Abstract 5′→3′ exoribonuclease 1 (XRN1) degrades single stranded mRNA and plays a key role in endogenous cellular mRNA turnover. XRN1 also degrades double-stranded RNA (dsRNA), thereby playing a role in innate immunity by preventing accumulation of dsRNA and pPKR induction in virus-infected cells. XRN1 was validated as a target with selective vulnerability in lung cancer cells with intrinsically elevated Type I interferon signaling, a cellular state that phenocopies viral infection. XRN1 knockout using CRISPR resulted in robust and selective antiproliferative effects in colony formation and proliferation assays. Analysis of Caspase 3/7 confirmed antiproliferation activity was due to apoptosis in sensitive cell lines. With genetic target validation activities completed, efforts to enable identification and characterization of XRN1 inhibitors were undertaken. Biochemical and biophysical assays and crystallography with human XRN1 were enabled. This assay suite allowed full characterization of a non-selective, nucleotide-based tool compound (pAp) as well as identification and validation of Compound 1, a selective, allosteric, RNA-competitive inhibitor of XRN1. Citation Format: Maureen M. Lynes, Gordon J. Lockbaum, Brian A. Sparling, Sophie A. Shen, Sunaina P. Nayak, Kevin Knockenhauer, Simina Grigoriu, Shane M. Buker, Kenneth W. Duncan, Robert A. Copeland, Stephen J. Blakemore, Serena J. Silver, P. Ann Boriack-Sjodin. Target validation and drug discovery efforts on exoribonuclease XRN1 [abstract]. In: Proceedings of the AACR Special Conference in Cancer Research: RNAs as Drivers, Targets, and Therapeutics in Cancer; 2024 Nov 14-17; Bellevue, Washington. Philadelphia (PA): AACR; Mol Cancer Ther 2024;23(11_Suppl):Abstract nr PR006.
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