynamic therapy is a more effective therapy model than single chemotherapy and photodynamic therapy. This work demonstrates the first attempt at folic acid antagonist (MTA) modification for NMOFs, providing a new concept for the design of MOFs with folate receptor targeting capacity for clinical applications.

Ligand-Modified Erythrocyte Membrane-Cloaked Metal-Organic Framework Nanoparticles for Targeted Antitumor Therapy

Systemic chemotherapy for treating tumors often leads to serious systemic side effects and affects patient compliance. Although the emerging technology of drug delivery systems (DDSs) can deliver the required cargo to tumor sites, DDSs are limited due to insufficient targeting ability or deficient pharmacokinetics. Herein, we assembled a novel targeting DDS for precision tumor therapy by applying a tumor-targeting polypeptide cyclic RGD (cRGD)-modified erythrocyte membrane (eM-cRGD) cloaked on zeolitic imidazolate framework-8 (ZIF-8) nanoparticles (NPs) with encapsulated doxorubicin (DOX). For a mass ratio of ZIF-8:DOX = 1:1, the loading capacity was up to 49%. The nanoscale-sized targeting DDS promoted NP accumulation in tumor tissues via enhanced permeability and retention (EPR) effects, and the NPs actively targeted ligands and were then transferred to endosomes. The pH-sensitive carriers released higher DOX levels under the low pH mimicking that of a tumor microenvironment and tumor intracellular organelles, allowing enhanced inhibition of cancer cell growth. The cumulative release rate of DOX from DOX@ZIF-8 NPs reached 82.8% at 48 h in acidic conditions of pH = 5.0, while the cumulative release rate of DOX from the DOX@ZIF-8 NPs reached only 24.92% at pH = 7.4. The internalization of the DDS was approximately 44.35% that of the unmodified DDS by immune cells, as confirmed by flow cytometry. In vivo studies verified that the RGD-modified DDS had the ability to prolong blood circulation (t_1/2 = 6.81 h), enhancing the tumor-specific accumulation of NPs by means of the integrin αvβ3 receptor-mediated pathway, which was further valuated in mice bearing human cervical cancer (HeLa) cells, and yielding a significant antitumor effect; the tumor inhibition rate was as high as 85.46%. Under the same conditions, the blood circulation half-life of the unmodified DDS was only 3.22 h, and the tumor inhibition rate of free DOX was 81.34%. Moreover, the RGD modified with a carrier could achieve a satisfactory chemotherapeutic effect while minimizing side effects. In summary, our novel targeting DDS could contribute to the development of intelligent DDSs for tumor precision therapy.

The Progress and Prospect of Zeolitic Imidazolate Frameworks in Cancer Therapy, Antibacterial Activity, and Biomineralization

The progressive development of zeolitic imidazolate frameworks (ZIFs), as a subfamily of metal-organic frameworks (MOFs), and their unique features, including tunable pore size, large surface area, high thermal stability, and biodegradability/biocompatibility, have made them attractive in the field of biomedicine, especially for drug delivery and biomineralization applications. The high porosity of ZIFs gives them the opportunity for encapsulating a high amount of therapeutic drugs, proteins, imaging cargos, or a combination of them to construct advanced multifunctional drug delivery systems (DDSs) with combined therapeutic and imaging capabilities. This review summarizes recent strategies on the design and fabrication of ZIF-based nansystems and their exploration in the biomedical field. First, recent developments for the adjustment of particle size, functionality, and morphology of ZIFs are discussed, which are important for achieving optimized therapeutic/theranostic nanosystems. Second, recent trends on the application of ZIF nanocarriers for the loading of diverse cargos, including anticancer medicines, antibiotic drugs, enzymes, proteins, photosensitizers, as well as imaging and photothermal agents, are investigated in order to understand how multifunctional DDSs can be designed based on the ZIF nanoparticles to treat different diseases, such as cancer and infection. Finally, prospects on the future research direction and applications of ZIF-based nanomedicines are discussed.

Irregularly Shaped Iron Nitride Nanoparticles as a Potential Candidate for Biomedical Applications: From Synthesis to Characterization

Magnetic nanoparticles (MNPs) have been extensively used in drug/gene delivery, hyperthermia therapy, magnetic particle imaging (MPI), magnetic resonance imaging (MRI), magnetic bioassays, and so forth. With proper surface chemical modifications, physicochemically stable and nontoxic MNPs are emerging contrast agents and tracers for in vivo MRI and MPI applications. Herein, we report the high magnetic moment, irregularly shaped γ'-Fe4N nanoparticles for enhanced hyperthermia therapy and T2 contrast agent for MRI application. The static and dynamic magnetic properties of γ'-Fe4N nanoparticles are characterized by a vibrating sample magnetometer (VSM) and a magnetic particle spectroscopy (MPS) system, respectively. Compared to the γ-Fe2O3 nanoparticles, γ'-Fe4N nanoparticles show at least three times higher saturation magnetization, which, as a result, gives rise to the stronger dynamic magnetic responses as proved in the MPS measurement results. In addition, γ'-Fe4N nanoparticles are functionalized with an oleic acid layer by a wet mechanical milling process. The morphologies of as-milled nanoparticles are characterized by transmission electron microscopy (TEM), dynamic light scattering (DLS), and nanoparticle tracking analyzer (NTA). We report that with proper surface chemical modification and tuning on morphologies, γ'-Fe4N nanoparticles could be used as tiny heating sources for hyperthermia and contrast agents for MRI applications with minimum dose.

