A nano-photosensitizer based on covalent organic framework nanosheets with high loading and therapeutic efficacy

Covalent Organic Frameworks: Opportunities for Rational Materials Design in Cancer Therapy

Nanomedicines are extensively used in cancer therapy. Covalent organic frameworks (COFs) are crystalline organic porous materials with several benefits for cancer therapy, including porosity, design flexibility, functionalizability, and biocompatibility. This review examines the use of COFs in cancer therapy from the perspective of reticular chemistry and function-oriented materials design. First, the modification sites and functionalization methods of COFs are discussed, followed by their potential as multifunctional nanoplatforms for tumor targeting, imaging, and therapy by integrating functional components. Finally, some challenges in the clinical translation of COFs are presented with the hope of promoting the development of COF-based anticancer nanomedicines and bringing COFs closer to clinical trials.

Biodegradable covalent organic frameworks achieving tumor micro-environment responsive drug release and antitumor treatment

The emergence of nanocarriers has greatly improved the therapeutic efficacy of chemotherapeutic drugs. As emerging nanocarriers, covalent organic frameworks (COFs) have been increasingly used in biomedicine in recent years. However, due to their inherent chemical stability, existing COF nanocarriers hardly undergo in vivo degradation, which brings potential safety hazards to further applications. In this work, we introduce the azo bond into COFs. When the nanocarrier enters the cell, ˙OH generated by the coordinated Fe response to the H2O2 in the cell will break the azo bond and cause the degradation of the framework structure, accelerating the release of internally loaded DOX to effectively realize tumor treatment. We verified the degradation ability of the materials by constructing model compounds, in vitro drug release, MTT assay and antitumor experiments. Compared with the control groups, the degradable COF accelerates the release of DOX and shows a stronger killing effect on 4T1 cells. Serum biochemical analysis and H&E sections of organs show good biocompatibility for both COFs and degradation products. This work provides a new idea for the design of biodegradable COFs in vivo, and greatly explores the potential application of COF materials in the biomedical field.

High performance carbon dots based prodrug Platform: Image-Guided photodynamic and chemotherapy with On-Demand drug release upon laser irradiation

The design of therapeutic nanoplatforms based on fluorescent carbon dots (CDs) has become a viable strategy because of their aqueous solubility, biocompatibility, and ease of further functionalization. By doping various heteroatoms into pristine CDs structures, we synthesized N-, Cl-, and S-doped CDs (NClS/CDs), as well as Se-, N-, and Cl-doped CDs (NClSe/CDs) with superior optoelectronic properties using rapid and straightforward microwave heating. The quantum efficiencies of these NClS/CDs and NClSe/CDs were enhanced to 30.7 % and 42.9 %, respectively, compared to those of undoped CDs (0.66 %). Owing to their better light absorption properties, NClS/CDs efficiently produced reactive oxygen species (ROS) under 532 nm laser irradiation for photodynamic therapy (PDT). Considering the ROS generation and surface carrier abilities of NClS/CDs, we designed the loading of camptothecin (CPT) drug via a thioketal linker (TL), resulting in h/CDs@CPT nanovesicles (NVs) with a drug-loading efficiency of 46.5 %. Under laser irradiation in an acidic environment, ROS-triggered CPT release was observed, with 50.2 % of CPT released following the breakdown of the ROS-sensitive TL. In vitro cellular studies revealed that h/CDs@CPT NVs possessed minimal cytotoxicity toward HeLa and 4 T1 cancer cells, despite the high clinical efficacy of PDT and ROS-induced chemotherapeutic response under laser treatment. Confocal microscopy of HeLa and 4 T1 cells revealed that h/CDs@CPT NVs produced red-emissive photographs for potential cancer cell detection. Therefore, our study presents an image-guided PDT and chemotherapeutic platform based on h/CDs@CPT NVs, which will be an attractive candidate for future cancer treatment.

