Transport of hypericin across chick chorioallantoic membrane and photodynamic therapy vasculature assessment

This study examined the transport of a photosensitizer (hypericin, HY) using the chick chorioallantoic membrane (CAM) as a model of transport after topical administration. The model correlates both the photosensitizer uptake and anti-vasculature effects after photodynamic therapy (PDT). HY formulations were prepared using N-methyl pyrrolidone (NMP) as a solvent and penetration enhancer. Fertilized chicken eggs were disinfected and incubated at 37.4 degrees C and 60% humidity. Formulations were applied on CAM and incubated for 30 min in the dark. Subsequently, the solutions were removed from the CAM surface and the HY concentration was determined. The CAM was exposed to a fixed light dose of 10 J/cm2 at 50 mW/cm2. The vascular damage induced by the light was quantitatively measured using image-processing techniques. The uptake ratio of HY in 4.8% NMP (HD group) to that of 0.6% NMP (LD group) was found to be 1.96. This ratio is correlated with the vascular damage caused by the PDT effect of HY. The HD treated CAM showed a vessel regression that was 2.37 times higher than that of LD treated CAM. This paper reports the first attempt to develop a quantitative transport study for HY using CAM and to explore the relationship between the vascular regression and amount of drug of uptake. The model has potential for other similar transport studies.     

General principles of photodynamic therapy (PDT) and gastrointestinal applications

The purpose of this review article is to describe the history of photodynamic therapy (PDT), its current medical applications, the mechanism of action, contraindications of the method, and different types of photosensitizers used. The second part of the article deals with applications for gastrointestinal diseases. The treatment of obstructing oesophageal cancer, early-stage oesophageal cancer, Barrett's esophagus, hilar cholangiocarcinoma, stomach-, colon- and pancreatic cancer are discussed. The final part focuses on future directions of PDT like certain innovative ideas, which are currently under investigation.     

Apoptosis following photodynamic tumor therapy: induction, mechanisms and detection

As a treatment modality for malign and certain non-malignant diseases, photodynamic therapy (PDT) involves a two step protocol which consists of the (selective) uptake and accumulation of a photosensitizing agent in target cells and the subsequent irradiation with light in the visible range. Reactive oxygen species (ROS) produced during this process cause cellular damage and, depending on the treatment dose/severity of damage, lead to either cellular repair/survival, apoptotic cell death or necrosis. PDT-induced apoptosis has been focused on during the last years due to the intimate connection between ROS generation, mitochondria and apoptosis; by this PDT employs mechanisms different to those in the action of radio- and chemotherapeutics, giving rise to the chance of apoptosis induction by PDT even in cells resistant to conventional treatments. In this review, the (experimental) variables determining the cellular response after PDT and the known mechanistic details of PDT-triggered induction and execution of apoptosis are discussed. This is accompanied by a critical evaluation of wide-spread methods employed in apoptosis detection with special respect to in vitro/cell-based methodology.     

Evaluation of photodynamic efficiency of an endogenous enzyme-NQO1 activated hypericin

OBJECTIVE To investigate the therapeutic efficiency of an endogenous enzyme-NQO1 activated hypericin in photodynamic therapy.METHODS An endogenous enzyme-NQO1 responsive photo sensitizer was designed and synthesized by conjugating aquinonebased ligand to a natural photosensitizer derived from Chinese herb.The photophysical and photochemical properties were investigated through UV-visible and fluorescence spectrophotometer,and the photodynamic activity was evaluated with MTT assay.RESULTS An endogenous enzyme-NQO1 activated hypericin was prepared and fully characterized with various spectroscopic methods.The electronic absorption was almost the same with the free hypericin,indicating the introducing of the ligand to hypericin has little effect to its ground state,while there is almost no detected fluorescence and reactive oxygen species(ROS)generation in PBS solution indicating the introducing of the ligand can effectively quench the fluorescence emission and ROS generation.The in vitro study showed that both compounds have almost no dark toxicity,but they are highlyphotocytoxic with an IC50 less than 1μmol·L-1 against A549 cell lines indicating the modified compound can be activated in the intracellular environment.CONCLUSION A simple and efficient hypericin-based activated photosensitizer was prepared.The ROS generation was quenched in PBS solution and it would be activated inside A549 cell lines.It may be served as apromising tumor selective fluorescent probe and photosensitizer for targeted photodynamic therapy.     

