Abstract:

Objective

To explore estrogen receptor (ER) expression and endocrine resistance of hormone-sensitive MCF-7 cells in normal culture or in stem cell culture in vitro.

Methods The MCF-7 cells were cultured in normal culture or in stem cell culture in vitro(suspension sphere). The proportion of CD44⁺ CD24^-/low phenotype and CD44⁺ CD24⁺phenotype cells were determined using flow cytometry (FCM). The ERa and ERβ expression was detected using immunohistochemical method. The susceptibility to tamoxifen was determined using MTT essay. The data were processed with t-test, Chi-square test and analysis of variance, respectively.

Results

In suspension culture as stem cells, the proportions of the CD44⁺CD24^-/low and CD44⁺CD24⁺ phenotype cells were (1.60±0.08)%and (30.63±4.40)% respectively, significantly higher than (0.27±0.08)% and (5.59±0.88)% in normal medium (t=-12.10,P=0.00; t=-5.58,P=0.00). The positive expressions of ERα and ERβ were 85.27% and 90.53% in normal medium, 69.43% and 73.20% in suspension culture, respectively,and the differences were statistically significant(χ²=214.64,P=0.00;χ²=303.58,P=0.00). With regards to tamoxifen sensitivity, IC₅₀ was(9.82±0.31)μmol/L in normal medium, and (16.46±0.50) μmol/L in suspension culture. After the second induced differentiation, the positive expression of ER was not upregulated and the susceptibility to tamoxifen remained low (F = 113.63, P = 0.00).

Conclusion

Suspension sphere with a high ratio of CD44⁺CD24^-/low cells and CD44⁺CD24⁺cells can be incubated in stem cell culture in vitro, with higher positive expression of ER and lower sensitivity to tamoxifen, which may be attributed to endocrine resistance.

Key words: breast neoplasms, stem cells, estrogen receptor α, estrogen receptor β, CD44⁺CD24^-/low cells