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P Langen

Publications and source records attributed to P Langen.

At least 19 recordsLinked to original sources
PubMed1992

Adherent-cell-dependent stimulation of CFU-GM by nucleobases, nucleosides, their analogues, and the hemoregulatory peptide dimer.

At suboptimal concentrations of granulocyte-macrophage colony-stimulating factor (GM-CSF), nucleobases and nucleosides as well as their analogues strongly stimulated aggregate (colony and cluster) formation from murine bone marrow granulocyte-macrophage colony-forming units (CFU-GM) in agar culture. Active compounds include 2'-deoxycytidine, thymidine, 5'-deoxyarabinosyl-cytosine, 5'-deoxy-5'-fluorothymidine, uracil, 6-methyluracil, orotic acid, and also purine derivatives as adenine, guanine, adenosine, and guanosine. The stimulation was almost identical to that obtained with the dimer of the hemoregulatory pentapeptide. In the absence of colony-stimulating factor (CSF) no stimulation was seen. After separation of adherent cells from the bone marrow cells, the stimulatory effect was lost. It also decreased when the number of bone marrow cells plated was diminished. This suggests that the tested compounds induce growth factor production in adherent cells. The structure/activity relationships indicate that the active compounds are nucleosides, or they may serve for nucleoside synthesis inside the cell. However, nucleotide formation is not necessary for activity.

Animals↗
PubMed1991

Modulation of the beta-adrenergic-response in cultured rat heart cells. II. Mammary-derived growth inhibitor (MDGI) blocks induction of beta-adrenergic supersensitivity. Dissociation from lipid-binding activity of MDGI.

'Mammary-derived growth inhibitor (MDGI)' is a 14.5 kDa polypeptide with growth-inhibitory activity for various mammary epithelial cells in vitro which is highly homologous to cardiac fatty acid-binding protein (H-FABP). Here we describe a new biological activity of MDGI: Inhibition of L(+)-lactate-, arachidonic acid- and 15-S-hydroxyeicosatetraenoic acid-induced supersensitivity of neonatal rat heart cells for beta-adrenergic stimulation, concerning particularly a small population of beta 2-receptors. Synthetic peptides corresponding to the MDGI-sequence, residue 121-131 mimic the effect of MDGI. Measurements of lipid-binding to MDGI and synthetic peptides excluded the binding of arachidonic acid, 15-S-hydroxyeicosatetraenoic acid or beta-adrenergic agonists to MDGI or the peptides as the mechanism for this effect. Also, no direct interference of MDGI and the synthetic peptides with the binding of the beta-adrenergic agent CGP 12177 to its receptor on A431 cells could be detected. We suggest that MDGI and the peptides act by interference with the function of the beta 2-adrenergic receptor and that this mechanism might also be relevant for the growth-inhibitory activity of MDGI. Furthermore, the data point to a possible function of H-FABP for the modulation of beta-adrenergic sensitivity of cardiac myocytes.

Amino Acid Sequence↗
PubMed1990

Evidence for involvement of a nuclear envelope-associated RNA helicase activity in nucleocytoplasmic RNA transport.

It seems well established that translocation of at least some mRNAs through the nuclear pore is (1) an energy-dependent process, and (2) dependent on the presence of the poly(A) segment attached to most mRNA species. We describe that RNA helicase (RNA duplex unwindase) activity is present in a nuclear envelope (NE) preparation, which also appears to be involved in nucleocytoplasmic RNA transport. This activity unwinds RNA: RNA hybrids. The helicase has a pH optimum of 7.5 and a temperature optimum of 30 degrees C. Applying the sealed NE vesicle system, it was shown that duplex RNA species are readily released from the vesicles in an unidirectional manner, in contrast to single-stranded RNA, which is much slower transported into the extravesicular space. Attachment of a poly(A) segment to the RNA duplex additionally increases the efflux rate of this RNA. Efflux of duplex RNA but not efflux of single-stranded RNA was strongly inhibited by formycin B 5'-triphosphate. Our results suggest that, besides poly(A), duplex structures, if present in a given RNA, modulate and control the export of RNA.

Animals↗
PubMed1990

Selectivity of hemoregulatory peptide (HP5b) action in culture.

