Interdependence of fluence, drug dose and oxygen on hematoporphyrin derivative induced photosensitization of tumor mitochondria

Imaging and Histopathological Analysis of Microvascular Angiogenesis in Photodynamic Therapy for Oral Cancer

The objective of this study is to use imaging and histopathological analysis to characterize and monitor microvascular responses to photodynamic therapy (PDT). In vivo chicken chorioallantoic membranes (CAMs) and a stimulated malignant oral lesions animal model were used to determine the blood flow and the biological activities of Photofrin^® (2.5 mg/kg) exposed to different laser power densities at 630 nm. The vascular changes, the velocity of the blood flow, the speckle flow index (SFI) of fluorescence changes, and ultrastructure damage in the microvasculature before and after PDT were recorded. The subcellular localization of Photofrin^® revealed satisfactory uptake throughout the cytoplasm of human red blood cells at 10 s and 20 s before PDT. The mean blood-flow velocities of the veins and arteries were 500 ± 40 and 1500 ± 100 μm/s, respectively. A significant decrease in the velocities of the blood flow in the veins and arteries was detected in the CAM model after PDT. The veins and arteries of CAMs, exposed to the power densities of 80, 100, and 120 mW/cm², had average blood-flow velocities of 100 ± 20, 60 ± 10, and 0 μm/s and 300 ± 50, 150 ± 30, and 0 μm/s, respectively. In the stimulated malignant oral lesions animal model, the treated tumors exhibited hemorrhage and red blood cell extravasation after PDT. The oxyhemoglobin and total hemoglobin levels decreased, which resulted in a decrease in tissue oxygen saturation, while the deoxyhemoglobin levels increased. PDT using Photofrin^® has the ability to cause the destruction of the targeted microvasculature under nonthermal mechanisms selectively.

Biophysical Characterization and Anticancer Activities of Photosensitive Phytoanthraquinones Represented by Hypericin and Its Model Compounds

Photosensitive compounds found in herbs have been reported in recent years as having a variety of interesting medicinal and biological activities. In this review, we focus on photosensitizers such as hypericin and its model compounds emodin, quinizarin, and danthron, which have antiviral, antifungal, antineoplastic, and antitumor effects. They can be utilized as potential agents in photodynamic therapy, especially in photodynamic therapy (PDT) for cancer. We aimed to give a comprehensive summary of the physical and chemical properties of these interesting molecules, emphasizing their mechanism of action in relation to their different interactions with biomacromolecules, specifically with DNA.

E, Cruces M. MP, Sánchez M. JC. Genetic damage induced by CrO3 can be reduced by low doses of Protoporphyrin-IX in somatic cells of Drosophila melanogaster

Several epidemiological studies have reported the relation between chromium exposure (used in different industrial processes) and cancer risk. Evidence indicates that the hexavalent form is mutagenic and carcinogenic. Chemoprevention has emerged as a good strategy for reducing the risk from exposure to heavy metals. There is evidence that some tetrapyrrols such as protoporphyrin IX (PP-IX), a porphyrin without a metal center and which is a precursor of hemoglobin and cytochrome, acts as an antioxidant modulating the induction of antioxidant enzymes. The present study was performed to evaluate their antimutagenic potential of PP-IX against genetic damage induced by chromium trioxide (CrO3). The wing spot test was used. Groups of 48 h-old larvae were pretreated for 24 h with 0, 0.69, 6.9, or 69 mM of PP-IX, after which groups of larvae were fed 0.025-2.5 mM CrO3 solution in Drosophila instant medium. The results indicated that the lower PP-IX concentration (0.69 mM) significantly reduced the genetic damage induced by all CrO3 concentrations tested. In contrast, 6.9 and 69 mM only inhibited the damage induced by CrO3 2.5 mM. Absence of an inhibitor effect of PP-IX against 20 Gy gamma rays suggested that this porphyrin acted primarily by forming complexes with chromium at low doses, inactivating its genotoxic action rather than capturing or inactivating the reactive oxygen species generated by the chromium.

Drug and light dose responses to focal photodynamic therapy of single blood vessels in vivo

As part of an ongoing program to develop two-photon (2-gamma) photodynamic therapy (PDT) for treatment of wet-form age-related macular degeneration (AMD) and other vascular pathologies, we have evaluated the reciprocity of drug-light doses in focal-PDT. We targeted individual arteries in a murine window chamber model, using primarily the clinical photosensitizer Visudyne/liposomal-verteporfin. Shortly after administration of the photosensitizer, a small region including an arteriole was selected and irradiated with varying light doses. Targeted and nearby vessels were observed for a maximum of 17 to 25 h to assess vascular shutdown, tapering, and dye leakage/occlusion. For a given end-point metric, there was reciprocity between the drug and light doses, i.e., the response correlated with the drug-light product (DLP). These results provide the first quantification of photosensitizer and light dose relationships for localized irradiation of a single blood vessel and are compared to the DLP required for vessel closure between 1-gamma and 2-gamma activation, between focal and broad-beam irradiation, and between verteporfin and a porphyrin dimer with high 2-gamma cross section. Demonstration of reciprocity over a wide range of DLP is important for further development of focal PDT treatments, such as the targeting of feeder vessels in 2-gamma PDT of AMD.

