Estradiol (E2) plays a key role in breast cancer progression. Most breast cancer recurrences express the estrogen receptor (ER), but nearly 50% of patients are resistant to anti-estrogen therapy. Novel therapeutic targets of ER positive breast cancers are needed. Protumoral neutrophils expressing the lymphocyte function-associated antigen 1 (LFA-1) integrin may mediate cancer metastasis and transforming growth factor β1 (TGFβ1) is the major chemoattractant for neutrophils. The role of E2 in neutrophil-ER+ breast cancer cell interactions is unknown. We studied this in vivo using murine breast cancers in immunocompetent mice and human breast cancers in nude mice. Cell dissemination was evaluated in a zebrafish model, and microdialysis of breast cancer patients was performed. In vitro studies were done with mammosphere cultures of breast cancer cells and human neutrophils. We found that E2 increased the number of LFA-1+ neutrophils recruited to the invasive edge of mouse tumors, increased TGFβ1 secretion and promoted neutrophil infiltration in mammospheres, and induced overexpression of LFA-1 in neutrophils. In zebrafish, in the presence of E2, neutrophils increased dissemination of ER+ breast cancer cells via LFA-1 and TGFβ1, thus causing noninvasive cancer cells to be highly metastatic. Time-lapse imaging in zebrafish revealed close interactions of neutrophils with cancer cells, which drove breast cancer metastasis. We also found that extracellular TGFβ1 was overproduced in human breast cancer tissue compared to adjacent normal breast tissue. Thus, E2 can regulate immune/cancer cell interactions in tumor microenvironments. Our results indicate that extracellular TGFβ1 is a relevant target in human breast cancer.
- Received July 1, 2016.
- Revision received January 18, 2017.
- Accepted January 20, 2017.
- Copyright ©2017, American Association for Cancer Research.