Co-Oncogenic Role of ECD in HER2-Driven Breast Cancer

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PROJECT SUMMARY/ABSTRACT Breast cancer (BC) is a genetically and clinically heterogeneous disease and molecular profiling has identified five major subtypes of BC. One subtype, the HER2+ (~20%) BC is driven by the receptor tyrosine kinase HER2. HER2-targeted therapies have significantly improved the survival of these patients, however, most advanced stage patients are incurable, and acquisition of resistance is universal. Recently, it has been shown that about 30% of HER2+ BC patients have activating mutations in PIK3CA. HER2+/PIK3CA double-transgenic mouse tumors are completely resistant to trastuzumab combination therapy but adding a PI3K inhibitor reversed the resistance. Therefore, elucidating additional co-oncogenic pathways that collaborate with HER2 to facilitate and/or enhance HER2-driven oncogenesis, is likely to broaden the potential to design combinatorial therapeutic approaches against advanced HER2-driven BC and to forestall and/or overcome resistance to existing therapies. This R03 proposal focuses on demonstrating a novel co-oncogenic role of ECD (Ecdysoneless) in HER2+ BC. ECD protein and mRNA is overexpressed in BC, particularly in HER2+, correlating with poor prognostic markers and shorter disease-free and overall survival. To directly address the role of ECD in BC, we generated mice with a mammary epithelium-targeted inducible (Tet-off) human ECD transgene (ECDTg). Significantly, 85% of ECDTg mice exhibit mammary hyperplasia in 5-6 months, and 33% show heterogeneous tumors within 18- 24 months. Importantly, 85% of the remaining mice show pre-neoplastic lesions. Significantly, ECDTg tumors showed increased c-MYC and β-catenin expression. Functionally, decrease in ECD levels decreased glucose uptake, suggesting a potential link of ECD and metabolism. Lack of HER2 overexpression in ECDTg tumors dictates the need to cross ECDTg model with huHER2Tg mice that recapitulates the co-overexpression of ECD seen in HER2+ BC patients. Thus, the rationale for studies proposed in this R03 grant application is very strong. Based on these data, we hypothesize that ECD co-overexpression in HER2-driven oncogenesis promotes further tumorigenesis and generating ECD;huHER2 double transgenic mice will test this hypothesis. Further characterization of the ECDTg vs. ECD;huHER2Tg models will help delineate the molecular mechanism of poor outcomes in patients overexpressing both ECD and HER2. Aim 1 will examine the co-oncogenic role of ECD in HER2-driven breast cancer using mouse mammary gland-targeted ECD transgene overexpression. Aim 2 will use unbiased approaches (RNA-seq and metabolomics) to delineate the mechanism of ECD- and HER2- dependent oncogenesis in BC. Validation of our hypothesis will help us understand how ECD overexpression promotes HER2-driven BC with worse outcomes. A validated ECD;huHER2Tg model will provide an invaluable tool to understand the mechanistic basis of their co-oncogenesis and future testing of novel therapeutics against HER2+/ECD-overexpressing BC and to address therapy resistance. Success of our studies may also open broader avenues for other malignancies where ECD overexpression is associated with tumor progression.