Novel nalidixic acid derivatives targeting topoisomerase II enzyme; Design, synthesis, anticancer activity and effect on cell cycle profile.

Aim: Design and synthesis of novel nalidixic acid derivatives of potent anticancer and topoisomerase II inhibitory activities were our major aim.
Materials & Methods: All the newly synthesized nalidixic acid derivatives were submitted to the National Cancer Institute (NCI), Bethesda, USA and were accepted for single dose screening. Further investigation via IC ₅₀ determination of the most potent compound 6a against K-562 and SR leukemia cell lines. Finally, the topoisomerase II inhibitory activity, the cell cycle analysis and molecular docking of 6a were performed in order to identify the possible mechanism of the anticancer activity.
Results: Compound 6a showed interesting selectivity against leukemia especially K-562 and SR subpanels with IC ₅₀ 35.29 µM and 13.85 µM respectively. Moreover, compound 6a revealed potent topoisomerase IIα and topoisomerase IIβ inhibitory activity compared with known topoisomerase inhibitors such as doxorubicin and topotecan with IC ₅₀ 1.30 µM and 0.017 µM respectively. Cell cycle analysis indicated that compound 6a induced cell cycle arrest at G2-M phase leading to inhibition of cell proliferation and apoptosis. Molecular modeling demonstrated that the potent topoisomerase inhibitory activity of 6a was due to the interaction with the topoisomerase II enzyme through coordinate bonding with the magnesium ion Mg ²⁺ , hydrogen bonding with Asp 545 and arene cation interaction with His 759.
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