DNA-PK Inhibition by NU7441 Enhances Chemosensitivity to Topoisomerase Inhibitor in Non-Small Cell Lung Carcinoma Cells by Blocking DNA Damage Repair.
DNA double-strand breaks (DSBs) are the most cytotoxic form of DNA damage and are induced by ionizing radiation and specific chemotherapeutic agents, such as topoisomerase inhibitors. Cancer cells acquire resistance to such therapies by repairing DNA DSBs. A major pathway for the repair of DNA DSBs is non-homologous end-joining (NHEJ), which requires DNA-dependent protein kinase (DNA-PK) activity. In this study, we investigated the effect of NU7441, a synthetic small-molecule compound, as a specific inhibitor of DNA-PK on the chemosensitization of non-small cell lung carcinoma (NSCLC) A549 cells.



The combined effects of chemotherapeutic agents and NU7441 were evaluated by isobologram analysis using Cell Counting Kit-8. DNA DSBs were assessed by immunofluorescence assay. Apoptosis was examined by flow cytometry using an Annexin V apoptosis kit. Activation of DNA-PK was assayed by western blotting.



The combination of NU7441 and topoisomerase inhibitors such as amrubicin and irinotecan had a synergistic effect on cell proliferation in A549 cells. NU7441 increased 53BP1 foci and apoptosis induced by topoisomerase inhibitors and decreased phospho-DNA-dependent protein kinase, catalytic subunit (pDNA-PKcs) (S2056) protein expression caused by topoisomerase inhibitors. Interestingly, mitotic inhibitors such as pacritaxel did not cause the pDNA-PKcs (S2056) protein expression and the combination of NU7441 and pacritaxel had an only additive effect.



NU7441 inhibited the growth of NSCLC cells and enhanced the chemosensitization to topoisomerase inhibitors by blocking DNA repair. A combination of NU7441 and topoisomerase inhibitor may be a promising treatment for NSCLC.
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Masaaki
M
Yanai
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Haruhiko
H
Makino
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Bingqiong
B
Ping
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Kenichi
K
Takeda
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Natsumi
N
Tanaka
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Tomohiro
T
Sakamoto
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Kosuke
K
Yamaguchi
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Masahiro
M
Kodani
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Akira
A
Yamasaki
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Tadashi
T
Igishi
Division of Medical Oncology and Molecular Respirology, Department of Multidisciplinary Internal Medicine, School of Medicine, Tottori University Faculty of Medicine, Yonago 683-8504, Japan.
Eiji
E
Shimizu
DNA-dependent protein kinase; NU7441; non-homologous end-joining; non-small cell lung carcinoma; topoisomerase inhibitor