Temperature regime of biological tissue under photodynamic therapy

An analytical model is proposed to calculate heating of human skin cover under laser light action of photodynamic therapy. A photosensitizer of "Fotolon" is taken as an example. Temperatures of skin surface and of deep dermis regions are studied as a function of time under pulsed and stationary irradiation of skin surface at the wavelength of 665 nm corresponding to the maximum of the photosensitizer absorption band. It is shown that, under the action of a short light pulse, the photosensitizer can lead to an essential temperature rise of dermis due to a considerable increase in its absorption coefficient. However, this rise does not destruct tissue cells because of the short action. Under stationary irradiation, the photosensitizer concentration has a low effect on the temperature regime of tissue. This is related with the specific features in heating of the medium by red light, where the main thermal process in skin is heat transfer over tissue volume from epidermis having a substantially larger absorption coefficient than that of dermis in the said spectral range. The role of blood perfusion in dermis and its effect on the temperature regime of tissue are evaluated.     

Molecular biological mechanisms of photodynamic therapy

The biological mechanisms of photodynamic therapy, a new approach to the treatment of malignant lesions, are considered. The data on chemical composition of hematoporphyrin derivative are given, the photophysical and photochemical reactions caused by photosensitizer distribution in organism and cell, as well mechanisms of photodestruction of cells and cell organelles.     

Synthesis and biological studies of 5-aminolevulinic acid-containing dendrimers for photodynamic therapy.

Using a convergent growth approach, a series of novel 5-aminolevulinic acid (ALA)-containing dendrimers have been synthesized. In these molecules, ALA residues are attached to the periphery by ester linkages, with amide bonds connecting the dendrons. Three first-generation dendrimers, bearing either 6 or 9 ALA residues, were synthesized by attachment of a tris(Boc-protected ALA)-containing wedge (1) to a di- or tripodent aromatic, or tripodent aliphatic core. Two second generation 18-ALA-containing dendrimers were also synthesized using a 3,3'-iminodipropionic acid spacer unit between wedge 1 and the aromatic core. These compounds differed only in the distance between the core and the linker unit. The Boc-protected dendrimers were deprotected using trifluoroacetic acid and isolated as their TFA salts. The potential of these ALA ester dendrimers as macromolecular prodrugs for photodynamic therapy has been demonstrated in the tumorigenic keratinocyte PAM 212 cell line.     

Antifungal photodynamic therapy

In photodynamic antimicrobial chemotherapy (PACT), a combination of a sensitising drug and visible light causes selective destruction of microbial cells. The ability of light-drug combinations to kill microorganisms has been known for over 100 years. However, it is only recently with the beginning of the search for alternative treatments for antibiotic-resistant pathogens that the phenomenon has been investigated in detail. Numerous studies have shown PACT to be highly effective in the in vitro destruction of viruses and protozoa, as well as Gram-positive and Gram-negative bacteria and fungi. Results of experimental investigations have demonstrated conclusively that both dermatomycetes and yeasts can be effectively killed by photodynamic action employing phenothiazinium, porphyrin and phthalocyanine photosensitisers. Importantly, considerable selectivity for fungi over human cells has been demonstrated, no reports of fungal resistance exist and the treatment is not associated with genotoxic or mutagenic effects to fungi or human cells. In spite of the success of cell culture investigations, only a very small number of in vivo animal and human trials have been published. The present paper reviews the studies published to date on antifungal applications of PACT and aims to raise awareness of this area of research, which has the potential to make a significant impact in future treatment of fungal infections.     

Synthesis and biological evaluation of new chlorin derivatives as potential photosensitizers for photodynamic therapy

Three new water-soluble chlorin derivatives 3, 5 and 8 for potential use as photosensitizers in photodynamic therapy (PDT) for cancer were synthesized from photoprotoporphyrin IX dimethyl ester (1). The in vivo biodistribution and clearance of chlorin derivatives 3, 5 and 8 were investigated in tumor-bearing mice. Iminodiacetic acid derivative 8 showed the greatest tumor-selective accumulation among the new chlorin derivatives with maximum accumulation in tumor tissue at 3 h after intravenous injection and rapid clearance from normal tissues within 24 h after injection. The in vivo therapeutic efficacy of PDT using 8 was evaluated by measuring tumor growth rates in tumor-bearing mice with 660 nm light-emitting diode irradiation at 3 h after injection of 8. Tumor growth was significantly inhibited by PDT using 8. These results indicate that iminodiacetic acid derivative 8 is useful as a new photosensitizer to overcome the disadvantages of photosensitizers that are currently in clinical use.     

