Photodynamic Agents Research Articles

Platinum(II) Ring-Fused Chlorins as Near-Infrared Emitting Oxygen Sensors and Photodynamic Agents.

Novel near-infrared luminescent compounds based on platinum(II) 4,5,6,7-tetrahydropyrazolo[1,5-a]pyridine-fused chlorins are described. These compounds have high photostability and display light emission, in particular simultaneous fluorescence and phosphorescence emission in solution at room temperature, in the biologically relevant 700-850 nm red and near-infrared (NIR) spectral region, making them excellent materials for biological imaging. The simultaneous presence of fluorescence and phosphorescence emission at room temperature, with the phosphorescence strongly quenched by oxygen whereas fluorescence remains unaffected, allows these compounds to be used as ratiometric oxygen sensors in chemical and biological media. Both steady-state (fluorescence vs phosphorescence intensities) and dynamic (dependence of phosphorescence lifetimes upon oxygen concentration) luminescence approaches can be used. Photocytotoxicity studies against human melanocytic melanoma cells (A375) indicate that these compounds display potential as photosensitizers in photodynamic therapy.

Synthesis, singlet oxygen generation, photocytotoxicity and subcellular localization of azobisporphyrins as potentially photodynamic therapeutic agents in vitro cell study

Three azobisporphyrins (Por1, Por2 and Por3) were synthesized by coupling two molecules of (4-nitrophenyl/pyridyl) porphyrins in the presence of KOH/butanol. The structures of porphyrins were confirmed by UV, IR, NMR and mass spectra and elemental analysis. With tetraphenylporphyrin (H2TPP) as a control, the singlet oxygen (1O[Formula: see text] generation of porphyrins was evaluated through 1,3-diphenylisobenzofuran (DPBF) method. The order of ability to generate 1O2 for three azobisporphyrins was Por 1 [Formula: see text]Por 2 > Por 3[Formula: see text] H2TPP. The photocytotoxicity and sub-cellular localization of azobisporphyrins over Hela cells were studied through MTT analysis and confocal laser scanning microscope, respectively. The results indicated Por 1 and Por 2 displayed the low dark-cytotoxicity, while Por 3 induced a concentration-dependent cytotoxicity to Hela cells with the concentration of porphyrins ranging from 1 to 100 [Formula: see text] M. With the light dose at 4 J/cm2, Por 3 killed more than 60% Hela cells at 2 [Formula: see text] M, indicating a high photocytoxicity. As seen from the laser scanning confocal microscopy images, Por 3 was mainly localized in cell membrane, while Por 1 and Por 2 do not displayed significant fluorescent emission in Hela cells. These results suggest the synthesized cationic azobisporphyrin could be used as a potential therapeutic agent for photodynamic therapy of cancers.

Cyclometalated IrIII Complexes as Mitochondria‐Targeted Photodynamic Anticancer Agents

Photodynamic therapy (PDT) is an attractive therapeutic modality with high therapeutic efficacy and less side effects compared with other therapies. Herein, we developed a series of cyclometalated IrIII complexes based on 2,2′‐biimidazole with different alkyl substitutions (methyl, ethyl, propyl, and butyl). These complexes can efficiently produce singlet oxygen upon light irradiation. In vitro photocytotoxicity towards four cell lines (HeLa, A549, A549R, and LO2) was examined. Ir1–Ir5 show quick penetration of cells, remarkable mitochondrial accumulation, strong phototoxicity, and they exhibit high selectivity between tumor cells and normal cells. With the highest 1O2 quantum yields, Ir5 presents the best PDT efficiency with a high phototoxicity index (PI) value (PI = 150) towards HeLa cells. This work provides a valuable avenue to improve the PDT effect by tuning the lipophilicity and other properties with variation of the alkyl substitution on the photosensitizer. In addition, their satisfying PDT effect to a cisplatin‐resistant cell line (A549R) may contribute to the future development of improved chemotherapeutics.

Cyclometalated iridium(iii) N-heterocyclic carbene complexes as potential mitochondrial anticancer and photodynamic agents.

