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The response to psychological stress can differ depending on the type and duration of the stressor. Acute stress can facilitate a "fight or flight response" and aid survival, whereas chronic long-term stress with the persistent release of stress hormones such as cortisol has been shown to be detrimental to health. We are now beginning to understand how this stress hormone response impacts important processes such as DNA repair and cell proliferation processes in breast cancer. However, it is not known what epigenetic changes stress hormones induce in breast cancer. Epigenetic mechanisms include modification of DNA and histones within chromatin that may be involved in governing the transcriptional processes in cancer cells in response to changes by endogenous stress hormones. The contribution of endogenous acute or long-term exposure of glucocorticoid stress hormones, and exogenous glucocorticoids to methylation patterns in breast cancer tissues with different aetiologies remains to be evaluated. In vitro and in vivo models were developed to investigate the epigenetic modifications and their contribution to breast cancer progression and aetiology. A panel of triple negative breast cancer cell lines were treated with the glucocorticoid, cortisol which resulted in epigenetic alteration characterised by loss of methylation on promoter regions of tumour suppressor genes including ESR1, and loss of methylation on LINE-1 repetitive element used as a surrogate marker for global methylation. This was verified in vivo in MDA-MB-231 xenografts; the model verified the loss of methylation on ESR1 promoter, and subsequent increase in ESR1 expression in primary tumours in mice subjected to restraint stress. Our study highlights that DNA methylation landscape in breast cancer can be altered in response to stress and glucocorticoid treatment.

Investigational in vitro models that reflect the complexity of the interaction between the immune system and tumours are limited and difficult to establish. Herein, we present a platform to study the tumour-immune interaction using a co-culture between cancer spheroids and activated immune cells. An algorithm was developed for analysis of confocal images of the co-culture to evaluate the following quantitatively; immune cell infiltration, spheroid roundness and spheroid growth. As a proof of concept, the effect of the glucocorticoid stress hormone, cortisol was tested on 66CL4 co-culture model. Results were comparable to 66CL4 syngeneic in vivo mouse model undergoing psychological stress. Furthermore, administration of glucocorticoid receptor antagonists demonstrated the use of this model to determine the effect of treatments on the immune-tumour interplay. In conclusion, we provide a method of quantifying the interaction between the immune system and cancer, which can become a screening tool in immunotherapy design., Al-Hity et al present a platform to study the tumour-immune interaction using a co-culture between cancer spheroids and activated immune cells. They assess the effects of cortisol application to the culture model as proof-of-concept, which demonstrates the potential for this platform as a screening tool for immunotherapy design.

Stress hormones have been shown to be important mediators in driving malignant growth and reducing treatment efficacy in breast cancer. Glucocorticoids can induce DNA damage through an inducible nitric oxide synthase (iNOS) mediated pathway to increase levels of nitric oxide (NO). Using an immune competent mouse breast cancer model and 66CL4 breast cancer cells we identified a novel role of NOS inhibition to reduce stress-induced breast cancer metastasis. On a mechanistic level we show that the glucocorticoid cortisol induces expression of keys genes associated with angiogenesis, as well as pro-tumourigenic immunomodulation. Transcriptomics analysis confirmed that in the lungs of tumour-bearing mice, stress significantly enriched pathways associated with tumourigenesis, some of which could be regulated with NOS inhibition. These results demonstrate the detrimental involvement of NOS in stress hormone signalling, and the potential future benefits of NOS inhibition in highly stressed patients.

Background Epigenetic changes are highly responsive to environmental changes, including stress. The release of stress hormones; such as glucocorticoids, in response to stress have been shown to induce epigenetic modifications in neuronal cells. However, the role of glucocorticoids on epigenetic changes underlying important processes such as cell cycle regulation, apoptosis, and proliferation in breast cancer are not yet established. Furthermore, it is not known if cortisol can induce irreversible epigenetic changes on these cellular processes and whether these changes relate to the duration of the stress response. In this study, cortisol-induced epigenetic changes and the potential involvement of DNA methylation was assessed. Methods We analyzed the expression levels of maintenance DNA methyltrasferase (DNMT1) in MDA-MB-231, Hs-578T, MCF7, and T47D breast cancer cell lines by real-time PCR. We also used Qiagen Epitect Methyl ll Complete PCR array for Tumour Suppressor genes to analyse the level of methylation in 94 tumour suppressor genes. The methylation level on the Long Interspersed Nuclear Element (LINE-1) was used as surrogate marker for global DNA methylation. Results Our results show that cortisol significantly decreased the expression of DNMT1 in the triple negative cells lines MDA-MB-231 (p Conclusions Taken together, cortisol induced aberrant methylation patterns which may have important implications on progression of the disease. Legal entity responsible for the study The authors. Funding Has not received any funding. Disclosure All authors have declared no conflicts of interest.