HUMAN PLASMA PROTEIN BINDING AND MOLCULAR MODELING OF NOVEL ZIDOVUDINE PRODRUGS: CHANGING THE BINDING PATTERN OF ZIDOVUDINE FROM SUDLOW 1 TO SUDLOW 2 OF HUMAN SERUM ALBUMIN

SCHENFELD, E.; RIBONE, S. R.; QUEVEDO, M. A.

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

The binding to human plasmatic proteins is a very important topic on the therapy with anti-HIV drugs; such is the case of Zidovudine (AZT). The Human Serum Albumin (HSA) is the main responsible for the transportation of drugs through the human plasma (HP). On previous work, several AZT acids prodrugs have been developed (AZT-Suc, AZT-Glu and AZT-Adi). The development of novel AZT prodrugs continues by the derivatization of the acid prodrugs with a methylated aminoacid (Phenylalanine). This work addresses the study of binding to total HP proteins of the novel AZT prodrugs: AZT-Suc-Ph (1), AZT-Glu-Ph (2) and AZT-Adi-Ph (3). A correlation between the experimental data and the molecular modeling studies is provided. The binding fraction of prodrugs was measured incubating stock solutions of the prodrugs (9µM) with HP at 37° during 30 min., isolating the free fraction by ultrafiltration. The identification of the specific binding site on the HSA was performed using salicylic acid (SA) and diazepam (DZP) as sudlow 1 and 2 markers, respectively. AZT prodrugs showed binding percentage to HP of: 51.0 ± 6.0% (1), 61.0 ± 4.0% (2) and 72 ± 4.0% (3), which are much higher than AZT (12.9%). The binding fractions to HP on the presence of SA were not different from results on pure plasma, but the binding experiments on the presence of DZP displayed different results: 38.0 ± 3.0% (1), 52.0 ± 7.0% (2) and 51.0 ± 7.0% (3). The first conclusion is that prodrugs 1-3 bind to sudlow 2. Molecular docking and free energy decomposition analysis were applied in order to study the interaction of DZP and prodrugs 1-3 with the residues on sudlow 2. This study showed that DZP make interaction with the same residues than in the crystallographic structure, with a driving force for the binding site produce by hydrophobic interactions. Prodrugs positioned their phenyl ring on the most buried area of the sudlow 2 and produce interaction with a higher number of residues than DZP. The sum of the residue free energy decomposition analysis considering the interacting residues displayed the following results: -12.26 kcal/mol (DZP), -13.22 kcal/mol (1), -14.13 kcal/mol (2) and -19.26 kcal/mol (3). These results showed that the 3 prodrugs have a higher free energy interaction than DZP, which indicates the small drop on the displacement experiments, and a direct correlation with the binding percentage to human plasma. Experimental and theoretical studies conclude that the presence of an apolar methylated phenylalanine on the structure of the novel prodrugs change the binding site of AZT from the hydrophilic sudlow 1 to a the more hydrophobic sudlow 2.