Discovery of ART5537: A Potent and Selective Small-Molecule Probe for EXO1

Exonuclease 1 (EXO1) is emerging
as a target of interest
in oncology
due to its involvement in multifaceted DNA metabolic processes, particularly
in homologous recombination (HR). Evidence is building that BRCA1-deficient cancers are sensitive to loss of EXO1, suggesting
therapeutic potential for treating certain subsets of patients. However,
EXO1 remains under-explored, with very few reported inhibitors, and
there is a paucity of good quality, potent, and selective pharmacological
tools to explore its biology. Here, we describe a metal-chelating
fragment screen, which resulted in highly selective, submicromolar
EXO1 hits. Our subsequent structure-based design and optimization
led to the discovery of ART5537, the first highly potent
and selective EXO1 inhibitor. We demonstrate that inhibition of EXO1
leads to potent suppression of HR in cells and that the HR inhibition
of ART5537 is driven exclusively by EXO1. Furthermore,
we show that ART5537 sensitizes cancer cells to ionizing
radiation (IR) and synergizes with PARP inhibitors (PARPi).