Phthalocyanine photodynamic therapy: disparate effects of pharmacologic inhibitors on cutaneous photosensitivity and on tumor regression

Photodynamic therapy using chloro-aluminum phthalocyanine decreases inflammatory response in an experimental rat periodontal disease model

BACKGROUND AND OBJECTIVE

Emerging evidence suggests that photodynamic therapy (PDT) can exhibit immunomodulatory activity. The purpose of the present study was to analyse cytokine profiles after application of PDT in gingival tissues of rats with ligature-induced periodontal disease (PD).

STUDY DESIGN/MATERIAL AND METHODS

Periodontal disease was induced through the introduction of a cotton thread around the first left mandibular molar, while the right side molars did not receive ligatures. After 7days of PD evolution, ligatures were removed from the left side, and the animals were randomically divided into the following treatment groups: I, rats without treatment; II, rats received chloro-aluminum phthalocyanine (AlClPc); III, rats received low-level laser alone; and IV, rats received AlClPc associated with low-level laser (PDT). The animals were killed 7days after the treatments, and the mandibles were histologically processed to assess morphological and immunohistochemical profile, while gingival tissues were removed for quantification of tumor necrosis factor (TNF)-α, interleukin (IL-)1β and IL-10 expression (by ELISA).

RESULTS

Histomorphological analysis of periodontal tissues demonstrated that PDT-treated animals show tissue necrosis, as well as lower TNF- α expression, compared to ligatured animals treated with AlClPc alone.

CONCLUSIONS

It was concluded that PDT using AlClPc entrapped in a lipid nanoemulsion may be useful in therapies, because of immunomodulatory effects that decreased the inflammatory response and cause tissue destruction.

Mechanisms in photodynamic therapy: part two-cellular signaling, cell metabolism and modes of cell death

Photodynamic therapy (PDT) has been known for over a hundred years, but is only now becoming widely used. Originally developed as a tumor therapy, some of its most successful applications are for non-malignant disease. In the second of a series of three reviews, we will discuss the mechanisms that operate in PDT on a cellular level. In Part I [Castano AP, Demidova TN, Hamblin MR. Mechanism in photodynamic therapy: part one-photosensitizers, photochemistry and cellular localization. Photodiagn Photodyn Ther 2004;1:279-93] it was shown that one of the most important factors governing the outcome of PDT, is how the photosensitizer (PS) interacts with cells in the target tissue or tumor, and the key aspect of this interaction is the subcellular localization of the PS. PS can localize in mitochondria, lysosomes, endoplasmic reticulum, Golgi apparatus and plasma membranes. An explosion of investigation and explorations in the field of cell biology have elucidated many of the pathways that mammalian cells undergo when PS are delivered in tissue culture and subsequently illuminated. There is an acute stress response leading to changes in calcium and lipid metabolism and production of cytokines and stress proteins. Enzymes particularly, protein kinases, are activated and transcription factors are expressed. Many of the cellular responses are centered on mitochondria. These effects frequently lead to induction of apoptosis either by the mitochondrial pathway involving caspases and release of cytochrome c, or by pathways involving ceramide or death receptors. However, under certain circumstances cells subjected to PDT die by necrosis. Although there have been many reports of DNA damage caused by PDT, this is not thought to be an important cell-death pathway. This mechanistic research is expected to lead to optimization of PDT as a tumor treatment, and to rational selection of combination therapies that include PDT as a component.

Synthesis and characterization of novel zinc phthalocyanines as potential photosensitizers for photodynamic therapy of cancers

Two novel water soluble zinc phthalocyanines (Pcs): tetramethyl tetrakis-2,(3)-[(4-methyl-2-pyridyloxy)phthalocyaninato] zinc(ii) (4) and tetrakis-2,(3)-[(3-carboxylicacid-6-sulfanylpyridine)phthalocyaninato] zinc(ii) (5) were synthesized and characterized.

