A comprehensive review on singlet oxygen generation in nanomaterials and conjugated polymers for photodynamic therapy in the treatment of cancer

A key role in lessening humanity's continuous fight against cancer could be played by photodynamic therapy (PDT), a minimally invasive treatment employed in the medical care of a range of benign disorders and malignancies. Cancerous tissue can be effectively removed by using a light source-excited photosensitizer. Singlet oxygen and reactive oxygen species are produced via the photosensitizer as a result of this excitation. In the recent past, researchers have put in tremendous efforts towards developing photosensitizer molecules for photodynamic treatment (PDT) to treat cancer. Conjugated polymers, characterized by their efficient fluorescence, exceptional photostability, and strong light absorption, are currently under scrutiny for their potential applications in cancer detection and treatment through photodynamic and photothermal therapy. Researchers are exploring the versatility of these polymers, utilizing sophisticated chemical synthesis and adaptable polymer structures to create new variants with enhanced capabilities for generating singlet oxygen in photodynamic treatment (PDT). The incorporation of photosensitizers into conjugated polymer nanoparticles has proved to be beneficial, as it improves singlet oxygen formation through effective energy transfer. The evolution of nanotechnology has emerged as an alternative avenue for enhancing the performance of current photosensitizers and overcoming significant challenges in cancer PDT. Various materials, including biocompatible metals, polymers, carbon, silicon, and semiconductor-based nanomaterials, have undergone thorough investigation as potential photosensitizers for cancer PDT. This paper outlines the recent advances in singlet oxygen generation by investigators using an array of materials, including graphene quantum dots (GQDs), gold nanoparticles (Au NPs), silver nanoparticles (Ag NPs), titanium dioxide (TiO2), ytterbium (Yb) and thulium (Tm) co-doped upconversion nanoparticle cores (Yb/Tm-co-doped UCNP cores), bismuth oxychloride nanoplates and nanosheets (BiOCl nanoplates and nanosheets), and others. It also stresses the synthesis and application of systems such as amphiphilic block copolymer functionalized with folic acid (FA), polyethylene glycol (PEG), poly(β-benzyl-L-aspartate) (PBLA10) (FA-PEG-PBLA10) functionalized with folic acid, tetra(4-hydroxyphenyl)porphyrin (THPP-(PNIPAM-b-PMAGA)4), pyrazoline-fused axial silicon phthalocyanine (HY-SiPc), phthalocyanines (HY-ZnPcp, HY-ZnPcnp, and HY-SiPc), silver nanoparticles coated with polyaniline (Ag@PANI), doxorubicin (DOX) and infrared (IR)-responsive poly(2-ethyl-2-oxazoline) (PEtOx) (DOX/PEtOx-IR NPs), particularly in NIR imaging-guided photodynamic therapy (fluorescent and photoacoustic). The study puts forward a comprehensive summary and a convincing justification for the usage of the above-mentioned materials in cancer PDT.

A Fluorinated BODIPY-Based Zirconium Metal-Organic Framework for In Vivo Enhanced Photodynamic Therapy

Photodynamic therapy (PDT), an emergent noninvasive cancer treatment, is largely dependent on the presence of efficient photosensitizers (PSs) and a sufficient oxygen supply. However, the therapeutic efficacy of PSs is greatly compromised by poor solubility, aggregation tendency, and oxygen depletion within solid tumors during PDT in hypoxic microenvironments. Despite the potential of PS-based metal-organic frameworks (MOFs), addressing hypoxia remains challenging. Boron dipyrromethene (BODIPY) chromophores, with excellent photostability, have exhibited great potential in PDT and bioimaging. However, their practical application suffers from limited chemical stability under harsh MOF synthesis conditions. Herein, we report the synthesis of the first example of a Zr-based MOF, namely, 69-L2, exclusively constructed from the BODIPY-derived ligands via a single-crystal to single-crystal post-synthetic exchange, where a direct solvothermal method is not applicable. To increase the PDT performance in hypoxia, we modify 69-L2 with fluorinated phosphate-functionalized methoxy poly(ethylene glycol). The resulting 69-L2@F is an oxygen carrier, enabling tumor oxygenation and simultaneously acting as a PS for reactive oxygen species (ROS) generation under LED irradiation. We demonstrate that 69-L2@F has an enhanced PDT effect in triple-negative breast cancer MDA-MB-231 cells under both normoxia and hypoxia. Following positive results, we evaluated the in vivo activity of 69-L2@F with a hydrogel, enabling local therapy in a triple-negative breast cancer mice model and achieving exceptional antitumor efficacy in only 2 days. We envision BODIPY-based Zr-MOFs to provide a solution for hypoxia relief and maximize efficacy during in vivo PDT, offering new insights into the design of promising MOF-based PSs for hypoxic tumors.

