Study on endogenous inhibitors against PD-L1: cAMP as a potential candidate

The discovery of new anticancer drugs targeting the PD-1/PD-L1 pathway has been research hotspots. In this study, a combination of biological affinity ultrafiltration (BAU), UPLC-HRMS, molecular dynamic (MD) simulations and molecular docking methods were applied to search for endogenous active compounds that can inhibit the binding of PD-L1 and PD-1. We screened dozens of potential cancer related endogenous compounds. The results showed that cyclic adenosine monophosphate (cAMP) had a direct inhibition effect on the PD-1/PD-L1 binding with an in vitro IC50 value of about 2.7 µM determined by homogeneous time-resolved fluorescence (HTRF) assay. The binding mode analyses for the cAMP - dimeric/monomeric PD-L1 complex indicated that cAMP was likely to bind to the dimeric PD-L1, since the binding free energies of the cAMP - dimeric and monomeric PD-L1 complex were about 23.6 and 15.1 kcal/mol, respectively, from MD simulations. The direct binding assay using surface plasmon resonance (SPR) method showed that cAMP could also bind to monomeric PD-L1 fixed on the sensor chip surface with a KD value of about 1.72 mM. Our findings suggested that cAMP may directly inhibit the PD-1/PD-L1 interaction.