Post-exposure processes in Temoporfin-photosensitized cells in vitro: reliance on energy metabolism

Synthesis, Characterization and Photodynamic Activity against Bladder Cancer Cells of Novel Triazole-Porphyrin Derivatives

Novel triazole-porphyrin derivatives (TZ-PORs) were synthesized through the Heck reaction and then incorporated into polyvinylpyrrolidone (PVP) micelles. After verifying that this incorporation did not compromise the photophysical and chemical features of TZ-PORs as photosensitizers, the phototoxicity of the formulations towards cancer cells was screened. Biological studies show high photodynamic activity of all PVP-TZ-POR formulations against a bladder cancer cell line with a particular highlight to PVP-TZ-POR 7e and 7f that are able to significantly reduce HT-1376 cell viability, while they had no effect on control ARPE-19 cells.

Comparison of Cellular Death Pathways after mTHPC-mediated Photodynamic Therapy (PDT) in Five Human Cancer Cell Lines

One of the most promising photosensitizers (PS) used in photodynamic therapy (PDT) is the porphyrin derivative 5,10,15,20-tetra(m-hydroxyphenyl)chlorin (mTHPC, temoporfin), marketed in Europe under the trade name Foscan^®. A set of five human cancer cell lines from head and neck and other PDT-relevant tissues was used to investigate oxidative stress and underlying cell death mechanisms of mTHPC-mediated PDT in vitro. Cells were treated with mTHPC in equitoxic concentrations and illuminated with light doses of 1.8-7.0 J/cm² and harvested immediately, 6, 24, or 48 h post illumination for analyses. Our results confirm the induction of oxidative stress after mTHPC-based PDT by detecting a total loss of mitochondrial membrane potential (Δψ_m) and increased formation of ROS. However, lipid peroxidation (LPO) and loss of cell membrane integrity play only a minor role in cell death in most cell lines. Based on our results, apoptosis is the predominant death mechanism following mTHPC-mediated PDT. Autophagy can occur in parallel to apoptosis or the former can be dominant first, yet ultimately leading to autophagy-associated apoptosis. The death of the cells is in some cases accompanied by DNA fragmentation and a G₂/M phase arrest. In general, the overall phototoxic effects and the concentrations as well as the time to establish these effects varies between cell lines, suggesting that the cancer cells are not all dying by one defined mechanism, but rather succumb to an individual interplay of different cell death mechanisms. Besides the evaluation of the underlying cell death mechanisms, we focused on the comparison of results in a set of five identically treated cell lines in this study. Although cells were treated under equitoxic conditions and PDT acts via a rather unspecific ROS formation, very heterogeneous results were obtained with different cell lines. This study shows that general conclusions after PDT in vitro require testing on several cell lines to be reliable, which has too often been ignored in the past.

Evaluation of mTHPC-loaded PLGA nanoparticles for in vitro photodynamic therapy on C6 glioma cell line

Photodynamic therapy (PDT) is a very attractive strategy to complement or replace common cancer treatments such as radiotherapy, surgery, and chemotherapy. Some molecules have shown their efficiency as photosensitizers (PS), still many issues have to be solved such as the inherent cytotoxicity of the PS or its hydrophobic properties causing limitation in their solubility, leading to side effects. In this study, the encapsulation of an approved PS, the meso-tetra hydroxyphenylchlorine (mTHPC, Foscan®) within biocompatible and biodegradable poly(D, l-lactide-co-glycolide) acid (PLGA) NPs prepared by the nanoprecipitation method was studied. The mTHPC-loaded NPs (mTHPC ⊂ PLGA NPs) were analyzed by UV-vis spectroscopy to determine the efficiency of mTHPC encapsulation, and by dynamic light scattering (DLS) and atomic force microscopy (AFM) to determine mTHPC ⊂ PLGA NPs sizes, morphologies and surface charges. The longitudinal follow-up of mTHPC release from the NPs indicated that 50% of the encapsulated PS was retained within the NP matrix after a period of five days. Finally, the cytotoxicity and the phototoxicity of the mTHPC ⊂ PLGA NPs were determined in murine C6 glioma cell lines and compared to the ones of mTHPC alone. The studies showed a strong decrease of mTHPC cytotoxicity and an increase of mTHPC photo-cytotoxicity when mTHPC was encapsulated. In order to have a better insight of the underlying cellular mechanisms that governed cell death after mTHPC ⊂ PLGA NPs incubation and irradiation, annexin V staining tests were performed. The results indicated that apoptosis was the main cell death mechanism.

