Oxidization enhances type I ROS generation of AIE-active zwitterionic photosensitizers for photodynamic killing of drug-resistant bacteria

Important Role of Triphenylamine in Modulating the Antibacterial Performance Relationships of Antimicrobial Peptide Mimics by Alkyl Chain Engineering

Multidrug resistance (MDR) bacteria pose a serious threat to human health, and the development of effective antimicrobial drugs is urgent. Herein, we used alkyl chain engineering to design and synthesize two series of antimicrobial peptide mimics with distinct cores: triphenylamine quaternary ammonium derivatives (TPQs) and diphenylethene quaternary ammonium derivatives (BPQs), and we investigated the effect of varying the alkyl chain lengths on antibacterial activity. We found that the introduction of a triphenylamine group significantly enhances the antibacterial activity of short-chain dimethyl quaternary ammonium derivatives while maintaining their excellent biocompatibility. Most notably, TPQ-1 exhibited negligible invasiveness toward living cells and possesses good antimicrobial activities, with good efficacy against biofilms and persisters. Moreover, TPQ-1 exhibited good antimicrobial effects in vivo and significantly accelerated the healing process of methicillin-resistant Staphylococcus aureus-infected wounds. This work promotes the practical application of antimicrobial peptide mimics and triphenylamine derivatives.

Elaborately Engineered Aggregation-Induced Emission Antibacterial Agents: Negligible Living Cell Invasiveness, Efficient Bacterial Biofilm Inhibition and Promoting Infected Wound Healing

Developing versatile photosensitizers capable of selectively eliminating pathogens over normal cells is an appealing yet highly challenging task. Herein, a novel strategy by exploiting the cationic and amphiphilic synergistic mechanism is introduced to synthesize four aggregation-induced emission (AIE)-active cationic antibacterial photosensitizers (PSs) TSPy-CH3, MeO-TSPy-Bu, MeO-TSPy-Va and MeO-TSPy-CH3. The four PSs generated both type I and type II reactive oxygen species (ROS) under white light irradiation. They can quickly stain Staphylococcus aureus (S. aureus) in 15 min, but exhibited different Escherichia coli (E.coil) affinity and living cell invasiveness. The four PSs caused devastating killing to S. aureus and methicillin-resistant Staphylococcus aureus (MRSA) at extremely low drug doses and significantly inhibited biofilm formation of drug-resistant strains by synergistic photocytotoxicity and inherent dark toxicity. Their low antibacterial concentrations and minimal invasiveness toward normal cells collectively ensured biosafety. MeO-TSPy-CH3 with moderate Clog P value stands out from others by virtues of most reliable biosafety, broad-spectrum bactericidal performance, and excellent biofilm inhibition ability. In vivo studies on bacteria-infected wounds confirmed that MeO-TSPy-CH3 reduced inflammation, promoted angiogenesis, and accelerated wound recovery, achieving comparable therapeutic outcomes to vancomycin. This work provides enlightenment for designing novel antibacterial phototherapy agents to overcome key limitations such as unpredictable biosafety risk, inadequate antibacterial potency, and poor anti-biofilm performance.

AIE-Active Antibacterial Photosensitizer Disrupting Bacterial Structure: Multicenter Validation against Drug-Resistant Pathogens

Antimicrobial resistance (AMR) has emerged as a global challenge in treating bacterial infections, creating an urgent need for broad-spectrum antimicrobial agents that can effectively combat multidrug-resistant (MDR) bacteria. Despite advancements in novel antimicrobial agents, many fail to comprehensively cover common resistant bacterial strains or undergo rigorous multi-center validation. Herein, a cationic AIE-active photosensitizers are developed, ITPM, derived from a triphenylamine-pyridine backbone to address the MDR challenge. Rigorous validation demonstrates that ITPM possesses superior fluorescence imaging capabilities and exceptional antibacterial efficacy. And its broad-spectrum activity is verified through a multi-center study involving six clinically relevant MDR strains. Additionally, resistance development studies and comparisons with advanced clinical antibiotics reveal that ITPM exhibits potent, broad-spectrum antimicrobial activity with minimal resistance development. This efficacy is attributed to its unique antibacterial mechanism involving disrupting bacterial internal structures. These findings establish ITPM as a promising candidate for broad-spectrum antimicrobial therapy, offering a potential solution to the growing crisis of AMR in clinical settings.

