AKR1B1 promotes tumorsphere formation and increases CSC population. (A–C) Tumorsphere formation of MDA-MB231 and SUM159 cells with stable empty vector (Ctr) or knockdown of AKR1B1 expression (A) and MDA-MB231 and SUM159 cells treated with or without 20 µM epalrestat (Epa; B), as well as T47D cells with stable empty vector or AKR1B1 expression (C) was measured. Data are presented as a percentage of empty vector cell lines. *, P < 0.01 by Student’s t test. (D–H) Populations of CSCs (CD44^high/CD24^low) were analyzed by flow cytometry in MDA-MB231 and SUM159 cells with stable empty vector or knockdown of AKR1B1 expression (D) and MDA-MB231 and SUM159 cells treated with or without 20 µM epalrestat (E and F), as well as T47D cells with stable empty vector or AKR1B1 expression (G and H). Representative images are shown in E and G. Data are presented as a percentage of empty vector cell lines. *, P < 0.05 by Student’s t test. Data are mean ± SD in three separate experiments.