SAR study of small molecule inhibitors of the programmed cell death-1/programmed cell death-ligand 1 interaction.

The development of small molecule inhibitors of programmed cell death-1/programmed cell death-ligand 1 (PD-1/PD-L1) has drawn research interest for the treatment of cancer. Recently, we reported the discovery of a novel dimeric core small molecule PD-1/PD-L1 inhibitor. In an effort to discover more potent inhibitors, we further explored the dimeric core scaffold. Our investigations of the structure-activity-relationship revealed that introduction of lipophilic substituents onto one of the di-alkoxylated phenyl rings improved binding affinities to PD-L1, and inhibitory activities of PD-1/PD-L1 in cellular assays. Furthermore, conversion of the ether linker part to an olefin linker not only improved binding affinity but also led to slow dissociation binding kinetics. We also explored more potent, as well as downsized, scaffolds. Compounds bearing a linear chain in place of one of the di-alkoxylated phenyl rings exhibited good binding affinity with improved ligand efficiency (LE). Representative compounds demonstrated potent inhibitory activities of PD-1/PD-L1 in the submicromolar range in cellular assays as well as cellular function in the mixed lymphocyte reaction (MLR) assay with efficacy comparable to anti-PD-1 antibody. Our results provide applicable information for the design of more potent inhibitors targeting PD-1/PD-L1 pathway.

Symmetry-based ligand design and evaluation of small molecule inhibitors of programmed cell death-1/programmed death-ligand 1 interaction.

The development of small molecule inhibitors of PD-1/PD-L1 is eagerly anticipated for treatment of cancer. We focused on the symmetry of the ternary complex structure of reported small molecule ligands and hPD-L1 homodimers, and designed partially- or fully-symmetric compounds for more potent inhibitors. The design of the new compounds was guided by our hypothesis that the designed symmetric compound would induce a flip of sidechain of ATyr56 protein residue to form a new cavity. The designed compound 4 exhibited substantially increased binding affinity to hPD-L1, as well as PD-1/PD-L1 inhibitory activity in physiological conditions. Compound 4 also showed a dose-dependent increase in IFN-γ secretion levels in a mixed lymphocyte reaction assay. These results not only indicate the feasibility of targeting the PD-1/PD-L1 pathway with small molecules, but illustrate the applicability of the symmetry-based ligand design as an attractive methodology for targeting protein-protein interaction stabilizers.