Intracellular localization of sulfonated meso-tetraphenylporphines in a human carcinoma cell line

Cellular Imaging and Time-Domain FLIM Studies of Meso-Tetraphenylporphine Disulfonate as a Photosensitising Agent in 2D and 3D Models

Fluorescence lifetime imaging (FLIM) and confocal fluorescence studies of a porphyrin-based photosensitiser (meso-tetraphenylporphine disulfonate: TPPS2a) were evaluated in 2D monolayer cultures and 3D compressed collagen constructs of a human ovarian cancer cell line (HEY). TPPS2a is known to be an effective model photosensitiser for both Photodynamic Therapy (PDT) and Photochemical Internalisation (PCI). This microspectrofluorimetric study aimed firstly to investigate the uptake and subcellular localisation of TPPS2a, and evaluate the photo-oxidative mechanism using reactive oxygen species (ROS) and lipid peroxidation probes combined with appropriate ROS scavengers. Light-induced intracellular redistribution of TPPS2a was observed, consistent with rupture of endolysosomes where the porphyrin localises. Using the same range of light doses, time-lapse confocal imaging permitted observation of PDT-induced generation of ROS in both 2D and 3D cancer models using fluorescence-based ROS together with specific ROS inhibitors. In addition, the use of red light excitation of the photosensitiser to minimise auto-oxidation of the probes was investigated. In the second part of the study, the photophysical properties of TPPS2a in cells were studied using a time-domain FLIM system with time-correlated single photon counting detection. Owing to the high sensitivity and spatial resolution of this system, we acquired FLIM images that enabled the fluorescence lifetime determination of the porphyrin within the endolysosomal vesicles. Changes in the lifetime dynamics upon prolonged illumination were revealed as the vesicles degraded within the cells.

Selective Cytotoxicity to HER2 Positive Breast Cancer Cells by Saporin-Loaded Nanobody-Targeted Polymeric Nanoparticles in Combination with Photochemical Internalization

In cancer treatment, polymeric nanoparticles (NPs) can serve as a vehicle for the delivery of cytotoxic proteins that have intracellular targets but that lack well-defined mechanisms for cellular internalization, such as saporin. In this work, we have prepared PEGylated poly(lactic acid- co-glycolic acid- co-hydroxymethyl glycolic acid) (PLGHMGA) NPs for the selective delivery of saporin in the cytosol of HER2 positive cancer cells. This selective uptake was achieved by decorating the surface of the NPs with the 11A4 nanobody that is specific for the HER2 receptor. Confocal microscopy observations showed rapid and extensive uptake of the targeted NPs (11A4-NPs) by HER2 positive cells (SkBr3) but not by HER2 negative cells (MDA-MB-231). This selective uptake was blocked upon preincubation of the cells with an excess of nanobody. Nontargeted NPs (Cys-NPs) were not taken up by either type of cells. Importantly, a dose-dependent cytotoxic effect was only observed on SkBr3 cells when these were treated with saporin-loaded 11A4-NPs in combination with photochemical internalization (PCI), a technique that uses a photosensitizer and local light exposure to facilitate endosomal escape of entrapped nanocarriers and biomolecules. The combined use of saporin-loaded 11A4-NPs and PCI strongly inhibited cell proliferation and decreased cell viability through induction of apoptosis. Also the cytotoxic effect could be reduced by an excess of nanobody, reinforcing the selectivity of this system. These results suggest that the combination of the targeting nanobody on the NPs with PCI are effective means to achieve selective uptake and cytotoxicity of saporin-loaded NPs.

Enhanced efficiency of cell death by lysosome-specific photodamage

Mobilization of specific mechanisms of regulated cell death is a promising alternative to treat challenging illness such as neurodegenerative disease and cancer. The use of light to activate these mechanisms may provide a route for target-specific therapies. Two asymmetric porphyrins with opposite charges, the negatively charged TPPS2a and the positively charged CisDiMPyP were compared in terms of their properties in membrane mimics and in cells. CisDiMPyP interacts to a larger extent with model membranes and with cells than TPPS2a, due to a favorable electrostatic interaction. CisDiMPyP is also more effective than TPPS2a in damaging membranes. Surprisingly, TPPS2a is more efficient in causing photoinduced cell death. The lethal concentration on cell viability of 50% (LC50) found for TPPS2a was ~3.5 (raw data) and ~5 (considering photosensitizer incorporation) times smaller than for CisDiMPyP. CisDiMPyP damaged mainly mitochondria and triggered short-term phototoxicity by necro-apoptotic cell death. Photoexcitation of TPPS2a promotes mainly lysosomal damage leading to autophagy-associated cell death. Our data shows that an exact damage in lysosome is more effective to diminish proliferation of HeLa cells than a similar damage in mitochondria. Precisely targeting organelles and specifically triggering regulated cell death mechanisms shall help in the development of new organelle-target therapies.

pH-Response Optimization of Amino-Substituted Tetraphenylporphyrin Derivatives as pH-Activatable Photosensitizers

Amino-substituted tetraphenylporphyrin derivatives have been designed as pH-activatable photosensitizers for photodynamic cancer therapy. The photophysical processes of the monoamino-substituted derivative N1 and nonsubstituted derivative N0 have been studied. The quantum yields of the fluorescence and photosensitization of singlet oxygen by N1 were very low in the neutral condition (OFF state), but these quantum yields were recovered by adding acid (ON state). These changes were not observed for N0; therefore, N1 is expected to be applicable as a pH-activatable photosensitizer. The ON/OFF switching mechanism of N1 has also been clarified. To optimize the pH response, tri- and tetraamino-substituted derivatives (N3 and N4) have also been explored. The pH response intensified as the number of amino groups increased. Furthermore, the ON/OFF switching ratio of N3 was 100, which is quite high.

