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P Stadler

Publications and source records attributed to P Stadler.

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

Severe anemia is associated with poor tumor oxygenation in head and neck squamous cell carcinomas.

PURPOSE: To investigate the relationship between tumor oxygenation and the blood hemoglobin (Hb) concentration in patients with squamous cell carcinoma of the head and neck (SCCHN). METHODS AND MATERIALS: A total of 133 patients with SCCHN underwent pretreatment polarographic pO2 measurements of their tumors. In 66 patients measurements were also made in sternocleidomastoid muscles. The patients were divided into three groups according to their Hb concentration-severe anemia (Hb < 11.0 g/dl), mild anemia (female: Hb 11.0-11.9 g/dl; male: Hb 11.0-12.9 g/dl), and normal Hb concentration (female: Hb > or =12.0 g/dl; male: > or =13.0 g/dl). RESULTS: No significant difference in tumor oxygenation could be detected between mildly anemic patients and patients with a normal Hb level. However, the tumor oxygenation in the severely anemic group was significantly below that of each of the other two groups (p < 0.0001). There was no significant difference between the Hb groups in oxygenation of sternocleidomastoid muscles. In a multivariate analysis including Hb group, tumor volume, smoking habits, gender, T-stage, N-stage, and histologic grade a Hb level < 11 g/dl was found to be the strongest predictor for a poor tumor oxygenation. Smoking also had a marginal influence on median pO2. CONCLUSION: Our data suggest that a low Hb concentration and cigarette smoking contribute to inadequate oxygenation of SCCHN and thus for increased radioresistance. Consequently, Hb correction and abstinence from smoking may significantly improve tumor oxygenation.

Anemia↗
PubMed2000

[No association between p53 overexpression and polarographically measured tumor oxygenation in patients with head and neck carcinomas].

PURPOSE: Clinical investigation of a potential relationship between the polarographically measured tumor oxygenation and the p53 status in patients with squamous cell carcinoma of the head and neck. PATIENTS AND METHODS: In 99 patients with mostly advanced, histologically proven squamous cell carcinoma of the head and neck we estimated the classical tumor parameters (TNM stage, histological grading) the immunohistochemical p53-overexpression (DO-7) and the tumor oxygenation status (Eppendorf pO2 Histograph). The tumor volume and the hemoglobin concentration were evaluated simultaneously. RESULTS: No statistically significant difference could be detected between immunohistological p53-positive (p53 > or = 10% stained cells) and p53-negative tumors (p53 < 10% stained cells) regarding both the median pO2 and the relative frequency of values < or = 5 mm Hg. Moreover, no statistically relevant differences could be seen between both p53-groups considering the hemoglobin concentration, the TNM stage, the histological grading and the tumor volume. CONCLUSION: Our data imply that there is no association between p53-overexpression and tumor hypoxia in head and neck carcinomas. However, this is not necessarily in contradiction to experimental or clinical data that confirmed a relationship between hypoxia and p53-mediated increased malignancy of tumor cells in other tumor entities. The comparable oxygenation status of p53-positive and p53-negative tumors in our study is associated with an analogous clinical tumor aggressiveness of both groups. That could be caused by a hypoxia related but p53-independent selection of tumor cells with a more malignant phenotype in head and neck carcinomas. However, further research is needed to prove this possible relationship.

Adult↗
PubMed1999

Influence of the hypoxic subvolume on the survival of patients with head and neck cancer.

