LP23 is a non-arylmethylamine PD-1/PD-L1 inhibitor ( IC 50 : 16.7 nM) with anti-tumor activity. LP23 restores immune cell function in HepG2/Jurkat T cells and promotes HepG2 cell death. LP23 is active in vivo in the B16-F10 tumor model (TGI=88.6% at 30 mg/kg).