Covalent Organic Framework-Based Nanomotor for Multimodal Cancer Photo-Theranostics

Developing efficient integrated diagnosis and treatment agents based on fuel-free self-movement nanomotors remains challenging in antitumor therapy. In this study, a covalent organic framework (COF)-based biomimetic nanomotor composed of polypyrrole (PPy) core, porphyrin-COF shell, and HCT116 cancer cell membrane coating is reported. Under near-infrared (NIR) light irradiation, the obtained mPPy@COF-Por can overcome Brownian motion and achieves directional motion through self-thermophoretic force generated from the PPy core. The HCT116 cancer cell membrane coating enables the nanomotor to selectively recognize the source cell lines and reduces the bio-adhesion of mPPy@COF-Por in a biological medium, endowing with this NIR light-powered nanomotor good mobility. More importantly, such multifunctional integration allows the COF-based nanomotor to be a powerful nanoagent for cancer treatment, and the high infrared thermal imaging/photoacoustic imaging/fluorescence trimodal imaging-guided combined photothermal/photodynamic therapeutic effect on HCT116 tumor cell is successfully achieved. The results offer considerable promise for the development of COF nanomotors with integrated imaging/therapy modalities in biomedical applications.

Coordination Polymers from an Amino-Functionalized Terphenyl-Tetracarboxylate Linker: Structural Multiplicity and Catalytic Properties

An amino-functionalized terphenyl-tetracarboxylic acid, 2'-amino-[1,1':4',1″-terphenyl]-3,3″,5,5″-tetracarboxylic acid (H4tpta), was used as an adaptable linker to synthesize, under hydrothermal conditions, eight coordination polymers (CPs). The obtained products were formulated as [Co(μ6-H2tpta)]n (1), [Co(μ3-H2tpta)(2,2'-bipy)]n (2), [M3(μ6-Htpta)2(2,2'-bipy)2]n (M = Mn (3), Cd (4)), [Ni2(μ4-tpta)(phen)2(H2O)4]n (5), [Zn2(μ6-tpta)(phen)2]n (6), {[Zn2(μ6-tpta)(μ-4,4'-bipy)]·H2O}n (7), and [Zn2(μ6-tpta)(μ-H2biim)(H2O)2]n (8), wherein 2,2'-bipyridine (2,2'-bipy), 4,4'-bipyridine (4,4'-bipy), 1,10-phenanthroline (phen), or 2,2'-biimidazole (H2biim) are present as additional stabilizing ligands. The structural types of 1-8 vary from one-dimensional (1D) (2, 5) and two-dimensional (2D) (3, 4, 6) CPs to three-dimensional (3D) metal-organic frameworks (MOFs) (1, 7, and 8) with a diversity of topologies. The products 1-8 were investigated as catalysts in the Knoevenagel condensation involving aldehydes and active methylene derivatives (malononitrile, ethyl cyanoacetate, or tert-butyl cyanoacetate), leading to high condensation product yields (up to 99%) under optimized conditions. Various reaction conditions, substrate scope, and catalyst recycling were investigated. This work broadens the application of H4tpta as a versatile tetracarboxylate linker for the generation of diverse CPs/MOFs.

