Hydrophobic Derivatives of Glycopeptide Antibiotics as Inhibitors of Protein Kinases

As key regulators of cell signaling, protein kinases (PKs) are attractive targets for therapeutic intervention in a variety of diseases. Herein, we report for the first time the inhibitory activity of polycyclic peptides, particularly, derivatives of glycopeptide antibiotics teicoplanin and eremomycin, against a panel of 12 recombinant human protein kinases and two protein kinases (CK1 and CK2) isolated from rat liver. Several of the investigated compounds inhibited various PKs with IC50 values below 10 μM and caused >90% suppression of the enzyme activity at 10 µM concentration. Kinetic analysis of the protein kinase CK2α inhibition by the teicoplanin aglycon analogue (7) demonstrated the non-competitive mechanism of inhibition (with regard to ATP). Interestingly, the inhibitory activity of some investigated compounds correlated with the earlier described antiviral activity against HIV, HCV, and other corona- and flaviviruses.

7-Bromoindirubin-3'-oxime induces caspase-independent cell death

Indirubin, an isomer of indigo, is a reported inhibitor of cyclin-dependent kinases (CDKs) and glycogen synthase kinase-3 (GSK-3) as well as an agonist of the aryl hydrocarbon receptor (AhR). Indirubin is the active ingredient of a traditional Chinese medicinal recipe used against chronic myelocytic leukemia. Numerous indirubin analogs have been synthesized to optimize this promising kinase inhibitor scaffold. We report here on the cellular effects of 7-bromoindirubin-3'-oxime (7BIO). In contrast to its 5-bromo- and 6-bromo- isomers, and to indirubin-3'-oxime, 7BIO has only a marginal inhibitory activity towards CDKs and GSK-3. Unexpectedly, 7BIO triggers a rapid cell death process distinct from apoptosis. 7-Bromoindirubin-3'-oxime induces the appearance of large pycnotic nuclei, without classical features of apoptosis such as chromatin condensation and nuclear fragmentation. 7-Bromoindirubin-3'-oxime-induced cell death is not accompanied by cytochrome c release neither by any measurable effector caspase activation. Furthermore, the death process is not altered either by the presence of Q-VD-OPh, a broad-spectrum caspase inhibitor, or the overexpression of Bcl-2 and Bcl-XL proteins. Neither AhR nor p53 is required during 7BIO-induced cell death. Thus, in contrast to previously described indirubins, 7BIO triggers the activation of non-apoptotic cell death, possibly through necroptosis or autophagy. Although their molecular targets remain to be identified, 7-substituted indirubins may constitute a new class of potential antitumor compounds that would retain their activity in cells refractory to apoptosis.

Soluble VEGFR-1 secreted by endothelial cells and monocytes is present in human serum and plasma from healthy donors

It was shown before that the soluble form of VEGFR-1 (sVEGFR-1) is present in serum of pregnant women. The aim of the present study was to investigate the presence of this endogenous vascular endothelial growth factor-A (VEGF-A) antagonist in human serum in more detail. sVEGFR-1 was detected in human serum and plasma from normal healthy male and female donors by ELISA. sVEGFR-1 levels ranged from non-detectable up to 440 pg/ml, with no significant difference between male and female donors. In addition, vein endothelial cells (ECs) from an intact vascular bed, the umbilical cord, were shown to secrete sVEGFR-1. Furthermore, human peripheral blood monocytes, a non-EC type expressing VEGFR-1, were shown to contribute to the sVEGFR-1 detectable in human serum and plasma for the first time. EC- and monocyte-derived sVEGFR-1 proved capable of inhibiting the VEGF-induced proliferation and migration of ECs in vitro. Finally, secretion of sVEGFR-1 was increased by the angiogenic factor basic fibroblast growth factor (bFGF) in human ECs and was also enhanced in lipopolysaccharide-activated human monocytes. In human umbilical vein endothelial cells, both the membrane-bound and the sVEGFR-1 seem to be equally regulated on the mRNA as well as the protein level. The presence of an sVEGFR-1 in human serum and plasma of normal male and female donors strongly suggests that it plays an important role as a naturally occurring VEGF antagonist in the regulation and availability of VEGF-mediated biological activities in vivo.

Anthraquinones and betaenone derivatives from the sponge-associated fungus Microsphaeropsis species: novel inhibitors of protein kinases

An undescribed fungus of the genus Microsphaeropsis, isolated from the Mediterranean sponge Aplysina aerophoba, produces two new betaenone derivatives (1, 2) and three new 1,3,6, 8-tetrahydroxyanthraquinone congeners (5-7). The structures of the compounds were established on the basis of NMR spectroscopic and mass spectrometric data and by CD spectroscopy. This is the first report wherein the (1)H and (13)C NMR data of the betaenone congeners are fully and unambiguously assigned on the basis of two-dimensional NMR spectroscopy. Furthermore, we describe the first elucidation of the absolute configuration of 1-(2'-anthraquinonyl)ethanols such as 5 and 6, by quantum chemical calculation of their circular dichroism (CD) and comparison with experimentally measured spectra. Moreover, it was shown that compounds 1, 5, 6, and 7 are inhibitors of PKC-epsilon, CDK4, and EGF receptor tyrosine kinases.

