Rational design and synthesis of flavonolactam derivatives as potent topo I inhibitors with antitumor activity.

Targeting topoisomerase I (Topo I) remains a pivotal strategy for the treatment of colorectal cancer (CRC). In this study, we rationally designed and synthesized a series of flavonolactam derivatives and systematically evaluated their biological activities and mechanisms of action. Among these, compounds NL-26 and NL-28 exhibited potent inhibitory effects on Topo I activity, arresting the cell cycle at the G2/M phase and inducing apoptosis to suppress tumor cell proliferation. Notably, NL-26 displayed the most potent Topo I inhibitory activity, which was comparable to that of the reference inhibitor camptothecin (CPT). In vivo pharmacokinetic studies revealed that NL-26 possesses a desirable profile, characterized by an AUC0-t of 1979.7 h ng/mL and a t1/2 of 3.7 h. Furthermore, NL-26 demonstrated robust antitumor efficacy in HCT116 xenograft models, achieving a tumor growth inhibition (TGI) of 55.1%. Collectively, these findings identify NL-26 as a promising lead compound and validate the flavonolactam scaffold as a privileged template for the development of next-generation Topo I-targeting therapeutics.