Non polymeric nanoparticles for photodynamic therapy applications: recent developments

Photodynamic therapy has emerged as an alternative to chemotherapy and radiotherapy for cancer treatment. Nanoparticles have recently been proposed as effective carriers for photosensitizers. Depending on their chemical composition, these can be used for diagnosis and therapy due to the selective accumulation of the photosensitizer in cancer cells in vitro or in tumors in vivo. Multifunctional nanoplatforms combining several applications within the same nano-object emerge as potential important theranostic tools. This review, based on the chemical nature of the nanoparticles will discuss recent advances in the area of non polymeric nanoparticles for photodynamic therapy applications.     

Texaphyrins: new drugs with diverse clinical applications in radiation and photodynamic therapy

The texaphyrins are quintessential metal-coordinating expanded porphyrins. They constitute a new series of synthetic porphyrin analogues that show promise as drugs for use in a range of medical therapies. Currently, two different water-solubilized lanthanide(III) texaphyrin complexes, namely the gadolinium(III) and lutetium(III) derivatives 1 and 2 (Gd-Tex and Lu-Tex, respectively), are being tested clinically. The first of these, XCYTRIN, is in a pivotal Phase III clinical trial as a potential enhancer of radiation therapy for patients with metastatic cancers to the brain receiving whole brain radiation therapy. The second, in various formulations, is being tested as a photosensitizer for use in: (i) the photodynamic treatment of recurrent breast cancer (LUTRIN; Phase II clinical trials complete), (ii) photoangioplastic reduction of atherosclerosis involving peripheral arteries (ANTRIN; now in Phase II testing), and (iii) light-based treatment of age-related macular degeneration (OPTRIN; currently in Phase I clinical trials), a vision-threatening disease of the retina. Taken in concert, these two metallotexaphyrins provide a powerful new class of experimental drugs whose diverse potential utility is abetted by a combination of well-optimized physical features, favorable tissue biolocalization characteristics, and novel mechanisms of action. Interestingly, these mechanisms may alter conventional wisdom regarding mechanisms of radiation therapy and the pathophysiology of atherosclerosis.     

Molecular reaction mechanisms of combination treatments of low-dose cisplatin with radiotherapy and photodynamic therapy

Combination of low-dose cisplatin with radiotherapy or photodynamic therapy (PDT) is a novel cancer treatment. Using time-resolved femtosecond laser spectroscopy, we reveal the molecular mechanisms of the combinations of cisplatin with radiotherapy and PDT using indocyanine green (ICG) excited at 800 nm. DNA damage measurements confirm that electron-transfer reactions of cisplatin with electrons generated in ionizing radiation and with the ICG singlet excited state in PDT are responsible for the cytotoxic enhancements.     

Study of the stabilization of zinc phthalocyanine in sol-gel TiO2 for photodynamic therapy applications

Photodynamic therapy (PDT) has emerged as an alternative and promising noninvasive treatment for cancer. It is a two-step procedure that uses a combination of molecular oxygen, visible light, and photosensitizer (PS) agents; phthalocyanine (Pc) was supported over titanium oxide but has not yet been used for cell inactivation. Zinc phthalocyanine (ZnPc) molecules were incorporated into the porous network of titanium dioxide (TiO₂) using the sol-gel method. It was prepared from stock solutions of ZnPc and TiO₂. ZnPc-TiO₂ was tested with four cancer cell lines. The characterization of supported ZnPc showed that phthalocyanine is linked by the N-pyrrole to the support and is stable up to 250°C, leading to testing for PDT. The preferential localization in target organelles such as mitochondria or lysosomes could determine the cell death mechanism after PDT. The results suggest that nanoparticulated TiO₂ sensitized with ZnPc is an excellent candidate as sensitizer in PDT against cancer and infectious diseases.From the Clinical EditorPhotodynamic therapy is a two-step procedure that uses a combination of molecular oxygen, visible light and photosensitizer agents as an alternative and promising non-invasive treatment for cancer. The results of this study suggest that nanoparticulated TiO₂ sensitized with ZnPc is an excellent photosensitizer candidate against cancer and infectious diseases.     

The synthesis and applications of 5-aminolevulinic acid (ALA) derivatives in photodynamic therapy and photodiagnosis

A route has been developed to high-purity precursors, viz., ALA esters, to be used in photodiagnosis and photodynamic therapy. Hexyl, butyl and methyl 5-aminolevulinates are similar to the ALA acid in chemical stability and efficacy in producing the appropriate photosensitizer PpIX. Tests carried out on animal models showed the method based on the esters to be the more selective.     

