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Biomedical subjects

A L Laborde

Publications and source records attributed to A L Laborde.

At least 19 recordsLinked to original sources
PubMed2001

Small molecule peptidomimetics containing a novel phosphotyrosine bioisostere inhibit protein tyrosine phosphatase 1B and augment insulin action.

Protein tyrosine phosphatase 1B (PTP1B) attenuates insulin signaling by catalyzing dephosphorylation of insulin receptors (IR) and is an attractive target of potential new drugs for treating the insulin resistance that is central to type II diabetes. Several analogues of cholecystokinin(26)(-)(33) (CCK-8) were found to be surprisingly potent inhibitors of PTP1B, and a common N-terminal tripeptide, N-acetyl-Asp-Tyr(SO(3)H)-Nle-, was shown to be necessary and sufficient for inhibition. This tripeptide was modified to reduce size and peptide character, and to replace the metabolically unstable sulfotyrosyl group. This led to the discovery of a novel phosphotyrosine bioisostere, 2-carboxymethoxybenzoic acid, and to analogues that were >100-fold more potent than the CCK-8 analogues and >10-fold selective for PTP1B over two other PTP enzymes (LAR and SHP-2), a dual specificity phosphatase (cdc25b), and a serine/threonine phosphatase (calcineurin). These inhibitors disrupted the binding of PTP1B to activated IR in vitro and prevented the loss of tyrosine kinase (IRTK) activity that accompanied PTP1B-catalyzed dephosphorylation of IR. Introduction of these poorly cell permeant inhibitors into insulin-treated cells by microinjection (oocytes) or by esterification to more lipophilic proinhibitors (3T3-L1 adipocytes and L6 myocytes) resulted in increased potency, but not efficacy, of insulin. In some instances, PTP1B inhibitors were insulin-mimetic, suggesting that in unstimulated cells PTP1B may suppress basal IRTK activity. X-ray crystallography of PTP1B-inhibitor complexes revealed that binding of an inhibitor incorporating phenyl-O-malonic acid as a phosphotyrosine bioisostere occurred with the mobile WPD loop in the open conformation, while a closely related inhibitor with a 2-carboxymethoxybenzoic acid bioisostere bound with the WPD loop closed, perhaps accounting for its superior potency. These CCK-derived peptidomimetic inhibitors of PTP1B represent a novel template for further development of potent, selective inhibitors, and their cell activity further justifies the selection of PTP1B as a therapeutic target.

3T3 Cells↗
PubMed1999

Synthesis of a series of stromelysin-selective thiadiazole urea matrix metalloproteinase inhibitors.

The synthesis and enzyme inhibition data for a series of thiadiazole urea matrix metalloproteinase (MMP) inhibitors are described. A broad screening effort was utilized to identify several thiadiazoles which were weak inhibitors of stromelysin. Optimization of the thiadiazole leads to include an alpha-amino acid side chain with variable terminal amide substituents provided a series of ureas which were moderately effective stromelysin inhibitors, with Ki's between 0.3 and 1.0 microM. The most effective analogues utilized an L-phenylalanine as the amino acid component. In particular, unsubstituted 46 had a Ki of 710 nM, while the p-fluoro analogue 52 displayed increased potency (100 nM). Stromelysin inhibition was further improved using a pentafluorophenylalanine substituent which resulted in 70, a 14 nM inhibitor. While gelatinase inhibition was generally poor, the use of 1-(2-pyridyl)piperazine as the amide component usually provided for enhanced activity, with 71 inhibiting gelatinase with a Ki of 770 nM. The combination of this heterocycle with a p-fluorophenylalanine substituent provided the only analogue, 69, with collagenase activity (13 microM). The SAR for analogues described within this series can be rationalized through consideration of the X-ray structure recently attained for70 complexed to stromelysin. Uniquely, this structure showed the inhibitor to be completely orientated on the left side of the enzyme cleft. These results suggest that thiadiazole urea heterocycles which incorporate a substituted phenylalanine can provide selective inhibitors of stromelysin. Careful selection of the amide substituent can also provide for analogues with modest gelatinase inhibition.

Binding Sites↗
PubMed1998

The constituent tryptophans and bisANS as fluorescent probes of the active site and of a secondary binding site of stromelysin-1 (MMP-3).

The active site of the catalytic domain of stromelysin-1 (matrix metalloproteinase-3, MMP-3) was probed by fluorescence quenching, lifetime, and polarization of its three intrinsic tryptophans and by the environmentally sensitive fluorescent reporter molecule bisANS. Wavelength-dependent acrylamide quenching identified three distinct emitting tryptophan species, only one of which changes its emission and fluorescence lifetime upon binding of the competitive inhibitor Batimastat. Significant changes in the tryptophan fluorescence polarization occur upon binding by any of the three hydroxamate inhibitors Batimastat, CAS108383-58-0, and Celltech CT1418, all of which bind in the P2'-P3' region of the active site. In contrast, the inhibitor CGS27023A, which is thought to bind in the P1-P1' region, does not induce any change in tryptophan fluorescence polarization. The use of the fluorescent probe bisANS revealed the existence of an auxiliary binding site extrinsic to the catalytic cleft. BisANS acts as a competitive inhibitor of stromelysin with a dissociation constant of Ki=22 microM. In addition to this binding to the active site, it also binds to the auxiliary site with a dissociation constant of 3.40+/-0.17 microM. The auxiliary site is open, hydrophobic, and near the fluorescing tryptophans. The binding of bisANS to the auxiliary site is greatly enhanced by Batimastat, but not by the other competitive inhibitors tested.