In vitro analysis of photosensitizer accumulation for assessment of applicability of fluorescence diagnosis of squamous cell carcinoma of epidermolysis bullosa patients

Epidermolysis bullosa (EB) is a group of inherited skin disorders characterized by blistering following mechanical trauma. Chronic wounds of EB patients often lead to tumors such as squamous cell carcinoma (SCC). Early diagnosis may prevent its invasive growth--frequently the reason of premature mortality of EB-patients. Early detection of tumors is achieved by fluorescence diagnosis (FD), where photosensitizers localize selectively in tumors and fluoresce upon illumination. Excessive accumulation of photosensitizers in inflamed areas, as occasionally found at chronic wounds and tumors due to inflammatory processes, leads to false-positive results in FD. This study analyzed accumulation kinetics of the photosensitizers hypericin and endogenous protoporphyrin IX (PpIX) in different skin cell lines including the three EB subtypes under normal and proinflammatory conditions (stimulated with TNF-alpha). The aim was to assess the applicability of FD of SCC in EB. All cell lines accumulate hypericin or PpIX mostly increasing with incubation time, but with different kinetics. SCC cells of recessive dystrophic EB (RDEB) accumulate less hypericin or PpIX than nonmalignant RDEB cells. Nevertheless, tumor selectivity in vivo might be existent. Non-EB cell lines are more active concerning photosensitizer enrichment. Proinflammatory conditions of skin cell lines seem to have no major influence on photosensitizer accumulation.

Syntheses and photochemical properties of octasubstituted phthalocyaninato zinc complexes

In this work a selection of octasubstituted phthalocyaninato zinc complexes were synthesized and their photochemistry studied. The substituents included cholesterol (3a), estrone (3b), naphthol (3c) and phenoxy groups substituted with CH3 (3d), C ( CH 3)3 (at two positions, 3e), C ( CH 3)3 (3f), NO2 (3g), NH 2 (3h), COH (3i), COOH (3j), and H (3k). In general, complexes containing electron-donating groups attached to the phenoxy ring (e.g. 3e and 3f) were found to be photochemically unstable with photobleaching quantum yields of the order of 10-3. In the presence of electron-withdrawing groups (3g, 3i, and 3j) the photobleaching quantum yields were of the order of 10-6 to 10-5. Singlet oxygen quantum yields (ΦΔ) ranged from 0.01 to 0.73. The lowest ΦΔ was observed for the highly aggregated complex 3c. All the complexes showed aggregation at high concentrations. Electrochemical reduction using a thin-layer spectroelectrochemistry cell showed that the complexes become more monomeric following reduction.

Current status of phthalocyanines in the photodynamic therapy of cancer

Photodynamic therapy is a binary treatment now accepted in clinic for various malignancies in several countries around the world. Phthalocyanine molecules are second-generation photosensitizers with enhanced photophysical and photochemical properties over those of porphyrins. They have been shown to be phototoxic against a number of cell types and tumor models. A great deal of research has been devoted to the elucidation of their mechanism of action and mode of cell death. The present paper reviews phthalocyanine pre-clinical anti-cancer research with emphasis on phthalocyanine induced apoptosis using a silicon phthalocyanine, Pc 4. A brief summary of the latest clinical results using phthalocyanines is presented.

Synthesis and spectral characterization of bis(β-diketonato)zirconium(IV) and -hafnium(IV) phthalocyaninates

The reaction of PcMCl 2 ( M = Zr , Hf ) with β-diketones is reported. 1 H NMR and elemental analysis suggest the substitution of two Cl atoms for two β-diketone fragments takes place as a result of this reaction and the complexes PcM(β-dik)2 are formed. All obtained complexes are stable and highly soluble in most organic solvents. The data from 1 H and 19 F NMR, and UV-vis spectroscopy suggest the coordination of two β-diketone ligands in a cis geometry about the central atom of the macrocycle. It was shown bis(β-diketonato)zirconium(IV) and hafnium(IV) phthalocyanines containing β-diketones with donor or acceptor groups or with bulky substituents can be obtained.