Metal N-heterocyclic carbene (NHC) complexes represent a promising class of anticancer therapeutic agents. In this work, four cyclometalated iridium(iii) complexes (Ir1-Ir4) containing N-heterocyclic carbene ligands have been explored as mitochondrial anticancer and photodynamic agents. These complexes are more cytotoxic than cisplatin against the cancer cells screened, can quickly penetrate into A549 cells and are mainly localized in the mitochondria. Mechanism studies show that these complexes exert their anticancer efficacy by increasing the intracellular ROS level, reducing the mitochondrial membrane potential (MMP) and inducing apoptosis. Additionally, Ir1-Ir4 exhibited two orders of magnitude higher cytotoxicity upon irradiation at 450 nm LED light. Our work provides a strategy for the design of highly effective anticancer photodynamic therapeutic agent based phosphorescent iridium complexes.

Chemical antagonism between photodynamic agents and chemotherapeutics: mechanism and avoidance.

We report a photochemical reaction-induced antagonism between the photodynamic agent (PS) and anti-cancer drugs during combined therapy. The annihilation of singlet oxygen and alkene-containing drugs into inactive drug hydroperoxides is responsible for the antagonism, and results in decreased efficacy against several cancer cell lines. Experimental and simulation results reveal that the annihilation abates with increasing distance between the PS and drugs via confining the PS and drugs into separated vehicles. As a result, antagonism can be switched to synergism in treating both drug sensitive and resistant cancer cells.

Mixed-ligand iridium(iii) complexes as photodynamic anticancer agents.

Many phosphorescent iridium complexes are potent candidates as photodynamic therapeutic agents. In this work, a series of mixed-ligand phosphorescent iridium complexes (Ir1: [Ir(L1)(bpy)Cl](PF6)2; Ir2: [Ir(L1)(ppy)Cl](PF6); Ir3: [Ir(L2)(bpy)Cl](PF6)2; Ir4: [Ir(L2)(ppy)Cl](PF6). L1 = 2,6-bis(2-benzimidazolyl)pyridine; bpy = 2,2'-bipyridine; L2 = 2,6-bis(1-methyl-benzimidazol-2-yl)pyridine; ppy = 2-phenylpyridine) have been synthesized and characterized. These complexes display high luminescence quantum yields and long phosphorescence lifetimes. All the complexes are resistant to hydrolysis in aqueous solutions, and can produce singlet oxygen (1O2) effectively upon irradiation. Ir1 and Ir2 show pH-sensitive emission properties. Interestingly, higher cellular uptake efficiency is observed for Ir2 and Ir4 with the cyclometalated ppy ligand in human lung adenocarcinoma A549 cells. Ir2 with pH-sensitive emission properties can selectively image lysosomes, and Ir4 can specifically target mitochondria. Both Ir2 and Ir4 exhibit potent photodynamic therapy (PDT) effects, with Ir2 displaying a higher phototoxicity index (PI) especially in A549 cells (PI > 54). Mechanism studies indicate that Ir2 and Ir4 can induce apoptosis through reactive oxygen species (ROS) generation and caspase activation upon visible light (425 nm) irradiation. As expected, Ir2 can damage lysosomes more effectively with a pH-sensitive singlet oxygen (1O2) yield, while Ir4 tends to impair mitochondrial function. Nevertheless, the practical application of Ir2 and Ir4 for PDT may be limited to superficial tumors due to the short excitation wavelength (425 nm). Our study gives insights into the design and anticancer mechanisms of new metal-based PDT anticancer agents.

Lovastatin Inhibits Cancer Stem Cells and Sensitizes to Chemo- and Photodynamic Therapy in Nasopharyngeal Carcinoma

Nasopharyngeal carcinoma (NPC) is an Epstein-Barr virus-associated malignancy occurring at high incidence in Southeast Asia and southern China. In spite of the good response to radio- and chemo-therapy at the early stage, resistance and recurrence develop in NPC patients in the advanced setting. Cancer stem cells (CSCs) play an important role in drug resistance and cancer recurrence. Here we report that lovastatin, a natural compound and a lipophilic statin that has already been used in the clinic to treat hypercholesterolemia, inhibited the CSC properties and induced apoptosis and cell cycle arrest in sphere-forming cells derived from the 5-8F and 6-10B NPC cell lines. Furthermore, lovastatin conferred enhanced sensitivity to the chemotherapeutic and photodynamic agents in NPC CSCs. Together our findings suggest that targeting CSCs by lovastatin in combination with routine chemotherapeutic drugs or photodynamic therapy might be a promising approach to the treatment of NPC.

