TOP2 and NOS2 Orchestrate the Generation of DNA Breaks to Promote Colitis Cancer Initiation

Background: Inflammatory bowel disease (IBD), including ulcerative colitis (UC) and Crohn's disease (CD), increase colorectal cancer (CRC) risk. Methods: Mouse IBD and CRC models with a combination of pharmacological, knockout and knock-in approaches was employed to analyze the involvement of TOP2s and NOS2 in CRC tumorigenesis. Key pathologies, such as inflammatory and neoplastic scores, were examined by immunohistochemical assays. Results: In colon tissues from acute, chronic colitis and CRC mouse models and from CD patients, the biomarkers γH2AX and 53BP1_pS25/S29 of DNA breaks (mainly representing DSBs) accumulated, alongside increases in topoisomerase II (TOP2) and nitric oxide synthase 2 (NOS2). Genetic ablation of NOS2 (Nos2^-/-) or TOP2β (Top2β^f/f) as well as pharmacological inhibition with ICRF-193 (a TOP2 inhibitor) or PTIO (a NO scavenger) reduced DSB formation and disease severity. Consistently, Nos2^-/-, or ICRF-treated, mice exhibited decreased tumor burden. DSBs and tumor accumulation were pronounced in the distal colon, mirroring human CRC distribution. While ICRF-193 suppressed tumor growth, Top2β^f/f deficiency (with a compensatory TOP2α upregulation) enhanced tumor development, indicating potential roles for TOP2 isozymes in tumor formation and progression. Conclusion: Collectively, these findings identify the cooperative action of TOP2 and NOS2 in driving DSBs, highlighting a potential therapeutic target in inflammation-associated CRC.