Influence of Polymer Charge on the Localization and Dark- and Photo-Induced Toxicity of a Potential Type I Photosensitizer in Cancer Cell Models

Type I photodynamic antimicrobial therapy: Principles, progress, and future perspectives

The emergence of drug-resistant bacteria has significantly diminished the efficacy of existing antibiotics in the treatment of bacterial infections. Consequently, the need for finding a strategy capable of effectively combating bacterial infections has become increasingly urgent. Photodynamic therapy (PDT) is considered one of the most promising emerging antibacterial strategies due to its non-invasiveness, low adverse effect, and the fact that it does not lead to the development of drug resistance. However, bacteria at the infection sites often exist in the form of biofilm instead of the planktonic form, resulting in a hypoxic microenvironment. This phenomenon compromises the treatment outcome of oxygen-dependent type-II PDT. Compared to type-II PDT, type-I PDT is not constrained by the oxygen concentration in the infected tissues. Therefore, in the treatment of bacterial infections, type-I PDT exhibits significant advantages over type-II PDT. In this review, we first introduce the fundamental principles of type-I PDT in details, including its physicochemical properties and how it generates reactive oxygen species (ROS). Next, we explore several specific antimicrobial mechanisms utilized by type-I PDT and summarize the recent applications of type-I PDT in antimicrobial treatment. Finally, the limitations and future development directions of type-I photosensitizers are discussed. STATEMENT OF SIGNIFICANCE: The misuse and overuse of antibiotics have accelerated the development of bacterial resistance. To achieve the effective eradication of resistant bacteria, pathfinders have devised various treatment strategies. Among these strategies, type I photodynamic therapy has garnered considerable attention owing to its non-oxygen dependence. The utilization of non-oxygen-dependent photodynamic therapy not only enables the effective elimination of drug-resistant bacteria but also facilitates the successful eradication of hypoxic biofilms, which exhibits promising prospects for treating biofilm-associated infections. Based on the current research status, we anticipate that the novel type I photodynamic therapy agent can surmount the biofilm barrier, enabling efficient treatment of hypoxic biofilm infections.

Recent advances in type I organic photosensitizers for efficient photodynamic therapy for overcoming tumor hypoxia

Photodynamic therapy (PDT) with an oxygen-dependent character is a noninvasive therapeutic method for cancer treatment. However, its clinical therapeutic effect is greatly restricted by tumor hypoxia. What's more, both PDT-mediated oxygen consumption and microvascular damage aggravate tumor hypoxia, thus, further impeding therapeutic outcomes. Compared to type II PDT with high oxygen dependence and high oxygen consumption, type I PDT with less oxygen consumption exhibits great potential to overcome the vicious hypoxic plight in solid tumors. Type I photosensitizers (PSs) are significantly important for determining the therapeutic efficacy of PDT, which performs an electron transfer photochemical reaction with the surrounding oxygen/substrates to generate highly cytotoxic free radicals such as superoxide radicals (˙O₂^-) as type I ROS. In particular, the primary precursor (˙O₂^-) would progressively undergo a superoxide dismutase (SOD)-mediated disproportionation reaction and a Haber-Weiss/Fenton reaction, yielding higher cytotoxic species (˙OH) with better anticancer effects. As a result, developing high-performance type I PSs to treat hypoxic tumors has become more and more important and urgent. Herein, the latest progress of organic type I PSs (such as AIE-active cationic/neutral PSs, cationic/neutral PSs, polymer-based PSs and supramolecular self-assembled PSs) for monotherapy or synergistic therapeutic modalities is summarized. The molecular design principles and strategies (donor-acceptor system, anion-π⁺ incorporation, polymerization and cationization) are highlighted. Furthermore, the future challenges and prospects of type I PSs in hypoxia-overcoming PDT are proposed.

Amphiphilic Rhenium-Oxo Corroles as a New Class of Sensitizers for Photodynamic Therapy

A set of rhenium(V)-oxo meso-triarylcorroles bearing ester and carboxylic acid functionalities were synthesized with a view to determining their potential for photodynamic therapy. Toward this end, we measured their near-IR phosphorescence and their ability to sensitize singlet oxygen formation. The two esters studied, Re^VO 5,10,15-tris(meta-carbomethoxyphenyl)corrole and Re^VO 5,10,15-tris(para-carbomethoxyphenyl)corrole, were found to exhibit phosphorescence quantum yields of around 1% and fairly long phosphorescence lifetimes of about 60 μs in toluene. The corresponding carboxylic acids, which were examined in ethanolic/aqueous media, in contrast, showed much lower phosphorescence quantum yields on the order of 0.01% and somewhat shorter phosphorescent lifetimes. The quantum yields for singlet oxygen formation, on the other hand, turned out to be equally high (0.72 ± 0.02) for the esters and corresponding carboxylic acids. For the two carboxylic acids, we also carried out photocytotoxicity measurements on rat bladder cancer cells (AY27) and human colon carcinoma cells (WiDr). Cell viability measurements (MTT assays) indicated 50% cell death (LD₅₀) for AY27 cells upon 5 min of blue light exposure with the meta carboxylic acid and upon 7 min of exposure with the para carboxylic acid; complete cell death resulted after 20 min for both compounds. The WiDr cells proved less sensitive, and LD₅₀ values were reached after 8 and 12 min illumination with the meta and para carboxylic acids, respectively.