AIE-active luminogens as highly efficient free-radical ROS photogenerator for image-guided photodynamic therapy

Image-guided photodynamic therapy (PDT) can realize highly precise and effective therapy via the integration of imaging and therapy, and has created high requirements for photosensitizers. However, the PDT modality usually utilizes conventional type II photosensitizers, resulting in unsatisfactory imaging and therapeutic outcomes due to aggregation-caused quenching (ACQ), “always on” fluorescence and strong oxygen dependence. Herein, we report the type I-based aggregation-induced emission (AIE) photosensitizer TCM-CPS with low oxygen dependence, near-infrared (NIR) emission and “off–on” fluorescence; in particular, it produces more reactive oxygen species (ROS) than commercially available Chlorin e6 and Rose Bengal. In the rational design of the AIE-based photosensitizer TCM-CPS, the strongly electron-donating carbazole unit and π-thiophene bridge distinctly extend the emission wavelength and decrease the autofluorescence interference in bio-imaging, and the hydrophilic pyridinium salt group guarantees good molecular dispersion and maintains the fluorescence-off state in the aqueous system to decrease the initial fluorescence background. Moreover, the strong donor–π–acceptor (D–π–A) character in TCM-CPS greatly separates the HOMO–LUMO distribution, enhancing the ROS generation, and TCM-CPS was constructed as a type I photosensitizer with the assistance of strong intramolecular charge transfer in the electron-rich anion–π⁺ structure. Based on its favorable hydrophilicity and photosensitivity, TCM-CPS was found to be a highly efficient free-radical ROS photogenerator for both visualizing cells using light-up NIR fluorescence and efficiently killing cancer cells upon light irradiation. The positively charged TCM-CPS could quickly bind to bacteria via electrostatic interactions to provide a light-up signal and kill bacteria at a low concentration. In the PDT treatment of bacteria-infected mice, the mice exhibited accelerated wound healing with low wound infection. Thus, the AIE-based type I photosensitizer TCM-CPS has great potential to replace commercially available photosensitizers in the image-guided PDT modality for the treatment of cancer and bacterial infection.

The AIE-based type I photosensitizer TCM-CPS exhibits high free radical generation and light-up fluorescence characteristics, giving it great potential in the image-guided PDT modality for the treatment of cancer and bacterial infections.     

Combined treatment with photodynamic therapy and chemotherapy for advanced cardiac cancers.

In all, 144 patients with advanced cardiac cancers have been treated by photodynamic therapy (PDT), combined chemotherapy and chemotherapy alone from September 1982 to July 1990. A total of 5 mg kg-1 haematoporphyrin derivative (HpD) was intravenously given 48-72 h prior to PDT. The light source was an argon dye laser with an output beam of 630 nm. The irradiation time varied between 12 and 25 min with a fluence of 100-350 mW cm-2. The entire tumour was irradiated with a light dose of 100-250 J cm-2. The combination of UFT and mitomycin C was used as standard chemotherapy. There were 26 responders out of 55 patients (47.3%) in the group treated with PDT alone, 24 out of 41 (58.5%) in the PDT+chemotherapy group, and 24 out of 48 (50.0%) in the chemotherapy alone group. In the PDT+chemotherapy group 19.5% patients had complete remission, which was better than the other two groups (5.5%, 8.3%, p less than 0.05). The following survey of all patients lasted from six months to seven years. The results suggest that a combination of PDT and chemotherapy may prove effective.     

Perfluorocarbon nanomaterials for photodynamic therapy

Photodynamic therapy (PDT) is a treatment modality in which a photosensitizer is irradiated with light, producing reactive oxygen species, often via energy transfer with oxygen. As it is common for tumors to be hypoxic, methods to deliver photosensitizer and oxygen are desirable. One such approach is the use of perfluorocarbons, molecules in which all C–H bonds are replaced with C–F bonds, to co-deliver oxygen because of the high solubility of gases in perfluorocarbons. This review highlights the benefits and limitations of several fluorinated nanomaterial architectures for use in PDT.     

