Mechanisms of tumor necrosis induced by photodynamic therapy

Molybdenum-Iodine Cluster Loaded Polymeric Nanoparticles Allowing a Coupled Therapeutic Action with Low Side Toxicity for Treatment of Ovarian Cancer

The ability of cancer cells to develop resistance to anti-cancer drugs, known as multidrug resistance, remains a major cause of tumor recurrence and cancer metastasis. This work explores the double mechanism of toxicity of (D, L-lactide-co-glycolide) acid (PLGA) nanoparticles encapsulating a molybdenum cluster compound, namely Cs₂[{Mo₆I₈}(OOCC₂F₅)₆] (CMIF). Hemocompatibility and biocompatibility assays show the safe potential of CMIF loaded nanoparticles (CNPs) as delivery systems intended for tumor targeting for PDT of ovarian cancer with a slight hemolytic activity and a lack of toxicity up to 50 µM CMIF concentration. Cellular uptake shows a preferential uptake of CNPs in lysosomes, which is not interfering with CMIF activity. The double mechanism of CNPs consists in a production of ROS and a DNA damage activity, from 5 µM and 0.5 µM respectively (CMIF concentration). The cellular death mechanism comprises 80% of necrosis and 20% of direct apoptosis by direct DNA damages. This work confirms CMIF loaded PLGA nanoparticles as an efficient and relevant delivery system for PDT.

Boosting the Immune Response—Combining Local and Immune Therapy for Prostate Cancer Treatment

Due to its slow progression and susceptibility to radical forms of treatment, low-grade PC is associated with high overall survival (OS). With the clinical progression of PC, the therapy is becoming more complex. The immunosuppressive tumor microenvironment (TME) makes PC a difficult target for most immunotherapeutics. Its general immune resistance is established by e.g., immune evasion through Treg cells, synthesis of immunosuppressive mediators, and the defective expression of surface neoantigens. The success of sipuleucel-T in clinical trials initiated several other clinical studies that specifically target the immune escape of tumors and eliminate the immunosuppressive properties of the TME. In the settings of PC treatment, this can be commonly achieved with radiation therapy (RT). In addition, focal therapies usually applied for localized PC, such as high-intensity focused ultrasound (HIFU) therapy, cryotherapy, photodynamic therapy (PDT), and irreversible electroporation (IRE) were shown to boost the anti-cancer response. Nevertheless, the present guidelines restrict their application to the context of a clinical trial or a prospective cohort study. This review explains how RT and focal therapies enhance the immune response. We also provide data supporting the combination of RT and focal treatments with immune therapies.

Impact of mono- and di-β-galactose moieties in in vitro / in vivo anticancer efficacy of pyropheophorbide-carbohydrate conjugates by photodynamic therapy

To investigate the impact of mono- and di-β-galactose moieties in tumor uptake and photodynamic therapy (PDT) efficacy, HPPH [3-(1'-hexyloxy)ethyl-3-devinylpyropheophorobide-a], the meso pyropheophorbide-a [3-ethyl-3-devinyl-pyropheophorbide-a], and the corresponding 20-benzoic acid analogs were used as starting materials. Reaction of the intermediates containing one or two carboxylic acid functionalities with 1-aminogalactose afforded the desired 17²- or 20(4')- mono- and 17², 20(4')-di galactose conjugated photosensitizers (PSs) with and without a carboxylic acid group. The overall lipophilicity caused by the presence of galactose in combination with either an ethyl or (1'-hexyloxy)ethyl side chain at position-3 of the macrocycle made a significant difference in in vitro uptake by tumor cells and photoreaction upon light exposure. Interestingly, among the PSs investigated, compared to HPPH 1 the carbohydrate conjugates 2 and 11 in which β-galactose moieties are conjugated at positions 17² and 20(4') of meso-pyro pheophorbide-a showed similar in vitro efficacy in FaDu cell lines, but in SCID mice bearing FaDu tumors (head & neck) Ps 11 gave significantly improved long-term tumor cure.

Current Management of Age-Related Macular Degeneration

Age-related macular degeneration (AMD) remains a leading cause of blindness worldwide. The assessment and management of patients with this condition has evolved in the last decades. In this chapter, current standards for diagnosis, follow-up, and treatment of patients with AMD are reviewed and summarized. Namely, we highlight how current assessment has moved from conventional ophthalmoscopy and fluorescein angiography testing to a multimodal approach, and its important advantages. Alternatives to visual acuity for functional assessment of patients with AMD are also presented. Regarding strategies for follow-up and treatment, we provide specific information for the different stages (i.e., early, intermediate, and late) and forms (for example, choroidal neovascularization and geographic atrophy) of AMD. Specifically, we discuss the relevance and options for self-monitoring and non-pharmacological interventions. Additionally, a summary of the important trials (both on exudative and non-exudative AMD) that have helped inform clinical practice is provided, including data on antiangiogenic agents currently available, and outcomes of the different regimens that have been studied. The influence of advances in imaging on treatment strategies is also discussed.In summary, this chapter is a resource for all clinicians engaged in providing state of the art care for patients with AMD, and can help improve diagnosis, management, and outcomes of individuals with this blinding condition.

The effect of chlorin e₆ drug on platelet aggregation activity

The goal of the study is to evaluate the effect of Radachlorin (OOO “RADA-PHARMA”, Russia) (RC) on platelet aggregation in ex vivo and in vivo experiments. The experiments were conducted on male Wistar rats. Platelet aggregation activity was determined in platelet-rich plasma (PRP) using a turbidimetric method and the aggregation inducer was ADP at a final concentration of 1.25 μM. PRP samples containing RC were irradiated with ALOD-Granat laser device (OOO “Alkom Medika”, Russia) at 662 nm wavelength with 0.05 W/cm2 power density. After a 5-minute incubation of PRP with RC in the dark, dose-dependent inhibition of platelet aggregation was observed. Laser irradiation (12.5 J/cm2 and, especially, 25 J/cm2) increased the inhibitory effect of RC. 3 hours after intravenous administration of RC, the rate and intensity of platelets aggregation did not change, while disaggregation slowed down significantly. Irradiation at a dose of 5 J/cm2 did not affect the platelets aggregation kinetics, and disaggregation slowed down even more at 10 J/cm2, and at 20 J/cm2 the rate and intensity of platelets aggregation decreased, and no disaggregation occurred.