A synthetic analog of a hemoregulatory peptide associated with mature human granulocytes (HP5b) has been investigated for inhibitory effects on various cell types in culture as compared to inhibitory action on mouse and human myelopoietic colonies (CFU-gm), which occurs from 1 X 10(-13) to 1 X 10(-6) M in vitro. This includes colony formation by lymphoid T and B cells in capillary cultures, as well as mitogen activation of T, B and NK cells. At higher concentrations, i.e., above 1 X 10(-7) M, an inhibitory effect was found on colony formation. Neither the production of interleukin (IL) 3 by mitogen-activated T cells, nor the proliferation of the IL-3-dependent L/B cell line were affected by the peptide up to 1 X 10(-5) M. A slight inhibitory effect was found above 1 X 10(-9) M on mouse 3T3 fibroblasts. A series of malignant cell lines was also tested. No effect was seen between 1 X 10(-11) and 1 X 10(-7) M on human mammary carcinoma cells in culture. On Ehrlich ascites mouse mammary carcinoma cells a 30% inhibition was seen at 10(-6) M. On a human glioblastoma cell line (GaMg) no effect was seen, and on a rat glioma cell line (BT5C) an inhibitory effect was seen at 1 X 10(-7) M and above. No significant inhibition of cell growth was seen on SC1 mouse lymphoma cells from 1 X 10(-9) to 1 X 10(-5) M during 7 days of culture. The investigated normal and malignant cell types in culture were thus not inhibited in very low concentrations which act on CFU-gm. However, a variable inhibitory effect was found at higher concentrations where the inhibition of myelopoiesis was maximal and at concentrations where the inhibition is released. The hemoregulatory peptide thus seems to be a concentration-dependent selective inhibitor of myelopoiesis. The finding that various malignant cells do not respond at lower concentrations supports the possibility of using the peptide as a protector of normal cells during cancer chemotherapy.

Amino Acid Sequence↗
PubMed1990

Halo lipids. 10. Synthesis and cytostatic activity of O-alkylglycerophospho-L-serine analogs.

The synthesis of O-alkylglycerophospho-L-serine analogs is described, which represent a new class of cytostatically active agents based on phospholipids. The new compounds were obtained by conversion of O-alkylglycerophosphoric ester analogs by means of phospholipase D and by condensing O-alkylglycerophosphoric acid analogs with protected L-serine followed by the removal of protective groups of the resulting intermediates. The structure of the O-alkylglycerophospho-L-serines was confirmed by fast atom bombardment mass spectrometry. The compounds were found to inhibit the growth of Ehrlich ascites tumor cells in vitro. Half maximum inhibition was observed at concentrations between 7 and 15 microM. For the 1-O-alkyl-2-methoxy glycerophosphoserine only a higher value (30 microM) was found. With most of the substances tested growth was completely inhibited at a concentration of 40 microM.

Animals↗
PubMed1990

Alteration of DNA topoisomerase II activity during infection of H9 cells by human immunodeficiency virus type 1 in vitro: a target for potential therapeutic agents.

Infection of H9 cells with human immunodeficiency virus type 1 (HIV-1) was found to decrease the phosphorylation of DNA topoisomerase II during the initial phase of infection. Simultaneously, with a later overshoot of phosphorylation and the subsequent activation of DNA topoisomerase II, the production of HIV-1 started. Applying three new protein kinase C inhibitors from the class of O-alkylglycerophospholipids we demonstrated that inhibition of protein kinase C-mediated phosphorylation of DNA topoisomerase II resulted in an inhibition of HIV-1 production. Based on the differential effect of the two protein kinase C activators, phorbol ester and bryostatin, we conclude that phosphorylation of DNA topoisomerase II is mediated by the form alpha and gamma of protein kinase C. These data suggest that agents which inhibit these two forms of protein kinase C are also potential candidates for an anti-HIV therapy.

Animals↗
PubMed1990

Quenching of tyrosine radicals of M2 subunit from ribonucleotide reductase in tumor cells by different antitumor agents: an EPR study.

The inhibition of ribonucleotide reductase (RR) of intact Ehrlich ascites tumor cells by different antitumor agents was compared using EPR spectroscopy. The inactivation of M2 subunit was measured via quenching of the functionally essential tyrosine radical. Inhibitors of different classes, for example, hydroxyurea, pyrogallol, and thiosemicarbazones, differ in their efficiency by three orders of magnitude. Most effective inhibition was found for isoquinoline-1-aldehyde-thiosemicarbazone (IQ-1) with an IC50 value of 0.18 microM. Inhibition of RR inside tumor cells is comparable with that reported for isolated enzymes.

Animals↗
PubMed1990

Potent inhibition of hepatitis B virus production in vitro by modified pyrimidine nucleosides.

