Breast cancer (BrCa) is the second leading cause of cancer related deaths in women and the majority of mortality is due to metastatic BrCa disease. Although our understanding and treatment of advanced breast cancer has improved, the 5-year survival rate remains at a dismal 22%. Two-thirds of all BrCa is positive for estrogen receptor (ESR1, ER), which can be exploited by targeted anti-estrogen therapeutics. Unfortunately, 25% of ER-positive primary disease patients and nearly all ER-positive metastatic BrCa patients will go on to develop treatment refractory disease to these targeted regimens. ER is a prominent component of cancer progression; thus, it is imperative to understand how advance ER-positive patients confer treatment resistance. The Lee-Oesterreich lab recently discovered a novel genomic alternation to ESR1, an in-frame translocation event creating a fusion gene product. A subsequent panel of ESR1 fusions have been discovered and these ESR1 fusions are estimated to be prevalent in at least 1-5% of advanced ER-positive BrCa disease. Importantly, these fusions were identified in patients who developed resistance to hormonal therapy. The functional role of these genomic fusion genes requires further investigation. We will investigate how ESR1 fusions influence cellular proliferation, treatment insensitivity and migration/invasion. Our preliminary data of a fusion stably expressed in a BrCa cell line exhibited enhanced growth and lack of response to hormonal treatment. We will also analyze transcriptional and mechanistic changes invoked by ESR1 fusion expression. Preliminary data of ESR1 fusions transiently transfected into a BrCa cell line exhibited enhanced ER activation compared to parental and wildtype ER expressing cells. Direct mutagenesis of the fusion partner will better elucidate the contribution of ESR1 or the fusion partner to global cellular changes. Lastly, we will study the prevalence of the fusion genes in metastatic refractory disease to determine clinical significance. We will analyze exosomal RNA isolated from patient blood draws to detect presence of known and novel fusions. This proposal will ultimately 1) better analyze the metastatic properties of ESR1 fusions both in the presence and absence of treatment, 2) gain a greater appreciation of ESR1 fusion influence on the transcriptome and cistrome and lastly 3) define fusion prevalence in advance BrCa and detection of novel fusions over the course of a controlled clinical trial utilizing anti-estrogen treatment. Successful completion of these Aims will help inform clinicians and researchers the clinical relevance of ESR1 fusions and if these genomic alternations can serve as biomarkers for identifying treatment resistant breast cancer and rationale for alternative treatment strategies.

Public Health Relevance

Breast cancer is the most frequently diagnosed women?s cancer (271,270 estimated new cases diagnosed in 2019) and even in the wake of novel treatment regimens and revised screening criteria, it remains a leading cause of cancer death among women, predominately due to malignant transformation and treatment resistance. Analyzing patient blood samples for genomic disturbances, such as gene fusion products involving the estrogen receptor, would be both more efficient and accessible for patients at risk of metastases and for monitoring development of treatment resistance in those already diagnosed with late-stage breast cancer. The proposed study will utilize molecular techniques, breast cancer models, including a patient derived xenograft, and clinical samples to examine the functionality, structure-function relationship and prevalence of gene fusions as well as analyze the feasibility of extracting gene fusion products from liquid biopsy isolated exosomal RNA that could ultimately lead to improved diagnosis, outcomes and treatment guidance.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Individual Predoctoral NRSA for M.D./Ph.D. Fellowships (ADAMHA) (F30)
Project #
1F30CA250167-01
Application #
9990043
Study Section
Special Emphasis Panel (ZRG1)
Program Officer
Damico, Mark W
Project Start
2020-04-01
Project End
2025-03-31
Budget Start
2020-04-01
Budget End
2021-03-31
Support Year
1
Fiscal Year
2020
Total Cost
Indirect Cost
Name
University of Pittsburgh
Department
Biology
Type
Schools of Medicine
DUNS #
004514360
City
Pittsburgh
State
PA
Country
United States
Zip Code
15260