Suppression of sphingomyelin synthase 1 by small interference RNA is associated with enhanced ceramide production and apoptosis after photodamage

We have shown that overexpression of SMS1, an enzyme that converts de novo ceramide into sphingomyelin, is accompanied by attenuated ceramide response and apoptotic resistance after photodamage with the photosensitizer Pc 4 (photodynamic therapy; PDT). To test whether SMS1 overexpression-related effects after PDT can be reversed, in this study SMS1 was downregulated in Jurkat T lymphoma/leukemia cells using small inhibitory RNA (siRNA) for SMS1. Compared to scrambled (control) siRNA-transfectants, in SMS1 siRNA-transfected cells the activity of SMS at rest was downregulated with concomitant decrease in sphingomyelin mass. In SMS1 siRNA-transfected cells increases in ceramides were higher than in control siRNA-transfectants after PDT. Similar findings were obtained for dihydroceramides suggesting the involvement of de novo ceramide pathway. PDT-induced DEVDase (caspase-3-like) activation was enhanced in SMS1 siRNA-transfected cells compared to their control counterparts. The data show that RNA interference-dependent downregulation of SMS1 is associated with increased accumulation of ceramide and dihydroceramide with concomitant sensitization of cells to apoptosis after photodamage. Similarly, in SMS2 siRNA-transfected cells, downregulation of SMS activity was accompanied by potentiated DEVDase activation post-photodamage. These findings suggest that SMS is a potential novel molecular target that can augment therapeutic efficacy of PDT.

A role for manganese superoxide dismutase in apoptosis after photosensitization

The oxidative stress triggered by photodynamic therapy (PDT) involves generation of cytotoxic reactive oxygen species, including superoxide radical, accumulation of de novo-generated ceramide, and induction of apoptosis. Since PDT with the photosensitizer phthalocyanine Pc 4 induces mitochondrial damage and the superoxide scavenger manganese superoxide dismutase (MnSOD) is localized to mitochondria, here we tested genetically the role of MnSOD in apoptosis and ceramide accumulation after photosensitization with Pc 4. Jurkat cells overexpressing wild-type MnSOD were protected from Pc 4-PDT-initiated apoptosis, but not from increased ceramide response to Pc 4-PDT. In Jurkat cells overexpressing mutant MnSOD, however, DEVDase activation and ceramide formation were promoted post-Pc 4-PDT. Similarly, in MnSOD-null cells, Pc 4-PDT-induced apoptosis, as well as ceramide accumulation, were enhanced compared to their normal counterparts. The data show that MnSOD affects sensitivity of cells to Pc 4-PDT-initiated apoptosis, and partly ceramide accumulation, suggesting that the processes are superoxide-mediated.

Redox ratio of mitochondria as an indicator for the response of photodynamic therapy

The effect of photodynamic therapy (PDT) treatment on the metabolic state of tumor mitochondria is investigated by imaging of tumor redox status. PDT is performed using the photosensitizer pyropheophorbide-2-deoxyglucosamide (Pyro-2DG), which utilizes the glucose import pathway. It is found that Pyro-2DG-induced PDT resulting in a highly oxidized state of tumor mitochondria. This is determined from the redox ratio changes derived from the intrinsic oxidized flavoprotein (Fp) and reduced pyridine nucleotide (PN) [i.e., reduced nicotinamide adenine dinucleotide (NADH)] fluorescence signals observed using a cryoimager. Thus, the redox ratio is a sensitive indicator for providing reliable and informative measurements of PDT-induced tissue damage. In the PDT treated region of the tumor, highly oxidized flavoprotein and diminishing NADH fluorescence is detected, suggesting that flavoprotein and NADH are oxidized by singlet oxygen produced in the photosensitization process.

Characterization of the photoproducts of protoporphyrin IX bound to human serum albumin and immunoglobulin G

Clinically useful photosensitisers (PSs) are likely bound to subcellular and molecular targets during phototherapy. Binding to a macromolecule has the potential to change the photophysical and photochemical characteristics of the PSs that are crucial for their phototoxicity and cell-killing activity. We investigated the effects of binding of a specific PS (protoporphyrin IX or PPIX) to two proteins, human serum albumin (HSA) and a commercially available immunoglobulin (IgG). These two proteins provide two different environments for PPIX. The albumin binds PPIX in hydrophobic binding sites located in subdomain IIA and IIIA, conversely IgG leaves PPIX exposed to the solvent. We show that photophysical parameters such as emission maxima and fluorescence lifetime depend on the binding site. Our results indicate that the different binding site yields very different rates of formation of photoproducts (more than three times higher for PPIX bound to HSA than to IgG) and that different mechanisms of formation may be occurring. Our characterization shows the relevance of protein binding for the photochemistry and ultimately the phototoxicity of PSs.

Monitoring in situ dosimetry and protoporphyrin IX fluorescence photobleaching in the normal rat esophagus during 5-aminolevulinic acid photodynamic therapy

Experimental therapies for Barrett's esophagus, such as 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT), aim to ablate the premalignant Barrett's epithelium. However, the reproducibility of the effects should be improved to optimize treatment. Accurate irradiation with light of a proper wavelength (633 nm), fluence and fluence rate has shown to be critical for successful ALA-PDT. Here, we have used in situ light dosimetry to adjust the fluence rate measured within the esophagus for individual animals and monitored protoporphyrin IX (PpIX) fluorescence photobleaching simultaneously. Rats were administered 200 mg kg-1 ALA (n = 14) or served as control (n = 7). Animals were irradiated with an in situ measured fluence rate of 75 mW cm-2 and a fluence of 54 J cm-2. However, this more accurate method of light dosimetry did not decrease the variation in tissue response. Large differences were also observed in the dynamics of PpIX fluorescence photobleaching in animals that received the same measured illumination parameters. We found that higher PpIX fluorescence photobleaching rates corresponded with more epithelial damage, whereas lower rates corresponded with no response. A two-phased decay in PpIX fluorescence could be identified in the response group, with a rapid initial phase followed by a slower rate of photobleaching. Non-responders did not show the rapid initial decay and had a significantly lower rate of photobleaching during the second phase of the decay (P = 0.012).

