Antitumor agents 7. Synthesis, antiproliferative activity and molecular modeling of new L-lysine-conjugated pyridophenoxazinones as potent DNA-binding ligands and topoisomerase IIα inhibitors

A series of L-lysine-conjugated pyridophenoxazinones 2–5 and 2′-5′ were designed and synthesized for developing compounds with multimodal anticancer potentialities. All compounds inhibited the proliferation of a panel of human liquid and solid neoplastic cell lines. 2 and 5 were the most active compounds with IC50 values in the submicromolar range. UV–vis, 1H NMR, unwinding, and docking experiments demonstrated that they intercalate between the middle 5′-GC-3′ base pairs with the carboxamide side chain lying into major groove. Charge-transfer contribution to the complex stability, evaluated by ab initio calculations, was found to correlate with cytotoxicity. Relaxation and cleavage assays showed that 2 and 5 selectively target Topo IIα over Topo IIβ and stimulate the formation of covalent Topo II–DNA complexes, functioning as poisons. Moreover, compound 5 induced DNA damage and arrested MCF-7 cells at the G2/M phase. Altogether, the work provides interesting structure-activity relationships in the pyridophenoxazinone-L-lysine conjugate series and identifies 5 as a promising candidate for further in vivo evaluation.