PURPOSE: Tumor hypoxia is regarded as an important factor influencing radiation response, disease-free, and overall survival of patients with squamous cell carcinoma of the head and neck (SCCHN). This study was performed to reevaluate the prognostic significance of the "classical oxygenation parameters" hypoxic fraction (percentage of pO2 values < 5 mmHg or < 2.5 mmHg, respectively) and median pO2, and to determine the influence of a new radiobiological factor. This factor was termed the "hypoxic subvolume" (HSV) and was defined as percentage of pO2-values below 5 mmHg multiplied by the total tumor volume. The rationale of this parameter was to quantify approximately the amount of hypoxic tissue which should be correlated to the number of hypoxic cells in the tumor. It is obvious that a tumor of 100 cm3 with a hypoxic fraction of 20% (HSV = 20 cm3) contains more hypoxic cells than a tumor of 1 cm3 with a hypoxic fraction of 50% (HSV = 0.5 cm3). METHODS AND MATERIALS: Pretreatment pO2 was assessed in 59 patients with SCCHN with the Eppendorf histograph, and pretreatment volume was determined by ultrasonography (lymphnode metastases) and computer tomography (primaries). All patients were referred to our departments for radiotherapy (n = 27, median dose 70 Gy) or radiochemotherapy (n = 32; 5-FU, mitomycin C, median dose 70 Gy), respectively. All parameters were evaluated using the Kaplan-Meier analysis, and significance was assumed at a p-value of < 0.05 (log-rank test, Cox-Mantel). A multivariate analysis was performed to control for confounding factors. The median follow-up was 233 days. At the time of the evaluation, 34 of the 59 patients were dead. RESULTS: In univariate analyses, the hypoxic fraction (pO2 < 5 mmHg, PO2 < 2.5 mmHg [p < 0.05]), the hemoglobin concentration (p < 0.05), and the hypoxic subvolume (p < 0.01) were of prognostic significance for overall survival. In multivariate analysis, the hemoglobin concentration and the hypoxic subvolume (p = 0.01) were significant prognosticators. We found no significant correlation between tumor volume or median pO2 and overall survival. No clear correlation was found between tumor volume and hypoxic fraction. CONCLUSION: These data suggest that the total amount of hypoxic tissue, as determined by the hypoxic subvolume, influences the prognosis of patients suffering from SCCHN. In addition, our data confirm the statements of previous studies that low pretherapy pO2-values indicate a worse prognosis.

Analysis of Variance↗
PubMed1999

Interactions of fluorescent triacylglycerol analogs covalently bound to the active site of a lipase from Rhizopus oryzae.

Fluorescent triacylglycerol analogs were synthesized as covalent inhibitors of lipase activity. The respective 1(3), 2-O-dialkylglycero-3(1)-alkyl-phosphonic acid p-nitrophenyl esters contain a fluorescent pyrenealkyl chain and a long-chain alkyl residue bound to the sn-2 and sn-1(3) positions of glycerol, respectively. The phosphonic acid p-nitrophenyl ester bond is susceptible to nucleophilic substitution by the active serine residue in the catalytic triad of a lipase, leading to inactivation of the enzyme. The fluorescent dialkylglycerophosphonates contain two chiral centers, the sn-2 carbon of glycerol and the phosphorus atom. The (1-O-hexadecyl-2-O-pyrenedecyl-sn-glycero)-O-(p-nitrophenyl)-n-hex yl- phosphonate, first peak during HPLC separation and the (3-O-hexadecyl-2-O-pyrenedecyl-sn-glycero)-O-(p-nitrophenyl)-n-hex yl- phosphonate, second peak during HPLC separation were found to be potent lipase inhibitors. After incubation of an equimolar amount of these isomers with lipase from Rhizopus oryzae complete inactivation was observed. Stable conjugates containing a 1 : 1 molar ratio of lipid to protein were formed. The spatial proximity of the fluorescently labeled sn-2 alkyl chain of the inhibitor and tryptophan residues of the lipase was assessed by fluorescence resonance energy transfer. The extent of tryptophan fluorescence quenching and the concomitant increase in pyrene fluorescence upon excitation of lipase tryptophans was found to be similar for the above-mentioned isomers. Thus, the (labeled) sn-2 alkyl chains of a triacylglycerol analog are likely to interact with the same binding site of the R. oryzae lipase, irrespective of their steric configuration. However, it was shown that the extent of resonance energy transfer is strongly influenced by the reaction medium, indicating conformational changes of the lipase in different environments.

Binding Sites↗
PubMed1999

Changes in head and neck tumor hypoxic fraction during split-course radiochemotherapy.

