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.

Small-Molecule Drug Repurposing for Counteracting Phototoxic A2E Aggregation.

Despite the well-established role of oxidative stress in the pathogenesis of age-related macular degeneration (AMD), the mechanism underlying phototoxicity remains unclear. Herein, we used a drug repurposing approach to isolate an FDA-approved drug that blocks the aggregation of the photoinducible major fluorophore of lipofuscin, the bis-retinoid N-retinylidene-N-retinylethanolamine (A2E). Our fluorescence-based screening combined with dynamic light scattering (DLS) analysis led to the identification of entacapone as a potent inhibitor of A2E fluorescence and aggregation. The entacapone-mediated inhibition of A2E aggregation blocks its photodegradation and offers photoprotection in A2E-loaded retinal pigment epithelial (RPE) cells exposed to blue light. In-depth mechanistic analysis suggests that entacapone prevents the conversion of toxic aggregates by redirecting A2E into off-pathway oligomers. These findings provide evidence that aggregation contributes to the phototoxicity of A2E.