In vitro, RC inhibited the ADP-induced platelet aggregation in rats in a dose-dependent manner; after laser irradiation, this effect was enhanced significantly. The effect of RC on circulating platelets leads to a change in their functional state, which manifests in slowing down the disaggregation after exposure to ADP. After laser irradiation (10 J/cm2 and, especially, 20 J/cm2), the severity of the functional changes increases. The role of decreasing the disaggregation activity of platelets in the mechanism of vascular thrombosis in the affected area of photodynamic therapy (PDT) is discussed.

Photodynamic Therapy Activity of New Porphyrin-Xylan-Coated Silica Nanoparticles in Human Colorectal Cancer

Photodynamic therapy (PDT) using porphyrins has been approved for treatment of several solid tumors due to the generation of cytotoxic reactive oxygen species (ROS). However, low physiological solubility and lack of selectivity towards tumor sites are the main limitations of their clinical use. Nanoparticles are able to spontaneously accumulate in solid tumors through an enhanced permeability and retention (EPR) effect due to leaky vasculature, poor lymphatic drainage, and increased vessel permeability. Herein, we proved the added value of nanoparticle vectorization on anticancer efficacy and tumor-targeting by 5-(4-hydroxyphenyl)-10,15,20-triphenylporphyrin (TPPOH). Using 80 nm silica nanoparticles (SNPs) coated with xylan-TPPOH conjugate (TPPOH-X), we first showed very significant phototoxic effects of TPPOH-X SNPs mediated by post-PDT ROS generation and stronger cell uptake in human colorectal cancer cell lines compared to free TPPOH. Additionally, we demonstrated apoptotic cell death induced by TPPOH-X SNPs-PDT and the interest of autophagy inhibition to increase anticancer efficacy. Finally, we highlighted in vivo, without toxicity, elevated anticancer efficacy of TPPOH-X SNPs through improvement of tumor-targeting compared to a free TPPOH protocol. Our work demonstrated for the first time the strong anticancer efficacy of TPPOH in vitro and in vivo and the merit of SNPs vectorization.

Light intensity effect on the mechanisms of tumor damage photosensitized by a substituted Zn(II)-naphthalocyanine

Cytotoxicity induced by photodynamic therapy (PDT) is connected with the phenomena of photo-oxidation. Generation of singlet oxygen and free radicals (superoxide or hydroxide) is accepted as a mechanism for the photo-oxidation action of PDT. Very little is however known about the validity of metabolitic and biochemical events observed in cell culture systems to in vivo tumor shrinkage following PDT. In the present work using the well-studied tetrabenzamido-substituted zinc (II)-naphthalocyanine ( ZnNc ) including towards pigmented melanoma, we accessed its efficacy for apoptotic processes during PDT of Lewis lung carcinoma (LLC) in mice in dependence on light intensity. Early photodynamic therapy responses were examined at 1, 3, 6, 10 and 24 h after coherent 774 nm illumination of the tumors applied 24 h after intraperitoneal (i.p.) injection of dipalmitoylphosphatidylcholine (DPPC)-liposome-incorporated 0.5 mg kg-1 b.w. ZnNc . Fluence rates of 260, 380 and 500 mW cm-2 at a fluence of 360 J cm-2 were used. Macroscopic observations showed that tumor reduction (and its eventual elimination) depends on optimal conditions for the occurring of photochemical reaction during PDT. At the same time, electron microscopy (EM) assays demonstrated strongly expressed dependence of apoptotic processes on the applied light intensities. Features of apoptotic processes were most clearly expressed at the highest used fluence rate.

Photodynamic antifungal chemotherapy

The growing resistance against antifungal drugs has renewed the search for alternative treatment modalities, and antimicrobial photodynamic therapy (PDT) seems to be a potential candidate. Preliminary findings have demonstrated that dermatophytes and yeasts can be effectively sensitized in vitro and in vivo by administering photosensitizers (PSs) belonging to four chemical groups: phenothiazine dyes, porphyrins and phthalocyanines, as well as aminolevulinic acid, which, while not a PS in itself, is effectively metabolized into protoporphyrin IX. Besides efficacy, PDT has shown other benefits. First, the sensitizers used are highly selective, i.e., fungi can be killed at combinations of drug and light doses much lower than that needed for a similar effect on keratinocytes. Second, all investigated PSs lack genotoxic and mutagenic activity. Finally, the hazard of selection of drug resistant fungal strains has been rarely reported. We review the studies published to date on antifungal applications of PDT, with special focus on yeast, and aim to raise awareness of this area of research, which has the potential to make a significant impact in future treatment of fungal infections.

Melanomas display increased cytoprotection to hypericin-mediated cytotoxicity through the induction of autophagy

Photodynamic therapy (PDT) as a regime for melanoma is of limited success due to factors such as the efficacy of the photosensitizer used, penetration depth and the presence of pigment. We characterised a pigmented and an unpigmented melanoma cell line with respect to their phenotypes. Cell viability was assessed after exposure to hypericin, a UVA-activated photosensitizer. Exposure to 3 microM activated hypericin induced a cytoprotective (autophagic) response from both cell lines. However, the pigmented cells accumulated a large amount of glycogen in their cytoplasm. We hypothesise that the treatment induces an initial cytoprotective response through autophagy, but with increased stress results in a different mode of cell death in pigmented melanoma cells from unpigmented cells. These results indicate that hypericin-PDT could be an adjuvant therapy for melanoma.

