Chronology of the Apoptotic Events Induced in the K562 Cell Line by Photodynamic Treatment with Hematoporphyrin and Monoglucosylporphyrin

Synthesis and radiosensitizing properties of brominated tetrapyridine porphyrins

Brominated derivatives of tetrapyridinium copper porphyrin were prepared via bromination of the β-positions (pyrrole rings) and/or the peripheral alkyl side-chains attached to the pyridine moieties. The radiosensitizing properties of these new cationic, brominated porphyrins were tested on MDA-MB-231 breast cancer cells in vitro using a 60 Co source or an X-ray irradiator. The non-brominated porphyrin and the porphyrin containing bromines at β-positions only were devoid of any radiosensitizing activity. However, a pronounced radiosensitizing effect was observed with the porphyrin containing bromo atoms at both β-positions and the peripheral side-chains. A similar radiosensitizing effect was detected for different radiation energies, suggesting that high energy photons could be used to treat tumors in conjunction with this novel brominated, porphyrin-based radiosensitizer.

ESR detection of 1O2 reveals enhanced redox activity in illuminated cell cultures

Low-energy visible light (LEVL) has previously been found to modulate various processes in different biological systems. One explanation for the stimulatory effect of LEVL is light-induced reactive oxygen species formation. In the present study, both sperm and skin cells were illuminated with LEVL and were found to generate singlet oxygen (1O2). The detection of 1O2 was performed using a trapping probe, 2,2,6,6-tetramethyl-4-piperidone, coupled with electron paramagnetic resonance spectroscopy. In addition, we have shown that, together with O2 generation, LEVL illumination increases the reductive capacity of the cells, which explains the difficulties encountered in 1O2 detection. The potential of visible light to change the cellular redox state may explain the recently observed biostimulative effects exerted by LEVL.

Extracellular pH influences the mode of cell death in human colon adenocarcinoma cells subjected to photodynamic treatment with chlorin p6

Effect of varying extracellular pH on mode of cell death induced by photodynamic action of chlorin p6 was investigated in human colon carcinoma (Colo-205) cells. At an extracellular pH of 7.4, compared to cells treated with chlorin p6 in dark, the photodynamically treated cells showed reduction in mitochondrial membrane potential, an increase in ADP/ATP ratio (1:2) and a large percentage of cells with chromatin condensation. In contrast, when photodynamic treatment and post irradiation incubation was carried out in acidic medium (pH 6.5), total loss of mitochondrial membrane potential, a marked increase in ADP/ATP ratio (1:33) and increased damage to plasma membrane were observed. Further, cells subjected to photodynamic treatment in a medium of pH 7.4 showed twofold increase in caspase-3 activity as compared to photodynamic treatment at pH 6.5. These results suggest that chlorin p6 mediated photodynamic action induces apoptotic cell death when extracellular pH is 7.4 whereas necrosis is more predominant under condition when extracellular pH is 6.5.

Intracellular signaling mechanisms in photodynamic therapy

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

Chromosomal aberrations in human lymphocytes exposed to the anticholinesterase pesticide isofenphos with mechanisms of leukemogenesis

Human lymphocytes were exposed to the leukemogenic pesticide isofenphos (IFP) to investigate its effects on chromosomal DNA and cholinergic homeostasis using cholinesterase activity as a marker. Isolated peripheral lymphocytes were administered concentrations of IFP ranging from 0.1 ng/ml to 10 microg/ml. The absence (Group 1) and presence (Group 2) of DNA repair inhibitors 4 mM hydroxyurea (HU), 40 microM cytosine arabinoside (ARA-C) and an NADPH regenerating system (NRS) (Group 3) were analyzed at 1, 6 and 24 h by single cell gel electrophoresis using the comet assay. Significant damage to DNA directly from IFP at 1 h by remarkably low concentrations was observed in Group 1, escalating in Group 2 with DNA repair inhibition, while Group 3 disruptions were highest due to the presence of the NRS P-450 microsomal fraction conducive to producing reactive IFP-oxon and N-desalkyl metabolites. The extent of DNA aberrations increased further in parallel within the groups at 6 and 24 h. Male and female chemical sensitivities were similar on average (P < 0.01). Cholinesterase activity measured in a satellite group was inhibited with 0.1 microg/ml IFP by 69, 62, and 48% at 1, 6, and 24 h, respectively, indicating gradual induction of compensatory synthesis. Restoration of cholinergic homeostasis may be exceptionally impaired at higher IFP concentrations from acetyl-CoA depletion [Leuk. Res. 25 (2001) 883]. In summary, these studies reveal that exposure to the organophosphate pesticide isofenphos induces human DNA mutation beyond endogenous repair capacity and disrupts cholinergic nuclear signaling affectively constructing the mutator phenotype of leukemogenesis.

