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T Szekeres

Publications and source records attributed to T Szekeres.

At least 37 records · Page 2Linked to original sources
PubMed2000

The ribonucleotide reductase inhibitor trimidox induces c-myc and apoptosis of human ovarian carcinoma cells.

Trimidox (3,4,5-trihydroxybenzohydroxamidoxime), a recently synthesized inhibitor of ribonucleotide reductase (RR), was shown to exert anti-proliferative activities in HL-60 and K562 human leukemia cell lines and to prolong the life span of mice inoculated with L1210 mouse leukemia cells. Here we test whether trimidox also exhibits anti-neoplastic properties in ovarian carcinoma cells. Since the mode of action of trimidox on cell fate has not been investigated so far, we addressed this unresolved item and find that this polyhydroxybenzoic acid derivative induces apoptosis of N.1 human ovarian carcinoma cells when tested in growth factor deprived medium. Utilizing an improved analysis, based on Hoechst 33258/propidium iodide double staining, apoptosis is quantified and discriminated from necrosis. Trimidox induces c-myc expression, which is indispensible for apoptosis of N.1 cells, and expression of plasminogen activator/urokinase type (upa), which supports the apoptotic process under more physiological conditions. Surprisingly, trimidox does not block dNTP synthesis in N.1 cells at the concentrations tested and, therefore, trimidox induces apoptosis independent of RR-inhibition. Like TNFalpha or benzamide riboside, which are also inducers of apoptosis of N.1 cells, trimidox also down-regulates the G1 cell cycle phosphatase cdc25A, whereas cyclin D1 becomes up-regulated. This report shows that trimidox destroys human ovarian carcinoma cells by inducing them to undergo apoptosis as well as corroborating previous investigations which demonstrated that apoptosis of these cells depends on c-myc over-expression when survival factors are withdrawn.

Antineoplastic Agents↗
PubMed2000

Pancreatic elastase 1 in stool: variations within one stool passage and individual changes from day to day.

Concentration of fecal pancreatic elastase 1 has been claimed to be a highly sensitive and specific noninvasive test for exocrine pancreatic function. The aim of our study was to investigate variations in elastase concentration within one stool passage and from day to day. For the analysis of the variation of fecal elastase within one stool passage, we utilized 3 different samples collected from 8 patients. Further, we assessed the individual day to day variation of fecal elastase using stools collected on 3 consecutive days from 40 patients. For the determination of pancreatic elastase 1 in stool we used an ELISA kit. We found a relatively considerable variation of fecal elastase concentration within one stool passage (n = 8, mean CV = 22%, range 4.6-83.1%) and from day to day (n = 40; mean CV = 26%, range 2.4-61.1%). Therefore, we recommend routine analysis of more than 1 stool sample collected on different days for fecal elastase and to use a borderline area of +/- 25% of the recommended cut off of 200 micrograms/g stool for the diagnosis of pancreatic insufficiency.

Enzyme-Linked Immunosorbent Assay↗
PubMed2000

Trimidox, an inhibitor of ribonucleotide reductase, induces apoptosis and activates caspases in HL-60 promyelocytic leukemia cells.

Ribonucleotide reductase (RR) is the rate-limiting enzyme for the de novo synthesis of deoxyribonucleotides. Its activity is significantly increased in tumor cells related to the proliferation rate. Therefore, the enzyme is considered to be an excellent target for cancer chemotherapy. In the present study, we investigated whether the antineoplastic effects of trimidox (3,4, 5-trihydroxybenzamidoxime), a novel inhibitor of RR, were due to induction of apoptosis.HL-60 cells were incubated with various concentrations of trimidox. Consequently, cell morphology, DNA condensation, annexin binding, DNA fragmentation, and signature type cleavage of poly(ADP-ribose)polymerase and gelsolin were determined. We also tested the involvement of CD95 and CD95 ligand in apoptosis induction. Furthermore, we examined the c-myc expression of HL-60 cells after incubation with trimidox in order to elucidate a possible association between c-myc expression and induction of apoptosis in the case of trimidox. Trimidox incubation caused a time-dependent increase of c-myc RNA expression and this was accompanied by the induction of apoptosis. Apoptosis was triggered independently of CD95 by the activation of caspases and PARP cleavage. We conclude that trimidox is able to induce programmed cell death. The induction of apoptosis was demonstrated by various biochemical and morphological methods and seems to be associated with the induction of c-myc. Apoptosis was induced by the activation of caspases and without change of the CD95 and CD95 ligand expression.

