A combined photophysical and computational study on the binding of mycophenolate mofetil and its major metabolite to transport proteins

Abstract

Binding of the immunosuppressive agent mycophenolate mofetil (MMP) and its pharmacologically active metabolite mycophenolic acid (MPA) to human serum albumin (HSA) and α-acid glycoprotein (HAAG) has been investigated by means of an integrated approach involving selective excitation of the drug fluorophore, following their UV-A triggered fluorescence and docking studies. The formation of the protein/ligand complexes was evidenced by a dramatic enhancement of the fluorescence intensity and a hypsochromic shift of the emission band. In HSA, competitive studies using oleic acid as site I probe revealed site I as the main binding site of the ligands. Binding constants revealed that the affinity of the active metabolite by HSA is four-fold higher than its proactive form. Moreover, the affinity of MMP by HSA is three-fold higher than by HAAG. Docking studies revealed significant molecular binding differences in the binding of MMP and MPA to sub-domain IIA of HSA (site 1). For MPA, the aromatic moiety would be in close contact to Trp214 with the flexible chain pointing to the other end of the sub-domain; on the contrary, for MMP, the carboxylate group of the chain would be fixed nearby Trp214 through electrostatic interactions with residues Arg218 and Arg222.

Structural Basis of the Change in the Interaction Between Mycophenolic Acid and Subdomain IIA of Human Serum Albumin During Renal Failure

“…Molecular modeling experiments conducted by Ma et al suggested that a hydrogen bond is formed between oxygen atoms of the carboxyl group of MP and the nitrogen atom of Arg257 in subdomain IIA . Vendrell-Criado et al also used a molecular modeling approach and reported the formation of a hydrogen bond between the phenol group of MP and the side chain of Arg257, and they also reported electrostatic interactions between the carboxylate moiety of MP and the guanidinium groups of Arg222 and Arg212, which are located close to Trp214 . Despite this discrepancy, our crystallographic data indicated that the isobenzofuran group of MP is located at the entrance of the subdomain IIA pocket and forms a hydrogen bond with Arg257 through its carboxyl group.…”

“…A modeling study of the HSA−MP-Mof complex reported previously by Vendrell-Criado indicated that the binding position of MP-Mof is located in the inner pocket of subdomain IIA, in contrast to that of MP, as determined by crystal structure analysis. 14 This model structure showed that the isobenzofuran group of MP-Mof forms hydrogen bonds with Arg218 and Arg222. The binding position of the morpholine ring of MP-Mof is near Gln196 and the disulfide bonds of Cys200/Cys246 or Cys245/Cys253, whereas this pocket appears to be closed by Tyr150 in the HSA−MP complex structure.…”

“…Our data obtained from equilibrium dialysis experiments in which free MP was directly measured were consistent with the data from fluorescence quenching experiments reported by Vendrell-Criado et al (K = 1.3 × 10 5 M −1 for HSA and K = 0.11 × 10 5 M −1 for AAG). 14 Considering the approximate plasma concentrations of HSA (600 μM), 7 AAG (20 μM), 26 and MP (30 μM) 1 at steady state, MP appears to preferentially bind to a high-affinity site of HSA in plasma.…”

“…10 Studies mainly using spectroscopic and molecular modeling approaches have suggested that MP binds to subdomain IIA. 13,14 It is known that this plasma protein binding of MP is decreased in patients with acute and chronic renal dysfunction, resulting in an increased unbound (free) fraction of MP and/or a pharmacologically active free concentration of MP. 15−18 van Hest et al identified low creatinine clearance (i.e., renal function) as well as low HSA level and high MP-Glu level as factors that decrease the plasma protein binding of MP.…”

Photobehavior of the antipsychotic drug cyamemazine in a supramolecular gel protective environment

“…The equipments employed for recording the emission spectra, for determining the fluorescence lifetimes and for transient absorption spectroscopic measurements have been described elsewhere [28,29]. Experiments were performed at 22 °C; concentration of CMZ was 2 × 10 -5 M and concentration of SVN was 6.3 × 10 -3 M.…”