Discovery of Novel PD-L1 Small-Molecular Inhibitors with Potent In Vivo Anti-tumor Immune Activity

Programmed death-ligand 1 (PD-L1) has surfaced as a promising therapeutic target for various cancers due to its pivotal role in facilitating tumor immune evasion. Herein, we report a series of novel small-molecule PD-L1 inhibitors exhibiting remarkable inhibitory activity against the PD-1/PD-L1 interaction (X18: IC₅₀ = 1.3 nM) and reinstating the suppressive effect of PD-L1 on T cells (X18: EC₅₀ = 152.8 nM). Crystallographic studies revealed the binding mode of X18 and PD-L1. Through a rational prodrug design approach, we have successfully optimized the oral pharmacokinetic properties of X22, effectively addressing the poor oral pharmacokinetic profile of PD-L1 small-molecule inhibitors. Notably, X22 demonstrated significant antitumor efficacy in murine models of MC38 and CT26 colon cancer through the upregulation of tumor infiltration and cytotoxicity of CD8⁺ T cells partially. These findings offer promising prospects for the advancement of PD-L1 inhibitors as innovative agents in cancer immunotherapy.