Paracrine Secretion of IL8 by Breast Cancer Stem Cells Promotes Therapeutic Resistance and Metastasis

Breast cancer stem cells (CSCs) play pivotal roles in cancer therapeutic failure and metastasis. However, it remains indeterminate how CSCs determine the progression of the bulk cancer cell population. Using a co-culture system in vitro and a co-implantation system in vivo, it is demonstrated herein that the breast cancer stem cell (BCSC) secretome rendered the bulk cancer cell population resistant to anti-estrogen and CDK4/6 inhibitor therapy; as well as increased the metastatic burden attributable to bulk cancer cells. Screening of BCSC secretome identified IL8 as a pivotal factor that potentiated ERa activity, endowed tamoxifen resistance and enhanced metastatic burden by regulation of bulk cancer cell behavior. Pharmacological inhibition of IL8 increased the efficacy of fulvestrant and/or palbociclib by reversing tamoxifen resistance and abrogated metastatic burden. Hence, this study has delineated the mechanism by which BCSCs determine the therapeutic response and metastatic of bulk cancer cells; and thereby suggests novel therapeutic strategies to ameliorate breast cancer outcomes. Overall design: The BCSCs isolated from flow cytometry sorting or mammospheres culturing were seeded with the regular medium in monolayer culture for 48 hours. The medium from parallelly cultured parental cells was used as the control medium. The conditioned medium was centrifuged at 4,000 g for 3 minutes and filtered with a 0.22 µm filter unit (Millipore) to deplete any cell debris.the BCSCs isolated from flow cytometry sorting or mammospheres culturing were seeded with the regular medium in monolayer culture for 48 hours. The medium from parallelly cultured parental cells was used as the control medium. The conditioned medium was centrifuged at 4,000 g for 3 minutes and filtered with a 0.22 µm filter unit (Millipore) to deplete any cell debris. The MDA-MB-231 cells were cultured with the CM derived from BCSCs or parental cells for 48 hours, and the RNA was isolated and sequenced.