Characterization of binding mode of imatinib to human α1-acid glycoprotein.

Imatinib (IMT) is a selective tyrosine kinase inhibitor, used in the treatment of chronic myeloid leukemia and gastrointestinal stromal tumors. Its strong plasma protein binding was found to belong to the F1*S genetic variant of α(1)-acid glycoprotein (AGP). In this work, comparative AGP binding studies were performed with IMT fragment molecules to reveal which parts of the molecule are important in the high-affinity interaction provoking specific spectral changes. Molecular modeling calculations indicated that IMT docked into the X-ray structure of AGP/F1 adopts a bent, compact conformation. This binding mode is similar to those found in its complexes with some low-affinity kinases and a quinone reductase, being strikingly different from the extended conformation of IMT in its high-affinity kinase targets.

Species-dependency in chiral-drug recognition of serum albumin studied by chromatographic methods.

Stereoselective binding of benzodiazepine and coumarin drugs to serum albumin from human and six mammalian species were studied by chiral chromatographic techniques. The applied methods were affinity chromatography on the albumins immobilized on Sepharose 4B, high-performance liquid chromatography (HPLC) separation on columns based on human serum albumin (HSA) and bovine serum albumin (BSA), and chiral HPLC analysis of ultrafiltrates of solutions containing the racemic drug and the native protein. Substantial differences in preferred configurations and conformations were detected among the species. The binding stereoselectivity of the 2,3-benzodiazepine drug, tofisopam, in human, is opposite to that in all other species. In the binding of 1,4-benzodiazepines, dog albumin is very similar to HSA. Highly preferred binding of (S)-phenprocoumon was found with dog albumin.

Stereoselective allosteric binding interaction on human serum albumin between ibuprofen and lorazepam acetate.

The effect of ibuprofen enantiomers on the stereoselective binding of 3-acyloxy-1,4-benzodiazepines to human serum albumin (HSA) was studied using both native and Sepharose-immobilized protein. (S)-Lorazepam acetate exhibited considerably enhanced binding, especially in the presence of (+)-(S)-ibuprofen. The phenomenon is an indication of cooperative allosteric interaction between different binding sites during multiple cobinding of two ligands.

Binding studies with recombinant human serum albumin obtained by expression of a synthetic gene in yeast. Stereoselective binding and allosteric interaction with benzodiazepine and coumarin ligands.

The specific ligand binding ability of recombinant human serum albumin produced in yeast using the synthetic gene was studied by affinity chromatographic method. It was found that synthetic protein possesses those stereoselective binding and binding interactions for several chiral benzodiazepine and coumarin compounds which are characteristic of the natural human serum albumin, suggesting identical tertiary structures.

Stereoselective distribution of acenocoumarol enantiomers in human plasma: chiral chromatographic analysis of the ultrafiltrates.

Stereoselectivities for the binding of rac-acenocoumarol to human serum albumin (HSA), alpha 1-acid glycoprotein (AGP), and human plasma were determined by chiral HPLC analysis of the ultrafiltrates on a Chiral-AGP column. The results confirmed the previously detected inverse stereoselectivities; for HSA the ratio of the enantiomeric constants was KR/KS approximately 2, while for AGP it was KR/KS approximately 0.3. In plasma the contribution of HSA dominates, although in pathological states, elevated AGP levels may compensate for stereoselective distribution.

Chiral high-performance liquid chromatographic separations of vinca alkaloid analogues on alpha 1-acid glycoprotein and human serum albumin columns.

Separations of the stereoisomers of a series of tetracyclic and pentacyclic vinca alkaloid analogues having two or three chiral centres were performed on Chiral-AGP and Chiral-HSA high-performance liquid chromatographic columns. Phosphate buffers with pH 5-7 containing 5-35% acetonitrile or 2-propanol were used as mobile phases. The results were in accordance with previous binding data obtained with native AGP and on an HSA-Sepharose column. Whereas on Chiral-AGP the retention of the trans isomers having 1(R),12b(S)-indolo[2,3-a]quinolizidine or the corresponding 3(S),16(R)-eburnane absolute configurations was exceedingly high, on Chiral-HSA the trans isomers, independently of their absolute configurations, were more retained. Eburnane-type compounds could also be separated according to the configuration of the chiral centre at position 14. A comparison of the chromatographic properties of the vinca alkaloids on the Chiral-AGP and Chiral-HSA columns demonstrates that these compounds are bound with higher affinity to the AGP phase. The AGP column resolves a very broad range of vinca alkaloids compared with the HSA column. Higher stereoselectivity and a much better chromatographic performance were also obtained on the Chiral-AGP column.

Stereoselective effect of phenprocoumon enantiomers on the binding of benzodiazepines to human serum albumin.

The effect of phenprocoumon enantiomers on the stereoselective binding of 3-substituted 1,4-benzodiazepines to human serum albumin (HSA) was studied by chromatography on HSA-Sepharose column. (S)-Phenprocoumon exerts stereoselective allosteric interaction on the binding of benzodiazepines. The structural requirements of enhanced stereoselectivities are similar to those found previously with (S)-warfarin.

