Synthesis and biological evaluation of phenanthridine derivatives as dual-target inhibitors of DNA topoisomerase IB (TOP1) and tyrosyl-DNA phosphodiesterase 1 (TDP1), and potential antitumor agents.

Tumor resistance to chemotherapy, driven in part by DNA repair mechanisms, presents a major obstacle in cancer treatment. DNA topoisomerase 1B (TOP1) and tyrosyl-DNA phosphodiesterase 1 (TDP1) are key enzymes involved in DNA replication and repair, and their coordinated activity can contribute to tumor cell survival and resistance to TOP1-targeted agents. In this study, a novel series of phenanthridine derivatives was rationally designed, synthesized, and evaluated for their potential as dual inhibitors of TOP1 and TDP1. Several compounds exhibited potent inhibitory activity against both targets, with compound C13 identified as a lead candidate, displaying strong inhibition of TOP1 (++++) and effective inhibition of TDP1 (IC50 = 17.8 ± 1.3 μM). In vitro, C13 showed notable antiproliferative effects against multiple cancer cell lines, particularly A549 cells (IC50 = 0.89 ± 0.25 μM), and induced apoptosis and suppressed clonogenic growth in a dose-dependent manner. Mechanistic studies revealed that C13 disrupts DNA repair pathways, and its combination with topotecan resulted in synergistic antitumor efficacy. Molecular dynamics simulations confirmed stable binding between C13 and both targets, while in vivo studies demonstrated low acute toxicity, favorable pharmacokinetic parameters, and pronounced tumor suppression. These findings highlight the promise of dual TOP1/TDP1 inhibition for overcoming tumor drug resistance and support the further development of C13 as a potential anticancer agent.