Functional organic nanoparticles for photodynamic therapy

In recent years, cancer has been one of the leading causes of death in the world. Much effort has been devoted to developing cancer treatments. Photodynamic therapy (PDT) is a noninvasive therapeutic modality by combining the light of a specific wavelength, a photosensitizer (PS) and oxygen, which has been widely applied for the treatment of cancers. However, the application of PDT in clinic is greatly limited due to lack of tumor selectivity and often causing skin photosensitivity. The use of organic nanoparticles (NPs) as an advanced technology in the field of PDT shows a great promise to overcome these shortcomings. Therefore, in this review, we summarize several functional organic NPs as PS carriers that have been developed to enhance the efficacy of PDT against cancers.     

Strategies for enhanced photodynamic therapy effects

Photodynamic therapy (PDT) is a treatment modality for the selective destruction of cancerous and nonneoplastic pathologies that involves the simultaneous presence of light, oxygen and a light-activatable chemical called a photosensitizer (PS) to achieve a cytotoxic effect. The photophysics and mechanisms of cell killing by PDT have been extensively studied in recent years, and PDT has received regulatory approval for the treatment of a number of diseases worldwide. As the application of this treatment modality expands with regard to both anatomical sites and disease stages, it will be important to develop strategies for enhancing PDT outcomes. This article focuses on two broad approaches for PDT enhancement: (1) mechanism-based combination treatments in which PDT and a second modality can be designed to either increase the susceptibility of tumor cells to PDT or nullify the treatment outcome-mitigating molecular responses triggered by PDT of tumors, and (2) the more recent approaches of PS targeting, either by specific cellular function-sensitive linkages or via conjugation to macromolecules.     

Polymeric photosensitizer prodrugs for photodynamic therapy

A targeting strategy based on the selective enzyme-mediated activation of polymeric photosensitizer prodrugs (PPP) within pathological tissue has led to the development of agents with the dual ability to detect and treat cancer. Herein, a detailed study of a simple model system for these prodrugs is described. We prepared "first-generation" PPP by directly tethering the photosensitizer (PS) pheophorbide a to poly-(L)-lysine via epsilon amide links and observed that by increasing the number of PS on a polymer chain, energy transfer between PS units improved leading to better quenching efficiency. Fragmentation of the PPP backbone by trypsin digestion gave rise to a pronounced fluorescence increase and to more efficient generation of reactive oxygen species upon light irradiation. In vitro tests using the T-24 bladder carcinoma cell line and ex vivo experiments using mouse intestines illustrated the remarkable and selective ability of these PPP to fluoresce and induce phototoxicity upon enzymatic activation. This work elucidated the basic physicochemical parameters, such as water solubility and quenching/activation behavior, required for the future elaboration of more adaptable "second-generation" PPP, in which the PS is tethered to a proteolytically stable polymer backbone via enzyme-specific peptide linkers. This polymer architecture offers great flexibility to tailor make the PPP to target any pathological tissue known to over-express a specific enzyme.     

Semiconductor quantum dots for photodynamic therapy

The applicability of semiconductor QDs in photodynamic therapy (PDT) was evaluated by studying the interaction between CdSe QDs with a known silicon phthalocyanine PDT photosensitizer, Pc4. The study revealed that the QDs could be used to sensitize the PDT agent through a fluorescence resonance energy transfer (FRET) mechanism, or interact directly with molecular oxygen via a triplet energy-transfer process (TET). Both mechanisms result in the generation of reactive singlet oxygen species that can be used for PDT cancer therapy.     

Enhancing the ROS generation ability of a rhodamine-decorated iridium(iii) complex by ligand regulation for endoplasmic reticulum-targeted photodynamic therapy

The endoplasmic reticulum (ER) is a very important organelle responsible for crucial biosynthetic, sensing, and signalling functions in eukaryotic cells. In this work, we established a strategy of ligand regulation to enhance the singlet oxygen generation capacity and subcellular organelle localization ability of a rhodamine-decorated iridium(iii) complex by variation of the cyclometallating ligand. The resulting metal complex showed outstanding reactive oxygen species generation efficiency (1.6-fold higher than that of rose bengal in CH₃CN) and highly specific ER localization ability, which demonstrated the promise of the metal-based photo-theranostic agent by simultaneously tuning the photochemical/physical and biological properties. Additionally, low dark cytotoxicity, high photostability and selective tumour cell uptake were featured by this complex to demonstrate it as a promising candidate in photodynamic therapy (PDT) applications. In vivo near infrared fluorescence (NIRF) imaging and tumour PDT were investigated and showed preferential accumulation at the tumour site and remarkable tumour growth suppression, respectively.

