Mixed-Ligand Metal-Organic Frameworks for All-in-One Theranostics with Controlled Drug Delivery and Enhanced Photodynamic Therapy

Metal-organic frameworks as candidates for tumor sonodynamic therapy: Designable structures for targeted multifunctional transformation

Sonodynamic therapy (SDT), utilizing ultrasound (US) as the trigger, has gained popularity recently as a therapeutic approach with significant potential for treating various diseases. Metal-organic frameworks (MOFs), characterized by structural flexibility, are prominently emerging in the SDT realm as an innovative type of sonosensitizer, offering functional tunability and biocompatibility. However, due to the inherent limitations of MOFs, such as low reactivity to reactive oxygen species and challenges posed by the complex tumor microenvironment, MOF-based sonosensitizers with singular functions are unable to demonstrate the desired therapeutic efficacy and may pose risks of toxicity, limiting their biological applications to superficial tissues. MOFs generally possess distinctive crystalline structures and properties, and their controlled coordination environments provide a flexible platform for exploring structure-effect relationships and guiding the design and development of MOF-based nanomaterials to unlock their broader potential in biological fields. The primary focus of this paper is to summarize cases involving the modification of different MOF materials and the innovative strategies developed for various complex conditions. The paper outlines the diverse application areas of functionalized MOF-based sonosensitizers in tumor synergistic therapies, highlighting the extensive prospects of SDT. Additionally, challenges confronting SDT are briefly summarized to stimulate increased scientific interest in the practical application of MOFs and the successful clinical translation of SDT. Through these discussions, we strive to foster advancements that lead to early-stage clinical benefits for patients. STATEMENT OF SIGNIFICANCE: 1. An overview for the progresses in SDT explored from a novel and fundamental perspective. 2. Different modification strategies to improve the MOFs-mediated SDT efficacy are provided. 3. Guidelines for the design of multifunctional MOFs-based sonosensitizers are offered. 4. Powerful tumor ablation potential is reflected in SDT-led synergistic therapies. 5. Future challenges in the field of MOFs-based SDT in clinical translation are suggested.

Multi-level Reactive Oxygen Species Amplifier to Enhance Photo-/Chemo-Dynamic/Ca2+ Overload Synergistic Therapy

Reactive oxygen species (ROS)-involved photodynamic therapy (PDT) and chemodynamic therapy (CDT) hold great promise for tumor treatment. However, hypoxia, insufficient H2O2, and overexpressed glutathione (GSH) in the tumor microenvironment (TME) hinder ROS generation significantly. Herein, we reported CaO2@Cu-TCPP/CUR with O2/H2O2/Ca2+ self-supply and GSH depletion for enhanced PDT/CDT and Ca2+ overload synergistic therapy. CaO2 nanospheres were first prepared and used as templates for guiding the coordination between the carboxyl of tetra-(4-carboxyphenyl)porphine (TCPP) and Cu2+ ions as hollow CaO2@Cu-TCPP, which facilitated GSH-activated TCPP-based PDT and Cu+-mediated CDT. The hollow structure was then loaded with curcumin (CUR) to form CaO2@Cu-TCPP/CUR composites. Cu-TCPP prevented degradation of CaO2, while Cu2+ ions reacted with GSH to deplete GSH, produce Cu+ ions, and release TCPP, CaO2, and CUR. CaO2 reacted with H2O to generate O2, H2O2, and Ca2+ to achieve O2/H2O2/Ca2+ self-supply for TCPP-based PDT, Cu+-mediated CDT, and CUR-enhanced Ca2+ overload therapy. Thus, this multilevel ROS amplifier enhances synergistic therapy with fewer side effects and drug resistance.

Biomedical application of metal-organic frameworks (MOFs) in cancer therapy: Stimuli-responsive and biomimetic nanocomposites in targeted delivery, phototherapy and diagnosis

The nanotechnology is an interdisciplinary field that has become a hot topic in cancer therapy. Metal-organic frameworks (MOFs) are porous materials and hybrid composites consisted of organic linkers and metal cations. Despite the wide application of MOFs in other fields, the potential of MOFs for purpose of cancer therapy has been revealed by the recent studies. High surface area and porosity, significant drug loading and encapsulation efficiency are among the benefits of using MOFs in drug delivery. MOFs can deliver genes/drugs with selective targeting of tumor cells that can be achieved through functionalization with ligands. The photosensitizers and photo-responsive nanostructures including carbon dots and gold nanoparticles can be loaded in/on MOFs to cause phototherapy-mediated tumor ablation. The immunogenic cell death induction and increased infiltration of cytotoxic CD8+ and CD4+ T cells can be accelerated by MOF platforms in providing immunotherapy of tumor cells. The stimuli-responsive MOF platforms responsive to pH, redox, enzyme and ion can accelerate release of therapeutics in tumor site. Moreover, MOF nanocomposites can be modified ligands and green polymers to improve their selectivity and biocompatibility for cancer therapy. The application of MOFs for the detection of cancer-related biomarkers can participate in the early diagnosis of patients.