Synthesis, photophysical and photochemical studies of germanium and tin phthalocyanine complexes

This work reports on the synthesis of tin and germanium phthalocyanine complexes containing phenoxy and substituted phenoxy groups as phthalocyanine ring substituents. The compounds studied are: dichlorogermanium phthalocyanine complexes containing eight phenoxy (4a), o-methyl phenoxy (4b) or estrone (4c) groups on the ring. The corresponding dichlorotin complexes (5a, 5b and 5c) and diiodotin complex (6a) were also investigated, as well as diestrone phthalocyaninato tin (7). Germanium octaphenoxy phthalocyanine complexes undergo phototransformation rather than direct photobleaching, whereas tin octaphenoxy phthalocyanine complexes undergo a photobleaching process, which is mediated by photoreduction of the phthalocyanine ring. Tin octaphenoxy phthalocyanine complexes gave higher ΦΔ values than the corresponding germanium complexes. Also tin phthalocyanine complexes containing an unsubstituted ring gave higher ΦΔ values than the corresponding octaphenoxy substituted complexes. The triplet quantum yields increased with the increase in electron-donating power of the ring substituents.

Like a bolt from the blue: phthalocyanines in biomedical optics

The purpose of this review is to compile preclinical and clinical results on phthalocyanines (Pcs) as photosensitizers (PS) for Photodynamic Therapy (PDT) and contrast agents for fluorescence imaging. Indeed, Pcs are excellent candidates in these fields due to their strong absorbance in the NIR region and high chemical and photo-stability. In particular, this is mostly relevant for their in vivo activation in deeper tissular regions. However, most Pcs present two major limitations, i.e., a strong tendency to aggregate and a low water-solubility. In order to overcome these issues, both chemical tuning and pharmaceutical formulation combined with tumor targeting strategies were applied. These aspects will be developed in this review for the most extensively studied Pcs during the last 25 years, i.e., aluminium-, zinc- and silicon-based Pcs.

Preliminary clinical and pharmacologic investigation of photodynamic therapy with the silicon phthalocyanine photosensitizer pc 4 for primary or metastatic cutaneous cancers

Photodynamic therapy (PDT) for cutaneous malignancies has been found to be an effective treatment with a range of photosensitizers. The phthalocyanine Pc 4 was developed initially for PDT of primary or metastatic cancers in the skin. A Phase I trial was initiated to evaluate the safety and pharmacokinetic profiles of systemically administered Pc 4 followed by red light (Pc 4-PDT) in cutaneous malignancies. A dose-escalation study of Pc 4 (starting dose 0.135 mg/m(2)) at a fixed light fluence (135 J/cm(2) of 675-nm light) was initiated in patients with primary or metastatic cutaneous malignancies with the aim of establishing the maximum tolerated dose (MTD). Blood samples were taken at intervals over the first 60 h post-PDT for pharmacokinetic analysis, and patients were evaluated for toxicity and tumor response. A total of three patients (two females with breast cancer and one male with cutaneous T-cell lymphoma) were enrolled and treated over the dose range of 0.135 mg/m(2) (first dose level) to 0.54 mg/m(2) (third dose level). Grade 3 erythema within the photoirradiated area was induced in patient 2, and transient tumor regression in patient 3, in spite of the low photosensitizer doses. Pharmacokinetic observations fit a three-compartment exponential elimination model with an initial rapid distribution phase (∼0.2 h) and relatively long terminal elimination phase (∼28 h), Because of restrictive exclusion criteria and resultant poor accrual, the trial was closed before MTD could be reached. While the limited accrual to this initial Phase I study did not establish the MTD nor establish a complete pharmacokinetic and safety profile of intravenous Pc 4-PDT, these preliminary data support further Phase I testing of this new photosensitizer.

