GSH and H2O2 Co-Activatable Mitochondria-Targeted Photodynamic Therapy under Normoxia and Hypoxia

Currently, photosensitizers (PSs) that are microenvironment responsive and hypoxia active are scarcely available and urgently desired for antitumor photodynamic therapy (PDT). Presented herein is the design of a redox stimuli activatable metal-free photosensitizer (aPS), also functioning as a pre-photosensitizer as it is converted to a PS by the mutual presence of glutathione (GSH) and hydrogen peroxide (H₂O₂) with high specificity on a basis of domino reactions on the benzothiadiazole ring. Superior to traditional PSs, the activated aPS contributed to efficient generation of reactive oxygen species including singlet oxygen and superoxide ion through both type 1 and type 2 pathways, alleviating the aerobic requirement for PDT. Equipped with a triphenylphosphine ligand for mitochondria targeting, ^mito aPS showed excellent phototoxicity to tumor cells with low light fluence under both normoxic and hypoxic conditions, after activation by intracellular GSH and H₂O₂. The ^mito aPS was also compatible to near infrared PDT with two photon excitation (800 nm) for extensive bioapplications.     

A Mitochondria‐Targeted Photosensitizer Showing Improved Photodynamic Therapy Effects Under Hypoxia

Organelle‐targeted photosensitizers have been reported to be effective photodynamic therapy (PDT) agents. In this work, we designed and synthesized two iridium(III) complexes that specifically stain the mitochondria and lysosomes of living cells, respectively. Both complexes exhibited long‐lived phosphorescence, which is sensitive to oxygen quenching. The photocytotoxicity of the complexes was evaluated under normoxic and hypoxic conditions. The results showed that HeLa cells treated with the mitochondria‐targeted complex maintained a slower respiration rate, leading to a higher intracellular oxygen level under hypoxia. As a result, this complex exhibited an improved PDT effect compared to the lysosome‐targeted complex, especially under hypoxia conditions, suggestive of a higher practicable potential of mitochondria‐targeted PDT agents in cancer therapy.     

Novel Lysosome-Targeting Fluorescence Off-On Photosensitizer for Near-Infrared Hypoxia Imaging and Photodynamic Therapy In Vitro and In Vivo

Photodynamic therapy (PDT) has emerged as a new antitumor modality. Hypoxia, a vital characteristic of solid tumors, can be explored to stimulate the fluorescence response of photosensitizers (PSs). Considering the characteristics of PDT, the targeting of organelles employing PS would enhance antitumor effects. A new multifunctional cyanine-based PS (CLN) comprising morpholine and nitrobenzene groups was prepared and characterized. It generated fluorescence in the near-infrared (NIR) region in the presence of sodium dithionite (Na₂S₂O₄) and nitroreductase (NTR). The response mechanism of CLN was well investigated, thus revealing that its obtained reduction product was CLNH. The obtained fluorescence and singlet oxygen quantum yield of CLNH were 8.65% and 1.60%, respectively. Additionally, the selective experiment for substrates indicated that CLN exhibited a selective response to NTR. Thus, CLN fluorescence could be selectively switched on and its fluorescence intensity increased, following a prolonged stay in hypoxic cells. Furthermore, fluorescence colocalization demonstrated that CLN could effectively target lysosomes. CLN could generate reactive oxygen species and kill tumor cells (IC50 for 4T1 cells was 7.4 μM under a hypoxic condition), following its response to NTR. NIR imaging and targeted PDT were finally applied in vivo.     

Emerging Design Principle of Near-Infrared Upconversion Sensitizer Based on Mitochondria-Targeted Organic Dye for Enhanced Photodynamic Therapy

Upconversion luminescent (UCL) triggered photodynamic therapy (PDT) affords superior outcome for cancer treatment. However, conventional UCL materials which all work by a multiphoton absorption (MPA) process inevitably need extremely high power density far over the maximum permissible exposure (MPE) to laser. Here, a one-photon absorption molecular upconversion sensitizer Cy5.5-Br based on frequency upconversion luminescent (FUCL) is designed for PDT. The unusual super heavy atom effect (SHAE) in Cy5.5-Br strongly enhances its spin-orbit coupling (0.23 cm⁻¹), triplet quantum yield (11.1 %) and triplet state lifetime (18.8 μs) while the potential hot-band absorption of Cy5.5-Br is well maintained. Importantly, Cy5.5-Br can efficiently target the tumour site and kill cancer cells by destroying mitochondria under a biosafety MPE to 808 nm laser. The photostability and antitumor results are obviously superior to that of a Stokes process. This work provides a design criterion for FUCL dyes to realize effective PDT upon a biosafety optical density, possibly bringing more clinical benefits than conventional MPA materials.     