Antineoplastic Agents↗
PubMed2000

Cyclosporine metabolism in patients after kidney, bone marrow, heart-lung, and liver transplantation in the early and late posttransplant periods.

Cyclosporine is used in the prevention of allograft rejection. Owing to its narrow therapeutic index, regular monitoring of the whole blood levels of cyclosporine is required. We observed that immunoassays measured significantly higher cyclosporine levels than did high-performance liquid chromatography (HPLC) over time after transplantation. As cyclosporine metabolites cross-react even with immunoassays, this observation might be due to alterations of the cyclosporine metabolism. We analyzed cyclosporine metabolite concentrations in the early and in the late posttransplantation periods in 127 patients after kidney, bone marrow, heart-lung, and liver transplantation by HPLC and determined whole blood levels of cyclosporine by 4 immunoassays (enzyme-multiplied immunoassay [EMIT], cloned enzyme donor immunoassay [CEDIA], AxSYM [Abbott Laboratories, Chicago, IL], and TDx [Abbott Laboratories]). Despite reduced dose, we found significantly higher cyclosporine concentrations measured by the EMIT, AxSYM, and TDx assays in various patient groups. These results are due to the increased metabolite/cyclosporine ratio in the late posttransplantation period. In particular, the metabolites AM1 and AM19 increased significantly over time in bone marrow transplant recipients. Therefore, cyclosporine levels measured by immunoassays should be interpreted with caution.

Bone Marrow Transplantation↗
PubMed1999

Studies on the antitumor activity and biochemical actions of cyclopentenyl cytosine against human colon carcinoma HT-29 in vitro and in vivo.

Cyclopentenyl cytosine (CPEC) is cytotoxic to several tumor cell lines. CPEC inhibits CTP synthesis resulting in depletion of cytidylate pools. The aim of this study was to examine CPEC's cytotoxic and antitumor activity in vitro and in vivo against human colon carcinoma HT-29, and to relate its action on CTP synthesis. CPEC exhibits potent cytotoxicity in vitro to HT-29 cells with an LC50 (concentration that is lethal to the survival of 50% cell colonies) of 2.4 microM and 0.46 microM following 2 h and 24 h exposure, respectively. Incubation of cells with CPEC for 2 h resulted in a dose-dependent decrease in cytidylate pools. The in vivo antitumor activity of CPEC in athymic mice transplanted subcutaneously (s.c.) with 3 million HT-29 cells was examined. Antitumor activity of CPEC was elucidated in early-staged tumor, wherein CPEC (1.5 mg/kg, QD x 9 or 3 mg/kg, QOD x 9) was administered intraperitoneally (i.p.) 24 h after tumor implantation and it resulted in a significant reduction in tumor weight to 48% of control. The effect of CPEC on established solid tumors in vivo was examined in athymic mice transplanted s.c. 14 days earlier with HT-29 cells and treated i.p. with 1.5 mg/kg CPEC, QD x 5 for 4 courses, with a 10 day-interval between courses. This treatment resulted in a significant reduction in tumor weight (72%) in the treated group. HPLC analysis of HT-29 tumor obtained from mice after treatment with CPEC showed a depletion of the CTP concentration reaching a nadir at 8 h. In conclusion, the present studies demonstrate potent antitumor activity of CPEC against freshly transplanted and established human colon carcinoma which can be corroborated with the drug's biochemical actions.

Adenosine Triphosphate↗
PubMed1999

Benzamide riboside induces apoptosis independent of Cdc25A expression in human ovarian carcinoma N.1 cells.