Photodynamic Efficiency: From Molecular Photochemistry to Cell Death

Photodynamic therapy (PDT) is a clinical modality used to treat cancer and infectious diseases. The main agent is the photosensitizer (PS), which is excited by light and converted to a triplet excited state. This latter species leads to the formation of singlet oxygen and radicals that oxidize biomolecules. The main motivation for this review is to suggest alternatives for achieving high-efficiency PDT protocols, by taking advantage of knowledge on the chemical and biological processes taking place during and after photosensitization. We defend that in order to obtain specific mechanisms of cell death and maximize PDT efficiency, PSes should oxidize specific molecular targets. We consider the role of subcellular localization, how PS photochemistry and photophysics can change according to its nanoenvironment, and how can all these trigger specific cell death mechanisms. We propose that in order to develop PSes that will cause a breakthrough enhancement in the efficiency of PDT, researchers should first consider tissue and intracellular localization, instead of trying to maximize singlet oxygen quantum yields in in vitro tests. In addition to this, we also indicate many open questions and challenges remaining in this field, hoping to encourage future research.

Photodynamic therapy (PDT) of cancer: from local to systemic treatment

Photodynamic therapy (PDT) requires a medical device, a photosensitizing drug and adequate use of both to trigger biological mechanisms that can rapidly destroy the primary tumour and provide long-lasting protection against metastasis.

Enhancing nucleic acid delivery by photochemical internalization

Photochemical internalization (PCI) is a method for releasing macromolecules from endosomal and lysosomal compartments. The PCI approach uses a photosensitizer that localizes to endosomal and lysosomal compartments, and a light source with appropriate light spectra for excitation of the photosensitizer. Upon photosensitizer excitation, endosomal and lysosomal membranes are destroyed, due to the formation of reactive oxygen species, followed by release of the endocytosed material. PCI has been demonstrated to enhance and control (site- and time-specific) delivery of various macromolecules such as viruses, proteins, chemotherapeutics, nucleic acid, and so on. In this Review we present past and current studies of PCI-controlled delivery of natural and artificial nucleic acids, such as peptide nucleic acids, siRNA molecules, mRNA molecules and plasmids. We also discuss critical aspects to further the possibilities for successful gene targeting in space and time.

Molecular characterization of photosensitizer-mediated photodynamic therapy by gene expression profiling

Photodynamic therapy (PDT) is a novel cancer treatment based on the tumor-specific accumulation of a photosensitizer followed by irradiation with visible light, which induces selective tumor cell death via production of reactive oxygen species. To elucidate the underlying mechanisms, microarray analysis was used to analyze the changes in gene expression patterns during PDT induced by various photosensitizers. Cancer cells were subjected to four different photosensitizer-mediated PDT and the resulting gene expression profiles were compared. We identified many differentially expressed genes reported previously as well as new genes for which the functionfunctions in PDT are still unclear. Our current results not only advance the general understanding of PDT but also suggest that distinct molecular mechanisms are involved in different photosensitizer-mediated PDT. Elucidating the signaling mechanisms in PDT will provide information to modulate the antitumor effectiveness of PDT using various photosensitizers.

From elementary reactions to chemical relevance in the photodynamic therapy of cancer

Theories of radiationless conversions and of chemical processes were employed to design better photosensitizers for photodynamic therapy (PDT). In addition to photostability and intense absorption in the near infrared, these photosensitizers were required to generate high yields of long-lived triplet states that could efficiently transfer their energy, or an electron, to molecular oxygen. The guidance provided by the theories was combined with the ability to synthesize large quantities of pure photosensitizers and with the biological screening of graded hydrophilicities/lipophilicities. The theoretical prediction that halogenated sulfonamide tetraphenylbacteriochlorins could satisfy all the criteria for ideal PDT photosensitizers was verified experimentally.

Combined effects of singlet oxygen and hydroxyl radical in photodynamic therapy with photostable bacteriochlorins: evidence from intracellular fluorescence and increased photodynamic efficacy in vitro

Sulfonamides of halogenated bacteriochlorins bearing Cl or F substituents in the ortho positions of the phenyl rings have adequate properties for photodynamic therapy, including strong absorption in the near-infrared (λ(max) ≈ 750 nm, ε ≈ 10(5) M(-1) cm(-1)), controlled photodecomposition, large cellular uptake, intracellular localization in the endoplasmic reticulum, low cytotoxicity, and high phototoxicity against A549 and S91 cells. The roles of type I and type II photochemical processes are assessed by singlet oxygen luminescence and intracellular hydroxyl radical detection. Phototoxicity of halogenated sulfonamide bacteriochlorins does not correlate with singlet oxygen quantum yields and must be mediated both by electron transfer (superoxide ion, hydroxyl radicals) and by energy transfer (singlet oxygen). The photodynamic efficacy is enhanced when cellular death is induced by both singlet oxygen and hydroxyl radicals.

Relationship between structure and photoactivity of porphyrins derived from protoporphyrin IX

Protoporphyrin (Pp IX) derivatives were prepared to study the relationship between photosensitizer structure and photoactivity, with an emphasis on understanding the role of membrane interactions in the efficiency of photosensitizers used in photodynamic therapy (PDT). The synthetic strategies described here aimed at changing protoporphyrin periferic groups, varying overall charge and oil/water partition, while maintaining their photochemical properties. Three synthetic routes were used: (1) modification of Pp IX at positions 31 and 81 by addition of alkyl amine groups of different lengths (compounds 2–5), (2) change of Pp IX at positions 133 and 173, generating alkyl amines (compounds 6 and 7, a phosphate amine (compound 8, and quarternary ammonium compounds (compounds 9 and 10), and (3) amine-alkylation of Hematoporphyrin IX (Hp IX) at positions 31, 81, 133 and 173(compound 12). Strategy 1 leads to hydrophobic compounds with low photocytotoxicity. Strategy 2 leads to compounds 6–10 that have high levels of binding/incorporation in vesicles, mitochondria and cells, which are indicative of high bioavailability. Addition of the phosphate group (compound 8), generates an anionic compound that has low liposome and cell incorporation, plus low photocytotoxicity. Compound 12 has intermediate incorporation and photocytotoxic properties. Compound modification is also associated with changes in their sub-cellular localization: 30% of 8 (anionic) is found in mitochondria as compared to 95% of compound 10 (cationic). Photocytotoxicity was shown to be highly correlated with membrane affinity, which depends on the asymmetrical and amphiphilic characters of sens, as well as with sub-cellular localization.

