Discovery of a Small Molecule Probe to Rpn-6, an Essential Subunit of the 26S Proteasome

Rpn-6 is among several essential proteins that facilitate assembly of the 26S proteasome. We were interested in discovering a small molecule binder to Rpn-6 that could be used to further our understanding of the association of the 19S regulatory particle with the 20S core particle and if a small molecule-Rpn-6 interaction could potentially be cytotoxic to cancer cells that heavily rely on proteasome activity for survival. A workflow to utilize a one-bead-one-compound library and a thermal shift assay was developed to discover such a molecule. TXS-8 was discovered to have low micromolar range binding affinity for Rpn-6 and showed with very limited binding to other proteins. Cytotoxicity of TXS-8 was evaluated in several cell lines, revealing increased cytotoxicity to hematological cancers.