Inhibitory Effects of Erythrosine/Curcumin Derivatives/Nano-Titanium Dioxide-Mediated Photodynamic Therapy on Candida albicans

This study focuses on the role of photosensitizers in photodynamic therapy. The photosensitizers were prepared in combinations of 110/220 µM erythrosine and/or 10/20 µM demethoxy/bisdemethoxy curcumin with/without 10% (w/w) nano-titanium dioxide. Irradiation was performed with a dental blue light in the 395–480 nm wavelength range, with a power density of 3200 mW/cm² and yield of 72 J/cm². The production of ROS and hydroxyl radical was investigated using an electron paramagnetic resonance spectrometer for each individual photosensitizer or in photosensitizer combinations. Subsequently, a PrestoBlue^® toxicity test of the gingival fibroblast cells was performed at 6 and 24 h on the eight highest ROS-generating photosensitizers containing curcumin derivatives and erythrosine 220 µM. Finally, the antifungal ability of 22 test photosensitizers, Candida albicans (ATCC 10231), were cultured in biofilm form at 37 °C for 48 h, then the colonies were counted in colony-forming units (CFU/mL) via the drop plate technique, and then the log reduction was calculated. The results showed that at 48 h the test photosensitizers could simultaneously produce both ROS types. All test photosensitizers demonstrated no toxicity on the fibroblast cells. In total, 18 test photosensitizers were able to inhibit Candida albicans similarly to nystatin. Conclusively, 20 µM bisdemethoxy curcumin + 220 µM erythrosine + 10% (w/w) nano-titanium dioxide exerted the highest inhibitory effect on Candida albicans.     

Towards Novel Photodynamic Anticancer Agents Generating Superoxide Anion Radicals: A Cyclometalated IrIII Complex Conjugated to a Far‐Red Emitting Coumarin

Although cyclometalated Ir^III complexes have emerged as promising photosensitizers for photodynamic therapy, some key drawbacks still hamper clinical translation, such as operability in the phototherapeutic window and reactive oxygen species (ROS) production efficiency and selectivity. In this work, a cyclometalated Ir^III complex conjugated to a far‐red‐emitting coumarin, Ir^III–COUPY, is reported with highly favourable properties for cancer phototherapy. Ir^III–COUPY was efficiently taken up by HeLa cells and showed no dark cytotoxicity and impressive photocytotoxicity indexes after irradiation with green and blue light, even under hypoxia. Importantly, a clear correlation between cell death and intracellular generation of superoxide anion radicals after visible light irradiation was demonstrated. This strategy opens the door to novel fluorescent photodynamic therapy agents with promising applications in theragnosis.     

Highly Charged Ruthenium(II) Polypyridyl Complexes as Effective Photosensitizer in Photodynamic Therapy

A comparative study between two novel, highly water soluble, ruthenium(II) polypyridyl complexes, [Ru(phen)₂ L ′] and [Ru(phen)₂Cu(II) L ′] ( L and L -Cu^II), containing the polyaazamacrocyclic unit 4,4′-(2,5,8,11,14-pentaaza[15])-2,2′-bipyridilophane ( L ′), is herein reported. L and L -Cu^II interact with calf-thymus DNA and efficiently cleave DNA plasmid when light-activated. They also possess great penetration abilities and photo-induced biological activities, evaluated on an A375 human melanoma cell line, with L -Cu^II being the most effective. Our study highlights the key role of the Fenton active Cu^II center within the macrocycle framework, that would play a synergistic role with light activation in the formation of cytotoxic ROS species. Based on these results, an optimal design of Ru^II polypyridyl systems featuring specific Cu^II-chelating polyamine units could represent a suitable strategy for the development of novel and effective photosensitizers in photodynamic therapy.     

