Molecular hybridization used to design and synthesize neo-tanshinlactone derivatives as PD-1/PD-L1 inhibitors

Four series of molecular hybrids (37 final products) of neo-tanshinlactone, a natural product extracted from Salvia miltiorrhiza Bunge, and known PD-1/PD-L1 interaction inhibitors were prepared as possible chemotherapeutic agents against triple negative breast cancer. Screening using a homogenous time-resolved fluorescence method resulted in three lead compounds (MZ52 IC₅₀ 74 ± 4 nM; MZ58 IC₅₀ 134 ± 17 nM; MZ61 IC₅₀ 225 ± 19 nM). With less T cell cytotoxicity and effects in activating CD8⁺ T cells in a T cell proliferation assay and a functionality experiment, MZ58 was selected as the best candidate for animal experiments. MZ58 exhibited antitumor effects in a subcutaneous transplantation tumor model as well as effects in reducing T cell exhaustion. In conclusion, after in vivo and in vitro experiments, we successfully acquired an effective candidate (MZ58) showing antitumor effects with low cytotoxicity toward T cells as well as the ability to activate CD8⁺ T cells and reduce T cell exhaustion.