Acrylamides↗
PubMed1994

K252a, KT5720, KT5926, and U98017 support paclitaxel (taxol)-dependent cells and synergize with paclitaxel.

We have used paclitaxel-dependent Tax 2-4 cells to screen for compounds that have paclitaxel-like functional activity. The indolocarbazole serine/threonine kinase inhibitor K252a and analogues such as KT5926, KT5720, and K252b partially support the growth of the paclitaxel-dependent cells in the absence of paclitaxel. A novel kinase inhibitor of similar structure, U98017, supports the growth of the dependent cells to 48% of that seen with paclitaxel. Used in combination with paclitaxel, these compounds reduce the amount of paclitaxel required for maximum growth of the dependent cells. Isobologram analysis demonstrates that these compounds also act synergistically with paclitaxel to promote toxicity in wild-type Chinese hamster ovary cells. These selected indolocarbazoles may act at sites distinct from that of paclitaxel and may specifically inhibit kinases that contribute to the destabilization of microtubules. Other indolocarbazoles such as staurosporine and rebeccamycin do not support paclitaxel-dependent cell growth. Structurally unrelated serine/threonine kinase inhibitors such as H-9 and H-7 or tyrosine kinase inhibitors such as lavendustin do not support the growth of these cells. These results define a screen for functional paclitaxel analogues and suggest that it may be useful to investigate the possible synergy of selected indolocarbazoles and paclitaxel in vivo.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1993

Endovascular canine anastomotic stenting.

The healing characteristics and morphological features of a trans-anastomotic endovascular multifilament flexible metallic stent (Wallstent, Schneider) were investigated in a canine end-to-end arterial model. Both femoral arteries of 12 conditioned mongrel dogs were exposed, then transversely divided and reanastomosed. One anastomosis was randomly chosen for stent placement. Stents were chosen to match the diameter of the femoral arteries and were 25 mm in unconstrained length. Animals were sacrificed at intervals of 3, 6, 9, and 12 weeks. The anastomotic segments were pressure perfusion fixed and sectioned. The cross-sectional luminal, intimal, and medial areas were calculated from computer digitized images of the individual sections. Data were analyzed by univariate repeated measures analysis of variance. Stented anastomoses had an increased luminal area as compared with the anastomosis of non stented sections (P < 0.002). However, stended segments had a significantly increased intimal area when compared to control segments in the same animal (P < 0.001). Stented anastomoses had a significantly increased lumen area over controls despite a marked intimal response to the stent.

Anastomosis, Surgical↗
PubMed1992

An evaluation of color duplex scanning in the primary diagnosis and management of carotid body tumors.

Carotid body tumors present a diagnostic challenge. Despite technologic diagnostic advances, misdiagnosis resulting in blind biopsy or exploration through a limited incision still occur. Color duplex scanning has recently been used to evaluate carotid body tumors in our institution. A characteristic feature of these tumors found with this modality is wide splaying of the carotid bifurcation by a hypervascular mass. Color duplex scanning is the noninvasive modality of choice for the primary diagnosis of carotid body tumors. Additionally, it may be of use in screening for familial carotid body tumors and sequential follow-up of nonoperatively managed tumors.

Adult↗
PubMed1992

A simple technique of renal transplant preservation during aortic reconstruction.

Various methods of insuring renal transplant perfusion during aortic reconstruction have been described but these are often complex and troublesome. Although short periods of warm ischemia are probably well tolerated, reinstitution of pulsatile flow is more desirable. A simple method of rapidly restoring renal perfusion during aortic reconstruction is described.

Anastomosis, Surgical↗
PubMed1990

Purification and characterization of interleukin 1 receptor level antagonist proteins from THP-1 cells.

Culture medium conditioned by phorbol 12-myristate 13-acetate-differentiated THP-1 cells contained interleukin 1 (IL-1) antagonist activity as measured by inhibition of both IL-1 beta binding to receptors on YT cells and inhibition of IL-1/phytohemagglutinin-stimulated IL-2 synthesis by LBRM-33-1A5 T cells. Based on their ability to compete for 125I-IL-1 beta binding to receptors on YT cells, four distinct antagonist proteins were purified from THP-1 cell conditioned medium using a combination of ion-exchange, hydrophobic interaction, and size exclusion chromatographies. The four proteins had different isoelectric points with molecular masses in the range 22-26 kDa and had similar specific activities for inhibition of IL-1 beta binding to cell surface receptors (Ki values 0.33-0.64 nM) and for inhibition of IL-1/phytohemagglutinin-stimulated IL-2 synthesis by 1A5 cells (IC50 values 25-100 pM). Amino-terminal sequence analysis of the two major forms (25 kDa/pI 5.1 and 22 kDa/pI 5.8) revealed complete identity for the first 27 residues in both forms. Based on the results of peptide mapping, amino acid compositional analysis and immune blotting, all of the forms were deduced to be variants of a common protein. Deglycosylation of the antagonist proteins with N-glycanase converted them to a common form (22 kDa/pI 5.8), indicating that the four isoforms represent glycosylation variants of a common protein and that asparagine-linked oligosaccharides are responsible for the observed size and charge heterogeneity.