Photodynamic therapy of cottontail rabbit papillomavirus-induced papillomas in a severe combined immunodeficient mouse xenograft system

OBJECTIVES/HYPOTHESIS

To evaluate the efficacy of photodynamic therapy (PDT) with the phthalocyanine photosensitizer Pc 4 for treating an animal model of recurrent respiratory papillomatosis (RRP).

METHODS

Rabbit skin was grafted onto the dorsum of severe combined immunodeficient mice, two xenografts per animal. After the graft healed, it was inoculated with cottontail rabbit papillomavirus (CRPV). When papillomas developed, Pc 4 (0.6 or 1.0 mg/kg) was administered systemically, and 48 hours later, one papilloma of the two on each animal was exposed to 675-nm photoactivating light at either 100 or 150 J/cm(2). In addition to the contralateral tumors, which received Pc 4 but no light, other controls included animals receiving light only or neither agent. Response was assessed by measuring papilloma size with a caliper. Some papillomas and residual skin were harvested for histological assessment.

RESULTS

For the lower-dose PDT regimens, papilloma growth rates were not significantly different from the controls. In contrast, 13 of 15 papillomas receiving the higher Pc 4 dose (1.0 mg/kg) and the higher light fluence (150 J/cm(2)) regressed completely and did not regrow within the observation period of up to 79 days. The response of these papillomas was significantly different from the controls (P < .001). Histological analysis confirmed the absence of residual tumor following complete response and replacement with near-normal epithelium.

CONCLUSIONS

Pc 4-PDT is highly effective in treating virally induced (CRPV) papillomas in a murine model of RRP, and thus warrants further study as a treatment for HPV-induced papillomas.

Expression of IL-10, TGF-beta(1) and TNF-alpha in Cultured Keratinocytes (HaCaT Cells) after IPL Treatment or ALA-IPL Photodynamic Treatment

BACKGROUND

Depending on the light dose and concentration of photosensitizer for photodynamic treatment (PDT), a multitude of dose-related events are demonstrable in PDT-treated cells. Sublethal doses may result in the alteration of cytokine release and consequently modify immune actions, rather than cause cell death.

OBJECTIVE

The purpose of this study was to investigate cytokine expression in cultured HaCaT cells after intense pulse light (IPL) treatment or PDT utilizing 5-aminolevulinic acid (ALA) and IPL at sublethal doses.

METHODS

Cultured HaCaT cells were treated with either IPL only (4, 8 and 12 J/cm(2)) or ALA-IPL PDT (100micromol/L of ALA; 0, 4, 8, and 12 J/cm(2) of IPL). The expression of IL-10, TGF-beta(1) and TNF-alpha was investigated by reverse transcription-polymerase chain reaction and enzyme linked immunosorbent assay.

RESULTS

IL-10 protein increased up to 5.95-fold after IPL treatment and up to 2.85-fold after PDT. TGF-beta(1) mRNA and protein showed slight increases after both IPL treatment and PDT, of which the latter induced slightly larger increases. TNF-alpha mRNA and protein showed no induction or reduction after PDT.

CONCLUSION

Increased expressions of IL-10 and TGF-beta(1) was observed after PDT. The induction of IL-10 may contribute to the anti-inflammatory effect, which explains the therapeutic benefit of PDT for inflammatory dermatoses, and that of TGF-beta(1) may be related to the therapeutic effect for psoriasis. The finding that IL-10 induction was more marked after IPL treatment than after PDT suggests that other mechanisms than IL-10 induction in keratinocytes after PDT may participate in the anti-inflammatory effect of PDT.

