Abstract 4777: A small-molecule SMUG1 activator enhances repair of 5-hydroxymethyl-2’-deoxyuridine-mediated pyrimidine lesions in DNA

Abstract Background: Pharmacological upregulation of DNA repair pathways presents a potentially promising approach for cancer prevention in populations that are genetically high-risk. SMUG1, an enzyme involved in base excision repair, removes uracil and certain oxidized bases from DNA to mitigate adverse genotoxic and mutagenic effects and represents a promising target for cancer therapy. A growing body of evidence suggests that SMUG1 is involved in tumorigenesis, and deficiency of SMUG1 correlates with poor prognosis in several cancers. We hypothesize that upregulation of SMUG1 by a small molecule activator may be a viable strategy for reducing tumorigenesis in at-risk populations. We report on the properties of SU0547 - a SMUG1 activator that was derived from the EGFR inhibitor drug gefitinib - which shows reduced kinase inhibition and potent activation of SMUG1 both in vitro and in human cell lines. Methods: MTT proliferation assays were used to screen for toxicity and to determine the effect of SU0547 on 5-hydroxymethyl-2’-deoxyuridine (5-hmdU)-treated cell lines. The effect of the compound on SMUG1 expression was determined by Western blot and RT-qPCR while its effect on DSBs via γH2AX expression in 5-hmdU-treated cells was determined by immunofluorescence and Western blot. Results: SU0547 activates SMUG1 by 347 ± 50% in vitro at 100 nM, with an AC50 of 2.55 ± 0.62 µM. We examined whether it can modulate SMUG1 activity in a panel of human cell lines by artificially inducing DNA damage with the native SMUG1 substrate 5-hmdU and treating cells with the activator. In all five human cancer cell lines tested, SU0547 caused the cells to become significantly more resistant to 5-hmdU by factors of 2.1 to 5.3-fold. A series of CRISPR-Cas9 generated SMUG1 KO cell lines showed resistance to 5-hmdU and SU0547 had no effect on these treated cells, confirming that this activator acts on endogenous SMUG1. To determine the effect of the activator on double-strand breaks (DSBs), cells were treated with 5-hmdU with or without the compound and DSBs were visualized and quantitated by examining γH2AX foci. 5-hmdU treatment induced γH2AX foci while SU0547 treatment significantly reduced these foci to near or below baseline levels. These results were confirmed using Western blot quantitation of γH2AX. Conclusions: We envision that this activator will serve as a useful tool for further studying the role of SMUG1 in mediating 5-hmdU toxicity and will enable the testing of our hypothesis that enhancing DNA repair processes may serve to inhibit mutagenesis and slow progression of pre-neoplastic lesions to invasive cancers associated with genomic instability. Citation Format: Lisa A. McPherson, Yixuan Gao, Shanthi Adimoolam, Samyuktha Suresh, David L. Wilson, Ishani Das, Elizabeth R. Park, Christine S. Ng, Yong Woong Jun, James M. Ford, Eric T. Kool. A small-molecule SMUG1 activator enhances repair of 5-hydroxymethyl-2’-deoxyuridine-mediated pyrimidine lesions in DNA [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 4777.