Metal-Organic Framework Composites for Theragnostics and Drug Delivery Applications

Among a plethora of nano-sized therapeutics, metal-organic frameworks (MOFs) have been some of the most investigated novel materials for, predominantly, cancer drug delivery applications. Due to their large drug uptake capacities and slow-release mechanisms, MOFs are desirable drug delivery vehicles that protect and transport sensitive drug molecules to target sites. The inclusion of other guest materials into MOFs to make MOF-composite materials has added further functionality, from externally triggered drug release to improved pharmacokinetics and diagnostic aids. MOF-composites are synthetically versatile and can include examples such as magnetic nanoparticles in MOFs for MRI image contrast and polymer coatings that improve the blood-circulation time. From synthesis to applications, this review will consider the main developments in MOF-composite chemistry for biomedical applications and demonstrate the potential of these novel agents in nanomedicine. It is concluded that, although vast synthetic progress has been made in the field, it requires now to develop more biomedical expertise with a focus on rational model selection, a major comparative toxicity study, and advanced targeting techniques.

Multivariate Modulation of the Zr MOF UiO-66 for Defect-Controlled Combination Anticancer Drug Delivery

Metal-organic frameworks (MOFs) are emerging as leading candidates for nanoscale drug delivery, as a consequence of their high drug capacities, ease of functionality, and the ability to carefully engineer key physical properties. Despite many anticancer treatment regimens consisting of a cocktail of different drugs, examples of delivery of multiple drugs from one MOF are rare, potentially hampered by difficulties in postsynthetic loading of more than one cargo molecule. Herein, we report a new strategy, multivariate modulation, which allows incorporation of up to three drugs in the Zr MOF UiO-66 by defect-loading. The drugs are added to one-pot solvothermal synthesis and are distributed throughout the MOF at defect sites by coordination to the metal clusters. This tight binding comes with retention of crystallinity and porosity, allowing a fourth drug to be postsynthetically loaded into the MOFs to yield nanoparticles loaded with cocktails of drugs that show enhancements in selective anticancer cytotoxicity against MCF-7 breast cancer cells in vitro. We believe that multivariate modulation is a significant advance in the application of MOFs in biomedicine, and anticipate the protocol will also be adopted in other areas of MOF chemistry, to easily produce defective MOFs with arrays of highly functionalised pores for potential application in gas separations and catalysis.

Metal Organic Frameworks as Drug Targeting Delivery Vehicles in the Treatment of Cancer

: In recent years, metal organic frameworks (MOFs) have been widely developed as vehicles for the effective delivery of drugs to tumor tissues. Due to the high loading capacity and excellent biocompatibility of MOFs, they provide an unprecedented opportunity for the treatment of cancer. However, drugs which are commonly used to treat cancer often cause side effects in normal tissue accumulation. Therefore, the strategy of drug targeting delivery based on MOFs has excellent research significance. Here, we introduce several intelligent targeted drug delivery systems based on MOFs and their characteristics as drug-loading systems, and the challenges of MOFs are discussed. This article covers the following types of MOFs: Isoreticular Metal Organic Frameworks (IRMOFs), Materials of Institute Lavoisier (MILs), Zeolitic Imidazolate Frameworks (ZIFs), University of Oslo (UiOs), and MOFs-based core-shell structures. Generally, MOFs can be reasonably controlled at the nanometer size to effectively achieve passive targeting. In addition, different ligands can be modified on MOFs for active or physicochemical targeting. On the one hand, the targeting strategy can improve the concentration of the drugs at the tumor site to improve the efficacy, on the other hand, it can avoid the release of the drugs in normal tissues to improve safety. Despite the challenges of clinical application of MOFs, MOFs have a number of advantages as a kind of smart delivery vehicle, which offer possibilities for clinical applications.

Facile Strategy to Synthesize Magnetic Upconversion Nanoscale Metal-Organic Framework Composites for Theranostics Application

Recently, the design of a theranostics system has involved increasing attention in the area of biomedical applications. In many cases, the intricate synthesis process of upconversion nanoparticle-based composite materials limits the use of theranostics applications. To address this challenge, a nanocomposite has been successfully fabricated by the conjugation of magnetic NaGdF₄:Yb/Er nanoparticles as an imaging agent and MIL-53(Fe) as a drug carrier through a single step. Simultaneously, folic acid is encapsulated on the surface of the nanocomposite by conjugation chemistry to achieve the targeted drug delivery applications. The synthesized nanocomposite exhibits a sufficient amount of loading ability toward the model anticancer doxorubicin and possesses pH-responsive drug release. The functionalized nanocomposite not only possesses excellent colloidal stability and good magnetic and fluorescence property but also shows superior biocompatibility, strong tumor cell growth inhibitory effect, and cancer-enhanced cellular uptake. It is expected that the synthesized nanocomposite can also serve as a platform for both T₁ and T₂ MRI contrast agents.