Tumor Microenvironment Stimuli-Responsive Fluorescence Imaging and Synergistic Cancer Therapy by Carbon-Dot–Cu2+ Nanoassemblies

A method is developed to fabricate tumor microenvironment (TME) stimuli-responsive nanoplatform for fluorescence (FL) imaging and synergistic cancer therapy via assembling photosensitizer (chlorine e6, Ce6) modified carbon dots (CDs-Ce6) and Cu²⁺. The as-obtained nanoassemblies (named Cu/CC nanoparticles, NPs) exhibit quenched FL and photosensitization due to the aggregation of CDs-Ce6. Their FL imaging and photodynamic therapy (PDT) functions are recovered efficiently once they entering tumor sites by the stimulation of TME. Introducing of Cu²⁺ not only provides extra chemodynamic therapy (CDT) function through reaction with hydrogen peroxide (H₂O₂), but also depletes GSH in tumors by a redox reaction, thus amplifying the intracellular oxidative stress and enhancing the efficacy of reactive oxygen species (ROS) based therapy. Cu/CC NPs can act as a FL imaging guided trimodal synergistic cancer treatment agent by photothermal therapy (PTT), PDT, and thermally amplified CDT.     

Photodynamic Therapy Efficacy Enhanced by Dynamics: The Role of Charge Transfer and Photostability in the Selection of Photosensitizers

Progress in the photodynamic therapy (PDT) of cancer should benefit from a rationale to predict the most efficient of a series of photosensitizers that strongly absorb light in the phototherapeutic window (650–800 nm) and efficiently generate reactive oxygen species (ROS=singlet oxygen and oxygen‐centered radicals). We show that the ratios between the triplet photosensitizer–O₂ interaction rate constant (k_D) and the photosensitizer decomposition rate constant (k_d), k_D/k_d, determine the relative photodynamic activities of photosensitizers against various cancer cells. The same efficacy trend is observed in vivo with DBA/2 mice bearing S91 melanoma tumors. The PDT efficacy intimately depends on the dynamics of photosensitizer–oxygen interactions: charge transfer to molecular oxygen with generation of both singlet oxygen and superoxide ion (high k_D) must be tempered by photostability (low k_d). These properties depend on the oxidation potential of the photosensitizer and are suitably combined in a new fluorinated sulfonamide bacteriochlorin, motivated by the rationale.     

A photo-sensitizable phage for multidrug-resistant Acinetobacter baumannii therapy and biofilm ablation

Antibiotic abuse causes the emergence of bacterial resistance. Photodynamic antibacterial chemotherapy (PACT) has great potential to solve serious bacterial resistance, but it suffers from the inefficient generation of ROS and the lack of bacterial targeting ability. Herein, a unique cationic photosensitizer (NB) and bacteriophage (ABP)-based photodynamic antimicrobial agent (APNB) is developed for precise bacterial eradication and efficient biofilm ablation. Thanks to the structural modification of the NB photosensitizer with a sulfur atom, it displays excellent reactive oxygen species (ROS)-production ability. Moreover, specific binding to pathogenic microorganisms can be provided by bacteriophages. The developed APNB has multiple functions, including bacteria targeting, near-infrared fluorescence imaging and combination therapy (PACT and phage therapy). Both in vitro and in vivo experiments prove that APNB can efficiently treat A. baumannii infection. Particularly, the recovery from A. baumannii infection after APNB treatment is faster than that with ampicillin and polymyxin B in vivo. Furthermore, the strategy of combining bacteriophages and photosensitizers is employed to eradicate bacterial biofilms for the first time, and it shows the excellent biofilm ablation effect as expected. Thus, APNB has huge potential in fighting against multidrug-resistant bacteria and biofilm ablation in practice.

APNB for multidrug-resistant A. Baumannii therapy and biofilms ablation.     

