Self-Illuminating Photodynamic Therapy with Enhanced Therapeutic Effect by Optimization of the Chemiluminescence Resonance Energy Transfer Step to the Photosensitizer

Self-Chemiluminescence-Triggered Ir(III) Complex Photosensitizer for Photodynamic Therapy against Hypoxic Tumor

The limited optical penetration depth and hypoxic tumor microenvironment (TME) are key factors that hinder the practical applications of conventional photodynamic therapy (PDT). To fundamentally address these issues, self-luminescent photosensitizers (PSs) can achieve efficient PDT. Herein, a self-chemiluminescence (CL)-triggered Ir complex PS, namely, IrL2, with low-O2-dependence type I photochemical processes is reported for efficient PDT. The rational design achieves efficient chemiluminescence resonance energy transfer (CRET) from covalently bonded luminol units to the Ir complex in IrL2 under the catalysis of H2O2 and hemoglobin (Hb) to generate O2•- and 1O2. Liposome IrL2H nanoparticles (NPs) are constructed by loading IrL2 and Hb. The intracellular H2O2 and loaded Hb catalyze the luminol part of IrL2H, and the Ir2 part is then excited to produce types I and II reactive oxygen species (ROS) through CRET, inducing cell death, even under hypoxic conditions, and promoting cell apoptosis. IrL2H is used for tumor imaging and inhibits tumor growth in 4T1-bearing mouse models through intratumoral injection without external light sources. This work provides new designs for transition metal complex PSs that conquer the limitations of external light sources and the hypoxic TME in PDT.

Development of a Self-Luminescent Living Bioreactor for Enhancing Photodynamic Therapy in Breast Cancer

The penetration ability of visible light (<2 mm) and near-infrared (NIR) light (∼1 cm) remarkably impairs the therapeutic efficacy and clinical applications of photodynamic therapy (PDT). To address the limitation of light penetration depth, a novel self-luminescent bacterium, teLuc.FP-EcN, has been engineered through transfection of a fusion expression plasmid containing the luciferase gene teLuc and bright red fluorescent protein mScarlet-I into Escherichia coli Nissle 1917 (EcN). The engineered teLuc.FP-EcN can specifically target and colonize tumors without significant toxicity to the host. Acting as a continuous internal light source, teLuc.FP-EcN can activate the photosensitizer chlorin e6 (Ce6) to generate reactive oxygen species (ROS) and then effectively destroy tumor tissue from the inside. As a result, a significant reduction in tumor proliferation and extension of the overall survival in mouse tumor models has been observed. Furthermore, teLuc.FP-EcN-boosted PDT amplified its therapeutic effect by activating antitumor immune response, including the conversion of M2 macrophages into pro-inflammatory M1 macrophages, as well as an increase in the proportion of CD3+ T cells and a decrease in T-cell exhaustion. In conclusion, teLuc.FP-EcN can be used as an implantable light source for tumor phototherapy, which simultaneously possesses ROS generation and immune regulation.

Carbon Dots in the Pathological Microenvironment: ROS Producers or Scavengers?

Reactive oxygen species (ROS), as metabolic byproducts, play pivotal role in physiological and pathological processes. Recently, studies on the regulation of ROS levels for disease treatments have attracted extensive attention, mainly involving the ROS-induced toxicity therapy mediated by ROS producers and antioxidant therapy by ROS scavengers. Nanotechnology advancements have led to the development of numerous nanomaterials with ROS-modulating capabilities, among which carbon dots (CDs) standing out as noteworthy ROS-modulating nanomedicines own their distinctive physicochemical properties, high stability, and excellent biocompatibility. Despite progress in treating ROS-related diseases based on CDs, critical issues such as rational design principles for their regulation remain underexplored. The primary cause of these issues may stem from the intricate amalgamation of core structure, defects, and surface states, inherent to CDs, which poses challenges in establishing a consistent generalization. This review succinctly summarizes the recently progress of ROS-modulated approaches using CDs in disease treatment. Specifically, it investigates established therapeutic strategies based on CDs-regulated ROS, emphasizing the interplay between intrinsic structure and ROS generation or scavenging ability. The conclusion raises several unresolved key scientific issues and prominent technological bottlenecks, and explores future perspectives for the comprehensive development of CDs-based ROS-modulating therapy.

Nanoparticles as carriers of photosensitizers to improve photodynamic therapy in cancer

Photodynamic therapy (PDT) has emerged as a promising non invasive therapeutic approach for cancer treatment, offering unique advantages over conventional treatments. The combination of light activation and photosensitizing agents allows for targeted and localized destruction of cancer cells, reducing damage to surrounding healthy tissues. In recent years, the integration of nanoparticles with PDT has garnered significant attention due to their potential to enhance therapeutic outcomes. This review article aims to provide a comprehensive overview of the current state-of-the-art in utilizing nanoparticles for photodynamic therapy in cancer treatment. We summarized various nanoparticle-based approaches, their properties, and their implications in optimizing PDT efficacy, and discussed challenges and prospects in the field.

