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J Pohl

Publications and source records attributed to J Pohl.

At least 145 records · Page 8Linked to original sources
PubMed1988

Basis and new developments in the field of oxazaphosphorines.

All the research results summarized herein were gained in the attempt to improve selectivity in cancer chemotherapy: "Chemotherapeutic agents are not only ends in themselves, they are also beginnings,. . . Selectivity must be our goal and understanding its basis our guide to the future" (138). The development of the OAP cytostatics CP, IFO, TRO, and SUFO derives from the idea of applying the principle of transport form/active form to the highly reactive nitrogen mustard compounds. The desired conversion of the reactive nitrogen mustard into an inactive transport form (latentiation) was performed by chemical synthesis. The requirement for an enzymatic activation of the transport form to give the active form in the target organ cancer cell was met and has been shown to occur in a sequence of various metabolic reactions. The goal of a substantial increase in the therapeutic range of alkylating agents has been achieved with the development of the OAP cytostatics. The higher cancerotoxic selectivity is closely correlated with the cytotoxic specificity of their activated primary metabolites. A further increase in the cancerotoxic selectivity in OAPs was achieved by the development of mesna as a regional uroprotector. Mesna eliminates the danger of therapy-limiting urotoxic side effects of OAPs, allowing administration of higher dosages and more safely optimizing their therapeutic efficacy and partly overcoming resistance phenomena. The stabilization of the primary OAP metabolites (MAFO), opens up new possibilities in clinical therapy and in preclinical tests, for examination in the clonogenic stem cell test, for in vitro purging in ABMT, and for the regional therapy of tumors. A completely new type of therapy is emerging for OAP, specifically for low-dosage MAFO, as an immunomodulator, under certain circumstances, in combination with further substances, from the biological response modifier group.

Animals↗
PubMed1988

Identification of the second (buried) cysteine residue and of the C-terminal disulfide bridge of bovine spleen cathepsin B.

Quantitative differences were found when bovine spleen cathepsin B was subjected to SH-group titration in the presence and in the absence of denaturing agents, as well as when the pH of the titration buffer was increased. The intra- and interchain thiol-disulfide exchange reactions accompanying the denaturation of cathepsin B were investigated by polyacrylamide gel electrophoresis in SDS and by gel filtration experiments. An identical behavior in these experiments showed also cathepsin B whose active site Cys29 only had been carboxymethylated; these findings suggested the presence of one additional SH-group. After conditions preventing thiol-disulfide exchange reactions, had been developed, the second SH-group (Cys240) was demonstrated independently in carboxymethylated cathepsin B by labeling with 4-(dimethylamino)azobenzene-4'-iodoacetamide and by selective isolation of the SH-peptide containing Cys240 on thiopropyl-Sepharose. As the second important result, a disulfide bridge formed by Cys148 and Cys252 in the C-terminal part of the chain was identified.

Amino Acid Sequence↗
PubMed1987

Chromophoric and fluorophoric peptide substrates cleaved through the dipeptidyl carboxypeptidase activity of cathepsin B.

The action of bovine spleen cathepsin B as a dipeptidyl carboxypeptidase on newly synthesized substrates of the type peptidyl-X-p-nitrophenylalanyl (Phe(NO2))-Y (X,Y = amino acid residue) or 5-dimethylaminonaphthalene-1-sulfonyl (Dns)-peptidyl-X-Phe(NO2)-Y was investigated. The kinetic parameters of hydrolysis of the X-Phe(NO2) bond were determined by difference spectrophotometry (delta epsilon 310 = 1600 M-1 cm-1) or by spectrofluorometry by following the five- to eightfold increase of Dns-group fluorescence with excitation at 350 nm and emission at 535 nm. The substrates were moderately sensitive to cathepsin B; kcat varied from 0.7 to 4 s-1 at pH 5 and 25 degrees C; Km varied from 6 to 240 microM. The very acidic optima of pH 4-5 are characteristic for dipeptidyl carboxypeptidase activity of cathepsin B. Bovine spleen cathepsins S and H had little and no activity, respectively, when assayed with Pro-Glu-Ala-Phe(NO2)-Gly. These peptides should be a valuable tool for routine assays and for mechanistic studies on cathepsin B.

