Estrogen receptor-a positive (ER?+) breast cancer (BC) represents 70-80% of newly diagnosed cases. While potentially responsive to anti-estrogens, progression of ER?+ BC to anti-estrogen refractory disease in the metastatic setting is a common occurrence. Endocrine resistance mechanisms may differ between subtypes of ER?+ BC and involve both ER?-independent and ER?-dependent forms that remain poorly understood. Prolactin (PRL) interacts with estrogens to stimulate growth of certain subtypes of ER?+ BC. At the same time, the PRL-Jak-Stat5 pathway promotes differentiation and inhibits invasive features of BC, and loss of Stat5a signaling in a subgroup of ER?+ BC is associated with anti-estrogen therapy failure. The involvement of PRL pathways in growth and progression of anti-estrogen refractory BC subtypes remains to be determined. There is a lack of preclinical human ER?+ BC models that recapitulate progression from localized mammary gland growth to distant metastasis. Xenografts of patient-derived ER?+ BC exhibit poor take rate in mice. We have discovered that murine PRL is a poor agonist and a potent antagonist for human PRL receptor (PRLr). Bovine PRL is also a poor agonist with antagonist activity for human PRLr. Laboratory human BC lines therefore have been selected for PRL-independent growth and may only represent subtype(s) of ER?+ BC. To address this problem, we generated hPRL knock-in mice in the immunodeficient Nod-Scid-IL2R? strain that express physiological levels of circulating hPRL. Remarkably, PRL-humanized mice display greatly increased take rate of patient-derived xenografts of ER?+ BC. We established a novel panel of serially transplantable ER?+ Luminal B BC lines, several of which spontaneously metastasize to lungs and liver. The distant metastases become anti-estrogen refractory despite continued expression of ER?+, but show PRL-dependence. Our long-range goal is to determine mechanisms of anti-estrogen refractoriness of BC to improve clinical management.
Aim 1 is focused on a recently identified Luminobasal subtype of ER?+ BC (ER?+/CK5+).
Aim 1 explores a distinct ER?-independent mechanism of anti-estrogen refractory BC in pre-existing ER?+ laboratory cell lines. We hypothesize that in Luminobasal BC, loss of PRL-Stat5 signaling promotes loss of ER? and subsequent anti-estrogen resistance due to defective Stat5a-driven differentiation.
Aim 2 is focused on the Luminal B BC subtype (ER?+/CK5-/Ki67high) and is centered on our new PRL-dependent patient-derived xenograft lines.
Aim 2 will test the hypothesis that in Luminal B BC, unlike in Luminobasal BC, PRL facilitates growth and survival of metastases and that PRLr-pathway targeting cooperates with anti-estrogens to eliminate distant metastases.

Public Health Relevance

Most patients who die from breast cancer are diagnosed with estrogen receptor (ER)-positive disease. Through genetic engineering of mice to better mimic the hormone environment of patients, we have established the first patient-derived ER-positive breast cancer xenograft lines that progress to therapy-resistant distant metastases. The preclinical studies of the improved tumor models may lead to better treatments.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA188575-03
Application #
9042998
Study Section
Tumor Progression and Metastasis Study Section (TPM)
Program Officer
Sathyamoorthy, Neeraja
Project Start
2015-04-01
Project End
2020-03-31
Budget Start
2017-04-01
Budget End
2018-03-31
Support Year
3
Fiscal Year
2017
Total Cost
$314,626
Indirect Cost
$71,694
Name
Medical College of Wisconsin
Department
Pathology
Type
Schools of Medicine
DUNS #
937639060
City
Milwaukee
State
WI
Country
United States
Zip Code
53226