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F Pajonk

Publications and source records attributed to F Pajonk.

12 recordsLinked to original sources
PubMed2005

Hypericin-an inhibitor of proteasome function.

Hypericin is the presumed active moiety within Saint John's wort. Extracts of Saint John's wort are widely used as an effective treatment for depression. Available as "over-the-counter" drugs, they are frequently part of the self-medication of patients undergoing radiation therapy for malignant diseases. In addition to antidepressive properties, hypericin has been shown to be able to induce apoptosis and radiosensitize tumor cells, and to have antiinflammatory and phototoxic skin effects. However, the underlying mechanisms are not clear. In this study, we investigated possible inhibitory effects of hypericin on proteasome function and related pathways. Extracts from U373 human glioma cells were incubated with different concentrations of hypericin. Three proteasome activities were monitored using a fluorogenic peptide assay. Activity of the transcription factor NF-kappaB and protein levels of p65, p50, IkappaBalpha and caspase-3 were investigated by EMSA and Western blotting, respectively. Hypericin caused a dose-dependent and photoactivation-independent inhibition of proteasome function. Hypericin treatment (6.25-50 microM) inhibited NF-kappaB, caused accumulation of phosphorylated IkappaBalpha, decreased p50 protein levels and induced cleavage of p65 protein in U373 cells. These effects were observed in MCF-7 cells only at higher concentrations of hypericin (12.5-50 microM). Additionally, inhibition of NF-kappaB activity in U373 cells by hypericin was prevented by caspase inhibition. Although hypericin clearly inhibits proteasome function, its effect NF-kappaB DNA-binding activity was not exclusively proteasome-dependent. The underlying mechanism might also involve caspase activation, a consequence of proteasome inhibition.

Anthracenes↗
PubMed2001

Epithelial cells in the peripheral blood of patients with cancer of the head and neck: incidence, detection and possible clinical significance.

In this study amplification of cytokeratin-19 mRNA by Reverse transcriptase-polymerase chain reaction (RT-PCR) was used to detect circulating tumor cells in the peripheral blood of patients with cancer of the head and neck before, during and after radiation therapy. Detection of cytokeratin-19-positive cells coincided with local failure, distant metastasis and anemia.

Adult↗
PubMed2001

Ionizing radiation affects 26s proteasome function and associated molecular responses, even at low doses.

BACKGROUND AND PURPOSE: Ionizing radiation is known to activate certain signal transduction pathways, the regulation of which could involve post-transcriptional as well as transcriptional mechanisms. One of the most important post-transcriptional pathways in eukaryotic cells is the ATP- and ubiquitin-dependent degradation of proteins by the 26s proteasome. This process controls initiation of many cellular stress responses, as well as inflammatory responses under control of the transcription factor NF-kappaB. The literature on the relationship between radiation and inflammation seems somewhat paradoxical. At high doses, radiation is generally pro-inflammatory. On the other hand, low dose radiation has a long history of use in the treatment of inflammatory disease. This suggests the involvement of multiple mechanisms that may operate differentially at different dose levels. MATERIALS AND METHODS: In this paper, the ability of different doses of ionizing radiation to directly affect 26s proteasome activity was tested in ECV 304 cells. Proteasome activity, IkappaBalpha protein levels, and NF-kappaB activation were monitored. RESULTS: Inhibition of chymotrypsin-like 20s and 26s proteasome activity was observed immediately after low- and high-dose irradiation either of cells or purified proteasomes. The inhibitory effect was independent of the availability of the known endogenous proteasome inhibitor heat shock protein 90 (hsp90). Levels of IkappaBalpha, a physiological 26s proteasome substrate, were increased only at low doses (0.25 Gy) and unaltered at higher doses whereas only the highest doses (8 and 20 Gy) activated NF-kappaB. CONCLUSIONS: We conclude that the proteasome is a direct target of ionizing radiation and suggest that inhibition of proteasome function provides a molecular framework within which low dose anti-inflammatory effects of radiation, and radiation-induced molecular responses in general, should be considered.

Cells, Cultured↗
PubMed2001

Molecular pathways that modify tumor radiation response.

Aberrant expression of signal transduction molecules in pathways controlling cell survival, proliferation, death, or differentiation are a common feature of all tumors. The identification of the molecules that are involved allows the development of novel tumor-specific strategies. Not surprisingly, targeting these pathways often also results in radiosensitization. The efficacy of such directed therapies may, however, be limited by the heterogeneity and the multiple mutations that are associated with the cancerous state. A more robust alternative may be to target global mechanisms of cellular control. The ubiquitin/proteasome degradation pathway is one candidate for such therapeutic intervention. This pathway is the main posttranscriptional mechanism that controls levels of many short-lived proteins involved in regulation of cell cycle progression, DNA transcription, DNA repair, and apoptosis. Many of these proteins are involved in various malignancies and/or radiation responses. In recent years, proteasome inhibitors have gained interest as a promising new group of antitumor drugs. PS-341, a reversible inhibitor of proteasome chymotryptic activity, is currently being tested in phase I clinical trials. In this study, we show that proteasome inhibition by PS-341 can alter cellular radiosensitivity in vitro and in vivo, in addition to having direct antitumor effects.