Covalent Organic Frameworks: Recent Progress in Biomedical Applications

Covalent organic frameworks (COFs) are a type of crystalline organic porous material with specific features and interesting structures, including porosity, large surface area, and biocompatibility. These features enable COFs to be considered as excellent candidates for applications in various fields. Recently, COFs have been widely demonstrated as promising materials for biomedical applications because of their excellent physicochemical properties and ultrathin structures. In this review, we cover the recent progress of COF materials for applications in photodynamic therapy, gene delivery, photothermal therapy, drug delivery, bioimaging, biosensing, and combined therapies. Moreover, the critical challenges and further perspectives with regards to COFs for future biology-facing applications are also discussed.

Green synthesis of broccoli-derived carbon quantum dots as effective photosensitizers for the PDT effect testified in the model of mutant Caenorhabditis elegans

The clinical application of photodynamic therapy (PDT) is still limited because of the drawbacks of the traditional photosensitizers, such as low singlet oxygen (¹O₂) quantum yield and the problem of photobleaching. Herein, carbon quantum dots (CQDs) derived from broccoli natural biomass as a carbon source were fabricated via a simple hydrothermal method and showed outstanding PDT ability as an effective photodynamic agent tested in Caenorhabditis elegans (C. elegans) models. The as-prepared broccoli-derived CQDs (BCQDs) showed excellent water solubility and optical properties and could generate singlet oxygen (¹O₂) effectively under irradiated light with a wavelength of 660 nm. The in vivo experiment revealed that the PDT efficiency of the BCQDs was dependent on the induction of germline apoptosis through the cep-1/p53 pathway. Further investigation confirmed the DNA damage of the worm by the BCQDs after sufficient light irradiation, which was tested by measuring the egl-1-fold induction in hus-1(op244), and cep-1(w40) mutants that have a loss of function in the genes involved in DNA damage response such as hus-1 (DNA checkpoint gene) and cep-1/p53 (tumor suppressor). The lack of germline apoptosis in the loss of function mutants egl-1(n487), hus-1(op244), and cep-1(w40) exposed to light irradiation compared with the control proved the necessity of these genes in DNA damage-induced germline apoptosis. Therefore, this work has not only provided a new photodynamic agent but also introduced C. elegans as an easy and high-throughput model for the rapid evaluation of the efficiency of PDT.

Characteristic Synthesis of a Covalent Organic Framework and Its Application in Multifunctional Tumor Therapy

For decades, covalent organic frameworks (COFs) have attracted wide biomedical interest due to their unique properties including ease of synthesis, porosity, and adjustable biocompatibility. Versatile COFs can easily encapsulate various therapeutic drugs due to their extremely high payload and porosity. COFs with abundant functional groups can be surface-modified to achieve active targeting and enhance biocompatibility. In this paper, the latest developments of COFs in the biomedical field are summarized. First, the classification and synthesis of COFs are discussed. Cancer diagnosis and treatment based on COFs are studied, and the advantages and limitations of each method are discussed. Second, the specific preparation methods to obtain specific therapeutic properties are summarized. Finally, based on the combination and modification of COFs with various components, this review system summarizes different combination therapies. In addition, the main challenges faced in COF research and prospects for applying COFs to cancer diagnosis and treatment are evaluated. This review provides enlightening insights into the interdisciplinary research on COFs and applications in biomedicine, which highlight the great expectations for their further clinical transformation.

2D and 3D Covalent Organic Frameworks: Cutting-Edge Applications in Biomedical Sciences

Covalent organic frameworks (COFs) are crystalline porous organic structures with two- or three-dimensional (2D or 3D) features and composed of building blocks being connected via covalent bonds. The manifold applications of COFs in optoelectronic devices, energy conversion and storage, adsorption, separation, sensing, organocatalysis, photocatalysis, electrocatalytic reactions, and biomedicine are increasing because of their notable intrinsic features such as large surface area, porosity, designable structure, low density, crystallinity, biocompatibility, and high chemical stability. These properties have rendered 2D and 3D COF-based materials as desirable entities for drug delivery, gene delivery, photothermal therapy, photodynamic therapy, combination therapy, biosensing, bioimaging, and anticancer activities. Herein, different reactions and methods for the synthesis of 2D and 3D COFs are reviewed with special emphasis on the construction and state-of-the-art progress pertaining to the biomedical applications of 2D and 3D COFs of varying shapes, sizes, and structures. Specifically, stimuli-responsive COFs-based systems and targeted drug delivery approaches are summarized.

