Biomedical subjects

G Comte

Publications and source records attributed to G Comte.

8 recordsLinked to original sources

PubMed2002

Modulation by flavonoids of cell multidrug resistance mediated by P-glycoprotein and related ABC transporters.

Cancer cell resistance to chemotherapy is often mediated by overexpression of P-glycoprotein, a plasma membrane ABC (ATP-binding cassette) transporter which extrudes cytotoxic drugs at the expense of ATP hydrolysis. P-glycoprotein (ABCB1, according to the human gene nomenclature committee) consists of two homologous halves each containing a transmembrane domain (TMD) involved in drug binding and efflux, and a cytosolic nucleotide-binding domain (NBD) involved in ATP binding and hydrolysis, with an overall (TMD-NBD)2 domain topology. Homologous ABC multidrug transporters, from the same ABCB family, are found in many species such as Plasmodiumfalciparum and Leishmania spp. protozoa, where they induce resistance to antiparasitic drugs. In yeasts, some ABC transporters involved in resistance to fungicides, such as Saccharomyces cerevisiae Pdr5p and Snq2p, display a different (NBD-TMD)2 domain topology and are classified in another family, ABCG. Much effort has been spent to modulate multidrug resistance in the different species by using specific inhibitors, but generally with little success due to additional cellular targets and/or extrusion of the potential inhibitors. This review shows that due to similarities in function and maybe in three-dimensional organization of the different transporters, common potential modulators have been found. An in vitro 'rational screening' was performed among the large flavonoid family using a four-step procedure: (i) direct binding to purified recombinant cytosolic NBD and/or full-length transporter, (ii) inhibition of ATP hydrolysis and energy-dependent drug interaction with transporter-enriched membranes, (iii) inhibition of cell transporter activity monitored by flow cytometry and (iv) chemosensitization of cell growth. The results indicate that prenylated flavonoids bind with high affinity, and strongly inhibit drug interaction and nucleotide hydrolysis. As such, they constitute promising potential modulators of multidrug resistance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

C-Isoprenylation of flavonoids enhances binding affinity toward P-glycoprotein and modulation of cancer cell chemoresistance.

Previous studies have shown that flavones bind to P-glycoprotein (Pgp) with higher affinity than isoflavones, flavanones, and glycosylated derivatives. In the present work, a series of C- or O-substituted hydrophobic derivatives of chrysin were synthesized to further investigate structural requirements of the A ring toward Pgp modulation. Increasing hydrophobicity at either position 6, 8, or 7 increased the affinity of in vitro binding to a purified cytosolic domain of Pgp, but only benzyl and 3,3-dimethylallyl C-substitution produced a high maximal quenching of the protein intrinsic fluorescence. Inhibition of membrane Pgp within leukemic cells, characterized by intracellular drug accumulation, was specifically produced by isoprenylated derivatives, with 8-(3,3-dimethylallyl)chrysin being even more efficient than the commonly used cyclosporin A.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

Natural and synthetic benzophenones: interaction with the cytosolic binding domain of P-glycoprotein.

A benzophenone glycoside has been isolated from Davallia solida. Its structure was elucidated by chemical and spectral means as 4-O-beta-D-glucopyranosyl-2,6,4'-trihydroxybenzophenone. It bound with moderate affinity to the purified C-terminal cytosolic domain of P-glycoprotein, but the binding affinity was 6- to 10-fold increased for its aglycone derivative and other related benzophenones.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2001

High-affinity binding of silybin derivatives to the nucleotide-binding domain of a Leishmania tropica P-glycoprotein-like transporter and chemosensitization of a multidrug-resistant parasite to daunomycin.

