Radiation Resistance in Glioma Cells Determined by DNA Damage Repair Activity of Ape1/Ref-1

Abstract

Since radiation therapy remains a primary treatment modality for gliomas, the radioresistance of glioma cells and targets to modify their radiation tolerance are of significant interest. Human apurinic endonuclease 1 (Ape1, Ref-1, APEX, HAP1, AP endo) is a multifunctional protein involved in base excision repair of DNA and a redox-dependent transcriptional co-activator. This study investigated whether there is a direct relationship between Ape1 and radioresistance in glioma cells, employing the human U87 and U251 cell lines. U87 is intrinsically more radioresistant than U251, which is partly attributable to more cycling U251 cells found in G2/M, the most radiosensitive cell stage, while more U87 cells are found in S and G1, the more radioresistant cell stages. But observed radioresistance is also related to Ape1 activity. U87 has higher levels of Ape1 than does U251, as assessed by Western blot and enzyme activity assays (approximately 1.5-2 fold higher in cycling cells, and approximately 10 fold higher at G2/M). A direct relationship was seen in cells transfected with CMV-Ape1 constructs; there was a dose-dependent relationship between increasing Ape1 overexpression and increasing radioresistance. Conversely, knock down by siRNA or by pharmacological down regulation of Ape1 resulted in decreased radioresistance. The inhibitors lucanthone and CRT004876 were employed, the former a thioxanthene previously under clinical evaluation as a radiosensitizer for brain tumors and the latter a more specific Ape1 inhibitor. These data suggest that Ape1 may be a useful target for modifying radiation tolerance.

Human Apurinic/Apyrimidinic Endonuclease 1

“…Hyper-sensitivity of APE1 KD cells has been reported for other clinical DNA-damaging agents, including ionizing radiation (32,150,237), bleomycin (56,170,218), gemcitabine (239), cisplatin (222,246), etoposide (185,221), and photodynamic therapy (236,243). While in some cases it is not obvious what role APE1 would play in repairing the direct DNA damage (e.g., for the crosslinking agent cisplatin), some level of oxidative stress is involved in most genotoxin exposures.…”

A new curcumin analogue exhibits enhanced antitumor activity in nasopharyngeal carcinoma

“…Mammalian cells exhibit significant variation in radiosensitivity as the cell cycle progresses. Cells in the G2/M phase are the most radiosensitive (24). These findings show that accumulation of cells in the most radiosensitive G2/M phase caused by GL63 may enhance the radiosensitization effect in NPC cells.…”

DNA Repair Endonucleases: Physiological Roles and Potential as Drug Targets

“…105 In addition, treatment of radiotherapy-resistant glioblastoma cell lines with lucanthone has been shown to sensitize cells to radiotherapy. 106 Lucanthone has been shown to readily cross the blood-brain barrier in both the presence and absence of brain tumors in mice and rats. 107 In a small study of eight patients with brain metastases, lucanthone treatment in combination with radiotherapy resulted in a significant increase in tumor regression.…”