Heparin-Coated Photosensitive Metal-Organic Frameworks as Drug Delivery Nanoplatforms of Autophagy Inhibitors for Sensitized Photodynamic Therapy against Breast Cancer

Photosensitive nanosized metal-organic frameworks (nanoMOFs) with a tunable structure and high porosity have been developed recently as nanophotosensitizers (nanoPSs) for photodynamic therapy (PDT). However, the effect of photodynamic therapy is greatly limited by the fast blood clearance and poor tumor retention of the ordinary nanoPSs. Besides, autophagy, a prosurvival self-cannibalization pathway mediated by autolysosomes, was elevated by cytotoxic reactive oxygen species (ROS) produced during PDT. Herein, a chloroquine phosphate (CQ)-loaded photosensitive nanoMOF coated by heparin was fabricated for sensitized PDT by increasing the tumor accumulation of nanoPSs and abolishing the self-protective autophagy within cancer cells. After internalization by cancer cells, the encapsulated CQ alkalizes autolysosomes and blocks the postautophagy process, which disarm the vigilant cancer cells irritated by PDT and finally enhance the therapeutic effect. Furthermore, the accompanied antiangiogenesis ability of the heparin coat also helps improve the cancer therapy outcomes. This study would open up new horizons for building heparin-coated nanoMOFs and understanding the role of autophagy in cancer therapy.

Nanoscale covalent organic frameworks: from controlled synthesis to cancer therapy

Covalent organic frameworks (COFs), as a new type of crystalline porous materials, mainly consist of light-weight elements (H, B, C, N and O) linked by dynamic covalent bonds to form periodical structures of two or three dimensions. As an attribute of their low density, large surface area, and excellent adjustable pore size, COFs show great potential in many fields including energy storage and separation, catalysis, sensing, and biomedicine. However, compared with metal organic frameworks (MOFs), the relatively large size and irregular morphology of COFs affect their biocompatibility and bioavailability in vivo, thus impeding their further biomedical applications. This Review focuses on the controlled design strategies of nanoscale COFs (NCOFs), unique properties of NCOFs for biomedical applications, and recent progress in NCOFs for cancer therapy. In addition, current challenges for the biomedical use of NCOFs and perspectives for further improvements are presented.

Self-Remedied Nanomedicine for Surmounting the Achilles' Heel of Photodynamic Tumor Therapy

Oxygen-dependent photodynamic therapy (PDT) could exacerbate tumor hypoxia to induce the upregulation of hypoxia-inducible factor-1α (HIF-1α), which would promote tumor growth and metastasis. In this paper, a self-remedied nanomedicine is developed based on a photosensitizer and a HIF-1α inhibitor to surmount the Achilles' heel of PDT for enhanced antitumor efficacy. Specifically, the nanomedicine (designated as CYC-1) is prepared by the self-assembly of chlorine e6 (Ce6) and 3-(5'-hydroxy-methyl-2'-furyl)-1-benzylindazole (YC-1) through π-π stacking and hydrophobic interactions. Of special note, carrier-free CYC-1 holds an extremely high drug loading rate and avoids excipient-triggered adverse reactions. Intravenously administered CYC-1 prefers to accumulate in the tumor tissue for effective cellular uptake. More importantly, it is verified that CYC-1 is capable of inhibiting the HIF-1α activity, thereby improving its PDT efficacy on tumor suppression. Besides, CYC-1 has the overwhelming superiority in restraining tumor proliferation over the combined administration of Ce6 and YC-1, which highlights the advantage of this self-remedied strategy in drug delivery and tumor therapy. This study sheds light on the development of self-delivery nanomedicine for efficient PDT against malignancies.