Animals↗
PubMed2001

The proteasome in cancer biology and treatment.

During the last 30 years, investigation of the transcriptional and translational mechanisms of gene regulation has been a major focus of molecular cancer biology. More recently, it has become evident that cancer-related mutations and cancer-related therapies also can affect post-translational processing of cellular proteins and that control exerted at this level can be critical in defining both the cancer phenotype and the response to therapeutic intervention. One post-translational mechanism that is receiving considerable attention is degradation of intracellular proteins through the multicatalytic 26S proteasome. This follows growing recognition of the fact that protein degradation is a well-regulated and selective process that can differentially control intracellular protein expression levels. The proteasome is responsible for the degradation of all short-lived proteins and 70-90% of all long-lived proteins, thereby regulating signal transduction through pathways involving factors such as AP1 and NFKB, and processes such as cell cycle progression and arrest, DNA transcription, DNA repair/misrepair, angiogenesis, apoptosis/survival, growth and development, and inflammation and immunity, as well as muscle wasting (e.g. in cachexia and sepsis). In this review, we discuss the potential involvement of the proteasome in both cancer biology and cancer treatment.

Animals↗
PubMed2000

Apoptosis and radiosensitization of hodgkin cells by proteasome inhibition.

PURPOSE: Malignant cells from Hodgkin's disease have been reported to be defective in regulation of NF-kappaB activity. Ionizing radiation is known to activate NF-kappaB, and it has been suggested that this pathway may protect cells from apoptosis following exposure to radiation and other therapeutic agents. Defective NF-kappaB regulation in Hodgkin cells could therefore dictate the response of this disease to therapy, as well as be responsible for maintaining the malignant phenotype. The purpose of this study was to explore whether NF-kappaB activity could be modulated in Hodgkin cells and whether it determines the response of these cells to treatment with ionizing radiation and/or dexamethasone. METHODS AND MATERIALS: Activation of NF-kappaB in cells is accomplished in large part by degradation of its inhibitor IkappaB through the 26s proteasome. HD-My-Z Hodgkin cells were treated with the proteasome inhibitor MG-132 or transduced with a dominant negative super-repressor IkappaBalpha. Clonogenic survival, apoptosis, proteasome activity, and NF-kappaB binding activity were monitored in response to ionizing radiation and/or dexamethasone treatment. RESULTS: HD-My-Z Hodgkin cells had modest NF-kappaB levels but, unlike other cell types, did not decrease their level of constitutively active NF-kappaB in response to proteasome inhibition with MG-132. In contrast, transduction with a non-phosphorable IkappaBalpha construct abolished expression. MG-132 did, however, induce apoptosis in HD-My-Z cells and sensitized them to ionizing radiation. Dexamethasone treatment had no effect on NF-kappaB activity or clonogenic survival of Hodgkin cells, but protected them from irradiation. CONCLUSION: We conclude that inhibition of 26s proteasome activity can induce apoptosis in HD-My-Z Hodgkin cells and radiosensitize them, in spite of the fact that their constitutively active NF-kappaB levels are unaltered. The proteasome may be a promising new therapeutic target for intervention in this disease. In contrast, the use of glucocorticoids in conjunction with radiation treatment for this tumor may require re-evaluation.

Antineoplastic Agents, Hormonal↗
PubMed1999

Inhibition of NF-kappaB, clonogenicity, and radiosensitivity of human cancer cells.

BACKGROUND: Activation of the transcription factor NF-kappaB is part of the immediate early response of tissues to ionizing irradiation. This pathway has been shown to protect cells from tumor necrosis factor-alpha, chemotherapy, and radiation therapy-induced apoptosis (programmed cell death). However, because the role of NF-kappaB as a modifier of the intrinsic radiosensitivity of cancer cells is less clear, we have studied the impact of NF-kappaB on the intrinsic radiosensitivity of human cancer cells. METHODS: We used PC3 prostate cancer cells and HD-MyZ Hodgkin's lymphoma cells transduced with an adenovirus vector that contains a gene encoding a form of IkappaB (an inhibitor of NF-kappaB) that cannot be phosphorylated. This form of IkappaB will remain bound to NF-kappaB; thus, NF-kappaB cannot be activated. We monitored NF-kappaB activity with a gel-shift assay and used a colony-forming assay to assess clonogenicity and radiosensitivity. RESULTS: Constitutive DNA-binding activity of NF-kappaB was dramatically decreased in PC3 cells transduced with the IkappaB super-repressor gene. The clonogenicity of transduced PC3 cells declined to 19.6% of that observed for untreated control cells, a finding similar to one we have previously demonstrated for IkappaB-transduced HD-MyZ cells. However, inhibition of NF-kappaB activity in the surviving PC3 and HD-MyZ cells failed to alter their intrinsic radiosensitivity. CONCLUSIONS: We conclude that activation of NF-kappaB does not determine the intrinsic radiosensitivity of cancer cells, at least for the cell lines tested in this study.