Monitoring In Situ Dosimetry and Protoporphyrin IX Fluorescence Photobleaching in the Normal Rat Esophagus During 5-Aminolevulinic Acid Photodynamic Therapy¶

Experimental therapies for Barrett's esophagus, such as 5-aminolevulinic acid (ALA)-based photodynamic therapy (PDT), aim to ablate the premalignant Barrett's epithelium. However, the reproducibility of the effects should be improved to optimize treatment. Accurate irradiation with light of a proper wavelength (633 nm), fluence and fluence rate has shown to be critical for successful ALA-PDT. Here, we have used in situ light dosimetry to adjust the fluence rate measured within the esophagus for individual animals and monitored protoporphyrin IX (PpIX) fluorescence photobleaching simultaneously. Rats were administered 200 mg kg-1 ALA (n = 14) or served as control (n = 7). Animals were irradiated with an in situ measured fluence rate of 75 mW cm-2 and a fluence of 54 J cm-2. However, this more accurate method of light dosimetry did not decrease the variation in tissue response. Large differences were also observed in the dynamics of PpIX fluorescence photobleaching in animals that received the same measured illumination parameters. We found that higher PpIX fluorescence photobleaching rates corresponded with more epithelial damage, whereas lower rates corresponded with no response. A two-phased decay in PpIX fluorescence could be identified in the response group, with a rapid initial phase followed by a slower rate of photobleaching. Non-responders did not show the rapid initial decay and had a significantly lower rate of photobleaching during the second phase of the decay (P = 0.012).

The role of apoptosis in response to photodynamic therapy: what, where, why, and how

Photodynamic therapy (PDT), a treatment for cancer and for certain benign conditions, utilizes a photosensitizer and light to produce reactive oxygen in cells. PDT is primarily employed to kill tumor and other abnormal cells, so it is important to ask how this occurs. Many of the photosensitizers currently in clinical or pre-clinical studies of PDT localize in or have a major influence on mitochondria, and PDT is a strong inducer of apoptosis in many situations. The purpose of this review is to critically evaluate all of the recently published research on PDT-induced apoptosis, with a focus on studies providing mechanistic insights. Components of the mechanism whereby PDT causes cells to undergo apoptosis are becoming understood, as are the influences of several signal transduction pathways on the response. Future research should be directed to elucidating the role(s) of the multiple steps in apoptosis in directing damaged cells to an apoptotic vs. necrotic pathway and for producing tumor ablation in conjunction with tissue-level mechanisms operating in vivo.

Photosensitization with hematoporphyrin derivative compared to 5-aminolaevulinic acid for photodynamic therapy of esophageal carcinoma

BACKGROUND

Hematoporphyrin derivatives (HpD) as sensitizers for photodynamic therapy (PDT) in advanced esophageal cancer carry the risk of prolonged photosensitivity of the skin. New sensitizers such as 5-aminolaevulinic acid (ALA) with low rates of skin phototoxicity appear to be promising alternatives. The aim of this study was to evaluate the efficacy of ALA compared with HpD for PDT in advanced esophageal carcinoma regarding phototoxicity of the skin, reduction of dysphagia, tumor stenosis and length, and Karnovsky performance status.

METHODS

After diagnostic workup, photosensitization was done in 22 patients with ALA (60 mg/kg body weight, oral, 6 to 8 hours before PDT) and in 27 patients with a hematoporphyrin derivative (2 mg/kg body weight, intravenously, 48 hours before PDT). The light dose was calculated as 300 J/cm fiber tip. Light at 630 nm was applied using a pumped dye laser. In both groups, additional hyperbaric oxygenation was applied at a level of 2 absolute atmospheric pressure.

RESULTS

Improvement regarding dysphagia, stenosis diameter, and tumor length could be obtained in both treatment arms with a significant difference in favor of the HpD group (p = 0.02; p = 0.0000; and p = 0.000014, respectively). A questionnaire of patients in the HpD group confirmed that the ability of swallowing a meal was superior compared with the discomfort from limitation to sun exposure. No sunburn or other major treatment-related complication occurred in both treatment arms.

CONCLUSIONS

Despite the limitations of a nonrandomized study, photosensitzation with HpD seems to be more effective in PDT of advanced esophageal carcinoma compared with ALA.

Combined photodynamic therapy and hyperbaric oxygenation in carcinoma of the esophagus and the esophago-gastric junction

OBJECTIVES

The photochemical reaction of photodynamic therapy (PDT) depends on the presence of molecular oxygen. Due to anoxic regions in tumor tissue and vascular shutdown during PDT the efficiency is limited. Therefore, the use of hyperbaric oxygen which increases the oxygen in tumor tissue, as well as the amount of singlet oxygen, may enhance the efficiency of PDT.

PATIENTS AND METHODS

After diagnostic work-up, photosensitization was carried out with a hematoporphyrin-derivate 2 mg/kg BW 48 h prior to PDT. The light dose was calculated as 300 J/cm fiber tip. Thirty-one patients were treated by PDT alone and 44 patients received PDT under hyperbaric oxygen at a level of two absolute atmospheric pressure.

RESULTS

Improvement regarding stenosis-diameter could be obtained in both treatment arms with no significant difference (P=0.82). The dysphagia-score and tumor-length also decreased in both groups and showed a significant difference in favour of the PDT/HBO-group (P=0. 0064 and P=0.0002, respectively). The median overall survival for the PDT-group was 7 months and for the PDT/HBO-group 12 months (P=0. 0098).

CONCLUSION

According to this prospective non-randomized study, combined PDT/HBO represents a new approach in the treatment of esophageal and cardia cancer which appears to have enhanced the efficiency of PDT.