Exploring the activity of a polyazine bridged Ru(ii)-Pt(ii) supramolecule in F98 rat malignant glioma cells.

The mixed-metal supramolecular complex, [(Ph2phen)2Ru(dpp)PtCl2]2+, displays significant DNA modification, cell growth inhibition, and toxicity towards F98 malignant glioma cells following visible light irradiation. The design of this complex affords superior cellular uptake and antiproliferative activity compared to the classic chemotherapeutic agent, cisplatin.

A NIR phosphorescent osmium(ii) complex as a lysosome tracking reagent and photodynamic therapeutic agent.

A novel near infrared (NIR) phosphorescent osmium complex (Os1) was developed for lysosome tracking and photodynamic therapy. Owing to its NIR photophysical properties, cellular imaging ability and phototoxicity, it has advantages over its ruthenium analogue (Ru1).

Near-infrared-emitting heteroleptic cationic iridium complexes derived from 2,3-diphenylbenzo[g]quinoxaline as in vitro theranostic photodynamic therapy agents.

Five heteroleptic cationic iridium complexes with a π-expansive cyclometalating 2,3-diphenylbenzo[g]quinoxaline (dpbq) ligand (C^N ligand) and different diimine ligands (N^N ligands) (i.e. 2,2'-bipyridine (bpy, 1), phenanthroline (phen, 2), 2-(2-pyridinyl)quinoline (pqu, 3), 2,2'-bisquinoline (bqu, 4), and 2-(quinolin-2-yl)quinoxaline (quqo, 5)) were synthesized and characterized. The lowest-energy singlet electronic transitions (S1 states) were mainly dpbq ligand-centred 1ILCT (intraligand charge transfer)/1MLCT (metal to ligand charge transfer) transitions mixed with some 1π,π* transitions for complexes 1-4 with increased contributions from 1LLCT (ligand to ligand charge transfer) in 3 and 4. For complex 5, the S1 state was switched to the 1LLCT/1MLCT transitions. All five complexes displayed weak near-infrared (NIR) phosphorescence, with maximal emission output spanning 700-1400 nm and quantum yields being on the order of 10-3. The triplet state absorptions of 1-4 all resembled that of the [Ir(dpbq)2Cl]2 dimer with lifetimes of ca. 400 ns, while the TA spectrum of 5 possessed the characteristics of both the quqo ligand and the [Ir(dpbq)2Cl]2 dimer with a bi-exponential decay of ca. 5 μs and 400 ns. While the photophysics of these complexes differ slightly, their theranostic photodynamic therapy (PDT) effects varied drastically. All of the complexes were biologically active toward melanoma cells. Complexes 2 and 3 were the most cytotoxic, with 230-340 nM activity and selectivity factors for melanoma cells over normal skin fibroblasts of 34 to 40 fold. Complexes 2, 3, and 5 became very potent cytotoxins with light activation, with EC50 values as low as 12-18 nM. This potent nanomolar light-triggered activity combined with a lower dark toxicity resulted in 5 having a phototherapeutic index (PI) margin of almost 275. The bpy coligand led to the least amount of dark toxicity of 1, while phen and pqu produced cytotoxic but selective complexes 2 and 3. The quqo coligand produced the most potent complex 5 for in vitro PDT, both in terms of photocytotoxicity and PI. All Ir(iii) complexes exhibited very bright NIR phosphorescence in melanoma cells. The wide range of cytotoxicity and photocytotoxicity effects within a relatively small class of complexes highlights the importance of the identity of the coligand in the biological activity of the π-expansive biscyclometalated Ir(iii) complexes, and their bright NIR emission in live cells demonstrates their potential as theranostic PDT agents.