Mechanisms of porphyrinoid localization in tumors

The photosensitizing and pharmacokinetic properties of porphyrin-type compounds have been investigated for nearly a century. In the last decade, two porphyrin derivatives were approved in the U.S.A. and in several other countries for the photodynamic treatment of various lesions. An overview of the different mechanisms for preferential porphyrinoid localization in malignant tumors is presented herein. Several uptake pathways are possible for each photosensitizer, which are determined by its structure, mode of delivery and tumor type. Comparisons of the different mechanisms and correlations with the structure of the sensitizer are presented. Current delivery systems for porphyrin sensitizers are described, as well as recent strategies for enhancing their tumor-specificity, including conjugation to a carrier system that selectively targets a tumor-associated receptor or antigen.

Light-directed delivery of nucleic acids

A major barrier within the field of non-viral gene therapy toward therapeutic strategies, e.g., tumor therapy, has been lack of appropriate specific delivery strategies to the intended target tissues or cells. In this chapter, we describe a protocol for light-directed delivery of nucleic acids through the use of photochemical internalization (PCI) technology. PCI is based on a photosensitizing compound that localizes to endocytic membranes. Upon illumination, the photosensitizing compound induces damage to the endocytic membranes, resulting in release of endocytosed material, i.e., nucleic acids into cytosol. The main benefit of the strategy described is the possibility for site-specific delivery of nucleic acids to a place of interest.

Kinetics of singlet oxygen photosensitization in human skin fibroblasts

The roles played by singlet oxygen ((1)O(2)) in photodynamic therapy are not fully understood yet. In particular, the mobility of (1)O(2) within cells has been a subject of debate for the last two decades. In this work, we report on the kinetics of (1)O(2) formation, diffusion, and decay in human skin fibroblasts. (1)O(2) has been photosensitized by two water-soluble porphyrins targeting different subcellular organelles, namely the nucleus and lysosomes, respectively. By recording the time-resolved near-IR phosphorescence of (1)O(2) and that of its precursor the photosensitizer's triplet state, we find that the kinetics of singlet oxygen formation and decay are strongly dependent on the site of generation. (1)O(2) photosensitized in the nucleus is able to escape out of the cells while (1)O(2) photosensitized in the lysosomes is not. Despite showing a lifetime in the microsecond time domain, (1)O(2) decay is largely governed by interactions with the biomolecules within the organelle where it is produced. This observation may reconcile earlier views that singlet oxygen-induced photodamage is highly localized, while its lifetime is long enough to diffuse over long distances within the cells.

Photophysics and photochemistry of photodynamic therapy: fundamental aspects

Photodynamic therapy (PDT) is a treatment modality for cancer and various other diseases. The clinical protocol covers the illumination of target cells (or tissue), which have been loaded with a photoactive drug (photosensitizer). In this review we describe the photophysical and primary photochemical processes that occur during PDT. Interaction of light with tissue results in attenuation of the incident light energy due to reflectance, absorption, scattering, and refraction. Refraction and reflection are reduced by perpendicular light application, whereas absorption can be minimized by the choice of a photosensitizer that absorbs in the far red region of the electromagnetic spectrum. Interaction of light and the photosensitizer can result in degradation, modification or relocalization of the drug, which differently affect the effectiveness of PDT. Photodynamic therapy itself, however, employs the light-induced chemical reactions of the activated photosensitizer (triplet state), resulting in the production of various reactive oxygen species, amongst them singlet oxygen as the primary photochemical product. Based on these considerations, the properties of an ideal photosensitizer for PDT are discussed. According to the clinical experience with PDT, it is proposed that the innovative concept of PDT is most successfully implemented into the mainstream of anticancer therapies by following an application-, i.e. tumor-centered approach with a focus on the actual clinical requirements of the respective tumor type.

Structural and physico-chemical determinants of the interactions of macrocyclic photosensitizers with cells

New therapies have been developed using reactive oxygen species produced by light-activation of photosensitizers (PS). Since the lifetime of these species is extremely short and their diffusion in space is limited, the photo-induced reactions primarily affect the cell organelles labeled by the PS. In addition to the development of molecules with the best optical and photosensitizing properties, considerable research has been done to understand the physico-chemical parameters governing their subcellular localization. In this review, we examine these parameters to establish the structure/efficacy relationships, which allow specific targeting of PS. We examine the effect of subcellular localization on the cellular response to photosensitization processes. We discuss the determinants of subcellular localization, including the hydrophobic/hydrophilic balance, the specific charge effects and the dynamics of PS' transfer through membranes. Specific targeting can also be achieved with molecular structures able to recognize cellular or intracellular receptors, and this is also dealt with in this paper.

The history of PDT in Norway Part one: Identification of basic mechanisms of general PDT

Photodynamic therapy (PDT) is now an established treatment of malignant and premalignant dysplasias. A number of first and second generation photosensitizers have been studied in Norway. The aim has been to improve PDT efficiency and applicability. Many critical details regarding the mechanisms of PDT were elucidated by researchers in Norway. In this review we focus on the most important findings related to these basic mechanisms, such as generation of singlet oxygen, estimations of its lifetime, the oxygen effect itself, the subcellular localization of photosensitizers with different properties, their photodegradation during PDT and their tumour selectivity.

Photochemical treatment with endosomally localized photosensitizers enhances the number of adenoviruses in the nucleus

BACKGROUND

In the present study the physical targeting technique photochemical internalization (PCI) has been used in combination with adenovirus. We have previously shown that PCI enhances transgene expression from AdhCMV-lacZ, and the aim of the present study was to further increase the understanding of photochemically mediated adenoviral transduction.