A selenopyrylium photosensitizer for photodynamic therapy related in structure to the antitumor agent AA1 with potent in vivo activity and no long-term skin photosensitization

Cationic chalcogenopyrylium dyes 5 were synthesized in six steps from p-aminophenylacetylene (9), have absorption maxima in methanol of 623, 654, and 680 nm for thio-, seleno-, and telluropyrylium dyes, respectively, and generate singlet oxygen with quantum yields [Phi((1)O(2))] of 0.013, 0.029, and 0.030, respectively. Selenopyrylium dye 5-Se was phototoxic to cultured murine Colo-26 and Molt-4 cells. Initial acute toxicity studies in vivo demonstrate that, at 29 mg (62 micromol)/kg, no toxicity was observed with 5-Se in animals followed for 90 days under normal vivarium conditions. In animals given 10 mg/kg of 5-Se via intravenous injection, 2-8 nmol of 5-Se/g of tumor was found at 3, 6, and 24 h postinjection. Animals bearing R3230AC rat mammary adenocarcinomas were treated with 10 mg/kg of 5-Se via tail-vein injection and with 720 J cm(-2) of 570-750-nm light from a filtered tungsten lamp at 200 mW cm(-2) (24 h postinjection of 5-Se). Treated animals gave a tumor-doubling time of 9 +/- 4 days, which is a 300% increase in tumor-doubling time relative to the 3 +/- 2 days for untreated dark controls. Mechanistically, the mitochondria appear to be a target. In cultured R3230AC rat mammary adenocarcinoma cells treated with 0.1 and 1.0 microM 5-Se and light, mitochondrial cytochrome c oxidase activity was inhibited relative to cytochrome c oxidase activity in untreated cells. Irradiation of isolated mitochondrial suspensions treated with 10 microM dye 5-Se inhibited cytochrome c oxidase activity. The degree of enzyme inhibition was abated in a reduced oxygen environment. Superoxide dismutase, at a final concentration of 30 U, did not alter the photosensitized inhibition of mitochondrial cytochrome c oxidase by dye 5-Se. The data suggest that singlet oxygen may play a major role in the photosensitized inhibition of mitochondrial cytochrome c oxidase.

In vivo photodynamic characteristics of the near-infrared photosensitizer 5,10,15,20-tetrakis(M-hydroxyphenyl) bacteriochlorin

This paper describes the photodynamic characteristics of the new near-infrared photosensitizer 5,10,15,20-tetrakis(m-hydroxyphenyl)bacteriochlorin (mTHPBC or SQN400) in normal rat and mouse tissues. A rat liver model of photodynamic tissue necrosis was used to determine the in vivo action spectrum and the dose-response relationships of tissue destruction with drug and light doses. The effect of varying the light irradiance and the time interval between drug administration and light irradiation on the biological response was also measured in the rat liver model. Photobleaching of mTHPBC was measured and compared with that of its chlorine analog (mTHPC) in normal mouse skin and an implanted mouse colorectal tumor. The optimum wavelength for biological activation of mTHPBC in rat liver was 739 nm. mTHPBC was found to have a marked drug-dose threshold of around 0.6 mg kg-1 when liver tissue was irradiated 48 h after drug administration. Below this administered drug dose, irradiation, even at very high light doses, did not cause liver necrosis. At administered doses above the photodynamic threshold the effect of mTHPBC-PDT was directly proportional to the product of the drug and light doses. No difference in the extent of liver necrosis produced by mTHPBC was found on varying the light irradiance from 10 to 100 mW cm-2. The extent of liver necrosis was greatest when tissue was irradiated shortly after mTHPBC administration and necrosis was absent when irradiation was performed 72 h or later after drug administration, suggesting that the drug was rapidly cleared from the liver. In vivo photobleaching experiments in mice showed that the rate of bleaching of mTHPBC was approximately 20 times greater than that of mTHPC. It is argued that this greater rate of bleaching accounts for the higher photodynamic threshold and this could be exploited to enhance selective destruction of tissues which accumulate the photosensitizer.

In vitro and in vivo photosensitizing capabilities of 5-ALA versus photofrin in vascular endothelial cells

BACKGROUND AND OBJECTIVE

The objective of the present study was to evaluate the feasibility of photodynamic therapy (PDT) for complicated hemangiomas. The photosensitizing activities of 5-aminolevulinic acid (5-ALA) and Photofrin were evaluated in vitro with human dermal microvascular endothelial cells (MEC) and in vivo with the chicken cox comb.

STUDY DESIGN/MATERIALS AND METHODS

The in vitro absorption and photosensitizing activities of 5-ALA and Photofrin were examined in a MEC culture system. The percentages of MEC killed by different drug concentrations at a wavelength of 630 nm were measured by either live/dead or lactate dehydrogenase-released assays. Similarly, the in vivo biological activities of 5-ALA and Photofrin exposed to different total light dosages at 630 nm were studied by determining the amount of necrosis produced in chicken combs.

RESULTS

MEC incubated with 5-ALA at a concentration of 35 microg/ml and exposed to laser light at 630 nm at a power density of 100 mW/cm2 showed a 50% cell kill. MEC incubated with Photofrin at a concentration of 3.5 microg/ml and exposed to laser light at 630 nm at a power density of 100 mW/cm2 showed a 50% cell kill. Chicken combs that received 200 mg/kg of 5-ALA exposed to laser light at 630 nm at a power density of 100 mW/cm2 had an injury depth of 362.5+/-27.6 microm at histologic examination. Combs exposed to a power density of 100 or 120 mW/cm2 showed injury depths of 732.5+/-29.1 and 792.5+/-36.0 microm, respectively. Chicken combs that received 2.5 mg/kg of Photofrin exposed to laser light at 630 nm at a power density of 80 mW/cm2 had an injury depth of 535.6+/-22.3 microm at histologic examination. Combs exposed to a power density of 100 or 120 mW/cm2 showed injury depths of 795.8+/-32.5 and 805.2+/-49.1 microm, respectively.

