Design, Synthesis, Evaluation, and Structural Studies of -Symmetric Small Molecule Inhibitors of Programmed Cell Death-1/Programmed Death-Ligand 1 Protein-Protein Interaction.

A series of -symmetric inhibitors was designed and evaluated for inhibitory activity against the programmed cell death-1/programmed death-ligand 1(PD-1/PD-L1) protein-protein interaction (PPI) in a homogenous time-resolved fluorescence (HTRF) assay and PD-1 signaling in cell-based coculture assays. -symmetric inhibitors (LH1306) and (LH1307) exhibited IC values of 25 and 3.0 nM, respectively, in the HTRF assay. While was ∼3.8-fold more potent than previously reported inhibitor , could not be differentiated from due to their high potency and the limit of our HTRF assay conditions. In one cell-based coculture PD-1 signaling assay, and were 8.2- and 2.8-fold more potent in inhibiting PD-1 signaling than and , respectively. NMR and X-ray cocrystal structural studies provided more structural insights into the interaction between and PD-L1; binds to PD-L1 at the PD-1 binding site and induces the formation of a more symmetrically arranged PD-L1 homodimer than that previously reported for other inhibitors.