Postsynthetic Modification of Thermo-Treated Metal-Organic Framework for Combined Photothermal/Photodynamic Antibacterial Therapy

Metal-organic frameworks (MOFs) are emerging porous materials that can serve as carriers of photosensitizers and photothermal agents. Meanwhile, a large number of active sites in MOFs endow them with the characteristics of modification by postsynthetic modification. Herein, a dual-modal PDT/PTT therapeutic agent HMIL-121-acriflavine-tetrakis (4-amoniophenyl) porphyrin (HMIL-ACF-Por), prepared by the postsynthetic modification of the MOF (HMIL-121), was reported for antibacterial applications. The prepared HMIL-ACF-Por enables the generation of abundant reactive oxygen species, including the superoxide anion radical (O2-) and singlet oxygen (1O2), and thermal energy under 808 nm NIR laser irradiation. HMIL-ACF-Por showed good antibacterial ability against Escherichia coli and Staphylococcus aureus in vitro. Meanwhile, HMIL-ACF-Por can effectively inhibit the inflammatory response caused by bacterial infection and accelerate S. aureus-infected wound healing under laser irradiation owing to the synergistic effect of photodynamic therapy (PDT) and photothermal therapy (PTT). These results demonstrate that HMIL-ACF-Por is a promising PDT/PTT therapeutic agent. This work also contributes to offering an effective solution for treating bacterial infections and promotes the application of MOF-based materials in biomedicine.

Tailoring the topology of ZIF-67 metal-organic frameworks (MOFs) adsorbents to capture humic acids

Chlorination is a versatile technique to combat water-borne pathogens. Over the last years, there has been continued research interest to abate the formation of chlorinated disinfection by-products (DBPs). To prevent hazardous DBPs in drinking water, it is decided to diminish organic precursors, among which humic acids (HA) resulting from the decomposition and transformation of biomass. Metal-organic frameworks (MOFs) such as zeolitic imidazolate frameworks (ZIFs) have recently received tremendous attention in water purification. Herein, customized ZIF-67 MOFs possessing various physicochemical properties were prepared by changing the cobalt source. The HA removal by ZIF-67-Cl, ZIF-67-OAc, ZIF-67-NO3, and ZIF-67-SO4 were 85.6%, 68.9%, 86.1%, and 87.4%, respectively, evidently affected by the specific surface area. HA uptake by ZIF-67-SO4 indicated a removal efficiency beyond 90% in 4  90% after 60 min mixing the solution with 0.3 g L-1 ZIF-67-SO4. Notably, an acceptable removal performance (∼72.3%) was obtained even at HA concentrations up to 100 mg L-1. The equilibrium data fitted well with the isotherm models in the order of Langmuir> Hill > BET> Khan > Redlich-Peterson> Jovanovic> Freundlich > and Temkin. The maximum adsorption capacity qm for HA uptake by ZIF-67-SO4 was 175.89 mg g-1, well above the majority of adsorbents. The pseudo-first-order model described the rate of HA adsorption by time. In conclusion, ZIF-67-SO4 presented promising adsorptive properties against HA. Further studies would be needed to minimize cobalt leaching from the ZIF-67-SO4 structure and improve its reusability safely, to ensure its effectiveness and the economy of adsorption system.

Biomedical Application of Porphyrin-Based Amphiphiles and Their Self-Assembled Nanomaterials

Porphyrins have been vastly explored and applied in many cutting-edge fields with plenty of encouraging achievements because of their excellent properties. As important derivatives of porphyrins, porphyrin-based amphiphiles (PBAs) not only maintain the advanced properties of porphyrins (catalysis, imaging, and energy transfer) but also possess self-assembly and encapsulation capability in aqueous solution. Accordingly, PBAs and their self-assembles have had important roles in diagnosing and treating tumors and inflammation lesions in vivo, but not limited to these. In this article, we introduce the research progress of PBAs, including their constitution, structure design strategies, and performances in tumor and inflammation lesion diagnosis and treatments. On that basis, the defects of synthesized PBAs during their application and the possible effective strategies to overcome the limitations are also proposed. Finally, perspectives on PBAs exploration are updated based on our knowledge. We hope this review will bring researchers from various domains insights about PBAs.

