To investigate the effect of miRNA-3178 and genistein on chemosensitivity of triple negative breast cancer MDA-MB-231 cells.

(1) MDA-MB-231 cells were treated by doxorubicin (0.125, 0.250, 0.500 μmol/L) and paclitaxel (0.20, 0.40, 0.80 μmol/L) alone or combined with genistein (2.5 μmol/L). MTT assay was performed to detect the cell growth. IC₅₀ was also determined. (2) Using small interfering RNA (siRNA) technique, MDA-MB-231 cells were transfected with small interference fragment miRNA-3178 (miRNA-3178 siRNA group), and the cells transfected with nonsense siRNA served as negative control. The real-time PCR was used to detect the interference results. The miRNA-3178 siRNA group and negative control group were treated with different concentrations of doxorubicin or paclitaxel respectively to detect the chemosensitivity of cells between two groups. (3) MDA-MB-231 cells were treated with 0.250 μmol doxorubicin, 0.40 μmol/L paclitaxel and 2.5 μmol/L genistein, respectively, and the expression of miRNA-3178 in all treated and untreated groups was detected by real-time PCR. The t test was used to compare the growth inhibition rate of cells and miRNA-3178 expression between two groups. One-way analysis of variance was used to compare the expression of miRNA-3178 among multiple groups. The LSD method was used for pairwise comparison.

(1) After being treated with 0.125, 0.250, 0.500 μmol/L doxorubicin for 48 h, the growth inhibition rate of MDA-MB-231 cells was 16.7%±0.4%, 25.9%±0.1% and 44.9%±0.1%, respectively. If combined with 2.5 μmol/L genistein, the growth inhibition rate was 29.8%±0.3%, 45.3%±0.4% and 68.5%±0.4%, respectively, indicating a significant difference (t=38.12, 61.57, 82.70, P<0.001). After MDA-MB-231 cells were treated with 0.20, 0.40, 0.80 μmol/L paclitaxel for 48 h, the growth inhibition rate was 15.3%±0.3%, 27.9%±0.5% and 39.2%±0.1% respectively. If combined with 2.5 μmol/L genistein, the growth inhibition rate was 32.7%±0.7%, 48.3%±0.1% and 63.3%±0.2%, respectively, indicating a significant difference (t=34.41, 58.63, 213.91, all P<0.001). The IC₅₀ was 1.230 μmol/L when MDA-MB-231 cells were treated with doxorubicin alone, and decreased to 0.440 μmol/L if combined with 2.5 μmol/L genistein. The IC₅₀ was 0.64 μmol/L when MDA-MB-231 cells were treated with paclitaxel alone, and decreased to 0.27 μmol/L if combined with 2.5 μmol/L genistein. (2) Under different concentrations of doxorubicin (0.125, 0.250, 0.500 μmol/L) or paclitaxel (0.20, 0.40, 0.80 μmol/L), the growth inhibition rate of MDA-MB-231 cells in miRNA-3178 siRNA group was significantly lower than that in negative control group (transfected with non-sense siRNA) (12.3%±0.6% vs 16.7% ± 0.4%, 21.2% ± 0.9% vs 25.9% ± 0.1%, 27.2% ± 0.9% vs 44.9% ± 0.1%, t=8.99, 7.33, 27.34, all P<0.050; 8.8%±0.5% vs 15.3%±0.3%, 13.4%±1.1% vs 27.9%±0.5%, 20.2%±0.9% vs 39.2%±0.1%, t=16.80, 17.57, 30.48, all P<0.001). (3) The difference in miRNA-3178 expression was statistically significant between treatment groups and untreated groups (F=66.57, P< 0.001). The results of pairwise comparison showed that compared with untreated group, the expression of miRNA-3178 in MDA-MB-231 cells treated with 0.40 μmol/L paclitaxel and 0.250 μmol/L doxorubicin treatment group presented no significant difference (P=0.611, 0.235), and the combination with 2.5 μmol/L genistein significantly increased the expression of miRNA-3178 in MDA-MB-231 cells (11.10±0.33 vs 5.77±0.21, P<0.010).

miRNA-3178 combined with genistein may increase the chemosensitivity of triple negative breast cancer MDA-MB-231 cells to paclitaxel and doxorubicin.