- Title
- The link between aberrations in the p53 pathway and outcomes from DNA-damaging therapies in breast cancer
- Creator
- Steffens Reinhardt, Luiza
- Relation
- University of Newcastle Research Higher Degree Thesis
- Resource Type
- thesis
- Date
- 2023
- Description
- Research Doctorate - Doctor of Philosophy (PhD)
- Description
- Breast cancer is the most common cancer in women and treatment resistance and the development of metastasis are the primary cause of death from this disease. Despite the progress in breast cancer treatments and improved patient quality of life, breast cancer-related deaths remain a worldwide challenge. Accordingly, the identification of therapeutic targets and effective prognostic markers to improve breast cancer’s overall clinical outcome is imperative. Given the heterogeneous nature of breast cancers, the mechanisms that contribute to resistance to therapies are largely unknown. Despite the significant diversity in the genes associated with tumorigenesis, TP53 is a key regulator of several signalling pathways involved in tumorigenesis and is frequently mutated in cancers. In breast cancer, TP53 pathogenic mutations are detected in less than a quarter of cases and hence, it is likely that other mechanisms affect the activities of this important tumour suppressor. The focus of this thesis was on characterising the molecular alterations in the p53 pathway that result in resistance to DNA-damaging therapies and worse outcomes in breast cancer. Previous studies from our group have shown that p53 isoform expression at the mRNA level is altered in breast cancer and related to clinical features. In particular, a high Δ40p53:p53 ratio is associated with worse disease-free survival. In this thesis, the influence of altered Δ40p53 levels on the response to DNA-damaging agents used in breast cancer treatment and cellular state was investigated. Breast cancer cell sublines with overexpression or knockdown of Δ40p53 and control sublines were used and the effects of variable Δ40p53:p53 ratios in cells following treatment with DNA-damaging therapies or at the basal level were assessed in 2D and 3D in vitro assays and xenograft models. To infer aberrant activity of cellular pathways in tumours with high or low ∆40p53 expression, cDNA microarray data of 64 invasive ductal carcinomas were reanalysed. The data presented in this thesis strongly indicates that a high Δ40p53:p53 ratio significantly affects breast cancer cell fate decisions and that p53 functions in breast cancer are modulated by the levels of the Δ40p53 isoform. Endogenously, Δ40p53 is highly expressed in a subpopulation of cells with stem-like features and the levels of this isoform are associated with enhanced pluripotency. Following doxorubicin, Δ40p53 acts as a pro-survival p53 isoform by preventing p53 canonical DNA damage response and apoptosis, contributing to enhanced chemoresistance. Δ40p53 knockdown had the opposite effect, suggesting that targeting Δ40p53 in breast cancer may enhance the efficacy of standard-of-care therapies such as doxorubicin. In breast cancer, p53 expression signatures are a better predictor of treatment response and clinical outcome than TP53 mutations. Given that p53 isoform expression contributes to p53 dysregulation, the p53 isoform expression was evaluated at the protein level using a suite of p53 isoform novel antibodies. The results demonstrated that the immunostaining of p53 isoforms is associated with breast cancer clinical features, in particular, high levels of p53β expressed in the cytoplasm and most likely to be Δ133p53β, were significantly associated with worse disease-free survival in invasive ductal carcinomas. Furthermore, the p53 expression pattern was strongly associated with breast cancer clinicopathological features and outcomes. Finally, with the imperative roles of the p53 pathway in the DNA damage response, genetic alterations in genes within this pathway were evaluated in a cohort of 137 therapy-naïve breast cancers by targeted next-generation sequencing. Novel mutations in several genes were discovered, resulting in a substantial mutation burden. Mutations in PARP1 and ATR predicted worse breast cancer-free survival, especially for patients who received chemotherapies. These results have important implications for developing targeted therapies. Moreover, the findings indicate an opportunity for utilising PARP1 and ATR mutations as biomarkers to guide the selection of patients most likely to benefit from therapies that target these genes or pathways they are involved in. Overall, in this thesis, promising therapeutic targets and prognostic markers associated with the p53 pathway were identified and future work envisages translating these findings to clinical approaches, providing guidance for treatment decisions and improving breast cancer outcomes.
- Subject
- breast cancer; treatment; p53 pathway; clinical approaches; thesis by publication
- Identifier
- http://hdl.handle.net/1959.13/1505526
- Identifier
- uon:55676
- Rights
- This thesis is currently under embargo and will be available from 13.10.2024, Copyright 2023 Luiza Steffens Reinhardt
- Language
- eng
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