Triple negative breast cancers (TNBCs) do not express estrogen receptor-? (ER?), progesterone receptor (PR), or human epidermal growth factor receptor 2 (HER2), and therefore, none of the targeted drugs currently in use for breast cancer are effective against them. Approximately 60-80% of TNBCs express estrogen receptor-? (ER?). However, pro- versus anti-tumorigenic capabilities of ER? remains controversial. Another key molecular characteristic of TNBC is the high frequency (80%) of p53 mutation. In addition to losing tumor suppressor properties and exerting dominant-negative regulation over any remaining wild type p53 (WTp53), mutant p53 also acquires oncogenic gain-of-function. Increasing evidence suggests that not all mutant p53s function similarly. Although ER? and p53 have been implicated in TNBC pathology, whether p53 has a role in the pro- versus anti-proliferative functional duality of ER? remains an open question. The long-term goal is to understand and exploit the role of ER?-p53 crosstalk in breast cancer for the development of better therapeutic strategies. The objective is to study how specific mutations in p53 impinges upon ER? function in TNBC, with the prediction that specific p53 mutation will determine its role in the ER?-mutant p53-p73 signaling axis impacting multiple aspects of tumor progression and metastasis. The hypothesis is that ER? binds to and inhibits both WTp53 and mutant p53, leading to opposite effects on progression and therapeutic response of TNBC to agents such as Tamoxifen (Tam). The rationale for the proposed research is that understanding how ER? elicits opposite functions in a p53 status-dependent manner will be critical to stratify TNBC patients to repurpose established therapeutic agents such as Tam to treat large percentage of TNBC patients.
The specific aims are: (1 Determine the interaction of different p53 mutants with p73 and ER? in TNBC cells; (2) Analyze the differential effects of p53 mutants on tumor progression, metastasis and therapeutic response in vivo; and (3) Evaluate the clinical significance of the ER?-p53-p73 signaling axis.
In specific aim 1, Isogenic TNBC cells expressing different combinations of ER? and WT and p53 mutants generated using CRISPR technology and shRNA-mediated conditional knockdown will be used for analyzing the mechanisms underlying the interaction and its impact on cellular functions in vitro and tumor progression in vivo.
In specific aim 2, the effect of different p53 mutations on tumor growth and metastasis will be analyzed in vivo. The clinical relevance of these studies will be evaluated using well-characterized patient derived xenografts (PDXs); patient tumor-derived organoids (PDOs); and patient tumor tissues with linked clinical database (specific aim 3). The contribution of this research is expected to be better understanding of the mechanisms by which ER?-p53-p73 axis in the context of different p53 mutations affects the disease progression and therapeutic response. The proposal is innovative because analyzing the differential effects of different p53 mutations as part of an integrated ER?-mutant p53-p73 signaling axis is a departure from the status quo and has the potential of developing novel therapeutic strategies against TNBC.
The proposed research is relevant to public health because the project is expected to have a positive impact by providing information on the mechanisms by which tumor suppressor p53 status determines estrogen receptor beta (ER?) function in breast cancer, especially triple negative breast cancer (TNBC). There is an urgent need to identify novel targets and develop new therapies against TNBC because targeted therapies are not currently available against these aggressive cancers, and the remaining option, chemotherapy, is also relatively ineffective. The proposed study will facilitate better understanding of ER? and p53 signaling crosstalk and has the potential to facilitate developing new therapeutic strategies against TNBC, and therefore, is relevant to the part of NIH's mission that pertains to research on causes, diagnosis, prevention, and cure of human diseases.