Temoporfin (Foscan®, 5,10,15,20-tetra(m-hydroxyphenyl)chlorin)--a second-generation photosensitizer

This review traces the development and study of the second-generation photosensitizer 5,10,15,20-tetra(m-hydroxyphenyl)chlorin through to its acceptance and clinical use in modern photodynamic (cancer) therapy. The literature has been covered up to early 2011.

Cell de-energization prevents plasmid transformation of yeast Saccharomyces cerevisiae: evidence for the requirement of ATP

The dependence of the yeast Saccharomyces cerevisiae transformation on energy requirement was studied. The inhibitory effect of sodium arsenate, used for the depletion of the intracellular ATP pool, was determined. Incubation of the yeast cells in 5 mM sodium arsenate diminished ATP accumulation by 50% and the transformation efficiency decreased by 65%. To discriminate between ATP produced by substrate level phosphorylation and oxidative phosphorylation, the inhibitory analysis of a mutant with defective mitochondria was performed. Sodium fluoride (10–50 mM), as inhibitor of glycolysis, elicited a concentration-dependent decrease in intracellular ATP levels in both parental and mutant cells. The equal transformation efficiency of the mitochondrial mutant and parental strain, in addition to experiments with oligomycin, demonstrated the independence of plasmid transformation on mitochondrial ATP synthesis. This is consistent with our hypothesis that yeast transformation efficiency is associated with ATP produced by substrate level phosphorylation.

Schedule-dependent interaction between Doxorubicin and mTHPC-mediated photodynamic therapy in murine hepatoma in vitro and in vivo

PURPOSE

To evaluate cytotoxic and antitumor effects of a conventional anticancer drug Doxorubicin (Dox) and photodynamic therapy (PDT) mediated by a promising photosensitizer of second generation meta-tetra (3-hydroxyphenyl)-chlorin (mTHPC) in combination.

METHODS

Murine hepatoma MH-22A was used for investigation in vitro and in vivo. In vitro, the cells were incubated with 0.15 microg/ml mTHPC for 18 h and exposed to light from LED array (lambda = 660+/-20 nm) at 0.6-2.4 kJ/m2. 0.05-0.2 microg/ml Dox was administered either 24 h prior to or immediately after light exposure (Dox-->PDT or PDT + Dox, respectively). The cytotoxicity was tested by staining with crystal violet. The character of the combined effect was assessed by multiple regression analysis. In vivo, the antitumor activity was estimated by monitoring the tumor volume over time, in mice transplanted subcutaneously with MH-22A and treated with Dox and/or PDT. For PDT, mice were exposed to light from diode laser (lambda = 650+/-2 nm) at 12 kJ/m2 following 24 h after administration of 0.15 mg/kg mTHPC. A 3 mg/kg Dox was administered either within 15 min prior to mTHPC or within 15 min after light exposure (Dox-->PDT or PDT + Dox, respectively).

RESULTS

Both in vitro and in vivo, the combination of mTHPC-mediated PDT and Dox was evaluated to be more effective than each treatment alone. In vitro, the difference between cell viability curves after photodynamic treatment as a single modality and after combination of photodynamic treatment with Dox was statistically significant under most of the applied conditions (P < or = 0.02). In the case of PDT + Dox, the combination had an additive character, and the sequence Dox-->PDT caused a sub-additive interaction. In vivo, both regimens of combination were more effective in inhibiting tumor growth than any single treatment (P < 0.09). The antitumor activity of PDT + Dox regimen was more prominent than that of Dox-->PDT; however, significance of the difference was not high (P = 0.08).

CONCLUSIONS

These results indicate that Dox potentiates therapeutic efficacy of mTHPC-mediated PDT and vice versa, and the degree of potentiation is influenced by the combination schedule: administration of Dox immediately after light exposure is preferable to administration of Dox at 24 h prior to light exposure.

Correlation of death modes of photosensitized cells with intracellular ATP concentration

The impact of intensity of glycolysis and oxidative phosphorylation on death of photosensitized murine hepatoma MH22 cells in vitro has been investigated. Cells photosensitized with meso-tetra(4-sulfonatophenyl)-porphine localized to lysosomes died mostly by necrosis, and the mode of cell death did not depend on the energy metabolism. Photosensitization with 5-aminolevulinic acid-stimulated endogenous porphyrins localized mainly in mitochondria or 5,10,15,20-tetrakis(m-hydroxyphenyl)-chlorine localized to cell membranes, including mitochondria, led to cell death mostly by apoptosis. In this case, the mode of cell death depended on the medium: under conditions unfavorable to glycolysis the ratio apoptosis/necrosis decreased significantly.

