Abstract 7278: Discovery of a novel WRN inhibitor, ZM-3329 that efficiently inhibits MSI-H tumor growth

Abstract Microsatellite instability-high status (MSI-H) is typically associated with endometrial and gastrointestinal cancers. These tumors harbor large numbers of frameshift and single-nucleotide variants and are characterized by a high tumor mutational burden (TMB). The clinical benefits of immune checkpoint inhibitor (ICI) therapy on MSI-H cancers were well-demonstrated, however, 50% of these cancers are intrinsically resistant to PD-1 therapies and resistance inevitably develops with prolonged treatment. Thus, a novel efficient therapeutic strategy for MSI-H cancer is still needed. Werner syndrome ATP-dependent helicase (WRN) is a member of the RecQ helicases family and has recently emerged as a promising synthetic-lethal target in the treatment of MSI-H tumors. In MSI-H tumors, microsatellite sequences consisting of repeated nucleotides are unstable, and replication slippage causes a unique secondary structure that hinders the progression of replication forks. With its helicase activity, WRN unwinds this secondary structure to restart DNA synthesis and sustain MSI-H tumor cell growth. WRN knockdown or helicase enzyme-dead effectively inhibits cell proliferation and tumor growth in multiple preclinical MSI-H models. Here we identified ZM-3329, a novel and highly potent WRN inhibitor. Helicase activities were efficiently inhibited by ZM-3329 with IC50 less than 30 nM, and equal potency was identified on HCT-116 cell proliferation inhibition. In a panel of 124 tumor cell lines, ZM-3329 only specifically inhibited the growth of MSI-H but had no significant effects on the MSS (Microsatellite stable) tumor cell lines, indicating high selectivity against MSS. Additionally, ZM-3329 strongly inhibited the growth of MSI-H patient-derived organoids. The intracellular mechanism of action study revealed that inhibition of WRN by ZM-3329 in MSI-H cells led to the accumulative DNA damage signatures which was demonstrated by the increase of γH2AX and P21 expression, and arrested cell cycle to G2/M. ZM-3329 demonstrated favorable pharmacokinetic profiles in pre-clinical species, supporting oral administration in humans. ZM-3329 showed robust anti-tumor activities in multiple MSI-H xenograft models with significant tumor regression observed. Meanwhile, mice were tolerant well in all tested doses, and no abnormality was observed. In conclusion, a novel WRN inhibitor was developed, and robust antitumor activities were demonstrated in xenograft tumors and PDOs with different tissue types. In terms of synthetic lethality between MSI-H and WRN as well as broad anti-tumor activities across different tumor types, ZM-3329 would be developed as a tissue-agnostic therapy for MSI-H patients. Citation Format: Feng Zhou, Guimei Yang, Yajing Liu, Liting Xue, Yao Guo, Zhengtao Li, Weikun Wang, Jian Li, Renhong Tang. Discovery of a novel WRN inhibitor, ZM-3329 that efficiently inhibits MSI-H tumor growth abstract. In: Proceedings of the American Association for Cancer Research Annual Meeting 2024; Part 1 (Regular Abstracts) ; 2024 Apr 5-10; San Diego, CA. Philadelphia (PA): AACR; Cancer Res 2024;84 (6Suppl): Abstract nr 7278.