Comparative druggability of PD-1/PD-L1 inhibitors (A56, HD10): Cross-species differences in PD-L1 exposure and efficacy.

The PD-1/PD-L1 immune checkpoint plays a crucial role in tumor immune evasion, making it a prime target for cancer immunotherapy. While small-molecule inhibitors have emerged as promising alternatives to monoclonal antibodies, differences in PD-L1 exposure between human and murine models present challenges in preclinical evaluation. In this study, we investigate the cross-species druggability of two potent small-molecule inhibitors, A56 and HD10, by comparing their binding affinity, immune modulation, and anti-tumor efficacy in both human and mouse PD-L1 models. For the first time, we demonstrated that murine PD-1 and human PD-L1 form effective immune checkpoints and function in vivo. Our findings highlight the importance of species-specific evaluations in immune checkpoint inhibitor development and the careful selection of appropriate animal models. Flow cytometry and in vivo analyses reveal that A56 and HD10 enhance CD8 T cell infiltration and anti-tumor activity in both species, with notable variations in immune responses between human and murine PD-L1 contexts. The dual-targeting capability of A56 and HD10 supports their potential as cost-effective, orally available immunotherapies, warranting further clinical investigation.