One of the mechanisms of action of a new oncolytic agent, benzamide riboside (BR) is by inhibiting inosine 5'-monophosphate dehydrogenase (IMPDH) which catalyzes the formation of xanthine 5'-monophosphate from inosine 5'-monophosphate and nicotinamide adenine dinucleotide, thereby restricting the biosynthesis of guanylates. In the present study BR (10 - 20 microM) induced apoptosis in a human ovarian carcinoma N.1 cell line (a monoclonal derivative of its heterogenous parent line HOC-7). This was ascertained by DNA fragmentation, TUNEL assay, [poly(ADP)ribose polymerase]-cleavage and alteration in cell morphology. Apoptosis was accompanied by sustained c-Myc expression, concurrent down-regulation of cdc25A mRNA and protein, and by inhibition of Cdk2 activity. Both Cdk2 and cdc25A are G1 phase specific genes and Cdk2 is the target of Cdc25A. These studies demonstrate that BR exhibits dual mechanisms of action, first by inhibiting IMPDH, and second by inducing apoptosis, which is associated with repression of components of the cell cycle that are downstream of constitutive c-Myc expression.

Adenocarcinoma↗
PubMed1999

Evaluation of four automated methods for determination of whole blood cyclosporine concentrations.

Cyclosporine is a widely used and potent immunosuppressant drug with a narrow therapeutic index. Therefore, cyclosporine concentrations should be monitored closely. Various automated immunologic methods for cyclosporine whole blood determinations are available. Two new methods, fluorescence polarization immunoassay (FPIA) for the AxSYM by Abbott Laboratories, Chicago, IL, and the cloned enzyme donor immunoassay (CEDIA) by Boehringer Mannheim, Mannheim, Germany, have been introduced. In addition, Dade Behring improved its enzyme multiplied immunoassay (EMIT) assay. The present study evaluated all 3 new methods in comparison with high-performance liquid chromatography (HPLC) and the FPIA for the TDx analyzer. We measured whole blood cyclosporine concentrations of 179 samples obtained from 127 patients after kidney, bone marrow, heart-lung, and liver transplantation. All 4 automated immunologic methods can be used for routine measurement of cyclosporine whole blood concentrations. Disadvantages, such as higher cross-reactivity (Abbott TDx, CEDIA) or a limited linearity range (EMIT), are accompanied by advantages, such as a high precision (Abbott TDx) or an easy sample handling procedure (CEDIA). Information presented in this article should help to find the most adequate cyclosporine method for each medical laboratory.

Antibodies, Monoclonal↗
PubMed1998

Growth promotion by homocysteine but not by homocysteic acid: a role for excessive growth in homocystinuria or proliferation in hyperhomocysteinemia?

Excessive growth of long bones in patients with homocystinuria is still unexplained and previous work incriminating homocysteic acid could not be confirmed by others. In vitro studies from our laboratory showed that homocysteine stimulated growth in a clonogenic assay. This observation made us study plasma cyclin dependent kinase (CDK), homocyst(e)ine and homocysteic acid in 10 patients with homocystinuria and 20 controls. In addition, homocysteine and homocysteic acid were tested in a clonogenic assay to correlate the growth promoting activity with CDK. Plasma CDK (protein) correlated strongly with homocysteine (r=0.84) but not with homocysteic acid. Supernatants of the clonogenic assay samples showed up to three times higher CDK levels in the presence of homocyst(e)ine but not homocysteic acid. In vitro data and the strong correlation between homocysteine and CDK suggest a role for homocysteine stimulating CDK, the starter of mitosis, with subsequent stimulation of growth.

Adolescent↗
PubMed1998

Iron binding capacity of didox (3,4 dihydroxybenzohydroxamic acid) and amidox (3,4 dihydroxybenzamidoxime) two inhibitors of the enzyme ribonucleotide reductase.

Ribonucleotide reductase is the rate limiting enzyme of deoxynucleoside triphosphate synthesis and is considered to be an excellent target of cancer chemotherapy. Didox and amidox are newly synthesized compounds, which inhibit this enzyme and have in vitro and in vivo antitumor activity. We have now investigated the capability of didox and amidox to interfere with the iron metabolism. We show by photometric and polarographic methods, that didox and amidox are capable of forming an iron complex. However, their cytotoxic action cannot be circumvented by addition of Fe-ammoniumcitrate, indicating the iron complexing capacity not to be responsible for the mechanism of action of these compounds. When L1210 leukemia cells were incubated with the didox-iron or amidox-iron complex itself, only slight changes of the 50% growth inhibitory capacity of the complex in comparison with didox or amidox alone could be shown. We conclude, that didox and amidox are capable of forming an iron complex, but in contrast to other agents, the anticancer activity cannot be contributed to this effect alone. Further studies will have to elucidate the molecular mechanism of action of these new and promising anticancer agents.

