Women with estrogen receptor (ER)-positive breast cancer are treated with hormonal agents targeting the ER, and can remain free of disease for many years. However, resistance to treatment eventually develops, and these women will thus suffer a recurrence of their cancer. In our current grant period, we explored our proposal that the key to the successful treatment of these women is to focus on identifying novel mechanisms of resistance, using metastatic tumors resistant to hormone therapy in which tumor evolution and clonal selection for resistance have already occurred. Using this innovative approach, we have already discovered several new individual resistance mechanisms, including reduced levels of two key negative regulators of resistance - Rho guanine dissociation inhibitor alpha (Rho GDIa) and the growth factor receptor scaffolding protein SLC9A3R1, both of which enhance activation of ERa via its phosphorylation. We will focus on these two resistance mechanisms, and determine their effect on cells with wild-type ERa as well as two specific ERa mutations (lysine 303 and tyrosine 537) that we were the first to discover in breast tumors, and which significantly affect hormone response. We will exploit these resistance mechanisms to exert more precise control over resistant tumor growth, combining hormonal and targeted therapy along with knowledge of the activation status of the key ERa growth pathway. Therefore, we now propose to validate specific resistance mechanisms associated with losses of Rho GDIa or SLC9A3R1 and their effects on ERa, to target these specific mechanisms, and to translate these findings to pinpoint predictive clinical biomarkers and potential treatment targets.
Our Aims are: (1) To target SLC9A3R1 and Rho GDIa resistance mechanisms to restore hormone sensitivity and response to targeted therapies;(2) To determine how SLC9A3R1 and Rho GDIa.resistance pathways pact on mutant ERa function;and (3) To validate selected candidates from these two pathways for their ability to predict resistance to targeted hormone and biologic therapies, using our extensive retrospective clinical breast tumor resources. This work should lead to extended effective suppression of recurrence for the large numbers of women with ER-positive breast cancer who now daily fear reappearance of their disease in spite of continued endocrine treatment.

Public Health Relevance

Over 135,000 women per year are diagnosed with ER-positive breast cancer and hormonal agents are their best targeted option, however, many women will progress in spite of this therapy. We propose to identify novel mechanisms of hormone resistance, and utilize these as novel therapeutic biologic targets and as predictive biomarkers for patients receiving treatment with hormonal agents.

National Institute of Health (NIH)
National Cancer Institute (NCI)
Research Project (R01)
Project #
Application #
Study Section
Special Emphasis Panel (ZRG1-BMCT-C (01))
Program Officer
Sathyamoorthy, Neeraja
Project Start
Project End
Budget Start
Budget End
Support Year
Fiscal Year
Total Cost
Indirect Cost
Baylor College of Medicine
Internal Medicine/Medicine
Schools of Medicine
United States
Zip Code
Rimawi, Mothaffar F; De Angelis, Carmine; Contreras, Alejandro et al. (2018) Low PTEN levels and PIK3CA mutations predict resistance to neoadjuvant lapatinib and trastuzumab without chemotherapy in patients with HER2 over-expressing breast cancer. Breast Cancer Res Treat 167:731-740
Gates, Leah A; Gu, Guowei; Chen, Yue et al. (2018) Proteomic profiling identifies key coactivators utilized by mutant ER? proteins as potential new therapeutic targets. Oncogene 37:4581-4598
Carron, Emily C; Homra, Samuel; Rosenberg, Jillian et al. (2017) Macrophages promote the progression of premalignant mammary lesions to invasive cancer. Oncotarget 8:50731-50746
Gelsomino, Luca; Gu, Guowei; Rechoum, Yassine et al. (2016) ESR1 mutations affect anti-proliferative responses to tamoxifen through enhanced cross-talk with IGF signaling. Breast Cancer Res Treat 157:253-265
Gu, Guowei; Fuqua, Suzanne A W (2016) ESR1 Mutations in Breast Cancer: Proof-of-Concept Challenges Clinical Action. Clin Cancer Res 22:1034-6
Fuqua, Suzanne A W; Rechoum, Yassine; Gu, Guowei (2016) ESR1 Mutations in Cell-Free DNA of Breast Cancer: Predictive ""Tip of the Iceberg"". JAMA Oncol 2:1315-1316
Ciupek, Andrew; Rechoum, Yassine; Gu, Guowei et al. (2015) Androgen receptor promotes tamoxifen agonist activity by activation of EGFR in ER?-positive breast cancer. Breast Cancer Res Treat 154:225-37
Gu, Guowei; Gelsomino, Luca; Covington, Kyle R et al. (2015) Targeting thyroid hormone receptor beta in triple-negative breast cancer. Breast Cancer Res Treat 150:535-45
Rechoum, Yassine; Rovito, Daniela; Iacopetta, Domenico et al. (2014) AR collaborates with ER? in aromatase inhibitor-resistant breast cancer. Breast Cancer Res Treat 147:473-85
Fuqua, Suzanne A W; Gu, Guowei; Rechoum, Yassine (2014) Estrogen receptor (ER) ? mutations in breast cancer: hidden in plain sight. Breast Cancer Res Treat 144:11-9

Showing the most recent 10 out of 51 publications