A Water-Soluble Aggregation-Induced Emission Photosensitizer with Intrinsic Antibacterial Activity as an Antiplanktonic and Antibiofilm Therapeutic Agent

Photosensitizers (PSs) with aggregation-induced emission (AIE) properties have gained popularity for treating bacterial infections. However, most AIE PSs have a poor water solubility and low selectivity, limiting their applications in biological systems. Herein, we report a water-soluble and bacteria-targeting AIE PS that exhibits minimum cytotoxicity toward human cells with and without light irradiation. Acting as a narrow-spectrum antibacterial agent without light irradiation, TPA-1 eradicates planktonic Staphylococcus aureus and inhibits biofilm formation by targeting the S. aureus membrane, inhibiting the supercoiling activity of S. aureus DNA gyrase, and causing the downregulation of multiple essential proteins. Upon light irradiation, TPA-1 generates reactive oxygen species (ROS) that cause membrane damage, resulting in excellent antiplanktonic and antibiofilm activities against S. aureus and Pseudomonas aeruginosa, significantly reducing the number of viable bacteria in biofilms and promoting wound healing in vivo.

A pH stable fluoran-triphenylamine photosensitizer with efficient type I and type II ROS generation

Photosensitizers (PSs) with robust pH stability and the ability to generate both type I and type II reactive oxygen species (ROS) have gained significant attention due to their versatility in various applications. In this study, we employed an electron donor-acceptor engineering strategy to design and synthesize a fluoran-triphenylamine photosensitizer (Fl-TPA), using an ester-protected ring-opened fluoran cation as the electron acceptor and triphenylamine (TPA) as the electron donor. Compared to fluoran with a spirolactone structure, Fl-TPA exhibits a significant redshift in absorption, with good light capture capabilities in the 300-600 nm range. In comparison with the reference compound Fl-H, which lacks the TPA group, Fl-TPA shows a substantial decrease in fluorescence intensity. Transient fluorescence measurements reveal biexponential decay characteristics for both compounds. Specifically, Fl-TPA shows τ1 = 0.21 ns (41%) and τ2 = 2.92 ns (59%), while Fl-H shows τ1 = 0.14 ns (93%) and τ2 = 2.23 ns (7%). The longer-lived component in Fl-TPA is more pronounced, suggesting the presence of additional non-radiative decay pathways, as further supported by the steady-state fluorescence analysis. Additionally, Fl-TPA exhibits a significant Stokes shift in solvents of varying polarity. Time-dependent density functional theory (TD-DFT) calculations reveal that the introduction of the strong electron-donating TPA group reduces the ΔES-T of Fl-TPA to 1.25 eV, which is significantly lower than that of Fl-H (1.46 eV), facilitating intersystem crossing (ISC). Thus, in the ROS generation experiment, it can be observed that Fl-H produces almost no ROS. In contrast, Fl-TPA not only exhibits high type I ROS generation capability, but also demonstrates excellent type II and total ROS generation capabilities, with performance far superior to the clinically approved near-infrared PS, indocyanine green (ICG). Moreover, Fl-TPA exhibits excellent pH stability compared to the non-esterified fluoran. The results of this study present a new photosensitizer with strong ROS generation capability and good stability across a wide pH range, providing a theoretical foundation for the design of PSs.

AIE-based ruthenium complexes as photosensitizers for specifically photo-inactivate gram-positive bacteria

The emergence of multidrug-resistant bacterial have caused severe burden for public health. Particularly, Staphylococcus aureus as one of ESKAPE pathogens have induced various infectious diseases and resulted in increasing deaths. Developing new antibacterial agents is still urgent and challenging. Fortunately, in this study, based on aggregation-induced emission (AIE) ruthenium complexes were designed and synthesized, which realized the high efficiency of reactive oxygen species generation and remarkably killed S. aureus unlike conventional antibiotics action. Significantly, owing to good singlet oxygen production ability, Ru1 at only 4 μg/mL of concentration displayed good antibacterial photodynamic therapy effect upon white light irradiation and could deplete essential coenzyme NADH to disrupt intracellular redox balance. Also, the electrostatic interaction between Ru1 and bacteria enhanced the possibility of antibacterial. Under light irradiation, Ru1 could efficiently inhibit the biofilm growth and avoid the development of drug-resistant. Furthermore, Ru1 possessed excellent biocompatibility and displayed remarkable therapy effect in treating mice-wound infections in vivo. These findings indicated that AIE-based ruthenium complexes as new antibacterial agent had great potential in photodynamic therapy of bacteria and addressing the drug-resistance crisis.

