Repurposing Ilaprazole as a PP5 TPR Domain Binder with Modulatory Effects on MAPK Signaling

Small-molecule modulators targeting the N-terminal tetratricopeptide repeat (TPR) domain of protein phosphatase 5 (PP5) remain largely unexplored. Here, we report the repurposing of ilaprazole as a PP5 TPR domain binder identified via a fluorescence polarization-based competitive screen. Biophysical assays and molecular docking supported the interaction within the PP5 TPR binding pocket, revealing key structural features distinguishing ilaprazole from related proton pump inhibitors. In KRAS mutant colorectal cancer cells, ilaprazole engaged cellular PP5, leading to reduced RAF stability and suppressed mitogen-activated protein kinase (MAPK) signaling. While exhibiting minimal single-agent effects, ilaprazole sensitized cells to the MEK inhibitor binimetinib. These results validate the PP5 TPR domain as a druggable site and establish ilaprazole as a lead scaffold for pharmacological modulation of PP5-associated MAPK signaling.