Potent and Selective Caspase-2 Inhibitors: Biological Profiling, Structural Characterization, and Challenges of Molecular Instability

Caspase-2 (Casp2) has emerged as a promising therapeutic target for neurodegenerative diseases due to its role in pathological tau processing. Here, we designed and synthesized a series of 48 novel peptidomimetic Casp2 inhibitors organized into distinct structural classes. Compounds were evaluated for Casp2 inhibition and selectivity against Casp1, 3, 4, 5, 6, 7, 8, 9, and 10. Inhibitors Idc(hE)G(Dab)D-CHO (32) and Idc(hE)G((S)-Me-THIQ)D-CHO (33) exhibited low nanomolar potency and ≥537-fold selectivity over Casp3. These unprecedented scaffold modifications are consistent with preferred steric arrangements between the P2 and P3 positions. Biochemical assays demonstrated the blockade of tau truncation and impaired the formation of toxic Δtau314. High-resolution crystal structures of compounds 2 and 33 bound to Casp2 revealed binding interactions consistent with the observed SAR. Although Idc(hE)V((S)-Me-THIQ)D-CHO (3, MUR-65) showed favorable ADME and pharmacokinetic properties, limited membrane permeability, insufficient blood−brain barrier penetration, and P5 indoline instability remain key challenges for further development.