Figure 2

The combination of SC236 with VEGF inhibition alters vascular assembly as compared to either treatment alone. We performed immunohistochemistry for platelet endothelial cell adhesion molecule-1 to assess changes in endothelial vessels (PECAM; Figure 2, left column). Control tumors displayed abundant PECAM(+) neovasculature, with multiple fine branches (arrows). Morphologically, both SC236-treated and BV-treated tumors displayed reduction of branching. In tumors treated with both BV and SC236, surviving endothelial vessels were discontinuous, with irregularly spaced, moderately dilated segments, and near ablation of branches. Mean vascular density was decreased in all treated groups as compared to controls (Figure 2B). To examine differentiated VMC, we immunostained for α-smooth muscle actin (αSMA, Figure 2 right column). Quantitation of αSMA immunopositive vasculature demonstrated significant reduction only in BV+SC236 treated tumors as compared to controls (Figure 2C), potentially consistent with a combined effect on microvessel density and disrupted mural cell coverage of vessels as previously reported [14]. PECAM- and αSMA-immunostaining also suggested that SC236-treated xenografts were marked by erratically dilated larger vessels (arrowheads, Figure 2A). To quantify this morphologic change, we measured shifts in distribution of the inscribed radius of mural cell-covered vasculature (Figure 2D, using a previously described method [22]). SC236-treated tumor vasculature demonstrated a significant increase in the vessels with inscribed radius > 10 μm.