effects of L-NMMA in MDA-MB-231 xenografts. (A) Tumor volume of MDA-MB-231 breast xenografts (n = 10 per group) treated with vehicle, L-NMMA, docetaxel, and combination. (B) Illustrative images of Ki67 staining in the vehicle, L-NMMA, docetaxel, and combination groups. Original optical objective: 10×. Counterstain: hematoxylin. (C) Cell proliferation of tumor xenografts with Ki67 immunostaining. (D) Nuclear cleaved caspase-3 staining in the chemo and combo groups. (E) Primary and secondary mammosphere of breast cancer cells isolated from tumor tissue. (F) Tumor-initiating capacity of tumor cells. Results were normalized to vehicle. For proliferation and apoptosis, 1,000 cells were counted from 10 different fields, and the percentage was determined. Data are presented as mean ± standard error of the mean. *P <0.05, **P <0.01, ***P <0.001, ****P <0.0001. L-NMMA, NG-monomethyl-L-arginine; MSFE, mammosphere-forming efficiency.