Chemiluminescence and Bioluminescence as an Excitation Source in the Photodynamic Therapy of Cancer: A Critical Review

Photodynamic therapy (PDT) of cancer is known for its limited number of side effects, and requires light, oxygen and photosensitizer. However, PDT is limited by poor penetration of light into deeply localized tissues, and the use of external light sources is required. Thus, researchers have been studying ways to improve the effectiveness of this phototherapy and expand it for the treatment of the deepest cancers, by using chemiluminescent or bioluminescent formulations to excite the photosensitizer by intracellular generation of light. The aim of this Minireview is to give a précis of the most important general chemi‐/bioluminescence mechanisms and to analyze several studies that apply them for PDT. These studies have demonstrated the potential of utilizing chemi‐/bioluminescence as excitation source in the PDT of cancer, besides combining new approaches to overcome the limitations of this mode of treatment.     

Initiator‐Loaded Gold Nanocages as a Light‐Induced Free‐Radical Generator for Cancer Therapy

Tumor hypoxia greatly suppresses the therapeutic efficacy of photodynamic therapy (PDT), mainly because the generation of toxic reactive oxygen species (ROS) in PDT is highly oxygen‐dependent. In contrast to ROS, the generation of oxygen‐irrelevant free radicals is oxygen‐independent. A new therapeutic strategy based on the light‐induced generation of free radicals for cancer therapy is reported. Initiator‐loaded gold nanocages (AuNCs) as the free‐radical generator were synthesized. Under near‐infrared light (NIR) irradiation, the plasmonic heating effect of AuNCs can induce the decomposition of the initiator to generate alkyl radicals (R^.), which can elevate oxidative‐stress (OS) and cause DNA damages in cancer cells, and finally lead to apoptotic cell death under different oxygen tensions. As a proof of concept, this research opens up a new field to use various free radicals for cancer therapy.     

Bioluminescence imaging of the response of rat gliosarcoma to ALA-PpIX-mediated photodynamic therapy

Photodynamic therapy (PDT) is a promising modality for the treatment of solid tumors that combines a photosensitizing agent and light to produce cytotoxic reactive oxygen species that lead to tumor cell death. The recent introduction of bioluminescence imaging (BLI), involving the use of the luciferase gene (luc) transferred into target tumor cells, followed by systemic administration of luciferin and detection of the emitted visible chemiluminescence photons, offers the potential for longitudinal imaging of tumor growth and therapeutic response in single animals. We demonstrate in this study the first results of the use of BLI to assess the response of an intracranial brain tumor model (9L rat gliosarcoma) to aminolevulinic acid (ALA)-mediated PDT. Complementary in vitro experiments with the luciferase-transfected 9L cells show that the decrease in the luminescent signal after PDT correlates with cell kill. In vivo imaging shows a decrease in the BLI signal from the tumor after ALA-PDT treatment, followed by tumor regrowth. Furthermore, preliminary studies using cells transfected with a hypoxia-responsive vector show an increase in bioluminescence within 4 h after Photofrin-mediated PDT, demonstrating the ability to observe stress-gene responses. These results suggest that BLI can be used to provide spatiotemporal information of intracranial brain tumor responses after PDT and may serve as a valuable response-endpoint measure.     

A Photodynamic System based on Endogenous Bioluminescence for in vitro Anticancer Studies

Photodynamic therapy (PDT) is becoming an important cancer treatment in recent years. However, at present, the therapeutic effect of PDT is limited due to insufficient penetration depth of light. In this study, a new photodynamic system (d ‐Lu)PCN‐224 is constructed by porphyrin‐based metal‐organic framework (MOF) PCN‐224 and bioluminescent molecule d ‐fluorescein (d ‐Lu). The bioluminescence (BL) spectrum of the reaction overlaps with the absorption spectrum of PCN‐224, so it is speculated that bioluminescence resonance energy transfer (BRET) between the MOF and d ‐Lu which indicates inner light can be gained and used for PDT. Confocal imaging analysis and cytotoxicity assays have demonstrated that (d ‐Lu)PCN‐224 can produce singlet oxygen and decrease the cell viability of SKOV‐3. This system provides a possibility of PDT for deep‐level organization without an external light source.     