Enhanced Photodynamic Therapy by Reduced Levels of Intracellular Glutathione Obtained By Employing a Nano‐MOF with CuII as the Active Center

In photodynamic therapy (PDT), the level of reactive oxygen species (ROS) produced in the cell directly determines the therapeutic effect. Improvement in ROS concentration can be realized by reducing the glutathione (GSH) level or increasing the amount of photosensitizer. However, excessive amounts photosensitizer may cause side effects. Therefore, the development of photosensitizers that reduce GSH levels through synergistically improving ROS concentration in order to strengthen the efficacy of PDT for tumor is important. We report a nano‐metal–organic framework (Cu^II‐metalated nano‐MOF {CuL‐[AlOH]₂}_n (MOF‐2, H₆L=mesotetrakis(4‐carboxylphenyl)porphyrin)) based on Cu^II as the active center for PDT. This MOF‐2 is readily taken up by breast cancer cells, and high levels of ROS are generated under light irradiation. Meanwhile, intracellular GSH is considerably decreased owing to absorption on MOF‐2; this synergistically increases ROS concentration and accelerates apoptosis, thereby enhancing the effect of PDT. Notably, based on the direct adsorption of GSH, MOF‐2 showed a comparable effect with the commercial antitumor drug camptothecin in a mouse breast cancer model. This work provides strong evidence for MOF‐2 as a promising new PDT candidate and anticancer drug.     

Nanoscale Metal–Organic Layers for Deeply Penetrating X‐ray‐Induced Photodynamic Therapy

We report the rational design of metal–organic layers (MOLs) that are built from [Hf₆O₄(OH)₄(HCO₂)₆] secondary building units (SBUs) and Ir[bpy(ppy)₂]⁺‐ or [Ru(bpy)₃]²⁺‐derived tricarboxylate ligands (Hf‐BPY‐Ir or Hf‐BPY‐Ru; bpy=2,2′‐bipyridine, ppy=2‐phenylpyridine) and their applications in X‐ray‐induced photodynamic therapy (X‐PDT) of colon cancer. Heavy Hf atoms in the SBUs efficiently absorb X‐rays and transfer energy to Ir[bpy(ppy)₂]⁺ or [Ru(bpy)₃]²⁺ moieties to induce PDT by generating reactive oxygen species (ROS). The ability of X‐rays to penetrate deeply into tissue and efficient ROS diffusion through ultrathin 2D MOLs (ca. 1.2 nm) enable highly effective X‐PDT to afford superb anticancer efficacy.     

Advances in photodynamic antimicrobial chemotherapy

Photodynamic therapy (PDT) and photodynamic antimicrobial chemotherapy (PACT) combine light and photosensitizers to treat cancers and microbial infections, respectively. In PACT, the excitation of a photosensitizer drug with appropriate light generates reactive oxygen species (ROS) that kill pathogens in the proximity of the drug. PACT has considerably advanced with new light sources, biocompatible photosensitizers, bioconjugate methods, and efficient ROS production. The PACT technology has evolved to compete with or replace antibiotics, reducing the burden of antibiotic resistance. This review updates recent advances in PACT, with special references to light sources, photosensitizers, and emerging applications to microbial infestations. We also discuss PACT applied to COVID-19 causing SARS-CoV-2 treatment and disinfecting food materials and water. Finally, we discuss the pathogen selectivity and efficiency of PACT.     

Cationic fullerenes are effective and selective antimicrobial photosensitizers

Fullerenes are soccer ball-shaped molecules composed of carbon atoms, and, when derivatized with functional groups, they become soluble and can act as photosensitizers. Antimicrobial photodynamic therapy combines a nontoxic photosensitizer with harmless visible light to generate reactive oxygen species that kill microbial cells. We have compared the antimicrobial activity of six functionalized C(60) compounds with one, two, or three hydrophilic or cationic groups in combination with white light against gram-positive bacteria, gram-negative bacteria, and fungi. After a 10 min incubation, the bis- and tris-cationic fullerenes were highly active in killing all tested microbes (4-6 logs) under conditions in which mammalian cells were comparatively unharmed. These compounds performed significantly better than a widely used antimicrobial photosensitizer, toluidine blue O. The high selectivity and efficacy exhibited by these photosensitizers encourage further testing for antimicrobial applications.     