2',3'-Dideoxy-3'-fluorothymidine (FddThd), 2',3'-didehydro-2',3'- dideoxythymidine (ddeThd), and 3'-fluoro-5-methyl-deoxycytidine (FddMeCyt) are, in their triphosphate forms, selective inhibitors of human immunodeficiency virus type 1 reverse transcriptase. We report that 0.3 microM FddThd, FddMeCyt, or ddeThd as well as 3'-chloro-5-methyl-deoxycytidine (ClddMeCyt) or 3'-amino-5-methyl-deoxycytidine (AddMeCyt) almost completely blocked production of hepatitis B virus (HBV) particles by HBV DNA-transfected cell line 2.2.15 in vitro. Only at an at least 10-fold-higher concentration was a cytotoxic effect observed. These results indicate that FddThd, FddMeCyt, ClddMeCyt, AddMeCyt, and ddeThd are potent anti-HBV agents in vitro.

Antiviral Agents↗
PubMed1990

Toxic effects of alkyl-lysophospholipids on human bone marrow and de novo leukaemias. A short overview.

Alkyl-lysophospholipids (ALPs) are reported to have an antineoplastic activity against leukaemic cells. We have tested some halogen-containing ALPs from the Central Institute of Molecular Biology (H. Brachwitz) in comparison with racemic 1-ostadecyl-2-methyl-glycero-3-phosphocholine (ET-18-OCH3) (P.G. Munder, Max-Planck-Institut für Immunobiologie, Freiburg, FRG). We found freshly dissolved ALPs to be very toxic both to human bone marrow and to leukaemic cells of patients. ALP-incubation before cryopreservation is more toxic to bone marrow (but not to AML blasts) than after cryopreservation. All experiments to test the selectivity and to establish a purging protocol should be done using 1, remission marrow including a cryopreservation step and 2, blasts of de novo leukaemias instead of cell as sensitive as HL 60 to ALP-incubation. We found direct toxicity of ALPs to be not suitable for purging lines of bone marrow from patients in remission.

Alkylation↗
PubMed1989

Effect of a mammary-derived growth inhibitor on the expression of the oncogenes c-fos, c-myc and c-ras.

A mammary-derived growth inhibitor (MDGI) inhibits the resumption of growth of stationary Ehrlich ascites carcinoma (EAC) cells in vitro. The present study shows that the resumption of growth is accompanied by a rapid increase of the steady state mRNA level of the proto-oncogenes c-fos, c-myc and c-ras, which is reduced by MDGI. EAC cells from the exponential growth phase insensitive to MDGI did not show a reduced RNA expression. The effect of MDGI represents a novel activity at the level of gene expression and suggests a link to exist between growth inhibition and the reduction of c-fos, c-myc and c-ras expression.

Animals↗
PubMed1989

Sensitivity of CFU-GM from normal human bone marrow and leukaemic clonogenic cells (CFU-L) from blood of patients with myelogenous leukaemia to 3'-deoxy-3'-fluorothymidine in comparison to 3'-azido-3'-deoxythymidine.

3'-Deoxy-3'-fluorothymidine (FT), a thymidine analogue highly effective against HIV 1 in vitro was investigated as to its in vitro effect on normal human bone marrow CFU-GM (agar colony assay) and on human peripheral myeloid leukaemic clonogenic cells (CFU-L, colony assay in methylcellulose). For comparison, 3'-azido-3'-deoxythymidine (AZT), structurally related and used in AIDS treatment, was included in the study. Both compounds inhibit the formation of clusters and colonies from bone marrow stem cells with an [IC]50 between 10(-6) and 10(-5)M. In concentrations only 5-10 times lower than the [IC]50, FT begins to stimulate cluster and colony formation. AZT and FT also inhibit the formation of clusters and colonies from CFU-L. Compared to CFU-GM, CFU-L were more sensitive to FT, and a stimulation was not seen. It is concluded that similar side effects on bone marrow could be expected for possible use of FT against AIDS as have been found for AZT and that both compounds are potential candidates for anti-leukaemic drugs.

Adolescent↗
PubMed1989

Stability and reactivation of tyrosine radicals from ribonucleotide reductase in tumor cells studied by ESR.

Naturally occurring tyrosine radicals from the M2 subunit of ribonucleotide reductase (RR) have been recorded by ESR in proliferating ordinary Ehrlich-ascites (EA) tumor cells of mice. Tyrosine radicals are stable in EA cells at room temperature for 2 h. Up to 500 mW no microwave saturation occurs. The relatively high stability and non-saturation of tyrosine radicals in EA cells suggests a suitable protein conformation in the M2 subunit enabling a close contact between the tyrosine radical and the antiferromagnetic iron complex. This facilitates an ESR study of functionally essential tyrosine radicals of RR in EA cells at low temperature and recommends this cellular system for studying such processes as inhibition and activation, which change the content of tyrosine radicals of the proliferation-linked RR. Oxygen treatment of non-proliferating (quiescent) EA cells reactivates tyrosine radicals 2-3 fold as found in strongly proliferating cells. We conclude that in quiescent cells, suffering from a lack of oxygen due to their high density in the peritoneal cavity, a reactivation of tyrosine radicals occurs by oxidation of non-radical tyrosine residues of inactive M2 subunits.