Investigation of the Chemiluminescent Reaction of a Fluorinated Analog of Marine Coelenterazine

Bioluminescence (BL) and chemiluminescence (CL) are remarkable processes in which light is emitted due to (bio)chemical reactions. These reactions have attracted significant attention for various applications, such as biosensing, bioimaging, and biomedicine. Some of the most relevant and well-studied BL/CL systems are that of marine imidazopyrazine-based compounds, among which Coelenterazine is a prime example. Understanding the mechanisms behind efficient chemiexcitation is essential for the optimization and development of practical applications for these systems. Here, the CL of a fluorinated Coelenterazine analog was studied using experimental and theoretical approaches to obtain insight into these processes. Experimental analysis revealed that CL is more efficient under basic conditions than under acidic ones, which could be attributed to the higher relative chemiexcitation efficiency of an anionic dioxetanone intermediate over a corresponding neutral species. However, theoretical calculations indicated that the reactions of both species are similarly associated with both electron and charge transfer processes, which are typically used to explain efficiency chemiexcitation. So, neither process appears to be able to explain the relative chemiexcitation efficiencies observed. In conclusion, this study provides further insight into the mechanisms behind the chemiexcitation of imidazopyrazinone-based systems.

Dextran-based micelles for combinational chemo-photodynamic therapy of tumors via in vivo chemiluminescence

Natural polysaccharides, represented by dextran, chitosan, and hyaluronic acid, are widely approved for use as pharmaceutical excipients and are important carrier materials for the design of advanced drug delivery systems, particularly in the field of anticancer drug delivery. The combination of stimuli-activable prodrug based chemotherapy and photodynamic therapy (PDT) has attracted increasing attention. Recent studies have verified the effectiveness of this strategy in the treatment of multiple aggressive cancers. However, in such combination, the stimuli-responsive chemotherapy and PDT have their own problems that need to be overcome. The uneven distribution of endogenous stimuli within tumor tissues makes it difficult for prodrug to be completely activated. And the inadequate tissue penetration depth of external light results in low efficiency of PDT. Aiming at these two bottlenecks, we designed a biocompatible dextran based - multi-component nanomedicine (PCL-NPs) that integrate a chemiluminescence agent luminol, a photosensitizer chlorine e6 (Ce6), and a reactive oxygen species (ROS)-activable thioketal-based paclitaxel (PTX) prodrug. The presence of overexpressed hydrogen peroxide (H2O2) inside tumor oxidizes the luminol moiety to generate in-situ light for PDT through chemiluminescence resonance energy transfer (CRET). The singlet oxygen (1O2) produced in this process not only directly kills tumor cells but also amplifies oxidative stress to accelerate the activation of PTX prodrug. We propose that the PCL-NPs have great therapeutic potential by simultaneously enhancing chemotherapy and PDT in a combination therapy.

Host-Guest Interaction-Based Supramolecular Self-Assemblies for H2O2 Upregulation Augmented Chemiluminescence Resonance Energy Transfer-Induced Cancer Therapy

Given that light is hard to reach deep tumor tissue, how to enhance photodynamic therapy (PDT) efficacy is a big challenge. Herein, we proposed the supramolecular polymer self-assemblies (HACP) with bis[2,4,5-trichloro-6 (pentyloxycar-bonyl) phenyl] oxalate as the cargos (HACP@CPPO) to realize the chemiluminescence resonance energy transfer (CRET)-induced generation of 1O2 in situ. HACP was prepared by cinnamaldehyde-modified hyaluronic acid (HA-CA) and β-cyclodextrin-modified protoporphyrin IX (β-CD-PPIX) via host-guest interactions. The CA moiety could elevate H2O2 levels for the enhanced production of chemical energy and macrocyclic CD could enhance the stacking distance of PPIX for enhanced 1O2 yield. Thus, HACP@CPPO exhibited excellent antitumor performance without light irradiation.

Advanced techniques for performing photodynamic therapy in deep-seated tissues

Photodynamic therapy (PDT) is a promising localized cancer treatment modality. It has been used successfully to treat a range of dermatological conditions with comparable efficacy to conventional treatments. However, some drawbacks limit the clinical utility of PDT in treating deep-seated tumors. Notably, the penetration limitation of UV and visible light, commonly applied to activate photosensitizers, makes PDT incompetent in treating deep-seated tumors. Development in light delivery technologies, especially fiber optics, led to improved clinical strategies for accessing deep tissues for irradiation. However, PDT efficacy issues remained partly due to light penetration limitations. In this review, we first summarized the current PDT applications for deep-seated tumor treatment. Then, the most recent progress in advanced techniques to overcome the light penetration limitation in PDT, including using functional nanomaterials that can either self-illuminate or be activated by near-infrared (NIR) light and X-rays as transducers, and implantable light delivery devices were discussed. Finally, current challenges and future opportunities of these technologies were discussed, which we hope may inspire the development of more effective techniques to enhance PDT efficacy against deep-seated tumors.