Photodynamic therapy and Klatskin tumour: An overview

The prognosis of patients with an unresectable bile duct cancer is poor. In 60-70% of patients, cholangiocarcinoma is located in the hepatic duct bifurcation and known as Klatskin tumour. Surgical resection offers the only chance for 5-year survival, but less than 20% are surgical candidates. Patients with unresectable cholangiocarcinoma are treated with biliary drains, but commonly die of liver failure or cholangitis due to biliary obstruction within 6 to 12 months. Chemotherapy and/or radiotherapy have not been evaluated in randomized, controlled trials. Photodynamic therapy (PDT) is a new and promising locoregional treatment, the aim of which is to destroy tumour cells selectively. PDT involves the injection of a photosensitizer followed by percutaneous or endoscopic direct illumination of the tumour with light of a specific wavelength. In recent non-randomized studies of small numbers of patients with unresectable cholangiocarcinoma, PDT induced a decrease in serum bilirubin levels, improved quality of life and a slightly better survival. Other non-randomized trials failed to show clinical benefits. Recently, the first prospective, randomized controlled study with PDT in a selected group of non-resectable cholangiocarcinoma patients was stopped prematurely. The improvement in survival in the PDT-randomized patients was so impressive that it was considered to be unethical to continue randomization. However, further studies are awaited in unselected patients with unresectable cholangiocarcinoma before PDT can be considered as the standard adjuvant therapy.

Two years follow-up outcome of verteporfin therapy for subfoveal choroidal neovascularization in pathologic myopia in Indian eyes

CONTEXT

In India, refractive errors are a major cause of treatable blindness. Population surveys in southern India have shown prevalence of high myopia to be 4.32-4.54%. Photodynamic therapy (PDT) for choroidal neovascularization (CNV) caused by pathologic myopia is beneficial.

AIMS

To report the 24 months outcome of PDT with verteporfin for subfoveal CNV caused by pathologic myopia in Indian eyes.

SETTINGS AND DESIGN

Prospective case series.

MATERIALS AND METHODS

Review of prospectively collected data of Indian patients with pathologic myopia and subfoveal CNV treated with verteporfin therapy between 2001 and 2005 using standard regimen for PDT.

STATISTICAL ANALYSIS USED

Wilcoxon signed rank test was used to see the difference in the mean letter acuity at intervals compared to baseline. Kaplan Meier Survival analysis was done to estimate the success rate of verteporfin therapy for CNV caused by pathologic myopia.

RESULTS

Fifteen patients (15 eyes) treated with standard fluence PDT and who had completed 24 months follow-up were analyzed. The mean spherical equivalent was -13.36 +/- 5.88 diopter. Five out of 15 eyes in six months, three out of 15 eyes at 12 months and four eyes out of 15 at 24 months had improved vision by > 10 letters. The mean number of treatment session was 2.2 in two years.

CONCLUSIONS

PDT with verteporfin for subfoveal CNV caused by pathologic myopia in Indian eyes is effective.

Effect of drug-light interval on the mode of action of Photofrin photodynamic therapy in a mouse tumor model

Our objective was to examine the effect of time intervals between Photofrin injection and laser irradiation [i.e., drug-light interval (DLI)] on the mode of action of Photofrin photodynamic therapy (PDT). Kunming mice transplanted with sarcoma-180 cells were used as an animal model. The tumor-bearing mice in the control group were given neither photosensitizer nor laser irradiation. PDT groups were given intravenous (i.v.) injection of Photofrin (7.5 mg/kg) prior to being irradiated with a 630 nm laser at 120 J/cm(2) at different DLIs (1 min-48 h). Tumors and overlying skin were visually examined daily. Histopathological and electron microscopic examinations were carried out 48 h after PDT. Survival rates were recorded. The mice in the groups that had experienced short DLIs (<60 min) showed stronger skin reactions than the groups subjected to long DLIs (>6 h). Histological examination showed that antitumor effects were achieved mainly by the destruction of tumor blood vessels and the formation of thrombosis at short DLIs, whereas, at long DLIs, the tumor cells were killed directly by PDT-mediated cytotoxicity. Electron microscopy revealed various degrees of mitochondrial swelling. The survival rate of the mice subjected to long DLIs was slightly higher than that of the mice subjected to short DLIs. Both vascular (e.g., tumor vessel destruction) and cellular (e.g., cytotoxicity) effects contributed to Photofrin PDT-induced tumor ablation.

Hypericin phototoxicity induces different modes of cell death in melanoma and human skin cells

Hypericin, the major component of St. John's Wort, absorbs light in the UV and visible ranges whereupon it becomes phototoxic through the production of reactive oxygen species. Although photodynamic mechanisms (i.e. through endogenous photosensitizers) play a role in UVA phototherapy for the treatment of skin disorders such as eczema and psoriasis, photodynamic therapy employing exogenous photosensitizers are currently being used only for the treatment of certain forms of non-melanoma skin cancers and actinic keratoses. There are few reports however on its use in treating melanomas. This in vitro study analyses the phototoxic effect of UVA (400-315 nm) - activated hypericin in human pigmented and unpigmented melanomas and immortalised keratinocytes and melanocytes. We show that neither hypericin exposure nor UV irradiation alone reduces cell viability. We show that an exposure to 1 microM UVA-activated hypericin does not bring about cell death, while 3 microM activated hypericin induces a necrotic mode of cell death in pigmented melanoma cells and melanocytes and an apoptotic mode of cell death in non-pigmented melanoma cells and keratinocytes. We hypothesis that the necrotic mode of cell death in the pigmented cells is possibly related to the presence of melanin-containing melanosomes in these cells and that the hypericin-induced increase in reactive oxygen species leads to an increase in permeability of melanosomes. This would result in toxic melanin precursors (of an indolic and phenolic nature) leaking into the cytoplasm which in turn leads to cell death. Hypericin localisation in the endoplasmic reticulum in these cells shown by fluorescent microscopy, further support a disruption in cellular processing and induction of cell death. In contrast, this study shows that cells that do not contain melanosomes (non-pigmented melanoma cells and keratinocytes) die by apoptosis. Further, using a mitochondrial-specific fluorescent dye, we show that intracellular accumulation of hypericin induces a mitochondrial-associated caspase-dependent apoptotic mode of cell death. This work suggests that UVA is effective in activating hypericin and that this phototoxicity may be considered as treatment option in some cases of lentigo maligna or lentigo maligna melanoma that are too large for surgical resection.

