Chemoproteomic Identification of Spermidine-Binding Proteins and Antitumor-Immunity Activators.

Cancer immune therapies, particularly programmed cell death protein 1 (PD-1) blockade immunotherapy, falter in aged individuals due to compromised T-cell immunity. Spermidine, a biogenic polyamine that declines along with aging, shows promise in restoring antitumor immunity by enhancing mitochondrial fatty acid oxidation (FAO). Herein, we report a spermidine-based chemoproteomic probe (probe 2 ) that enables profiling of spermidine-binding proteins and screening for small-molecule enhancers of mitochondrial FAO. Chemoproteomic profiling by the probe revealed 140 proteins engaged in cellular interaction with spermidine, with a significant majority being mitochondrial proteins. Hydroxyl coenzyme A (CoA) dehydrogenase subunits α (HADHA) and other lipid metabolism-linked proteins are among the mitochondrial proteins that have attracted considerable interest. Screening spermidine analogs with the probe led to the discovery of compound 13 , which interacts with these lipid metabolism-linked proteins and activates HADHA. This simple and biostable synthetic compound we named "spermimic" mirrors spermidine's ability to enhance mitochondrial bioenergetics and displays similar effectiveness in augmenting PD-1 blockade therapy in mice. This study lays the foundation for developing small-molecule activators of antitumor immunity, offering potential in combination cancer immunotherapy.