METHODS

Two colorectal carcinoma cell lines, WiDr and HCT116, were pre-incubated with the photosensitizer TPPS(2a) or methylene blue derivates (MBD) followed by infection with adenovirus and light exposure. Transgene expression was measured by flow cytometry. Real-time polymerase chain reaction (PCR) and fluorescence in situ hybridization (FISH) were used to quantify the level of viral DNA in the nuclei. Real-time PCR was also used to measure the level of beta-galactosidase mRNA in samples infected with AdhCMV-lacZ.

RESULTS

Exposing TPPS(2a)-treated cells to light enhanced the quantity of viral DNA in the nucleus, the mRNA level of the transgene and the transgene expression compared to non-illuminated cells. The increased transgene expression was independent of the promoter used, but dependent on the time of light exposure and the cellular localization of the photosensitizer.

CONCLUSIONS

The enhanced transgene expression observed after photochemical treatment is most likely not a result of one event, but more an interplay between various mechanisms. An increased level of adenoviral DNA in the nucleus and a dependency of endosomal localization of the photosensitizer to obtain enhanced transgene expression suggested that endosomal rupture facilitated the transport of adenoviruses to the nucleus.

PCI-enhanced adenoviral transduction employs the known uptake mechanism of adenoviral particles

The development of methods for efficient and specific delivery of therapeutic genes into target tissues is an important issue for further development of in vivo gene therapy. In the present study, the physical targeting technique, photochemical internalization (PCI), has been used together with adenovirus. The combination of PCI and adenoviral transduction has previously been shown to be favorable compared to adenovirus used alone, and the aim of this study was to verify the role of the adenoviral receptors and identify the uptake pathway used by adenoviral particles in photochemically treated cells. All examined cell lines showed augmented transduction efficiency after PCI-treatment, with a maximum of 13-fold increase in transgene expression compared to conventionally infected cells. Blocking of CAR induced a complete inhibition of PCI-enhanced transgene expression. However, photochemical treatment managed to enhance the transduction efficiency of the retargeted virus AdRGD-GFP showing also that the virus-CAR interaction is not vital for obtaining a photochemical effect on adenoviral transduction. Blocking the alpha(V)-integrins reduced the gene expression significantly in photochemically treated cells. Subjecting HeLa cells expressing negative mutant-dynamin to light treatment after infection gave no significant increase in gene transfer, while the gene transfer were enhanced seven-fold in cells with wild-type dynamin. Furthermore, chlorpromazine inhibited photochemical transduction in a dose-dependent manner, whereas Filipin III had no effect on the gene transfer. In summary, the data presented imply that adenoviral receptor binding is important and clathrin-mediated endocytosis is the predominant uptake mechanism for adenoviral particles in photochemically treated cells.

Structural requirements for efficient cellular photoprotection by carotenoid derivatives

We have synthesized five carotenoid derivatives: (1) Girard's reagent P (GRP)-retinal from GRP and retinal; (2) GRP-carotenal from GRP and beta-apo-8'-carotenal; (3) Girard's reagent T (GRT)-carotenal from GRT and beta-apo-8'-carotenal; (4) (GRP2-canthaxanthin from 2 mol of GRP and 1 mol of canthaxanthin; and (5) dansyl hydrazine (DH)-carotenal from DH and beta-apo-8'-carotenal. The first three derivatives are cations, whereas the fourth is a dication and the fifth is a weak base. Using K562 cells, we compared the subcellular distribution of the synthetic carotenoid derivatives with two uncharged natural carotenoids, beta-carotene and beta-apo-8'-carotenal. The two natural carotenoids were present mainly within the cell membranes. The synthetic carotenoid derivatives were more broadly distributed among the cell organelles. The positively charged derivatives had relatively high concentrations in mitochondria, whereas DH-carotenal had a relatively high concentration in lysosomes. We also measured the amount of photoprotection provided by the synthetic and natural carotenoids for K562 cells labeled with a photosensitizer (hypericin, protoporphyrin IX or cis-di[4-sulfonatophenyl]diphenylporphine). In this model system, only carotenoid derivatives with a permanent positive charge provided significant photoprotection. Neither the two natural carotenoids nor DH-carotenal were effective photoprotectors.

Chloroaluminum phthalocyanine tetrasulfonate delivered via acid-labile diplasmenylcholine-folate liposomes: intracellular localization and synergistic phototoxicity

Folate-diplasmenylcholine (1,2-di-O-(Z-1'-hexadecenyl)-sn-glycero-3-phosphocholine; DPPlsC) liposomes have been shown to greatly enhance the potency of water-soluble antitumor agents via a selective folate-mediated uptake and acid-catalyzed endosomal escape mechanism (Rui et al. J. Am. Chem. Soc., 1998; 120:11213--18). This study describes an adaptation of this strategy for the delivery of chloroaluminum phthalocyanine tetrasulfonate ([AlPcS(4)](4-)), a water-soluble sensitizer used in photodynamic therapy, in a binary targeting scheme designed to enhance both its tumor selectivity and phototoxicity. [AlPcS(4)](4-)/DPPlsC:folate liposomes (9.8 microM bulk concentration, 2.5 mM intraliposomal concentration) were substantially more phototoxic to folate-deficient KB cells than 12.5 microM free [AlPcS(4)](4-) after a 30 min irradiation (630-910 nm). Considerable differences in phototoxicity were observed, however, between the commercially-available AlPcS(4)(4-) and an HPLC purified sample of [AlPcS(4)](4-) due to an increased tendency for the latter to aggregate. Experiments with [AlPcS(4)](4-)/DPPC:folate and folate-free [AlPcS(4)](4-)/DPPlsC liposomes (acid-insensitive and non-targeted controls, respectively) showed significantly reduced phototoxicities under the same illumination conditions. Our results imply that higher concentrations of water-soluble sensitizers can be delivered to target cells using the folate receptor-mediated pathway, which can change both the biodistribution and intracellular localization of the sensitizer when acid-labile DPPlsC liposomes are used as the delivery vehicle. Potential advantages of this approach include the use of lower bulk [AlPcS(4)](4-) concentrations, rapid plasma clearance of free [AlPcS(4)](4-), and better phototoxic responses, due to higher intracellular [AlPcS(4)](4-) concentrations combined with reduced collateral photodamage arising from misguided sensitizer accumulation, thereby enhancing the selective phototoxicity of PDT treatments.

