TPEN decreases the volume of colon cancer xenografts in mice. A) Graph showing a significant decrease in the volume of HCT116 colon cancer xenografts in mice injected with 20 mg/kg TPEN i.p., three times per week for 22 days. Tumor volumes were significantly smaller in TPEN-treated mice as compared to saline injected (Con) starting at day 6 after treatment (mean ± SEM, n = 7-8, ** p < 0.01, significant difference with respect to Con in A). B) Histological (H & E) and immunohistochemical (Ki-67 antibody) staining in tumor xenografts. C) Apoptosis staining is revealed by using the TUNEL assay. Tissue was processed as described in “Methods.” Identical fields are shown for propidium iodide (PI) stain of all nuclei (red fluorescence), and for fluorescein-labeled detection of TUNEL-positive nuclei (green fluorescence). Representative images were taken at 400× magnification. Scale Bar, 50 μm.