Photodynamic therapy of age-related macular degeneration: History and principles

We briefly review the history and principles of photodynamic therapy (PDT), especially as it is applied to choroidal neovascularization (CNV) in age-related macular degeneration (AMD). After a brief general history of PDT, we discuss the relationship between the physicochemical structure and photodynamic activity of the second-generation photosensitizers, such as those in current clinical use. We then discuss the basic photophysics of photosensitizer molecules, and describe the initial chemical reactions induced by activated sensitizers. We outline a novel method for screening photosensitizers to be used in treating CNV, as well as the complex biomolecular pathways modulated by PDT-induced oxidative stress and the vascular effects of PDT in solid tumors. The paper closes with a discussion of how all this information might be used to improve the selectivity and efficacy of clinically useful photosensitizers.

Spectroscopic properties and photodynamic effects of new lipophilic porphyrin derivatives: efficacy, localisation and cell death pathways

Photodynamic therapy (PDT) and photodynamic diagnostics (PDD) of cancer are based on the use of non-toxic dyes (photosensitisers) in combination with harmless visible light. This paper reports physicochemical properties, cell uptake, localisation as well as photodynamic efficiency of two novel lipophilic porphyrin derivatives, suitable for use as PDT sensitisers. Both compounds are characterised by high quantum yield of singlet oxygen generation which was measured by time-resolved phosphorescence. Photodynamic in vitro studies were conducted on three cancer cell lines. Results of cell survival tests showed negligible dark cytotoxicity but high phototoxicity. The results also indicate that cell death is dependent on energy dose and time following light exposure. Using confocal laser scanning microscopy both compounds were found to localise in the cytoplasm around the nucleus of the tumour cells. The mode of cell death was evaluated based on the morphological changes after differential staining. In summary, good photostability, high quantum yield of singlet oxygen and biological effectiveness indicate that the examined lipophilic porphyrin derivatives offer quite interesting prospects of photodynamic therapy application.

Photodynamic Therapy

ALA-PDT is a safe, well-tolerated, and effective treatment for many dermatologic conditions. Current data most strongly support its use in the treatment of actinic damage, but further investigation into alternative uses continues. Current efficacy is limited primarily by the depth of penetration of the photosensitizing agent and the activating light source. Even with this limitation, the potential applications of PDT are numerous. As new technology is developed to overcome current restraints, the future of PDT is wide open.

Photodynamic therapy systems and applications

Photodynamic therapy (PDT) is a form of photochemotherapy requiring the simultaneous presence of a photosensitiser, activating light of the proper wavelength and molecular oxygen in order to produce a localised therapeutic effect thought to be due to high-energy singlet oxygen generation. Neither drug nor light alone are effective as therapeutic agents and thus PDT treatment methods should be looked upon as true, necessary, drug and device combinations ('systems'). Selectivity of treatment is imparted by a combination of factors, including accumulation of photosensitiser by the target lesion and targeted application of activating light. The most common systemic side effect of systemically administered photosensitisers is cutaneous photosensitivity of varying periods of time. Local toxicities depend on the area of treatment. Sources of light which have been used in PDT include lasers, arc lamps, light-emitting diodes and fluorescent lamps. PDT has been used for a wide variety of clinical applications. In 1995, the first PDT system, using porfimer sodium (Photofrin, Axcan Pharma, Inc.), lasers and fibre optic light delivery methods, developed by QuadraLogic Technologies, was approved in the US for endoscopic palliation of malignant dysphagia caused by oesophageal cancer. A topical PDT system, aminolevulinic acid HCL (Levulan Kerastick) and the large-area BLU-U PDT Illuminator, was developed by DUSA Pharmaceuticals, Inc. for the treatment of actinic keratoses of the face and scalp and approved in the US in 2000. Topical PDT has applicability to a wide variety of skin cancers and precancerous conditions. In 2001, Novartis launched the systemically administered verteporfin (Visudyne) laser-based PDT system in the US as the first pharmacologic treatment for age-related macular degeneration. Development programmes are continuing to investigate PDT for the potential treatment of a variety of diseases, yielding therapeutic results with minimal toxicity.

A comprehensive overview of photodynamic therapy in the treatment of superficial fungal infections of the skin

Photodynamic therapy (PDT) is a two-step procedure, involving the topical or systemic administration of a photosensitizer followed by selective illumination of the target lesion with visible light, which triggers the oxidative photodamage and subsequent cell death within the target area. In dermatology, PDT has proven to be a useful treatment for a variety of malignant tumors and selected inflammatory diseases. In addition, PDT of several infective viral or bacterial skin diseases has been investigated. These investigations grew out of the positive findings of studies of another important use of PDT: that of disinfection of blood products. Up to now, little has been published concerning the application of PDT to fungi, probably due to the fact that research funding has been mainly directed towards blood disinfection, and these pathogens show a low risk of transfusion transmission. However, preliminary findings have demonstrated that dermatophytes and yeasts can be effectively sensitized in vitro by administering photosensitizers belonging to four chemical groups: phenothiazine dyes, porphyrins and phthalocyanines, as well as aminolevulinic acid, which, while not a photosensitizer in itself, is effectively metabolized into protoporphyrin IX. Besides efficacy, PDT has shown other benefits. First, the sensitizers used are highly selective, i.e., fungi were killed at combinations of drug and light doses much lower than that needed for a similar effect on keratinocytes. Second, all investigated photosensitizers lack genotoxic and mutagenic activity. Finally, the hazard of selection of drug resistant fungal strains was never reported. This paper intends to provide a comprehensive overview of investigative studies about the effects of PDT on yeasts and dermatophytes, and bring attention to this application of PDT which we believe very important in that skin mycosis is so common and PDT is not only cost-effective, but also has the advantages of being highly selective and avoiding the occurrence of drug resistant strains.

Protoporphyrin IX-accumulation in human tumor cells following topical ALA- and h-ALA-application in vivo

The fluorescence monitoring represents an innovative approach to detect tumor tissue by photosensitizer-mediated fluorescence. Therefore, information on cellular uptake, tumor selectivity and accumulation properties of photosensitizers are of essential interest. In this study we compared the accumulation properties of two photosensitizer precursors, the 5-aminolaevulinic acid (ALA) and a hexylester of ALA (h-ALA), in vivo using the hen's egg model and the human larynx carcinoma cell line HEp-2. The formation of the actual photosensitizer, protoporphyrin IX (PpIX), was determined both qualitatively and quantitatively. The intensity of the excited PpIX-fluorescence was observed as an indicator for the presence of PpIX after topical ALA- and h-ALA-applications. PpIX-fluorescence was measured using spatially resolved fluorescence spectroscopy.

