Discovery of a Potent Triazole-Based Reversible Targeted Covalent Inhibitor of Cruzipain

Cruzipain (CZP) is an essential cysteine protease of Trypanosoma cruzi, the etiological agent of Chagas disease, and a promising druggable target. To date, no CZP inhibitors have reached clinical use, with research efforts mostly hampered by insufficient potency, limited target selectivity or lack of bioactivity translation from the isolated enzyme to the parasite in cellular environments. In this study, we report the design of SH-1, a 1,2,3-triazole-based targeted covalent inhibitor with nanomolar potency (IC₅₀ = 28 nM) and null inhibition of human cathepsin L. SH-1 demonstrates bioactivity translation comparable to that of K777 (1-10 μM), a CZP inhibitor previously advanced to clinical trials. Experimental findings indicate that SH-1 forms a reversible covalent bond with Cys25 in CZP, while in silico and structure-activity relationship studies suggest that this interaction is guided by acid-base equilibrium dynamics. The potential of SH-1 for preclinical development is discussed alongside detailed structure-activity relationships for the further optimization of CZP inhibitors.