Primary photodamage sites and mitochondrial events after Foscan photosensitization of MCF-7 human breast cancer cells

To determine the initial photodamage sites of Foscan-mediated photodynamic treatment, we evaluated the enzymatic activities in selected organelles immediately after light exposure of MCF-7 cells. The measurements indicated that the enzymes located in the Golgi apparatus (uridine 5'-diphosphate galactosyl transferase) and in the endoplasmic reticulum (ER) (nicotinamide adenine dinucleotide [reduced] [NADH] cytochrome c [cyt c] reductase) are inactivated by the treatment, whereas mitochondrial marker enzymes (cyt c oxidase and dehydrogenases) were unaffected. This indicates that the ER and the Golgi apparatus are the primary intracellular sites damaged by Foscan-mediated PDT in MCF-7 cells. We further investigated whether the specific mitochondria events could be associated with Foscan photoinduced cell death. The dose response profiles of mitochondrial depolarization and cytochrome c release immediately after Foscan-based PDT were very different from that of overall cell death. By 24 h post-PDT the fluence dependency was strikingly similar for both mitochondrial alterations and cell death. Therefore, although mitochondria are not directly affected by the treatment, they can be strongly implicated in Foscan-mediated MCF-7 cell death by late and indirect mechanism.

Characterization of the cell death modes and the associated changes in cellular energy supply in response to AlPcS4-PDT

Photodynamic therapy (PDT) can result in both types of cell death, apoptosis or necrosis. Several steps in the induction and execution of apoptosis depend on ATP and the intracellular ATP level has been shown to be one determinant in whether apoptosis or necrosis occurs. Therefore, photochemical damage of cellular targets involved in energy supply might play a crucial role in the mode of cell death being executed. The present study is aimed at the characterization of changes in cellular energy supply and the associated cell death modes in response to PDT. Using the human epidermoid carcinoma cell line A431 and aluminium(III) phthalocyanine tetrasulfonate chloride (2.5 microM) as a photosensitizer, we studied the changes in mitochondrial function and intracellular ATP level after irradiation with different light doses. Employing assays for caspase-3 activation and nuclear fragmentation, 50% of the cells were found to undergo apoptosis after irradiation between 2.5 to 3.5 J cm(-2) while the remainder died by necrosis. At higher light doses (> 6 J cm(-2)), neither caspase-3 activation nor nuclear fragmentation was observed and this suggests that these cells died exclusively by necrosis. Necrotic cell death was also associated with a rapid decline in mitochondrial activity and intracellular ATP. By contrast, with apoptosis the loss of mitochondrial function was delayed and the ATP level was maintained at near control levels for up to eight hours which was far beyond the onset of morphological changes. These data suggest that, depending on the light dose applied, both, necrosis as well as apoptosis can be induced with AlPcS4 mediated PDT and that photodamage in energy supplying cellular targets may influence the mode of cell death. Further, it is speculated that cells undergoing apoptosis in response to PDT might maintain a high ATP level long enough to complete the apoptotic program.

Intracellular photobleaching of 5,10,15,20-tetrakis(m-hydroxyphenyl) chlorin (Foscan) exhibits a complex dependence on oxygen level and fluence rate

The understanding of photosensitizer photobleaching is important not only for mechanistic studies, but also for the development of monitoring techniques for clinical dosimetry in photodynamic therapy. In this study, we investigated the intracellular photobleaching of 5,10,15,20-tetrakis(m-hydroxyphenyl)chlorin (mTHPC, Foscan) in the murine macrophage cell line J774A.1, using quantitative fluorescence imaging microscopy, microspectrofluorometry and microspectrophotometry. Using 652 nm laser irradiation, it was found that mTHPC exhibits oxygen- and fluence rate-dependent intracellular photobleaching. The kinetics showed an inverse dose-rate behavior, i.e. a reduction of fluence rate resulted in more photobleaching at comparable fluences. The effect of deoxygenation was found to be more complex, with decreased bleaching at low fluence rates and increased bleaching at higher fluence rates. The intracellular formation of reactive oxygen species was measured using 2',7'-dichlorodihydrofluorescein diacetate. The results are analyzed in terms of competitive Type-I and Type-II mechanisms.

