DCAF16-Based Covalent Degradative Handles for the Modular Design of Degraders

While targeted protein degradation is a powerful strategy
for eliminating
disease-causing proteins, the rational design of monovalent or molecular
glue degraders remains challenging. In this study, we generated a
library of BET-domain inhibitor JQ1 analogs bearing elaborated electrophilic
handles to identify permissive covalent degradative handles and E3
ligase pairs. We identified an elaborated fumaramide handle that,
when appended onto JQ1, led to the proteasome-dependent degradation
of BRD4. We revealed that the E3 ubiquitin ligase CUL4DCAF16a common E3 ligase target of electrophilic degraderswas
responsible for BRD4 loss by covalently targeting C173 on DCAF16.
While this original fumaramide handle was not permissive to the degradation
of other neo-substrates, a truncated version of this handle attached
to JQ1 was still capable of degrading BRD4, now through targeting
both C173 and C178. This truncated fumaramide handle, when appended
to various protein targeting ligands, was also more permissive in
degrading other neo-substrates, including CDK4/6, SMARCA2/4, the androgen
receptor (AR), as well as the undruggable AR truncation variant AR-V7.
We have identified a unique DCAF16-targeting covalent degradative
handle that can be transplanted across several protein-targeting ligands
to induce the degradation of their respective targets for the modular
design of monovalent or bifunctional degraders.