Biomedical subjects

K Alexopoulos

Publications and source records attributed to K Alexopoulos.

16 recordsLinked to original sources

PubMed2001

Design, synthesis, and modeling of novel cyclic thrombin receptor-derived peptide analogues of the Ser42-Phe-Leu-Leu-Arg46 motif sequence with fixed conformations of pharmacophoric groups: importance of a Phe/Arg/NH2 cluster for receptor activation and implications in the design of nonpeptide thrombin receptor mimetics.

The novel cyclic analogues cyclo(Phe-Leu-Leu-Arg-epsilonLys-Dap) (1) and cyclo(D-Phe-Leu-Leu-Arg-epsilonLys-Dap) (2), which differ only in the absolute conformation of Phe, have been designed and synthesized based upon the minimal peptide sequence Phe-Leu-Leu-Arg which has been found to exhibit biological activity for the thrombin receptor. Compound 1, in which all amino acids have the L-configuration, exhibited higher activity in the rat aorta relaxation and rat longitudinal muscle bioassays compared to compound 2, in which the Phe residue is in the D-configuration. This is attributed to the spatial proximity of the Phe and Arg in compound 1 which does not exist in its diastereomeric compound 2, as is depicted from a combination of NMR studies and computational analysis. Structure-activity studies (SAR) showed that the Phe and Arg side chains along with a primary amino group form an active recognition motif that is augmented by the presence of a second primary amino group in the cyclic peptide. We suggest that a comparable cyclic conformation may be responsible for the interaction of linear TRAPs with the thrombin receptor. The validity of this proposition was tested by the synthesis of four active nonpeptide thrombin receptor mimetics. Substance (S)-N-(6-guanidohexanoyl)-N'-(2-amino-3-phenylpropionyl)piperazine (3), in which the pharmacophoric phenyl, guanidino, and amino groups were incorporated onto a piperazine template, was found to be the most active compared to the other synthesized compounds which lack the amino pharmacophoric group.

Animals↗

PubMed2001

Modulation of angiogenesis and progelatinase a by thrombin receptor mimetics and antagonists.

The angiogenic action of thrombin has been shown to be mediated by activation of the thrombin receptor. In this report we studied the effects of SFLLR, an agonist of the activated thrombin receptor and thrombin receptor peptide and non peptide antagonists on angiogenesis in the chick chorioallantoic membrane (CAM) system. As antagonists were used the tripeptide FPR and non-peptide 1,4-disubstituted piperazine derivatives. The pentapeptide SFLLR, like thrombin, caused a marked stimulation of angiogenesis in the CAM. FPR and the piperazine derivatives caused suppression of angiogenesis and in combination with thrombin antagonized its angiogenic effect. Thrombin and SFLLR activated progelatinase A (MMP-2) in the culture medium of human umbilical cord endothelial cells (HUVECs). MMP-2 is involved in the early steps of angiogenesis leading to local dissolution of basement membrane collagen and migration of the activated endothelial cells. FPR and the piperazine derivatives inhibited the activation of this enzyme. They also antagonised the effects of both thrombin and SFLLR on MMP-2 activation. These results suggest that non-thrombogenic agonists or antagonists of the activated thrombin receptor can be used as modulators of angiogenesis.

Animals↗

PubMed2000

Structural comparison between type I and type II antagonists: possible implications in the drug design of AT1 antagonists.

Analogues of sarilesin (type I AT1 antagonists), and sarmesin (type II AT1 antagonists) with homoserine (hSer) at position 8 were prepared and bioassayed. The presence of a Tyr4-Ile5-His6 bend found in sarmesin but not in sarilesin was identified. The obtained results coupled with conformational analysis studies, using a combination of NMR spectroscopy and computational chemistry, propose important conformational and stereoelectronic properties for agonist and antagonist activity at AT1 receptors.

Angiotensin I↗

PubMed1999

Docetaxel and granulocyte colony-stimulating factor in patients with advanced non-small-cell lung cancer previously treated with platinum-based chemotherapy: a multicenter phase II trial.