Synthesis and biological evaluation of thioglycosylated porphyrins for an application in photodynamic therapy.

The aim of this work is the synthesis of a new family of glycosylated porphyrins in which the sugar moieties are linked to the tetrapyrrole ring by a thioglycosidic bond. Two series have been designed. The first one corresponds to meso-aryl porphyrin derivatives. The second one has been obtained from protoporphyrin IX derivatization. Aryl-porphyrins were prepared from tristolyl o- and p-hydroxyporphyrins followed by bromoallylation and thioglycosylation with peracetylated S-glucose, mannose and galactose and deprotection. The other series has been synthesized from protoporphyrin IX dimethylester with a regioselective glycosylation of terminal alkenyl carbon. The UV-visible, NMR and MALDI mass spectra are presented. Photocytotoxicities of the synthesized compounds against K562 chronic leukaemia cell line has been evaluated.     

Stem cell-based photodynamic therapy

We have transfected murine neural stem cells (NSCs) and rat umbilical cord matrix-derived stem cells (RUCMSCs) with a plasmid expressing gaussia luciferase (gLuc). These cells are engineered to secrete the luciferase. We have used gLuc containing supernatant from culturing the NSCs to perform in vitro photodynamic therapy of murine melanoma cells (B16F10), and RUCMSCs to perform in vivo PDT of lung melanomas in C57BL/6 mice. The treatment system was comprised of aminolevulic acid as a prodrug for the synthesis of the photosensitizer protoporphyrin IX, gaussia luciferase, and its' substrate coelenterazine. A significant reduction of the number of live melanoma cells in vitro and a borderline significant retardation of tumour growth in vivo was observed after coelenterazine-mediated PDT.     

Aminolevulinic acid: from its unique biological function to its star role in photodynamic therapy

Porphyrins are molecules essential for life. They are involved in the key processes of photosynthesis and respiration. The biosynthesis of tetrapyrroles in all living cells occurs through several steps where the formation of aminolevulinic acid (ALA) is the first committed intermediate. Two alternative routes for the formation of ALA have been proposed: one involves the condensation of Succinyl CoA and glycine catalyzed by ALA synthetase taking place in the mitochondria, and the second one is the so called 5-carbon route, occurring in the stroma of plastids. Eight molecules of ALA are used in the formation of protoporphyrin IX. Specific deficiencies in one of the enzymes of the heme pathway produce the porphyrias. In the acute porphyrias, the pathogenesis of the neurological dysfunction is attributed to the accumulation of ALA. Fluorescent and photosensitizing properties of protoporphyrin accumulated after the exogenous administration of ALA, can be used to visualize and destroy malignant cells in the so-called photodynamic diagnosis (PDD) and photodynamic therapy (PDT) of cancer. Many clinical ALA-PDT applications to malignant and non-malignant pathologies are currently in use. Different approaches to enhance ALA penetration in cells are under investigation, including the use of more lipophilic ALA derivatives and studies of the transport mechanisms of ALA. ALA has also been proposed to be used as a biodegradable herbicide, as an insecticide and as a plant growth regulator.     

Effect of photosensitizers in chemical and biological processes: the MTO mechanism in photodynamic therapy.

It is suggested that in the course of the application of photosensitizers irradiated for cancer therapy a real competition occurs between the singlet oxygen mediated effects and the interactions between the triplet photosensitizers and doublet radicals formed in tumor cells while processes between photosensitizer radicals and molecules are negligible. This hypothesis is strongly supported by experimental findings and reveals a novel approach for the synthesis of new photosensitizers.     