CONCLUSION

Both 5-ALA and Photofrin have the capability to destroy MEC in vitro and vasculature in vivo. However, Photofrin achieved a higher degree of cell kill and tissue destruction at lower drug concentrations and at lower power densities.

Hyperbaric oxygen and photodynamic therapy in the treatment of advanced carcinoma of the cardia and the esophagus

BACKGROUND AND OBJECTIVE

The photochemical reaction of photodynamic therapy (PDT) depends on the presence of molecular oxygen. Because of anoxic regions in tumor tissue and vascular shutdown during PDT, the efficiency is limited. Therefore, the use of hyperbaric oxygen, which increases the oxygen in tumor tissue, as well as the amount of singlet oxygen, may enhance the efficiency of PDT.

STUDY DESIGN/MATERIALS AND METHODS

After diagnostic work-up, photosensitization was carried out with a hematoporphyrin-derivate 2 mg/kg body weight 48 hours before PDT. The light dose was calculated as 300 J/cm of fiber tip. Twenty-three patients were treated by PDT alone and 29 patients received PDT under hyperbaric oxygen at a level of two absolute atmospheric pressures.

RESULTS

Improvement regarding dysphagia and stenosis-diameter could be obtained in both treatment arms with no significant difference (P = 0.43 and P = 0. 065, respectively). The tumor length also decreased in both groups and showed a significant difference in favour of the PDT/HBO group (P = 0.002). The mean overall survival was 11.3 months. The mean survival time for the PDT group was 8.7 months and for the PDT/HBO group 13.8 months (P = 0.021).

CONCLUSION

According to this pilot study, combined PDT/HBO represents a new approach in the treatment of esophageal and cardia cancer, which appears to have enhanced the efficiency of PDT.

2,4,6-triarylchalcogenopyrylium dyes related in structure to the antitumor agent AA1 as in vitro sensitizers for the photodynamic therapy of cancer

Cationic chalcogenopyrylium dyes 2-4 were synthesized in six steps from 4-(dimethylamino)phenylethyne (7), have absorption maxima in methanol of 594, 631, and 672 nm, respectively, and generate singlet oxygen with quantum yields [Phi((1)O(2))] of 0.020, 0.064, and 0.037, respectively. Dyes 2-4 are hydrolytically more stable than other chalcogenopyrylium dyes evaluated previously as sensitizers for photodynamic therapy. At 10 microM final concentration, all dyes 2-4 inhibited cytochrome c oxidase during irradiation of tumor mitochondrial suspensions treated with 10 microM dye. The degree of enzyme inhibition was abated in a reduced oxygen environment and in the presence of imidazole, a singlet oxygen trap. Superoxide dismutase, at a final concentration of 30 U, did not alter the photosensitized inhibition of mitochondrial cytochrome c oxidase by dyes 2-4. These data suggest that singlet oxygen may play a major role in the photosensitized inhibition of mitochondrial cytochrome c oxidase. Irradiation of R3230AC rat mammary adenocarcinoma cells in the presence of dyes 2-4 caused a significant loss in cell viability with thiopyrylium dye 2 displaying the greatest phototoxicity. Initial acute toxicity studies in vivo demonstrate that, at 10 mg/kg, none of the three dyes displayed overt toxicity.

Photodynamic therapy-induced apoptosis in lymphoma cells: translocation of cytochrome c causes inhibition of respiration as well as caspase activation

L5178Y-R mouse lymphoma (LY-R) cells undergo rapid apoptosis when treated with photodynamic therapy (PDT) sensitized with the silicon phthalocyanine Pc 4. In this study we show that cytochrome c is released into the cytosol within 10 min of an LD99.9 dose of PDT. Cellular respiration is inhibited by 42% at 15 min, and 60% at 30 min after PDT treatment, and caspase 3-like protease activity is elevated by 15 min post-PDT. In digitonin-permeabilized cells addition of cytochrome c to the respiration buffer reverses PDT-induced inhibition of state 3 respiration via Complex I by 40-60%, and via Complex III by 50-90%. In contrast, extramitochondrial cytochrome c does not stimulate respiration in permeabilized control cells, and catalyzes only a low rate of oxygen consumption via electron transfer to cytochrome b5 on the outer mitochondrial membrane. These results demonstrate that PDT-induced inhibition of respiration is primarily due to leakage of cytochrome c into the cytosol rather than to damage to the major enzyme complexes of the electron transport chain. Whether or not inhibition of respiration influences the time course or extent of Pc 4-PDT-induced apoptosis in LY-R cells is not clear at the present time.

Pilot in vitro toxicity study of 5-ALA and Photofrin in microvascular endothelial cell cultures

Complicated hemangiomas are unique problems in which intervention with the proper laser can be an ideal solution. In this study we evaluated the toxicity of 5-Aminolevulinic acid (5-ALA) and Photofrin using in vitro models. The in vitro toxicity of 5-ALA and Photofrin was examined in a microvascular endothelial cell (MEC) culture system. The measurement of the percentage of MEC killed by various drug concentration using fluorescence viability assay. MEC incubated with 5-ALA at various concentrations for evaluation of dark toxicity showed less than a 50% cell kill. A comparison of different intervals of subcultured MEC showed that the early subculture (3 days after primary culture) is more vulnerable than later subculture (7 days after). Cells treated with Photofrin at various concentrations exhibited less than 50% cell kill (dark toxicity). The comparison of different intervals of subculture (3 days and 7 days after primary culture) showed a result similar to that of 5-ALA. All controls showed 0% cell kill. In conclusion, both 5-ALA and Photofrin are capable of destroying human microvascular endothelial cells in vitro. Drug concentrations and the power density for photodynamic therapy should be considered and will be included in our subsequent studies.

