Spectroscopic study on volasertib: Highly stable complexes with albumin and encapsulation into...

In the present work, we study different physicochemical properties related to LADME processes of volasertib, a Polo-like kinase 1 inhibitor in advanced clinical trials. Firstly, the protonation equilibria, the extent of ionization at the physiological pH and pK_a values of this drug are studied combining spectroscopic techniques and computational calculations. Secondly, the binding process of volasertib to the human serum albumin (HSA) protein is analyzed by fluorescence spectroscopy. We report a high binding constant to HSA (K_a = 4.10 × 10⁶ M^-1) and their pharmacokinetic implications are discussed accordingly. The negative enthalpy and entropy (ΔH⁰ = -54.49 kJ/mol; ΔS⁰ = -58.90 J K^-1 mol^-1) determined for the binding process suggests the implication of hydrogen bonds and van der Waals interactions in the formation of the HSA-volasertib complex. Additionally, volasertib is encapsulated in an alginate/montmorillonite bionanocomposite as a proof of concept for an oral delivery nanocarrier. The physical properties of that nanocomposite as well as volasertib delivery kinetics are analyzed.