A photodynamic pathway to apoptosis and necrosis induced by dimethyl tetrahydroxyhelianthrone and hypericin in leukaemic cells: possible relevance to photodynamic therapy.
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The mechanism of cell death induction by dimethyl tetrahydroxyhelianthrone (DTHe), a new second-generation photodynamic sensitizer, is analysed in human leukaemic cell lines in comparison with the structurally related hypericin. DTHe has a broad range of light spectrum absorption that enables effective utilization of polychromatic light. Photosensitization of HL-60 cells with low doses of DTHe (0.65 microM DTHe and 7.2 J cm(-2) light energy) induced rapid apoptosis of > or =90% of the cells. At doses > or =2 microM, dying cells assumed morphological necrosis with perinucleolar condensation of chromatin in HL-60 and K-562 cell lines. Although nuclear fragmentation that is characteristic to apoptosis was prevented, DNA digestion to oligonucleosomes proceeded unhindered. Such incomplete apoptosis was more prevalent with the related analogue hypericin throughout most doses of photosensitization. Despite hypericin being a stronger photosensitizer, DTHe exhibited advantageous phototoxic properties to tumour cells, initiating apoptosis at concentrations about threefold lower than hypericin. Photosensitization of the cells induced dissociation of the nuclear envelope, releasing lamins into the cytosol. DTHe also differed from hypericin in effects exerted on the nuclear lamina, causing release of an 86-kDa lamin protein into the cytosol that was unique to DTHe. Within the nucleus, nuclear envelope lamin B underwent covalent polymerization, which did not affect apoptotic nuclear fragmentation at low doses of DTHe. At higher doses, polymerization may have been extensive enough to prevent nuclear collapse. Hut-78, CD4+ cells were resistant to the photodynamically activated apoptotic pathway. Beyond the tolerated levels of photodynamic damage, these cells died exclusively via necrosis. Hut-78 cells overexpress Bcl-X(L) as well as a truncated Bcl-X(L)tr isoform that could contribute to the observed resistance to apoptosis. (+info)
Combination interferon-alpha2a and 13-cis-retinoic acid enhances radiosensitization of human malignant glioma cells in vitro.
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We investigated the individual and combined effects of cis-retinoic acid (CRA) and/or IFN-alpha (IFN) and/or radiation therapy (RT) against a human glioma cell line (American Type Culture Collection; U373MG) to evaluate the possible radiosensitization properties of these agents in vitro. Glioma cells were incubated for 24 h in 96-well plates (2 x 10(2) cells/well) in standard culture medium. Sets of U373 (n = 12) were exposed to CRA (3 x 10(6) microM), IFN (25 units/ml), CRA plus IFN, or standard culture medium. After an additional 24 h of incubation, the U373 cells were subjected to increasing radiation doses (up to 16 Gy). Glioma cells were harvested 92 h after irradiation, and cell survival curves were determined from [3H]thymidine incorporation data (over the last 24 h). The experiment was repeated for both the untreated control group and the combined CRA/IFN group. To verify the [3H]thymidine assays, a clonogenic assay was also performed. Single cell suspensions of U373 cells were plated out in six-well plates (n = 3). After chemical and RT treatment, colonies of 50 cells or more were counted, and cell survival curves were generated as fractions of nonirradiated controls. The amount of RT (in Gy) that would cause a 50% survival fraction (lethal dose 50 or LD50) was calculated from the survival curves by regression analysis. The following LD50s were obtained: [table: see text] The results showed that for both the [3H]thymidine incorporation assay and the clonogenic assay, the combination of IFN/CRA rendered U373 cells more susceptible to ionizing radiation than the untreated control or either single agent alone. (+info)
RSR13, an allosteric effector of haemoglobin, and carbogen radiosensitize FSAII and SCCVII tumours in C3H mice.
