Human serum albumin binding in a vial: a novel UV-pH titration method to assist drug design

The knowledge on human serum albumin (HSA) binding is of utmost importance as it affects pharmacokinetic behavior and bioavailability of drugs. In this article, we report a novel method to screen for ionizable molecules with high HSA binding affinity based on pKa shifts using UV-pH titration. We investigated the HSA binding of 27 drugs and compared the results to experimental data from conventional methods. In most cases, significant shifts (ΔpKa > 0.1) were observed for drugs with high HSA binding, while no change could be detected for low-affinity binders. We showed the pivotal role of ionization centers in the formation of strong interactions between drug and HSA using molecular docking studies. We also verified our findings by testing 5 modified analogs designed by structural considerations. Significant decreases in their HSA binding proved that the UV-pH titration method combined with in silico support can be used as a medicinal chemistry tool to assist rational molecular design.