Ubiquitin-rhodamine-110 (Ubiquitin-Rho-110) fluorometric activity assay, we discovered a novel inhibitor DC-U43. By structure optimization, DC-U43-10 reached a half-maximal inhibitory concentration (IC50) value of 2.6 ± 1.1 μM and exhibited 10-fold selectivity against USP7. The binding between DC-U43-10 and USP8 was validated by surface plasmon resonance (SPR) assay with a KD value of 10.5 ± 3.7 μM. It also