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Pre-clinical evaluation has demonstrated that 2-[4-(((3,5-dimethylanilino)carbonyl)methyl)phenoxy]-2-methylpropi onic acid (RSR13) acts as an allosteric effector of haemoglobin (Hb). RSR13 binding to Hb results in decreased haemoglobin-oxygen (Hb-O2) affinity, improved tumour oxygenation, and enhanced radiation-induced cell killing in several experimental tumour systems. In the present work, ex vivo clonogenic survival analyses are applied in two murine tumour systems to characterize the relationship between the magnitude of decrease in Hb-O2 affinity and radiosensitization, the influence of inspired pO2 upon this effect, and the efficacy of combining RSR13 and radiation during a course of repeated radiation exposures. For FSaII tumours in C3H mice breathing air, 100 mg kg(-1) RSR13 administered intraperitoneally produced an enhancement ratio (ER) of 1.3, but there was marked desensitization at a RSR13 dose of 300 mg kg(-1) (ER 0.6). The most likely reason for the increased radioresistance was insufficient oxygen loading of Hb in the pulmonary circulation due to reduced haemoglobin-oxygen affinity because carbogen breathing combined with 300 mg kg(-1) RSR13 reversed the effect and produced an ER of 1.8. In SCCVII tumours in C3H mice irradiated with eight fractions of 2.5 Gy over 4 days, the surviving fraction was reduced to 58-67% of control values when RSR13 was combined with radiation on days 1 and 2, days 3 and 4, or days 1-4. These results confirm that combining RSR13 and irradiation within a fractionated course of clinically relevant low-dose exposures provides significant radiosensitization. Additional preclinical experimentation is needed to define better the optimum dose-scheduling conditions for clinical applications. (+info)
Elimination of EVE protein by CALI in the short germ band insect Tribolium suggests a conserved pair-rule function for even skipped.
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The question of the degree of evolutionary conservation of the pair-rule patterning mechanism known from Drosophila is still contentious. We have employed chromophore-assisted laser inactivation (CALI) to inactivate the function of the pair-rule gene even skipped (eve) in the short germ embryo of the flour beetle Tribolium. We show that it is possible to generate pair-rule type phenocopies with defects in alternating segments. Interestingly, we find the defects in odd numbered segments and not in even numbered ones as in Drosophila. However, this apparent discrepancy can be explained if one takes into account that the primary action of eve is at the level of parasegments and that different cuticular markers are used for defining the segment borders in the two species. In this light, we find that eve appears to be required for the formation of the anterior borders of the same odd numbered parasegments in both species. We conclude that the primary function of eve as a pair rule gene is conserved between the two species. (+info)
The activation of the c-Jun N-terminal kinase and p38 mitogen-activated protein kinase signaling pathways protects HeLa cells from apoptosis following photodynamic therapy with hypericin.
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In this study, we elucidate signaling pathways induced by photodynamic therapy (PDT) with hypericin. We show that PDT rapidly activates JNK1 while irreversibly inhibiting ERK2 in several cancer cell lines. In HeLa cells, sustained PDT-induced JNK1 and p38 mitogen-activated protein kinase (MAPK) activations overlap the activation of a DEVD-directed caspase activity, poly(ADP-ribose) polymerase (PARP) cleavage, and the onset of apoptosis. The caspase inhibitors benzyloxycarbonyl-Val-Ala-Asp-fluoromethylketone (zVAD-fmk) and benzyloxycarbonyl-Asp-Glu-Val-Asp-fluoromethylketone (zDEVD-fmk) protect cells against apoptosis and inhibit DEVD-specific caspase activity and PARP cleavage without affecting JNK1 and p38 MAPK activations. Conversely, stable overexpression of CrmA, the serpin-like inhibitor of caspase-1 and caspase-8, has no effect on PDT-induced PARP cleavage, apoptosis, or JNK1/p38 activations. Cell transfection with the dominant negative inhibitors of the c-Jun N-terminal kinase (JNK) pathway, SEK-AL and TAM-67, or pretreatment with the p38 MAPK inhibitor PD169316 enhances PDT-induced apoptosis. A similar increase in PDT-induced apoptosis was observed by expression of the dual specificity phosphatase MKP-1. The simultaneous inhibition of both stress kinases by pretreating cells with PD169316 after transfection with either TAM-67 or SEK-AL produces a more pronounced sensitizing effect. Cell pretreatment with the p38 inhibitor PD169316 causes faster kinetics of DEVD-caspase activation and PARP cleavage and strongly oversensitizes the cells to apoptosis following PDT. These observations indicate that the JNK1 and p38 MAPK pathways play an important role in cellular resistance against PDT-induced apoptosis with hypericin. (+info)
Photodynamic therapy with mTHPC and polyethylene glycol-derived mTHPC: a comparative study on human tumour xenografts.