肿瘤光动力治疗临床应用的光敏剂及其研究概况

光动力治疗是一种非侵蚀性并具有一定靶向性的肿瘤治疗新方法。 光动力治疗需要光敏剂、光和氧结合产生光动力反应。 光敏剂是光动力治疗的关键和物质基础。 本文概括介绍了已上市的和已被批准进入临床试验中的光敏剂,并根据其分子的骨架结构,将其分为分卟啉类、二氢卟吩（叶绿素）类和菌绿素/酞菁三类。 同时从理想光敏剂应具备特点出发,探讨了研究中的光敏剂和光动力治疗的发展前景。     

Photostability of Silylated Coumarin Dyes in Polyceram Hosts

Numerous silylated coumarin dyes have been incorporated within silica : polydimethylsiloxane Polyceram hosts using the sol-gel process to form crack-free, polishable monoliths. The use of silylated laser dyes allows for covalently bonding the laser dyes to their hosts. Photostability of the samples was evaluated by measuring the decrease in the dye absorption in the Polyceram upon ultraviolet lamp exposure and by monitoring the fluorescence intensity as function of pump pulses from a N₂ laser at 337 nm. Both methods showed a significant improvement in photo- and thermal-stability of the silylated dye Polyceram compared to that of the unsilylated dye Polyceram at a dye : Si mole ratio of 10^-4 : 1. The improved stability is attributed to the immobilization and higher degree of caging of the silylated dye Polyceram with respect to the unsilylated dye Polyceram.     

Hypoxia Induced by Upconversion‐Based Photodynamic Therapy: Towards Highly Effective Synergistic Bioreductive Therapy in Tumors

Local hypoxia in tumors is an undesirable consequence of photodynamic therapy (PDT), which will lead to greatly reduced effectiveness of this therapy. Bioreductive pro‐drugs that can be activated at low‐oxygen conditions will be highly cytotoxic under hypoxia in tumors. Based on this principle, double silica‐shelled upconversion nanoparticles (UCNPs) nanostructure capable of co‐delivering photosensitizer (PS) molecules and a bioreductive pro‐drug (tirapazamine, TPZ) were designed (TPZ‐UC/PS), with which a synergetic tumor therapeutic effect has been achieved first by UC‐based (UC‐) PDT under normal oxygen environment, immediately followed by the induced cytotoxicity of activated TPZ when oxygen is depleted by UC‐PDT. Treatment with TPZ‐UC/PS plus NIR laser resulted in a remarkably suppressed tumor growth as compared to UC‐PDT alone, implying that the delivered TPZ has a profound effect on treatment outcomes for the much‐enhanced cytotoxicity of TPZ under PDT‐induced hypoxia.     

Smart Magnetic and Fluorogenic Photosensitizer Nanoassemblies Enable Redox-Driven Disassembly for Photodynamic Therapy

Stimuli-responsive smart photosensitizer (PS) nanoassemblies that allow enhanced delivery and controlled release of PSs are promising for imaging-guided photodynamic therapy (PDT) of tumors. However, the lack of high-sensitivity and spatial-resolution signals and fast washout of released PSs from tumor tissues have impeded PDT efficacy in vivo. Herein, we report tumor targeting, redox-responsive magnetic and fluorogenic PS nanoassemblies ( NP-RGD ) synthesized via self-assembly of a cRGD- and disulfide-containing fluorogenic and paramagnetic small molecule ( 1-RGD ) for fluorescence/magnetic resonance bimodal imaging-guided tumor PDT. NP-RGD show high r₁ relaxivity but quenched fluorescence and PDT activity; disulfide reduction by glutathione (GSH) promotes efficient disassembly into a small-molecule probe ( 2-RGD ) and an organic PS (PPa-SH), which could further bind with intracellular albumin, allowing prolonged retention and cascade activation of fluorescence and PDT to ablate tumors.     