Fluorescence photobleaching of ALA-induced protoporphyrin IX during photodynamic therapy of normal hairless mouse skin: the effect of light dose and irradiance and the resulting biological effect

The photobleaching of 5-aminolaevulinic acid (ALA)-induced protoporphyrin IX (PpIX) was investigated during superficial photodynamic therapy (PDT) in normal skin of the SKH HR1 hairless mouse. The effects of light dose and fluence rate on the dynamics and magnitude of photobleaching and on the corresponding PDT-induced damage were examined. The results show that the PDT damage cannot be predicted by the total light dose. Photobleaching was monitored over a wide range of initial PpIX fluorescence intensities. The rate of PpIX photobleaching is not a simple function of fluence rate but is dependent on the initial concentration of sensitizer. Also, at high fluence rates (50-150 mW/cm2, 514 nm) oxygen depletion is shown to have a significant effect. The rate of photobleaching with respect to light dose and the corresponding PDT damage both increase with decreasing fluence rate. We therefore suggest that the definition of a bleaching dose as the light dose that causes a 1/e reduction in fluorescence signal is insufficient to describe the dynamics of photobleaching and PDT-induced damage. We have detected the formation of PpIX photoproducts during the initial period of irradiation that were themselves subsequently photobleached. In the absence of oxygen, PpIX and its photoproducts are not photobleached. We present a method of calculating a therapeutic dose delivered during superficial PDT that demonstrates a strong correlation with PDT damage.

Measurements by fluorescence microscopy of the time-dependent distribution of meso-tetra-hydroxyphenylchlorin in healthy tissues and chemically induced "early" squamous cell carcinoma of the Syrian hamster cheek pouch

The influence of the time interval between dye administration and detection by fluorescence microscopy was assessed in "early" squamous cell carcinomas of the cheek pouch mucosa and different healthy tissues of the Syrian hamster. Following intracardiac injection of 0.15 mg (kg bodyweight)-1 of meso-tetra-hydroxyphenylchlorin (m-THPC), groups of three animals were sacrificed at different time intervals up to 30 days. A group of three non-injected animals was used to detect the endogene fluorescence of the corresponding normal tissues for autofluorescence subtraction. The following excised organs (oesophagus, trachea, liver, spleen, kidney, skin, striated muscle, healthy and tumoral cheek pouch mucosae) were fast frozen in liquid nitrogen and stored at -70 degrees C for fluorescence microscopy. The results show significant differences in the detectable m-THPC levels in different tissue layers (for instance, the epithelia and muscle of the oesophagus, trachea and cheek pouch) at different time intervals. These data indicate that pharmacokinetic studies may be useful for selecting the optimal time for the photodetection and phototherapy of cancer.

The apparent diffusion constant measured by MRI correlates with pO2 in a RIF-1 tumor

As tissue oxygen tension (pO2) is an important variable in cancer therapy, it would be of major clinical benefit to be able to measure pO2 noninvasively. Current methods for determining pO2 in clinical settings are limited to superficial tumors. The authors measured the apparent diffusion constant (ADC) in an implanted murine fibrosarcoma (RIF-1) using magnetic resonance imaging and correlated the ADC with tissue pO2 measured by electron paramagnetic resonance oximetry. The ADC correlates significantly with tissue pO2 in this tumor (r = 0.89; n = 14) and so may provide a noninvasive index of pO2 in tumors.

Enhancement of photodynamic therapy with 5-aminolaevulinic acid-induced porphyrin photosensitisation in normal rat colon by threshold and light fractionation studies

5-Aminolaevulinic acid (ALA)-induced prophyrin photosensitisation is an attractive option for photodynamic therapy (PDT) since skin photosensitivity is limited to 1-2 days. However, early clinical results on colon tumours using the maximum tolerated oral dose of 60 mg kg-1 showed only superficial necrosis, presumably owing to insufficient intratumoral porphyrin levels, although inadequate light dosimetry may also be a factor. We undertook experiments using ALA, 25-400 mg kg-1 intravenously, to establish the threshold doses required for a PDT effect. Laser light at 630 nm (100 mW, 10-200 J) was delivered to a single site in the colon of photosensitised normal Wistar rats at laparotomy. The animals were killed 3 days later and the area of PDT-induced necrosis measured. No lesion was seen with 25 mg kg-1. The lesion size increased with larger ALA doses and with the light dose but little benefit was seen from increasing the ALA dose above 200 mg kg-1 or the light dose above 100 J. Thus there is a fairly narrow window for optimum doses of drug and light. Further experiments showed that the PDT effect can be markedly enhanced by fractionating the light dose. A series of animals was sensitized with 200 mg kg-1 ALA and then treated with 25 J. With continuous irradiation, the lesion area was 13 mm2, but with a single interruption of 150 s the area rose to 94 mm2 with the same total energy. Results were basically similar for different intervals between fractions (10-900 s) and different numbers of fractions (2-25). This suggests that a single short interruption in the light irradiation may dramatically reduce the net light dose required to achieve extensive necrosis.

The importance of liposomes as models and tools in the understanding of photosensitization mechanisms

The various applications of liposomes in understanding photosensitization are described in this paper, with particular emphasis on the various kinds of information that these models allow to obtain in phototherapy. Liposomes are simple vesicles in which an aqueous phase is enclosed by a phospholipidic membrane. They are suitable models mimicking specific situations occurring in vivo and they allow study of the influence of physicochemical, photobiological and biochemical factors on the uptake of photosensitizers by tissues, their mechanisms of action and the subsequent photoinduced tumor necrosis. Moreover, solubilization of the sensitizer into the bilayer seems to improve its tumoral selectivity and its photodynamic efficiency.