Cathepsin B↗
PubMed1987

Anticancer agents coupled to N-(2-hydroxypropyl)methacrylamide copolymers. I. Evaluation of daunomycin and puromycin conjugates in vitro.

During recent years N-(2-hydroxypropyl)methacrylamide (HPMA) copolymers have been developed as targetable drug carriers. These soluble synthetic polymers are internalized by cells by pinocytosis and they can be tailor-made to include peptidyl side-chains degradable intracellularly by specific lysosomal enzymes. Thus they provide the opportunity fo achieve controlled intracellular delivery of anticancer agents. The anthracycline antibiotic daunomycin, and protein synthesis inhibitor puromycin, were bound to HPMA copolymers via several different peptide side-chains, including Gly-Gly, Gly-Phe-Leu-Gly and Gly-Phe-Phe-Leu. Incubation of polymer-drug conjugates with isolated lysosomal enzymes (either a mixture of rat liver lysosomal enzymes or purified thiol-dependent lysosomal proteinases, cathepsins L and B) showed that significant release of drug occurred over 20 h, more than 20% of daunomycin and more than 80% of puromycin being liberated. To test their pharmacological activity conjugates were incubated with either the mouse leukaemia L1210, or the human lymphoblastoid leukaemia CCRF in vitro. The conjugates tested were all less effective than free daunomycin, but they showed differential toxicity against L1210 depending on the aminoacid sequence of their drug-polymer linkage. Inclusion of fucosylamine-terminating side-chains into the HPMA copolymer structure increased the affinity of conjugates for the L1210 cell membrane and resulted in increased toxicity. In contrast HPMA-daunomycin conjugates with or without fucosylamine affected CCRF cells equally, but this cell line was more sensitive than the mouse leukaemia to both free and polymer-bound daunomycin. Incubation of L1210 cells in polymer-bound daunomycin for 72 h, followed by plating cells out in low density in drug-free medium, showed that a concentration of polymer-bound drug (184 micrograms ml-1) could be selected to achieve a cytotoxic effect.

Acrylates↗
PubMed1987

Electron microscopic investigations of the cyclophosphamide-induced lesions of the urinary bladder of the rat and their prevention by mesna.

Fully developed cyclophosphamide-induced cystitis is characterized by nearly complete detachment of the urothelium, severe submucosal edema owing to damage to the microvascular bed and focal muscle necroses. The initial response to the primary attack by the cyclophosphamide metabolites seems to be fragmentation of the luminal membrane. This damages the cellular barrier against the hypertonic urine. Subsequent breaks in the lateral cell membranes of the superficial cells and in all the plasma membranes of the intermediate and basal cells, intercellular and intracellular edema and disintegration of the desmosomes and hemidesmosomes lead to progressive degeneration and detachment of the epithelial cells with exposure and splitting of the basal membrane. The morphological changes of the endothelial cells, which become more pronounced in the later stages of the experiment, the involvement of blood vessels regardless of their diameter and the location-dependent extent of the damage indicate a direct type of damage which is preceded by a mediator-induced increase in permeability, the morphological correlate of which is the formation of gaps in the interendothelial cell connections on the venules. These changes can be effectively prevented by mesna. The only sign of a possible involvement is the increase in the number of specific granules with a presumed lysosomal function in the superficial cells.

Animals↗
PubMed1987

Oxazaphosphorine effects in L 5222 rat leukemia.

During the past two decades a few clinical reports have suggested that the therapeutic efficacy of cyclophosphamide against malignant tumors was partly mediated by drug effects on host immune mechanisms. This action was strictly dose-dependent: immunostimulation was only evident in the low dose range, whereas immunosuppression became significant at intermediate or high doses. In search for an experimental model of the immunoaugmenting effects of oxazaphosphorines it was found that the transplantable leukemia L 5222 of BD IX inbred rats could be cured by low doses of oxazaphosphorines, whereas this therapeutic activity was gradually lost with increasing doses. Dose-response relationship studies with cyclophosphamide and its stabilized 4-hydroxy-derivative mafosfamide showed a bell-shaped pattern. When the two compounds were compared, the immunotherapeutic range of mafosfamide was considerably broader. Further experiments suggested that the oxazaphosphorine effect was T-cell mediated. Treated and surviving animals were immune to additional tumor challenges. It was shown that mafosfamide at low concentrations inhibited preferentially T-suppressor cell proliferation in vitro; in analogy, an elimination of suppressor mechanisms could also be responsible for the in vivo effects. In clinical phase I studies, the maximally tolerated dose of mafosfamide was around 3 g/m2. The presented animal data, however, indicated that the immunopharmacological dose was approximately 10 times lower. Studies for immunotherapy with mafosfamide are currently ongoing in patients with non-small cell lung cancer and other malignant diseases.