PTK787/ZK 222584, a novel and potent inhibitor of vascular endothelial growth factor receptor tyrosine kinases, impairs vascular endothelial growth factor-induced responses and tumor growth after oral administration

PTK787/ZK 222584 (1-[4-chloroanilino]-4-[4-pyridylmethyl] phthalazine succinate) is a potent inhibitor of vascular endothelial growth factor (VEGF) receptor tyrosine kinases, active in the submicromolar range. It also inhibits other class III kinases, such as the platelet-derived growth factor (PDGF) receptor beta tyrosine kinase, c-Kit, and c-Fms, but at higher concentrations. It is not active against kinases from other receptor families, such as epidermal growth factor receptor, fibroblast growth factor receptor-1, c-Met, and Tie-2, or intracellular kinases such as c-Src, c-Abl, and protein kinase C-alpha. PTK787/ZK 222584 inhibits VEGF-induced autophosphorylation of kinase insert domain-containing receptor (KDR), endothelial cell proliferation, migration, and survival in the nanomolar range in cell-based assays. In concentrations up to 1 microM, PTK787/ZK 222584 does not have any cytotoxic or antiproliferative effect on cells that do not express VEGF receptors. After oral dosing (50 mg/kg) to mice, plasma concentrations of PTK787/ZK 222584 remain above 1 microM for more than 8 h. PTK787/ZK 222584 induces dose-dependent inhibition of VEGF and PDGF-induced angiogenesis in a growth factor implant model, as well as a tumor cell-driven angiogenesis model after once-daily oral dosing (25-100 mg/kg). In the same dose range, it also inhibits the growth of several human carcinomas, grown s.c. in nude mice, as well as a murine renal carcinoma and its metastases in a syngeneic, orthotopic model. Histological examination of tumors revealed inhibition of microvessel formation in the interior of the tumor. PTK787/ZK 222584 is very well tolerated and does not impair wound healing. It also does not have any significant effects on circulating blood cells or bone marrow leukocytes as a single agent or impair hematopoetic recovery after concomitant cytotoxic anti-cancer agent challenge. This novel compound has therapeutic potential for the treatment of solid tumors and other diseases where angiogenesis plays an important role.

Mapping of the sites for ligand binding and receptor dimerization at the extracellular domain of the vascular endothelial growth factor receptor FLT-1

The vascular endothelial growth factor (VEGF) receptor FLT-1 has been shown to be involved in vasculogenesis and angiogenesis. The receptor is characterized by seven Ig-like loops within the extracellular domain. Upon VEGF binding FLT-1 becomes phosphorylated, which has been thought to be preceded by receptor dimerization. To further investigate high affinity binding of VEGF to FLT-1 and ligand-induced receptor dimerization, we expressed in Sf9 cells the entire extracellular domain comprising all seven Ig-like loops: sFLT-1(7) and several truncated mutants consisting of loop one, one and two, one to three, one to four, and one to five. The corresponding proteins, named sFLT-1(1), (2), (3), (4), and (5) were purified. Only mutants sFLT-1(3) to (7) were able to bind 125I-VEGF with high affinity. No binding of VEGF was observed with sFLT-1(1) and sFLT-1(2), indicating that the first three Ig-like loops are involved in high affinity binding of VEGF. The binding of VEGF to sFLT-1(3) could be competed with placenta growth factor (PlGF), a VEGF-related ligand, suggesting that high affinity binding of VEGF and PlGF is mediated by the same or closely related contact sites on sFLT-1. Deglycosylation of the sFLT-1(3), (4), (5), and (7) did not abolish VEGF binding. Furthermore, unglycosylated sFLT-1(3), expressed in Escherichia coli, was able to bind VEGF with similar affinity as sFLT-1(3) or sFLT-1(7), both expressed in Sf9 cells. This indicates that receptor glycosylation is not essential for high affinity binding. Dimerization of the extracellular domains of FLT-1 upon addition of VEGF was detected with all mutants containing the Ig-like loop four. Although sFLT-1(3) was able to bind VEGF, dimerization of this mutant was inefficient, indicating that sites on Ig-like loop four are essential to stabilize receptor dimers.