Iridium(iii) complexes with five-membered heterocyclic ligands for combined photodynamic therapy and photoactivated chemotherapy.

Organometallic iridium complexes have emerged as potent anticancer agents in recent years. In this work, three cyclometalated iridium(iii) complexes Ir1-Ir3 containing monodentate five-membered heterocyclic ligands have been synthesized and characterized. Upon visible light (425 nm) irradiation, the five-membered heterocyclic ligands will dissociate from the metal centre. Moreover, Ir1-Ir3 can also act as effective singlet oxygen photosensitizers. Thus, Ir1-Ir3 can exert their light-mediated activation of anticancer effects by dual modes including ligand exchange reactions and generation of singlet oxygen (1O2) upon visible light irradiation. Notably, Ir1 displays a high phototoxicity index of 61.7 against human cancer cells. Further studies show that light-mediated anticancer properties exerted by Ir1-Ir3 occur through reactive oxygen species (ROS) generation, caspase activation, and eventually apoptosis induction. Our study demonstrates that these complexes can act as novel dual-mode light-mediated anticancer agents.

Methylene blue-containing liposomes as new photodynamic anti-bacterial agents.

Methylene blue (MB) can be employed as a photo-activatable antimicrobial drug in photodynamic therapy (PDT) due to its ability to release oxygen free radicals upon photo-activation. However, its poor ability to penetrate bacterial cell walls and bacterial biofilms limits its antimicrobial activity. To overcome these limitations, we propose some formulations of MB based on different cationic liposomes. The liposome-MB systems were characterized using dynamic light scattering (DLS), zeta potential analysis and UV-visible spectroscopy. Their ability to penetrate inside the cytoplasm of E. coli, taken as a bacterial model for Gram-negative strains, was investigated through laser scanning confocal microscopy (CLSM) and compared to the penetration of naked MB. Then, MB-loaded liposomes were photo-activated and their antimicrobial activity was tested against E. coli, showing a strong improvement with respect to MB solutions. The liposomal formulations dramatically enhance MB penetration in bacterial biofilms and reduce the inflammatory response due to lipopolysaccharide exposure in mammalian cells. The observed antimicrobial and anti-inflammatory efficacies show a clear correlation with some structural features of the carriers, namely the size and the surface charge density. Overall, these results provide fundamental knowledge that enables the design of novel efficient PDT treatments, which potentially overcome the rising incidence of antibiotic resistance of bacterial strains.

New cyclometalated Ir(iii) complexes with NCN pincer and meso-phenylcyanamide BODIPY ligands as efficient photodynamic therapy agents

A new class of cyclometalated iridium(iii) with NCN pincer andmeso-phenylcyanamide BODIPY ligands has been synthesized and studied for photodynamic therapy.

Hypericin targets multiple signaling mediators in cancer cells generating unique, diverse anti-tumoral, anti-metastatic, and anti-angiogenic activities with evidence for clinical applicability

The goals of this review are to comprehensively analyze the diverse biological activities displayed by a most potent photodynamic agent–hypericin. Hypericin is a lipophilic redox-reactive molecule possessing a redox potential low enough to act as electron acceptor, subsequently discharging these electrons to oxygen, generating ROS. This property enables intracellular hypericin to retain redox activities in the dark. In cells hypericin sequesters in endoplasmic reticulum and Golgi apparatus membranes and photo-oxidizes membranal lipoproteins. However, the most relevant cytosolic hypericin target is the Hsp90 chaperone. We have shown that hypericin selectively binds to and oxidizes Hsp90, inducing its forced polyubiquitiylation, functional inactivation and rapid degradation in a proteasome independent manner. Hsp90 physiological association with a myriad of client proteins is disrupted and several signaling mediators, cell cycling and proliferation regulators are destabilized and degraded. Secondarily affected cell cycle checkpoints cause uneven, premature mitosis, (karyokinesis with no cytokinesis), forming polykaryonic giant cells, hallmark of mitotic catastrophe also known as mitotic cell death. HIF-1a, the master regulator of VEGF synthesis and angiogenesis inducer is also an Hsp90 client protein. HIF-1a is physiologically degraded by oxygen but also by the hypericin-induced Hsp90 ablation, inducing potent tumor neoangiogenesis inhibition. Hsp90 is implicated in mediating inheritable epigenetic modifications, causing epigenetic signature changes in key developmentally regulated genes and tumor cell exit from proliferation cycles. Expression of EZH2, the Polycomb repressor complex-2 catalytic subunit, which trimethylates histone H3lys27 is suppressed, class-I HDACs expression downregulated and HDAC1-Dnmt1-EZH2 complex formations diminish. Deficiencies in HDACs cellular contents lead to histones H3 and H4 hyperacetylation, which together with diminished H3K27-trimethylation relax chromatin structure, activating transcription including of differentiation-promoting genes. In GBM cells neuroglial differentiation antigens are expressed, cytoarchitecture modulated and the cells undergo tumor cell differentiation. Indeed, clinically significant anti-GBM effects were obtained in a clinical trial in recurrent, progressive GBM patients.