Binding of vinca alkaloid analogues to human serum albumin and to alpha 1-acid glycoprotein.

The binding of a series of vinca alkaloid analogues having eburnane or indolo[2,3-a]quinolizidine skeletons was studied with human serum albumin (HSA) by affinity chromatography and with alpha 1-acid glycoprotein by means of competition experiments. On HSA the binding occurs at the benzodiazepine-indole binding site via hydrophobic interaction and shows slight stereoselectivity preferring the trans isomers. The binding to alpha 1-AGP proved to be highly stereoselective in favour of the trans isomers having 3(S),16(R)eburnane or 1(R),12b(S)indolo[2,3-a]quinolizidine absolute configurations.

Demonstration of stereoselective disposition of warfarin enantiomers by whole-body autoradiography.

The oral anticoagulant warfarin and its 14C-labelled derivative are commercially available in racemic forms. Two methods for the chromatographic resolution of the radiolabel were used to investigate the distribution of radioactivity of radioactivity of individual enantiomers in the rat by whole-body autoradiography. Computer-assisted quantification of autoradiograms indicated the average disappearance of levo-warfarin and its metabolites to be substantially slower than that of dextro-warfarin and its metabolites from the following organs: liver, pancreas, kidney, lung, blood, intestines.

Stereoselective effect of warfarin and bilirubin on the binding of 5-(o-chlorophenyl)-1,3-dihydro-3-methyl-7-nitro-2H-1,4-benzodiazepin-2- one enantiomers to human serum albumin.

The binding of the title benzodiazepine enantiomers and its modulation by warfarin and bilirubin were studied by chromatography on human serum albumin (HSA) immobilized on Sepharose 4B, and also by a combination of ultrafiltration and circular dichroism (UF-CD) methods. In the absence of warfarin and bilirubin the binding of the benzodiazepine was not stereoselective. (S)-Benzodiazepine and (S)-warfarin mutually increased the binding of each other, while the binding of (R)-benzodiazepine was preferentially enhanced on HSA saturated with bilirubin.

Inverse stereoselectivity in the binding of acenocoumarol to human serum albumin and to alpha 1-acid glycoprotein.

Stereoselective binding of rac-acenocoumarol to human serum albumin (HSA) and alpha 1-acid glycoprotein (alpha 1-AGP) was investigated by affinity chromatography and by combined ultrafiltration (UF) and circular dichroism (CD) methods. For HSA, the ratio of the enantiomeric constants was KR/KS = 2, while for alpha 1-AGP, KS/KR = 3.

Selective effect of clonazepam and (S)-uxepam on the binding of warfarin enantiomers to human serum albumin.

Both clonazepam and (S)-uxepam selectively increase the binding of (S)-warfarin to human serum albumin. By liquid affinity chromatography, improved resolution of rac-warfarin was achieved.

Stereoselective binding of 3-acetoxy-, and 3-hydroxy-1,4-benzodiazepine-2-ones to human serum albumin. Selective allosteric interaction with warfarin enantiomers.

Stereoselective binding of oxazepam, lorazepam, temazepam and methyl lorazepam as well as of their acetates to human serum albumin was investigated by different techniques. The 2'-chlorine and the N(1)-methyl substitution exert opposite effects on the antipodes. Enantiomers of oxazepam acetate (OAc) and lorazepam acetate (LAc) displace diazepam. Allosteric interactions with warfarin were manifested by either mutually increased or decreased binding depending on the structure of benzodiazepine and on the configuration of both benzodiazepine and warfarin. The most remarkable effect could be observed in the simultaneous binding of (S)-lorazepam acetate and (S)-warfarin.

Investigation on the binding of tryptophan enantiomers to human serum albumin.

The binding of radiolabelled tryptophan enantiomers to human serum albumin was investigated by ultrafiltration and by the microparticle technique. L-Trp was found to exhibit a high degree of secondary binding. D-Trp showed increased degree of binding when the HSA concentration was decreased. Stereoselective binding has also been detected in stereoselectively labelled racemic mixtures. Both L- and D-Trp were found to compete for the primary binding site with specific benzodiazepine markers. All the experiments indicate that stereoselectivity of binding is much lower than generally believed.

Stereoselective binding of a 2,3-benzodiazepine to human serum albumin. Effect of conformation on tofizopam binding.

The binding of Tofizopam enantiomers to human serum albumin has been investigated by ultrafiltration and affinity chromatography. In solution, Tofizopam molecules exist in two conformations which slowly interconvert into each other. Both conformers of (R)-Tofizopam have the same binding constant of 4.8 X 10(3) M-1. The binding of the (S)-enantiomer, however, depends on the conformation. The minor and major (S)-conformers were characterized by association constants of 2.3 X 10(3) and 15.1 X 10(3) M-1, respectively. Thus, the stereoselectivity of binding differs for the two conformations of the enantiomers. Kinetic parameters for the interconversion of conformations have been determined. Tofizopam displaces both bound diazepam and warfarin.