A mouse model for triple-negative breast cancer tumor-initiating cells (TNBC-TICs) exhibits similar aggressive phenotype to the human disease
1 Department of Pathology, Scott & White Memorial Hospital and Clinic and the Texas A&M Health Science Center, College of Medicine, Temple, TX 76504, USA
2 Department of Medicine, Scott & White Memorial Hospital and Clinic and the Texas A&M Health Science Center, College of Medicine, Temple, TX 76508, USA
3 Department of Surgery, Makerere University, P. O. Box 7072, Kampala, Uganda
4 Department of Radiation Oncology, MD Anderson Cancer Center, 1515 Holcombe Boulevard, Houston, TX, USA
5 Division of Investigative Pathology, Scott & White Memorial Hospital and Clinic and The Texas A&M Health Science Center College of Medicine, 1901 South 1st Street, Building 205, Temple, TX 76504, USA
BMC Cancer 2012, 12:120 doi:10.1186/1471-2407-12-120Published: 27 March 2012
Triple-negative breast cancer (TNBC) exhibit characteristics quite distinct from other kinds of breast cancer, presenting as an aggressive disease--recurring and metastasizing more often than other kinds of breast cancer, without tumor-specific treatment options and accounts for 15% of all types of breast cancer with higher percentages in premenopausal African-American and Hispanic women. The reason for this aggressive phenotype is currently the focus of intensive research. However, progress is hampered by the lack of suitable TNBC cell model systems.
To understand the mechanistic basis for the aggressiveness of TNBC, we produced a stable TNBC cell line by sorting for 4T1 cells that do not express the estrogen receptor (ER), progesterone receptor (PgR) or the gene for human epidermal growth factor receptor 2 (HER2). As a control, we produced a stable triple-positive breast cancer (TPBC) cell line by transfecting 4T1 cells with rat HER2, ER and PgR genes and sorted for cells with high expression of ER and PgR by flow cytometry and high expression of the HER2 gene by Western blot analysis.
We isolated tumor-initiating cells (TICs) by sorting for CD24+/CD44high/ALDH1+ cells from TNBC (TNBC-TICs) and TPBC (TPBC-TICs) stable cell lines. Limiting dilution transplantation experiments revealed that CD24+/CD44high/ALDH1+ cells derived from TNBC (TNBC-TICs) and TPBC (TPBC-TICs) were significantly more effective at repopulating the mammary glands of naïve female BALB/c mice than CD24-/CD44-/ALDH1- cells. Implantation of the TNBC-TICs resulted in significantly larger tumors, which metastasized to the lungs to a significantly greater extent than TNBC, TPBC-TICs, TPBC or parental 4T1 cells. We further demonstrated that the increased aggressiveness of TNBC-TICs correlates with the presence of high levels of mouse twenty-five kDa heat shock protein (Hsp25/mouse HspB1) and seventy-two kDa heat shock protein (Hsp72/HspA1A).
Taken together, we have developed a TNBC-TICs model system based on the 4T1 cells which is a very useful metastasis model with the advantage of being able to be transplanted into immune competent recipients. Our data demonstrates that the TNBC-TICs model system could be a useful tool for studies on the pathogenesis and therapeutic treatment for TNBC.