Cellular uptake, localization and photodynamic effects of haematoporphyrin derivative in human glioma and squamous carcinoma cell lines

Uptake, intracellular concentration, localization and photodynamic effects of a haematoporphyrin derivative (HpD, Photosan-3) were compared in human glioma (BMG-1, wild-type p53) and squamous carcinoma (4451, mutated p53) cell lines. Concentration and time dependence of cellular uptake of HpD was assayed from methanol extracts and whole cell suspension spectroscopy, while localization was studied by fluorescence microscopy-based image analysis. Colony-forming ability, apoptosis, cell-cycle progression and cytogenetic damage (micronuclei formation) were investigated as parameters of photodynamic response following irradiation with red light. BMG-1 cells were more sensitive to the photodynamic treatment than 4451 cells, although the 4451 cells accumulated a higher amount of HpD and did not differ significantly from BMG-1 cells with respect to intracellular localization. Photodynamically-induced cytogenetic damage and apoptosis were considerably higher in BMG-1 cells as compared to 4451 cells. The present results strongly suggest that manifestation of the photodynamically-induced lesions in the form of cytogenetic damage and apoptosis are among the important determinants of cellular sensitivity to HpD-PDT besides the photodynamic dose (intracellular concentration of the photosensitizer and the light dose).

Time- and concentration-dependent apoptosis and necrosis induced by free and HPMA copolymer-bound doxorubicin in human ovarian carcinoma cells

A2780 sensitive and A2780/AD doxorubicin (DOX) resistant human ovarian carcinoma cells were exposed to different concentrations (0.25, 0.5, 1, 5 and 10xIC(50)) of free and HPMA copolymer-bound DOX for 12, 24, 36, 48, 60 and 72 h. Apoptosis and necrosis were evaluated using the FITC-conjugated annexin V and propidium iodide staining. The data obtained showed that the induction of apoptosis and necrosis by both free DOX and HPMA copolymer-bound DOX were time- and concentration-dependent. The data also showed significant differences between the drugs. It was found that: (i) under the action of HPMA copolymer-bound doxorubicin the alterations in the plasma membrane permeability preceded disturbances in cellular metabolism; (ii) HPMA copolymer-bound doxorubicin kills the cells mainly by necrosis; (iii) HPMA copolymer-bound doxorubicin is a more effective anticancer drug than free doxorubicin.

Singlet oxygen, but not oxidizing radicals, induces apoptosis in HL-60 cells

Oxidizing species (OS), produced by photosensitization or derived from cytotoxic agents, activate apoptotic pathways. We investigated whether two different OS, formed at the same subcellular sites, have equivalent ability to initiate apoptosis in HL-60 cells. Our previous work showed that absorption of visible light by rose bengal (RB) produces singlet oxygen exclusively, whereas absorption of ultraviolet A produces RB-derived radicals in addition to singlet oxygen. Singlet oxygen, but not the RB-derived radicals, induced nuclear condensation and DNA fragmentation into nucleosome-size fragments in a dose dependent manner. In contrast, the RB-derived radicals caused greater lipid oxidation than singlet oxygen. These results indicate that different OS, produced at the same subcellular sites, do not have the same ability to induce apoptosis and that the ability of an OS to initiate lipid oxidation does not necessarily correlate with its ability to induce apoptosis.

Cellular uptake, subcellular localization and photodamaging effect of temoporfin (mTHPC) in nasopharyngeal carcinoma cells: comparison with hematoporphyrin derivative

Temoporfin (meta-tetra (hydroxyphenyl)chlorin; mTHPC) potentiated a 100-fold higher cytotoxic effect than hematoporphyrin derivative (HPD) on two nasopharyngeal carcinoma cell lines (HK1 and CNE2) in terms of the overall photodynamic therapy (PDT) dose. The cellular uptake, evaluated by flow cytometry and spectrophotometry demonstrated that mTHPC exhibited higher uptake ability than HPD. Confocal laser scanning microscopy detection for both the sensitizer and mitochondria probe on the same cell images revealed that both drugs accumulated diffusely in the cytoplasm and that mitochrondria is a target organelle. Photo-activation ruptured the mitochrondria, with more pronounced mitochondrial damage being observed in mTHPC-PDT course. This correlated well with the cell photokilling efficiency of mTHPC.