Girard's reagent P derivative of beta-Apo-8'-carotenal: a potent photoprotective agent

A cationic carotenoid derivative (GRP-carotenal) was synthesized by the reaction of Girard's reagent P and beta-apo-8'-carotenal. The singlet-oxygen quenching constants for GRP-carotenal were 1.3 +/- 0.1 x 10(10) and 1.0 +/- 0.1 x 10(10) M-1 s-1 in acetonitrile and in detergent micelles, respectively. Photosensitized damage to K562 leukemia cells from cis-di(4-sulfonatophenyl)diphenylporphine, hypericin and protoporphyrin IX was inhibited by GRP-carotenal under conditions where beta-apo-8'-carotenal, beta-carotene and crocetin were ineffective. The unique cytoprotective properties of GRP-carotenal, relative to the other carotenoids studied, could not be explained by the differences in the cell content of the various carotenoids or by the changes in the cell content of the photosensitizers used. Photosensitizer fluorescence from labeled K562 cells was reduced by GRP-carotenal but not by the other carotenoids studied. The novel photoprotective properties of GRP-carotenal may be due to its subcellular distribution. In photosensitizer-containing detergent micelles, novel properties of GRP-carotenal were not apparent. None of the carotenoids studied reduced photosensitizer fluorescence or singlet-oxygen generation. Singlet-oxygen quenching by GRP-carotenal and by beta-apo-8'-carotenal were roughly the same. Crocetin has a singlet-oxygen quenching constant that is about a factor of five lower. Singlet-oxygen quenching by beta-carotene was limited by its aggregation.

Bystander effects in cell death induced by photodynamic treatment UVA radiation and inhibitors of ATP synthesis

Confluent layers of MDCK II cells were treated with four different photosensitizers (a purified version of hematoporphyrin derivative [Photofrin], tetra(3-hydroxyphenyl)porphine [3-THPP], meso-tetra(4-sulphonatophenyl)porphine [TPPS4] and ALA-induced Protoporphyrin IX) and irradiated with blue light, with UVA without exogenous photosensitizers, or incubated with the metabolic inhibitors carbonyl cyanide m-chlorophenylhydrazone and 2-deoxy-D-glucose. Necrotic and apoptotic cells were detected about 4 h later by fluorescence microscopy. Dead cells appeared in distinct clusters in the confluent layers. The number of dead cells in these clusters was determined by manual counting and image analysis. Forty-one of the 43 experimental distributions of dead cells in clusters were found to be significantly different from a Monte Carlo simulation of the distribution of independently inactivated cells. However, a Monte Carlo simulation model, assuming that each dead cell increased the probability of inactivation of adjacent cells, fitted 34 of the 43 observed distributions of dead cells in clusters, indicating a significant bystander effect for all the investigated treatments. The bystander-effect model parameter, defined as a cell's increase in probability of dying when it has dead neighbors, was significantly lower for 3-THPP-PDT and TPPS4-PDT than for Photofrin-PDT, ALA-PDT and treatment with metabolic inhibitors.

Mitochondrial localization and photodamage during photodynamic therapy with tetraphenylporphines

The subcellular localization sites of TPPS4 and TPPS1 and the subsequent cellular site damage during photodynamic therapy were investigated in CT-26 colon carcinoma cells using spectroscopic and electron microscopy techniques. The association of both porphyrins with the mitochondria was investigated and the implications of this association on cellular functions were determined. Spectrofluorescence measurements showed that TPPS4 favors an aqueous environment, while TPPS1 interacts with lipophilic complexes. The subcellular localization sites of each sensitizer were determined using spectral imaging. Mitochondrial-CFP transfected cells treated with porphyrins revealed localization of TPPS1 in the peri-nuclear region, while TPPS4 localized in the mitochondria, inducing structural damage and swelling upon irradiation, as shown by transmission electron microscopy. TPPS4 fluorescence was detected in isolated mitochondria following irradiation. The photodamage induced a 38% reduction in mitochondrial activity, a 30% decrease in cellular ATP and a reduction in Na(+)/K(+)-ATPase activity. As a result, cytosolic concentrations of Na(+) and Ca(2+) increased, and the level of K(+) decreased. In contrast, the lipophilic TPPS1 did not affect mitochondrial structure or function and ATP content remained unchanged. We conclude that TPPS4 induces mitochondrial structural and functional photodamage resulting in an altered cytoplasmic ion concentration, while TPPS1 has no effect on the mitochondria.

The bystander effect in photodynamic inactivation of cells

Treatment of MDCK II cells with the lipophilic photosensitizer tetra(3-hydroxyphenyl)porphyrin and light was found to induce a rapid apoptotic response in a large fraction of the cells. Furthermore, the distribution of apoptotic cells in microcolonies of eight cells was found to be different from the binomial distribution, indicating that the cells are not inactivated independently, but that a bystander effect is involved in cell killing by photodynamic treatment. The observation of a bystander effect disagrees with the common view that cells are inactivated only by direct damage and indicates that communication between cells in a colony plays a role in photosensitized induction of apoptosis. The degree of bystander effect was higher for cells dying by necrosis than for cell dying by apoptosis.