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.

Photodynamic therapy: A next alternative treatment strategy for hepatocellular carcinoma?

Liver cancer is one of the most common cancers in the world. Of all types of liver cancer, hepatocellular carcinoma (HCC) is known to be the most frequent primary liver malignancy and has seriously compromised the health status of the general population. Locoregional thermal ablation techniques such as radiofrequency and microwave ablation, have attracted attention in clinical practice as an alternative strategy for HCC treatment. However, their aggressive thermal effect may cause undesirable complications such as hepatic decompensation, hemorrhage, bile duct injury, extrahepatic organ injuries, and skin burn. In recent years, photodynamic therapy (PDT), a gentle locoregional treatment, has attracted attention in ablation therapy for patients with superficial or luminal tumors as an alternative treatment strategy. However, some inherent defects and extrinsic factors of PDT have limited its use in clinical practice for deep-seated HCC. In this contribution, the aim is to summarize the current status and challenges of PDT in HCC treatment and provide potential strategies to overcome these deficiencies in further clinical translational practice.

Nano-photosensitizers for enhanced photodynamic therapy

Photodynamic therapy (PDT) utilizes photosensitizers (PSs) together with irradiation light of specific wavelength interacting with oxygen to generate cytotoxic reactive oxygen species (ROS), which could trigger apoptosis and/or necrosis-induced cell death in target tissues. During the past two decades, multifunctional nano-PSs employing nanotechnology and nanomedicine developed, which present not only photosensitizing properties but additionally accurate drug release abilities, efficient response to optical stimuli and hypoxia resistance. Further, nano-PSs have been developed to enhance PDT efficacy by improving the ROS yield. In addition, nano-PSs with additive or synergistic therapies are significant for both currently preclinical study and future clinical practice, given their capability of considerable higher therapeutic efficacy under safer systemic drug dosage. In this review, nano-PSs that allow precise drug delivery for efficient absorption by target cells are introduced. Nano-PSs boosting sensitivity and conversion efficiency to PDT-activating stimuli are highlighted. Nano-PSs developed to address the challenging hypoxia conditions during PDT of deep-sited tumors are summarized. Specifically, PSs capable of synergistic therapy and the emerging novel types with higher ROS yield that further enhance PDT efficacy are presented. Finally, future demands for ideal nano-PSs, emphasizing clinical translation and application are discussed.

Light Technology for Efficient and Effective Photodynamic Therapy: A Critical Review

Photodynamic therapy (PDT) is a cancer treatment with strong potential over well-established standard therapies in certain cases. Non-ionising radiation, localisation, possible repeated treatments, and stimulation of immunological response are some of the main beneficial features of PDT. Despite the great potential, its application remains challenging. Limited light penetration depth, non-ideal photosensitisers, complex dosimetry, and complicated implementations in the clinic are some limiting factors hindering the extended use of PDT. To surpass actual technological paradigms, radically new sources, light-based devices, advanced photosensitisers, measurement devices, and innovative application strategies are under extensive investigation. The main aim of this review is to highlight the advantages/pitfalls, technical challenges and opportunities of PDT, with a focus on technologies for light activation of photosensitisers, such as light sources, delivery devices, and systems. In this vein, a broad overview of the current status of superficial, interstitial, and deep PDT modalities-and a critical review of light sources and their effects on the PDT process-are presented. Insight into the technical advancements and remaining challenges of optical sources and light devices is provided from a physical and bioengineering perspective.

Tailoring photosensitive ROS for advanced photodynamic therapy

Photodynamic therapy (PDT) has been considered a noninvasive and cost-effective modality for tumor treatment. However, the complexity of tumor microenvironments poses challenges to the implementation of traditional PDT. Here, we review recent advances in PDT to resolve the current problems. Major breakthroughs in PDTs are enabling significant progress in molecular medicine and are interconnected with innovative strategies based on smart bio/nanomaterials or therapeutic insights. We focus on newly developed PDT strategies designed by tailoring photosensitive reactive oxygen species generation, which include the use of proteinaceous photosensitizers, self-illumination, or oxygen-independent approaches. While these updated PDT platforms are expected to enable major advances in cancer treatment, addressing future challenges related to biosafety and target specificity is discussed throughout as a necessary goal to expand the usefulness of PDT.