Emerging strategies in developing multifunctional nanomaterials for cancer nanotheranostics

Cancer involves a collection of diseases with a common trait - dysregulation in cell proliferation. At present, traditional therapeutic strategies against cancer have limitations in tackling various tumors in clinical settings. These include chemotherapeutic resistance and the inability to overcome intrinsic physiological barriers to drug delivery. Nanomaterials have presented promising strategies for tumor treatment in recent years. Nanotheranostics combine therapeutic and bioimaging functionalities at the single nanoparticle level and have experienced tremendous growth over the past few years. This review highlights recent developments of advanced nanomaterials and nanotheranostics in three main directions: stimulus-responsive nanomaterials, nanocarriers targeting the tumor microenvironment, and emerging nanomaterials that integrate with phototherapies and immunotherapies. We also discuss the cytotoxicity and outlook of next-generation nanomaterials towards clinical implementation.

Strategies and applications of covalent organic frameworks as promising nanoplatforms in cancer therapy

Cancer nanomedicine is the best option to face the limits of conventional chemotherapy and phototherapy methods, and thus the intensive quest for new nanomaterials to improve therapeutic efficacy and safety is still underway. Owing to their low density, well-defined structures, large surface area, finely tunable pore size, and metal ion free features, covalent organic frameworks (COFs) have been extensively studied in many research fields. The recent great interest in nanoscale COFs to improve the properties of bulk COFs has led to broadening of their applicability in the biomedical field, such as nanocarriers with an outstanding loading capacity and efficient delivery of therapeutic agents, smart theranostic nanoplatforms with excellent stability, high ROS generation, light-to-heat conversion capabilities, and different response and diagnostic characteristics. The COFs and related nanoplatforms with a wide variety of designability and functionalization have opened up a new avenue for exciting opportunities in cancer therapy. Herein we review the state-of-the-art technical and scientific developments in this emerging field, focusing on the overall progress addressed so far in building versatile COF-based nanoplatforms to enhance chemotherapy, photodynamic/photothermal therapy, and combination. Future perspectives for achieving the synergistic effect of cancer elimination and clinical translation are further discussed to motivate future contributions and explore new possibilities.

Recent advances in covalent organic frameworks for cancer diagnosis and therapy

In recent years, the number of patients diagnosed with cancer has been soaring. Therefore, the design, development, and implementation of new approaches for the diagnosis and therapy of different types of cancers have attracted an increasing amount of attention. To date, different methods have been used for cancer diagnosis and therapy with main drawbacks in terms of severe side effects, e.g., damage to healthy cells, development of drug resistance and tumor recurrence. Therefore, there is an urgent need for the introduction and application of innovative methods. Covalent organic frameworks (COFs) are versatile materials with excellent properties in terms of biocompatibility, porous and crystalline structure, and easy functionalization. The porous structure and organic monomers in COFs allow them to load different therapeutic drugs and/or functional species efficiently. These promising properties make COFs ideal candidates for medical application, especially in cancer diagnosis and therapy. To date, many studies have focused on the design and synthesis of novel COFs while their application as diagnostic and therapeutic materials remains less understood. In this review, different synthesis and functionalization approaches of COFs were summarized. In particular, cancer diagnosis and therapy based on COFs were investigated and the advantages and limitations of each method were discussed. Most importantly, the mechanism for cancer therapy of COFs and fundamental challenges and perspectives for the application of COFs in cancer theranostics were assessed.