Oxygen monitoring during 5-aminolaevulinic acid induced photodynamic therapy in normal rat colon. Comparison of continuous and fractionated light regimes

Currently, the clinical use of 5-aminolaevulinic acid (ALA) induced protoporphyrin IX (PPIX) for photodynamic therapy (PDT) is limited by the maximum tolerated oral ALA dose (60 mg/kg). Attempts have been made to enhance this treatment modality without increasing the administered dose of ALA. One way to do this is through light dose fractionation, where the irradiation is interrupted at a particular point for a short period of time. This can produce up to three times more necrosis than with the same light dose delivered without a break. An oxygen microelectrode was employed to study the effect of continuous and fractionated light regimes on the level of oxygen in the colon of normal Wistar rats during ALA PDT. A rapid decline in pO2 occurred close to the irradiation fibre as soon as the light dose commenced. With the fractionated regime, a partial recovery in pO2 was observed during the dark interval which was reversed soon after the second light fraction commenced. We have shown that the level of tissue oxygen at the treatment site is affected differently when the light dose is fractionated, than when continuous illumination is employed. This factor may at least partially explain the difference in outcome of these two treatment regimes. Further, oxygen measurements might prove to be a useful way of monitoring PDT treatments if they can predict whether tissue is likely to be viable following treatment.     

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.     

Monitoring photodynamic therapy of localized infections by bioluminescence imaging of genetically engineered bacteria

The increasing occurrence of multi-antibiotic resistant microbes has led to the search for alternative methods of killing pathogens and treating infections. Photodynamic therapy (PDT) uses the combination of non-toxic dyes and harmless visible light to produce reactive oxygen species that can kill mammalian and microbial cells. Although the photodynamic inactivation of bacteria has been known for over a hundred years, its use to treat infections has not been much developed. This may be partly due to the difficulty of monitoring the effectiveness of PDT in animal models of infection. In order to facilitate this monitoring process, we have developed a procedure that uses bioluminescent genetically engineered bacteria and a light sensitive imaging system to allow real-time visualization of infections. When these bacteria are treated with PDT in vitro, the loss of luminescence parallels the loss of colony-forming ability. We have developed several models of infections in wounds and soft-tissue abscesses in mice that can be followed by bioluminescence imaging. The size and intensity of the infection can be sequentially monitored in a non-invasive fashion in individual mice in real-time. When photosensitizers are introduced into the infected tissue followed by illumination with red light, a light-dose dependent loss of luminescence is seen. If the bacterium is invasive, the loss of luminescence correlates with increased survival of the mice, whilst animals in control groups die of sepsis within five days. Healing of the PDT treated wounds is not impaired and may actually be improved. This approach can allow many animal models of localized infections to be accurately monitored for efficacy of treatment by PDT.     

Initiator-Loaded Gold Nanocages as a Light-Induced Free-Radical Generator for Cancer Therapy

Tumor hypoxia greatly suppresses the therapeutic efficacy of photodynamic therapy (PDT), mainly because the generation of toxic reactive oxygen species (ROS) in PDT is highly oxygen-dependent. In contrast to ROS, the generation of oxygen-irrelevant free radicals is oxygen-independent. A new therapeutic strategy based on the light-induced generation of free radicals for cancer therapy is reported. Initiator-loaded gold nanocages (AuNCs) as the free-radical generator were synthesized. Under near-infrared light (NIR) irradiation, the plasmonic heating effect of AuNCs can induce the decomposition of the initiator to generate alkyl radicals (R^.), which can elevate oxidative-stress (OS) and cause DNA damages in cancer cells, and finally lead to apoptotic cell death under different oxygen tensions. As a proof of concept, this research opens up a new field to use various free radicals for cancer therapy.     

Synthesis of a Photostable Near‐Infrared‐Absorbing Photosensitizer for Selective Photodamage to Cancer Cells

A new class of near‐infrared (NIR)‐absorptive (>900 nm) photosensitizer based on a phenothiazinium scaffold is reported. The stable solid compound, o‐DAP, the oxidative form of 3,7‐bis(4‐methylaminophenyl)‐10H‐phenothiazine, can generate reactive oxygen species (ROS, singlet oxygen and superoxide) under appropriate irradiation conditions. After biologically evaluating the intracellular uptake, localization, and phototoxicity of this compound, it was concluded that o‐DAP is photostable and a potential selective photodynamic therapy (PDT) agent under either NIR or white light irradiation because its photodamage is more efficient in cancer cells than in normal cells and is without significant dark toxicity. This is very rare for photosensitizers in PDT applications.     

Oxygen dependence of two-photon activation of zinc and copper phthalocyanine tetrasulfonate in Jurkat cells

