Structure-activity relationship analysis of novel GSPT1 degraders based on benzotriazinone scaffold and its antitumor effect on xenograft mouse model

Molecular glue degraders, such as lenalidomide and pomalidomide, bind to cereblon (CRBN) E3 ligase and subsequently recruit neosubstrate proteins, Ikaros (IKZF1) and Aiolos (IKZF3), for the ubiquitination-proteasomal degradation process. In this study, we explored structure-activity relationship analysis for novel GSPT1 degraders utilizing a benzotriazinone scaffold previously discovered as a novel CRBN binder. In particular, we focused on the position of the ureido group on the benzotriazinone scaffold, substituent effect on the phenylureido group, and methyl substitution on the benzylic position of benzotriazinone. As a result, we identified 34f (TD-522), which exhibits strong anti-proliferative effects in both KG-1 (EC50 = 0.5 nM) and TMD-8 (EC50 = 5.2 nM) cell lines. Compound 34f effectively induced GSPT1 degradation with a DC50 of 0.269 nM and Dmax of > 95 % at 10 nM concentration in KG-1 cells. An in vivo xenograft study showed that compound 34f effectively suppressed TMD8-driven tumor growth, suggesting a potential role in the development of novel GSPT1 degraders.