Adjuvants, Immunologic↗
PubMed1986

Separation of human pepsin and gastricsin by affinity chromatography with an immobilized synthetic inhibitor.

Pepsin and gastricsin from human gastric juice were separated by affinity chromatography on Sepharose 4B containing the immobilized synthetic inhibitor of aspartic proteinases, Val-D-Leu-Pro-Phe-Phe-Val-D-Leu. These enzymes were bound to the support at low pH, and gastricsin was released at the same pH with buffer containing 20% dioxan. Pepsin was not released under these conditions, but was eluted at higher pH with buffer also containing 20% dioxan. To obtain perfect separations, it is recommended to use diluted samples. Proteinases from the homogenate of human gastric mucosa are isolated on DEAE-cellulose before separation by affinity chromatography. Pepsin and gastricsin from human gastric juice and human gastric mucosa separated on DEAE-cellulose and isolated by affinity chromatography, were electrophoretically pure.

Chromatography, Affinity↗
PubMed1986

[Hormone therapy of metastasizing breast cancer with tamoxifen].

Out of 79 patients with metastasized carcinoma of the breast in 33% (6 patients) a response to a Tamoxifen therapy could be observed. For complete remissions the remission periods were 12.3 months, for partial remissions 9.9 months and in the group of constant findings 4.9 months. Preferably metastases of the soft parts respond to the therapy. The side effects are very insignificant. The indications for the tamoxifen therapy are represented as well as the importance of the determination of hormone receptors.

Adult↗
PubMed1986

Cause and prevention of mafosfamide-induced venous pain.

An experimental rat model for the study of venous pain induced by 4-hydroxy-cyclophosphamide (4-OH-CP) derivatives was developed and validated. Using various metabolites and chemical variants of 4-OH-CP it was found that pain induction was independent from the compound's alkylating activity but possibly related to the spontaneous generation of minute amounts of acrolein from the 4-OH-CP molecule. Accordingly, the pain could be prevented by the addition of thiol compounds such as mesna or N-acetyl-cysteine.

Acetylcysteine↗
PubMed1986

[Acute focal bacterial nephritis].

Acute focal bacterial nephritis is a very rare type of infective nephritis. It is characterised by groups of abscesses of 1 to 5 mm. situated in the renal cortex with pus tracking to the papillae. Urography is normal or suggests a non-specific enlargement. On sonography, non-homogeneous foci with reduced echogenicity are observed. Unenhanced CT shows indefinite lesions of reduced density, which do not enhance as much as the surrounding parenchyma after contrast injection. On angiography these areas appear as hypovascular lesions. The disease must be differentiated from a malignant renal tumour and from an acute renal abscess. The clinical findings and the results of sonographic and radiological observations on five patients with acute focal bacterial nephritis are described.

Acute Disease↗
PubMed1986

Priapism: a three-phase concept of management according to aetiology and prognosis.

Priapism is a persistent, painful erection of the penis unassociated with sexual stimulation or desire, and detumescence does not occur following ejaculation. Prolonged pathological erections may occur and it is only when they are painful that the term priapism should be used. The erection is limited to the corpora cavernosa. Although the syndrome was named after Priapos, the mythical Greek god of fertility, impotence persists in one half of patients treated for priapism. The disease is rare; the literature consists mainly of case reports and comprehensive reviews are seldom found. Permanent sequelae cause a psychological and physical handicap and justify the present review, which is based upon recent literature as well as personal clinical experience of 15 patients. We have reviewed 170 reports describing 1400 cases of priapism and have based the analysis upon the 230 single case reports found in the literature.

Adolescent↗
PubMed1986

Urolithiasis in a patient ingesting pure silica: a scanning electron microscopy study.

A patient who repeatedly produced urinary calculi, had consumed about 3 g of cristobalite (SiO2) per day for many years. Investigations using scanning electron microscopy revealed minute particles containing silicon in the core of the stone as well as in urine sediment. A mechanism similar to that proposed for the effect of silicon-containing drugs against gastric ulcer, may play a role in this formation of silicon-containing urinary stones.