Abstract Photodynamic therapy (PDT), the use of light-activated drugs, is a promising treatment of cancer as well as several nonmalignant conditions. However, the efficacy of one-photon (1-gamma) PDT is limited by hypoxia, which can prevent the production of the cytotoxic singlet oxygen ((1)O(2)) species, leading to tumor resistance to PDT. To solve this problem, we propose an irradiation protocol based on a simultaneous, two-photon (2-gamma) excitation of the photosensitizer (Ps). Excitation of the Ps triplet state leads to an upper excited triplet state T(n) with distinct photochemical properties, which could inflict biologic damage independent of the presence of molecular oxygen. To determine the potential of a 2-gamma excitation process, Jurkat cells were incubated with zinc or copper phthalocyanine tetrasulfonate (ZnPcS(4) or CuPcS(4)). ZnPcS(4) is a potent (1)O(2) generator in 1-gamma PDT, while CuPcS(4) is inactive under these conditions. Jurkat cells incubated with either ZnPcS(4) or CuPcS(4) were exposed to a 670 nm continuous laser (1-gamma PDT), 532 nm pulsed-laser light (2-gamma PDT), or a combination of 532 and 670 nm (2-gamma PDT). The efficacy of ZnPcS(4) to photoinactivate the Jurkat cells decreased as the concentration of oxygen decreased for both the 1-gamma and 2-gamma protocols. In the case of CuPcS(4), cell phototoxicity was measured only following 2-gamma irradiation, and its efficacy also decreased at a lower oxygen concentration. Our results suggest that for CuPcS(4) the T(n) excited state can be populated after 2-gamma irradiation at 532 nm or the combination of 532 and 670 nm light. Dependency of phototoxicity upon aerobic conditions for both 1-gamma and 2-gamma PDT suggests that reactive oxygen species play an important role in 1-gamma and 2-gamma PDT.     

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.     

A Targeting Singlet Oxygen Battery for Multidrug-Resistant Bacterial Deep-Tissue Infections

Traditional photodynamic therapy (PDT) is dependent on externally applied light and oxygen, and the depth of penetration of these factors can be insufficient for the treatment of deep infections. The short half-life and short diffusion distance of reactive oxygen species (ROS) also limit the antibacterial efficiency of PDT. Herein, we designed a targeting singlet oxygen delivery system, CARG-Py, for irradiation-free and oxygen-free PDT. This system was converted to the “singlet oxygen battery” CARG-¹O₂ and released singlet oxygen without external irradiation or oxygen. CARG-¹O₂ is composed of pyridones coupled to a targeting peptide that improves the utilization of singlet oxygen in deep multidrug-resistant bacterial infections. CARG-¹O₂ was shown to damage DNA, protein, and membranes by increasing the level of reactive oxygen inside bacteria; the attacking of multiple biomolecular sites caused the death of methicillin-resistant Staphylococcus aureus (MRSA). An in vivo study in a MRSA-infected mouse model of pneumonia demonstrated the potential of CARG-¹O₂ for the efficient treatment of deep infections. This work provides a new strategy to improve traditional PDT for irradiation- and oxygen-free treatment of deep infections while improving convenience of PDT.     

Some Natural Photosensitizers and Their Medicinal Properties for Use in Photodynamic Therapy

Despite significant advances in early diagnosis and treatment, cancer is one of the leading causes of death. Photodynamic therapy (PDT) is a therapy for the treatment of many diseases, including cancer. This therapy uses a combination of a photosensitizer (PS), light irradiation of appropriate length and molecular oxygen. The photodynamic effect kills cancer cells through apoptosis, necrosis, or autophagy of tumor cells. PDT is a promising approach for eliminating various cancers but is not yet as widely applied in therapy as conventional chemotherapy. Currently, natural compounds with photosensitizing properties are being discovered and identified. A reduced toxicity to healthy tissues and a lower incidence of side effects inspires scientists to seek natural PS for PDT. In this review, several groups of compounds with photoactive properties are presented. The use of natural products has been shown to be a fruitful approach in the discovery of novel pharmaceuticals. This review focused on the anticancer activity of furanocoumarins, polyacetylenes, thiophenes, tolyporphins, curcumins, alkaloid and anthraquinones in relation to the light-absorbing properties. Attention will be paid to their phototoxic and anti-cancer effects on various types of cancer.     

Improvement of tumor response by manipulation of tumor oxygenation during photodynamic therapy

Photodynamic therapy (PDT) requires molecular oxygen during light irradiation to generate reactive oxygen species. Tumor hypoxia, either preexisting or induced by PDT, can severely hamper the effectiveness of PDT. Lowering the light irradiation dose rate or fractionating a light dose may improve cell kill of PDT-induced hypoxic cells but will have no effect on preexisting hypoxic cells. In this study hyperoxygenation technique was used during PDT to overcome hypoxia. C3H mice with transplanted mammary carcinoma tumors were injected with 12.5 mg/kg Photofrin and irradiated with 630 nm laser light 24 h later. Tumor oxygenation was manipulated by subjecting the animals to 3 atp (atmospheric pressure) hyperbaric oxygen or normobaric oxygen during PDT light irradiation. The results show a significant improvement in tumor response when PDT was delivered during hyperoxygenation. With hyperoxygenation up to 80% of treated tumors showed no regrowth after 60 days. In comparison, when animals breathed room air, only 20% of treated tumors did not regrow. To explore the effect of hyperoxygenation on tumor oxygenation, tumor partial oxygen pressure was measured with microelectrodes positioned in preexisting hypoxic regions before and during the PDT. The results show that hyperoxygenation may oxygenate preexisting hypoxic cells and compensate for oxygen depletion induced by PDT light irradiation. In conclusion, hyperoxygenation may provide effective ways to improve PDT efficiency by oxygenating both preexisting and treatment-induced cell hypoxia.     