Adenoviridae↗
PubMed1999

Erythropoietin for patients undergoing radiotherapy: a pilot study.

BACKGROUND AND PURPOSE: To evaluate the feasibility and efficacy of using recombinant human erythropoietin (rhEPO) to correct decreased hemoglobin levels in patients undergoing radiotherapy and to get an estimate of its influence on the efficacy of radiotherapy. MATERIALS AND METHODS: Fifty patients with cancer of the head and neck and the pelvis were randomized before radiotherapy to different rhEPO treatments (none, 3 x 150 U/kg per week i.v., 3 x 300 U/kg per week i.v. and 3 x 150 U/kg per week s.c.). Hematological parameters were evaluated weekly and the locoregional tumor control rates were determined in 38 patients with head and neck cancer. RESULTS: rhEPO-treated patients showed a significant increase in their hemoglobin values (0.7 g/100 ml per week). The rhEPO response was comparable for patients with cancer of the head and neck and the pelvis. A delayed recovery was seen when iron deficiency or impaired iron mobilization was present. No serious toxicity was observed. Locoregional tumor control was improved, although not statistically significantly, in those head and neck cancer patients who experienced a rapid rise of hemoglobin. CONCLUSIONS: Low hemoglobin levels can be safely and quickly corrected with rhEPO. This may improve the effectiveness of radiotherapy.

Adolescent↗
PubMed1995

Epidural scar tissue formation after spinal surgery: an experimental study.

Extensive epidural scar formation is a well-known complication after spine surgery. Fibrous adhesions around nerve roots are a major reason for recurrent neurological symptoms following lumbar discectomy. A large variety of materials, implanted onto the dura, have been used to prevent or reduce laminectomy membrane, with conflicting results. We therefore carried out an experimental study in dogs to compare those materials that seemed to be most suitable. In each of 30 adult beagles, three lumbar laminectomies were performed. Each level was covered with a different material--free autologous fat graft, cellulose mesh, Gelfoam or triamcinolone suspension. In a control group nothing was implanted. After 7 days or 1, 3 or 6 months the animals were killed. The lumbar vertebral columns were harvested and prepared for further histological examination. To compare the results, we designed a new classification scheme (scar index). The data were obtained without knowledge of implanted material or time since operation. We found that free autologous fat grafts are able to reduce epidural scar formation in a high proportion of cases, especially after 3 and 6 months; cellulose mesh showed the worst results. We conclude that free autologous fat grafts are superior to other materials because of simple operative handling, good compatibility and effective prevention of laminectomy membrane.

Adipose Tissue↗
PubMed1994

[The scar tissue protective effect of free autologous fatty tissue transplants. An animal experiment on spinal surgery].

All spinal operations can be followed by the formation of extensive epidural scar tissue. The development of fibrous adhesions around the nerve roots is known to be the main cause of recurrent symptoms after lumbar discectomy. In the past many materials have been used to prevent or to reduce postlaminectomy membrane, with very different results. They have to be implanted onto the dura at the end of the operation. Therefore, we carried out the following controlled experimental study in dogs to compare the materials that seemed to be most suitable. In 30 adult beagles three lumbar laminectomies were performed. For each level a different material was used--free autologous fat graft, cellulose mesh, gel foam, triamcinolone suspension. Animals were sacrificed after 7 days and 1, 3, and 6 months. The lumbar vertebral columns were prepared for further histological examination. We found that free autologous fat grafts reduce epidural scarring in a high percentage, especially after 3 and 6 months. Only in this group good or excellent results were found at all lumbar levels (n = 18). To compare the results with each other we used a newly developed classification scheme (I-IV). The consistency and extent of scar tissue, the kind of cellular infiltrations, and adhesions to the surrounding structures were estimated separately. Cellulose mesh yielded the worst results. We conclude that free autologous fat is superior to other materials, because of: (1) simple and uncomplicated operative handling, (2) good compatibility and (3) effective prevention of postlaminectomy membrane.

Adipose Tissue↗