Synthesis and biological evaluation of 173-dicarboxylethyl-pyropheophorbide-a amide derivatives for photodynamic therapy

Three novel 17³-dicarboxylethyl-pyropheophorbide-a amide derivatives as photosensitizers for photodynamic therapy (PDT) were synthesized from pyropheophorbide-a (Ppa). Their photophysical and photochemical properties, intracellular localization, photocytotoxicity in vitro and in vivo were investigated. All target compounds exhibited low cytotoxicity in the dark and remarkable photocytotoxicity against human esophageal cancer cells. Among them, 1a showed highest singlet oxygen quantum yield. Upon light activation, 1a exhibited significant photocytotoxicity. After PDT treatment, the growth of Eca-109 tumor in nude mice was significantly inhibited. Therefore, 1a is a powerful and promising antitumor photosensitizer for PDT.     

光动力学疗法剂量学的研究进展

随着光动力学疗法 ( photodynamic therapy,PDT ) 基础研究的不断深入和临床应用的广泛开展,如何精确量化光动力剂量,并根据患者的个体差异进行剂量的实时调整和优化已成为亟待解决的挑战性难题,属PDT研究的前沿热点．综述了现有PDT剂量学研究方法及其相应检测技术的研究进展,其中包括：a．测定光通量密度、光敏剂浓度和氧分压;b．测量光敏剂的光漂白速率和光致产物;c．监测PDT前后组织的光生物学响应;d．检测单态氧在1 270 nm的近红外发光．同时,还分析了这些PDT剂量学方法的优点和局限性．最后,讨论了PDT剂量学研究中所面临的挑战．     

Mitochondria are targets of photodynamic therapy

Photodynamic Therapy (PDT) is an evolving cancer treatment that depends on three known and variable components: photosensitizer, light and oxygen. Optimization of these variables yields reactive oxygen species, mainly singlet oxygen, that damage cellular components leading to cytotoxicity. Our research has demonstrated that porphyrin sensitizers, in particular, significantly inhibit the inner mitochondrial membrane enzymes cytochrome c oxidase and F ₀ F ₁ ATP synthase. These results were obtained from an in vivo-in vitro experimental protocol that exposes sensitizers to metabolic and pharmacokinetic events. The resulting inhibition of oxidative phosphorylation was expected to reduce ATP levels, which were quantitated in cells and were confirmed by ³¹P-NMR spectroscopy of tumors in situ in animals treated with PDT. Based on these findings, and more recent investigations of apoptosis, there is little doubt that mitochondria are critical targets in the actions of PDT.     

Dynamic model of vascular-targeted photodynamic therapy

Vascular-targeted photodynamic therapy has shown efficiency in treating port wine stains. A dynamic model that incorporates blood flow, kinetic diffusion, oxygen and photosensitizer consumption and reaction, and light modulation is proposed to reveal the interactions among light, photosensitizer, and oxygen. Simulation results show that pulse light modulation synchronized with heartbeats hold the advantage of increased singlet oxygen accumulation, higher oxygen concentration and lower temperature. Meanwhile, constant light treatment is advantageous in terms of higher temperature, lower total oxygen concentration and singlet oxygen accumulation. Therefore, the optimized treatment protocol may involve a balance among the phototoxicity, hypoxia, and photothermolysis.     

Properties and applications of photodynamic therapy

Photodynamic therapy (PDT) is the treatment of malignant lesions with visible light following the systemic administration of a tumor-localizing photosensitizer. Pharmacological and photochemical properties of the photosensitizer are combined with precise delivery of laser-generated light to produce a treatment which can offer selective tumoricidal action. Hematoporphyrin derivative (HD) and a purified component called Photofrin II are currently being used in clinical PDT. Initial patient results have been encouraging, and considerable interest has developed in the synthesis and evaluation of new photosensitizers with improved photochemical and pharmacological characteristics. In addition, there has been a gradual increase in knowledge related to in vitro and in vivo mechanisms of action of PDT. This report provides an overview of the properties and applications of PDT. Information and data related to drug development, photochemistry, subcellular targets, in vivo responses, and clinical trials of PDT are presented.     