姜黄素桥连卟啉光敏剂的合成及表征

为了开发新的高效光动力治疗光敏剂, 以2-(2-羟基萘基)-5,10,15,20-四苯基卟啉及其Cu(Ⅱ), Ni(Ⅱ), Zn(Ⅱ)配合物为原料, 利用1,6-二溴己烷桥连具有抗癌活性的小分子姜黄素, 设计合成4个新型的天然产物桥连卟啉化合物. 通过UV, ¹H NMR, IR, MS及元素分析等手段对该新型光敏药剂进行了结构表征; 在此基础上, 采用凝胶电泳法考察了化合物在光照和无光照条件下对pBR322质粒DNA的切割能力. 作为潜在光敏剂与DNA相互作用的初步研究表明, 其与DNA结合能力较强, 具有明显的光敏切割效果.     

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.     

Conjugated‐Polyelectrolyte‐Based Polyprodrug: Targeted and Image‐Guided Photodynamic and Chemotherapy with On‐Demand Drug Release upon Irradiation with a Single Light Source

Nanomaterials that combine diagnostic and therapeutic functions within a single nanoplatform are highly desirable for molecular medicine. Herein we report a novel theranostic platform based on a conjugated‐polyelectrolyte (CPE) polyprodrug that contains functionality for image, chemo‐ and photodynamic therapy (PDT), and on‐demand drug release upon irradiation with a single light source. Specifically, the PEGylated CPE serves as a photosensitizer and a carrier, and is covalently conjugated to doxorubicin through a linker that can be cleaved by reactive oxygen species (ROS). Under appropriate light irradiation, the CPE can generate ROS, not only for PDT, but also for on‐demand drug release and chemotherapy. This nanoplatform will offer on‐demand PDT and chemotherapy with drug release triggered by one light switch, which has great potential in cancer treatment.     

以上转换纳米颗粒和光动力疗法为基础的肿瘤联合治疗研究进展

光动力疗法作为一种非侵入性治疗手段已广泛应用于肿瘤的临床治疗。然而其疗效却深受紫外-可见光组织穿透深度的限制。镧系掺杂上转换纳米颗粒可以将近红外光转换为紫外-可见光,被广泛用于与传统光敏剂结合实现更为高效的光动力治疗。近年来,以上转换纳米颗粒和光动力疗法为基础的肿瘤联合治疗研究备受关注,本文重点介绍了该领域的最新研究进展,并对其未来发展方向作出了展望。     

Recent Progress in Boosted PDT Induced Immunogenic Cell Death for Tumor Immunotherapy

With the rapid development of materials science,photosensitive materials have been widely used in the field of immunogenic cell death(ICD),which was on account of the reactive oxygen species(ROS)generation by photosensitizer under light irradiation inducing cellular oxidative stress during the dying of cells.Considerable researches related to photodynamic therapy(PDT)induced ICD were conducted and exhibited brilliant performance in cancer immunotherapy.Herein,a variety of different strategies for PDT induced ICD have been summarized and discussed to provide researchers more inspiration for cancer immunotherapy.     

Research advances in the use of tetrapyrrolic photosensitizers for photodynamic therapy

Photodynamic therapy (PDT) is a promising new treatment modality for several diseases, most notably cancer. In PDT, light, O2, and a photosensitizing drug are combined to produce a selective therapeutic effect. Lately, there has been active research on new photosensitizer candidates, because the most commonly used porphyrin photosensitizers are far from ideal with respect to PDT. Finding a suitable photosensitizer is crucial in improving the efficacy of PDT. Recent synthetic activity has created such a great number of potential photosensitizers for PDT that it is difficult to decide which ones are suitable for which pathological conditions, such as various cancer species. To facilitate the choice of photosensitizer, this review presents a thorough survey of the photophysical and chemical properties of the developed tetrapyrrolic photosensitizers. Special attention is paid to the singlet-oxygen yield (PhiDelta) of each photosensitizer, because it is one of the most important photodynamic parameters in PDT. Also, in the survey, emphasis is placed on those photosensitizers that can easily be prepared by partial syntheses starting from the abundant natural precursors, protoheme and the chlorophylls. Such emphasis is justified by economical and environmental reasons. Several of the most promising photosensitizer candidates are chlorins or bacteriochlorins. Consequently, chlorophyll-related chlorins, whose PhiDelta have been determined, are discussed in detail as potential photosensitizers for PDT. Finally, PDT is briefly discussed as a treatment modality, including its clinical aspects, light sources, targeting of the photosensitizer, and opportunities.