8-5--cyclo-2--deoxyadenosine and Breast-Neoplasms

5',8-Cyclo-2'-deoxyadenosine (cdA) and 5',8-cyclo-2'-deoxyguanosine (cdG) in their two diastereomeric forms, 5'S and 5'R, are tandem lesions produced by the attack of hydroxyl radicals to the purine moieties of DNA. Their formation has been found to challenge the cells' repair machinery, initiating the nucleotide excision repair (NER) for restoring the genome integrity. The involvement of oxidatively induced DNA damage in carcinogenesis and the reduced capacity of some cancer cell lines to repair oxidised DNA base lesions, intrigued us to investigate the implication of these lesions in breast cancer, the most frequently occurring cancer in women. Using liquid chromatography tandem mass spectrometry (LC-MS/MS), we measured the levels of diastereomeric cdA's and cdG's in estrogen receptor-alpha positive (ER-α) MCF-7 and triple negative MDA-MB-231 breast cancer cell lines before and after exposure to two different conditions: ionising radiations and hydrogen peroxide, followed by an interval period to allow DNA repair. An increase at the measured levels of all four lesions, i.e. 5'S-cdA, 5'R-cdA, 5'S-cdG and 5'R-cdG, was observed either after γ-irradiation (5 Gy dose) or hydrogen peroxide treatment (300 μM) compared to the untreated cells (control), independently from the length of the interval period for repair. For comparison reasons, we also measured the levels of 8-oxo-2'-deoxyadenosine (8-oxo-dA), a well-known oxidatively induced DNA damage lesion and base excision repair (BER) substrate. The collected data indicate that MCF-7 and MDA-MB-231 breast cancer cells are highly susceptible to radiation-induced DNA damage, being mainly defective in the repair of these lesions.

Topics: Breast Neoplasms; Deoxyadenosines; DNA Damage; Epithelial Cells; Female; Humans; Mammary Glands, Human; MCF-7 Cells; Oxidative Stress; Reactive Oxygen Species

Breast cancer is a leading cause of cancer deaths in women. Although the causes of this disease are largely unknown, inefficient repair of oxidatively induced DNA lesions has been thought to play a major role in the transformation of normal breast tissue to malignant breast tissue. Previous studies have revealed higher levels of 8-hydroxyguanine in malignant breast tissue compared to non-malignant breast tissue. Furthermore, some breast cancer cell lines have greatly reduced capacity to repair this lesion suggesting that oxidatively induced DNA lesions may be elevated in breast cancer cells. We used liquid chromatography/mass spectrometry and gas chromatography/mass spectrometry to measure the levels of 8-hydroxy-2'-deoxyadenosine, (5'S)-8,5'-cyclo-2'-deoxyadenosine, 2,6-diamino-4-hydroxy-5-formamidopyrimidine, and 4,6-diamino-5-formamidopyrimidine in MCF-7 and HCC1937 breast cancer cell lines before and after exposure to H(2)O(2) followed by a DNA repair period. We show that H(2)O(2)-treated HCC1937 and MCF-7 cell lines accumulate significantly higher levels of these lesions than the untreated cells despite a 1 h repair period. In contrast, the four lesions did not accumulate to any significant level in H(2)O(2)-treated non-malignant cell lines, AG11134 and HCC1937BL. Furthermore, MCF-7 and HCC1937 cell lines were deficient in the excision repair of all the four lesions studied. These results suggest that oxidatively induced DNA damage and its repair may be critical in the etiology of breast cancer.

Topics: Analysis of Variance; Breast Neoplasms; Cell Extracts; Cell Line, Tumor; Chromatography, Liquid; Deoxyadenosines; DNA Damage; DNA Repair; Female; Gas Chromatography-Mass Spectrometry; Humans; Hydrogen Peroxide; Molecular Structure; Oligonucleotides; Oxidation-Reduction; Pyrimidines