Novel topoisomerase I/II dual inhibitors: Design, synthesis, and molecular docking studies of 1,3-thiazoline and 1,3,4-oxadiazole derivatives with anticancer activity against lung cancer

Despite significant advances in cancer therapy, the discovery of new anticancer agents with improved efficacy remains an important challenge. Human DNA topoisomerases I and II are well-established therapeutic targets because of their essential roles in DNA replication and transcription. Accordingly, a series of novel etofenamate-based thiosemicarbazide, 1,3-thiazole, and 1,3,4-oxadiazole derivatives were designed and synthesized, including a new synthetic approach for the preparation of the oxadiazole derivatives, and evaluated as potential topoisomerase-targeting anticancer agents. All synthesized compounds were structurally characterized and evaluated for antiproliferative activity against the A549 human lung cancer cell line and for their inhibitory effects on human DNA topoisomerases I and II. Based on their overall biological performance, compounds 3h, 5 h, and 5i were selected for further biological characterization, including thioredoxin reductase 1 (TrxR1) inhibition, total oxidative status (TOS), Bax/Bcl-2 protein expression, Annexin V analysis, and crystal violet staining. Molecular docking studies were performed to investigate the binding modes of the lead compounds toward topoisomerases I and II. Biological evaluation identified compounds 3 h, 5h, and 5i as the most promising derivatives. Enzymatic assays revealed distinct topoisomerase inhibition profiles, with compound 5h acting as a selective topoisomerase I inhibitor and compound 5i exhibiting dual inhibitory activity against topoisomerases I and II. Molecular docking analyses supported these findings by revealing target-specific binding modes consistent with the observed inhibition profiles. Complementary cellular studies demonstrated TrxR1 inhibition, increased oxidative stress, apoptosis-associated cellular responses, and morphological alterations, providing additional mechanistic characterization of the lead compounds. Collectively, these findings establish topoisomerases I and II as relevant molecular targets for the synthesized series while broadening the biological characterization of the lead compounds through complementary cellular investigations. Compound 5i emerged as the most promising dual topoisomerase I/II inhibitor and represents a valuable lead for the further development of novel topoisomerase-targeting anticancer agents.