%0 Journal Article
%T Structural basis for a Polθ helicase small-molecule inhibitor revealed by cryo-EM.
%A Ito F
%A Li Z
%A Minakhin L
%A Chandramouly G
%A Tyagi M
%A Betsch R
%A Krais JJ
%A Taberi B
%A Vekariya U
%A Calbert M
%A Skorski T
%A Johnson N
%A Chen XS
%A Pomerantz RT
%J Nat Commun
%V 15
%N 1
%D 2024 Aug 14
%M 39143110
%F 17.694
%R 10.1038/s41467-024-51351-4
%X DNA polymerase theta (Polθ) is a DNA helicase-polymerase protein that facilitates DNA repair and is synthetic lethal with homology-directed repair (HDR) factors. Thus, Polθ is a promising precision oncology drug-target in HDR-deficient cancers. Here, we characterize the binding and mechanism of action of a Polθ helicase (Polθ-hel) small-molecule inhibitor (AB25583) using cryo-EM. AB25583 exhibits 6 nM IC50 against Polθ-hel, selectively kills BRCA1/2-deficient cells, and acts synergistically with olaparib in cancer cells harboring pathogenic BRCA1/2 mutations. Cryo-EM uncovers predominantly dimeric Polθ-hel:AB25583 complex structures at 3.0-3.2 Å. The structures reveal a binding-pocket deep inside the helicase central-channel, which underscores the high specificity and potency of AB25583. The cryo-EM structures in conjunction with biochemical data indicate that AB25583 inhibits the ATPase activity of Polθ-hel helicase via an allosteric mechanism. These detailed structural data and insights about AB25583 inhibition pave the way for accelerating drug development targeting Polθ-hel in HDR-deficient cancers.