A design strategy for boosting the ROS generation of rhodamine-decorated cyclometallated iridium(iii) complexes by ligand regulation for endoplasmic reticulum-targeted precise photodynamic therapy.     

Polycationic chitosan-conjugated photosensitizer for antibacterial photodynamic therapy

The complex nature of bacterial cell membrane and structure of biofilm has challenged the efficacy of antimicrobial photodynamic therapy. This study was aimed to synthesize a polycationic chitosan-conjugated rose bengal (CSRB) photosensitizer and test its antibiofilm efficacy on Enterococcus faecalis (gram positive) and Pseudomonas aeruginosa (gram negative) using photodynamic therapy. During experiments, CSRB was tested along with an anionic photosensitizer rose bengal (RB) and a cationic photosensitizer methylene blue (MB) for uptake and killing efficacy on 7-day-old E. faecalis and P. aeruginosa biofilms. Microbiological culture based analysis was used to analyze the cell viability, while laser scanning confocal microscopy (LSCM) was used to examine the structure of biofilm. The synthesized CSRB showed absorbance spectrum similar to the RB. The concentration of CSRB uptaken by both the bacterial biofilms was significantly higher than that of RB and MB (P < 0.05). Photoactivation resulted in significantly higher elimination of both bacterial biofilms sensitized with CSRB than RB and MB. The structure of biofilm under LSCM was found to be disrupted following CSRB treatment. The present study highlighted the importance of inherent cell membrane permeabilizing effect of chitosan and increased cell/biofilm uptake of conjugated photosensitizer to produce significant antibiofilm efficacy during photodynamic therapy.     

Acetylenic quinoxalinoporphyrazines as photosensitisers for photodynamic therapy

A range of lipo- and hydrophilic derivatives of the new class of octaalkynyl tetra-[6,7]-quinoxalinoporphyrazines (TQuiPors), analogues of the naphthalocyanines, were prepared in two steps starting from functionalised hexa-1,5-diyne-3,4-diones. Divalent zinc and magnesium ions were introduced into the macrocyclic core. Whereas the triisopropylsilyl-, 3,5-di-tert-butylphenyl- and 4-triisopropylsilyloxyphenyl-terminated acetylenic TQuiPors are lipophilic and hence soluble in standard organic solvents, a polyethylene glycol-substituted derivative was found to dissolve in DMSO as well as in ethanol/water mixtures. The new chromophores are characterised by intense UV/Vis/NIR absorptions, most notably by bands at 770 nm with extinction coefficients exceeding 500 000 M(-1) cm(-1). With a view to possible photodynamic therapy applications, the potency of the chromophores to sensitise the formation of singlet oxygen was examined, both qualitatively using a 1,3-diphenylisobenzofuran assay, and quantitatively by the determination of the singlet oxygen quantum yields. It was found that all TQuiPors produce singlet oxygen when irradiated in the presence of air. In particular, the octaalkynyl Zn-TQuiPor generates singlet oxygen with a quantum yield of 56 %, thereby rivalling, and, in conjunction with its absorption profile, even exceeding the standards set by established PDT agents. The photostabilities of the TQuiPors were assessed and generally found to be satisfactory, but dependent on the solvent and the wavelength of the incident light.     

Cell-penetrating riboflavin conjugate for antitumor photodynamic therapy

Riboflavin (RF, vitamin B2) is an essential vitamin and has been considered as a promising natural photosensitizer for photodynamic therapy (PDT). However, further exploration of RF in antitumor application was limited by its poor cellular uptake. In this study, using cell-penetrating peptides Arg₈, (Cha-Arg)₃ and small molecule triphenylphosphine (TPP) as delivery compounds, three RF conjugates were prepared to increase the accumulation of RF in cells, termed as Arg₈-RF, (Cha-Arg)₃-RF and TPP-RF, respectively. Compared with TPP-RF and Arg₈-RF, (Cha-Arg)₃-RF exhibited better cell internalization and stronger cytotoxicity against HeLa cells upon exposure to blue light. Further researches proved that (Cha-Arg)₃-RF generated reactive oxygen species (ROS) under irradiation, which could indiscriminately destroy endogenous proteins and mitochondria, ultimately inducing cell death. This work provides a new approach to explore RF as a natural photosensitizer for antitumor photodynamic therapy.     