GSH and H2O2 Co‐Activatable Mitochondria‐Targeted Photodynamic Therapy under Normoxia and Hypoxia

Currently, photosensitizers (PSs) that are microenvironment responsive and hypoxia active are scarcely available and urgently desired for antitumor photodynamic therapy (PDT). Presented herein is the design of a redox stimuli activatable metal‐free photosensitizer (aPS), also functioning as a pre‐photosensitizer as it is converted to a PS by the mutual presence of glutathione (GSH) and hydrogen peroxide (H₂O₂) with high specificity on a basis of domino reactions on the benzothiadiazole ring. Superior to traditional PSs, the activated aPS contributed to efficient generation of reactive oxygen species including singlet oxygen and superoxide ion through both type 1 and type 2 pathways, alleviating the aerobic requirement for PDT. Equipped with a triphenylphosphine ligand for mitochondria targeting, ^mito aPS showed excellent phototoxicity to tumor cells with low light fluence under both normoxic and hypoxic conditions, after activation by intracellular GSH and H₂O₂. The ^mito aPS was also compatible to near infrared PDT with two photon excitation (800 nm) for extensive bioapplications.     

Multifunctional Logic in a Photosensitizer with Triple‐Mode Fluorescent and Photodynamic Activity

Herein we describe a photosensitizer (PS) with the capacity to perform multiple logic operations based on a pyrene‐containing phthalocyanine (Pc) derivative. The system presents three output signals (fluorescence at 377 and 683 nm, and singlet oxygen (¹O₂) production), which are dependent on three inputs: two chemical (concentration of dithiothreitol (DTT) and acidic pH) and one physical (visible light above 530 nm for ¹O₂ sensitization). The multi‐input/multioutput nature of this PS leads to single‐, double‐, and triple‐mode activation pathways of its fluorescent and photodynamic functions, through the interplay of various interrelated AND, ID, and INHIBIT gates. Dual fluorescence emissions are potentially useful for orthogonal optical imaging protocols while ¹O₂ is the main reactive species in photodynamic therapy (PDT). We thus expect that this kind of PS logic system will be of great interest for multimodal cellular imaging and therapeutic applications.     

噻吩基氟硼二吡咯近红外光敏染料的合成、双光子荧光成像及光动力治疗研究

设计并合成了两种新型噻吩基氟硼二吡咯(Thienyl-BODIPY)近红外光敏染料ITBDP-1和ITBDP-2. 两种光敏染料的吸收和发射波长均达到近红外区, ITBDP-1的吸收与发射峰分别是617 nm和650 nm; ITBDP-2的吸收与发射峰分别是687 nm和731 nm. 两种光敏剂均具有较高的单线态氧产率, ITBDP-1与ITBDP-2的单线态氧产率(Φ_Δ)分别为51%和24%. 通过密度泛函理论(DFT)计算研究了光敏染料激发态下的能量变化, 理论计算表明, ITBDP-1和ITBDP-2在激发至单重态后可通过系间窜越(ISC)到达三重态, 从而提高单线态氧产率. ITBDP-1和ITBDP-2在A549细胞内具有良好的的荧光成像效果, 并且在900 nm激光激发下, ITBDP-1能够在斑马鱼体内显示出清晰的双光子荧光成像. 单线态氧成像实验证明了光敏染料在光激发下可以在肿瘤细胞和斑马鱼中产生单线态氧. 通过噻唑蓝(MTT)比色法测定了两种光敏染料的光毒性和暗毒性, ITBDP-1和ITBDP-2的最大半抑制浓度(IC₅₀)分别为2.22 μmol•L^-1和2.86 μmol•L^-1, 并且无光照条件下细胞的存活率在80%以上, 证明了两种光敏染料均具有较高的光毒性和良好的生物相容性. ITBDP-1和ITBDP-2可以在近红外光激发下实现荧光成像指导的光动力学治疗, 并且可以实现生物体内的双光子荧光成像, 这一结果也为噻吩基氟硼二吡咯光敏染料在长波激发下的双光子光动力学治疗应用打下了基础.     

