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M Löffler

Publications and source records attributed to M Löffler.

At least 55 records · Page 3Linked to original sources
PubMed1996

Anti-peptide immunoglobulins from rabbit and chicken eggs recognise recombinant human dihydroorotate dehydrogenase and a 44-kDa protein from rat liver mitochondria.

Mitochondrially bound dihydroorotate dehydrogenase catalyses the fourth sequential step in the de novo synthesis of uridine monophosphate. 312-bp and 983-bp regions of the human dihydroorotate dehydrogenase sequence (1496 bp) were amplified by the polymerase chain reaction, and subcloned into the expression vector pQE 32. The identity of the PCR products was verified by dideoxynucleotide sequencing. Transformation of Escherichia coli strain M15 resulted in expression of 13-kDa and 36-kDa proteins with an affinity tag consisting of six consecutive histidine residues; these proteins could be purified by solubilisation in 8 M urea and by chromatography on a Ni2+-chelating resin. In immunoblotting analyses, the fusion proteins were recognised by polyclonal avian and mammalian anti-peptide immunoglobulins. These were generated against synthetic peptides corresponding to two amino acid sequences deduced from human and rat cDNA of dihydroorotate dehydrogenase. The peptides were synthesized as multiple copies on a branching lysyl matrix. Rabbits and laying hens were immunized with these peptides without conjugation to a carrier protein. Comparison of the anti-peptide immunoglobulins produced from egg yolk and rabbit serum demonstrated that avian anti-(dihydroorotate dehydrogenase) immunoglobulins may be considered a superior alternative to the mammalian equivalent; antibodies from both sources were applicable for all immunochemical purposes. Here, these antibodies were applied for identification of a 44-kDa protein from rat liver mitochondria, which was correlated with dihydroorotate dehydrogenase activity.

Amino Acid Sequence↗
PubMed1996

Catalytic enzyme histochemistry and biochemical analysis of dihydroorotate dehydrogenase/oxidase and succinate dehydrogenase in mammalian tissues, cells and mitochondria.

Dihydroorotate dehydrogenase (EC 1.3.3.1 or EC 1.3.99.11) catalyzes the fourth sequential step in the de novo synthesis of uridine monophosphate. In eukaryotes it is located in the inner mitochondrial membrane, with ubiquinone as the proximal and cytochrome oxidase as the ultimate electron transfer system, whereas the rest of pyrimidine biosynthesis takes place in the cytosol. Here, the distribution of dihydroorotate dehydrogenase activity in cryostat sections of various rat tissues, and tissue samples of human skin and kidney, was visualized by light microscopy using the nitroblue tetrazolium technique. In addition, a hydrogen peroxide-producing oxidase side-reactivity of dihydroorotate dehydrogenase could be visualized by trapping the peroxide with cerium-diaminobenzidine. The pattern of activity was similar to that of succinate dehydrogenase, but revealed a less intensive staining. High activities of dihydroorotate dehydrogenase were found in tissues with known proliferative, regenerative, absorptive or excretory activities, e.g., mucosal cells of the ileum and colon crypts in the gastrointestinal tract, cultured Ehrlich ascites tumor cells, and proximal tubules of the kidney cortex, whilst lower activities were present in the periportal area of the liver, testis and spermatozoa, prostate and other glands, and skeletal muscle. Dihydroorotate dehydrogenase and succinate dehydrogenase activity in Ehrlich ascites tumor cells grown in suspension culture were quantified by application of nitroblue tetrazolium or cyanotolyl tetrazolium and subsequent extraction of the insoluble formazans with organic solvents. The ratio of dihydroorotate dehydrogenase to succinate dehydrogenase activity was 1:4. This was in accordance with that of 1:5 obtained from oxygen consumption measurement of isolated mitochondria on addition of dihydroorotate or succinate. The ratio determined with mitochondria from animal tissues was up to 1:15 (rat liver, bovine heart). The application of the enzyme inhibitors brequinar sodium and toltrazuril verified the specificity of the histochemical and biochemical methods applied.

Animals↗
PubMed1995

[Participation in multicenter studies as quality control in the therapy of Hodgkin disease: an interim report].