Phthalocyanine‐Assembled Nanodots as Photosensitizers for Highly Efficient Type I Photoreactions in Photodynamic Therapy

Owing to their unique, nanoscale related optical properties, nanostructures assembled from molecular photosensitizers (PSs) have interesting applications in phototheranostics. However, most nanostructured PS assemblies are super‐quenched, thus, preventing their use in photodynamic therapy (PDT). Although some of these materials undergo stimuli‐responsive disassembly, which leads to partial recovery of PDT activity, their therapeutic potentials are unsatisfactory owing to a limited ability to promote generation reactive oxygen species (ROS), especially via type I photoreactions (i.e., not by ¹O₂ generation). Herein we demonstrate that a new, nanostructured phthalocyanine assembly, NanoPcA, has the ability to promote highly efficient ROS generation via the type I mechanism. The results of antibacterial studies demonstrate that NanoPcA has potential PDT applications.     

Type I photosensitizers based on phosphindole oxide for photodynamic therapy: apoptosis and autophagy induced by endoplasmic reticulum stress

Photodynamic therapy (PDT) is considered a pioneering and effective modality for cancer treatment, but it is still facing challenges of hypoxic tumors. Recently, Type I PDT, as an effective strategy to address this issue, has drawn considerable attention. Few reports are available on the capability for Type I reactive oxygen species (ROS) generation of purely organic photosensitizers (PSs). Herein, we report two new Type I PSs, α-TPA-PIO and β-TPA-PIO, from phosphindole oxide-based isomers with efficient Type I ROS generation abilities. A detailed study on photophysical and photochemical mechanisms is conducted to shed light on the molecular design of PSs based on the Type I mechanism. The in vitro results demonstrate that these two PSs can selectively accumulate in a neutral lipid region, particularly in the endoplasmic reticulum (ER), of cells and efficiently induce ER-stress mediated apoptosis and autophagy in PDT. In vivo models indicate that β-TPA-PIO successfully achieves remarkable tumor ablation. The ROS-based ER stress triggered by β-TPA-PIO-mediated PDT has high potential as a precursor of the immunostimulatory effect for immunotherapy. This work presents a comprehensive protocol for Type I-based purely organic PSs and highlights the significance of considering the working mechanism in the design of PSs for the optimization of cancer treatment protocols.

Phosphindole oxide-based photosensitizers with Type I reactive oxygen species generation ability are developed and used for endoplasmic reticulum stress-mediated photodynamic therapy of tumors.     

DNAzyme‐Loaded Metal–Organic Frameworks (MOFs) for Self‐Sufficient Gene Therapy

DNAzymes have been recognized as potent therapeutic agents for gene therapy, while their inefficient intracellular delivery and insufficient cofactor supply precludes their practical biological applications. Metal–organic frameworks (MOFs) have emerged as promising drug carriers without in‐depth consideration of their disassembled ingredients. Herein, we report a self‐sufficient MOF‐based chlorin e6‐modified DNAzyme (Ce6‐DNAzyme) therapeutic nanosystem for combined gene therapy and photodynamic therapy (PDT). The ZIF‐8 nanoparticles (NPs) could efficiently deliver the therapeutic DNAzyme without degradation into cancer cells. The pH‐responsive ZIF‐8 NPs disassemble with the concomitant release of the guest DNAzyme payloads and the host Zn²⁺ ions that serve, respectively, as messenger RNA‐targeting agent and required DNAzyme cofactors for activating gene therapy. The auxiliary photosensitizer Ce6 could produce reactive oxygen species (ROS) and provide a fluorescence signal for the imaging‐guided gene therapy/PDT.     

Design of Photosensitizing Agents for Targeted Antimicrobial Photodynamic Therapy

Photodynamic inactivation of microorganisms has gained substantial attention due to its unique mode of action, in which pathogens are unable to generate resistance, and due to the fact that it can be applied in a minimally invasive manner. In photodynamic therapy (PDT), a non-toxic photosensitizer (PS) is activated by a specific wavelength of light and generates highly cytotoxic reactive oxygen species (ROS) such as superoxide (O²⁻, type-I mechanism) or singlet oxygen (¹O₂*, type-II mechanism). Although it offers many advantages over conventional treatment methods, ROS-mediated microbial killing is often faced with the issues of accessibility, poor selectivity and off-target damage. Thus, several strategies have been employed to develop target-specific antimicrobial PDT (aPDT). This includes conjugation of known PS building-blocks to either non-specific cationic moieties or target-specific antibiotics and antimicrobial peptides, or combining them with targeting nanomaterials. In this review, we summarise these general strategies and related challenges, and highlight recent developments in targeted aPDT.     