Tuning the physicochemical properties of reticular covalent organic frameworks (COFs) for biomedical applications

Since the first report by Yaghi's group in 2005, research enthusiasm has been increasingly raised to synthesize diverse crystalline porous materials as -B-O-, -C-N-, -C-C-, and -C-O- linkage-based COFs. Recently, the biomedical applications of COFs have become more and more attractive in biomedical applications, including drug delivery, bioimaging, biosensing, antimicrobial, and therapeutic applications, as these materials bear well-defined crystalline porous structures and well-customized functionalities. However, the clinical translation of these research findings is challenging due to the formidable hindrances for in vivo use, such as low biocompatibility, poor selectivity, and long bio-persistence. Some attempts have raised a promising solution towards these obstacles by tailored engineering the functionalities of COFs. To speed up the clinical translations of COFs, a short review of principles and strategies to tune the physicochemical properties of COFs is timely and necessary. In this review, we summarized the biomedical utilities of COFs and discussed the related key physicochemical properties. To improve the performances of COFs in biomedical uses, we propose approaches for the tailored functionalization of COFs, including large-scale manufacture, standardization in nanomedicines, enhancing targeting efficacy, maintaining predesigned functions upon transformations, and manipulation of multifunctional COFs. We expect that this minireview strengthens the fundamental understandings of property-bioactivity relationships of COFs and provides insights for the rational design of their high-order reticular structures.

Near-Infrared Photothermal/Photodynamic-in-One Agents Integrated with a Guanidinium-Based Covalent Organic Framework for Intelligent Targeted Imaging-Guided Precision Chemo/PTT/PDT Sterilization

Phototherapy holds great promise in the treatment of bacterial infections, especially the multidrug resistant bacterial infections. However, most therapeutic agents are based on the integration of individual photothermal agents and photosensitizers, always in the activated state, and generally lack bacterial specificity, resulting in uncertain pharmacokinetics and serious nonspecific damage to normal tissues. Herein, we report a pH-responsive nanoplatform with synergistic chemo-phototherapy function for smart fluorescence imaging-guided precision sterilization. pH reversible activated symmetric cyanine was designed and prepared as a bacterial-specific imaging unit and PTT/PDT-in-one agent. Meanwhile, a guanidinium-based covalent organic framework (COF) was employed as a nanocarrier and chemotherapy agent to build the intelligent nanoplatform via electrostatic self-assembly. The self-assembly of the PTT/PDT-in-one agent and the COF greatly improves the stability and blood circulation of the PTT/PDT-in-one agent and provides charge-reversed intelligent targeting ability. The developed smart nanoplatform not only enables bacterial-targeted imaging but also possesses chemo/PTT/PDT synergetic high-efficiency bactericidal effects with little side effects, showing great potential in practical applications.

Design of ZIF-based hybrid nanoparticles with hyaluronic acid-augmented ROS behavior for dual-modality PA/NIR-II FL imaging

Photoacoustic (PA) imaging has emerged as a promising bio-imaging technique due to its non-invasive visualization of lesions at great penetration depths. Fluorescence (FL) imaging in the second near-infrared window (NIR-II, 1000-1700 nm) achieves a higher imaging resolution and lower background signals compared to NIR-I. However, the single imaging method possesses its own disadvantages. Thus, we have demonstrated ZIF-8-IR820-MnPc-HA nanoparticles (ZIMH NPs) that can achieve visualization and localization of tumors in mice models with the help of a dual-modality PA/NIR-II FL imaging performance. Meanwhile, these excellent nanoparticles also induce the efficient generation of singlet oxygen (1O2) upon 808 nm laser illumination, and display excellent photodynamic therapy efficacy in cells, further indicating their potential application for in vivo PDT. In ZIMH NPs, hyaluronic acid (HA) impressively acts as a "sponge", enhancing the generation of 1O2 and facilitating the cellular therapeutic effects. We believe that ZIF-8-IR820-MnPc-HA NPs present a brand-new strategy for the exploration of efficient PDT photosensitizers with dual-modality imaging performance for use in various biomedical applications.

Targeted nanobody complex enhanced photodynamic therapy for lung cancer by overcoming tumor microenvironment

Background

To investigate the efficacy of a PLGA-based nanobody complex in photodynamic therapy (PDT) and NIR-II imaging in A549 tumor hypoxic model.