In vitro photodynamic therapy of musculoskeletal neoplasms

Photodynamic therapy is a tumoricidal modality that utilizes an inactive pharmacologic agent that becomes activated on exposure to visible light. Neoplasms selectively retain and accumulate photosensitizers at levels generally higher than surrounding non-neoplastic tissues. The purpose of this study was to establish a testing method for in vitro investigation of the effects of photodynamic therapy on human musculoskeletal neoplasms by examination of the sensitivity of these tumors to photoactivation. Three human musculoskeletal neoplasms were cultured, exposed to the photosensitizer Photofrin, and then studied for their response to photodynamic therapy after laser activation. Giant-cell tumor, dedifferentiated chondrosarcoma, and osteosarcoma were examined with use of strict experimental controls. The photoradiation conditions during photodynamic therapy were kept constant. Cell viability was determined as a function of energy dose. We concluded that the three musculoskeletal tumors were susceptible to in vitro photodynamic therapy and the test system was reproducible. The optimal in vitro nontoxic incubation concentration of Photofrin was 3 micrograms/ml. A differential cytotoxic response to photodynamic therapy was exhibited by the musculoskeletal neoplasms as a function of increased dosages of energy.

Distribution and photosensitizing efficiency of porphyrins induced by application of exogenous 5-aminolevulinic acid in mice bearing mammary carcinoma

By means of a chemical extraction procedure and confocal laser scanning microscopy, we investigated the kinetic patterns of uptake and biolocalization of 5-aminolevulinic acid (ALA)-induced porphyrins in s.c. transplanted tumors, adjacent normal skin and muscle, and liver of mice bearing mammary carcinoma, after i.p. injection of 250 mg/kg ALA or topical application of ALA (20% in an oil-in-water emulsion). Furthermore, we evaluated the tumor responses after either i.p. injection or topical application of 5-ALA followed by laser irradiation (632 nm, 150 mW/cm2, 25 min) by measuring the treated tumor regression/regrowth time and by light and electron microscopy. Strong fluorescence of ALA-induced porphyrins was detected in the tumor, skin and liver tissues, while little fluorescence was seen in the adjacent muscle tissue. Moreover, the highest amounts of ALA-induced porphyrins in the tumor and skin tissues were found 1 hr after i.p. injection, whereas the amounts of the porphyrins in both tissues increased with increasing time after topical application of ALA. The fluorescence of the porphyrins was localized in several components of the skin tissue (epidermis, hair follicles and their associated sebaceous glands). Furthermore, the fluorescence was diffusely distributed in the s.c. transplanted tumor tissue. Little could be observed under a confocal laser scan microscope (CLSM) in the muscle tissue. The uptake and biolocalization data correlate well with the results of PCT efficiency of the same tumor model with ALA-induced porphyrins. Light and electron microscopy showed that the mitochondria of the tumor cells and of the endothelial cells and the basal lamina of vascular walls beneath the endothelium in the tumor tissue were initially extensively destroyed after PCT with ALA-induced porphyrins. Thereafter, diffuse degeneration followed by local and/or diffuse severe necrosis of the tumor cells was found. This may be due mainly to the initial damage to mitochondria in the cancerous and endothelial cells and also to the destruction of the vascular wall in the tumor tissue.

Mechanisms of cell killing in photodynamic therapy using a novel in vivo drug/in vitro light culture system

Photodynamic therapy of certain neoplasms has emerged as a promising form of cancer treatment. This type of therapy involves the exogenous administration of a photosensitizer with subsequent exposure to light. The ensuing photochemical reaction results in destruction of the tumor. Whether tumor cells are destroyed directly by the photodynamic treatment or indirectly as a result of destruction of the tumor microvascular bed is unknown. To address this question, methods were adapted to test whether combinations of a photosensitizer and light resulted in direct cell killing of precision cut tissue slices placed in culture. The major advantages of this culture system are that photosensitizers are administered in vivo, tissue slices produced in minutes, placed in culture medium, and irradiated in vitro. Any resulting cellular destruction occurs in the absence of a functioning vascular system and indicates that photodynamic therapy acts through a direct cell killing mechanism. Tissue slice viability was monitored by two standard methods: assay for intracellular potassium and morphological examination at the electron microscopic level. The effects of hematoporphyrin derivative and light were examined on tissue slices produced from a prostate adenocarcinoma transplanted into male Copenhagen rats. The data indicate that direct killing of tumor slices occurs and is dependent on the irradiation protocol used.

Pheophorbide a-induced photo-oxidation of cytochrome c: implication for photodynamic therapy

Pheophorbide a-induced photo-oxidation, in vitro, of cytochrome c oxidase and cytochrome c results in irreversible modifications to both protein components. Photo-oxidation of cytochrome c, as exhibited by change in its heme oxidation state, displays exponential kinetics and is detected with a lag period. Both the photo-induced inactivation of the enzyme, and destruction of the substrate ability of cytochrome c occur as complex multi-process events. Under similar experimental conditions, the loss of the substrate capability of cytochrome c develops approximately three times faster than inactivation of the enzyme. The slight lag in the photo-oxidation of cytochrome c is due to pheophorbide a-induced superoxide production. However, the relative amount of photo-oxidant produced is considerably more effective than the cytochrome c reducing capacity of the superoxide. Neither hydroxyl radical nor hydrogen peroxide are involved in the photo-oxidation of the heme function. The possibilities of heme oxidation by a singlet oxygen mediated pathway or direct electron abstraction involving the heme or apoprotein are not excluded. It is proposed that a multi-site oxidation of numerous reduced energy cofactors within cells may augment collateral enzyme inactivation in maximizing photosensitizer-induced cytotoxicity. Accordingly, amphipathic photosensitizers, capable of accessing both lipid and aqueous compartments containing reduced cofactors, may be more effective agents for photodynamic therapy than those which exhibit a high specificity of subcellular localization.