Animals↗
PubMed1998

Are allergic reactions to skin clips associated with delayed wound healing?

BACKGROUND: Metal skin clips are used in surgery. They may contain metals that might cause allergic reactions and delayed wound healing. METHODS: The metal composition of 18 different surgical clamps was examined. The allergy status of 184 patients was determined by patch tests and was correlated with the clinical outcome of wound healing after application of skin clips. RESULTS: Skin clips contained chromium, nickel, molybdenum, cobalt, and titanium in concentrations high enough to cause allergic reactions. Eighteen percent of the men and 23% of the women were sensitive to nickel and 16% of the men to chromium. We found a positive correlation between the grade of nickel allergy and the reaction to the skin clips. CONCLUSIONS: Our study suggests that allergic reactions and delayed wound healing can be caused by the use of surgical skin clips. Therefore skin clips are not recommended for patients with a history of contact dermatitis to metals and/or atopy.

Adolescent↗
PubMed1998

Enhanced effects of adriamycin by combination with a new ribonucleotide reductase inhibitor, trimidox, in murine leukemia.

Ribonucleotide reductase is the rate limiting enzyme of de novo DNA synthesis; its activity is significantly increased in tumor cells related to the proliferation rate. Therefore the enzyme is considered to be an excellent target for cancer chemotherapy. In the present study we tested the in vitro and in vivo antitumor effects of a drug combination using trimidox (3,4,5-trihydroxybenzamidoxime), a novel inhibitor of ribonucleotide reductase with adriamycin, a widely used anticancer drug. This combination was selected because adriamycin generates free radicals being responsible for cardiotoxic side effects; trimidox has been shown to be a good free radical scavenger. The in vitro cytotoxic effect of the drug combination was examined in L1210 mouse leukemia cells employing a MTT chemosensitivity assay. Incubation of these cells with adriamycin and trimidox together yielded less than additive cytotoxic effects compared to either drug alone. These effects were not caused by the involvement of p-glycoprotein mediated drug efflux. However, when the effect of trimidox and adriamycin in combination was examined in L1210 leukemia bearing mice antitumor effects of adriamycin could be enhanced by the presence of trimidox. Our data indicate, that the in vivo combination of adriamycin together with trimidox might be beneficial for the treatment of malignancies.

Animals↗
PubMed1998

Low-dose aspirin does not lower in vivo platelet activation in healthy smokers.

Smoking causes atherosclerosis, and smokers have increased thromboxane (TXA2) formation. As aspirin inhibits TXA2 production we speculated that smokers would preferentially profit from inhibition of the TXA2 pathway by aspirin. Increased expression of P-selectin, a constituent of the alpha-granules of platelets, and increased levels of circulating (c)P-selectin in plasma are markers for platelet activation. The aim of this study was to compare P-selectin expression on platelets between smokers and nonsmokers, and to compare with placebo the effect of 2 weeks administration of 100 mg/d aspirin on platelet activation in smokers. Smokers exhibited higher P-selectin expression on platelets than non-smokers (2.7+/-1.8% v 1.6+/-0.6%, P=0.018), thus confirming increased platelet activation. Aspirin did not reduce platelet activation as demonstrated by unchanged P-selectin expression on platelets and cP-selectin plasma levels.

Adult↗
PubMed1998

Staurosporine enhanced benzamide riboside-induced apoptosis in human multidrug-resistant promyelocytic leukemia cells (HL-60/VCR) in vitro.

The inosine monophosphate (IMP) dehydrogenase inhibitor benzamide riboside (BR) induced apoptosis (detected with the aid of flow cytometric identification of cells with sub-G0 DNA content and increased side angle light scatter) equally or slightly more intensively in the multidrug-resistant human promyelocytic leukemia cell line (HL-60/VCR: MDR-1 gene, Pgp positive) in comparison with the parental drug sensitive HL-60 cells. Staurosporine alone induced relatively low level of apoptosis in parental HL-60 cells but higher level (approximately 35%) of apoptosis in multidrug-resistant HL-60/VCR cells after 24 hour induction. The combination of benzamide riboside and staurosporine induced in both drug-sensitive and drug-resistant HL-60 cells a marked proportion of apoptotic cells already after short (6 hour) induction (more than 30% of apoptotic cells).