Thrombopoietin and the TPO receptorduring platelet storage

BACKGROUND

For most cells, the addition of a specific growth factor has improved cellular viability by preventing programmed cell death (apoptosis). To determine whether the platelet-specific hematopoietic growth factor thrombopoietin (TPO) might improve platelet viability, endogenous TPO and the platelet TPO receptor were analyzed during storage, and the effect of recombinant TPO on platelet viability was assessed.

STUDY DESIGN AND METHODS

During platelet storage, TPO stability was assessed by SDS-PAGE, TPO receptor function was measured, and the platelet TPO receptor was characterized by a (125)I-rHuTPO competitive-binding assay. A recombinant TPO, pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), was added to platelet concentrates during storage, and its effect on pH, LDH, and metabolic activity was determined.

RESULTS

During storage, the molecular weight and concentration of endogenous TPO (125 +/- 19 pg/mL) and exogenous TPO (5720 +/- 140 pg/mL) were constant for 12 days; the number (33 +/- 4), binding affinity (149 +/- 33 pM), and function of the platelet TPO receptors were constant for 7 days. Metabolic activity measured with the MTT and MTS assays closely correlated with changes in the pH and LDH. The addition of PEG-rHuMGDF did not alter the pH, LDH, or metabolic activity of platelets during storage, but it did increase by 65 percent the uptake of (35)S-methionine into platelets. Finally, platelet concentrates obtained from donors treated with PEG-rHuMGDF retained normal metabolic activity for 12 days, as compared with 5 to 6 days for normal platelet concentrates.

CONCLUSIONS

TPO and its platelet receptor are present in normal amounts and have normal function during platelet storage. The addition of recombinant TPO increased platelet methionine transport but did not alter platelet viability during storage. Other means to prevent apoptosis during platelet storage should be considered, and the measurement of platelet metabolic activity by MTT and MTS assays may assist this effort.

Metabolic effects of photodynamically induced apoptosis in an erythroleukemic cell line. A (31)P NMR spectroscopic study of Victoria-Blue-BO-sensitized TF-1 cells

Victoria Blue BO (VB BO) is a new and promising photosensitizer currently being evaluated for photodynamic therapy (PDT). Its photochemical processes are mediated by oxygen radicals, but do not involve singlet oxygen. We used (31)P NMR spectroscopy of VB-BO sensitized TF-1 leukemic cells to gain further insight into the biochemical mechanisms underlying PDT-induced cell death. Sham-treatment experiments were performed to evaluate the effects of this photosensitizer in the absence of light irradiation. Significant metabolic differences were detected for TF-1 cells incubated with VB BO but not exposed to light, as compared with native cells (controls). These changes include reductions in phosphocreatine, UDP-hexose and phosphodiester levels (as percentage of total phosphate) and slightly reduced intracellular pH. Complete phosphocreatine depletion, significant acidification and concomitant inorganic-phosphate accumulation were observed for TF-1 cells irradiated after incubation with VB BO. Moreover, significant changes in phospholipid metabolites, i.e., accumulation of cytidine 5'-diphosphate choline and a decrease in phosphodiester levels, were observed for PDT-treated vs. sham-treated cells. Perturbations of phospholipid metabolism may be involved in programmed cell death, and the detection of a characteristic DNA ladder pattern by gel electrophoresis confirmed the existence of apoptosis in PDT-treated TF-1 cells.

Subcellular localization of meta-tetra (hydroxyphenyl) chlorin in human tumor cells subjected to photodynamic treatment

Subcellular localization of meta-tetra (hydroxyphenyl) chlorin (mTHPC) in HT29 human colon adenocarcinoma cells has been studied by means of fluorescence microscopy. The observed diffuse intracellular distribution of mTHPC fluorescence outside the nucleus indicates general staining of cellular organelles. No changes in dye fluorescence pattern are evident during and immediately after cell illumination. Alternatively, the changes in mTHPC fluorescence pattern are observed upon subsequent cell incubation, and are characterized by the appearance of distinct bright fluorescence zones. Reaching a maximum 1 h after illumination, modifications of the fluorescence pattern then gradually disappear in parallel with the formation of plasma membrane blebs, suggesting that cell necrotic lysis is taking place. Photosensitized damage to mitochondria and the Golgi apparatus has been studied using fluorescent probes 1 h after irradiation, the stage of extensive cytoplasm vacuolization, and reveal alterations of these organelles. Changes in the mTHPC fluorescence pattern and mTHPC photocytotoxicity, as measured by the MTT test 24 h after illumination, are inhibited by sodium azide, a singlet oxygen quencher.