Recoverable peroxidase-like Fe3O4@MoS2-Ag nanozyme with enhanced antibacterial ability

Antibacterial agents with enzyme-like properties and bacteria-binding ability have provided an alternative method to efficiently disinfect drug-resistance microorganism. Herein, a Fe₃O₄@MoS₂-Ag nanozyme with defect-rich rough surface was constructed by a simple hydrothermal method and in-situ photodeposition of Ag nanoparticles. The nanozyme exhibited good antibacterial performance against E. coli (~69.4%) by the generated ROS and released Ag⁺, while the nanozyme could further achieve an excellent synergistic disinfection (~100%) by combining with the near-infrared photothermal property of Fe₃O₄@MoS₂-Ag. The antibacterial mechanism study showed that the antibacterial process was determined by the collaborative work of peroxidase-like activity, photothermal effect and leakage of Ag⁺. The defect-rich rough surface of MoS₂ layers facilitated the capture of bacteria, which enhanced the accurate and rapid attack of •OH and Ag⁺ to the membrane of E. coli with the assistance of local hyperthermia. This method showed broad-spectrum antibacterial performance against Gram-negative bacteria, Gram-positive bacteria, drug-resistant bacteria and fungal bacteria. Meanwhile, the magnetism of Fe₃O₄ was used to recycle the nanozyme. This work showed great potential of engineered nanozymes for efficient disinfection treatment.

Recent Advances in Self-Exciting Photodynamic Therapy

Photodynamic therapy (PDT) is already (Food and Drug Administration) FDA approved and used in the clinic for oncological treatment of pancreatic, lung, esophagus, bile duct, and of course several cancers of skin. It is an important tool in the oncological array of treatments, but for it exist several shortcomings, the most prominent of which is the shallow depth penetration of light within tissues. One-way researchers have attempted to circumvent this is through the creation of self-exciting "auto-PDT" nanoplatforms, which do not require the presence of an external light source to drive the PDT process. Instead, these platforms are driven either through oxidative chemical excitation in the form of chemiluminescence or radiological excitation from beta-emitting isotopes in the form of Cherenkov luminescence. In both, electronic excitations are generated and then transferred to the photosensitizer (PS) via Resonance Energy Transfer (RET) or Cherenkov Radiation Energy Transfer (CRET). Self-driven PDT has many components, so in this review, using contemporary examples from literature, we will breakdown the important concepts, strategies, and rationale behind the design of these self-propagating PDT nanoplatforms and critically review the aspects which make them successful and different from conventional PDT. Particular focus is given to the mechanisms of excitation and the different methods of transfer of excited electronic energy to the photosensitizer as well as the resulting therapeutic effect. The papers reviewed herein will be critiqued for their apparent therapeutic efficiency, and a basic rationale will be developed for what qualities are necessary to constitute an "effective" auto-PDT platform. This review will take a biomaterial engineering approach to the review of the auto-PDT platforms and the intended audience includes researchers in the field looking for a new perspective on PDT nanoplatforms as well as other material scientists and engineers looking to understand the mechanisms and relations between different parts of the complex "auto-PDT" system.

Photodynamic Therapy of Cancers With Internal Light Sources: Chemiluminescence, Bioluminescence, and Cerenkov Radiation

Photodynamic therapy (PDT) is a promising and minimally invasive modality for the treatment of cancers. The use of a self-illuminating system as a light source provides an intriguing solution to the light penetration issues of conventional PDT, which have gained considerable research interest in the past few years. This mini review aimed to present an overview of self-illuminating PDT systems by using internal light sources (chemiluminescence, bioluminescence, and Cerenkov radiation) and to give a brief discussion on the current challenges and future perspectives.

Photodynamic therapy regulates fate of cancer stem cells through reactive oxygen species

Photodynamic therapy (PDT) is an effective and promising cancer treatment. PDT directly generates reactive oxygen species (ROS) through photochemical reactions. This oxygen-dependent exogenous ROS has anti-cancer stem cell (CSC) effect. In addition, PDT may also increase ROS production by altering metabolism, endoplasmic reticulum stress, or potential of mitochondrial membrane. It is known that the half-life of ROS in PDT is short, with high reactivity and limited diffusion distance. Therefore, the main targeting position of PDT is often the subcellular localization of photosensitizers, which is helpful for us to explain how PDT affects CSC characteristics, including differentiation, self-renewal, apoptosis, autophagy, and immunogenicity. Broadly speaking, excess ROS will damage the redox system and cause oxidative damage to molecules such as DNA, change mitochondrial permeability, activate unfolded protein response, autophagy, and CSC resting state. Therefore, understanding the molecular mechanism by which ROS affect CSCs is beneficial to improve the efficiency of PDT and prevent tumor recurrence and metastasis. In this article, we review the effects of two types of photochemical reactions on PDT, the metabolic processes, and the biological effects of ROS in different subcellular locations on CSCs.