This study explored patterns of oxygen distribution in human tumors during primary radiochemotherapy. Patients with positive nodes from head and neck squamous cell carcinoma (n = 15) were investigated before therapy, before and after a 2-week respite, and at the end of the treatment. Intratumoral tissue oxygen tension (pO2) was measured with sterile polarographic needle electrodes and a computerized histography system. The 2 lowest pO2 classes, ie, 0 and 5 mm Hg, were designated the hypoxic fraction, and the mean and median pO2 were evaluated for each tumor. In the beginning, a marked variability in tissue pO2 was found. The initial size of the hypoxic fraction ranged from 0% to 61% of measured values. At the end of treatment, 4 tumors showed an increase in mean pO2, and 7 tumors a lower mean pO2 in comparison to the initial values. However, an impressive finding was that the hypoxic fraction of 9 tumors became smaller during the pause, 1 tumor showed no change, and 1 showed an increase in hypoxic fraction. The results show that there is a widely distributed tissue oxygenation with marked hypoxic zones in human neck nodes. During radiochemotherapy, tissue oxygenation changed, with great intertumor variability. A tendency toward a decrease of the hypoxic fraction after the respite could be seen. This change in tumor oxygenation during therapy needs further evaluation.

Adult↗
PubMed1998

Changes in tumor oxygenation during combined treatment with split-course radiotherapy and chemotherapy in patients with head and neck cancer.

PURPOSE: To evaluate the changes in tumor oxygenation during definitive split-course radiochemotherapy in locally advanced head and neck cancer (lymph nodes and primaries). MATERIALS AND METHODS: Twenty-four patients with locally advanced head and neck cancer were investigated pretherapeutically and during a defined course of radiochemotherapy (RCTh) with a total dose of 70 Gy given in 35 fractions over 9 weeks (2-week break after 30 Gy). In weeks 1 and 6, the patients received chemotherapy (5 FU and mitomycin C) concomitant with irradiation. The oxygen partial pressure measurements were carried out using polarographic needle probes in combination with a microprocessor-controlled device (pO2 histograph/KIMOC). Times of measurements were before therapy, at the end of week 3 (30 Gy), after a 2-week break (30 Gy) and at the end of therapy if measurable lesion was found (70 Gy). RESULTS: There was a significant reduction in the median pO2 (P < 0.005, n = 18) and an increase in the hypoxic fraction (defined as the percentage of pO2 values of <5 mm Hg) after application of 30 Gy (P < 0.05, n = 18). This effect was partially reversed at the end of the 2-week break. During the break an increase in the median PO2 (P = 0.05, n = 12) and a decrease in the hypoxic fraction could be observed. Towards the end of therapy (70 Gy) a significant decrease (P = 0.02, n = 13) in the median pO2 occurred. Corresponding to this, the hypoxic fraction increased during the last 4 weeks of therapy (P = 0.06, n = 13). CONCLUSION: Statistically significant changes in oxygenation in locally advanced head and neck cancer were found during a split-course radiochemotherapy. This information was obtained in a homogenous group of patients under well-defined therapeutic conditions. The decrease in the tumor oxygenation status at doses of 30 and 70 Gy are important findings because they are in contrast to the concept of continuous improvement of the oxygenation status during fractionated radiotherapy.

Adult↗
PubMed1998

Rational design of Rhizopus oryzae lipase with modified stereoselectivity toward triradylglycerols.

The binding site of sn-1(3)-regioselective Rhizopus oryzae lipase (ROL) has been engineered to change the stereoselectivity of hydrolysis of triacylglycerol substrates and analogs. Two types of prochiral triradylglycerols were considered: 'flexible' substrates with ether, benzylether or ester groups, and 'rigid' substrates with amide or phenyl groups, respectively, in the sn-2 position. The molecular basis of sn-1(3) stereoselectivity of ROL was investigated by modeling the interactions between substrates and ROL, and the model was confirmed by experimental determination of the stereoselectivity of wild-type and mutated ROL. For the substrates, the following rules were derived: (i) stereopreference of ROL toward triradylglycerols depends on the substrate structure. Substrates with 'flexible' sn-2 substituents are preferably hydrolyzed at sn-1, 'rigid' substrates at sn-3. (ii) Stereopreference of ROL toward triradylglycerols can be predicted by analyzing the geometry of the substrate docked to ROL: if the torsion angle phiO3-C3 of glycerol is more than 150 degrees, the substrate will preferably be hydrolyzed in sn-1, otherwise in sn-3. For ROL, the following rules were derived: (i) residue 258 affects stereoselectivity by steric interactions with the sn-2 substituent rather than polar interactions. To a lower extent, stereoselectivity is influenced by mutations further apart (L254) from residue 258. (ii) With 'rigid' substrates, increasing the size of the binding site (mutations L258A and L258S) shifts stereoselectivity of hydrolysis toward sn-1, decreasing its size (L258F and L258F/L254F) toward sn-3.

