In this first period of TrickE3, we have successfully established some of our intended cellular and computational approaches to identify monovalent degraders. In brief, we have delivered proof of concept that phenotypic and virtual drug screenings can deliver both, monovalent degraders with known mechanisms of action, but also compounds with novel unexpected working features. The engineering of additional reporters has been completed, unlocking more drug screens in the near future.
In addition, we unraveled new concepts around degrader resistance and how to overcome it. Conceptually, the loss of function of a broad E3 ligase regulator poses an advantageous mechanism to evade the action of a wide range of degraders (Barbosa et al., Angewandte Chemie, 2024). We conducted a target-agnostic chemical screening to identify synthetic lethal vulnerabilities of cancer cells that exhibit widespread resistance to degraders. This comparative profiling followed by tailored optimization delivered the small molecule RBS-10, which shows preferential cytotoxicity against cells pan-resistant to degraders. Multiomics deconvolution of the mechanism of action revealed that RBS-10 acts as a prodrug bioactivated by the enzyme NQO1, which is highly overexpressed in our resistance models.
Mechanistically, we showed that inactivation of one particular E3 leads to NQO1 upregulation. Our findings motivate translational investigation via the chemical probe RBS-10 and similar molecules in cancer types with elevated NQO1.