Discovery of a 53BP1 Small Molecule Antagonist Using a Focused DNA-Encoded Library Screen

Methyl-lysine reader p53 binding protein 1 (53BP1) is
a central
mediator of DNA break repair and is associated with various human
diseases, including cancer. Thus, high-quality 53BP1 chemical probes
can aid in further understanding the role of 53BP1 in genome repair
pathways. Herein, we utilized focused DNA-encoded library screening
to identify the novel hit compound UNC8531, which binds the 53BP1
tandem Tudor domain (TTD) with an IC50 of 0.47 ± 0.09
μM in a TR-FRET assay and Kd values
of 0.85 ± 0.17 and 0.79 ± 0.52 μM in ITC and SPR,
respectively. UNC8531 was cocrystallized with the 53BP1 TTD to guide
further optimization efforts, leading to UNC9512. NanoBRET and 53BP1-dependent
foci formation experiments confirmed cellular target engagement. These
results show that UNC9512 is a best-in-class small molecule 53BP1
antagonist that can aid further studies investigating the role of
53BP1 in DNA repair, gene editing, and oncogenesis.