Porphyrin-anthracene covalent organic frameworks for sustainable photosterilization

Covalent organic frameworks (COFs) have promising applications in enhanced phototherapy. However, COFs that can sustainably play a role in phototherapy without continuous irradiation are extremely scarce. Herein, we report the fabrication of porphyrin-anthracene multifunctional COFs (Por-DPA) for sustainable photosterilization and bacterial-infected wound healing. A porphyrin photosensitizer, as one of the monomers, was used to provide photothermal and photodynamic activities under irradiation. An anthracene derivative, a good chemical source of singlet oxygen (1O2), was selected as another monomer to capture 1O2 and release it continuously via cycloreversion in the dark. The prepared Por-DPA COF prevents the self-aggregation quenching of the photosensitizer and thermal damage caused by continuous exposure to external light sources. Besides, Por-DPA exhibits good photothermal conversion performance and efficient 1O2 production capacity through dual pathways of photosensitization and cycloreversion. The developed sustainable photosterilization platform not only has good bactericidal effects on Escherichia coli and Staphylococcus aureus, but also promotes wound healing without obvious side effects, and is expected to be a novel efficient bactericide.

Research development of porphyrin-based metal-organic frameworks: targeting modalities and cancer therapeutic applications

Porphyrins are naturally occurring organic molecules that have attracted widespread attention for their potential in the field of biomedical research. Porphyrin-based metal-organic frameworks (MOFs) that utilize porphyrin molecules as organic ligands have gained attention from researchers due to their excellent results as photosensitizers in tumor photodynamic therapy (PDT). Additionally, MOFs hold significant promise and potential for other tumor therapeutic approaches due to their tunable size and pore size, excellent porosity, and ultra-high specific surface area. Active delivery of nanomaterials via targeted molecules for tumor therapy has demonstrated greater accumulation, lower drug doses, higher therapeutic efficacy, and reduced side effects relative to passive targeting through the enhanced permeation and retention effect (EPR). This paper presents a comprehensive review of the targeting methods employed by porphyrin-based MOFs in tumor targeting therapy over the past few years. It further discusses the applications of porphyrin-based MOFs for targeted cancer therapy through various therapeutic methods. The objective of this paper is to provide a valuable reference and source of ideas for targeted therapy using porphyrin-based MOF materials and to inspire further exploration of their potential in the field of cancer therapy.

Advances in surface-modified nanometal-organic frameworks for drug delivery

Nanometal-organic frameworks (NMOFs) are porous network structures composed of metal ions or metal clusters through self-assembly. NMOFs have been considered as a promising nano-drug delivery system due to their unique properties such as pore and flexible structures, large specific surface areas, surface modifiability, non-toxic and degradable properties. However, NMOFs face a series complex environment during in vivo delivery. Therefore, surface functionalization of NMOFs is vital to ensure that the structure of NMOFs remain stable during delivery, and can overcome physiological barriers to deliver drugs more accurately to specific sites, and achieve controllable release. In this review, the first part summarizes the physiological barriers that NMOFs faced during drug delivery after intravenous injection and oral administration. The second part summarizes the current main ways to load drugs into NMOFs, mainly including pore adsorption, surface attachment, formation of covalent/coordination bonds between drug molecules and NMOFs, and in situ encapsulation. The third part is the main review part of this paper, which summarizes the surface modification methods of NMOFs used in recent years to overcome the physiological barriers and achieve effective drug delivery and disease therapy, which are mainly divided into physical modifications and chemical modifications. Finally, the full text is summarized and prospected, with the hope to provide ideas for the future development of NMOFs as drug delivery.

