Search PubMed⌕ Search

Biomedical subjects

Horst Kessler

Publications and source records attributed to Horst Kessler.

At least 37 records · Page 2Linked to original sources
PubMed2005

Benzylprotected aromatic phosphonic acids for anchoring peptides on titanium.

The development of biocompatible coatings is an ongoing issue. Mimicking the physiological adhesion process of osteoblasts to the extracellular matrix improves cell adhesion of osteoblasts in vitro and results in improved and earlier osseous integration of implants in vivo. Titanium, an often used material in implant surgery, can be easily coated by peptides bearing phosphonic acid groups. We report here, the synthesis of benzyl protected phosphonic acids suitable for solid-phase peptide synthesis (SPPS), which can be easily deprotected with TFA.

Animals↗
PubMed2005

3-Substituted indolizine-1-carbonitrile derivatives as phosphatase inhibitors.

In the course of studies directed toward the discovery of novel scaffolds for medicinal application, we synthesized a series of 3-substituted indolizine-1-carbonitrile derivatives. Some of them displayed activity against MPtpA/MPtpB phosphatases which are involved in infectious diseases. We report here the solid-phase synthesis and antiphosphatase activity of a series of indolizines.

Acetic Acid↗
PubMed2005

Lateral spacing of integrin ligands influences cell spreading and focal adhesion assembly.

Cell-extracellular matrix (cell-ECM) interactions mediated by integrin receptors are essential for providing positional and environmental information necessary for many cell functions, such as proliferation, differentiation and survival. In vitro studies on cell adhesion to randomly adsorbed molecules on substrates have been limited to sub-micrometer patches, thus preventing the detailed study of structural arrangement of integrins and their ligands. In this article, we illustrate the role of the distance between integrin ligands, namely the RGD (arginine-glycine-aspartate) sequence present in ECM proteins, in the control of cell adhesion. By using substrates, which carry cyclic RGD peptides arranged in highly defined nanopatterns, we investigated the dynamics of cell spreading and the molecular composition of adhesion sites in relation to a fixed spacing between the peptides on the surface. Our novel approach for in vitro studies on cell adhesion indicates that not only the composition, but also the spatial organization of the extracellular environment is important in regulating cell-ECM interactions.

Animals↗
PubMed2005

Ligand binding analysis for human alpha5beta1 integrin: strategies for designing new alpha5beta1 integrin antagonists.

We report a three-dimensional model of the alpha5beta1 integrin headgroup bound to the most potent and selective ligand (SJ749) known to date. The model was built using the comparative protein modeling method, and it is consistent with experimental data. From this study, we identified two potentially important regions in the alpha5beta1 receptor that are peculiar to this integrin and might be worth considering for drug targeting.

Amino Acid Sequence↗
PubMed2005

Convenient synthesis of N-methylamino acids compatible with Fmoc solid-phase peptide synthesis.

N(alpha)-Methylamino acid containing peptides exhibit interesting therapeutic profiles and are increasingly recognized as potentially useful therapeutics. Unfortunately, their synthesis is hampered by the high price and unavaibility of many N(alpha)-methylamino acids. An efficient and practical preparation of N(alpha)-methyl-N(alpha)-(o-nitrobenzenesulfonyl)-alpha-amino acids without extensive purification is described. The procedure is based on the well-known N-alkylation of N(alpha)-arylsulfonylamino esters which was improved by using dimethyl sulfate and DBU as base. Ester cleavage is efficiently achieved by using an S(N)2-type saponification with lithium iodide, avoiding racemization observed with lithium hydroxide hydrolysis. Compatibility of the synthesized N(alpha)-methylamino acids with Fmoc solid-phase peptide synthesis is demonstrated by using normal coupling conditions to efficiently prepare N-methyl dipeptides. The described procedure allows the preparation of N(alpha)-methylamino acids in a very short period of time and a rapid synthesis of N-methyl peptides using Fmoc solid-phase peptide synthesis.

Amino Acids↗
PubMed2005

Orientational properties of stretched polystyrene gels in organic solvents and the suppression of their residual 1H NMR signals.

While residual dipolar couplings (RDCs) are an established method in high-resolution biomolecular NMR, their use for structure determination of small molecules in organic solvents is limited by the alignment media available. Only recently stretched polystyrene (PS) gels were introduced for the measurement of RDCs on small compounds that allowed urgently needed free scalability of the induced anisotropy. Here, the properties of such stretched PS gels in different organic solvents as well as for different magnetic field strengths and temperatures are studied and practical NMR-spectroscopic aspects are discussed.

Journal Article↗
PubMed2005

Structure-activity relationship studies optimizing the antiproliferative activity of novel cyclic somatostatin analogues containing a restrained cyclic beta-amino acid.