Synergistic in vivo photodynamic and photothermal antitumor therapy based on collagen-gold hybrid hydrogels with inclusion of photosensitive drugs

Phototherapies, including photodynamic therapy (PDT) and photothermal therapy (PTT), have shown great potential in non-invasive tumor treatments. To achieve targeted and effective antitumor therapy, it is highly desirable to combine the advantages of PDT and PTT in a delivery platform. Herein, we report a strategy to achieve synergistic PDT and PTT based on collagen-gold hybrid hydrogels, in which gold nanoparticles are incorporated as photothermal agents for PTT and photosensitive drugs are entrapped as photodynamic agents for PDT. In vivo antitumor results reveal that synergistic PDT and PTT exhibit the best antitumor effect with a tumor elimination rate up to 80% while PDT and PTT alone show less effective tumor inhibition. This synergistic therapy by the designed hydrogels does not cause body weight loss as compared to the control group without any treatment. Taken together, such a therapeutic strategy based on collagen-gold hybrid hydrogels with inclusion of photosensitive drugs may provide new alternatives for developing a type of delivery nanosystems toward synergistic antitumor therapy.

Gold-Nanoclustered Hyaluronan Nano-Assemblies for Photothermally Maneuvered Photodynamic Tumor Ablation.

Optically active nanomaterials have shown great promise as a nanomedicine platform for photothermal or photodynamic cancer therapies. Herein, we report a gold-nanoclustered hyaluronan nanoassembly (GNc-HyNA) for photothermally boosted photodynamic tumor ablation. Unlike other supramolecular gold constructs based on gold nanoparticle building blocks, this system utilizes the nanoassembly of amphiphilic hyaluronan conjugates as a drug carrier for a hydrophobic photodynamic therapy agent verteporfin, a polymeric reducing agent, and an organic nanoscaffold upon which gold can grow. Gold nanoclusters were selectively installed on the outer shell of the hyaluronan nanoassembly, forming a gold shell. Given the dual protection effect by the hyaluronan self-assembly as well as by the inorganic gold shell, verteporfin-encapsulated GNc-HyNA (Vp-GNc-HyNA) exhibited outstanding stability in the bloodstream. Interestingly, the fluorescence and photodynamic properties of Vp-GNc-HyNA were considerably quenched due to the gold nanoclusters covering the surface of the nanoassemblies; however, photothermal activation by 808 nm laser irradiation induced a significant increase in temperature, which empowered the PDT effect of Vp-GNc-HyNA. Furthermore, fluorescence and photodynamic effects were recovered far more rapidly in cancer cells due to certain intracellular enzymes, particularly hyaluronidases and glutathione. Vp-GNc-HyNA exerted a great potential to treat tumors both in vitro and in vivo. Tumors were completely ablated with a 100% survival rate and complete skin regeneration over the 50 days following Vp-GNc-HyNA treatment in an orthotopic breast tumor model. Our results suggest that photothermally boosted photodynamic therapy using Vp-GNc-HyNA can offer a potent therapeutic means to eradicate tumors.