Liposomes in topical photodynamic therapy

Introduction: Topical photodynamic therapy (PDT) refers to topical application of a photosensitizer onto the site of skin disease which is followed by illumination and results in death of selected cells. The main problem in topical PDT is insufficient penetration of the photosensitizer into the skin, which limits its use to superficial skin lesions. In order to overcome this problem, recent studies tested liposomes as delivery systems for photosensitizers.

Areas covered: This paper reviews the use of different types of liposomes for encapsulating photosensitizers for topical PDT. Liposomes should enhance the photosensitizers' penetration into the skin, while decreasing its absorption into systemic circulation. Only few photosensitizers have currently been encapsulated in liposomes for topical PDT: 5-aminolevulinic acid (5-ALA), temoporfin (mTHPC) and methylene blue.

Expert opinion: Investigated liposomes enhanced the skin penetration of 5-ALA and mTHPC, reduced their systemic absorption and reduced their cytotoxicity compared with free drugs. Their high tissue penetration should enable the treatment of deep and hyperkeratotic skin lesions, which is the main goal of using liposomes. However, liposomes still do not attract enough attention as drug carriers in topical PDT. In vivo studies of their therapeutic effectiveness are needed in order to obtain enough evidence for their potential clinical use as carriers for photosensitizers in topical PDT.     

Prodrugs in photodynamic anticancer therapy

Photodynamic therapy (PDT), the concept of cancer treatment through the selective uptake of a light-sensitive agent followed by exposure to a specific wavelength, is limited by the transport of a photosensitizer (PS) to the tumor tissue. Porphyrin, an important PS class, can be used in PDT in the form of its prodrug molecule 5-aminolevulinic acid (5-ALA). Unfortunately, its poor pharmacokinetic properties make this compound difficult to administer. Two different methods for eliminating this problem can be distinguished. The first approach is to play with its formulation in order to improve the drug's applicability. The second approach, which is to find possible 5- ALA prodrugs, is an example of the double-prodrug method, a strategy often used in modern drug design. In this approach, the biological mechanisms in a long biosynthetic pathway involving several steps must be completed before the active drug appears. Recently, an idea of enhancing PDT sensitization using the so-called iron chelators seemed to increase the accumulation of protoporphyrin in cells. At the same time, iron chelators can destroy tumor cells by producing active oxygen after the formation of an active drug by chelating iron in the cancer cells. Thus, in the latter case, the therapy resembles a prodrug strategy. The mechanism can be explained by the Fenton reaction. Vitamin C is another example of a potential anticancer agent of this type.     

Liposomes in topical photodynamic therapy

INTRODUCTION: Topical photodynamic therapy (PDT) refers to topical application of a photosensitizer onto the site of skin disease which is followed by illumination and results in death of selected cells. The main problem in topical PDT is insufficient penetration of the photosensitizer into the skin, which limits its use to superficial skin lesions. In order to overcome this problem, recent studies tested liposomes as delivery systems for photosensitizers. AREAS COVERED: This paper reviews the use of different types of liposomes for encapsulating photosensitizers for topical PDT. Liposomes should enhance the photosensitizers' penetration into the skin, while decreasing its absorption into systemic circulation. Only few photosensitizers have currently been encapsulated in liposomes for topical PDT: 5-aminolevulinic acid (5-ALA), temoporfin (mTHPC) and methylene blue. EXPERT OPINION: Investigated liposomes enhanced the skin penetration of 5-ALA and mTHPC, reduced their systemic absorption and reduced their cytotoxicity compared with free drugs. Their high tissue penetration should enable the treatment of deep and hyperkeratotic skin lesions, which is the main goal of using liposomes. However, liposomes still do not attract enough attention as drug carriers in topical PDT. In vivo studies of their therapeutic effectiveness are needed in order to obtain enough evidence for their potential clinical use as carriers for photosensitizers in topical PDT.     

光动力疗法及光动力治疗研究应用

随着光动力的研究、光敏剂和光源的不断发展,光动力治疗在肿瘤治疗中的应用已日趋成熟。光动力疗法的基础与理论研究,以及新产品的不断上市,也给患者带来了福音。笔者总结今年光动力基础研究和临床研究,并阐述相关观点。     

