Abstract 4247: Discovery of GH3595: a novel allosteric DHX9 inhibitor for cancer therapy

Abstract DExH-Box helicase 9 (DHX9), also known as RNA helicase A (RHA), belongs to the DExD/H-Box superfamily II of helicases. Due to its fundamental roles in processes such as transcription and maintenance of genomic stability, DHX9 has emerged as a key regulator in various cancer types. Specifically, microsatellite instable (MSI) cancers, such as MSI-high (MSI-H) colorectal cancer, and tumors with defective homologous recombination exhibit a strong dependency on DHX9, suggesting that targeting DHX9 could offer a significant therapeutic opportunity. Employing fragment-based drug design, we have discovered GH3595, a novel allosteric DHX9 inhibitor that selectively targets the DHX9 protein. In vitro, GH3595 displayed a low nM potency in ATPase and helicase activity assays, which translated to specific low nM inhibition of MSI-H colorectal cancer and BRCA loss of function breast cancer proliferation. In vivo, GH3595 demonstrated favorable pharmacokinetic properties in different species and showed an acceptable safety profile. Furthermore, daily oral dosing of GH3595 led to the regression of MSI-H xenograft tumors without adverse effects on body weight. More importantly, GH3595 induced dose-dependent intra-tumoral circular RNA induction, showing a well-correlated PK/PD/Efficacy relationship. In summary, we report the discovery and characterization of GH3595, a potent and selective inhibitor of DHX9, which effectively disrupts DHX9-mediated signaling pathways. These findings highlight its significant therapeutic potential for the treatment of malignancies characterized by microsatellite instability or deficiencies in homologous recombination. Citation Format: Faridoon Faridoon, Jiapeng Li, Jiyue Zheng, Xiang Wang, Guiping Zhang. Discovery of GH3595: a novel allosteric DHX9 inhibitor for cancer therapy [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2025; Part 1 (Regular Abstracts); 2025 Apr 25-30; Chicago, IL. Philadelphia (PA): AACR; Cancer Res 2025;85(8_Suppl_1):Abstract nr 4247.