Zinc-Substituted Myoglobin Is a Naturally Occurring Photo-antimicrobial Agent with Potential Applications in Food Decontamination.

Zinc-substituted myoglobin (ZnMb) is a naturally occurring photosensitizer that generates singlet oxygen with a high quantum yield. Using a combination of photophysical and fluorescence imaging techniques, we demonstrate the interaction of ZnMb with Gram-positive Staphylococcus aureus and Gram-negative Escherichia coli. An efficient antibacterial action against S.aureus was observed, with a reduction up to 99.9999% in the number of colony-forming units, whereas no sizable effect was detected against E.coli. Because ZnMb is known to form during the maturation of additive-free not-cooked cured ham, the use of this protein as a built-in photodynamic agent may constitute a viable method for the decontamination of these food products from Gram-positive bacteria.

Multifunctional Cu2-xTe Nanocubes Mediated Combination Therapy for Multi-Drug Resistant MDA MB 453.

Hypermethylated cancer populations are hard to treat due to their enhanced chemo-resistance, characterized by aberrant methylated DNA subunits. Herein, we report on invoking response from such a cancer lineage to chemotherapy utilizing multifunctional copper telluride (Cu2−XTe) nanocubes (NCs) as photothermal and photodynamic agents, leading to significant anticancer activity. The NCs additionally possessed photoacoustic and X-ray contrast imaging abilities that could serve in image-guided therapeutic studies.

The role of galectin-1 in in vitro and in vivo photodynamic therapy with a galactodendritic porphyrin

Conventional photodynamic agents used in clinic are porphyrin-based photosensitizers. However, they have low tumour selectivity, which may induce unwanted side-effects and damage to healthy tissues. In this study, we used a porphyrin with dendritic units of galactose (PorGal8) developed by us, which can target the galactose-binding protein, galectin-1, known to be overexpressed in many tumour tissues. In vitro and in vivo studies had been conducted for the validation of PorGal8 effectiveness. We showed a specific uptake of PorGal8 and induction of apoptotic cell death by generating oxidative stress and alterations in the cytoskeleton of bladder cancer cells overexpressing galectin-1. We further validated the photodynamic efficiency of PorGal8 in athymic nude mice (Balb/c nu/nu) bearing subcutaneously implanted luciferase-positive bladder cancer xenografts, overexpressing galectin-1 protein. PorGal8 (5 μmol/kg, intraperitoneal), injected 24 h before light delivery (50.4 J/cm2), inhibited tumour growth. We conclude that the use of PorGal8 enables selective target and cytotoxicity by photodynamic therapy in cancer cells overexpressing galectin-1, preventing undesired phototoxicity in the surrounding healthy tissues.

A HER2 selective theranostic agent for surgical resection guidance and photodynamic therapy.

In many cancers early intervention involves surgical resection of small localised tumour masses. Inadequate resection leads to recurrence whereas overzealous treatment can lead to organ damage. This work describes production of a HER2 targeting antibody Fab fragment dual conjugated to achieve both real time near-infrared fluorescent imaging and photodynamic therapy. The use of fluorescence emission from a NIR-dye could be used to guide resection of tumour bulk, for example during endoscopic diagnosis for oesophago-gastric adenocarcinoma, this would then be followed by activation of the photodynamic therapeutic agent to destroy untreated localised areas of cancer infiltration and tumour infiltrated lymph nodes. This theranostic agent was prepared from the Fab fragment of trastuzumab initially by functional disulfide re-bridging and site-specific click reaction of a NIR-dye. This was followed by further reaction with a novel pre-activated form of the photosensitiser chlorin e6 with the exposed fragments' lysine residues. Specific binding of the theranostic agent was observed in vitro with a HER2 positive cell line and cellular near-infrared fluorescence was observed with flow cytometry. Specific photo-activity of the conjugates when exposed to laser light was observed with HER2 positive but not HER2 negative cell lines in vitro, this selectivity was not seen with the unconjugated drug. This theranostic agent demonstrates that two different photo-active functions can be coupled to the same antibody fragment with little interference to their independent activities.