The cyclic somatostatin analogue cyclo[Pro(1)-Phe(2)-D-Trp(3)-Lys(4)-Thr(5)-Phe(6)] (L-363,301) displays high biological activity in inhibiting the release of growth hormone, insulin, and glucagon. According to the sequence of L-363,301, we synthesized a number of cyclic hexa- and pentapeptides containing nonnatural alpha- and beta-amino acids. The N- fluorenylmethoxycarbonyl protected cyclic beta-amino acid [1S, 2S, 5R]-2-amino-3,5-dimethyl-2-cyclohex-3-enecarboxylic acid (cbetaAA), for the replacement of the Phe(6)-Pro(1) moiety of L-363,301, was synthesized in two steps by an enantioselective multicomponent reaction using (-)-8-phenylmenthol as a chiral auxiliary. The resulting peptide cyclo[cbetaAA(1)-Tyr(2)-D-Trp(3)-Nle(4)-Thr(Trt)(5)] (Trt = triphenylmethyl) shows high antiproliferative effects in an in vitro assay with A431 cancer cells. The same peptide without the Trt group does not reveal any biological activity, whereas L-363,301 and closely related hexapeptides show only minor activity. By comparison of the solution structure of cyclo[cbetaAA(1)-Tyr(2)-D-Trp(3)-Nle(4)-Thr(Trt)(5)] with the structure of l-363,301, a nearly perfect match of the betaII'-turn region with d-Trp in the i + 1 position was observed. The cyclic beta-amino acid cbetaAA is likely needed for the bioactive conformation of the peptide.

Amino Acids, Cyclic↗
PubMed2005

Noninvasive visualization of the activated alphavbeta3 integrin in cancer patients by positron emission tomography and [18F]Galacto-RGD.

BACKGROUND: The integrin alphavbeta3 plays an important role in angiogenesis and tumor cell metastasis, and is currently being evaluated as a target for new therapeutic approaches. Several techniques are being studied to enable noninvasive determination of alphavbeta3 expression. We developed [(18)F]Galacto-RGD, a (18)F-labeled glycosylated alphavbeta3 antagonist, allowing monitoring of alphavbeta3 expression with positron emission tomography (PET). METHODS AND FINDINGS: Here we show by quantitative analysis of images resulting from a small-animal PET scanner that uptake of [(18)F]Galacto-RGD in the tumor correlates with alphavbeta3 expression subsequently determined by Western blot analyses. Moreover, using the A431 human squamous cell carcinoma model we demonstrate that this approach is sensitive enough to visualize alphavbeta3 expression resulting exclusively from the tumor vasculature. Most important, this study shows, that [(18)F]Galacto-RGD with PET enables noninvasive quantitative assessment of the alphavbeta3 expression pattern on tumor and endothelial cells in patients with malignant tumors. CONCLUSIONS: Molecular imaging with [(18)F]Galacto-RGD and PET can provide important information for planning and monitoring anti-angiogenic therapies targeting the alphavbeta3 integrins and can reveal the involvement and role of this integrin in metastatic and angiogenic processes in various diseases.

Animals↗
PubMed2005

NMR studies reveal structural differences between the gallium and yttrium complexes of DOTA-D-Phe1-Tyr3-octreotide.

The somatostatin analogue DOTATOC, DOTA-[Tyr(3)]octreotide, is used for in vivo diagnosis and targeted therapy of somatostatin-receptor-positive tumors. DOTATOC consists of a disulfide-bridged octapeptide, d-Phe(1)-Cys(2)-Tyr(3)-d-Trp(4)-Lys(5)-Thr(6)-Cys(7)-Thr(8)-ol, connected to the metal chelator DOTA (1,4,7,10-tetraazacyclododecane-1,4,7,10-tetraacetic acid). Two metal complexes, Ga(III)- and Y(III)-DOTATOC, were reported to differ significantly in somatostatin receptor affinity and tumor uptake. Our (1)H and (13)C solution NMR data and modeling studies of both compounds are in agreement with a fast conformational equilibrium of the peptide part, as previously reported for octreotide itself. However, the different coordination geometry of Ga(3+) and Y(3+) (6-fold and 8-fold, respectively, as known from model compounds) causes pronounced differences for the d-Phe(1) residue. For Y(III)-DOTATOC this leads to two conformers exchanging slowly on the NMR time scale. From various NMR measurements, they could be identified as cis-trans isomers at the amide bond between DOTA chelator and first residue (d-Phe(1)H(N)) of the peptide.

Gallium↗
PubMed2005

Titanium implant materials with improved biocompatibility through coating with phosphonate-anchored cyclic RGD peptides.

One key point for improving osseous integration of implants is to render them osteopromotive by specifically favoring the adhesion of osteoblasts. Mimicking the physiological adhesion process of osteoblasts to the extracellular matrix improves cell adhesion in vitro and results in improved and earlier osseous integration of implants in vivo. Our approach involves coating titanium implants with a tailor-made cyclic-RGD peptide, thus allowing them to bind to specific integrin receptors on the cell surface through multimeric phosphonates. The advantages of this very stable, new type of anchoring for practical application are presented.

Animals↗
PubMed2005

Diffusion NMR spectroscopy: folding and aggregation of domains in p53.