UNLABELLED: From 1988 to 1992 the Swiss Group for Clinical Cancer Research (SAKK) entered 113 patients with Hodgkin's disease into three stage adapted trials (HD-4-6) from the German Hodgkin Study Group (DHSG). In an interim analysis freedom from treatment failure (FFTF) and overall survival (OS) of the SAKK patients (SAKK-pt) were compared to the remaining study population (GHSH-pt) (median follow-up: 30 months for HD-4 and HD-5, 24 months for HD-6). RESULTS: HD-4: SAKK (n = 16), DHSG (n = 241), FFTF-SAKK: 100%, FFTF-DHSG: 85%, p: ns, OS-SAKK: 100%, OS-DHSG: 99%, p: ns, HD-5: SAKK (n = 66), DHSG (n = 639), FFTF-SAKK: 90%, FFTF-DHSG: 85%, p: ns, OS-SAKK: 93%, OS-DHSG: 95%, p: ns, HD-6; SAKK (n = 31), DHSG (n = 411): FFTF-SAKK: 62%, FFTF-DHSG: 68%, p: ns, OS-SAKK: 70%, OS-DHSG: 88%, p < 0.008. The results in the SAKK patients with advanced disease are unsatisfactory. Despite the fact that the treatment was given on time with full doses, 10/30 patients achieved no complete remission (CR). Only one patient relapsed after an initial CR. 6 patients had primary progressive disease. 6 patients died despite conventional salvage chemotherapy. High dose chemotherapy/autologous bone marrow transplantation (HDC/ABMT) was only given to 3 out of 8 potential candidates. Only 2/11 patients are still alive and disease-free after relapse or initial progression. Both had received HDC/ABMT as part of their salvage regimen. This interim analysis identifies a group of patients in which treatment strategies need to be optimized.

Adult↗
PubMed1995

Localization of dihydroorotate oxidase in myocardium and kidney cortex of the rat. An electron microscopic study using the cerium technique.

Biochemical studies have demonstrated that dihydroorotate dehydrogenase (DHOdehase; EC 1.3.3.1 or 1.3.99.11) is the sole enzyme of de novo pyrimidine synthesis in mitochondria, whereas the rest of the pathway takes place in the cytosol. The dehydrogenation of dihydroorotate to orotate is linked to the respiratory chain via ubiquinone. In this study, we show for the first time the ultrastructural localization of DHOdehase. Since the purified enzyme was found to act both as dehydrogenase and as oxidase, the cerium capture technique for detecting enzymatically generated hydrogen peroxide could be applied to pin-point the in situ activity of DHOdehase oxidase in mitochondria of rat heart and kidney cortex. Cerium perhydroxide as the final reaction product was detected predominantly in the matrix with some focal condensation along the inner membrane, but not in the intermembrane space. From this pattern of localization, it is concluded that the active site of the membrane-bound enzyme could face the mitochondrial matrix similar to succinate dehydrogenase. The reliability of the applied method for the demonstration of DHOdehase oxidase was demonstrated by the addition of Brequinar sodium to the incubation medium. This quinoline-carboxylic acid derivative is a potent inhibitor of DHOdehase and has proven anti-proliferative activity. The present observations do not ascertain whether the oxidase is permanently active as a constant portion of the enzyme in vivo, similar to xanthine oxidase/dehydrogenase. However, DHOdehase should be considered as a source of radical oxygen species under pathophysiological conditions.

Animals↗
PubMed1994

Regulation of cell proliferation under extreme and moderate hypoxia: the role of pyrimidine (deoxy)nucleotides.

In the present study we have used flow cytometric DNA measurements on synchronised human NHIK 3025 cells to measure cell cycle progression under various conditions of reduced oxygenation. Our data indicate that addition of 0.1 mM deoxycytidine or uridine has no effect on the oxygen-dependent arrest in late G1 or on the inhibition of cell proliferation through S-phase under extremely hypoxic conditions. Following reoxygenation of cells exposed to extremely hypoxic conditions in G2 initiation of DNA synthesis in the subsequent cell cycle is delayed by several hours. This G2-induced delay is completely abolished for approximately 60% of the cell population by addition of deoxycytidine to hypoxic G2 cells. This finding supports our previous proposal that important steps in the preparation for DNA synthesis occur during G2 of the previous cell cycle, and it indicates that this preparation is connected to the de novo synthesis of pyrimidine deoxynucleotide precursors. The results show that cells are able to enter S-phase in the presence of 100-1,300 p.p.m. (0.01-0.13%) oxygen (here denoted 'moderate hypoxia'), but they are not able to complete DNA synthesis under such conditions. However, the cell cycle inhibition induced under moderate hypoxia is partially reversed in the presence of exogenously added deoxycytidine and uridine, while no such reversal is seen in the presence of purine deoxynucleosides (deoxyadenosine and deoxyguanosine). Thus, both deoxycytidine and uridine could replace reoxygenation under these conditions. These results indicate that the reduction of CDP to dCTP by ribonucleotide reductase, an enzyme which requires oxygen as an essential factor for the formation of tyrosyl radicals for its catalytic activity, does not seem to be the limiting step responsible for the reduced dCTP pool observed under moderate hypoxia. We conclude that the oxygen-dependent catalytic activity of the M2 subunit of ribonucleotide reductase is still intact and functional in NHIK 3025 cells even at oxygen concentration as low as 100 p.p.m. Therefore the cell cycle inhibition observed is probably due to inhibition of the respiratory chain-dependent UMP synthesis at the stage of dihydroorotate dehydrogenase.

