Phospho-ibuprofen inhibited the growth of breast cancer cells and xenografts. (A) Proliferation (BrdU/propidium iodide staining; upper panel) and cell cycle (propidium iodide staining; lower panel) of MCF-7 cells treated with phospho-ibuprofen (P-I) was evaluated by flow cytometry and the results were quantified (right panel). (B) Apoptosis of MCF-7 cells treated with P-I was evaluated by annexin V and propidium iodide staining. Tumor growth curves of (C) MDA-MB231 xenografts (treated with P-I 400 mg/kg/day or vehicle) and (D) MCF-7 xenografts (treated with P-I 300 mg/kg/day, liposome-encapsulated phospho-ibuprofen (Lipo-P-I) 300 mg/kg/day, or vehicle) are shown. Quantification of cell proliferation (Ki67) or cell death (TUNEL) staining is shown on the right of their representative images (200× magnification) as indicated. IC50, concentration that inhibits cell growth by 50%.