The RecQ DNA helicase WRN was identified as a synthetic lethal target in tumors with microsatellite instability (MSI) by several genetic screens. Despite recent advances in the treatment of MSI tumors by immune checkpoint inhibitors, a significant proportion of patients still fails to respond to or relapses after single agent anti-PD1 or combination of anti-PD1 plus anti-CTLA4 treatments. We present the biochemical, cellular and pharmacological characterization of the first potent and selective WRN helicase inhibitor, HRO761. We show that HRO761 is an allosteric WRN inhibitor that binds at the interface of the D1 and D2 helicase domains, locking WRN in an inactive conformation. Pharmacological inhibition of WRN by HRO761 recapitulates the phenotype observed by WRN genetic suppression, leading to activation of the DNA damage response and inhibition of tumor cell growth selectively in MSI but not in MSS cells. We further show that WRN inhibition leads to WRN protein degradation only in MSI tumor cells. Although HRO761 activates a p53-related response, anti-proliferative effects were observed in both p53 wild-type as well as p53 null or mutated tumor cells. HRO761 exposure in mice is linear with oral dose and results in dose-dependent in vivo DNA damage induction and tumor growth inhibition in MSI cell- and patient-derived xenograft models. Altogether these findings represent preclinical pharmacological validation of WRN as a selective therapeutic target in MSI cancers. A global first in human clinical trial with HRO761 (NCT05838768) is currently ongoing to assess the safety, tolerability and preliminary anti-tumor activity in patients with MSI colorectal cancer and other MSI solid tumors.

Citation Format: Marta Cortes-Cros, Henrik Moebitz, Stephanie Barbe, Jutta Blank, Vincent Bordas, Giorgia Clementi, Ernesta Dammassa, Andrea Decker, Noemi Di Nanni, Ruben de Kanter, Marion Dourdoigne, Elena Gavioli, Stephane Ferretti, Marc Hattenberger, Christelle Hemmerlin, Jacques Hamon, Juergen Hinrichs, Isabel Jaco, Dragana Jankovic, Eloisa Jimenez Nunez, Yifang Li, Hans-Joerg Martus, Michele Moschetta, Cornelia Quadt, Markus Reschke, Vincent Romanet, Clemens Scheufler, Joseph Schoepfer, Ross Strang, Maxime Therier, Hans Voshol, Markus Wartmann, Sarah Welly, Monica Pham, Laurent Laborde. Discovery of HRO761, a novel, first-in-class clinical stage WRN inhibitor with potent and selective anti-tumor activity in cancers with microsatellite instability [abstract]. In: Proceedings of the AACR-NCI-EORTC Virtual International Conference on Molecular Targets and Cancer Therapeutics; 2023 Oct 11-15; Boston, MA. Philadelphia (PA): AACR; Mol Cancer Ther 2023;22(12 Suppl):Abstract nr PR007.