Carcinoma in Situ↗
PubMed1994

Prognosis of high dose chemotherapy/autologous bone marrow transplantation candidates not receiving this treatment after failure of primary therapy of Hodgkin's disease.

In a multicenter study on the therapy of Hodgkin's disease, in 88 out of 297 patients with primary advanced stages IIIB/IV, a failure to the treatment with the alternating chemotherapy COPP/ABVD +/- radiation was recorded. The cause of failure was as follows: tumor progression under current therapy (PD) 23/88, partial response at the end of therapy (PR) 28/88, early nodal relapses 13/88, late nodal relapses 16/88, extranodal relapses 7/88, undetermined localization 1/88.36 months after manifestation of the failure to treatment, 45% of all patients were still alive. In cases of primary PD the prognosis was the worst of all. Only 1/23 of these patients received a long-term continuous complete remission (cCR) with the salvage therapy. 11 patients with only a nodal relapse received a cCR with irradiation alone. These cases could be regarded as low risk relapses. For the high risk relapse group (n = 57) an indication for high dose chemotherapy with subsequent autologous bone marrow transplantation (HDC/ABMT) would have been imperative, following the present-day definition. The probability of survival of these patients who, however, only received a conventional salvage therapy was up to 38% (95% confidence interval 22-54%). Comparing these data with the literature our results seem not to be substantially worse than those for patients who underwent HDC/ABMT. Only in a randomized comparison can the decision be made on whether HDC/ABMT would be superior to high dose conventional chemotherapy supported by hematopoietic growth factors. It is suggested that such a therapy study be performed as soon as possible.

Adolescent↗
PubMed1992

[Recurrence of Hodgkin's disease after advanced primary stages. German Hodgkin's Study Group].

In a multicentre study on the treatment of Hodgkin's disease, 88 out of 297 patients with primary advanced stages IIIB/IV failed to respond to alternating COPP/ABVD chemotherapy +/- radiotherapy. They may be broken down as follows: tumour progression under current therapy (PD) 23/28, partial remission at the end of treatment (PR) 28/88, early nodal recurrence 13/88, late nodal recurrence 15/88, extranodal recurrence 7/88, unclear localisation 1/88. Thirty-six months after noting failure of treatment, 45% of all patients were still alive. The prognosis was poorest in the case of primary PD. Only 1/23 of these patients experience lasting complete remission thanks to salvage treatment (cCR). Eleven patients with an exclusively nodal recurrence experienced a cCR on treatment with radiation alone, and may be considered a low-risk recurrence group. For a high-risk recurrence group (n = 57), indication for high-dose chemotherapy with subsequent autologous bone marrow transplantation (HDC/ABMT) should have been recognized on the basis of the present definition. The survival probability of these patients, who only received conventional salvage treatment, was 38% after 30 months (95% confidence limit, 22 to 54%). These data would not appear to be appreciably poorer than those reported in the literature for comparable patients receiving HDC/ABMT. Only a randomized comparison would be capable of showing whether HDC/ABMT is superior to high-dose conventional chemotherapy with haematopoietic growth factors. It is proposed that such a therapeutic trial should be initiated as soon as possible.

Adolescent↗
PubMed1992

The "anti-pyrimidine effect" of hypoxia and brequinar sodium (NSC 368390) is of consequence for tumor cell growth.

