Discovery of a Napabucasin PROTAC as an Effective Degrader of the E3 Ligase ZFP91

Napabucasin, undergoing multiple clinical trials, was reported to inhibit the signal transducer and transcription factor 3 (STAT3). To better elucidate its mechanism of action, we designed a napabucasin-based proteolysis targeting chimera (PROTAC), XD2-149 that resulted in inhibition of STAT3 signaling in pancreatic cancer cell lines without inducing proteasome-dependent degradation of STAT3. Proteomics analysis of XD2-149 revealed the downregulation of the E3 ubiquitin-protein ligase ZFP91. XD2-149 degrades ZFP91 with DC-50 values in the nanomolar range. The cytotoxicity of XD2-149 was significantly, but not fully, reduced with ZFP91 knockdown providing evidence for its multi-targeted mechanism of action. The NQO1 inhibitor, dicoumarol, rescued the cytotoxicity of XD2-149 but not ZFP91 degradation, suggesting that the NQO1-induced cell death is independent of ZFP91. ZFP91 plays a role in tumorigenesis and is involved in multiple oncogenic pathways including NF-kappa B and HIF-1 alpha.

Automated summary

XD2-149, a PROTAC based on napabucasin, has a multi-targeted mechanism of action, inhibiting the STAT3 signaling pathway and degrading the ZFP91 protein. ZFP91 plays a critical role in tumorigenesis and is involved in oncogenic pathways such as NF-κB and HIF-1α.