Experimental photodynamic therapy with MESO-tetrakisphenylporphyrin (TPP) in liposomes leads to disintegration of human amelanotic melanoma implanted to nude mice

Liposomal meso-tetrakis-phenylporphyrin (TPP) was tested for photodynamic therapy (PDT) of human amelanotic melanomas implanted in nude mice. After intratumoural TPP application (15 mg x kg(-1)) followed by PDT lamp irradiation (600-700 nm, 635 nm peak), tumours retained their original volume up to the 23rd day post-PDT, whereas volumes increased 6 times in controls. PDT with intravenously (i.v.) administered liposomal (3.2 mg x kg(-1)) TPP mostly disintegrated tumours to zero volumes. Melanoma remissions were accompanied by tumour surface necroses and were documented by the appearance of nontumourous cells with nonpycnotic nuclei. Spatial arrangement of capillaries in remissing tumour was the same as in healthy surrounding tissue. Lower TPP doses (1, 0.3 and 0.1 mg x kg(-1)) were more or equally efficient than hydrophilic TPPS(4) (3.2 mg x kg(-1), i.e., sulfonated TPP), i.v. administered also in liposomes. Liposomal TPPS(4) only delayed the onset of subsequent tumour growth. Commercial Photosan 3 disintegrated tumours only in doses of approx. 7.5 mg x kg(-1); in lower doses it was less efficient than TPPS(4). The second PDT cycle (3.2 mg x kg(-1) TPP or 7.5 mg x kg(-1) Photosan 3), performed in a few unsuccessfully cured mice, predominantly led again to tumour remissions. Since the measured TPP and TPPS(4) content in melanomas was similar, these results demonstrate the advantage of PDT with a hydrophobic photosensitizer such as TPP. Photophysical properties of TPP and TPPS(4) are equal, but TPP has probably more favorable intracellular distribution, as documented by our studies, which leads to more efficient PDT. Consequently, liposomal TPP is suggested as a potentially suitable efficient preparation for PDT.

Photoeradication of Helicobacter pylori using 5-aminolevulinic acid: preliminary human studies

BACKGROUND AND OBJECTIVES

Helicobacter pylori (HP) is an endemic pathogenic bacterium causing gastritis and gastroduodenal ulceration in humans and is linked to the development of gastric malignancies. These first human in vivo studies investigated the photoeradication of HP using laser and white light.

STUDY DESIGN/MATERIALS AND METHODS

In 13 HP-positive volunteers, a zone of gastric antrum was irradiated with laser (410 nm, 50 J/cm(2)) or endoscopic white light (10 J/cm(2)) 45 minutes after oral 5-aminolevulinic acid (5-ALA) 20 mg/kg. HP-eradication was assessed by biopsy urease test and HP-culture from irradiated and control zones 5 minutes, 4 and 48 hours post-irradiation.

RESULTS

A maximum eradication effect was achieved at 4 hours post-irradiation when 85% of biopsies in the monochromatic and 66% in the white light exposed zones, and 58 and 33% in the respective control zones were HP-negative.

CONCLUSIONS

HP numbers were greatly reduced following exposure to 5-ALA and either laser or white light in vivo. Photoeradication appears feasible, but further light dosimetry and the development of convenient application methods is required.

The use of 5-aminolaevulinic acid as a photosensitiser in photodynamic therapy and photodiagnosis

Photodynamic therapy (PDT) is a treatment for cancer and pre-malignant conditions, which involves the administration of a photosensitising agent followed by exposure of the tissue to light. 5-Aminolaevulinic acid (ALA) is a naturally occurring compound in the haem biosynthetic pathway, which is metabolised to a photosensitive product, protoporphyrin IX (PpIX). The major advantage of ALA when compared to synthetic photosensitisers is the rapid metabolism, which significantly reduces the period of cutaneous photosensitivity. This review focuses on the development of ALA as a photosensitiser in photodynamic therapy and photodiagnosis, and the wide range of clinical applications in which ALA is now being used as a therapeutic modality.

Low-density lipoprotein receptors in the uptake of tumour photosensitizers by human and rat transformed fibroblasts

Low-density lipoproteins (LDL) increase the selectivity of tumour targeting by drugs, including sensitisers for photodynamic therapy, because of the enhanced expression of specific LDL receptors in many types of transformed as compared with non-transformed cells. This investigation aims at gaining more information on the role of LDL receptors in the accumulation of photosensitizer-LDL complexes by human and rat transformed fibroblasts, and the interference of the photosensitizer with LDL recognition by the specific receptors. Both an amphiphilic hematoporphyrin IX (Hp) and a hydrophobic Zn(II)-phthalocyanine (ZnPc) photosensitizers bind to human LDL with molar ratios of 5-6:1 and 10-12:1, respectively. The hematoporphyrin-LDL complex is accumulated by human HT1080 fibroblasts mainly through the high affinity LDL receptors, while the Zn-phthalocyanine-LDL complex is internalised through non specific endocytosis because of changes in the apoB LDL structure induced by phthalocyanine association, as suggested by spectroscopic studies. The uptake of LDL-delivered hematoporphyrin, but not Zn-phthalocyanine, is about 4-fold higher in HT1080 cells stimulated for maximal expression of LDL receptors as compared with non-stimulated cells. This difference is abolished by LDL acetylation. Human LDL-bound hematoporphyrin and Zn-phthalocyanine are up taken by stimulated and non-stimulated 4R rat fibroblasts with similar efficiency. Scatchard plot analysis of human (125)I-LDL binding to 4R cells shows the presence of only low affinity receptors while 350,000 high affinity receptors are expressed per HT1080 cell. It is concluded that a careful evaluation of the lack of conformational changes of LDL is critical for guaranteeing the selectivity and efficiency of photosensitizer delivery to tumour cells.