The rationale of the present study was to investigate the simultaneous effect of hypoxia and drugs with an "anti-pyrimidine effect" on tumor cell proliferation to evaluate putative changes in the sensitivity of cells to these kinds of chemotherapeutic treatment on reduced O2 tension. Pyrimidine de novo biosynthesis, at the stage of respiratory chain-dependent dihydroorotate dehydrogenase, was found to be a biochemical target site for oxygen deficiency as well as for Brequinar Sodium (6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinoline carboxylic acid sodium salt) (Brequinar). Increasing drug concentrations (0.1-50 microM) reduced the proliferation rate of in vitro cultured Ehrlich ascites tumor cells (IC50 = 0.25 microM). Decreasing concentrations of O2 reduced the proliferation rate (50% at approximately 3.5% O2). Brequinar at 2.5 microM stimulated the incorporation of exogenous [14C]uridine into RNA to 140 and 190% of controls, respectively, as a result of active salvage pathways, whereas it decreased the incorporation of [14C]NaHCO3 by the de novo pathway (to 20 and 5% of controls, respectively). Cells routinely grown in glucose-free, uridine-supplemented medium were resistant to 12.5 microM of the drug. The complete growth pattern of the tumor cells (increase in cell number and protein, RNA and DNA content of cultures during a 24-hr culture period) was examined (i) on reducing the O2 tension of the atmosphere stepwise from 20 to 1% O2; (ii) on addition of 0.125 microM Brequinar; and (iii) under both conditions. The combination was found to give an additive inhibitory effect under moderate hypoxia (5-20% O2) and a greater than additive effect if the oxygen tension was further reduced (1-5%).

Animals↗
PubMed1992

Differential susceptibility of dihydroorotate dehydrogenase/oxidase to Brequinar Sodium (NSC 368 390) in vitro.

To verify the assumption of a specific and potent drug action on de novo pyrimidine biosynthesis, isolated dihydroorotate dehydrogenase (DHO-DH) (EC 1.3.3.1) was exposed to Brequinar Sodium (6-fluoro-2-(2'-fluoro-1,1'-biphenyl-4-yl)-3-methyl-4-quinoline carboxylic acid sodium salt, NSC 368 390) (Brequinar). The membrane-bound DHO-DH was purified to apparent homogeneity (25,000-fold) from rat liver mitochondria in six steps via detergent extraction and subsequent chromatography using the dye ligand Matrex Gel Orange A. Using molecular mechanistic studies (MM2) this ligand was found to mimic closely the stereochemical conformation of Brequinar. SDS-PAGE revealed two protein bands for the purified enzyme with apparent molecular masses of 58 (major) and 68 kDa (minor). In vitro, two modes of action of the DHO-DH are possible: (i) acting as a dehydrogenase in the presence of ubiquinone as proximal electron acceptor and (ii) direct reaction with oxygen as oxidase. A novel assay for the measurement of the oxidase activity was adapted using leuco-dichlorofluorescein-diacetate. Inhibition experiments revealed a striking difference in the susceptibility of DHO-dehydrogenase/oxidase to Brequinar: apparent Ki = 6.09 +/- 0.05 (SD) nM (DHO; ubiquinone n = 10), but Ki = 3.10 +/- 0.09 (SD) mM (DHO; O2). Analyses of initial velocity experiments showed non-competitive inhibition of Brequinar with respect to the substrate dihydroorotic acid in both assays (dehydrogenase and oxidase). The inhibitory effect of the latter was compared to that of the competitive inhibitor 5-aza-dihydroorotate (apparent Ki = 15 +/- 0.25 (SD) microM). The present kinetic data on the action of the purified rodent DHO-DH with Brequinar and computer-aided analyses provide a better insight into the drug-enzyme interaction.

Animals↗
PubMed1992

HLö 7 dimethanesulfonate, a potent bispyridinium-dioxime against anticholinesterases.

HLö 7 dimethanesulfonate (1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]-2,4-bis [(hydroxyimino)methyl]pyridinium dimethanesulfonate) is a broad-spectrum reactivator against highly toxic organophosphorus compounds. The compound was synthesized by a new route with the carcinogenic bis(chloromethyl)ether being substituted by the non-mutagenic bis(methylsulfonoxymethyl)ether. The very soluble dimethanesulfonate of obidoxime was also prepared by this way. HLö 7 dimethanesulfonate is the first water-soluble salt of HLö 7 that should be suitable for the wet/dry autoinjector technology, because aqueous solutions of HLö 7 are not very stable (calculated shelf-life 0.2 years when stored at 8 degrees C, 1 M solution, pH 2.5). The crystalline preparation contains 96% of the syn/syn-isomer, less than 2% of the syn/anti-isomer and some minor identified by-products. HLö 7 was very efficient in reactivating acetylcholinesterase (AChE) blocked by organophosphates as long as ageing did not prevent dephosphylation. HLö 7 was superior to HI 6 (1-[[[4-(aminocarbonyl)pyridinio]methoxy]methyl]-2- [(hydroxyimino)methyl]pyridinium dichloride) in reactivating soman and sarin-inhibited AChE from erythrocytes, and literature data indicate that HLö 7 exceeds HI 6 by far in reactivating tabun-inhibited AChE. In atropine-protected, soman-poisoned mice HLö 7 was three times more potent than HI 6 (protective ratio 5 versus 2.5), and in sarin-poisoned mice HLö 7 was 10 times more potent than HI 6 (protective ratio 8 for both oximes). In atropine-protected guinea-pigs HLö 7 was less effective than HI 6 (protective ratio: 2.3 versus 5.2 for soman; 5.2 versus 6.8 for sarin; 4.3 versus 3.8 for tabun). The mean survival time of anaesthetized guinea-pigs exposed to 5 LD50 soman (6.3 min) was increased by atropine (27 min) and atropine + HLö (57 min). HLö 7 alone did not prolong the survival. The most impressive effect of HLö 7 was on respiration: 3 min after i.v. injection of HLö 7 and atropine, the depressed respiration increased rapidly to 60% of control and remained at that level during the observation period (60 min). With atropine alone, respiration recovered only slowly. Behavioural and physiologic parameters were determined in atropine-protected mice exposed to a sublethal soman dose. The running performance was significantly improved by HLö 7. Even central symptoms, e.g. hypothermia and convulsions, were decreased markedly by HLö 7 (evaluation 60 min after poisoning). The pharmacokinetic data for HLö 7 in male beagle dogs are similar to those of HI 6.(ABSTRACT TRUNCATED AT 400 WORDS)

