Abstract A22: Association of breast cancer risk and concentrations of tissue estrogens to single strand breaks in DNA

Introduction: Single-strand breaks (SSB) in DNA are discontinuities in one strand of the DNA and are usually accompanied by loss of a single base and by damaged 5- or 3-termini at the site of the break. If not repaired rapidly or appropriately, chromosomal SSBs pose a serious threat to genetic stability and cancer development. We hypothesize that if the presence of single strand DNA breaks can be quantified directly, it will provide a means of detecting a process that puts cells at high risk of developing cancer. The association between a quantitative measure of SSB and other measures of breast cancer risk was determined. Subjects: 206 postmenopausal and 99 premenopausal, healthy women with intact, healthy bilateral breasts, without implants or history of radiation, willing to undergo a random fine-needle aspiration (rFNA) of the breast within 3.5 months of a normal mammogram were recruited to the study. Exclusions: use of tamoxifen, raloxifene, or aromatase inhibitor within 2 years of participation or oral contraceptives or other hormone treatments within 3 months of study enrollment. Participants completed personal and medical history questionnaires. Blood for hormone levels and random fine needle aspirates of the breast (rFNA) were collected following a breast exam. Methods: rFNA of the breast of women at unspecified risks for breast cancer were analyzed for SSB by a nick translation procedure. SSB levels digital two-dimensional breast density of the entire breast (PBD), mRNA of genes associated with DNA damage, and breast steroid concentrations by a LC/MS/MS procedure. Results: Based on the cpm in the purified sample, the specific activity of the 3H-dCTP, and quantity of DNA in the sample, the incorporation of 3H-dCTP ranged from 0.03 to 8.59 pmol/µg DNA. The β-coefficients for the relationships between SSB and measures of breast cancer risk were determined by a multiple regression procedure. PBD adjusted for age was associated with SSB in postmenopausal women (P = 0.007) but was not associated with SSB in premenopausal women. Further adjustment for BMI reduced the PBD relationship to SSB by 35% but adjustment for BMI. APEX1 was not significantly associated with SSB. XRCC1 mRNA was negatively associated with SSB in premenopausal women (p = 0.016), and was not altered by adjustment for age. The antioxidant functions NRF-1 and SOD2 were both significantly negatively associated with SSBs, P = 0.001 and 0.045, respectively, and both were decreased by less than 5% after adjustment for age. Breast tissue concentrations of 4-hydroxyestradiol exceeded those of estradiol, were correlated with tissue estradiol, and were significantly (P = 0.011) negatively related to SSB levels. Breast tissue concentrations of estradiol, estrone, 4-hydroxyestrone, and androstenedione were not significantly related to SSB. Conclusions: The most likely mechanism by which 4-OHE2 or 2-OHE1 could protect against formation of SSBs in the breast is by their antioxidative properties. 4-OHE2 and other catechol estrogens are capable of undergoing redox reactions, cycling between the catechol structure, semiquinone radical, and o-quinone. They are also capable of forming metal complexes, sequestering metals, preventing them from undergoing redox reactions. In addition, 4-OHE2 has a binding affinity relative to that of estradiol of 1.51; that of 2-OHE1 is 1.02 Therefore, the catechol estrogens have activity similar to or greater than that of estradiol in terms of activation of NRF-1 and Mn SOD, both of which were elevated in association with lower SSB levels. We conclude that SSBs measured by the nick translation procedure are associated with, but not redundant with, measures of breast cancer risk and with deficiencies of both DNA damage responses and antioxidant mechanisms. Concentrations of 4-hydroxyestradiol in breast tissue may serve an antioxidant function and may be protective. Citation Format: Mathavi Sahadevan, Oukseub Lee, Miguel Muzzio, Belinda Phan, Lisa Jacobs, Nagi Khouri, Jun Wang, Hong Hu, Vered Stearns, Robert T. Chatterton. Association of breast cancer risk and concentrations of tissue estrogens to single strand breaks in DNA. [abstract]. In: Proceedings of the AACR Special Conference: Improving Cancer Risk Prediction for Prevention and Early Detection; Nov 16-19, 2016; Orlando, FL. Philadelphia (PA): AACR; Cancer Epidemiol Biomarkers Prev 2017;26(5 Suppl):Abstract nr A22.