Structural Optimization of Benzyl-5-methyl-1 <i>H</i> -Imidazole Derivatives as Human Glutaminyl Cyclase Inhibitors

Human secretory glutaminyl cyclase (sQC) and Golgi-resident glutaminyl cyclase (gQC) catalyze the conversion of protein N-terminal glutamine into pyroglutamate (pE), a modification implicated in human diseases including cancer. Small-molecule inhibitors targeting sQC/gQC represent a promising therapeutic strategy. Here, we report a series of benzyl-5-methyl-1<i>H</i>-imidazole derivatives as inhibitors of sQC/gQC. Through structural optimization, we identified <b>CL121</b>, a nanomolar potent inhibitor of both enzymes. Thermal shift assays revealed that <b>CL121</b> enhances the thermal stability of both sQC (Δ<i>T</i> _m = 5.9 °C) and gQC (Δ<i>T</i> _m = 6.0 °C), indicating strong binding interactions. Cellular assays revealed that <b>CL121</b> substantially reduced the level of pE-CD47 modification on the surface of MDA-MB-231 and KYSE30 cells. Furthermore, <b>CL121</b> exhibited antitumor activity in a mouse xenograft tumor model. The results highlight the potential of <b>CL121</b> as a lead compound for developing drugs targeting sQC/gQC-mediated diseases.