PURPOSE: To investigate the activity of docetaxel and granulocyte colony-stimulating factor support (G-CSF) in patients with advanced non-small-cell lung cancer (NSCLC) previously treated with cisplatin. PATIENTS AND METHODS: A total of 60 patients with locoregional and metastatic NSCLC who had relapsed or progressed after first-line treatment with cisplatin-based regimens were enrolled into the trial. Docetaxel at 100 mg/m2 was given as a 1-h infusion with G-CSF (rhG-CSF given s.c. at 150 microg/m2) support from day 2 to day 8 every 3 weeks; all patients received premedication with corticosteroids. RESULTS: In all, 1 (1.6%) and 14 (23.3%) patients achieved a complete response (CR) and a partial response (PR), respectively, for an overall response rate of 25% (95% CI 14.0-35.9%); stable disease (SD) and progressive disease (PD) were documented in 18 (30%) and 27 (45%) patients, respectively. The median duration of response was 20 weeks and the median time to tumor progression was 28 weeks. The median overall survival was 32 weeks and the 1-year survival rate was 23%. A total of 263 courses were given at a median of 3 cycles/patient. Grade 3 and 4 neutropenia occurred in 11 (18%) and 14 (23%) patients, respectively, with 18 (30%) patients requiring hospitalization for neutropenic fever; 1 patient died of sepsis. Grade 2 peripheral neuropathy occurred in 9 patients (15%) and grade 3 asthenia, in 4 (7%). Other toxicities were mild. CONCLUSIONS: Docetaxel has considerable single-agent activity in patients with NSCLC who have relapsed or progressed after first-line chemotherapy with cisplatin-based regimens.

Adult↗

PubMed1999

Design and synthesis of thrombin receptor-derived nonpeptide mimetics utilizing a piperazine scaffold.

Focal thrombus formation and vasoconstriction serve to defend vessels when vascular damage occurs, but may be detrimental when an atherosclerotic plaque is disrupted. Recently, the identification of the platelet thrombin receptor opened a new area in the development of agents that may selectively inhibit the effects of thrombin on cells, without affecting fibrin formation. In this regard, we have synthesized a number of 1,4-disubstituted piperazines which are designed to be analogues of thrombin receptor activating peptides (TRAP) and carry the pharmacophoric features of Phe and Arg residues present in the active pentapeptide SFLLR. These compounds were tested in the rat aorta relaxation assay and in platelet aggregation studies and their biological activity was consistent with a direct action on thrombin receptor. Furthermore, the structure activity relationships confirmed the importance of Phe and Arg for receptor activation and the molecular modeling revealed an intriguing relationship between their amphipathic similarity with SFLLR and their biological activity.

Animals↗

PubMed1998

Design and synthesis of small semi-mimetic peptides with immunomodulatory activity based on myelin basic protein (MBP).

Experimental allergic encephalomyelitis (EAE) is induced in susceptible animals by immunodominant determinants of myelin basic protein (MBP). Analogs of these disease-associated peptides have been identified with disease progression upon coimmunization. Usage of peptides, with disease-specific immunomodulatory capacity in vivo is limited, however, due to their sensitivity to proteolytic enzymes. Alternative approaches include the development of mimetic molecules which maintain the biological function of an original peptide, yet are stable and able to elicit their response in pharmacological quantities. A novel technique was employed to design a series of semi-mimetic peptides, based on the guinea pig MBP72-85 peptide used to induce EAE in Lewis rats. We used isonipecotic (iNip) and aminocaproic (Acp) acids as templates. Acp-MBP72-85 peptide derived analogues were effective in inducing EAE compared to iNip-peptide analogues which were ineffective at 350 micrograms. These findings suggest that the design and synthesis of semi-mimetic peptide molecules with immunomodulatory potential is possible and that eventually these molecules may form the basis for the development of novel and more effective disease-specific therapeutic agents.

Amino Acid Sequence↗

PubMed1998

A comparative SAR study of thrombin receptor derived non peptide mimetics: importance of phenyl/guanidino proximity for activity.

Thrombin, the most potent physiological platelet agonist interacts with cells through a specific G protein-coupled receptor which has been cloned and sequenced. Synthetic thrombin receptor peptides (TRAPs) comprising the first 5 amino acids (SFLLR and SFLLR-NH2) of the new N-terminus tethered ligand of the thrombin receptor that is generated by thrombin's proteolytic activity were found to cause full platelet aggregation. During the screening of novel thrombin receptor derived non-peptide mimetics in the platelet aggregation assay we found that 1-phenylacetyl-4-(6-guanidohexanoyl)-piperazine (1) and 1-(6-guanidohexanoyl)-4-(phenylacetylamidomethyl)-piperidine (2) exerted in vitro antagonist activities (56% and 40% correspondingly) as it is depicted by the platelet aggregation assay. Using Molecular Modeling, the synthetic compounds were overlayed with SFFLR. All three superimposed low energy structures had Phe and Arg amino acids in spatial close proximity. The superimposition results revealed that 1 resembled more the stereoelectronic environment of SFLLR than 2. This difference may be related to their different antagonist efficacy.