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The photosensitizing properties of m-tetrahydroxyphenylchlorin (mTHPC) and polyethylene glycol-derivatized mTHPC (pegylated mTHPC) were compared in nude mice bearing human malignant mesothelioma, squamous cell carcinoma and adenocarcinoma xenografts. Laser light (20 J/cm2) at 652 nm was delivered to the tumour (surface irradiance) and to an equal-sized area of the hind leg of the animals after i.p. administration of 0.1 mg/kg body weight mTHPC and an equimolar dose of pegylated mTHPC, respectively. The extent of tumour necrosis and normal tissue injury was assessed by histology. Both mTHPC and pegylated mTHPC catalyse photosensitized necrosis in mesothelioma xenografts at drug-light intervals of 1-4 days. The onset of action of pegylated mTHPC seemed slower but significantly exceeds that of mTHPC by days 3 and 4 with the greatest difference being noted at day 4. Pegylated mTHPC also induced significantly larger photonecrosis than mTHPC in squamous cell xenografts but not in adenocarcinoma at day 4, where mTHPC showed greatest activity. The degree of necrosis induced by pegylated mTHPC was the same for all three xenografts. mTHPC led to necrosis of skin and underlying muscle at a drug-light interval of 1 day but minor histological changes only at drug-light intervals from 2-4 days. In contrast, pegylated mTHPC did not result in histologically detectable changes in normal tissues under the same treatment conditions at any drug-light interval assessed. In this study, pegylated mTHPC had advantages as a photosensitizer compared to mTHPC. Tissue concentrations of mTHPC and pegylated mTHPC were measured by high-performance liquid chromatography in non-irradiated animals 4 days after administration. There was no significant difference in tumour uptake between the two sensitizers in mesothelioma, adenocarcinoma and squamous cell carcinoma xenografts. Tissue concentration measurements were of limited use for predicting photosensitization in this model. (+info)
Radiosensitization of hypoxic tumour cells by S-nitroso-N-acetylpenicillamine implicates a bioreductive mechanism of nitric oxide generation.
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The radiosensitizing activity of S-nitroso-N-acetylpenicillamine (SNAP), a nitric oxide (NO) donor, was assessed in a model of non-metabolic hypoxia achieved in an atmosphere of 95% nitrogen-5% carbon dioxide. A 10 min preincubation of hypoxic EMT-6 cells (10 x 10(6) ml(-1)) with 0.1 and 1 mM SNAP before radiation resulted in an enhancement ratio of 1.6 and 1.7 respectively. The level of spontaneous NO release, measured by a NO specific microsensor, correlated directly with the concentration of SNAP and was enhanced 50 times in the presence of cells. Dilution of the cell suspension from 10 to 0.1 x 10(6) ml(-1) resulted in a 16-fold decline in NO release, but only a twofold decrease in radiosensitization was observed. Preincubation of hypoxic cells with SNAP for 3 min up to 30 min caused an increasing radiosensitizing effect. Extended preincubation of 100 min led to the loss of radiosensitization although the half-life of SNAP is known to be 4-5 h. Taken together, these observations suggest that SNAP generates NO predominantly by a bioreductive mechanism and that its biological half-life is unlikely to exceed 30 min. The lack of correlation between free NO radical and radiosensitizing activity may reflect a role of intracellular NO adducts which could contribute to radiosensitization as well. (+info)
Phase I/II study of weekly irinotecan and concurrent radiation therapy for locally advanced non-small cell lung cancer.
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A study was undertaken to determine the maximum tolerated dose, the dose-limiting toxicities, and the response rate of irinotecan administered weekly with concurrent thoracic radiation therapy in patients with locally advanced non-small-cell lung cancer. In a phase I/II clinical trial, patients with histologically documented, surgically unresectable stage IIIA or IIIB non-small cell lung cancer (NSCLC) were enrolled. Irinotecan was administered as a 90 min intravenous infusion once weekly for 6 weeks. The starting dose was 30 mg m(-2) and dose escalation was done in 15 mg m(-2) increments. Dose-limiting toxicity was defined as grade 3 nonhaematologic toxicity (excluding nausea, vomiting and alopecia) or grade 4 haematologic toxicity according to the WHO criteria. Radiation was delivered to the primary tumour and regional lymph nodes (40 Gy), followed by a boost to the primary tumour (20 Gy). Twenty-seven patients were entered into this study at three irinotecan dose levels (30, 45 and 60 mg m(-2)). Twenty-six eligible patients were evaluated for toxic effects and clinical outcome. Severe oesophagitis, pneumonitis, and diarrhoea occurred at 45 and 60 mg m(-2). Three of the five patients given 60 mg m(-2) developed grade 3 or 4 oesophagitis and pneumonitis. In addition, one patient died of pneumonitis after completing therapy at 45 mg m(-2) in the phase II study. The objective response rate was 76.9% (95% CI, 53.0-88.9%). Oesophagitis, pneumonitis, and diarrhoea are the dose-limiting toxicities of weekly irinotecan combined with thoracic irradiation. The maximum tolerated dose and the dose for the phase II study were 60 and 45 mg m(-2) wk(-1), respectively. This combined therapy for locally advanced non-small cell lung cancer is promising and shows acceptable toxicity. (+info)