Animals↗
PubMed1992

A cytokinetic approach to determine the range of O2-dependence of pyrimidine(deoxy)nucleotide biosynthesis relevant for cell proliferation.

In vitro cultured Ehrlich ascites tumour (EAT) cells were used because of the ease of their manipulation under different levels of hypoxia. They were used to clarify further the complex mechanism of oxygen-dependent cell proliferation. On reducing the oxygen concentration from 20% to lower levels (1-7%) an increase in the length of the population doubling time with concomitant reductions in protein, RNA and DNA content of cultures were observed. The incorporation of [14C]HCO3- into the RNA fraction of cells by de novo biosynthesis of uridine monophosphate (UMP) was reduced proportionally to the microenvironmental O2 tension. Uptake of this labelled precursor by cells in the presence of N-phosphonoacetyl-L-aspartate was found to be similarly inhibited. To correlate the reduction of cell growth under hypoxia with the functional pyrimidine supply, hypoxic cells were cultured in the presence of a balanced mixture of deoxynucleosides and/or uridine (100 microM deoxycytidine, 10 microM deoxyadenosine, 10 microM deoxyguanosine, 100 microM uridine). Above 3% O2 in the protective atmosphere, no improvement of growth parameters by the exogenous pyrimidinenucleotide precursors was obtained, whereas these compounds had a positive influence below this level. The increase in cell number was raised to about 60% of that of control cultures (20% O2) irrespective of the oxygen tension. In addition, when above 3% O2 the incorporation of HCO3- into RNA was comparable to that of controls, indicating that the pyrimidine de novo pathway is not a limiting factor in RNA biosynthesis. In conclusion, whereas at suboptimal O2 levels (5-7%) no correlation between pyrimidine metabolism and reduction of proliferation rate appears to exist, at low O2 concentrations (less than 3%) the rate of orotate/UMP production seems to be an important factor in the growth cessation of EAT cells; at critical O2 tensions (less than 1%) the lack of pyrimidine-deoxynucleosides substantially reduces cell cycle progression.

Animals↗
PubMed1992

The Second International Symposium on Hodgkin's Disease. Workshop III: Recommendations for future clinical trials.

In the opinion of the participants of the workshop, the following problems should be addressed with high priority: 1st, a clear definition of the 10%-15% of patients who should receive radiotherapy only; 2nd, reduction of toxicity of combined modality approaches for patients in localized stages with risk factors; and 3rd, definition of a poor-prognosis subgroup of patients in stages IIIB/IV for whom more efficient treatment programs must be developed. Dose intensification in the form of ABMT as the prominent example of high dose intensity should be tested in these patients. If this approach proves its efficacy, the concept of dose intensification could be extended to other patients with advanced disease. Results of recent trials in Hodgkin's disease suggest that the cure rates which increased considerably between 1960 and 1980 have reached a plateau. Further improvements that can be realistically expected will be small and studies to prove such progress need large numbers of patients ('megatrials') to avoid 'false negative' results. Such megatrials could be performed as large international or even intercontinental trials. To some extent, overviews could substitute for megatrials, if sufficient high-quality randomized studies addressing a specific question are available for a meta-analysis. The installation of an international steering committee was recommended, which should stimulate and coordinate world-wide efforts for the solution of the remaining problems in the treatment of Hodgkin's disease.

Antineoplastic Combined Chemotherapy Protocols↗