Biomedical subjects

U Klar

Publications and source records attributed to U Klar.

5 recordsLinked to original sources

PubMed2001

Subcellular distribution of epothilones in human tumor cells.

Epothilones are a new class of natural and potent antineoplastic agents that stabilize microtubules. Although 12,13-epoxide derivatives are potent antiproliferative agents, the activities of the corresponding 12,13-olefin analogs are significantly decreased. These data were confirmed for two new analogs, 6-propyl-EpoB (pEB) and 6-propyl-EpoD (pED), in comparison with the natural compounds EpoB/EpoD, by using human A431, MCF7, and MDR1-overexpressing NCI/Adr cells. By using tritiated pEB/pED, compound uptake, release, and nuclear accumulation were investigated in A431 and NCI/Adr cells. In these cells, epothilones can principally be recognized and exported by Verapamil-sensitive efflux pumps, which are not identical to MDR1. The degree of export depends on the structure, olefin vs. epoxide-analog, and also on the intracellular drug concentration. The accumulation of pED used at 3.5 or 70 nM, respectively, was increased in the presence of 10 microM Verapamil in both cell lines 2- to 8-fold. In contrast, the intracellular levels of pEB were affected by Verapamil only at 3.5 nM pEB in NCI/Adr (2-fold) and not in A431 cells. In addition, strong nuclear accumulation was observed for pEB (40-50%) but not paclitaxel or pED (5-15%) in both cell lines. Our study suggests that differences in growth inhibitory efficacy between epoxide and olefin analogs may be based on different mechanisms of drug accumulation and subcellular distribution.

Antineoplastic Agents, Phytogenic↗

PubMed2001

Signaling-inactive epidermal growth factor receptor/ligand complexes in intact carcinoma cells by quinazoline tyrosine kinase inhibitors.

Several inhibitors of EGF receptor (EGFR) tyrosine kinase activity have been developed that compete with ATP at its binding site such as the quinazolines PD 153035 and ZD 1839 or the 4,5-dianilino-phthalimides DAPH1 and DAPH2. When tested on human A431 cells, the quinazolines completely blocked EGF-induced receptor phosphorylation at 100 nM, whereas it was inhibited by DAPH1 and DAPH2 by only 20% at 3 microM. Quinazoline-treated A431 as well as tumor cells expressing less EGFR (A549, MDA MB 231, and T47D) bound 3- to 6-fold more (125)I-labeled EGF than untreated intact control cells. Scatchard analysis revealed the disappearance of low- and high-affinity EGFR on A431 cells upon PD 153035 treatment. A single receptor class of intermediate ligand binding affinity emerged and its number corresponded to the sum of the two classes. DAPH1 and DAPH2 did not change ligand binding properties of EGFR. PD 153035 exerted the most potent effects on EGF binding to A431 or on inhibiting EGF-stimulated growth of rat MTLn3 cells at low ligand concentrations. Cross-linking of EGFR on PD 153035-treated A431 cells indicated the formation of inactive dimers that further increased upon addition of EGF. Chemical cross-linking of (125)I-labeled EGF to PD 153035-treated A431 cells revealed increased binding to monomeric and dimeric EGFR. Thus, the quinazolines sequestered EGFR plus the ligand into inactive receptor/ligand complexes. This novel mode of action of quinazoline tyrosine kinase inhibitors may be the basis for their extraordinary potency especially in conditions when the ligand is present in limiting amounts.

Animals↗

PubMed1998

New synthetic inhibitors of microtubule depolymerization.

A new class of borneol esters that might be considered as biological analogs of paclitaxel regarding their action on microtubules has been found. By structure-activity optimizations, compounds stabilizing microtubules much better than paclitaxel while showing a remarkably reduced cytotoxic activity were obtained. This dissoziation will open completely new therapeutic areas.

Antineoplastic Agents↗

PubMed1995

Novel prostanoid thromboxane A2 agonists.

The chemistry and biology of novel TXA2(TP)-receptor agonists based on the prostanoid skeleton is described and structure-activity-relationships are discussed. One compound,(5Z,13E), (9R,15R)-9-fluoro-15-hydroxy-16-phenoxy-17,18,19,20-tetranor- 5,13-prostadienoic acid (33), was identified which is 10 times more potent than the standard TP-receptor against U 46619.

Blood Platelets↗

PubMed1990

Development, validation and practical use of a sensitive and specific radioimmunoassay for the determination of iloprost.

Iloprost is a potent, clinically effective PGI2-mimetic. Therapeutic plasma levels are in the low pg-range and currently analyses of biological samples are performed by GC/MS after antiserum-column extraction. Although this method exhibits high sensitivity and specificity it permits only limited numbers of samples to be analyzed owing to time-consuming work-up. The present report describes the development of a novel highly selective antiserum and its use for the RIA determination of iloprost in biological samples. An antiserum was raised against "iloprost-9-pentynyl"-BSA in rabbits. Iloprost-[3H]-methylester with a specific activity of 66.9 Ci/mmol was used as a tracer. RIA-analyses were carried out with 0.05-0.5 ml plasma adjusted to pH2 with 1 N HCl and extracted with 2.5 ml diethylether. Separation of antiserum bound and unbound iloprost was achieved by the charcoal method. Extraction recovery of iloprost was approximately 90% at pH less than or equal to 4. The detection limit of the novel assay was 1-2 pg/tube corresponding to 5-10 pg/ml plasma (if 0.1-0.2 ml plasma was used). Coefficients of variations were 8% and 2% (within-day, n = 3) and 17% and 12% (day-to-day, n = 5) at 50 and 100 pg/ml. RIA- and GC/MS-levels of iloprost measured in human samples were similar (p less than 0.001). Cross-reactivity HPLC-chromatograms of plasma extracts did not reveal any peak apart from iloprost. The RIA-method exhibits both a similar specificity and detection limit to GC/MS and will be used for further analyses.

Animals↗