Iridium(III)-Based Infrared Two-Photon Photosensitizers: Systematic Regulation of Their Photodynamic Therapy Efficacy

Cyclometalated iridium(III) complexes are of significant importance in the field of antitumor photodynamic therapy (PDT), whether they exist as single molecules or are incorporated into nanomaterials. Nevertheless, a comprehensive examination of the relationship between their molecular structure and PDT effectiveness remains awaited. The influencing factors of two-photon excited PDT can be anticipated to be further multiplied, particularly in relation to intricate nonlinear optical properties. At present, a comprehensive body of research on this topic is lacking, and few discernible patterns have been identified. In this study, through systematic structure regulation, the nitro-substituted styryl group and 1-phenylisoquinoline ligand containing YQ2 was found to be the most potent infrared two-photon excitable photosensitizer in a 4 × 3 combination library of cyclometalated Ir(III) complexes. YQ2 could enter cells via an energy-dependent and caveolae-mediated pathway, bind specifically to mitochondria, produce 1O2 in response to 808 nm LPL irradiation, activate caspases, and induce apoptosis. In vitro, YQ2 displayed a remarkable phototherapy index for both malignant melanoma (>885) and non-small-cell lung cancer (>1234) based on these functions and was minimally deleterious to human normal liver and kidney cells. In in vivo antitumor phototherapy, YQ2 inhibited tumor growth by an impressive 85% and could be eliminated from the bodies of mice with a half-life as short as 43 h. This study has the potential to contribute significantly to the development of phototherapeutic drugs that are extremely effective in treating large, profoundly located solid tumors as well as the understanding of the structure-activity relationship of Ir(III)-based PSs in PDT.

Six metal-organic architectures from a 5-methoxyisophthalate linker: assembly, structural variety and catalytic features

A methoxy-functionalized isophthalic acid, 5-methoxy isophthalic acid (H2mia), was used a versatile linker for assembling six new metal(ii) compounds under hydrothermal conditions. The obtained products were [Cu2(μ2-mia)2(phen)2(H2O)2]·2H2O (1), [Mn(μ3-mia)(phen)]n (2), [Co(μ2-mia)(2,2'-bipy)(H2O)]n·nH2O (3), [Co(μ3-mia)(μ2-4,4'-bipy)]n·nH2O (4), [Co(μ3-mia)(py)2]n (5), and [Cd(μ2-mia)(py)(H2O)2]n·nH2O (6), where phen(1,10-phenanthroline), 2,2'-bipy(2,2'-bipyridine), 4,4'-bipy(4,4'-bipyridine) or py(pyridine) were incorporated as auxiliary ligands. The crystal structures of 1-6 range from 0D (1) and 1D (2, 3, 5, 6) CPs to a 2D network (4) with a variety of topological types. The catalytic behavior of 1-6 was studied in the cyanosilylation reaction between trimethylsilyl cyanide and aldehydes, resulting in up to 99% yields of products under optimized conditions. Various reaction parameters as well as catalyst recycling and substrate scope were investigated. This study widens the use of H2mia as a versatile dicarboxylate linker for assembling a diversity of functional metal-organic architectures with remarkable structural features and catalytic properties.

A biodegradable covalent organic framework for synergistic tumor therapy

Stimulus-responsive biodegradable nanocarriers with tumor-selective targeted drug delivery are critical for cancer therapy. Herein, we report for the first time a redox-responsive disulfide-linked porphyrin covalent organic framework (COF) that can be nanocrystallized by glutathione (GSH)-triggered biodegradation. After loading 5-fluorouracil (5-Fu), the generated nanoscale COF-based multifunctional nanoagent can be further effectively dissociated by endogenous GSH in tumor cells, releasing 5-Fu efficiently to achieve selective chemotherapy on tumor cells. Together with the GSH depletion-enhanced photodynamic therapy (PDT), an ideal synergistic tumor therapy for MCF-7 breast cancer via ferroptosis is achieved. In this research, the therapeutic efficacy was significantly improved in terms of enhanced combined anti-tumor efficiency and reduced side effects by responding to significant abnormalities such as high concentrations of GSH in the tumor microenvironment (TME).

