Discovery of a Napabucasin PROTAC as an Effective Degrader of the E3 Ligase ZFP91
Maha Hanafi, Xinde Chen, Nouri Neamati
Abstract
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 DC50 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-κB and HIF-1α.