Dynamic observation of selective accumulation of a photosensitizer and its photodynamic effects in rat experimental choroidal neovascularization

PURPOSE

The authors investigated the selective accumulation of a photosensitizer, ATX-S10(Na), in experimental choroidal neovascularization (CNV) in rats using a highly sensitive colorchromatic charge coupled device (CCD) camera.

METHODS

To detect the development of experimental CNV in 30 rats, the animals were followed weekly with simultaneous fluorescein and indocyanine green angiography. After injecting ATX-S10(Na), the authors detected fluorescence from the photosensitizer using a highly sensitive color CCD camera. The camera was connected to a surgical microscope, under which rat fundi were observed through a coverglass in contact with the cornea. The retinas were excited with 405-435 nm light, and the light emitted from the photosensitizer passed through a 680-nm bandpass filter before being detected by the CCD camera.

RESULTS

Immediately after injection, fluorescence appeared in the retinal vessels and then the entire retina. Thirty minutes postinjection, the intensity of the fluorescence was still strong from the whole retina, and the CNV was not detected. One hour after injection, retinal fluorescence was weak but still observable; 1.5 hours postinjection, retinal fluorescence was undetectable but fluorescence was strong from the CNV. Under the optimum therapeutic conditions, CNV was effectively occluded.

CONCLUSION

ATX-S10(Na) selectively accumulates in the CNV in rats. The optimum therapeutic timing is approximately 1.5 hours postinjection of the dye in this CNV model.

Photodynamic therapy in the treatment of subfoveal choroidal neovascularisation

Subfoveal choroidal neovascularisation (CNV) is a major cause of visual disability, with age-related macular degeneration (AMD) the commonest cause. Confluent laser to CNV significantly reduces severe visual loss but the profound visual loss after treatment of subfoveal lesions and the high recurrence rate has meant its restriction to extrafoveal lesions. Developed initially as a treatment for cancers, photodynamic therapy (PDT) has been shown to successfully close CNV in the eye. Large international randomised placebo-controlled studies of the safety and efficacy of PDT with verteporfin are under way. The Treatment of Age-related Macular Degeneration with Photodynamic Therapy (TAP) study has demonstrated a reduction of visual loss in treated patients with any classic CNV. Subgroup analysis showed a greater benefit in predominantly classic lesions (p < 0.001, NNT: 3.6), increasing further for lesions with no occult component, roughly equivalent to pure classic (p < 0.01, NNT: 2.2) A significant benefit at 12 months has been shown in patients with CNV secondary to myopia in the Verteporfin in AMD (VIP) trial, but no benefit in pure occult lesions. Further research is required to establish cost-effectiveness and appropriate referral patterns in the UK and optimise treatment strategies. Further data are awaited from TAP/VIP. At present verteporfin PDT is indicated in eyes with subfoveal predominantly classic CNV secondary to AMD with visual acuity of 6/60 or better and lesions < 5,400 microm in diameter. Juxtafoveal lesions meeting the above criteria and CNV secondary to pathological myopia should also be considered for treatment. The efficacy of treatment of larger lesions, juxtapapillary CNV, occult/no classic with high-risk characteristics (HRC) and CNV from other causes remains unclear. The treatment of minimally classic lesions and those with occult/no classic without HRC is not indicated.

meso-tetraphenylporphyrin dimer derivatives as potential photosensitizers in photodynamic therapy. Part 2

Studies on the synthesis, singlet oxygen and fluorescence yields and pharmacokinetic properties of three different dimeric porphyrins with an amide linkage (D2-D4) are described and compared with the results recently reported for a dimeric porphyrin (D1). The pharmacokinetic behavior of all dimers were examined in Balb/c mice bearing MS-2 fibrosarcomas. The maximal efficiency and selectivity of photosensitizer accumulation in each tumor tissue takes place at 24 h after drug administration of 1.0 mg kg-1 into DL-alpha-dipalmitoylphosphatidylcholine liposomes by intravenous injection. Since the dimeric porphyrins exhibit high quantum yields of singlet oxygen generation, long triplet lifetimes and high photostability, the results obtained suggest that the evaluated dimeric structures may be promising candidates for further use in PDT experiments. The results also allow the possibility to establish a correlation between the chemical structure of the dyes and the efficiency/selectivity of the tumor accumulation and can be used for building up optimal photosensitizing agents for tumors.

Subcellular phototoxicity of 5-aminolaevulinic acid (ALA)

BACKGROUND AND OBJECTIVE

5-aminolaevulinic acid (ALA) is a new, promising photosensitizer for PDT of cancer. Subcellular toxicity induced by ALA and light exposure in single cells was studied to elucidate the mechanism of cell damage.

STUDY DESIGN/MATERIALS AND METHODS

CPAE, PTK2, and rat neonatal myocardial cells treated with ALA were examined for localization using fluorescence microscopy and for subcellular phototoxicity using 630 nm laser microbeam irradiation of specific subcellular regions.

RESULTS

In CPAE and PTK2 cells, a large amount of fluorescence was detected in the peri-nuclear cytoplasm. In rat neonatal myocardial cells, the sensitizer selectively localized in the large mitochondria. In both cell types, there was little phototoxicity when the peripheral cytoplasmic region was exposed, as compared to considerable phototoxicity with exposure of either the perinuclear or nuclear regions.

CONCLUSION

Both the CPAE and PTK2 cells demonstrated that the nucleus followed by the perinuclear cytoplasm are the most sensitive cell areas with no sensitivity in the peripheral cytoplasm.

