Stress hormones in BRCA mutation carriers increase susceptibility to the development of breast cancer

This project is designed to discover whether psychological stress can affect the onset of cancer in patients at high risk of getting cancer.

The importance of psychological stress in breast cancer is recognized and being studied from a biobehavioral aspect. However, there are few, if any, studies on the mechanisms by which stress hormones impact breast cancer initiation. We have previously shown that stress hormones, cortisol, and catecholamines induce rapid DNA damage, impact DNA repair, and can also affect the efficacy of certain chemotherapy drugs.

However, the interplay between stress and breast cancer in women with germline mutations in BRCA genes is yet to be fully understood. Mutations in the BRCA genes are associated with a substantially increased lifetime risk of cancer, particularly premenopausal risk in the case of BRCA mutation carriers.

BRCA proteins are known to be involved in DNA repair pathways, which are thought to play a role in the increased risk for cancer. We hypothesize that increases in cortisol and 8-hydroxy-2’-deoxyguanosine (8-OHdG; a biomarker of oxidative DNA damage) in patients with mutations in DNA repair pathways promote genetic instability and increase susceptibility to the development of breast cancer. To test these hypotheses, we will characterize the mechanism whereby stress hormones affect DNA damage and repair pathways in wild type and BRCA deficient immortalised mammary epithelia cells.

We will next assess cortisol and 8-OHdG levels in patients with or without BRCA mutations and determine if these stress measures lead to cancer initiation. The findings from the research proposed here will allow us to determine if biochemical responses that occur during psychological stress have consequences on disease initiation. Such findings will provide valuable insight for patients and clinicians that stress is an important determinant in the aetiology of breast cancer, in particular in patients with defective DNA repair mechanisms such as BRCA mutated carriers. This would then be an avenue for intervention.

Objective 1:
We have shown that cortisol at physiological concentrations can induce phosphorylation of H2AX (an indicator of DNA damage) and BRCA1 in immortalised mammary epithelial cells and this is mediated through the glucocorticoid receptor as evidenced by blockade of the glucocorticoid receptor, using RU486. In addition, using the comet assay (used to detect single and double-stranded DNA breaks and alkali-labile sites) we found that cortisol impairs the cells ability to effectively repair this DNA damage. 
Furthermore, we showed that cortisol increased the formation of 8-OH DG; a marker of oxidative damage to DNA. We have successfully knocked down BRCA1 in MCF10A cells and although cortisol did not increase DNA damage compared to BRCA wild type, there was significantly less DNA repair in BRCA-deficient cells as evidence by the γ-H2AX assay. 
This finding was further confirmed using the comet assay. BRCA1-knockdown cells treated with cortisol has significantly increased levels of DNA damage compared to control cells after a period of repair.
Objective 2:
The goal of this objective is to links our mechanistic findings from Objective 1 to translate our findings to patient samples. 
We used patient serum and blood samples to: 1) determine if patients with BRCA mutations have elevated cortisol and 8-OHdG in the serum/urine compared to patients without BRCA mutations 2) determine if stress levels differ between patients who go on to develop cancer compared to those who remain cancer free. 
We have demonstrated a trend towards a greater increase in cortisol levels (% change from baseline) in patients who developed cancer during the study compared to matched controls. We also demonstrated that an increase in urinary 8OHDG was significantly increased in women who developed cancer during the study. 
Mean plasma cortisol levels for women who developed during and after the study and their matched controls were stratified into within range (0.15-0.73µg/dL) and high (>0.73µg/dL) groups. A significant association was also observed in women who were classified as having a high overall mean cortisol level and cancer incidence (OR, 9; 95% CI, 2.62-30.87).