Apoptosis mechanisms related to the increased sensitivity of Jurkat T-cells vs A431 epidermoid cells to photodynamic therapy with the phthalocyanine Pc 4

To examine the clinical applicability of Pc 4, a promising second-generation photosensitizer, for the photodynamic treatment of lymphocyte-mediated skin diseases, we studied the A431 and Jurkat cell lines, commonly used as surrogates for human keratinocyte-derived carcinomas and lymphocytes, respectively. As revealed by ethyl acetate extraction and absorption spectrophotometry, uptake of Pc 4 into the two cell lines was linear with Pc 4 concentration and similar on a per cell basis but greater in Jurkat cells on a per mass basis. Flow cytometry showed that uptake was linear at low doses; variations in the dose-response for uptake measured by fluorescence supported differential aggregation of Pc 4 in the two cell types. As detected by confocal microscopy, Pc 4 localized to mitochondria and endoplasmic reticulum in both cell lines. Jurkat cells were much more sensitive to the lethal effects of phthalocyanine photodynamic therapy (Pc 4-PDT) than were A431 cells, as measured by a tetrazolium dye reduction assay, and more readily underwent morphological apoptosis. In a search for molecular factors to explain the greater photosensitivity of Jurkat cells, the fate of important Bcl-2 family members was monitored. Jurkat cells were more sensitive to the induction of immediate photodamage to Bcl-2, but the difference was insufficient to account fully for their greater sensitivity. The antiapoptotic protein Mcl-1 was extensively cleaved in a dose- and caspase-dependent manner in Jurkat, but not in A431, cells exposed to Pc 4-PDT. Thus, the greater killing by Pc 4-PDT in Jurkat compared with A431 cells correlated with greater Bcl-2 photodamage and more strongly to the more extensive Mcl-1 degradation. Pc 4-PDT may offer therapeutic advantages in targeting inflammatory cells over normal keratinocytes in the treatment of T-cell-mediated skin diseases, such as cutaneous lymphomas, dermatitis, lichenoid tissue reactions and psoriasis, and it will be instructive to evaluate the role of Bcl-2 family proteins, especially Mcl-1, in the therapeutic response.

Histamine Is Released following Aminolevulinic Acid-Photodynamic Therapy of Human Skin and Mediates an Aminolevulinic Acid Dose-Related Immediate Inflammatory Response

Acute skin inflammation occurs following topical aminolevulinic acid-photodynamic therapy (ALA-PDT), but its nature and mediation are ill defined. As we observed an urticarial response, a potential role for histamine was explored. In 13 healthy volunteers, we assessed the time course and dose-response of the acute cutaneous response(s) to ALA-PDT, the impact of H(1) antihistamine blockade, and measured dermal histamine release. An ALA dose series was iontophoresed into ventral forearm skin and exposed to red light. All participants exhibited an immediate urticarial response, both wheal and flare correlating with log ALA dose. Subsequently, a dose-related erythema developed at treatment sites by 3 hours and persisted at 24 hours. H(1) blockade with oral cetirizine doubled the median minimal urticating dose of ALA and reduced the slope of dose-response for wheal and flare, whereas at the highest ALA dose, mean wheal and flare areas reduced by 68 and 60%, respectively. In contrast, cetirizine did not influence the 24 hour minimal phototoxic dose or erythema dose-response. Histamine release after ALA-PDT mirrored the urticarial response, levels peaking within 30 minutes and returning to baseline by 24 hours. Thus, two discrete acute inflammatory responses to topical ALA-PDT occur in human skin; histamine mediates the immediate response, but does not appear involved in the delayed phototoxicity.

Pc 4 photodynamic therapy of U87-derived human glioma in the nude rat

BACKGROUND AND OBJECTIVES

As a potential therapy for malignant glioma, we tested the phthalocyanine photosensitizer Pc 4 for: (1) rapid clearance from the vasculature, (2) specificity for glioma, and (3) tumoricidal photosensitizing capability.

STUDY DESIGN/MATERIALS AND METHODS

Parenchymal injection of U87 cells into athymic rat brains (N = 100) was followed after 12 days by tail vein injection of 0.5 mg/kg Pc 4. After 1 day, the tumor was illuminated with either 5 (N = 11) or 30 (N = 16) J/cm(2) red light at 672 nm. Sacrifice was 1 day later. The brains from these 27 animals underwent H&E (necrosis) and TUNEL assay (apoptosis) histology. Pc 4 concentration of explanted brains and tumors (N = 16), and all blood samples (N = 52) were determined by HPLC-MS 1 day post Pc 4 administration.

