Investigating the interaction mechanism of five flavonoids and PD-L1 based on multi-spectroscopy and molecular dynamics

PD-L1 is an important protein overexpressed in various types of cancer. Flavonoids as common antioxidants have extensive bioactivities. In this study, the interaction mechanism and the structure-activity relationship between the five flavonoids and extracellular domain of PD-L1 (PD-L1-ECD) were investigated using integrated spectroscopy and computational simulation. Fluorescence spectra showed that the quenching mechanisms of the interaction between the five flavonoids and PD-L1-ECD were static quenching. Circular dichroism (CD) spectra showed that the five flavonoids caused conformational changes of PD-L1-ECD. Computational simulation data showed the different binding patterns between five flavonoids and PD-L1-ECD. The binding affinity of the five flavonoids which affected by hydrogenation of C2=C3 bond and the substitution of C3 decreased in the following order: luteolin > kaempferol > spinacetin > axillarin > hesperetin. This study suggested that five flavonoids could bind to the PD-L1-ECD, thereby establishing a foundation for developing these compounds as small-molecule PD-L1 inhibitors. Subsequent structure-activity relationship was studied based on distinct binding modes and binding affinity, and it will contribute to structural modifications to optimize therapeutic potency.