Apatites↗
PubMed1986

Prevention of urotoxic side effects by regional detoxification with increased selectivity of oxazaphosphorine cytostatics.

Urotoxic side effects, particularly haemorrhagic cystitis, have been a limiting factor for the therapeutic use of the oxazaphosphorine cytostatics cyclophosphamide, ifosfamide and trofosfamide. The development of mesna (Uromitexan) has made it possible to carry out regional detoxification in the kidneys and the efferent urinary tract and thus to achieve clinically prophylaxis against the urotoxic side effects of oxazaphosphorines. In the body, mesna is rapidly converted to the biologically inactive disulfide form (dimesna). After glomerular filtration, dimesna is reduced by interaction with the glutathione system of the renal tubular cells and is excreted in the urine as mesna, the free thiol compound. This compound is then capable of definitively detoxifying the oxazaphosphorine metabolites in the urine. In extensive experiments on rats, it has been demonstrated that the cyclophosphamide-induced occurrence of urinary bladder tumours could be reduced or even eliminated by simultaneous administration of mesna. Detoxification by mesna enables the clinical use of higher doses and, consequently, a possible increase in therapeutic efficiency.

Animals↗
PubMed1986

[Separation and pharmaco-toxicological studies of the enantiomers of Ifosfamide].

The enantiomers of ifosfamide were isolated chromatographically by the use of an optically active adsorbent. The biological activities of the racemic product and of the enantiomers (+)- and (-)-ifosfamide were compared as to the acute toxicity after single intraperitoneal administration on mice. Futhermore, the antitumor activity has been compared with regard to the rat leukemia L 5222 and the haematotoxicological effect. Under the conditions given, no biological differences between these 3 ifosfamide preparations were observed.

Animals↗
PubMed1985

Identification and quantification of metabolite conjugates of activated cyclophosphamide and ifosfamide with mesna in urine by ion-pair extraction and fast atom bombardment mass spectrometry.

The high bladder toxicity of the alkylating oxazaphosphorine anticancer drugs, cyclophosphamide and ifosfamide is effectively reduced by the concomitant administration of mesna (sodium 2-mercaptoethane sulphonate). The formation and rapid urinary excretion of conjugates of the activated (4-hydroxylated) oxazaphosphorine metabolites with mesna has been suggested as the pharmacological basis for the selective detoxification, but separation and identification of such metabolites in vivo have been extremely difficult due to their high polarity and chemical lability. In this study an ion-pair extraction procedure in combination with positive and negative ion fast atom bombardment mass spectrometry has been developed which enabled the identification and quantification of the conjugation products of activated oxazaphosphorine metabolites with mesna in urine. The conjugates extracted as the tetra-n-butylammonium salts are directly identified by their characteristic positive molecular ion adducts and fragment ions, and the corresponding abundant molecular anions. The pattern of molecular and fragment ion formation was established by comparison of the fast atom bombardment mass spectra of synthetic cyclophosphamide-mesna conjugates with various organic and inorganic counter ions. The ifosfamide-4-(2-thioethylsulphonate) (ifosfamide-mesna) conjugate was identified as a metabolite in the urine of rats, and in patients after administration of the combination, ifosfamide + mesna. By means of a two-step extraction and with the use of suitable analogues as internal standards, procedures for the quantification of parent oxazaphosphorine and of oxazaphosphorine-mesna conjugates by negative ion fast atom bombardment mass spectrometry have been developed, and first examples for the determination of excretion kinetics are described.

Acrolein↗
PubMed1985

On the importance of resection length and tension for ureter end-to-end anastomoses.

40 end-to-end anastomoses in dogs were made, partially under considerable tension, in the lower part of the ureter after transverse division and after resection of segments between 3 and 10 cm. In three operative modifications the influence of resection length, tension, and microsurgical technique on the function of anastomoses was examined. As an equivalent to tension the approximation distance of the ends of the ureter was measured after resection of segments. Controls prove the superiority of the microsurgical procedure. In our experiments the resection length lies far above the reported maximum resection length of 3-5 cm. The results are not dependent on the resection length. There is every reason to believe that even the tension that lies on the anastomosis is not very important for the results.

Animals↗