Plasma membrane associated location of sulfonated meso-tetraphenylporphyrins of different hydrophilicity probed by total internal reflection fluorescence spectroscopy

Sulfonated meso-tetraphenylporphyrins of different hydrophilicity were microspectrofluorimetrically examined in endothelial cells using total internal reflection (TIR) illumination or epi-illumination. Since the penetration depth of the evanescent field during TIR illumination is limited to a few hundred nanometers, photosensitizers were almost selectively examined in close vicinity to the plasma membrane. Pronounced fluorescence signals during TIR illumination were observed for the hydrophilic compounds meso-tetraphenylporphyrin tetrasulfonate (TPPS4) and meso-tetraphenylporphyrin trisulfonate (TPPS3), whereas the more lipophilic compounds meso-tetraphenylporphyrin disulfonate (TPPS2a) and meso-tetraphenylporphyrin monosulfonate (TPPS1) could only be detected under epi-illumination. Irradiation of TPPS1 and TPPS2a in the Soret band led to an increase in fluorescence intensity and formation of a photoproduct with an emission maximum around 610 nm, which was limited to intracellular compartments. In contrast, fluorescence spectra of TPPS3 and TPPS4 obtained by TIR and epi-illumination remained almost unchanged after irradiation in the Soret band. Extralysosomal location of TPPS3 and TPPS4 in close proximity to the plasma membrane was deduced from experiments with the lysosomal markers acridine orange (AO) or lysotracker yellow (LY), which were not detectable under TIR illumination. In conclusion, these results provide for the first time direct evidence for a plasma membrane-associated fraction of the hydrophilic compounds TPPS3 and TPPS4 in living cells.

Spectral analysis of the porphyrins incorporation into human blood

The porphyrins seem to be the most effective photosensitizers in photodynamic therapy of cancer. Monomers and dimers of sulfonated and nonsulfonated porphyrins [5,10,15,20-tetra-phenyl-porphyrin, 5,10,15,20-tetra-naphtyl-porphyrin (TNP), 5,10,15,20-tetra-p-sulfonato-phenyl-porphyrin (TS4PP) and 5,10,15,20-tetra-p-sulfonato-naphtyl-porphyrin], are studied in this paper by means of different spectral methods (UV-vis, fluorescence and polarization fluorescence). The porphyrins as TNP seem to be the most effective photosensitizer especially in a DMSO:water binary mixture of solvent. Monomer-dimer and J-aggregation equilibria and the temperature dependence of TS4PP spectra are also studied in this paper. The incorporation of the forms of these porphyrins into blood cells is studied by means of the cytofluorimetric method. © 1999 Society of Photo-Optical Instrumentation Engineers.

Different apoptotic pathways are induced from various intracellular sites by tetraphenylporphyrins and light

The induction of apoptosis from different intracellular sites was studied by exposing V79 Chinese hamster fibroblasts to photodynamic therapy (PDT) with various porphyrins and light. The effects of two lipophilic, intracellular membrane-localized porphyrins, tetra(3-hydroxyphenyl)porphyrin (3THPP) and Photofrin, were compared with that of two sulphonated meso-tetraphenylporphines (TPPS2a and TPPS4), which are taken up into lysosomes by endocytosis. Apoptotic fractions induced by the various dyes and light were quantified by flow cytometry using the terminal deoxynucleotidyl transferase (TdT) assay. Cell fragmentation was measured in parallel, while the nuclear morphology of apoptotic cells was studied by fluorescence microscopy. Different kinetics were found for the induction of DNA strand breaks characteristic of apoptotic cells. PDT-induced damage to membranes resulted in an increasing number of apoptotic cells for about 12 h after PDT After damage to lysosomes, apoptotic cells were not detected until more than 12 h after PDT. Furthermore, apoptotic bodies were not observed after PDT-induced damage to intracellular membranes, whereas apoptosis induced from lysosomal sites was characterized by extensive cell fragmentation. Cell fragmentation occurred in combination with or in the absence of nuclear fragmentation. The results support the idea that the degradation phase of apoptosis can consist of a sequence of independent steps rather than a common final pathway.

Verapamil enhances the uptake and the photocytotoxic effect of PII, but not that of tetra(4-sulfonatophenyl)porphine

The influence of the calcium channel blocker verapamil on the sensitivity of mouse fibrosarcoma cells of the line EMT-6 to treatment with Photofrin II (PII) or tetra(4-sulfonatophenyl)porphine (TPPS4) and light has been assessed. Cells were treated with 1.5 microg/ml PII or 75 microg/ml TPPS4 overnight in the absence or presence of 50 microg/ml verapamil and subsequently exposed to light. Verapamil increased the sensitivity of the EMT-6 cells to PII-induced photoinactivation by a factor of 2. In contrast, verapamil decreased the sensitivity of the cells to TPPS4-induced photoinactivation by 50-60%. Both sensitizers were found to be located to a large extent in lysosomes as revealed by fluorescence microscopy and by photochemical inactivation of the lysosomal marker enzyme beta-N-acetyl-D-glucosaminidase. Verapamil increased the uptake of PII by 30% and reduced the uptake of TPPS4 by 20%. Furthermore, verapamil enhanced the binding and uptake of LDL by about 40%. In conclusion, the effects of verapamil-induced sensitization of EMT-6 cells treated with PII or TPPS4 and light can to a large extent be attributed to the modulatory effects of verapamil on endocytosis.

Photodynamic efficacy of naturally occurring porphyrins in endothelial cells in vitro and microvasculature in vivo

Photodynamic therapy (PDT) has been described in terms of cellular and vascular effects. The precise mechanisms of cellular and vascular damage are still unknown. In this study, the photodynamic inactivation of endothelial cells in vitro and damage to the microvasculature in vivo by naturally occurring porphyrins (uroporphyrin III (UP), coproporphyrin III (CP) and protoporphyrin IX (PP)) were investigated. The chick chorioallantoic membrane model (CAM model) was used, which is convenient for the study of damage to the microcirculation induced by PDT. The hydrophilic porphyrins UP and CP exhibited low cytotoxicity towards endothelial cells. Only small amounts of UP and CP were taken up, resulting in weak inactivation after irradiation. In contrast, the more lipophilic PP showed a marked cytotoxicity. Considerable amounts of PP were accumulated in the cells, leading to pronounced inactivation after light exposure. For the three porphyrins, damage to the microvasculature was observed. The damage caused by the hydrophilic porphyrins UP and CP was strongly dependent on the drug and light dose. For vascular injury, the efficacy was graded as UP < CP < PP.

