Human breast cancer cell lines contain stem-like cells that self-renew, give rise to phenotypically diverse progeny and survive chemotherapy

TLDR

Phenotypic and functional differences between breast cancer stem cells and bulk tumor cells are difficult to study using only primary tumor tissue. The study tests whether breast cancer cell lines harbor hierarchical differentiation programs analogous to those in primary tumors. Eight breast cell lines were profiled by flow cytometry for CD44, CD24, and ESA, and subjected to limiting‑dilution orthotopic injections, colony‑forming, reconstitution, tumorsphere assays, BrdU pulse‑chase, and chemotherapy with paclitaxel and 5‑fluorouracil to assess self‑renewal, differentiation, label retention, and drug resistance. CD44⁺/CD24⁻/ESA⁺ cells, though not correlated with tumorigenicity, can form tumors from as few as 100 cells, self‑renew, reconstitute the parental line, retain BrdU, and preferentially survive chemotherapy, validating cell lines as models for targeting cancer stem cells.

Abstract

Abstract Introduction The phenotypic and functional differences between cells that initiate human breast tumors (cancer stem cells) and those that comprise the tumor bulk are difficult to study using only primary tumor tissue. We embarked on this study hypothesizing that breast cancer cell lines would contain analogous hierarchical differentiation programs to those found in primary breast tumors. Methods Eight human breast cell lines (human mammary epithelial cells, and MCF10A, MCF7, SUM149, SUM159, SUM1315 and MDA.MB.231 cells) were analyzed using flow cytometry for CD44, CD24, and epithelial-specific antigen (ESA) expression. Limiting dilution orthotopic injections were used to evaluate tumor initiation, while serial colony-forming unit, reconstitution and tumorsphere assays were performed to assess self-renewal and differentiation. Pulse-chase bromodeoxyuridine (5-bromo-2-deoxyuridine [BrdU]) labeling was used to examine cell cycle and label-retention of cancer stem cells. Cells were treated with paclitaxol and 5-fluorouracil to test selective resistance to chemotherapy, and gene expression profile after chemotherapy were examined. Results The percentage of CD44 + /CD24 - cells within cell lines does not correlate with tumorigenicity, but as few as 100 cells can form tumors when sorted for CD44 + /CD24 -/low /ESA + . Furthermore, CD44 + /CD24 - /ESA + cells can self-renew, reconstitute the parental cell line, retain BrdU label, and preferentially survive chemotherapy. Conclusion These data validate the use of cancer cell lines as models for the development and testing of novel therapeutics aimed at eradicating cancer stem cells.