Glycerol↗
PubMed1998

Relevance of oxygen in radiation oncology. Mechanisms of action, correlation to low hemoglobin levels.

At the beginning of this century Schwarz (1909) and Holthusen (1921) observed the influence of oxygen on the radiosensitivity of cells. In 1951 Hollaender et al. described that E. coli needed 3-fold higher radiation doses when treated under anoxic conditions compared to normoxic conditions. This led to the evaluation of the oxygen enhancement ratio (OER) for photons (X-rays), neutrons and heavy ions. It was found that the OER for conventional radiation therapy (RT) with photons is much higher (about 3) than the OER for neutron-RT (only 1.5) or heavy ions. According to a hypothesis free radicals which are produced by radiation are fixed in the presence of oxygen. Radicals are interacting with DNA, macromolecules and membranes. The DNA lesion can be followed by cell death. There is some evidence that tumor cells respond to hypoxia with the expression of a variety of genes coding for oxygen regulated proteins such as c-jun, VEGF or p53. Hypoxia also enhances the genetic instability of tumor cells. Oxygen tensions in malignant tumors can be determined under clinical routine conditions by using a computerized polarographic needle electrode system (Eppendorf, Hamburg, Germany). Several studies in the past years showed that tumors are in general more hypoxic than the surrounding normal tissue and that a marked variability of intra- as well as intertumoral pO2 values exist (for review see Vaupel and Höckel 1998). Moreover, it has been shown in different tumor entities that the oxygenation status influences the local control rate and overall survival. Furthermore, the oxygenation status obtained at one site (primary) is significantly related at other sites (lymph node metastases) in patients with squamous cell carcinoma of the head and neck (SCCHN). In addition, there is a significant correlation between hemoglobin level and tumor oxygenation in patients with SCCHN. There is some evidence that the oxygenation status can be improved by the correction of a low hemoglobin level and consequently, the curative chance might rise.

Cell Hypoxia↗
PubMed1997

Modern pharmaceutical biotechnology. Situation worldwide and in Germany 1995.

A variety of new diagnostics and drugs have been developed with the aid of modern biotechnology which has opened up new medical possibilities and will yield novel solutions in the future. The remarkable dynamics of the innovation process in the pharmaceutical sector is reflected by the number of drugs under development. In 1995, 771 projects were known to be in development worldwide. The leadership of North America in research and development of drugs from modern biotechnology is clearly demonstrated. Whereas the number of development recombinant DNA products remained practically constant in the triade (North America, Europe, Japan), the number of preclinical and clinical somatic gene therapy projects increased considerably in 1995 compared to 1994 in the United States and in Europe; Japan is virtually absent in this new emerging research field. In Europe, the vast majority of drugs from modern biotechnology, are developed in Great Britain, Germany, Switzerland, France, the Netherlands, and Italy. The number of gene therapy projects show a remarkable growth of more than 60% in 1995 compared with 1994; at the same time, the absolute and relative share of recombinant DNA products decreased distinctly. In Germany, about two thirds of the development of biotechnological drugs are conducted in cooperation with a foreign partner, mostly hightech companies from the United States. A variety of drugs manufactured with modern biotechnology, however, has not only provided significant medical progress and has closed therapeutic gaps but has also demonstrated considerable economic success. In 2000, further significant growth is expected especially for growth factors and cytokines.

Biotechnology↗
PubMed1996

Inhibition of microbial lipases with stereoisomeric triradylglycerol analog phosphonates.