Scavenger-receptor targeted photodynamic therapy

Covalent conjugation of a photosensitizer to a ligand that specifically recognized and internalized by a cell-surface receptor may be a way of improving the selectivity of photodynamic therapy (PDT). The class A Type-I scavenger receptor of macrophages, which among other ligands recognizes maleylated serum albumin and has a high capacity is a good candidate for testing this approach. Chlorin(e6) was covalently attached to bovine serum albumin to give conjugates with molar substitution ratios of 1:1 and 3:1 (dye to protein), and these conjugates could then be further modified by maleylation. A novel way of purifying the conjugates by acetone precipitation was developed in order to remove traces of unbound dye that could not be accomplished by size-exclusion chromatography. Conjugates were characterized by polyacrylamide gel electrophoresis and thin-layer chromatography. Photosensitizer uptake was measured by target J774 murine macrophage-like cells and nontarget OVCAR-5 human ovarian cancer cells, and phototoxicity was examined after illumination by a 660 nm diode laser by a tetrazolium assay. All of the purified conjugates were taken up by and after illumination killed J774 cells while there was only small uptake and no phototoxicity toward OVCAR-5 cells. The higher dye:protein ratio and maleylation of the conjugates both produced higher uptakes and lower survival ratios in J774 cells. The uptake and phototoxicity by J774 cells were decreased after incubation at 4 degrees C demonstrating internalization, and confocal microscopy with organelle-specific green fluorescent probes showed largely lysosomal localization. Uptake and phototoxicity by J774 cells could both be competed by addition of the scavenger receptor ligand maleylated albumin. These data show that scavenger receptor-targeted PDT gives a high degree of specificity toward macrophages and may have applications in the treatment of tumors and atherosclerosis.     

Two-photon excitation studies of hypocrellins for photodynamic therapy

The photophysical and photochemical properties of hypocrellins (HA and HB) are examined with two-photon excitations at 800 nm using femtosecond pulses from a Ti:sapphire laser. The two-photon excited fluorescence spectra of HA and HB are very similar to those obtained by one-photon excitation, which may indicate that the two-photon induced photodynamic processes of hypocrellins are similar to one-photon induced photodynamic processes. The two-photon excitation cross sections of HA and HB are measured at 800 nm as about 34.8 x 10(-50) cm(4) s/photon and 21.3 x 10(-50) cm(4) s/photon, respectively. The large two-photon cross sections of both HA and HB, suggest that the hypocrellins can be potential two-photon phototherapeutic agents. As an example for two-photon photodynamic therapy of hypocrellins, we also further examine the cell-damaging effects of HA upon two-photon illumination. Our preliminary results of cell viability test indicate hypocrellins can effectively damage the Hela cells under two-photon illumination.     

PEGylated BODIPY assembling fluorescent nanoparticles for photodynamic therapy

Two PEGylated BODIPY which could self-assemble into nanoparticles were synthesized via multicomponent Passerini reaction for cellular imaging and photodynamic therapy.     

Optimizing meso-tetra-hydroxyphenyl-chlorin-mediated photodynamic therapy for basal cell carcinoma

Meso-tetra-hydroxyphenyl-chlorin (mTHPC)-mediated photodynamic therapy (PDT) has shown to be effective in the treatment of patients with multiple basal cell carcinoma (BCC). In the present study we further optimized the drug-light interval and examined the correlation between plasma drug levels and treatment efficacy. Thirteen patients with multiple BCC (a total of 366 lesions) were included in the study. Following intravenous administration of 0.1 mg kg(-1) mTHPC, lesions were illuminated with 10 J cm(-2) light (652 nm, 100 mW cm(-2)) at 12, 24, 48, 72 or 96 h. Plasma samples were taken prior to each illumination for determination of mTHPC levels, and tumor response was evaluated at 6 months and 1 year. Both univariable and multivariable analyses showed that optimal treatment outcome was obtained for a drug-light interval of 24 h when plasma drug levels were high. Overall, good cosmetic results with little or no scarring were obtained in 87% of the treated lesions and no serious side effects were observed. We optimized mTHPC-mediated PDT for patients suffering from multiple BCC by determining the most effective drug-light interval and showed that this treatment offers significant advantages over surgical resection.