Blood vessel architecture in the peptide-treated murine neuroblastoma xenografts. (A) Endothelial cells and pericytes were visualized with green CD31 and red SMA staining respectively. Aberrant blood vessel architecture was evident at ×400 magnification in control xenografts treated with the vehicle or scrambled peptide. Peptide-treated tumors had more structurally normal, thin-walled blood vessels. (B) Quantitative analysis of blood vessel architecture. Circularity estimates roundness of an object, modified aspect ratio measures its elongation, and solidity approximates the density. On a scale from 0 to 1, where 1 is a perfect circle, all descriptors were significantly closer to 1 in the SPARC peptide-treated versus the control tumors, indicating that blood vessels are more round, less elongated and more compact. Vessel abnormality was calculated as 1 - (circularity × aspect ratio × solidity), and was significantly reduced in tumors treated with peptides FSEN and FSEC, showing that treatment induced normalization of tumor vasculature. All p-values versus PBS-treated control tumors are shown below the respective bars.