RESULTS

Tumor-specific apoptosis was almost uniformly seen; however, necrosis was found mostly in the high-light-dose group. Pc 4 concentration in bulk tumor averaged 3.8 times greater than in normal brain.

CONCLUSIONS

These results warrant expanding this pre-clinical study to seek effective baseline Pc 4 drug- and light-doses and infusion-to-photoirradiation timing that would be necessary for a Pc 4-mediated PDT clinical trial for glioma patients.

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.

Intracellular signaling mechanisms in photodynamic therapy

In photodynamic therapy (PDT) a sensitizer, light and oxygen are used to induce death of tumor cells and in the treatment of certain noncancerous conditions. Cell death in PDT may occur by apoptosis or by necrosis, depending on the sensitizer, on the PDT dose and on the cell genotype. Some sensitizers that have been used in PDT are accumulated in the mitochondria, and this may explain their efficiency in inducing apoptotic cell death, both in vitro and in vivo. In this review we will focus on the events that characterize apoptotic death in PDT and on the intracellular signaling events that are set in motion in photosensitized cells. Activation of phospholipases, changes in ceramide metabolism, a rise in the cytosolic free Ca2+ concentration, stimulation of nitric oxide synthase (NOS), changes in protein phosphorylation and alterations in the activity of transcription factors and on gene expression have all been observed in PDT-treated cells. Although many of these metabolic reactions contribute to the demise process, some of them may antagonize cell death. Understanding the signaling mechanisms in PDT may provide means to modulate the PDT effects at the molecular level and potentiate its antitumor effectiveness.

Photodynamic therapy for superficial bladder cancer under local anaesthetic

OBJECTIVES

To evaluate the use of local anaesthesia (LA) in 5-aminolaevulinic acid (ALA) photodynamic therapy (PDT) for superficial transitional cell carcinoma (TCC) of the bladder, and to provide further toxicity and tolerability data on this new method within the context of a phase 1 trial.

PATIENTS AND METHODS

ALA PDT was administered to 19 patients with recurrent superficial TCC (stage Ta/carcinoma in situ, grades 1-3) using escalating doses of ALA (3-6%) and 633 nm laser light (25-50 J/cm2) under various LA (lignocaine) protocols. Pain was assessed using a linear analogue scale from 0 to 10. The endpoints of tolerability and toxicity were assessed for the different LA, light and ALA doses, with lignocaine levels.

RESULTS

ALA PDT is painful and requires some form of anaesthesia. The discomfort was immediate, associated with bladder spasm, and was a function of the ALA concentration rather than the total light dose given. Simple passive diffusion (PD) of 2% lignocaine instilled for 40 min before PDT gave adequate anaesthesia with 3% ALA (n=8; median pain score 1, range 0-2). With 6% ALA the pain was dramatically increased using PD (n=6; median pain score 8, range 5-10) and therefore the more potent LA technique of electromotive drug administration (EMDA) of 2% lignocaine was used, with excellent results (n=3; median pain score 1, range 0-2). All patients had transient bladder irritability that typically lasted 9-12 days, with no subjective/objective change in long-term bladder function. No other toxicity was reported. Serum lignocaine levels were minimal.

CONCLUSION

Bladder ALA PDT is both safe and feasible under LA. At a dose of 3% ALA, the procedure was well-tolerated using PD of lignocaine. At higher doses (6% ALA) more effective anaesthesia is required and this can be obtained satisfactorily with EMDA of lignocaine. With refinement, ALA PDT may be feasible as an outpatient treatment for superficial bladder TCC.

