Ethyl 2-(3,5-Dioxo-2-p-tolyl-1,2,4-thiadiazolidin-4-yl) Acetate: A New Inhibitor of Insulin-Degrading Enzyme

Background: Insulin-degrading enzyme (IDE) has become an essential target for the clinical treatment of various important diseases, including type 2 diabetes, Alzheimer’s disease, and breast cancer, owing to its diverse substrate specificity. Particularly in cancer therapy, IDE inhibitors have received significant attention. Methods: We evaluated the in vitro inhibitory activity (IC50) of ethyl 2-(3,5-dioxo-2-p-tolyl-1,2,4-thiadiazolidin-4-yl) acetate (1) against wild-type IDE. The mechanism of action was investigated using Lineweaver–Burk double reciprocal plots and molecular docking analyses. Additionally, we examined the structure–activity relationship, cytotoxicity, selectivity, and effects on cell migration to assess its potential druggability. Based on molecular docking results, we prepared the mutant protein T142A and compared its inhibitory effects with those of the wild-type and mutant proteins. Results: Compound 1 exhibited an inhibitory effect on IDE (IC50 = 3.60 μM). This compound exerts its inhibitory effect through competitive binding to the catalytic site of IDE. Compound 1 demonstrated selective cytotoxicity toward cancer cells compared to normal cells, effectively inhibiting IDE at concentrations ≤ 10 μM. At a concentration of 3.6 μM, the inhibitory effect of the compound on cancer cell migration was significantly stronger than that observed in normal cells. Although the T142A mutant retained catalytic hydrolysis activity with a similar Km value, its reaction rate was markedly lower than that of the wild-type enzyme. Conclusions: Compound 1 exhibits a competitive inhibitory effect on IDE, selectively targeting IDE with greater toxicity toward cancer cells compared to normal cells. It also inhibits cancer cell migration. Notably, 1 demonstrates significantly stronger inhibitory activity against the T142A mutant than the wild-type IDE, indicating that the Thr142 residue plays a crucial role in the interaction between the IDE hydrophobic pocket and 1. These findings suggest that 1 holds potential as a chemotherapeutic agent for treating IDE-related cancers, including breast, prostate, and pancreatic cancers.