Decrease in tumor initiation and lung metastases in MDA-MB-231 xenografts. (A) Tumor volume of MDA-MB-231 breast xenografts (n = 5 per group) after daily injection of L-NAME (80 mg/kg, intraperitoneal). (B) Primary and secondary mammosphere of cancer cells isolated from tumor tissue. (C) Luminescence of MDA-MB-231 L/G tumor cells in lungs of vehicle- and L-NAME-treated mice. (D) Tumor-initiating capacity of tumor cells (limiting dilution assay). Results were normalized to vehicle. Data are presented as mean ± standard error of the mean. *P <0.05, **P <0.01, ***P <0.001. L-NAME, N5-[imino(nitroamino)methyl]-L-ornithine methyl ester; MSFE, mammosphere-forming efficiency.