A multiphoton transition activated iron based metal organic framework for synergistic therapy of photodynamic therapy/chemodynamic therapy/chemotherapy for orthotopic gliomas

Although photodynamic therapy (PDT) has exhibited good potential in therapy of gliomas, the limited penetration depth of light and the obstacle of the blood-brain barrier (BBB) lead to unsatisfactory treatment effects. Herein, a multifunctional nanodrug (UMD) was constructed with up-conversion nanoparticles (NaGdF₄:Yb,Tm@NaYF₄:Yb,Nd@NaYF₄, UCNPs) as the core, the photosensitizer NH₂-MIL-53 (Fe) as the shell and a carrier for loading chemotherapy drug doxorubicin hydrochloride (Dox) for synergistic therapy of gliomas. Lactoferrin (LF) was finally modified on the surface of the UMD to endow it with the ability to traverse the BBB and target cells (UMDL). The UCNP core can convert 808 nm near-infrared (NIR) light to ultraviolet light (UV light) for exciting NH₂-MIL-53 (Fe), achieving NIR-mediated PDT. In addition, Fe³⁺ on the surface of the NH₂-MIL-53 (Fe) shell could be reduced to Fe²⁺ in a tumor microenvironment (TME), and then reacted with over-expressed H₂O₂ in the TME to generate hydroxyl radicals (˙OH) for chemodynamic therapy (CDT). The Dox drug could be released in response to acidic conditions in the TME, inhibiting the growth of gliomas with low side effects. The synergistic effect of PDT/CDT/chemotherapy leads to effective suppression of orthotopic gliomas.

Theranostic doxorubicin encapsulated FeAu alloy@metal-organic framework nanostructures enable magnetic hyperthermia and medical imaging in oral carcinoma

Metal-organic frameworks (MOFs) have emerged as attractive candidates in cancer theranostics due to their ability to envelop magnetic nanoparticles, resulting in reduced cytotoxicity and high porosity, enabling chemodrug encapsulation. Here, FeAu alloy nanoparticles (FeAu NPs) are synthesized and coated with MIL-100(Fe) MOFs to fabricate FeAu@MOF nanostructures. We encapsulated Doxorubicin within the nanostructures and evaluated the suitability of this platform for medical imaging and cancer theranostics. FeAu@MOF nanostructures (FeAu@MIL-100(Fe)) exhibited superparamagnetism, magnetic hyperthermia behavior and displayed DOX encapsulation and release efficiency of 69.95 % and 97.19 %, respectively, when stimulated with alternating magnetic field (AMF). In-vitro experiments showed that AMF-induced hyperthermia resulted in 90 % HSC-3 oral squamous carcinoma cell death, indicating application in cancer theranostics. Finally, in an in-vivo mouse model, FeAu@MOF nanostructures improved image contrast, reduced tumor volume by 30-fold and tumor weight by 10-fold, which translated to enhancement in cumulative survival, highlighting the prospect of this platform for oral cancer treatment.

A covalent organic framework with a self-contained light source for photodynamic therapy

External light-independent antitumor PDT is successfully realized with a covalent organic framework (COF)-based host-guest nanosystem. Its highly effective antitumor behavior is fully demonstrated by both H₂O₂-overexpressed 4T1 and H₂O₂-less expressed HCT116 and MCF-7 xenograft models.

A CuS- and BODIPY-loaded nanoscale covalent organic framework for synergetic photodynamic and photothermal therapy

Herein, we report an inorganic photothermal agent, CuS- and an organic photosensitizer, BODIPY-loaded composite nanoscale COF material via a stepwise post-synthetic modification. The obtained CuS@COF-BDP can be a dual-modal therapeutic agent to highly inhibit MCF-7 tumor cell proliferation due to its efficient singlet oxygen generation and photothermal conversion abilities.

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.

MOF/COF hybrids as next generation materials for energy and biomedical applications

The rapid increase in the number and variety of metal organic frameworks (MOFs) and covalent organic frameworks (COFs) has led to groundbreaking applications in the field of materials science and engineering. New MOF/COF hybrids combine the outstanding features of MOF and COF structures, such as high crystallinities, large surface areas, high porosities, the ability to decorate the structures with functional groups, and improved chemical and mechanical stabilities. These new hybrid materials offer promising performances for a wide range of applications including catalysis, energy storage, gas separation, and nanomedicine. In this highlight, we discuss the recent advancements of MOF/COF hybrids as next generation materials for energy and biomedical applications with a special focus on the use of computational tools to address the opportunities and challenges of using MOF/COF hybrids for various applications.

MOF/COF hybrids combine the outstanding features of MOF and COF structures, such as high crystallinities, large surface areas, high porosities, and improved chemical and mechanical stabilities.