1,2(2,3)-Diradylglycero O-(p-nitrophenyl) n-hexylphosphonates were synthesized, with the diradylglycerol moiety being di-O-octylglycerol, 1-O-hexadecyl-2-O-pyrenedecanylglycerol, or 1-O-octyl-2-oleoyl-glycerol, and tested for their ability to inactivate lipases from Chromobacterium viscosum (CVL) and Rhizopus oryzae (ROL). The experimental data indicate the formation of stable, covalent 1:1 enzyme-inhibitor adducts with the di-O-alkylglycero phosphonates. The differences in reactivity of diastereomeric phosphonates with opposite configuration at the glycerol backbone was less expressed with both enzymes tested as compared to the influence of the stereochemistry at the phosphorus. Both lipases exhibited the same preference for the chirality at the phosphorus that was independent from the absolute configuration at the glycerol backbone. However, with CVL and ROL the inhibitors with the active site serine-directed phosphonate linked at position sn-1 of the glycerol moiety reacted significantly faster than the corresponding sn-3 analogs, reflecting the sn-1 stereopreference of the enzymes towards triacylglycerol analogs with a sn-2 O-alkyl substituent. In contrast, the phosphonates based on the 1-O-octyl-2-oleoylglycerol did not significantly inactivate CVL. Unexpectedly, these substances were hydrolyzed in the presence of lipase.

Chromatography, High Pressure Liquid↗
PubMed1996

Hydrolysis and esterification of acylglycerols and analogs in aqueous medium catalyzed by microbial lipases.

The stereoselectivity of microbial lipases from Chromobacterium viscosum (CVL) and Rhizopus arrhizus (RAL) towards monoacylglycerols (rac-1(3)-oleoylglycerol and 2-oleoylglycerol), diacylglycerols (1,3-dioleoylglycerol and rac-1,2(2,3)-dioleoylglycerol) and 2-O-ether analogs (rac-1(3)-oleoyl-2-O-hexadecylglycerol and rac-1(3)-octanoyl-2-O-hexadecylglycerol) was determined. The results of the hydrolysis of 2-O-ether analogs confirmed the importance of the substituent at C-2 of acylglycerols in the stereoselective recognition by microbial lipases and also showed that acylation of mono- and diradylglycerols with oleic acid overlaps the hydrolysis reaction in aqueous medium. With the short-chain, water-soluble octanoic acid no significant esterification occurred. Using rac-1,2(2,3)-dioleoylglycerol as a substrate for the hydrolysis with RAL and CVL, the appearance of 1,3-dioleoylglycerol and of 1(3)-monooleoylglycerol was demonstrated. The possibility of chemical vs. enzyme-catalyzed isomerization of 1,2-dioleoylglycerol and of 2-oleoylglycerol is discussed.

Chromobacterium↗
PubMed1996

Reduction of the infectivity of scrapie agent as a model for BSE in the manufacturing process of Trasylol.

The Trasylol manufacturing process was investigated with respect to its capacity for the inactivation/removal of infectivity causing bovine spongiform encephalopathy (BSE). Four process steps were selected for this investigation and scaled down to laboratory scale. Authentic samples of bovine lungs used in the Trasylol manufacturing plant were taken and spiked in laboratory scale experiments with high infectious titres of the rodent adapted scrapie strain ME 7 which served as model for BSE. After performing the respective process steps the output samples collected were tested in C57BL mice carrying the Sinc gene. An overall reduction of the infectious agent in the order of 18 log10 was observed, indicating a very high capacity of the Trasylol process for the inactivation/removal of the BSE/scrapie agent. The discussed safety strategy for the product leads to the conclusion that Trasylol is BSE safe.

Animals↗
PubMed1996

Quality assessment issues of new immunosuppressive drugs and experimental experience.

There are established quality assessment schemes for the two immunosuppressive drugs that have entered routine clinical use: cyclosporine and tacrolimus. These two drugs, together with sirolimus and mycophenolic acid, have been the subject of recent consensus panel reports that have reached broad agreement on several issues relating to therapeutic monitoring of these agents. While the current quality assessment schemes are not based on validated reference methods, the data they yield on comparative assay performance are of value as a guide to patient management and for clinical studies of drug efficacy.

