Abstract
The role of stress hormone receptors in the progression of triple-negative breast cancer brain metastases remains underexplored, particularly their contribution to tumour invasion and the brain microenvironment. This thesis investigates the modulation of stress hormone receptors, including the GR and β2-adrenergic receptor (ADRB2), in TNBC progression through a combination of in vitro, in vivo, and molecular approaches.In vitro experiments using TNBC cell lines demonstrated that dual blockade of GR and ADRB2, using Relacorilant and Propranolol, significantly reduced cell migration and invasion, highlighting the role of these receptors in driving metastatic behaviour. These findings led to the next phase of the study, where primary murine astrocytes were cultured alone or together with the TNBC cell line 4T1. Cytokine profiling and RNA sequencing revealed that stress hormones and tumour-astrocyte interactions promote a pro-inflammatory brain microenvironment characterised by elevated cytokines such as CXCL1 and TIMP-1, and a dysregulated extracellular matrix. This inflammatory environment may exacerbate brain damage and excitotoxicity, potentially worsening patient outcomes.
To further explore the clinical relevance, in vivo studies were conducted using BALB/c mice. Chronic dexamethasone (a synthetic glucocorticoid) treatment led to increased microglial nodules in the brain and upregulation of stem cell markers in primary tumours, as determined by flow cytometry, western blotting, and histology. These changes corresponded to worse prognosis in mice receiving high doses of dexamethasone, implicating GR signalling in tumour progression and brain metastases.
Finally, a metastatic animal model was developed using the highly brain-metastatic 4T1-BM2 cell line. Mice were subjected to stress three times per week and treated with Propranolol, Relacorilant, Paclitaxel, or combinations thereof. Histology, H&E staining, and IHC confirmed higher brain metastatic burden in stressed mice, with metastatic foci confirmed by Ki67, CK7, and pan-cytokeratin IHC. Notably, stressed mice also exhibited cytoskeletal dysregulation in astrocytes, leading to extracellular matrix instability in vitro. While Propranolol delivery via pumps was ineffective, Relacorilant alone improved survival and reduced metastatic outgrowth in stressed mice.
This thesis provides novel insights into the impact of stress hormone signalling on triple-negative breast cancer brain metastasis, highlighting the role of glucocorticoids and β-adrenergic signalling in reshaping the tumour microenvironment, promoting cancer stemness, and driving metastatic progression. By integrating in vitro, in vivo, and transcriptomic approaches, this work identifies astrocytes as key mediators of stress-induced brain metastasis and establishes the first evidence of stress-driven cytoskeletal and cytokine alterations in astrocytes that may contribute to a more permissive metastatic niche. Furthermore, this work demonstrates the potential therapeutic value of targeting stress pathways, showing that GR antagonism mitigates some of the pro-metastatic effects of stress. These findings expand our understanding of how systemic stress influences TNBC brain metastases and offer a strong rationale for incorporating stress-targeting strategies into future treatment approaches.
| Date of Award | Mar 2025 |
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| Original language | English |
| Awarding Institution |
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| Supervisor | Melanie Flint (Supervisor), Nicolas Stewart (Supervisor) & Andrew E. Greenstein (Supervisor) |