Metalloporphyrin and Ionic Liquid-Functionalized Covalent Organic Frameworks for Catalytic CO2 Cycloaddition via Visible-Light-Induced Photothermal Conversion

We report the construction of a porphyrin and imidazolium-ionic liquid (IL)-decorated and quinoline-linked covalent organic framework (COF, abbreviated as COF-P1-1) via a three-component one-pot Povarov reaction. After post-synthetic metallization of COF-P1-1 with Co(II) ions, the metallized COF-PI-2 is generated. COF-PI-2 is chemically stable and displays highly selective CO₂ adsorption and good visible-light-induced photothermal conversion ability (ΔT = 26 °C). Furthermore, the coexistence of Co(II)-porphyrin and imidazolium-IL within COF-PI-2 has guaranteed its highly efficient activity for CO₂ cycloaddition. Of note, the needed thermal energy for the reactions is derived from the photothermal conversion of the Co(II)-porphyrin COF upon visible-light irradiation. More importantly, the CO₂ cycloaddition herein is a "window ledge" reaction, and it can proceed smoothly upon natural sunlight irradiation. In addition, a scaled-up CO₂ cycloaddition can be readily achieved using a COF-PI-2@chitosan aerogel-based fixed-bed model reactor. Our research provides a new avenue for COF-based greenhouse gas disposal in an eco-friendly and energy- and source-saving way.

A Ferrocene-Functionalized Covalent Organic Framework for Enhancing Chemodynamic Therapy via Redox Dyshomeostasis

Chemodynamic therapy (CDT), which induces cell death by decomposing high levels of H₂ O₂ in tumor cells into highly toxic ·OH, is recognized as a promising antineoplastic approach. However, current CDT approaches are often restricted by the highly controlled and upregulated cellular antioxidant defense. To enhance ·OH-induced cellular damage by CDT, a covalent organic framework (COF)-based, ferrocene (Fc)- and glutathione peroxidase 4 (GPX4) inhibitor-loaded nanodrug, RSL3@COF-Fc (2b), is fabricated. The obtained 2b not only promotes in situ Fenton-like reactions to trigger ·OH production in cells, but also attenuates the repair mechanisms under oxidative stress via irreversible covalent GPX4 inhibition. As a result, these two approaches synergistically result in massive lipid peroxide accumulation, subsequent cell damage, and ultimately ferroptosis, while not being limited by intracellular glutathione. It is believed that this research provides a paradigm for enhancing reactive oxygen species-mediated oncotherapy through redox dyshomeostasis and may provide new insights for developing COF-based nanomedicine.

A covalent organic framework-based nanoagent for H2S-activable phototherapy against colon cancer

Herin, we report a Cu(ii)-porphyrin-derived nanoscale COF, which can be triggered by endogenous H₂S via an intracellular sulfidation reaction to generate a metal-free COF-photosensitizer for PDT against H₂S-enriched colon tumors with controllable singlet oxygen release; meanwhile in situ generated CuS can be synchronously used as a photothermal agent for PTT.

A Bio-Conjugated Chlorin-Based Metal-Organic Framework for Targeted Photodynamic Therapy of Triple Negative Breast and Pancreatic Cancers

The field of photodynamic therapy (PDT) has continued to show promise as a potential method for treating tumors. In this work a photosensitizer (PS) has been delivered to cancer cell lines for PDT by incorporation into the metal-organic framework (MOF) as an organic linker. By functionalizing the surface of MOF nanoparticles with maltotriose the PS can efficiently target cancer cells with preferential uptake into pancreatic and breast cancer cell lines. Effective targeting overcomes some current problems with PDT including long-term photosensitivity and tumor specificity. Developing a PS with optimal absorption and stability is one of the foremost challenges in PDT and the synthesis of a chlorin which is activated by long-wavelength light and is resistant to photo-bleaching is described. This chlorin-based MOF shows anti-cancer ability several times higher than that of porphyrin-based MOFs with little toxicity to normal cell lines and no dark toxicity.

Metal–organic architectures designed from a triphenyl-pentacarboxylate linker: hydrothermal assembly, structural multiplicity, and catalytic Knoevenagel condensation

Eight new metal(ii) coordination compounds driven by a triphenyl-pentacarboxylate linker were hydrothermally assembled and fully characterized. Their structural features and catalytic behavior were investigated.