nu-7441 and Nasopharyngeal-Neoplasms

The DNA-dependent protein kinase (DNA-PK) complex plays a pivotal role in non-homologous end-joining (NHEJ) repair. We investigated the mechanism of NU7441, a highly selective DNA-PK inhibitor, in NHEJ-competent mouse embryonic fibroblast (MEF) cells and NHEJ-deficient cells and explored the feasibility of its application in radiosensitizing nasopharyngeal carcinoma (NPC) cells. We generated wild-type and DNA-PKcs-/- MEF cells. Clonogenic survival assays, flow cytometry, and immunoblotting were performed to study the effect of NU7441 on survival, cell cycle, and DNA repair. NU7441 profoundly radiosensitized wild-type MEF cells and SUNE-1 cells, but not DNA-PKcs-/- MEF cells. NU7441 significantly suppressed radiation-induced DSB repair post-irradiation through unrepaired and lethal DNA damage, the cell cycle arrest. The effect was associated with the activation of cell cycle checkpoints. The present study revealed a mechanism by which inhibition of DNA-PK sensitizes cells to irradiation suggesting that radiotherapy in combination with DNA-PK inhibitor is a promising paradigm for the management of NPC which merits further investigation.

Topics: Animals; Apoptosis; Carcinoma; Cell Proliferation; Cells, Cultured; Chromones; DNA Breaks, Double-Stranded; DNA End-Joining Repair; DNA-Activated Protein Kinase; DNA-Binding Proteins; Fibroblasts; Gamma Rays; Humans; Mice; Mice, Knockout; Morpholines; Nasopharyngeal Carcinoma; Nasopharyngeal Neoplasms; Nuclear Proteins; Radiation-Sensitizing Agents

DNA-dependent protein kinase catalytic subunit (DNA-PKcs) is a distinct factor in the non-homologous end-joining (NHEJ) pathway involved in DNA double-strand break (DSB) repair. We examined the crosstalk between key proteins in the DSB NHEJ repair pathway and cell cycle regulation and found that mouse embryonic fibroblast (MEF) cells deficient in DNA-PKcs or Ku70 were more vulnerable to ionizing radiation (IR) compared with wild-type cells and that DSB repair was delayed. γH2AX was associated with phospho-Ataxia-telangiectasia mutated kinase (Ser1987) and phospho-checkpoint effector kinase 1 (Ser345) foci for the arrest of cell cycle through the G2/M phase. Inhibition of DNA-PKcs prolonged IR-induced G2/M phase arrest because of sequential activation of cell cycle checkpoints. DSBs were introduced, and cell cycle checkpoints were recruited after exposure to IR in nasopharyngeal carcinoma SUNE-1 cells. NU7441 radiosensitized MEF cells and SUNE-1 cells by interfering with DSB repair. Together, these results reveal a mechanism in which coupling of DSB repair with the cell cycle radiosensitizes NHEJ repair-deficient cells, justifying further development of DNA-PK inhibitors in cancer therapy.

Topics: Animals; Apoptosis; Ataxia Telangiectasia Mutated Proteins; Carcinoma; Cell Cycle Checkpoints; Cell Proliferation; Checkpoint Kinase 1; Chromones; DNA Breaks, Double-Stranded; DNA End-Joining Repair; DNA-Activated Protein Kinase; DNA-Binding Proteins; Embryo, Mammalian; Fibroblasts; Ku Autoantigen; Mice; Mice, Knockout; Morpholines; Nasopharyngeal Carcinoma; Nasopharyngeal Neoplasms; Nuclear Proteins; Radiation Tolerance; Radiation-Sensitizing Agents; Radiation, Ionizing; Tumor Cells, Cultured