Stereoselective Binding of Flurbiprofen Enantiomers and their Methyl Esters to Human Serum Albumin Studied by Time‐Resolved Phosphorescence

Abstract

The interaction of the nonsteroidal anti-inflammatory drug flurbiprofen (FBP) with human serum albumin (HSA) hardly influences the fluorescence of the protein's single tryptophan (Trp). Therefore, in addition to fluorescence, heavy atom-induced room-temperature phosphorescence is used to study the stereoselective binding of FBP enantiomers and their methyl esters to HSA. Maximal HSA phosphorescence intensities were obtained at a KI concentration of 0.2 M. The quenching of the Trp phosphorescence by FBP is mainly dynamic and based on Dexter energy transfer. The Stern-Volmer plots based on the phosphorescence lifetimes indicate that (R)-FBP causes a stronger Trp quenching than (S)-FBP. For the methyl esters of FBP, the opposite is observed: (S)-(FBPMe) quenches more than (R)-FBPMe. The Stern-Volmer plots of (R)-FBP and (R)-FBPMe are similar although their high-affinity binding sites are different. The methylation of (S)-FBP causes a large change in its effect on the HSA phosphorescence lifetime. Furthermore, the quenching constants of 3.0 × 10(7) M(-1) s(-1) of the R-enantiomers and 2.5 × 10(7) M(-1) s(-1) for the S-enantiomers are not influenced by the methylation and indicate a stereoselectivity in the accessibility of the HSA Trp to these drugs.

Stereoselective binding of chiral drugs to plasma proteins

“…To illustrate enantioselective drug-protein binding, classical methods, such as equilibrium dialysis (ED), ultrafiltration (UF) and ultracentrifugation (UC), are commonly combined with chiral separation techniques 27,28,29 . ED is an apparatus with two compartments separated by a semipermeable membrane, and only unbound drug molecules can permeate through the membrane.…”

“…Additionally, detailed information on the identity of the ligand binding pocket(s) and specific amino acid(s) of HSA that are responsible for this allosteric effect is needed. Lammers et al 90 showed the stereoselective binding of flurbiprofen (FBP) enantiomers and their methyl esters to HSA using time-resolved phosphorescence. Based on the phosphorescence lifetimes, R -flurbiprofen quenched Trp more effectively than S -flurbiprofen, in contrast to its methyl esters.…”

Metabolic chiral inversion of 2-arylpropionic acid derivatives (profens)

“…3). Nevertheless, clinically (R,S)-flurbiprofen is used as a racemic mixture, not as an individual enantiomer [10][11][12]. (S)-enantiomer exhibits an inhibitory effect on cyclooxygenase (COX-2), thus anti-inflammatory action is determined.…”

Can Förster Theory Describe Stereoselective Energy Transfer Dynamics in a Protein–Ligand Complex?

“…Rather, it is a novel site located between subdomains IIA and IIB. This finding explains why there is only a partial quenching of HSA phosphorescence in the presence of FBP, 47 as FBP in that secondary site is not in direct contact with Trp214 as would be in site I, but at a distance ~10 Å. 50 In addition to the FBP/HSA complex, we also examine covalently linked dyads formed by (S)-and (R)-enantiomers of FBP and (S)-tryptophan methyl ester (TrpMe), in which the enantioselectivity is reversed.…”

“…In addition, flurbiprofen exhibits stereoselectivity in its pharmacokinetics, 45 and stereoselective binding to HSA has been shown to occur. 46,47 It is known that flurbiprofen binds preferentially to site II (benzodiazepine binding site) of HSA but also binds with remarkable affinity to another site. 46,48,49 Often this secondary binding site has been identified with well-known site I (warfarin binding site) of HSA.…”