Enhanced Photodynamic Efficacy Using 1,8-Naphthalimides: Potential Application in Antibacterial Photodynamic Therapy

This study addresses the need for antibacterial medication that can overcome the current problems of antibiotics. It does so by suggesting two 1,8-naphthalimides (NI1 and NI2) containing a pyridinium nucleus become attached to the imide-nitrogen atom via a methylene spacer. Those fluorescent derivatives are covalently bonded to the surface of a chloroacetyl-chloride-modified cotton fabric. The iodometric method was used to study the generation of singlet oxygen (¹O₂) by irradiation of KI in the presence of monomeric 1,8-naphthalimides and the dyed textile material. Both compounds generated reactive singlet oxygen, and their activity was preserved even after they were deposited onto the cotton fabric. The antibacterial activity of NI1 and NI2 in solution and after their covalent bonding to the cotton fabric was investigated. In vitro tests were performed against the model gram-positive bacteria B. cereus and gram-negative P. aeruginosa bacteria in dark and under light iradiation. Compound NI2 showed higher antibacterial activity than compound NI1. The light irradiation enhanced the antimicrobial activity of the compounds, with a better effect achieved against B. cereus.     

A Bifunctional Photosensitizer for Enhanced Fractional Photodynamic Therapy: Singlet Oxygen Generation in the Presence and Absence of Light

The photosensitized generation of singlet oxygen within tumor tissues during photodynamic therapy (PDT) is self‐limiting, as the already low oxygen concentrations within tumors is further diminished during the process. In certain applications, to minimize photoinduced hypoxia the light is introduced intermittently (fractional PDT) to allow time for the replenishment of cellular oxygen. This condition extends the time required for effective therapy. Herein, we demonstrated that a photosensitizer with an additional 2‐pyridone module for trapping singlet oxygen would be useful in fractional PDT. Thus, in the light cycle, the endoperoxide of 2‐pyridone is generated along with singlet oxygen. In the dark cycle, the endoperoxide undergoes thermal cycloreversion to produce singlet oxygen, regenerating the 2‐pyridone module. As a result, the photodynamic process can continue in the dark as well as in the light cycles. Cell‐culture studies validated this working principle in vitro.     

Response of MCF-7 Breast Cancer Cells Overexpressed with P-Glycoprotein to Apoptotic Induction after Photodynamic Therapy

Multidrug resistance (MDR) has posed a significant threat to cancer treatment and has led to the emergence of a new therapeutic regime of photodynamic therapy (PDT) to curb the menace. The PDT modality employs a photosensitiser (PS), excited at a specific wavelength of light to kill cancer cells. In the present study, we used a zinc phthalocyanine tetrasulfonic acid PS to mediate the photodynamic killing of MCF-7 cells overexpressed with P-glycoprotein (P-gp) and investigate the response to cell death induction. After photodynamic treatment, MCF-7 cells undergo cell death, and indicators like Annexin V/PI staining, DNA fragmentation, and measurement of apoptotic protein expression were investigated. Results showed increased externalisation of phosphatidylserine protein, measured as a percentage in flow cytometry indicative of apoptotic induction. This expression was significant (p < 0.006) for the untreated control cells, and there was no detection of DNA fragments after a laser fluence of 20 J/cm². In addition, a statistically significant difference (p < 0.05) was seen in caspase 8 activity and Bax protein expression. These findings were indicative of apoptotic induction and thus seem to represent the extrinsic apoptotic pathway. This study shows the role of PDT in the treatment of a resistant phenotype breast cancer.     

Multilayer Microcapsules for FRET Analysis and Two‐Photon‐Activated Photodynamic Therapy

Microcapsules obtained by layer‐by‐layer assembly provide a good platform for biological analysis owing to their component diversity, multiple binding sites, and controllable wall thickness. Herein, different assembly species were obtained from two‐photon dyes and traditional photosensitizers, and further assembled into microcapsules. Fluorescence resonance energy transfer (FRET) was shown to occur between the two‐photon dyes and photosensitizers. Confocal laser scanning microscopy (CLSM) with one‐ and two‐photon lasers, fluorescence lifetime imaging microscopy (FLIM), and time‐resolved fluorescence spectroscopy were used to analyze the FRET effects in the microcapsules. The FRET efficiency could easily be controlled through changing the assembly sequence. Furthermore, the capsules are phototoxic upon one‐ or two‐photon excitation. These materials are thus expected to be applicable in two‐photon‐activated photodynamic therapy for deep‐tissue treatment.     

