Human plasma protein binding of novel zidovudine prodrugs: Targeting the site II of Human Serum Albumin

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

Buenos Aires

Congreso; Reunión Conjunta de Sociedades de Biociencias; 2017

The binding of anti HIV drugs to plasma proteins is key to their antiviral efficacy. Human serum albumin (HSA) constitutes the main plasma protein that binds and transport drugs, with several binding sites been reported. In this work, we explore the binding of the zidovudine (AZT) and AZT prodrugs obtained by combination with organic diacids (succinic (Suc), glutaric (Glu) and adipic (Adi) acid) and a methylated phenylalanine moiety. The binding of AZT-Suc-Ph (1), AZT-Glu-Ph (2) and AZT-Adi-Ph (3) to plasma proteins was studied experimental and molecular modeling techniques.The binding of AZT and 1-3 was measured by incubating solutions of the prodrugs (9µM, 37C) with human plasma (HP), isolating the free fraction by ultrafiltration. The binding site to HSA was determined using salicylic acid (SA) and diazepam (DZP) as site 1 and 2 markers, respectively. The prodrugs exhibited a significantly increased binding to HP (1: 52.1±5.3%, 2: 59.7±4.3% and 3: 72.5± 4.3%) compared to AZT (13.8±1.4%), with their bound fraction being slightly displaced by DZP, indicating a high affinity for site 2 in HSA. Molecular docking and free energy decomposition analyses were applied to study the interaction of DZP and 1-3. While DZP maintained the interaction pattern observed in the crystallographic structure, with a binding driven mainly by hydrophobic interactions, prodrugs 1-3 positioned the aromatic ring within a highly buried hydrophobic subpocket of site 2, establishing a higher number of interactions. The calculated interaction energies were: -12.26 kcal/mol (DZP), -13.22 kcal/mol (1), -14.13 kcal/mol (2) and -19.26 kcal/mol (3), evidencing that the prodrugs exhibited a more stable interaction with HSA than DZP. A correlation between the bound fractions and the interactions energies was found. In conclusion, the novel prodrugs exhibited a higher affinity for HSA than AZT and a change in their binding site, which may in turn result in different pharmakinetic properties.