Metallophthalocyanine‐Based Conjugated Microporous Polymers as Highly Efficient Photosensitizers for Singlet Oxygen Generation

Singlet oxygen (¹O₂) is of great interest because of its potential applications in photodynamic therapy, photooxidation of toxic molecules, and photochemical synthesis. Herein, we report novel metallophthalocyanine (MPc) based conjugated microporous polymers (MPc‐CMPs) as photosensitizers for the generation of ¹O₂. The rigid microporous structure efficiently improves the exposure of the majority of the MPc units to oxygen. The MPc‐CMPs also exhibit an enhanced light‐harvesting capability in the far‐red region through their extended π‐conjugation systems. Their microporous structure and excellent absorption capability for long‐wavelength photons result in the MPc‐CMPs showing high efficiency for ¹O₂ generation upon irradiation with 700 nm light, as evident by using 1,3‐diphenylisobenzofuran as an ¹O₂ trap. These results indicate that MPc‐CMPs can be considered as promising photosensitizers for the generation of ¹O₂.     

Facile Synthesis of Fe3O4@Au/PPy-DOX Nanoplatform with Enhanced Glutathione Depletion and Controllable Drug Delivery for Enhanced Cancer Therapeutic Efficacy

The complex physiological environment and inherent self-healing function of tumors make it difficult to eliminate malignant tumors by single therapy. In order to enhance the efficacy of antitumor therapy, it is significant and challenging to realize multi-mode combination therapy by utilizing/improving the adverse factors of the tumor microenvironment (TME). In this study, a novel Fe₃O₄@Au/PPy nanoplatform loaded with a chemotherapy drug (DOX) and responsive to TME, near-infrared (NIR) laser and magnetic field was designed for the combination enhancement of eliminating the tumor. The Fe²⁺ released at the low pH in TME can react with endogenous H₂O₂ to induce toxic hydroxyl radicals (·OH) for chemodynamic therapy (CDT). At the same time, the generated Fe³⁺ could deplete overexpressed glutathione (GSH) at the tumor site to prevent reactive oxygen species (ROS) from being restored while producing Fe²⁺ for CDT. The designed Fe₃O₄@Au/PPy nanoplatform had high photothermal (PT) conversion efficiency and photodynamic therapy (PDT) performance under NIR light excitation, which can promote CDT efficiency and produce more toxic ROS. To maximize the cancer-killing efficiency, the nanoplatform can be successfully loaded with the chemotherapeutic drug DOX, which can be efficiently released under NIR excitation and induction of slight acidity at the tumor site. In addition, the nanoplatform also possessed high saturation magnetization (20 emu/g), indicating a potential magnetic targeting function. In vivo and in vitro results identified that the Fe₃O₄@Au/PPy-DOX nanoplatform had good biocompatibility and magnetic-targeted synergetic CDT/PDT/PTT/chemotherapy antitumor effects, which were much better than those of the corresponding mono/bi/tri-therapies. This work provides a new approach for designing intelligent TME-mediated nanoplatforms for synergistically enhancing tumor therapy.     

Membrane-Anchoring Photosensitizer with Aggregation-Induced Emission Characteristics for Combating Multidrug-Resistant Bacteria

Traditional photosensitizers (PSs) show reduced singlet oxygen (¹O₂) production and quenched fluorescence upon aggregation in aqueous media, which greatly affect their efficiency in photodynamic therapy (PDT). Meanwhile, non-targeting PSs generally yield low efficiency in antibacterial performance due to their short lifetimes and small effective working radii. Herein, a water-dispersible membrane anchor (TBD-anchor) PS with aggregation-induced emission is designed and synthesized to generate ¹O₂ on the bacterial membrane. TBD-anchor showed efficient antibacterial performance towards both Gram-negative (Escherichia coli) and Gram-positive bacteria (Staphylococcus aureus). Over 99.8 % killing efficiency was obtained for methicillin-resistant S. aureus (MRSA) when they were exposed to 0.8 μm of TBD-anchor at a low white light dose (25 mW cm⁻²) for 10 minutes. TBD-anchor thus shows great promise as an effective antimicrobial agent to combat the menace of multidrug-resistant bacteria.     