Dual-ligand two-dimensional terbium-organic frameworks nanosheets for ratiometric fluorescence detection of phosphate

Here, we reported a ratiometric fluorescence strategy for the detection of phosphate (Pi) in artificial wetland water. The strategy was based on dual-ligand two-dimensional terbium-organic frameworks nanosheets (2D Tb-NB MOFs). 2D Tb-NB MOFs were prepared through blending 5-boronoisophthalic acid (5-bop), 2-aminoterephthalic acid (NH₂-BDC) and Tb³⁺ ions at room temperature in the presence of triethylamine (TEA). The dual-ligand strategy realized dual emission originated from ligand NH₂-BDC and Tb³⁺ ions at 424 and 544 nm, respectively. Pi could compete with ligands to coordinate Tb³⁺ due to the strong binding ability between Pi and Tb³⁺, resulting in structural destruction of 2D Tb-NB MOFs, so static quenching and antenna effect between ligands and metal ions were interrupted, and emission at 424 nm was enhanced and emission at 544 nm was weakened. This novel probe had excellent linearity with Pi concentrations from 1 to 50 μmol/L; the detection limit was 0.16 μmol/L. This work revealed that mixed ligands improved sensing efficiency of MOFs by enhancing the sensitivity of the coordination between the analyte and MOFs.

A review of recent developments of metal-organic frameworks as combined biomedical platforms over the past decade

Metal-organic frameworks (MOFs), also called porous coordination polymers, represent a class of crystalline porous materials made up of organic ligands and metal ions/metal clusters. Herein, an overview of the preparation of different metal-organic frameworks and the recent advances in MOF-based stimuli-responsive drug delivery systems (DDSs) with the drug release mechanisms including pH-, temperature-, ion-, magnetic-, pressure-, adenosine-triphosphate (ATP)-, H₂S-, redox-, responsive, and photoresponsive MOF were rarely introduced. The combination therapy containing of two or more treatments can be enhanced treatment effectiveness through overcoming limitations of monotherapy. Photothermal therapy (PTT) combined with chemotherapy (CT), chemotherapy in combination with PTT or other combinations were explained to overcome drug resistance and side effects in normal cells as well as enhancing the therapeutic response. Integrated platforms containing of photothermal/drug-delivering functions with magnetic resonance imaging (MRI) properties exhibited great advantages in cancer therapy.

Mn-doped Ti-based MOFs for magnetic resonance imaging-guided synergistic microwave thermal and microwave dynamic therapy of liver cancer

Currently, precise ablation of tumors without damaging the surrounding normal tissue is still an urgent problem for clinical microwave therapy of liver cancer. Herein, we synthesized Mn-doped Ti MOFs (Mn–Ti MOFs) nanosheets by in-situ doping method and applied them for microwave therapy. Infrared thermal imaging results indicate Mn–Ti MOFs can rapidly increase the temperature of normal saline, attributing to the porous structure improving microwave-induced ion collision frequency. Moreover, Mn–Ti MOFs show higher ¹O₂ output than Ti MOFs under 2 W of low-power microwave irradiation due to the narrower band-gap after Mn doping. At the same time, Mn endows the MOFs with a desirable T₁ contrast of magnetic resonance imaging (r₂/r₁ = 2.315). Further, results on HepG2 tumor-bearing mice prove that microwave-triggered Mn–Ti MOFs nearly eradicate the tumors after 14 days of treatment. Our study offers a promising sensitizer for synergistic microwave thermal and microwave dynamic therapy of liver cancer.

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Mn-doped Ti-MOFs nanosheets (Mn–Ti MOFs) were synthesized as novel microwave sensitizers.

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Mn–Ti MOFs can significantly generate heat and produce ROS under low-power microwave irradiation.

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The combination of microwave thermal therapy and microwave dynamic therapy can effectively inhibit the growth of tumor cells in vitro and in vivo.

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The microwave sensitizers have potential application in MRI-guided microwave therapy for liver cancer.

Intelligent Dual-Lock Deoxyribonucleic Acid Automatons Boosting Precise Tumor Imaging

An early and accurate cancer diagnosis holds the potential to improve treatment and prognosis. Nevertheless, the complexity of the biological system limits the selectivity of existing approaches and makes tumor imaging in vivo particularly challenging. In this study, tumor-specific fluorescence imaging was achieved by building intelligent dual-lock deoxyribonucleic acid automatons (IDEAs) that employed a DNA walking system standing on ZrMOF@MnO₂ multifunctional nanocomposites for controllable molecular recognition. The IDEAs exhibited significantly enhanced fluorescence signals only in the coexistence of both miRNA and GSH of tumor cells, enabling accurate distinguishing of tumor cells from healthy ones. Furthermore, the feasibility and specificity of IDEAs were also validated in vivo with tumor bearing mice successfully. This work highlights the potential of the proposed IDEA strategy for tumor-specific imaging, paving the way for successful precision diagnosis and treatment.

