Breast cancer stem cells in HER2-negative breast cancer cells contribute to HER2-mediated radioresistance and molecular subtype conversion: clinical implications for serum HER2 in recurrent HER2-negative breast cancer

Abstract

Although it has been proposed that the beneficial effect of HER2-targeted therapy in HER2-negative breast cancer is associated with the molecular subtype conversion, the underlying mechanism and the clinical biomarkers are unclear. Our study showed that breast cancer stem cells (BCSCs) mediated HER2 subtype conversion and radioresistance in HER2-negative breast cancer cells and evaluated serum HER2 as a clinical biomarker for HER2 subtype conversion. We found that the CD44+/CD24–/low BCSCs from HER2-negative breast cancer MCF7 cells overexpressed HER2 and EGFR and showed the radioresistant phenotype. In addition, we showed that trastuzumab treatment sensitized the radioresistant phenotype of the CD44+/CD24–/low cells with decreased levels of HER2 and EGFR, which suggested that HER2-targeted therapy in HER2-negative breast cancer could be useful for targeting BCSCs that overexpress HER2/EGFR. Importantly, our clinical data showed that serial serum HER2 measurement synchronously reflected the disease relapse and the change in tumor burden in some patients who were initially diagnosed as HER2-negative breast cancer, which indicated that serum HER2 could be a clinical biomarker for the evaluation of HER2 subtype conversion in patients with recurrent HER2-negative breast cancer. Therefore, our data have provided in vitro and in vivo evidence for the molecular subtype conversion of HER2-negative breast cancer.

MASTL inhibition promotes mitotic catastrophe through PP2A activation to inhibit cancer growth and radioresistance in breast cancer cells

“…To further examine the role of MASTL in the radioresistance associated with breast cancer stem cells (BCSCs), we sorted BCSCs from MCF7 cells by using CD44 high /CD24 low , a marker for BCSCs [ 27 ]. We have previously demonstrated that CD44 high /CD24 low MCF7 cells are breast cancer stem cells with a radioresistant phenotype [ 19 ]. MASTL depletion significantly reduced the colony formation of CD44 high /CD24 low MCF7 cells in response to irradiation (Fig.…”

“…All media types were supplemented with 10% fetal bovine serum (Corning) and 1% penicillin/streptomycin, and maintained in a humidified 5% CO 2 incubator at 37 °C. The radioresistant CD44 high /CD24 low MCF7 cells were established by using a previously described method [ 19 , 20 ]. Briefly, CD44 + /CD24 − subpopulations from MCF7 cells were isolated by their surface markers using a FACS Aria II (BD Biosciences, San Diego, CA).…”

MKI-1, a Novel Small-Molecule Inhibitor of MASTL, Exerts Antitumor and Radiosensitizer Activities Through PP2A Activation in Breast Cancer

“…Cell survival after irradiation was determined by using a clonogenic assay (27). The sphere formation assay was performed as previously reported (14,26).…”

Predicting Radiation Resistance in Breast Cancer with Expression Status of Phosphorylated S6K1

“…2a). Furthermore, we found that CD44 high /CD24 low MCF7 cells, a breast cancer stem cell line with a radioresistant phenotype 24,25 ( Supplementary Fig. S2), expressed higher levels of p-S6K1 compared to those of control MCF7 cells ( Fig.…”

“…All media were supplemented with 10% foetal bovine serum (Corning) and 1% penicillin/streptomycin, and maintained in a humidified 5% CO 2 incubator at 37 °C. Radioresistant CD44 high /CD24 low MCF7 cells were established using a previously described method 24,25 . In brief, CD44 + /CD24 − subpopulations from MCF7 cells were isolated according to their surface markers with flow cytometry using a FACS Aria II system (BD Biosciences, San Diego, CA, USA).…”