Art and science of photodynamic therapy

1. Photodynamic therapy is an established modality for the treatment of solid tumours and other accessible lesions. Although the concept and practice of combining light with a photosensitizing agent for the treatment of disease states has been around for almost a century, the understanding of the art and science therein has been tremendously enhanced over the past few years. 2. Photosensitized reactions are dependent on the generation of reactive oxygen species, in particular singlet oxygen, which accounts for the damaging effects on biological macromolecules, such as membrane lipids and proteins. Therefore, compounds that give a good yield of (1)O(2) are used as photosensitizers. 3. The main photosensitizers used in the clinical setting belong to the photofrin family; however, newer and more effective sensitizers are being evaluated for their potential clinical effectiveness. 4. Light sources have moved from the use of white light with specific filters in the old days to the more recent use of monochromatic light sources, such as lasers, to more sophisticated light-emitting diodes. However, dosimetry remains a big issue mainly because of difficulties in establishing the optimum treatment conditions for an approach that requires the fine-tuning of several variables, such as sensitizer and light doses and drug-to-light interval, as well as the issues of skin photosensitivity and low selectivity. A newer development to circumvent these and provide a broader application for this concept has been the phenomenon of photo-activation, whereby photo-exposure of chromophores to generate novel, small biologically active compounds has been demonstrated successfully. 5. The aim of the present review was to provide a general overview of the art and science of photodynamic therapy and to highlight some of the issues and recent developments in further advancing this modality of treatment.     

光源对金丝桃素光动力体外抗肿瘤作用的影响

目的 研究金丝桃素和贯叶金丝桃中金丝桃素提取物对人肝癌细胞株HepG2的体外杀伤效应及光源对其抗肿瘤作用的影响.方法 分析金丝桃素及金丝桃素提取物的吸收光谱,用不同波长的光源激发进行体外细胞毒试验,采用显微镜观察、MTT法分析和DNA电泳等方法评价金丝桃素及金丝桃素提取物的抗肿瘤效果.结果 590 nm的黄光激发金丝桃素和金丝桃素提取物对HepG2细胞有显著的体外杀伤效应,生长抑制率分别为51.5%、83.1%,其他波长光源的作用不显著.结论 金丝桃素的光动活性依赖于光源的波长,受适当光源激发的金丝桃素及金丝桃素提取物能显著抑制HepG2细胞的生长,显示金丝桃素有良好的光动力治疗肝癌的开发前景.     

Cellular mechanisms of digitalis action

Although the therapeutic actions of digitalis glycosides have been known for over 200 years, their direct inotropic actions on the heart were not established until the last 50 years. Digitalis has undergone intense research, particularly with respect to its mechanisms of action. Many authors have claimed to have found the true mechanism of action, compounding the complexity of literature. Recent subcellular studies have pointed to specific areas of action of the digitalis glycosides. Each discovery has been dependent on the greater understanding of the electrophysiologic characteristics of cardiac muscle and excitation-contraction coupling. The current hypothesis suggests that digitalis specifically inhibits Na-K ATPase. This produces an elevation in intracellular sodium level that in turn produces an increase in the intracellular calcium level. The increased quantities of calcium available to the contractile elements of cardiac muscle provide the observed increased inotropy.     

Cellular mechanisms of nicotine addiction

In developed countries, tobacco use is estimated to be the largest single cause of premature death [Lancet 339 (1992) 1268]. Nicotine is the main addictive component of tobacco that motivates continued use despite the harmful effects. Nicotinic acetylcholine receptors (nAChRs) are widely distributed throughout the mammalian central nervous system (CNS), where they normally respond to acetylcholine (ACh) and modulate neuronal excitability and synaptic communication. Nicotinic receptors are structurally diverse and have varied roles. Presynaptic and preterminal nAChRs enhance neurotransmitter release. Postsynaptic and somal nAChRs mediate a small proportion of fast excitatory transmission and modulate cytoplasmic second messenger systems. Although the impact of nicotine obtained from tobacco is not completely understood, a portion of nicotine's addictive power is attributable to actions upon the dopaminergic systems, which normally help to reinforce rewarding behaviors. As obtained from tobacco, nicotine activates and desensitizes nAChRs, and both processes contribute to the cellular events that underlie nicotine addiction.     

Immunomodulatory aspects of photodynamic therapy

In its conventional form, photodynamic therapy (PDT) is a clinically effective technique with which to treat tumours accessible to visible light. PDT utilises light absorbing compounds which catalyse the generation of toxic oxygen species, to produce localised antitumour effects. It has become apparent over the past decade that PDT also exhibits immunomodulatory attributes. Experimental animals may possess heightened antitumour immunity after tumour ablation with PDT. In contrast, at sub-phototoxic levels of photosensitiser, in combination with whole body light irradiation, PDT lessened disease severity when applied in different models of autoimmunity. Although the behaviour of lymphocytes may be affected by treatment, the ability of PDT to down-regulate autoimmune processes appears to be related to its capacity to influence the immunostimulatory attributes of antigen presenting cells.