Regioselective reactions of methyl pyropheophorbide a with formaldehyde based on hydroxymethylation

Regioselective reactions of methyl pyropheophorbide a (MPPa) with formaldehyde based on hydroxymethylation have been studied. It was found that MPPa can react regioselectively with formaldehyde under different conditions to produce a series of 3-dioxane, 12-, 13²- or 20-hydroxymethyl and 12-/13²-alkenyl-substituted chlorins via Prins reaction, Blanc chloromethylation and aldol reaction, respectively. The first examples of direct C–C bond formation at 12-position of chlorophyll derivatives were also reported to give a series of 12-vinyl-substituted chlorins. These chlorins showed extend Qy absorptions and efficient singlet oxygen generation property, indicating their potential as photosensitizers for application in photodynamic therapy.     

Doubly N‐Confused Calix[6]phyrin Bis‐Organopalladium Complexes: Photostable Triplet Sensitizers for Singlet Oxygen Generation

Triplet photosensitizers that generate singlet oxygen efficiently are attractive for applications such as photodynamic therapy (PDT). Extending the absorption band to a near‐infrared (NIR) region (700 nm≈) with reasonable photostability is one of the major demands in the rational design of such sensitizers. We herein prepared a series of mono‐ and bis‐palladium complexes ( 1‐Pd‐H₂ , 2‐Pd‐H₂ , 1‐Pd‐Pd , and 2‐Pd‐Pd ) based on modified calix[6]phyrins as photosensitizers for singlet oxygen generation. These palladium complexes showed intense absorption profiles in the visible‐to‐NIR region (500–750 nm) depending on the number of central metals. Upon photoirradiation in the presence of 1,5‐dihydroxynaphthalene (DHN) as a substrate for reactive oxygen species, the bis‐palladium complexes generated singlet oxygen with high efficiency and excellent photostability. Singlet oxygen generation was confirmed from the characteristic spectral feature of the spin trapped complex in the EPR spectrum and the intact ¹O₂ emission at 1270 nm.     

A collaborative CeO2@metal-organic framework nanosystem to endow scaffolds with photodynamic antibacterial effect

Antibacterial photodynamic therapy had attracted considerable attention in implant-associated infections treatment due to its high selectivity and no resistance. Actually, bacteria readily formed protective biofilm to cover themselves and impede the permeation of photosensitizers, severely impairing the therapeutic effect. Herein, a collaborative nanosystem was constructed by in-situ growing cerium oxide (CeO₂) nanoparticles on porphyrinic metal-organic framework PCN-224, and then mixed with poly-l-lactic acid (PLLA) powder to fabricate CeO₂@PCN-224/PLLA scaffold. In the nanosystem, CeO₂ was expected to disrupt the biofilm integrity by releasing Ce⁴⁺, exposing bacteria. Subsequently, PCN-224 could grab this opportunity to kill the bacteria by generating reactive oxygen species (ROS) under light irradiation, thereby achieving the desired antibacterial effect. Crystal violet staining and agarose gel electrophoresis results demonstrated that the bacterial biofilm was effectively eliminated by cleaving the extracellular DNA chains. Coomassie brilliant blue and acridine orange staining revealed that the generated ROS effectively killed bacteria by destroying their cell membrane, causing DNA hydrolysis and protein leakage. Furthermore, ROS could also weaken the antioxidant capacity of bacteria by consuming their glutathione, further accelerating bacterial death. As a consequence, the scaffolds presented a robust antibacterial rate of 97% against S. aureus. Collectively, this work provides a promising strategy for efficient implant-related infection treatment.