Processing and Photostability of Pyrromethene 567 Polycerams

Polyceram materials are attractive hosts for laser dyes because they can have high optical transparencies, high laser damage thresholds, and the ability to tailor optical properties by varying the composition and synthetic routes. Pyrromethene 567 has been successfully incorporated within silica: polydimethylsiloxane (PDMS) Polycerams to obtain polishable, crack-free, transparent monoliths using the sol-gel process. Fluorescence photostability was measured by pumping with aQ-switched, frequency doubled Nd: YAG laser (532 nm) at a pulse rate of 10 Hz. Fluorescence intensity dropped to 50% after approximately 50,000 pulses at a fluence of 0.10 J/cm². UV degradation studies were performed on Polycerams with different polymer contents, and the absorption photostability is related to the solubility and type of caging of the dye.     

铱(Ⅲ)配合物乏氧肿瘤光动力治疗

光动力治疗因其无创、可控和不易产生耐药性等显著优点,成为一种新型的肿瘤靶向治疗模式。光敏化过程涉及光敏剂对氧分子的光激活反应,然而实体肿瘤的乏氧环境严重限制了传统有机光敏剂的疗效。金属铱配合物具有良好的光物理和光化学性质,是理想的新一代光敏剂,近些年,铱光敏剂被发现可以应用于乏氧肿瘤的光动力治疗。本文总结了近些年金属铱配合物应用于乏氧肿瘤光动力治疗的研究;同时介绍了基于铱配合物的乏氧纳米复合体系的构建和乏氧肿瘤的光动力治疗研究,为开发新型高效的乏氧肿瘤治疗光敏剂及其载体提供参考。     

An Assembled Nanocomplex for Improving both Therapeutic Efficiency and Treatment Depth in Photodynamic Therapy

Photodynamic therapy (PDT) shows unique selectivity and irreversible destruction toward treated tissues or cells, but still has several problems in clinical practice. One is limited therapeutic efficiency, which is attributed to hypoxia in tumor sites. Another is the limited treatment depth because traditional photosensitizes are excited by short wavelength light (<700 nm). An assembled nano‐complex system composed of oxygen donor, two‐photon absorption (TPA) species, and photosensitizer (PS) was synthesized to address both problems. The photosensitizer is excited indirectly by two‐photon laser through intraparticle FRET mechanism for improving treatment depth. The oxygen donor, hemoglobin, can supply extra oxygen into tumor location through targeting effect for enhanced PDT efficiency. The mechanism and PDT effect were verified through both in vitro and in vivo experiments. The simple system is promising to promote two‐photon PDT for clinical applications.     

Rhodium Nanoparticles as a Novel Photosensitizing Agent in Photodynamic Therapy against Cancer

Photodynamic therapy (PDT) is a promising alternative treatment for different types of cancer due to its high selectivity, which prevents healthy tissues from being damaged. The use of nanomaterials in PDT has several advantages over classical photosensitizing agents, due to their unique properties and their capacity for functionalization. Especially interesting is the use of metallic nanoparticles, which are capable of absorbing electromagnetic radiation and either transferring this energy to oxygen molecules for the generation of reactive oxygen species (ROS) or dissipating it as heat. Although previous reports have demonstrated the capacity of Rh derivatives to serve as anti-tumor drugs, to the best of our knowledge there have been no studies on the potential use of small-sized Rh nanoparticles as photosensitizers in PDT. In this study, 5 nm Rh nanoparticles have been synthesized and their potential in PDT has been evaluated. The results show that treatment with Rh nanoparticles followed by NIR irradiation induces apoptosis in cancer cells through a p53-independent mechanism.     

Comparative Photostability Studies of BODIPY and Fluorescein Dyes by Using Fluorescence Correlation Spectroscopy

In single‐molecule applications, the photostability of fluorescent molecules is a key parameter. We apply fluorescence correlation spectroscopy to compare the photostability of four fluorescein and four borondipyrromethene (BODIPY) dyes of similar structure but different triplet yields. The latter class of dyes are more stable. In the kinetic analysis the, diffusion and photobleaching are treated as competitive processes. Corrections, which account for saturation and for experimental artefacts, are achieved solely by using experimental data. Photobleaching is found to occur mainly through the first excited singlet state S₁, in contrast to previous findings.