Protein interactions and aggregation phenomena are probably amongst the most ubiquitous types of interactions in biological systems; they play a key role in many cellular processes. The ability to identify weak intermolecular interactions is a unique feature of NMR spectroscopy. In recent years, pulsed-field gradient NMR spectroscopy has become a convenient method to study molecular diffusion in solution. Since the diffusion coefficient of a certain molecule under given conditions correlates with its effective molecular weight, size, and shape, it is evident that diffusion can be used to map intermolecular interactions or aggregation events. Complex models can be derived from comparison of experimental diffusion data with those predicted by hydrodynamic simulations. In this review, we will give an introduction to pulsed-field gradient NMR spectroscopy and the hydrodynamic properties of proteins and peptides. Furthermore, we show examples for applying these techniques to a helical peptide and its hydrophobic oligomerization, as well as to the dimerization behavior and folding of p53.

Diffusion↗
PubMed2005

Structure refinement of cyclosporin A in chloroform by using RDCs measured in a stretched PDMS-gel.

New developments concerning alignment media for apolar solvents like chloroform make it possible to measure anisotropic parameters such as residual dipolar couplings (RDCs) at relatively low concentrations and natural isotopic abundance. As RDCs provide structural restraints with respect to an external coordinate system, long-range structural arrangements of the time-averaged structure can be determined with high precision. The method is demonstrated on the well-studied cyclo-undecapeptide Cyclosporin A (CsA), for which crystal and conventionally derived NMR structures are available. Neither crystal nor NMR structure are consistent with heteronuclear D(CH) RDCs measured in a stretched poly(dimethylsiloxane) gel, and refinement by using the anisotropic parameter results in a highly defined structure with a slightly changed backbone conformation. The applied methods and interpretation of the structural model are discussed.

Chloroform↗
PubMed2005

ADAM15 decreases integrin alphavbeta3/vitronectin-mediated ovarian cancer cell adhesion and motility in an RGD-dependent fashion.

We have recently described that integrin alphavbeta3 upon interaction with its major extracellular matrix ligand vitronectin induces adhesion, motility, and proliferation of human ovarian cancer cells. Due to the important function of alphavbeta3 in cancer cell biology, it has been the effort of many scientific approaches to specifically target alphavbeta3-mediated cell adhesion and tumorbiological effects arising thereof by synthetic integrin antagonists. More recently, proteins of the ADAM family have been recognized as naturally occurring integrin ligands. Among those, human ADAM15 which encompasses the integrin binding RGD motif was shown to interact with integrin alphavbeta3. Thus, we investigated in human ovarian OV-MZ-6 cancer cells, expressing both ADAM15 and alphavbeta3, whether ADAM15 might affect alphavbeta3-mediated tumorbiological effects. We stably (over)expressed ADAM15 or its extracellular domain in OV-MZ-6 cells as well as respective ADAM15 mutants containing the tripeptide SGA instead of RGD. Cells (over)expressing ADAM15-RGD exhibited a significantly reduced alphavbeta3-mediated adhesion to vitronectin. Also, a significant time-dependent decline in numbers of cells cultivated on vitronectin was noticed. This effect was found to be rather due to impaired alphavbeta3-mediated cell adhesion than decreased cell proliferation rates, since de novo DNA synthesis was not significantly altered by elevated ADAM15 expression. Moreover, a substantially decreased random cellular motility was noticed as a function of ADAM15 encompassing an intact RGD motif. In conclusion, our results point to a physiological role of ADAM15 as a natural binding partner of integrin alphavbeta3 thereby loosening tumor cell adhesion to the underlying matrix and regulating tumor cell migration and invasion.

ADAM Proteins↗
PubMed2005

Prokaryotic Kdp-ATPase: recent insights into the structure and function of KdpB.

P-type ATPases are amongst the most abundant enzymes that are responsible for active transport of ions across biological membranes. Within the last 5 years a detailed picture of the structure and function of these transport ATPases has emerged. Here, we report on the recent progress in elucidating the molecular mechanism of a unique, prokaryotic member of P-type ATPases, the Kdp-ATPase. The review focuses on the catalytic parts of the central subunit, KdpB. The structure of the nucleotide-binding domain was solved by NMR spectroscopy at high resolution and a model of the nucleotide-binding mode was presented. The nucleotide turned out to be 'clipped' into the binding pocket by a pi-pi interaction to F377 on one side and a cation-pi interaction to K395 on the other. The 395KGXXD/E motif and thus the nucleotide-binding mode seems to be conserved in all P-type ATPases, except the heavy metal-transporting (class IB) ATPases. Hence, it can be concluded that KdpB is currently misgrouped as class IA. Mutational studies on two highly conserved residues (D583 and K586) in the transmembrane helix 5 of KdpB revealed that they are indispensable in coupling ATP hydrolysis to ion translocation. Based on these results, two possible pathways for the reaction cycle are discussed.

Adenosine Triphosphatases↗