Abstract
The utilization of BRAF and MEK inhibitors in combination therapy has demonstrated superior outcomes in the treatment of melanoma as compared to monotherapy. In the present scenario, the combination therapy of Encorafenib (ENC), a BRAF inhibitor, and Binimetinib (BINI), a MEK inhibitor, has been identified as one of the most efficacious treatment modalities for this malignancy. Investigations of protein binding, particularly with human serum albumin (HSA), are essential to understand drug performance and enhance therapeutic outcomes. The investigation of the interplay between small molecule drugs and HSA is of paramount importance, given that such interactions can exert a substantial influence on the pharmacokinetics of these therapeutic agents. The present study aims to bridge these lacunae by implementing a comprehensive approach that integrates fluorescence spectroscopy (FS), isothermal titration calorimetry (ITC), far-ultraviolet circular dichroism (far-UV CD), and molecular simulations. Through analysis of the fluorescence quenching of HSA at three distinct temperatures, it was ascertained that the association constants for the complexes formed between drugs and HSA were of the magnitude of 104 M-1. This suggests that the interactions between the compounds and albumin were moderate and comparable. Simultaneously, the investigation of fluorescence indicated a contrasting binding mechanism for the two inhibitors: ENC predominantly binds to HSA through enthalpic interaction, while BINI/HSA is stabilized by entropic contributions. The data obtained was confirmed through experimental procedures conducted using the ITC method. The results of ligand-competitive displacement experiments indicate that ENC and BINI can bind to HSA within subdomain IIA, specifically Sudlow site I. However, far-UV CD studies show that there are no notable alterations in the structure of HSA upon binding with either of the two inhibitors. Ultimately, the results were supported by computational molecular analysis, which identified the key interactions that contribute to the stabilization of the two ligand/HSA complexes.