Method

IR1048-MZ was firstly synthesized by conjugating a nitro imidazole group to IR1048. IR1048-MZ and Cat were then encapsulated in PLGA-SH solution. Anti-EGFR-Nanobody was also expressed and purified, and finally Anti-EGFR-Nanobody@PLGA-IR1048MZ-Cat (Nb@IC-NPs) nanobody complex was obtained based on the formation of desulfide bond between PLGA-SH and Anti-EGFR-Nanobody. Size distribution and morphology were characterized by TEM and DLS. Spectrum of Nb@IC-NPs towards NTR was measured by UV and fluorescence, while the particle’s selective response was studied using fluorescence. The uptake of Nb@IC-NPs in A549 cells was observed by flow cytometry and CLSM. In the meantime, its’ catalytic ability that decomposes H₂O₂ both extra-and intra-cellular was observed by fluorescence and CLSM. In vitro photodynamic toxicity of Nb@IC-NPs was examined by MTT, Live/Dead Cell Staining, Flow Cytometry and Apoptosis Assay. Tumor-bearing model was constructed to observe a semi-quantitative fluorescent distribution and the possibility of NIR-II fluorescence/photoacoustic (PA) imaging. Effect of Nb@IC-NPs on enhancing A549 tumor hypoxia and expression profile of HIF-1α was investigated in the presence of NIR. An A549 tumor metastasis model was also constructed to confirm the complex’ potential to destroy primary tumor, inhibit lung metastasis, and prolong mice’ survival. Lastly, impact of Nb@IC-NPs on mice’ main organs and blood indices was observed.

Results

Nb@IC-NPs was successfully fabricated with good homogeneity. The fluorescent absorbance of Nb@IC-NPs showed a linear relationship with the concentration of NTR, and a higher concentration of NTR corresponded to a stronger photoacoustic signal. In addition, Nb@IC-NPs showed a stable selectivity toward NTR. Our results also suggested a high efficient uptake of Nb@IC-NPs in A549 cells, which was more efficient than IC-NPs and IR1048-MZ alone. In vitro assays confirmed the effects of Nb@IC-NPs on catalytic O₂ generation even in hypoxic cells. The cell viability was upregulated with the nanocomplex at the absence of the laser, whereas it was dramatically declined with laser treatment that excited at 980 nm. Nb@IC-NPs achieved tumor hypoxia NIR-II/PA imaging through assisting A549 gathering. When NIR was applied, Nb@IC-NPs can significantly relieve A549 cellular/tumor hypoxia by generating more reactive oxygen species (ROS), which in turn helps lower the expression level of HIF-1α. In summary, Nb@IC-NPs based PDT can efficiently decimate A549 primary tumor, inhibit metastatic lung cancer, and prolong the lifespan of the mice under tolerable dosage. At last, in vivo toxicity tests of the nanocomplex showed its biosafety to the main organs and normal blood indices values.

Conclusion

Nb@IC-NPs improves tumor hypoxia through catalytic reaction and lowers the expression level of HIF-1α. It achieves tumor PA imaging through intensified NIR-II fluorescence signal that caused by response of the complex to the lesion’s nitroreductase (NTR). Nb@IC-NPs based PDT can efficiently kill A549 primary tumor, inhibit a lung metastasis, as well as prolong mice’ survival cycle.

Nanoscale covalent organic frameworks as theranostic platforms for oncotherapy: synthesis, functionalization, and applications

Cancer nanomedicine is one of the most promising domains that has emerged in the continuing search for cancer diagnosis and treatment. The rapid development of nanomaterials and nanotechnology provide a vast array of materials for use in cancer nanomedicine. Among the various nanomaterials, covalent organic frameworks (COFs) are becoming an attractive class of upstarts owing to their high crystallinity, structural regularity, inherent porosity, extensive functionality, design flexibility, and good biocompatibility. In this comprehensive review, recent developments and key achievements of COFs are provided, including their structural design, synthesis methods, nanocrystallization, and functionalization strategies. Subsequently, a systematic overview of the potential oncotherapy applications achieved till date in the fast-growing field of COFs is provided with the aim to inspire further contributions and developments to this nascent but promising field. Finally, development opportunities, critical challenges, and some personal perspectives for COF-based cancer therapeutics are presented.