Molecular Engineering of AIE-Active Photosensitizers with High Biosafety for Effect Extracellular Antibacteria

Developing versatile photosensitizers to actualize selective antibacteria over normal cells presents an appealing yet significantly challenging task. In this study, a novel photosensitizer named DMMA-SCPI is rationally designed and facilely synthesized, which is demonstrated as a type-I photosensitizer featured by aggregation-induced emission tendency. DMMA-SCPI is capable of effectively eliminating both Galanz positive bacteria and Galanz negative bacteria in vitro and in vivo, and showed insignificant injury to normal cells and tissues, probably resulting from its pyridinium halide that has stronger adsorption property on negatively charged bacteria compared to normal cells, as well as its suitable antimicrobial activity. The antimicrobial activity of pyridinium salt type photosensitizer depends on the adsorptive activities on the surface of bacterial cells as well as the antimicrobial activity of the reactive oxygen species (ROS). Among three photosensitizers, DMMA-SCPI has better water solubility, which provides greater surface activity to adsorb bacteria. Moreover, DMMA-SCPI produces more superoxide anion radicals as ROS, which has proper antimicrobial activity with high biosafety for effect extracellular antibacteria.

Expanding Our Horizons: AIE Materials in Bacterial Research

Bacteria share a longstanding and complex relationship with humans, playing a role in protecting gut health and sustaining the ecosystem to cause infectious diseases and antibiotic resistance. Luminogenic materials that share aggregation-induced emission (AIE) characteristics have emerged as a versatile toolbox for bacterial studies through fluorescence visualization. Numerous research efforts highlight the superiority of AIE materials in this field. Recent advances in AIE materials in bacterial studies are categorized into four areas: understanding bacterial interactions, antibacterial strategies, diverse applications, and synergistic applications with bacteria. Initial research focuses on visualizing the unseen bacteria and progresses into developing strategies involving electrostatic interactions, amphiphilic AIE luminogens (AIEgens), and various AIE materials to enhance bacterial affinity. Recent progress in antibacterial strategies includes using photodynamic and photothermal therapies, bacterial toxicity studies, and combined therapies. Diverse applications from environmental disinfection to disease treatment, utilizing AIE materials in antibacterial coatings, bacterial sensors, wound healing materials, etc., are also provided. Finally, synergistic applications combining AIE materials with bacteria to achieve enhanced outcomes are explored. This review summarizes the developmental trend of AIE materials in bacterial studies and is expected to provide future research directions in advancing bacterial methodologies.

Sulfur oxidation states manipulate excited state electronic configurations for constructing highly efficient organic type I photosensitizers

The multiple relaxation processes of excited states are a bridge connecting molecular structures and properties, providing enormous application potential for organic luminogens. However, a systematic understanding and manipulation of the relationship between the molecular structure, excited state relaxation processes, and properties of organic luminogens is still lacking. Herein, we report a strategy for manipulating excited state electronic configurations through the regulation of the sulfur oxidation state to construct eminent organic type I PSs. Combined with the experimental results and theoretical calculations, we have successfully revealed the decisive role of high sulfur oxidation states in promoting ROS production capacity. Impressively, a higher sulfur oxidation state can reduce the singlet-triplet energy gap (ΔE ST), increase the matching degree of transition configurations, promote the changes of the excited state electronic configurations, and boost the effective ISC proportion by enhancing intramolecular interactions. Therefore, DBTS2O with the highest sulfur oxidation state exhibits the strongest type I ROS generation ability. Additionally, guided by our strategy, a water-soluble PS (2OA) is designed and synthesized, showing selective imaging capacity and photokilling ability against Gram-positive bacteria. This study broadens the horizons for both molecular design and mechanism study of high-performance organic type I PSs.

An Asymmetric NIR-II Organic Fluorophore with an Ultra-Large Stokes Shift for Imaging-Guided and Targeted Phototherapy

NIR-II imaging-guided phototherapy is an attractive, yet challenging, tumor treatment strategy. By monitoring the accumulation of phototherapy reagents at the tumor site through imaging and determining the appropriate therapy window, the therapeutic effect could be significantly improved. Probes with NIR-II (1000-1700 nm) fluorescence emission and a large Stokes shift hold great promise for fluorescence imaging with deep penetration, minimized self-quenching, and high spatiotemporal resolution. However, due to the lack of a suitable molecular framework, the design of a simple small-molecule dye with a large Stokes shift and NIR-II fluorescence emission has rarely been reported. Herein, we prepare an asymmetric D-π-A type NIR-II fluorescence probe (TBy). The probe is incapsulated in an amphiphilic polymer and modified with a fibronectin targeting peptide CREKA, which could recognize the fibrin-fibronectin complex overexpressed in multiple malignant tumors. The nanoparticles thus constructed (TByC-NPs) have maximum fluorescence emission at 1037 nm with a large Stokes shift of 426 nm, which is the largest Stokes shift among organic NIR-II fluorescent dyes reported in the literature. The TByC-NPs exhibit a good NIR-II imaging performance, active tumor targeting, and good photothermal and photodynamic capabilities. In vitro and in vivo studies verify that the TByC nanoplatform shows outstanding biocompatibility for NIR-II imaging-guided phototherapy and provides an excellent antitumor effect.