Arginine↗

PubMed1998

Comparison between two fat emulsions: Intralipid 30 cent vs intralipid 10 cent in critically ill patients.

Fat emulsions, Intralipid 30% and Intralipid 10% were compared in terms of the resulting plasma levels of different lipid components and clinical tolerance in critically-ill patients with multi-injuries. Sixteen critically-ill patients with severe systemic inflammatory response were randomly assigned to two groups, each one comprised of eight patients. Each group was administered the same quantity of fat/Kg/day either Intralipid 30% or Intralipid 10%. The infusion lasted 12|h daily for 6 days. During the infusion of the fat emulsion, a lower median plasma concentration of triglycerides, phospolipids and free cholesterol was observed in patients who received Intralipid 30% compared with those who received Intralipid 10%. The above observations were sustained 4 h after the termination of the infusion. Free fatty acids had a higher mean plasma concentration in the group of patients who received Intralipid 30%. There were no differences between the two groups as far as the median plasma concentration of cholesterol and lipoproteins (LDL, HDL, VLDL) are concerned. On the contrary, there was an increase in LpX in the Intralipid 10% group. From the above findings, we draw the conclusion that Intralipid 30% revealed better profiles of different lipid components than Intralipid 10% in critically-ill patients. The new emulsion of higher concentration in triglyceride was proved clinically safe and its use is suggested for critically-ill patients who require total parenteral nutrition.

Adult↗

PubMed1997

Conformational analysis of the thrombin receptor agonist peptides SFLLR and SFLLR-NH2 by NMR: evidence for a cyclic bioactive conformation.

The conformational properties of the pentapeptide Ser-Phe-Leu-Leu-Arg (P5), a human thrombin receptor-derived sequence forming part of a tethered ligand which activates the thrombin receptor, and its more active amide derivative Ser-Phe-Leu-Leu-Arg-NH2 (P5-NH2), have been studied by proton NMR spectroscopy in dimethylsulfoxide. Measurements of nuclear Overhauser effects, performed using two-dimensional rotating frame nuclear Overhauser (ROESY) and one-dimensional nuclear Overhauser enhancement (NOE) spectroscopy, revealed that P5 exists mainly in an extended conformation. However, proton-proton 1D-NOEs between Phe C alpha H and Ser C alpha H Leu3 C alpha H and Leu3 NH, and Leu4 C alpha H and Leu4 NH, as well as between the Ser and Arg sidechains, also implicated a minor conformer for P5 having a curved backbone and a near-cyclic structure. In contrast to P5, measurements of NOEs and ROEs for P5-NH2 revealed a more stabilized cyclic structure which may account for its higher biological potency. Thus strong interresidue sequential NH (i)-NH (i + 1) interactions, as well as C-terminal carboxamide to N-terminal side-chain interactions, i.e., Arg CONH2 to Phe ring and Arg CONH2 to Ser C alpha/C beta beta', observed at lower levels of the ROESY spectrum, supported a curved backbone structure for SFLLR-NH2. Since the higher potency P5-NH2 analogue adopts predominantly a cyclic structure, a cyclic bioactive conformation for thrombin receptor agonist peptides is suggested.

Amino Acid Sequence↗

PubMed1994

Effects of propofol and thiopentone on polymorphonuclear leukocyte functions in vitro.

Anesthetic agents may impair host defense mechanisms including polymorphonuclear leukocyte (PMNL) function. We have studied the effects of thiopentone and propofol in low (thiopentone 10 mg/L, propofol 2 mg/l) and high (thiopentone 40 mg/L, propofol 6 mg/L) clinically relevant concentrations on PMNL adherence, chemotaxis, phagocytosis and killing in vitro. The results demonstrated that thiopentone in both concentrations significantly decreases all PMNL functions tested and had a direct influence on the PMNLs in terms of their chemotactic response. In contrast, propofol decreases significantly only PMNL chemotaxis but not adherence, phagocytosis and killing. The effect of propofol was not attributable to the lipid carrier vehicle, as Intralipid with same formulation had no effect on PMNL function. We conclude that propofol is a relatively safe agent from the viewpoint of PMNL function in vitro, which may be of potential clinical benefit.

Adult↗

PubMed1991