PRLX-93936 and BMS-214662 are cytotoxic molecular glues that leverage TRIM21 to degrade nucleoporins

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".