Abstract 3114: Development of HTS enzymatic assays for RNA helicases: DDX3, DDX5, DDX17, RIG-1 and MDA5

Abstract RNA helicases are a broad class of enzymes that bind and modify RNA in an ATP-dependent manner and play diverse roles in RNA metabolism, regulation of gene expression, and innate immunity. Several RNA helicases, especially in the dead box helicase (DDX) family, have been shown to be dysregulated in cancer, and there have been limited efforts to develop small molecule inhibitors. To accelerate development of selective helicase inhibitors while avoiding off target effects, especially with helicases that promote tumor immunity, we are assembling a panel of high throughput biochemical assays using the Transcreener ADP2 assay for homogenous detection of RNA-dependent ATPase activity with a far-red fluorescence polarization (FP) readout. Here we describe development of assays for DDX3, DDX17 and DDX5, which have all been implicated in cancer, and the Rig-1-like receptor (RLR) helicases, RIG-1 and MDA5, which trigger expression of type I interferons important for tumor immunity. We produced the recombinant enzymes using BaV-infected insect cells, as full-length polypeptides, or in some cases truncated to remove disordered N-terminal domains. We determined RNA substrate and cofactor requirements and kinetic parameters with the purified enzymes and optimized the assays for initial velocity detection of RNA-dependent ATPase activity with a Z’ value greater than 0.7, ensuring a sufficient signal window for inhibitor screening and dose response assays. We validated each of the helicase ATPase assays for HTS by screening a collection of bioactives (Tocris 2.0) and confirming hits in dose response mode with the enzymatic assay and with thermal shift assays to confirm target binding. These assays will enable screening and hit-to-lead/SAR for DDX helicases that drive tumorigenesis as well as selectivity profiling to avoid off target effects with RLR helicases that promote tumor immunity. Citation Format: Mahbbat Ali, Ha Pham, Anibal Ramos Martinez, Robert Lowery. Development of HTS enzymatic assays for RNA helicases: DDX3, DDX5, DDX17, RIG-1 and MDA5 [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(6_Suppl):Abstract nr 3114.