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1997

Simultaneous determination of the new anticancer agent amidox and its metabolites in rat bile and plasma by high-performance liquid chromatography.

A new reversed-phase ion-pair high-performance liquid chromatography method was developed to study the first-pass hepatic metabolism of the anti cancer drug amidox in bile. Separation of the metabolites was achieved on a Spherisorb C18 column after liquid-liquid extraction using a linear gradient system of heptanesulfonic acid in potassium phosphate monobasic (pH 4.0) with increasing amounts of methanol (0-40%). The method was further applied to a pharmacokinetic study of amidox in rats after 200 mg kg-1 intraperitoneal administration. Using 50 microliters of rat bile and 300 microliters of rat plasma the limit of detection for amidox was 60 ng and 85 ng, respectively, and the assay was linear from 0.1 to 150 micrograms ml-1. This method appears to be sensitive enough to be used in further pharmacokinetic studies of amidox in human volunteers.

Animals↗
PubMed1997

Iron binding capacity of didox (3,4-dihydroxybenzohydroxamic acid) and amidox (3,4-dihydroxybenzamidoxime) new inhibitors of the enzyme ribonucleotide reductase.

Ribonucleotide reductase is the rate limiting enzyme of deoxynucleoside triphosphate synthesis and is considered to be an excellent target of cancer chemotherapy. Didox and amidox are newly synthesized compounds, which inhibit this enzyme and have in vitro and in vivo antitumor activity. We have now investigated the capability of didox and amidox to interfere with the iron metabolism. We show by photometric and polarographic methods, that didox and amidox are capable of forming an iron complex. However, their cytotoxic action cannot be completely circumvented by addition of Fe-ammoniumcitrate, indicating that the iron complexing capacity may not be responsible for the mechanism of action of these compounds. When L1210 leukemia cells were incubated with the didox-iron or amidox-iron complex itself, changes of the 50% growth inhibitory capacity of the complex in comparison with didox or amidox alone could be shown. We conclude, that didox and amidox are capable of forming iron complexes, but in contrast to other agents, the anticancer activity cannot be contributed to this effect alone. Future studies will have to elucidate the molecular mechanism of action of these new and promising anticancer agents.

Animals↗
PubMed1997

The new inhibitors of ribonucleotide reductase--comparison of some physico-chemical properties.

Amidox (AX), didox (DX) and trimidox (TX), compounds synthetized as new ribonucleotide reductase inhibitors, have been investigated by ultraviolet (UV) spectrophotometry, polarography and high performance liquid chromatography (HPLC). The experiments have been performed at various pH values. The changes in UV absorption of the compounds studied were recorded and it was demonstrated that these changes are related to the pH and to structural features of the investigated molecules. From the compounds included in our series of experiments, only amidox and trimidox are reduced during polarographic experiments in Britton-Robinson buffer. The reduction of both compounds proceeded in two one-electron steps in acidic pH. One two-electron diffuse irreversible wave was observed at basic pH. The values of the half-wave potential became more negative in accordance with the increasing pH. HPLC assay also showed changes in the retention of compounds investigated, particularly when the pH of the mobile phase was close to the dissociation constant of the particular drug. The changes of physico-chemical properties detected by the all used methods are related to different chemical structures (the most significant changes were observed in alkaline pH).

Benzamidines↗
PubMed1997

The enzyme ribonucleotide reductase: target for antitumor and anti-HIV therapy.

Ribonucleotide reductase is the rate-limiting enzyme of DNA synthesis, and it has been shown to be linked with malignant transformation and tumor cell proliferation. It was therefore considered as an excellent target for cancer chemotherapy. This article reviews the in vitro and in vivo effects of hydroxyurea the first inhibitor of the enzyme, which is currently used in general clinical practice. In addition, we summarize the results obtained with other inhibitors of the enzyme; for instance, polyhydroxy-substituted benzohydroxamic acid derivatives, a promising group of inhibitors of ribonucleotide reductase that was synthesized by Bart van'T Riet and investigated by our group. In vitro as well as animal data and pharmacokinetic results are reviewed and possible implications for an improvement in the management of various patient groups are outlined.

Antineoplastic Agents↗