Pharmacokinetics, tissue distribution and photodynamic therapy efficacy of liposomal-delivered hypocrellin A, a potential photosensitizer for tumor therapy

Hypocrellin A, from Hypocrella bambusae, is a novel photosensitizer of high singlet oxygen quantum yield for photodynamic therapy (PDT). Tissue distributions were studied in tumor-bearing mice as a function of time following administration. The tumor model was S-180 sarcoma transplanted into one hind leg of male Kunming mice; hypocrellin A (HA) was delivered to the mice by intravenous injection of 5 mg/kg of body weight as a suspension either as a unilamellar liposome or in dimethyl sulfoxide (DMSO)-solubilized saline. The HA was isolated from several tissues and organs, as well as tumors and peritumoral muscles and skin. Quantitation was performed by a high-performance liquid chromatographic technique with detection that utilizes the native fluorescence of HA. Independent of the delivery system, the dye was retained in tumors at higher concentrations than in normal tissues, except for kidney, liver, lung and spleen. The dye retention in tumors was high and was vehicle dependent. For the liposomal system, the maximal accumulation in tumor and maximal ratios of dye in tumor versus peritumoral muscle and skin occurred 12 h postinjection; for the DMSO saline system, the maximal ratio occurred earlier, 6 h postadministration. Liposomal delivery improved the selective accumulation of the dye in tumor with higher maximal levels in tumor and higher ratios of tumor-to-muscle and tumor-to-skin. Levels of dye were very low or not detectable in the brain. The PDT efficacy of HA in the liposome and DMSO saline systems was determined by evaluating the tumor volume regression percent. The PDT efficacy of HA in liposomes was highest when light treatment was performed at 12 h postinjection, consistent with the highest retention of HA in tumors. Similarly, the maximal PDT efficacy in DMSO saline was attained at 6 h postinjection, the highest HA retention point in tumor. Moreover, the peak PDT efficacy of HA in liposomes was much higher than that of HA in DMSO saline and even hematoporphyrin monomethylether.

Role of ground and excited singlet state oxygen in the red light-induced stimulation of Escherichia coli cell growth

Irradiation of selected Escherichia coli defective strains with red-light induces a stimulation of the cell growth rate. Such effect is wavelength-dependent and is accompanied by a transient increase of the cell volume and some enzymic activities. The presence of oxygen appears to be essential for the occurrence of a significant photostimulatory effect. The results obtained upon irradiation in the presence of quenchers (tryptophan, histidine, azide) or enhancers (deuterium oxide) of singlet oxygen (1O2) strongly suggest that this activated oxygen derivative is generated by excitation of endocellular chromophores (possibly cytochromes). The reaction of 1O2 with nearby cellular targets could induce a sublethal cell damage which in turn promotes an accelerated cell metabolism.

Principles of treatment of choroidal neovascularization with photodynamic therapy in age-related macular degeneration

Age-related macular degeneration (AMD) is a common cause of legal blindness in the developed countries in people older than 50 years of age. AMD complicated by choroidal neovascular membranes (CNV) accounts for 12% of AMD, but for 88% of legal blindness cases. Because of the progressive aging of the population, it is expected that AMD will be one of the greater public health problems in ophthalmology in the first half of the next century. Laser photocoagulation remains the only proven treatment for CNV in AMD, but unfortunately, is applicable only to a minority of patients presenting with CNV in AMD. Photodynamic therapy (PDT) is a new experiment treatment for CNV that combines the application of low-intensity light with a photosensitizing agent in the presence of oxygen to produce tissue effects. It uses the noninvasive potential of the laser light to cause a nonthermal localized chemotoxic reaction and obtain highly selective occlusion of the neovascular channels, with sparing of the overlying photoreceptors. Animal studies showed that PDT accounts for the effective closure of experimentally induced CNV. Phase I-II clinical studies showed that PDT using BPD can safely stabilize leakage from CNV in a majority of patients for up to 3 months. Phase III clinical studies to assess the long term prognosis of PDT-treatment of CNV in AMD are ongoing.

Relative contributions of apoptosis and random necrosis in tumour response to photodynamic therapy: effect of the chemical structure of Zn(II)-phthalocyanines

Zn(II)-phthalocyanines (ZnPc) and its octapentyl (ZnOPPc) and octadecyl (ZnODPc) derivatives have been intravenously injected at a dose of 1.46 mumol/kg into female Balb/c mice bearing an intramuscularly transplanted MS-2 fibrosarcoma. Pharmacokinetic studies show that in all cases the maximal concentration of phthalocyanine in the tumour is reached at 24 h post-injection: the efficiency and selectivity of tumour targeting slightly increase upon increasing the length of the alkyl substituents. Irradiation of the neoplastic lesion (620-700 nm light, 180 MW/cm2, 300 J/cm2) 24 h after photosensitizer administration induces a significant delay of tumour growth, which was largest (approximately 11 days) for ZnPc and smallest (approximately 3.5 days) for ZnODPc. Electron microscopy investigations of irradiated tumour specimens show that ZnPc causes an early direct damage of malignant cells, largely via processes leading to random necrotic pathways, although a limited contribution of apoptotic pathways is detected. The importance of this increased upon using ZnOPPc and especially ZnODPc as the photosensitizers, possibly due to a different partitioning in different compartments of cell membranes.

Lipid peroxidation induced by meso-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl] porphyrin on photosensitization in hepatic and tumor microsomes

The ability of a novel porphyrin, meso-tetrakis[3,4-bis(carboxymethyleneoxy)phenyl]porphyrin (T3,4-CPP), to induce photodamage in subcellular membranes, in the form of rat hepatic and tumor microsomes, was evaluated with a view to locating suitable porphyrin derivative for possible use in photodynamic therapy. This water-soluble porphyrin, on exposure to visible light, induced a significant extent of membrane lipid peroxidation as assessed by the formation of thiobarbituric acid reactive substances, lipid hydroperoxides and conjugated dienes. The peroxidation induced in hepatic microsomes is both time- and concentration-dependent. Using inhibitors of reactive oxygen species and comparing products of peroxidation, it is shown that the damage induced is mainly due to singlet oxygen and partly due to other species like free radicals. T3,4-CPP also caused the generation of singlet oxygen as a function of illumination time. Since membrane damage induced by a sensitizer on photoexcitation has been considered to be an important mechanism by which photodynamic cell killing of tumor occurs, the studies on this novel porphyrin indicate the possible potential of this compound in photodynamic therapy.