Over-expression of protein kinase C-alpha enhances platelet-derived growth factor- and phorbol ester- but not calcium ionophore-induced formation of prostaglandins in NIH 3T3 fibroblasts

Over-expression of human protein kinase C-alpha in murine NIH 3T3 fibroblasts is associated with an increased platelet-derived growth factor- and phorbol ester-mediated formation of prostaglandins, whereas the calcium ionophore-induced release of arachidonic acid metabolites is unaffected; however, the differences of arachidonic acid and prostaglandin formation are much more pronounced with platelet-derived growth factor than with phorbol ester. Platelet-derived growth factor induces an identical elevation of intracellular free calcium in control and protein kinase C-alpha over-expressing cells: the phorbol ester has no effect on intracellular free calcium in both cell lines. These results demonstrate that protein kinase C-alpha may couple to arachidonic acid cascade in NIH 3T3 fibroblasts.

Over-expression of human phospholipase C-gamma 2 enhances platelet-derived growth factor-induced mobilization of intracellular Ca2+ and the release of arachidonic acid and prostaglandins in NIH 3T3 fibroblasts

Over-expression of human phospholipase C-gamma 2 in murine NIH 3T3 fibroblasts has been shown to result in an increased platelet-derived growth factor-mediated formation of inositol phosphates. Here we show that phospholipase C-gamma 2 over-expression is associated with an increased platelet-derived growth factor-mediated release of arachidonic acid, prostaglandin E2, 6-keto prostaglandin F1 alpha and prostaglandin F2 alpha. The phorbol ester, calcium ionophore- and fluoride-induced release of arachidonate and its metabolites is not affected by phospholipase C-gamma 2 over-expression. Over-expression of phospholipase C-gamma 2 is also associated with an enhancement of platelet-derived growth factor-induced change in intracellular Ca2+. These results demonstrate that stimulation of recombinant human phospholipase C-gamma 2 induces a change in the intracellular Ca2+ concentration, a release of arachidonic acid and formation of prostaglandins in NIH 3T3 cells. In control cells platelet-derived growth factor-induced activation of arachidonic acid cascade is rate-limited by the endogenous phospholipase C.

Inducible expression of human phospholipase C-gamma 2 and its activation by platelet-derived growth factor B-chain homodimer and platelet-derived growth factor A-chain homodimer in transfected NIH 3T3 fibroblasts

Growth factors such as platelet-derived growth factor (PDGF) have been shown to activate phospholipase C-gamma 1 (PLC-gamma 1). We have overexpressed the human PLC-gamma 2 (hPLC-gamma 2) cDNA in murine NIH 3T3 fibroblasts using the interferon-type-I inducible murine Mx promoter. Northern blot analysis revealed an induction of hPLC-gamma 2 mRNA by interferon (IFN) alpha of about 25-fold as compared to the uninduced transcript level. Western blot analysis with anti(bovine PLC-gamma 2) antiserum showed increased hPLC-gamma 2 protein levels in hPLC-gamma 2 transfected cells. Induction with IFN alpha resulted only in a slight further increase. After labelling the cells with [35S]methionine an increase of radioactive label in a protein migrating at 148 kDa could be detected in IFN-alpha-stimulated, hPLC-gamma 2 overexpressing cells. PLC activity in homogenates from hPLC-gamma 2 overexpressing cells was increased as compared to control cells transfected with the vector lacking the hPLC-gamma 2 cDNA insert. There was no difference between in vitro PLC activity in homogenates from PDGF B-chain homodimer (BB) treated and untreated cells. PLC activity was mainly present in the soluble fraction. After incubation of hPLC-gamma 2 overexpressing cells with IFN alpha, the in vitro activity of PLC increased significantly in the soluble fraction. Stimulation with PDGF BB increased inositol phosphate production about 3.5-fold in control cells and about 10-fold in hPLC-gamma 2 overexpressing cells. PDGF A-chain homodimer (AA) showed slightly smaller effects. These results demonstrate that human PLC-gamma 2 can be expressed functionally in murine NIH 3T3 fibroblasts and can be activated by both murine PDGF receptors, alpha and beta type.

The Drosophila melanogaster l(2)gl gene encodes a protein homologous to the cadherin cell-adhesion molecule family

Mutations in the recessive Drosophila tumor gene l(2)gl affect growth and structural properties of neural tissues and imaginal discs during larval development. We have analyzed the cellular localization of transcripts and a 130-kDa protein encoded by the l(2)gl gene, using in situ hybridization and immunofluorescence techniques. Transcripts of maternal origin are detected in freshly laid eggs and are homogeneously incorporated into blastoderm cells. The protein is found at low levels in all embryonic tissues after blastoderm formation. In later stages differential expression of the protein is observed, particularly in cells of the nervous system. The protein is located at the cell surface of dissociated embryonic cells. Anti-l(2)gl sera show cross-reaction to a mouse protein that is localized at cell-cell contact sites in tissue culture cells. Moreover, amino acid sequence homology to deduced amino acid sequences of members of the vertebrate cadherin cell-adhesion molecule family suggests that the l(2)gl gene product may have properties of a cell-adhesion molecule.