Anion-π+ AIEgens for Fluorescence Imaging and Photodynamic Therapy

Fluorescence imaging-guided photodynamic therapy (PDT) has attracted extensive attention due to its potential of real-time monitoring the lesion locations and visualizing the treatment process with high sensitivity and resolution. Aggregation-induced emission luminogens (AIEgens) show enhanced fluorescence and reactive oxygen species (ROS) generation after cellular uptake, giving them significant advantages in bioimaging and PDT applications. However, most AIEgens are unfavorable for the application in organisms due to their severe hydrophobicity. Anion-π+ type AIEgens carry intrinsic charges that can effectively alleviate their hydrophobicity and improve their binding capability to cells, which is expected to enhance the bioimaging quality and PDT performance. This concept summarizes the applications of anion-π+ type AIEgens in fluorescence imaging, fluorescence imaging-guided photodynamic anticancer and antimicrobial therapy in recent years, hoping to provide some new ideas for the construction of robust photosensitizers. Finally, the current problems and future challenges of anion-π+ AIEgens are discussed.

Rational design of type-I photosensitizer molecules for mitochondrion-targeted photodynamic therapy

Photodynamic therapy (PDT) has emerged as a promising approach for tumor treatment. However, traditional type II PDT faces limitations due to its oxygen-dependent nature. Type-I photosensitizers (PSs) exhibit superiority over conventional type-II PSs owing to their diminished oxygen dependence. Nevertheless, designing effective type-I PSs remains a significant challenge. In this work, we provide a novel strategy to tune the PDT mechanism of an excited photosensitizer through aryl substituent engineering. Using S-rhodamine as the base structure, three PSs were synthesized by incorporating phenyl, furyl, or thienyl groups at the meso position. Interestingly, furyl- or thienyl-substituted S-rhodamine are type-I-dominated PSs that produce O2˙-, while phenyl S-rhodamine results in O2˙- and 1O2 through type-I and type-II mechanisms, respectively. Experimental analyses and theoretical calculations showed that the introduction of a five-membered heterocycle at the meso position promoted intersystem crossing (ISC) and electron transfer, facilitating the production of O2˙-. Furthermore, furyl- or thienyl-substituted S-rhodamine exhibited high phototoxicity at ultralow concentrations. Thienyl-substituted S-rhodamine showed promising PDT efficacy against hypoxic solid tumors. This innovative strategy provides an alternative approach to developing new type-I PSs without the necessity for creating entirely new skeletons.

A H2 S-Generated Supramolecular Photosensitizer for Enhanced Photodynamic Antibacterial Infection and Relieving Inflammation

Photodynamic therapy (PDT) is a promising treatment against bacteria-caused infections. By producing large amounts of reactive oxygen species (ROS), PDT can effectively eliminate pathogenic bacteria, without causing drug resistance. However, excessive ROS may also impose an oxidative stress on surrounding tissues, resulting in local inflammation. To avoid this major drawback and limit pro-inflammation during PDT, this work prepared a supramolecular photosensitizer (TPP-CN/CP5) based on host-guest interactions between a cysteine-responsive cyano-tetraphenylporphyrin (TPP-CN) and a water-soluble carboxylatopillar[5]arene (CP5). TPP-CN/CP5 not only possesses excellent photodynamic antibacterial properties, but also shows good anti-inflammatory and cell protection capabilities. Under 660 nm light irradiation, TPP-CN/CP5 could rapidly produce abundant ROS for sterilization. After the PDT process, the addition of cysteine (Cys) triggers the release of H2 S from TPP-CN. H2 S then stops the induced inflammation by inhibiting the production of related inflammatory factors. Both in vitro and in vivo experiments show the excellent antibacterial effects and anti-inflammatory abilities of TPP-CN/CP5. These results will certainly promote the clinical application of PDT in the treatment of bacterial infectious diseases.