Reactive oxygen-dependent production of novel photochemotherapeutic agents

The reactive nature of species derived from oxygen, such as singlet oxygen and hydrogen peroxide, has been exploited in the clinical setting for targeting bacteria, viruses, and tumor cells by photodynamic excitation of a variety of chromophores. This modality, termed photodynamic therapy (PDT), is currently being used to treat some forms of cancer. However, the applicability of conventional PDT is limited due to the absolute dependence on simultaneous exposure of the target to the photoactive compound and light. In 1990, we demonstrated that the need for simultaneous exposure of the biological target to light and photosensitizer could be circumvented by prior exposure (activation) of the sensitizer molecule to light and its subsequent use as any other anti-cancer or anti-viral drug. By dint of the nature of the protocol, this process was termed preactivation. Since then, the generation of biologically active molecules in vitro by preactivation has been validated using a variety of chromophores, such as merocyanine 540, Photofrin II, and naphthalimide. Here we briefly review the role of reactive oxygen species in the photodynamic effect, and provide an explanation for the mechanism of preactivation. We propose that photo-oxidation not only provides a novel means for the generation of biologically active molecules, but could also explain, at least in part the mechanism of conventional PDT. It is likely that the light-dependent breakdown of the chromophore to generate novel active compounds, in addition to reactive oxygen species, also contributes to the photodynamic damage observed on simultaneous exposure of the chromophore and target tissue to light during PDT.-Pervaiz, S. Reactive oxygen-dependent production of novel photochemotherapeutic agents.

FADD Null Mouse Embryonic Fibroblasts Undergo Apoptosis after Photosensitization with the Silicon Phthalocyanine Pc 4

Oxidative stress, such as photodynamic therapy with the silicon phthalocyanine Pc 4 (Pc 4-PDT), can induce apoptosis and tumor necrosis factor alpha (TNF) production. TNF receptors, as well as other death receptors, have been implicated in stress-induced apoptosis. To assess directly the role of FADD, a death receptor-associated protein, in induction of apoptosis post-Pc 4-PDT, embryonic fibroblasts from FADD knock out (k/o) and wild-type (wt) mice were used. Pc 4-PDT induced casp-3 activation and apoptosis in both cell types. In the presence of zVAD, a pancaspase inhibitor, Pc 4-PDT-induced apoptosis was abrogated in both cell lines. Fumonisin B1 (FB), an inhibitor of ceramide synthase, had no effect on apoptosis after Pc 4-PDT in either cell line. Similar to Pc 4-PDT, exogenous C6-ceramide bypassed FADD deficiency and induced zVAD-sensitive apoptosis. In contrast to Pc 4 photosensitization, TNF did not induce either apoptosis or ceramide accumulation in FADD k/o cells. In the absence of FADD deficiency, TNF-induced apoptosis was zVAD-sensitive and FB-insensitive. Induced ceramide levels remained elevated after cotreatment with TNF and zVAD in FADD wt cells. Taken together, these data provide genetic evidence for a lack of FADD requirement in Pc 4-PDT- or C6-ceramide-induced apoptosis. FB-sensitive ceramide production accompanies, but does not suffice, for apoptosis after Pc 4 photosensitization or TNF.

Photodynamic therapy in dermatology

The combination of light and chemicals to treat skin diseases is widely practiced in dermatology. Within this broad use of light and drugs, in recent years the concept of photodynamic therapy (PDT) has emerged. PDT is a promising modality for the management of various tumors and nonmalignant diseases, based on the combination of a photosensitizer that is selectively localized in the target tissue and illumination of the lesion with visible light, resulting in photodamage and subsequent cell death. Moreover, the fluorescence of photosensitizing compounds is also utilized as a helpful diagnostic tool for the detection of neoplastic tissue. Intensive basic and clinical research culminated in the worldwide approval of PDT for bladder, esophageal, and lung cancer. The expanding use of this relatively new therapeutic modality in dermatology at many centers around the world has revealed its efficacy for the treatment of cutaneous precancer and cancer, as well as selected benign skin disorders. The following article summarizes the main principles of PDT considering the most recent developments and provides a comprehensive synopsis of the present status of the use of PDT in dermatology. (J Am Acad Dermatol 2000;42:389-413.)

