DNA polymerase theta (Polθ)
is an attractive synthetic lethal
target for drug discovery, predicted to be efficacious against breast
and ovarian cancers harboring BRCA-mutant alleles. Here, we describe
our hit-to-lead efforts in search of a selective inhibitor of human
Polθ (encoded by POLQ). A high-throughput screening campaign
of 350,000 compounds identified an 11 micromolar hit, giving rise
to the N2-substituted fused pyrazolo series, which was validated by
biophysical methods. Structure-based drug design efforts along with
optimization of cellular potency and ADME ultimately led to the identification
of RP-6685: a potent, selective, and orally bioavailable
Polθ inhibitor that showed in vivo efficacy in an HCT116 BRCA2–/– mouse tumor xenograft model.
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