Cyclosporine↗
PubMed1996

Transmissible spongiform encephalopathies (TSE): minimizing the risk of transmission by biological/biopharmaceutical products: an industry perspective.

Several guidelines and recommendations have been published on assessing the potential risk of a biological product being contaminated with an agent causing a Transmissible Spongiform Encephalopathy (TSE). Basic principles which can be used during the manufacturing of biological products to minimize the risk of transmission of TSE agents include the following: (i) obtaining animals, tissues or animal-derived raw materials from countries in which the relevant TSE agent is reported to be absent; (ii) screening animal-derived material for appropriate animal husbandry, feeding practices, health certification, tissue procurement and processing practices, and human-derived material for appropriate medical history information and, if relevant, plasma donor exclusion criteria; (iii) selection of tissue source of raw material with reference to potential risk for harbouring or amplifying TSE agents; (IV) human tropism of TSE agent of concern; (v) quantity of raw material used to manufacture a dose of product; (vi) number of daily doses required for indication; (vii) route of administration; (viii) indication and age of patient; and (ix) clearance capabilities by the product purification scheme. A risk evaluation will be represented for Trasylol (Aprotinin) which is manufactured from bovine lung tissue. Trasylol is a protease inhibitor used in the control of blood loss during open heart surgery. Bovine Spongiform Encephalopathy (BSE) is a concern when a product is derived from a bovine source. Even though only bovine lung tissue from BSE-free countries is used to manufacture Trasylol, it was decided, based on the primary tissue source selection, to evaluate the potential of the purification process to clear a TSE agent. Duplicate "spiking experiments" were performed using a mouse-adapted strain of scrapie as the model for BSE. Four steps in the purification process were evaluated. Titration of "spiked" loading material and output samples was performed at dilutions of 10(-4) to 10(-7) and undiluted to 10(-7), respectively. The sum of the purification steps evaluated provided a clearance factor in excess of 18 log10 for a TSE agent. An overall safety factor of 30 is obtained using the notification document issued by the Federal Health Office (Germany), dated February 16, 1994, on "Safety Requirements for Medical Products Derived from Body Constituents of Cattle, Sheep, or Goats to Avoid Risk of Transmission of BSE or Scrapie". Based on a six-parameter risk assessment, this document considered a product of low-risk for transmitting TSE agents if obtaining or exceeding a score of 20. Principles for minimizing the risk of transmission of TSE agents in products derived from primary tissues are contrasted to strategies for biotechnology products.

Animals↗
PubMed1995

Stereoselectivity of microbial lipases. The substitution at position sn-2 of triacylglycerol analogs influences the stereoselectivity of different microbial lipases.

In the present study, the stereoselectivity of purified lipases from Candida rugosa, Chromobacterium viscosum, Pseudomonas species and Rhizopus arrhizus towards triacylglycerols in comparison to various structural analogs were investigated. Different triacylglycerol analogs with distinct polarities at position sn-2 of the glycerol backbone (1,3-diacyl-2-X-glycerol, where 2-X = 2-acyloxy, 2-alkyloxy, 2-deoxy-2-alkyl, or 2-deoxy-2-phenyl) were synthesized. Substrate hydrophobicity and steric requirement was modified by variation of the alkyl and acyl chain length. Hydrolysis of these substrates demonstrated that minor structural variations at C2 of triacylglycerol strongly affect the stereoselectivity of the lipases tested. It was noteworthy that the variation of substrate structure did not only affect the quantity of stereoselectivity expressed as percentage enantiomeric excess, but also resulted in a reversal of stereopreference in some cases. Replacement of the acylester in position 2 of glycerol by a non-ester-linked aliphatic moiety shifted the preference of Chromobacterium viscosum lipase from sn-3 to sn-1. Lipases from Chromobacterium viscosum. Pseudomonas species and Rhizopus arrhizus exhibited sn-3 preference with 2-deoxy-2-phenyl analogs, while towards substrates with a 2-deoxy-2-alkyl moiety sn-1 stereobias was recorded. Candida rugosa lipase was rather insensitive to substrate variations concerning the polarity at position 2 of the glycerol backbone. However, variation of the acyl chain length significantly influenced stereoselectivity of this lipase.

Candida↗