The effects of thrombocytopenia on vessel stasis and macromolecular leakage after photodynamic therapy using photofrin

Several studies have reported thrombus formation and/or the release of specific vasoactive eicosanoids, suggesting that platelet activation or damage after photodynamic therapy (PDT) may contribute to blood flow stasis. The role of circulating platelets on blood flow stasis and vascular leakage of macromolecules during and after PDT was assessed in an intravital animal model. Sprague-Dawley rats bearing chondrosarcoma on the right hind limb were injected intravenously (i.v.) with 25 mg/kg Photofrin 24 h before light treatment of 135 J/cm2 at 630 nm. Thrombocytopenia was induced in animals by administration of 3.75 mg/kg of rabbit anti-rat platelet antibody i.v. 30 min before the initiation of the light treatment. This regimen reduced circulating platelet levels from 300,000/mm3 to 20,000/mm3. Reductions in the luminal diameter of the microvasculature in normal muscle and tumor were observed in control animals given Photofrin and light. Venule leakage of macromolecules was noted shortly after the start of light treatment and continued throughout the period of observation. Animals made thrombocytopenic showed none of these changes after PDT in either normal tissues or tumor. The lack of vessel response correlated with the absence of thromboxane release in blood during PDT. These data suggest that platelets and eicosanoid release are necessary for vessel constriction and blood flow stasis after PDT using Photofrin.

Meso-tetraphenylporphyrin dimer derivative as a potential photosensitizer in photodynamic therapy

Studies on the synthesis, preliminary in vivo biological activity, singlet oxygen and fluorescence yields of a dimeric porphyrin (D1) are described. The pharmacokinetic behavior and photodynamic properties of the dimer D1 were examined in Balb/c mice bearing an MS-2 fibrosarcoma. Compound D1 shows a high selectivity for tumor localization (tumor/peritumoral tissue ratios of dye concentration ranging between ca 100 and 140 at 24 h after drug administration of 5.0-1.0 mg kg-1 into DL-alpha-dipalmitoylphosphatidylcholine liposomes). The phototherapeutic efficiency of dimer D1 was evaluated by following the growth curves of fibrosarcoma irradiated with red light (600-700 nm) with a total dose of 400 J cm-2, at 24 h after intravenous injection. Photodynamic therapy-treated tumors showed a significant delay in growth as compared to untreated control mice. The results obtained suggest that the porphyrin dimer D1 may be a promising candidate for further use in PDT experiments.

Pharmacokinetic and phototherapeutic properties of axially substituted Si(IV)-tetradibenzobarreleno-octabutoxyphthalocyanines

Three Si(IV)-tetradibenzobarreleno-octabutoxyphthalocyanines (TDiBOPcs) bearing different axial ligands on the metal ion were studied for their tumour-localizing and-photosensitizing properties after i.v. injection via a Cremophor emulsion (0.35 mumol kg-1 b.w.) to Balb/c mice bearing an intramuscularly implanted MS-2 fibrosarcoma. In all cases, the maximum tumour accumulation of the photosensitizer (0.8-1.9 nmol g-1 of tissue) was found at 24 h after injection. The efficiency and selectivity of tumour targeting appeared to be dependent on the nature of the axial ligands; optimal values of these parameters were obtained in the case of the bis(trihexyl-siloxy)-substituted Si(IV)-TDiBOPc, which gave a 7-9 tumour/muscle ratio of phthalocyanine concentration at 24-48 h after injection. The extent of tumour response to PDT treatment was correlated with the concentration of the photosensitizer in the tumour tissue: upon 740 nm irradiation (180 mW cm-2, 200 J cm-2) at 48 h after injection of 0.35 mumol kg-1 of Si(IV)-TDiBOPc-C6H13, the tumour growth exhibited a delay of about 7 days.

Photodynamic therapy of 9L gliosarcoma with liposome-delivered photofrin

The effect of Photofrin encapsulated in a liposome delivery vehicle for photodynamic therapy (PDT) of the 9L gliosarcoma and normal rat brain was tested. We hypothesized that the liposome vehicle enhances therapeutic efficacy, possibly by increasing tumor tissue concentration of Photofrin. Male Fisher rats bearing a 9L gliosarcoma were treated 16 days after intracerebral tumor implantation with either Photofrin in dextrose (n = 5) or Photofrin in liposome (n = 6). Nontumor-bearing animals were treated with Photofrin delivered either in dextrose (n = 4) or liposome (n = 4) vehicle. Tissue concentrations of Photofrin delivered either in dextrose (n = 4) or liposome (n = 4) vehicle were measured in tumor, brain adjacent to tumor and in normal brain tissue. Photofrin was administered (intraperitoneally) at a dose of 12.5 mg/kg and PDT (17 J/cm2 of 632 nm light at 100 mW/cm2) was performed 24 h after Photofrin administration. Brains were removed 24 h after PDT and stained with hematoxylin and eosin for analysis of cellular damage. The PDT using Photofrin in the liposome vehicle caused significantly more damage to the tumor (P < 0.001) than did PDT with Photofrin in dextrose. The PDT of tumor with Photofrin delivered in liposomes caused a 22% volume of cellular necrosis, while PDT of tumor with Photofrin delivered in dextrose caused only scattered cellular damage. Photofrin concentration in tumors was significantly higher (P = 0.021) using liposome (33.8 +/- 18.9 micrograms/g) compared to dextrose delivery (5.5 +/- 1.5 micrograms/g). Normal brain was affected similarly in both groups, with only scattered cellular necrosis. Our data suggest that the liposome vehicle enhances the therapeutic efficacy of PDT treatment of 9L tumors.

Evaluation of the immunotoxicity of benzoporphyrin derivative (BPD-MA) in mice

Photodynamic therapy has been shown to selectively eliminate activated lymphocytes in a number of experimental situations. These findings have important implications in therapies involving selective immunomodulation. In this study we report the effects of intravenous dosing with the photosensitizer benzoporphyrin derivative-monoacid A(BPD) on normal immunological function. Therapeutic doses of BPD and light had no effect on natural killer cell activity, the mixed lymphocyte reaction, cell-mediated lympholysis, the primary immune response to sheep red blood cells, or the secondary memory response to T cell-dependent antigens. In non-light treated controls, BPD at concentrations up to 10-fold higher had a limited effect on cell-mediated lympholysis. We conclude that the primary effect of BPD in several therapeutic modalities in not due to a generalized suppression of the immune system.