Scemama de Gialluly, M. A.; Allen, A. R.; Hayes, E. H.; Zhuang, P.; Goldfarb, R. B.; Farrar, A. N.; Fedorov, Y.; Adams, D. J.

Although molecular glues have emerged as innovative tools within the field of chemically induced proximity, approaches for their discovery remain limited. Here we report a phenotypic screening approach in which small molecules whose cytotoxic mechanisms require ubiquitination show gain of viability following pharmacological inhibition of the E1 enzyme UAE. This approach revealed two previously clinically-evaluated cytotoxins of unknown mechanism, PRLX-93936 and BMS-214662, as molecular glues that directly target the E3 ubiquitin ligase TRIM21. These molecules induce TRIM21-mediated proteasomal degradation of multiple nucleoporin proteins, leading to inhibition of nuclear export and ultimately cell death. Loss of nucleoporins and nuclear export accounts for past observations in which BMS-214662 led to disrupted subcellular protein localization. Furthermore, the cytotoxicity of these agents correlates strongly with TRIM21 expression, suggesting clinical re-evaluation of these agents in patients with TRIM21-high cancers. Additionally, relative to recently-reported TRIM21-targeting glues, these two scaffolds display high cellular potency, creating new opportunities for targeted protein degradation via the design of additional glues and \"TRIMTACs\".