Discovery of the programmed cell death-1/programmed cell death-ligand 1 interaction inhibitors bearing an indoline scaffold

Inhibiting the programmed cell death-1 (PD-1)/programmed cell death-ligand 1 (PD-L1) pathway is an attractive strategy for tumor immunotherapy. Here, a novel series of indoline-containing compounds were developed, among which, A13 was identified as the most promising PD-1/PD-L1 pathway inhibitor. At the biochemical level, A13 demonstrated strong inhibition of the PD-1/PD-L1 interaction, with an IC₅₀ of 132.8 nM. Notably, it exhibited outstanding immunoregulatory activity, and significantly elevated interferon-γ secretion in a Hep3B/OS-8/hPD-L1 and CD3 T cell co-culture model, without significant toxic effect. Therefore, A13 could be employed as a suitable lead compound for further design of non-peptide inhibitors targeting the PD-1/PD-L1 interaction. In addition, the preliminary structure-activity relationships of these new indoline compounds were investigated in this study, providing valuable information for future drug development.