The biophysical aspects of photodynamic therapy

The photodynamic effect, viz., photodamage of stained cells in the presence of oxygen, is used for destruction of tumors and other abnormal cells. The present review considers the biophysical mechanisms of the photodynamic action on cells. The importance of two major mechanisms of photodynamic damage of cells is discussed. The first one is mediated by electron or proton transfer, whereas the second one involves singlet oxygen. Another question that is considered is the importance of oxidation of membrane lipids or proteins for the photodynamic damage of cells. The phototransformation of photosensitizers and their intracellular localization and delivery to cells and tissues that have undergone abnormal changes are discussed. The current data on photosensitizer nanotransporters are presented. The potential sensors for reactive oxygen species in cells are discussed.     

Pyridone-containing phenalenone-based photosensitizer working both under light and in the dark for photodynamic therapy

Photosensitizer attracts great attentions and has potential applications in cancer treatment. We developed here a novel pyridone-containing phenalenone-based (PPN-PYR) photosensitizer with excellent singlet oxygen generating ability. Upon light irradiation, PPN-PYR can produce singlet oxygen and transform to its endoperoxide form which in turn release singlet oxygen via thermal cycloreversion at dark. The ability of PPN-PYR to generate reactive oxygen species (ROS) in cell culture and induce corresponding apoptosis both at dark and under light was demonstrated. The efficient PDT performance of PPN-PYR was further verified on cancer cell in vitro. Our study indicate that PPN-PYR can alleviate tumor hypoxia problem and enhance the availability of intermittent photodynamic therapy.     

光动力疗法治疗感染性疾病的动物模型

光动力疗法(photodynamic therapy,PDT)是利用特定波长的激发光照射生物靶标上的光敏剂,从而产生活性氧并有效杀伤多种耐药病原体的新型治疗方式,具有作用广、安全可控、不易耐受等优点。大量体外实验已证实了PDT疗效,但目前动物实验数据较少,且治疗参数不一,一定程度上影响了PDT在临床治疗中的广泛应用。本文综述近年来PDT用于体内抗感染治疗的动物模型构建、治疗方案设计等方面的研究进展,为未来PDT抗感染研究及临床应用提供参考。     

New directions in photodynamic therapy.

Photodynamic therapy (PDT), a treatment approach that makes use of a photosensitizer to generate a localized toxic species in diseased tissue, has recently become an approved treatment modality. So far, however, only a handful of photosensitizers have received regulatory approval and for a small number of diseases. This chapter outlines the major limitations of PDT and speculates on the possible improvements that are required in order to advance PDT to a front line therapy. Seven areas of improvements are discussed: drug selectivity, drug delivery, light delivery, combination therapies, pigmented tumors, other potential uses, and protocol optimization. For each area, current limitations are discussed, and further required studies are recommended.     

Antibacterial photodynamic therapy in dermatology.

Photodynamic therapy (PDT) appears to be endowed with several favourable features for the treatment of localized microbial infections, especially after the advent of cationic photosensitising agents (phenothiazines, meso-substituted porphyrins, polylysine-bound chlorins) which properly interact with the outer wall at the surface of several types of bacterial and yeast cells, increase their permeability, and allow significant amounts of photosensitizer to be accumulated at the level of the cytoplasmic membrane. These photosensitisers are characterized by a broad spectrum of activity, being effective toward both wild strain and antibiotic-resistant gram-positive and gram-negative bacteria and yeasts. In general, extensive eradication of pathogens can be achieved under mild irradiation conditions, such as short incubation times and low fluence-rates, which guarantees a high degree of selectivity in comparison with the main constituents of host tissues, such as keratinocytes and fibroblasts. Moreover, the photosensitised inactivation of microorganisms is typically a multi-target process; as a consequence, the selection of photoresistant microbial strains is very unlikely and has not been experimentally observed so far. Possible initial targets of antimicrobial PDT applications include periodontal diseases, impetigo, atopic dermatitis, acne vulgaris, infected wounds, and superinfected posriatic plaques.