Mitochondrial DNA damage by anticancer agents

Mitochondrial DNA (mtDNA) is susceptible to damage by a number of anticancer agents either directly or indirectly. This damage is of little consequence if only a few of the mtDNA molecules are damaged. However, multiple drug treatments could result in a significant effect on a cell's ability to survive. The differential effect of anticancer agents on either organ specific toxicities or selective tumor kill can be partially accounted for by differential mtDNA content of cells and on the basis of differential protective mechanisms within mitochondria of various organs or tumor tissue. The concept of damage to mitochondria, especially its genome, is a subject of active investigation in various laboratories. This area of research may provide mechanism(s) by which organ specific toxicities or tumor specific toxicities may be elaborated. Also, the concept of targeting tumor specific mitochondria and/or mtDNA by anticancer agents is very attractive but has not come to fruition due to a lack of understanding of the regulation of the genome in tumor cells. Future investigations in this arena will enhance our knowledge on the interaction between anticancer agents and extranuclear DNA.

Tumor hypoxia, reoxygenation and oxygenation strategies: possible role in photodynamic therapy

The concept of hypoxia and its role in tumor therapy are currently under re-evaluation. Poor oxygenation is no longer visualized as an independent feature promoting necrosis and resistance to treatments, but rather as one of the several interdependent microenvironmental parameters associated with impaired blood perfusion. Tumor cells display several survival strategies and remain clonogenic for long periods in nutrient-deprived situations. Reoxygenation may cause lethal damage, improve the response to therapy, or else allow the cell variants adapted to hypoxia to resume proliferation with enhanced aggressiveness and resistance to treatment. The blood supply parameters, oxygenation status and metabolism of malignant cells are discussed here from the standpoint of tumor photodynamic therapy. The role of the tumor interstitial fluid as oxygen- and sensitizer-carrier is discussed. Techniques for assessing tumor oxygenation and for mapping hypoxic territories are described. Strategies for locally improving the oxygenation levels or for selectively destroying the hypoxic populations are outlined.

Time-resolved polarization measurements of porphyrin fluorescence in solution and in single cells

Porphyrin monomers, dimers and aggregates, which can be differentiated on the basis of their fluorescence lifetimes, are shown to possess different degrees of fluorescence polarization. This opens up new possibilities for microscopic imaging of these individual components in photosensitization and tumour detection. A rough estimate of the size of the porphyrin aggregates is obtained from the data of time-resolved fluorescence anisotropy.

Influence of hyperbaric oxygenation on bilirubin and ditaurobilirubin auto-oxidation and porphyrin-sensitized photo-oxidation

Oxygen concentration controls the reaction rate of porphyrin-sensitized photo-oxidation under constant experimental conditions. The rate of bilirubin and ditaurobilirubin auto-oxidation and meso-tetra-(4-sulphonatophenyl) porphine-sensitized photo-oxidation in aqueous solution increases by about 3.5 times in 0.5 MPa of oxygen. Use of hyperbaric oxygenation in the photodynamic therapy of tumours and in the phototherapy of jaundice is proposed.

In vitro killing of human malignant mesothelioma by photodynamic therapy

Photodynamic therapy was investigated as a potential new modality for the treatment of human malignant mesothelioma (HMM) utilizing the H-MESO-1 HMM cell line and the photosensitizing agent, Photofrin-II (PF-II). Up-take of PF-II by H-MESO-1 was documented by incubating H-MESO-1 cells with PF-II and measuring the fluorescence at 625 nm following excitation at 400 nm. Cytotoxicity of photodynamic therapy was determined by incubating H-MESO-1 cells (2 X 10(5)) in microtiter plates for 24 hr with concentrations of PF-II varying from 0 to 10 micrograms/ml. The wells were exposed to gold vapor laser light (628 nm) in doses ranging from 0 to 24,000 J/m2. Twenty-four hours following treatment, [3H]thymidine (1 microCi) was added to each well. Cells were harvested 24 hr later and counted for tritium incorporation. Five replicates were performed for each combination of light and drug. Peak absorption of PF-II by H-MESO-1 was reached within 8 hr. Maximal doses of light alone caused minimal cell killing. PF-II without light was cytotoxic only at the highest concentrations. However, the combination of PF-II at concentrations at or above 2.5 micrograms/ml and light produced a significant increase in cytotoxicity. These data demonstrate that photodynamic therapy can effectively kill human malignant mesothelioma cells in vitro.

Effects of hematoporphyrin derivative on the cellular energy metabolism in the absence and presence of light

Effects of Photofrin II on energy metabolism and metabolic viability were studied in a mammalian transformed cell line (BHK-21) in dark and after photo-irradiation with visible light. Cells were allowed to accumulate Photofrin by incubating for 4 h in buffer containing Photofrin (5-60 micrograms/ml). The results show that Photofrin significantly affects the cellular energy metabolism even in the absence of light; activity of cytochrome c oxidase is decreased and glucose utilization and lactate production (glycolysis) are increased. Irradiation with light resulted in a significant decrease in the activity of cytochrome c oxidase, glycolysis, ATP content, energy charge, ratios of adenine nucleotides like ATP/ADP, ATP/AMP and cell viability (dye exclusion test). Presence of inhibitors of energy metabolism, potassium cyanide (respiration) and 2-deoxyglucose (glycolysis), further enhanced the cytotoxic effects induced by hematoporphyrin derivative and light.