Amino Acid Sequence↗
PubMed1990

Purification, cloning, expression and biological characterization of an interleukin-1 receptor antagonist protein.

A human myelomonocytic cell line, U937, produced an interleukin-1 (IL-1) receptor antagonist protein (IRAP) which was purified and partially sequenced. A complementary DNA coding for IRAP was cloned and sequenced. The mature translation product of the cDNA has been expressed in Escherichia coli and was an active competitive inhibitor of the binding of IL-1 to the T-cell/fibroblast form of the IL-1 receptor. Recombinant IRAP specifically inhibited IL-1 bioactivity on T cells and endothelial cells in vitro and was a potent inhibitor of IL-1 induced corticosterone production in vivo.

Amino Acid Sequence↗
PubMed1990

In vitro antibacterial activity and interactions with beta-lactamases and penicillin-binding proteins of the new monocarbam antibiotic U-78608.

U-78608, a new monocarbam antibiotic, was evaluated for in vitro activity against 312 clinical isolates of aerobic and anaerobic bacteria and subjected to several in vitro biochemical tests characterizing its interactions with beta-lactamases and penicillin-binding proteins (PBPs). The antibacterial activity of the compound was compared directly with those of SQ 83,360 (pirazmonam) and aztreonam. U-78608, SQ 83,360, and aztreonam had generally poor activity against gram-positive aerobic bacteria and anaerobic bacteria. U-78608 demonstrated activity primarily against gram-negative aerobic bacteria, with potency generally comparable to that of SQ 83,360. U-78608 and SQ 83,360 were less active than aztreonam for some gram-negative species; however, both compounds were 8- to 64-fold more active than aztreonam against Acinetobacter species, Pseudomonas aeruginosa, and Pseudomonas maltophilia. All three compounds resisted inactivation by several different beta-lactamases from gram-positive and gram-negative bacteria. Neither U-78608 nor SQ 83,360 exhibited significant inhibition of these enzymes, while aztreonam inhibited beta-lactamases from P. aeurginosa and Klebsiella oxytoca. All three compounds exhibited strong affinity to PBP 3 of Escherichia coli and moderate to negligible affinity to the other E. coli PBPs; quantitative measurements indicated that U-78608 had greater PBP 3 affinity than either SQ 83,360 or aztreonam.

Anti-Bacterial Agents↗
PubMed1990

Regional autoregulatory responses during infusion of vasoconstrictor agents in conscious dogs.

We investigated pressure-dependent autoregulatory responses in mesenteric, iliac, and renal vascular beds of conscious dogs during intravenous infusion of angiotensin II, phenylephrine, or arginine vasopressin at rates which increased arterial pressure by 20-40 mmHg. The arteries supplying these beds were instrumented with an electromagnetic flow probe, a nonoccluding catheter, and an electromagnetic flow probe, a nonoccluding catheter, and an occluder cuff connected with a servo-amplifier, which enabled us to return perfusion pressure to control levels during infusion of the vasoconstrictor agents. We attempted to differentiate between the increase in vascular resistance due to the direct effect of the vasoconstrictor agent and the increase induced by an autoregulatory response induced by elevations of aortic perfusion pressure. We measured a strong degree of autoregulation in the renal vascular bed with a fractional compensation value close to 1. Moderate autoregulation occurred in the mesenteric vascular bed, where the compensation was 0.4-0.5 with angiotensin II and phenylephrine and between 0.74 and 0.94 with vasopressin. No autoregulatory capacity could be demonstrated in the hindlimb. The findings indicate that, under conditions of increased systemic blood pressure, both the renal and the mesenteric vascular beds contribute to the increase in total peripheral resistance by pressure-dependent vasoconstrictor responses.

Angiotensin II↗
PubMed1989

Interaction of cephalosporins with penicillin-binding proteins of methicillin-resistant Staphylococcus aureus.

The binding affinity of cefmetazole for penicillin binding proteins (PBPs) of methicillin resistant Staphylococcus aureus (MRSA) was compared with the affinities of cefazolin, cefotetan, and cefoxitin for these same sites. Overall, cefmetazole was found to have comparable or higher affinity for PBP1, PBP2, and PBP3 than cefoxitin or cefotetan; its affinity for these PBPs is lower than that of cefazolin. Interestingly, the antibiotic showed a somewhat greater affinity for PBP2' (PBP2a) than cefazolin, cefotetan, and cefoxitin. These results suggest that the somewhat lower MICs detected with cefmetazole for MRSA may be a consequence of the interaction of the antibiotic with PBP2'.

Bacterial Proteins↗