(A) Infantile) hemangioma tissue section stained for SOX18 (red), Ki67 (green), CD31 (orange), D2-40 (pink) and DAPI (blue) reveals the presence of SOX18 expression in a large subset of hemangioma endothelial cells (arrows). (B) Schematic representation of infantile hemangioma stem cell (HemSC) endothelial differentiation assay. VEGF-B stimulates HemSC to differentiate into hemangioma endothelial cells (HemEC). This differentiation process is inhibited by propranolol, the R(+) enantiomer of propranolol, and by SOX18 small molecule inhibitor Sm4 (all at 5 uM). (C) VEGF-B treatment of HemSC from four different infantile hemangiomas resulted in increased CDH5 (an endothelial cell marker), SOX18 and ADBR2 (β2 adrenergic receptor) mRNA. Means and standard deviations are shown. (D) The effects of SOX18 inhibitor Sm4, its scaffold aspirin as a negative control, propranolol and its purified R(+) and S(-) enantiomers on HemSC-to-HemEC differentiation from two infantile hemangioma patients. Endothelial differentiation markers, CD31 and CDH5 and hemangioma endothelial markers NOTCH1, PLXND1 and VEGFR1 under each treatment condition in four biological replicates, determined by qPCR, were standardized as described (Willems et al., 2008). Means and standard deviations are shown. Statistical analysis in 3C and 3D was done using one-way ANOVA, Fisher Tests, and two-tailed two independent sample T-Tests.