Abstract 5697: Targeting PARP inhibitor resistance with Polθ inhibitors

Abstract

To target DNA repair vulnerabilities in cancer, we discovered nanomolar potent, selective, low molecular weight (MW), allosteric inhibitors of the polymerase function of DNA polymerase Polθ, including ART558. ART558 inhibits the major Polθ-mediated DNA repair process, Theta-Mediated End Joining (TMEJ), without targeting Non-Homologous End Joining. Moreover, we show that exposure to ART558 can elicit DNA damage and synthetic lethality in BRCA1- or BRCA2-mutant tumor cells and enhances the effects of a PARP inhibitor. Genetic perturbation screening revealed that defects in the 53BP1/Shieldin complex, which are a cause of PARP inhibitor resistance, result in in vitro and in vivo sensitivity to Polθ polymerase inhibitors. Mechanistically, ART558 increases biomarkers of single-stranded DNA and synthetic lethality in 53BP1-defective cells. The inhibition of DNA nucleases that promote end-resection, such as Exo1 or Blm-Dna2 reversed these effects, implicating these in the synthetic lethal mechanism-of-action. Taken together, these observations describe a drug class that elicits BRCA-gene synthetic lethality and PARP inhibitor synergy, as well as targeting a biomarker-defined mechanism of PARPi-resistance. Citation Format: Diana Zatreanu, Helen Robinson, Omar Alkhatib, Marie Boursier, Harry Finch, Lerin Geo, Diego Grande, Vera Grinkevich, Robert Heald, Sophie Langdon, Jayesh Majithiya, Claire McWhirter, Niall Martin, Shaun Moore, Joana Neves, Eeson Rajendra, Marco Ranzani, Theresia Schaedler, Martin Stockley, Kimberley Wiggins, Rachel Brough, Sandhya Sridhar, Aditi Gulati, Nan Shao, Luted Badder, Daniela Novo, Eleanor Knight, Rebecca Marlow, Syed Haider, Elsa Callen, Graeme Hewitt, Joost Schimmel, Remko Prevo, Christina Alli, Amanda Ferdinand, Cameron Bell, Peter Blencowe, Chris Bot, Mathew Calder, Mark Charles, Jayne Curry, Tennyson Ekwuru, Andre Nussenzweig, Marcel Tijsterman, Andrew N. Tutt, Simon Boulton, Geoff Higgins, Stephen J. Pettitt, Graeme C. Smith, Christopher J. Lord. Targeting PARP inhibitor resistance with Polθ inhibitors [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2022; 2022 Apr 8-13. Philadelphia (PA): AACR; Cancer Res 2022;82(12_Suppl):Abstract nr 5697.

Pre-Existing and Acquired Resistance to PARP Inhibitor-Induced Synthetic Lethality

“…Acquired PARPi resistance could be prevented by the more aggressive “dual synthetic lethality” approach (simultaneously targeting PARP1 and RAD52 [ 33 ]), which eliminates more tumors cells in a shorter time, thus reducing the chances of the time-dependent emergence of resistant clones. Moreover, if PARPi resistance emerges, these clones could be eliminated by the inhibition of another DNA repair mechanism, e.g., Polθ-mediated TMEJ [ 130 , 131 , 159 ].…”

“…The over-activation of Polθ also confers resistance to radiation and chemotherapies including PARPi [ 138 , 140 , 141 , 142 ]. Therefore, the pharmacological inhibition of Polθ is being developed to overcome the resistance to PARPi in a cohort of HRD cancers [ 130 , 131 ].…”