Design and Synthesis of Metalloporphyrin Nanoconjugates for Dual Light-Responsive Antimicrobial Photodynamic Therapy

Antimicrobial photodynamic therapy (APDT) utilizes photosensitizers (PSs) that eradicate a broad spectrum of bacteria in the presence of light and molecular oxygen. On the other hand, some light sources such as ultraviolet (UVB and UVC) have poor penetration and high cytotoxicity, leading to undesired PDT of the PSs. Herein, we have synthesized conjugatable mesosubstituted porphyrins and extensively characterized them. Time-dependent density functional theory (TD-DFT) calculations revealed that metalloporphyrin EP (5) is a suitable candidate for further applications. Subsequently, the metalloporphyrin was conjugated with lignin-based zinc oxide nanocomposites (ZnOAL and ZnOKL) to develop hydrophilic nanoconjugates (ZnOAL@EP and ZnOKL@EP). Upon dual light (UV + green light) exposure, nanoconjugates showed enhanced singlet oxygen generation ability and also demonstrated pH responsiveness. These nanoconjugates displayed significantly improved APDT efficiency (4-7 fold increase) to treat bacterial infection under dual light irradiation.

Identification of a Sonically Activated Degrader of Methionine Adenosyltransferase 2A by an in Silico Approach Assisted with the Hole-Electron Analysis

Small molecules capable of modulating methionine adenosyltransferase 2A (MAT2A) are of significant interest in precise cancer therapeutics. Herein, we raised the hole-electron Coulombic attraction as a reliable molecular descriptor for predicting the reactive oxygen generation capacity of MAT2A inhibitors, based on which we discovered compound H3 as a sonically activated degrader of MAT2A. Upon sonication, H3 can generate reactive oxygen species to specifically degrade cellular MAT2A via rapid oxidative reactions. Combination of H3 and sonication induced 87% MAT2A depletion in human colon cancer cells, thus elevating its antiproliferation effects by 8-folds. In vivo, H3 had a favorable pharmacokinetic profile (bioavailability = 77%) and ADME properties. Owing to the MAT2A degradation merits, H3 at a dosage of 10 mg/kg induced 31% tumor regression in xenograft colon tumor models. The significantly boosted antitumor potency can potentially alleviate the toxicity of high-dose MAT2A inhibitors to normal cells and tissues, especially to the liver.

Recent advances in aggregation-induced emission-active type I photosensitizers with near-infrared fluorescence: From materials design to therapeutic platform fabrication

Near-infrared (NIR) fluorescence imaging-guided photodynamic therapy (PDT) technology plays an important role in treating various diseases and still attracts increasing research interests for developing novel photosensitizers (PSs) with outstanding performances. Conventional PSs such as porphyrin and rhodamine derivatives have easy self-aggregation properties in the physiological environment due to their inherent hydrophobic nature caused by their rigid molecular structure that induces strong intermolecular stacking π-π interaction, leading to serious fluorescence quenching and cytotoxic reactive oxygen species (ROS) reduction. Meanwhile, hypoxia is an inherent barrier in the microenvironment of solid tumors, seriously restricting the therapeutic outcome of conventional PDT. Aforementioned disadvantages should be overcome urgently to enhance the therapeutic effect of PSs. Novel NIR fluorescence-guided type I PSs with aggregation-induced emission (AIE), which features the advantages of improving fluorescent intensity and ROS generation efficiency at aggregation as well as outstanding oxygen tolerance, bring hope for resolving aforementioned problems simultaneously. At present, plenty of research works fully demonstrates the advancement of AIE-active PDT based on type I PSs. In this review, cutting-edge advances focusing on AIE-active NIR type I PSs that include the aspects of the photochemical mechanism of type I ROS generation, various molecular structures of reported type I PSs with NIR fluorescence and their design strategies, and typical anticancer applications are summarized. Finally, a brief conclusion is obtained, and the underlying challenges and prospects of AIE-active type I PSs are proposed.

Synthesis and properties of novel type I photosensitizer polycyclic amide

Herein, we have designed and synthesized a novel type-I photosensitizer (PhPA) via Rh-catalyzed oxidative cyclization of diacetoxyterephthalamide with alkynes. The photoelectric properties, photosensitivity and photodegradation process of PhPA have been systematically investigated. The remarkable fluorescence quenching effect (ΦPL < 0.01) of PhPA suggests that the intersystem crossing from the singlet excited state to the reactive triplet state is enhanced by the enlarged conjugated backbone. Additionally, the ability of superoxide radical (O2-˙) generation was confirmed by electron paramagnetic resonance spectroscopy. Finally, the mechanism of PhPA photo-oxidative degradation via the structure of two metabolites is proposed.