Interaction of hydro- or lipophilic phthalocyanines with cells of different metastatic potential

A highly metastatic (4R) and a nonmetastatic (RE4) transformed rat embryo fibroblast cell line were incubated with lipid-soluble Zn(II)-phthalocyanine (ZnPc) and its water-soluble tetrasulphonated derivative (ZnPcTS) and compared for phthalocyanine uptake. The hydrophobic liposome-delivered ZnPc showed a significantly greater uptake by both cell lines than did ZnPcTS. Moreover, the two phthalocyanines appear to interact with cells according to different pathways, as suggested by the different temperature-dependence of the binding process and the different inhibitory action exerted by selected serum proteins, such as lipoproteins and heavy proteins. Under all experimental conditions, the two cell lines exhibited similar interactions with ZnPc and ZnPcTS, suggesting that heterogeneity of the tumor cell population has a minor influence on the accumulation of photosensitizers.

Subcellular damage kinetics within co-cultivated WI38 and VA13-transformed WI38 human fibroblasts following 5-aminolevulinic acid-induced protoporphyrin IX formation

The generation of the photosensitizer protoporphyrin IX (PpIX) in cells can be induced by externally applied 5-aminolevulinic acid (ALA), with that bypassing the feedback control mechanism. The aim of the present study was to investigate the onset of destructive changes in living cocultivated WI38 and VA13-transformed WI38 human fibroblasts following ALA incubation, PpIX production and subsequent irradiation by white halogen light with a dose of 2.2 kJ/m2. Specific fluorescence markers such as 3,3'-dihexyloxacarbocyanine iodide for endoplasmic reticulum (ER) staining and dihydrorhodamine for intact mitochondria mapping combined with a low light imaging system are a versatile and sensitive tool to examine the photoinduced destruction of organelles in living cells, while artifacts are minimized. Mitochondria as primary targets of PpIX undergo a condensation under irradiation and are finally destroyed. Photodynamic treatment induces further a significant decomposition of ER, although PpIX localization could not be determined. Initial destabilization and vesiculation of ER is followed by a porous network with large cisternae (indicating the breakdown of cell integrity and cell/nucleus membrane damage). Normal cocultivated lung fibroblasts showed a delay in destruction compared to the transformed WI38-VA13 cells. The observed decomposition pattern resembles the morphological pattern of apoptosis.

Photophysical properties of porphyrins in biological membranes

This review illustrates the photophysical properties of some porphyrins, especially those used for biomedical applications, in relation to their photosensitizing efficiency in biological membranes. Porphyrin absorption and luminescence properties are mainly examined. The factors influencing the affinity of porphyrins for biological membranes, including the dye hydrophobicity, the charge and aggregation state, the pH of the medium and the physicochemical properties of the dye environment, are discussed. These factors determine the differences in the photophysical properties of porphyrins in biological membranes. Particular attention is paid to the porphyrin aggregation state: only monomeric species and possibly planar end-to-end aggregates are endowed with significant photosensitizing ability. Many conclusions presented are based on data obtained on membrane model systems such as micelles or liposomes which can mimic specific situations occurring in cells.

Intracellular fluorescence behaviour of meso-tetra(4-sulphonatophenyl)porphyrin during photodynamic treatment at various growth phases of cultured cells

Meso-tetra(4-sulphonatophenyl)porphyrin (TPPS4) taken up by cells is mainly localized in lysosomes as previously shown by fluorescence microscopical and fluorescence spectroscopical investigations. In the present study the intracellular fluorescence behaviour and the intracellular amount of this dye at various growth periods of cells were examined. For cells irradiated in the growth phase a relocalization of TPPS4 from the lysosomes into the cytoplasm and finally into the nucleus was observed. In contrast, for cells irradiated in the stationary phase no redistribution could be detected and therefore no evidence for severe damage of the lysosomal membranes and subsequently for the release of lytical enzymes is given. In both cases lethal damage of the cells was achieved as examined using the trypan blue exclusion test. This indicates that damage of the lysosomes is less important in the photodynamic inactivation of cells sensitized by TPPS4.

Photosensitization with derivatives of chlorin p6

Biophysical and photobiological properties of three derivatives of chlorin p6 were examined. These agents can be considered as lysyl analogs of the aspartyl chlorin NPe6. Lysyl chlorin p6 diester (LCP) and the triester analog (LCP2) were readily accumulated by murine leukemia L1210 cells, localized in lysosomes, and were relatively inefficient photosensitizing agents in vitro. In contrast, lysyl chlorin e6 imide (LCI) was poorly accumulated, concentrated in mitochondrial and plasma membranes, but was more efficacious. LCI was the most effective agent with regard to photosensitization of a murine tumor in vivo, but all three agents caused substantially more toxicity than was observed with NPe6.

Time-resolved pH-dependent fluorescence of hydrophilic porphyrins in solution and in cultivated cells

Fluorescence decay kinetics and time-gated (nanosecond) emission spectra of the hydrophilic photosensitizers meso-tetra(4-sulfonatophenyl)porphyrin (TPPS4) and uroporphyrin III (UP III) are reported. These substances are characterized by low aggregation, preferential accumulation within lysosomes and a pH-dependent composition of unprotonated and protonated species. A comparison of TPPS4 and UP III in buffer solutions and in confluently growing RR 1022 epithelial cells showed that the intracellular pH value of the environment of both photosensitizers was about 4.7. A slight decrease by 0.10-0.15 pH units occurred after light exposure which (in the case of TPPS4) was concomitant with a lethal damage of the cells. A photoproduct at 640 nm with a characteristic fluorescence lifetime of 4.3 +/- 0.8 ns was detected for UP III in buffer solutions at pH values above 5. The absence of this photoproduct in epithelial cells again indicated that UP III was located within lysosomes.