LEARNING OBJECTIVE

At the conclusion of this learning activity, participants should be able to describe the basic concepts of PDT, including fundamental knowledge of the most relevant photosensitizers, the light sources, the mechanisms involved in PDT-mediated cell destruction, as well as the indications and limitations of photodynamic treatment of skin diseases.

Comparative spectroscopic and electrochemical properties of bis(octakis(dodecylthio)naphthalocyaninato)europium(III) and bis(tetra-tert-butylnaphthalocyaninato)europium(III) complexes

Bis(substituted-2,3-naphthalocyaninato)europium(III) complexes: bis(octakis(dodecylthio)-2,3-naphthalocyaninato)europium(III) (Eu[2,3-Nc(SC12H25)8]2, 1) and bis(tetra-tert-butyl-2,3- naphthalocyaninato)europium(III) (Eu[2,3-Nc(t-Bu)4]2, 2) have been synthesized by cyclic tetramerization of naphthalonitriles with Eu(acac)3.H2O in the presence of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) in refluxing n-octanol. These compounds were characterized by UV-visible, magnetic circular dichroism (MCD), near-IR, IR, EPR, and mass spectroscopies. The absorption and MCD spectra of 1 showed splitting of the Q band, with peaks at 700 and 784 nm, red shifted from the Q band of 2 at 763 nm. The absorption and MCD spectral band deconvolution calculations of complex 1 gave two A terms in the Q-band region. The A terms are assigned to 2A2-->2E1 transitions. Cyclic voltammograms of 1 and 2 showed reversible oxidation couples at E1/2 = -0.28 V (for 2) and -0.25 V (for 1) vs ferrocenium/ferrocene (Fc+/Fc). The second oxidation exhibited a complicated behavior for both complexes. The reduction couples for 2 were observed at E1/2 = -0.61, -1.64, -1.97, and -2.42 V, and for 1 they were observed at E1/2 = -0.62, -1.60, -1.86, and -2.27 V vs Fc+/Fc. Spectral changes observed on chemical oxidation and reduction of the complexes are presented, and the behaviors of 1 and 2 are compared.

Foscan (mTHPC) photosensitized macrophage activation: enhancement of phagocytosis, nitric oxide release and tumour necrosis factor-alpha-mediated cytolytic activity

Photodynamic activation of macrophage-like cells contributes to an effective outcome of photodynamic therapy (PDT) treatment. The possibility for an enhancement of macrophage activity by photosensitization with meta-tetra(hydroxyphenyl)chlorin (mTHPC) (1 microg ml(-1)) was studied in U937, monocyte cell line differentiated into macrophages (U937) cells). Phagocytic activity of U937phi cells was evaluated by flow-cytometry monitoring of ingestion of fluorescein-labelled Escherichia coli particles. Increase in irradiation fluence up to 3.45 mJ cm(-2) (corresponding irradiation time 15 s) resulted in significant increase in fluorescence signal (145%), while at higher light fluences the signal lowered down to the untreated control values. A light energy-dependent production of tumour necrosis factor-alpha (TNF-alpha) by photosensitized macrophages was further demonstrated using the L929 assay. The maximum TNF-alpha mediated cytolysis was observed at 28 mJ cm(-2) and was 1.7-fold greater than that in control. In addition, we demonstrated a fluence-dependent increase in nitric oxide (NO) production by mTHPC-photosensitized macrophages. NO release increased gradually and reached a plateau after irradiation fluence of 6.9 mJ cm(-2). Cytotoxicity measurements indicated that the observed manifestations of mTHPC-photosensitized macrophage activation took place under the sublethal light doses. The relevance of the present findings to clinical mTHPC-PDT is discussed.