Tyrosine Kinase Inhibition of Multiple Angiogenic Growth Factor Receptors Improves Survival in Mice Bearing Colon Cancer Liver Metastases by Inhibition of Endothelial Cell Survival Mechanisms

Effect of SU6668 on tumor angiogenesis in liver metastases. A, immunofluorescence staining for CD31 in tumor-bearing liver sections was used to compare the number of tumor endothelial cells between the two groups after 14 and 20 days of therapy. SU6668 therapy led to a 46.2% decrease in endothelial cell number after 20 days (∗, P = 0.015) but did not have a significant effect at 14 days (P = 0.247) compared with control mice (bars, SEM). B, immunohistochemical staining for CD31 was used to quantify tumor vessel counts. SU6668 therapy led to a 39.6% decrease in vessel counts after 20 days of therapy compared with controls (∗, P = 0.012).

Effect of SU6668 therapy on tumor cell and endothelial cell apoptosis and pericyte vessel coverage in liver metastases. A, immunofluorescence staining for TUNEL (tumor cell apoptosis) and sequential staining for CD31 and TUNEL (endothelial cell apoptosis) were performed in liver metastases after 14 and 20 days of SU6668 therapy. SU6668 therapy significantly increased the percentage of tumor cells and endothelial cells undergoing apoptosis at both time points compared with controls. Tumor cell apoptosis and endothelial cell apoptosis in the control groups after 14 and 20 days of therapy were nearly undetectable (<1%; data not shown). Tumor cell apoptosis and endothelial cell apoptosis were increased at 20 days of therapy compared with 14 days of therapy (∗, P < 0.003 and P < 0.005, respectively). Bars, SEM. B, concurrent immunofluorescence staining for CD31 (endothelial cells) and SMA (pericytes) was performed to quantify the percentage of tumor microvessels covered with pericytes. SU6668 led to a significant decrease in pericyte vessel coverage compared with the control group after both 14 and 20 days of therapy. ∗, P < 0.041; ∗∗, P = 0.002.