Lysosomes as photochemical targets

Sulfonated tetraphenyl porphines (TPPSn) are photosensitizing dyes that localize in lysosomes of NHIK 3025 cells. In order to elucidate the mechanisms of cell inactivation by photochemical treatment with TPPSn, lysosomal enzyme inactivation and release of lysosomal contents were examined after treatment. In cells treated with TPPS4 and light, the lysosomal enzymes beta-N-acetyl-D-glucosaminidase (beta-AGA) and cathepsin(L+B) were almost completely inactivated and no enzyme activities were released from the lysosomes. In contrast, a maximum of 30 and 50% of the initial beta-AGA activity was released from lysosomes after treatment with TPPS1 and TPPS2a, respectively. Forty per cent of the initial beta-AGA activity was released after treatment with TPPS2a and a non-cytotoxic dose of light. After such a treatment only approximately 10% of the initial cathepsin activity was found in the cytosol fraction and in all other cases no cathepsin activity was recovered in the cytosol fraction after photochemical treatment. It was found that the constituents of the cytosol partly inhibited cathepsin activity. This inhibitory effect was not influenced by the photochemical treatment, neither was the colony-forming ability of photochemically treated cells influenced by pre-treatment with the cathepsin inhibitor E64. The present results indicate that NHIK 3025 cells are not killed by lysosomal disruption after photochemical treatment. This is partly due to photochemical inactivation of the lysosomal enzymes and to the action of cytosolic cysteine cathepsin inhibitors. The present results also indicate that cells can survive a partial lysosomal disruption.

No correlation between DNA strand breaks and HPRT mutation induced by photochemical treatment in V79 cells

DNA strand breaks, measured by alkaline elution, and hypoxanthine guanine phosphoribosyltransferase (HPRT) mutation were studied in V79 cells after photochemical treatment (PCT) or exposure to X-rays. Cells were incubated with the photosensitizers Photofrin II (PII) and three closely related porphyrins tetra-(3-hydroxyphenyl) porphyrin (3THPP), meso-tetra-(4-sulfonatophenyl) porphine (TPPS4) and meso-tetra-(N-methyl-4-pyridyl) porphine (TMPyPH2). These dyes are assumed to act on cellular targets mainly via singlet oxygen when excited by light. While the hydrophilic TPPS4 and TMPyPH2 did not photoinduce mutants to any significant extent, both lipophilic dyes, 3THPP and PII, were significantly mutagenic when excited by light. On the other hand, TPPS4 was the most efficient sensitizer of alkali-labile DNA strand breaks, while TMPyPH2 did not induce any significant amount of either type of DNA damage. Surprisingly, no correlation between the two parameters was found for PCT, either after exposures inactivating 50% of the cells or after exposures inactivating 90% of them. The lack of correlation between the yields of DNA strand breaks and of mutants could not be explained by differences in the intracellular localization pattern of the dyes.

Photochemical treatment with the lysosomally localized dye tetra(4-sulfonatophenyl)porphine results in lysosomal release of the dye but not of beta-N-acetyl-D-glucosaminidase activity

Tetra(4-sulfonatophenyl)porphine (TPPS4) sensitizes cells to photoinactivation mainly through formation of singlet oxygen. In human cervix carcinoma cells of the line NHIK 3025 TPPS4 localizes to a large extent in lysosomes as previously shown by fluorescence microscopical and spectroscopical techniques. In the present study photodamage to lysosomes was investigated. This was accomplished by measuring the activity of the lysosomal marker enzyme beta-N-acetyl-D-glucosaminidase (beta-AGA) after photochemical treatment (PCT). beta-AGA activity was highly sensitive to light exposure in the presence of TPPS4. The enzymatic activity was reduced by approximately 70% by non-lethal doses of photochemical treatment, indicating that inactivation of lysosomal hydrolases is not likely to contribute significantly to the cytotoxic effects of PCT. Centrifugation studies showed that TPPS4, but not beta-AGA activity, was released from lysosomes after light exposure. 20-30% of the total beta-AGA activity was resistant to the photochemical treatment. This was due to beta-AGA activity in Golgi-derived vesicles (4-5%) and in vesicles with similar density as lysosomes but not containing TPPS4. The present results indicate that lysosomal hydrolases are inactivated by photochemical treatment before they eventually escape the lysosomal compartment.

Lysosomes, a key target of hydrophobic photosensitizers proposed for photochemotherapeutic applications

Despite their important biological activity, lysosomes have been generally neglected as important primary targets of photosensitizers, because they are not easily accessible for experiments. This paper reviews factors favoring the localization of photosensitizers in lysosomes and the various experimental approaches which have been used so far for the characterization of the lysosomal staining by various photosensitizing dyes, including porphyrins, chlorins and phenoxazines. The experimental difficulties observed in combining several in vitro techniques for the unambiguous demonstration of lysosomal targeting are examined. New data on tetraphenylporphine derivatives and a pyropheophorbide, as well as previous data on photofrin II, are presented to illustrate the advantages and possibilities of microspectrofluorometry in the study of photosensitizer localization in single living cells. Both spectral and topographic information available from areas smaller than 1 microns2 make it possible to characterize fairly specific sites of localization through the use of specific and vital fluorescent probes of lysosomes, such as Lucifer Yellow. It is also shown by microspectrofluorometry on single living cells that the chronology of the photosensitized reactions induced by specific or unspecific lysosomal photosensitizers can be easily followed. The photosensitized lipofuscin formation observed at the plasma membrane level with the lysosomotropic tetraphenylporphine supports the contention that it is very rare to find a truly specific lysosomal photosensitizer.