Animals↗
PubMed1989

Response of different mammary epithelial cell lines to a mammary derived growth inhibitor (MDGI).

MDGI, a 14.5-KDa protein, is a chemically defined growth inhibitor, which we have purified from lactating bovine mammary gland and characterized biologically in a mouse Ehrlich ascites mammary tumour (EAT) short term suspension culture. It has now been tested for its inhibitory activity on proliferation of four malignant mammary epithelial cell lines of human and mouse origin and normal human mammary epithelial cells. In all experiments, cells were brought to quiescence by serum or growth factor deprivation. Using [3H]TdR pulse labelling the effect of MDGI was measured on the restimulation of proliferation after medium change. MaTu and T47 D, human malignant mammary epithelial cell lines, as well as the mouse malignant mammary epithelial cell line mMaCa 20177 could be inhibited, whereas the human malignant mammary epithelial cell line MCF7 showed a slight stimulation. MDGI showed no activity on the residual DNA synthesis of all cell lines after starvation. Normal human mammary epithelial cells (HMEC) of different passages could also be inhibited. Their responsiveness seemed to be dependent on the number of passages. Cells from high passages (10-14) showed a higher sensitivity, which is also about 10 times higher than that of the malignant cell lines. Furthermore, growth factors like insulin, epidermal growth factor (EGF) and fetal calf serum (FCS), known to be potent antagonists to the MDGI activity in the EAT and, in the case of insulin, also in the MaTu culture (shown in the present study), do not abolish the inhibitory activity of MDGI on HMEC cells. These results demonstrate that the inhibitory activity of MDGI is not exclusively restricted to EAT cells studied so far.

Animals↗
PubMed1988

Phosphorylation, anti-HIV activity and cytotoxicity of 3'-fluorothymidine.

3'-fluorothymidine (FddThd) is well phosphorylated to the 5'-triphosphate in various relevant cell-lines. This results in fairly stable levels of this compound without accumulation of the 5'-monophosphate to the extent described for 3'-azidothymidine (AzT). The di- and triphosphate of FddThd seems unable to influence the ribonucleotide reductase in permeable cells. FddThd protects 50% of the MT-4 cells against the cytopathic effect of HIV at 3 nM, but reduces the number of uninfected viable cells to 50% at 1.1 microM. All other tested human cell-lines displayed a far less antiproliferative sensitivity to FddThd, comparable with that of AzT.

Animals↗
PubMed1988

Deoxycytidine, insulin and epidermal growth factor overcome the effect of two natural inhibitors of the haemopoietic system.

The effect of 2'-deoxycytidine on a pluripotent haemopoietic stem cell proliferation inhibitor, as assayed in the mouse spleen colony technique and on the synthetic haemoregulatory pentapeptide (acting predominantly on myeloid determined cells) as assayed in the agar colony technique, was studied. 2'-deoxycytidine was able to overcome the effect of both inhibitors. The inhibition was also blocked by insulin or epidermal growth factor. Since these results are in agreement with those on other cells and other inhibitors, they may describe a more general phenomenon. It is suggested that the mode of action of the inhibitors involves, probably indirectly, interaction with the activity of ribonucleotide reductase.

Animals↗
PubMed1987

Inhibition of HIV-associated reverse transcriptase by sugar-modified derivatives of thymidine 5'-triphosphate in comparison to cellular DNA polymerases alpha and beta.

The sugar-modified dTTP analogues 2',3'-didehydro-2',3'-dideoxy-thymidine 5'-triphosphate (ddeTTP), 2',3'-dideoxythymidine 5'-triphosphate (ddTTP), 3'-fluorothymidine 5'-triphosphate (FdTTP), and 3'-azidothymidine 5'-triphosphate (N3dTTP) are demonstrated to be very effective and selective inhibitors of the HIV-associated reverse transcriptase (HIV-RT). This conclusion is based on a comparison of the ID50 values of the compounds for the HIV-RT (ranging from 0.03 microM for ddeTTP to 0.1 microM for ddTTP) and the cellular DNA polymerase alpha (greater than 200 microM). DNA polymerase beta is partially affected by N3dTTP (ID50 = 31 microM) and by the other analogues (ID50 = 1-2.2 microM). FdTTP has proved as effective as N3dTTP (ID50 = 0.05 microM) in suppressing the HIV-RT activity. Kinetic analysis revealed for both dTTP analogues a competitive type of inhibition and the same K1 values (about 0.05 microM).

Cell Line↗