Metal-Organic Frameworks-Based Optical Nanosensors for Analytical and Bioanalytical Applications

Metal-organic frameworks (MOFs)-based optical nanoprobes for luminescence and surface-enhanced Raman spectroscopy (SERS) applications have been receiving tremendous attention. Every element in the MOF structure, including the metal nodes, the organic linkers, and the guest molecules, can be used as a source to build single/multi-emission signals for the intended analytical purposes. For SERS applications, the MOF can not only be used directly as a SERS substrate, but can also improve the stability and reproducibility of the metal-based substrates. Additionally, the porosity and large specific surface area give MOF a sieving effect and target molecule enrichment ability, both of which are helpful for improving detection selectivity and sensitivity. This mini-review summarizes the advances of MOF-based optical detection methods, including luminescence and SERS, and also provides perspectives on future efforts.

Zn-Co metal organic frameworks coated with chitosand and Au nanoparticles for chemo-photothermal-targeted combination therapy of liver cancer

The toxic effects of chemotherapy drugs on normal tissues are still a major limiting factor in cancer treatment. In this paper, we report a metal-organic framework (Zn-Co ZIF) with chitosan-coated outer layer as a carrier for the drug adriamycin hydrochloride (DOX), a treatment for liver cancer, as a novel anti-cancer nanodrug-enhanced carrier. Gold nanoparticles, a good photothermal conversion agent, were combined with the target SH-RGD during surface functionalisation to prepare Zn-Co ZIF@DOX-CS-Au-RGD (ZD-CAR), a nanoplatform with good photothermal conversion properties and targeting for combined liver cancer therapy. ZD-CAR was developed after RGD accurately targeted the tumour and entered the tumour microenvironment (TME), it cleaves and releases the liver cancer therapeutic agent (DOX) in a weak acidic environment to effectively kill tumour cells. The metal skeleton cleavage releases Co²⁺, which catalyzes the production of oxygen from H₂O₂ to alleviate the tumour hypoxic environment. The dissolved oxygen could reach 14 mg/L after adding 80 mg/mL of ZD-CAR. Meanwhile, gold nanoparticles could convert light energy into heat energy under 808 NIR irradiation to induce local superheating and kill tumour cells. In summary, this study developed a nanoplatform that combines chemo-photothermal-targeted therapy. It has shown good therapeutic effeciency in cellular experiments and performance tests and has promising applications in anti-cancer therapy.

Ultrastable Photoluminescence Enabled by 1D Rare-Earth Metal-Organic Frameworks Based on Double Thiacalix[4]arene-Capped Nodes

Luminescent stability is a vital factor that dictates the application of lanthanide luminescent materials. Designing luminescent lanthanide cluster nodes that form an extended framework with predictable linking patterns may help enhance the structural stability of the lanthanide complexes and hence lead to improved luminescent stability. Herein, we report a series of one-dimensional (1D) rare-earth metal-organic framework compounds, {Ln₄(μ₄-OH)(TC4A)₂(H₂O)₂(CH₃O)(HCOO)₂(HCOOH)}·xCH₃OH (Ln = Sm (1), Eu (2), Tb (3), Dy (4); x = 1-5), based on double thiacalix[4]arene-capped Ln₄(μ₄-OH)(TC4A)₂ nodes. The axially capped Ln₄(μ₄-OH)(TC4A)₂ nodes are connected equatorially by formate bridges to form zigzag 1D-metal-organic framework (MOF) chains, which further assemble into a quasi-two-dimensional (2D) structure via hydrogen bonding. These unique features result in a stable structure and therefore superior luminescent stability. For example, the Tb-based 1D-MOF (3) exhibits intensive green photoluminescence with a quantum yield of 53% and an average decay time of 1.33 × 10⁶ ns. It maintains its integrated emission intensity at 96.5, 94.5, and 89.4% of the original value after being exposed to moisture (soaking in water for 10 days), elevated temperature (150 °C), and UV (15 days of continuous radiation), respectively, demonstrating excellent luminescent stability. We adopt the Tb-based 1D-MOF (3) as the green phosphor and successfully fabricate a prototype white-light-emitting diode (LED) with stable emission under long-term operation. Our synthetic strategy allows control over the linking pattern of lanthanide nodes, providing a predictive route to obtain lanthanide MOFs with improved luminescent stability.