In order to overcome the multidrug resistance mediated by P-glycoprotein-like transporters in Leishmania spp., we have studied the effects produced by derivatives of the flavanolignan silybin and related compounds lacking the monolignol unit on (i) the affinity of binding to a recombinant C-terminal nucleotide-binding domain of the L. tropica P-glycoprotein-like transporter and (ii) the sensitization to daunomycin on promastigote forms of a multidrug-resistant L. tropica line overexpressing the transporter. Oxidation of the flavanonol silybin to the corresponding flavonol dehydrosilybin, the presence of the monolignol unit, and the addition of a hydrophobic substituent such as dimethylallyl, especially at position 8 of ring A, considerably increased the binding affinity. The in vitro binding affinity of these compounds for the recombinant cytosolic domain correlated with their modulation of drug resistance phenotype. In particular, 8-(3,3-dimethylallyl)-dehydrosilybin effectively sensitized multidrug-resistant Leishmania spp. to daunomycin. The cytosolic domains are therefore attractive targets for the rational design of inhibitors against P-glycoprotein-like transporters.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2000

Prenyl-flavonoids as potent inhibitors of the Pdr5p multidrug ABC transporter from Saccharomyces cerevisiae.

The Pdr5p multidrug ABC ("ATP-binding cassette) transporter was highly overexpressed in plasma membranes from a yeast strain exhibiting both pdr1-3 gain-of-function mutation in the transcription factor-encoding gene PDR1 and disruption of genes encoding other plasma membrane ABC transporters. Solubilized and purified Pdr5p displayed a tryptophan-characteristic intrinsic fluorescence, whose quenching was used to monitor interactions with substrates and effectors. The transporter exhibited a magnesium-dependent binding affinity for ATP and its fluorescent analogue 2'(3')-N-methylanthraniloyl-ATP, producing a marked fluorescence resonance-energy transfer. It also bound a series of known drug substrates and modulators. Interestingly, yeast Pdr5p interacted with flavonoids recently found to bind to cancer cell P-glycoprotein and to the protozoan parasite multidrug transporter. The extent of high-affinity binding of prenyl-flavonoids to purified Pdr5p was correlated to their efficiency to inhibit energy-dependent quenching of rhodamine 6G fluorescence catalyzed by Pdr5p-enriched plasma membranes. The hydrophobic flavonoid derivative 6-(3, 3-dimethylallyl)galangin was the most efficient, with a K(i) of 0.18 microM for competitive inhibition of the MgATP-dependent quenching of rhodamine 6G fluorescence. In contrast, inhibition of either ATP or UTP hydrolysis occurred at much higher concentrations and appeared to be noncompetitive. Prenyl-flavonoids therefore behave as potent inhibitors of drug binding to the yeast Pdr5p ABC transporter.

ATP-Binding Cassette Transporters↗

PubMed2000

The flavanolignan silybin and its hemisynthetic derivatives, a novel series of potential modulators of P-glycoprotein.

A new series of potential flavonoidic modulators of P-glycoprotein activity has been prepared. The flavanolignan silybin was first oxidised to dehydrosilybin and then C-alkylated with either prenyl or geranyl bromide. The resulting isoprenoid dehydrosilybins were shown to display high in vitro affinities for direct binding to P-glycoprotein, which ranged them among the best flavonoids ever tested.

ATP Binding Cassette Transporter, Subfamily B, Mem↗

PubMed2000

Phenylpropanoids from Umbilicus pendulinus.

Phytochemical investigation of the leaves of Umbilicus pendulinus afforded in addition to 2-O-caffeoyl malate, isoquercitrin and Z-venusol, the new isomer E-venusol. Special NMR experiments were carried out to elucidate the configuration of the two latter compounds.

Caffeic Acids↗

PubMed1992

Protein synthesis in skeletal muscle of uremic patients: effect of low-protein diet and supplementation with ketoacids.

The purpose of this study was to investigate the modifications of muscle protein synthesis activity in uremic patients fed a low-protein diet and a low-protein diet supplemented with a keto acid-amino acid mixture. The protein synthesis activity was evaluated in vitro on isolated muscle ribosomes incubated in a cell-free medium with tritiated leucine. Simultaneously, nitrogen kinetics and amino acid patterns were examined. Protein synthesis activity is correlated with the protein content of the diet in uremic patients. The keto acid-amino acid supplementation enhances protein synthesis. Variations of protein synthesis can be correlated with the variations of nitrogen balance which implies a major role of protein synthesis activity in muscle protein metabolism. Variations in plasma levels of the essential amino acids, mainly leucine and valine, can be correlated with the variations of protein synthesis activity, and these amino acids seem therefore to be mediators of the dietary effects on protein synthesis in uremia.

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