Tumor growth enhancing effects of vascular endothelial growth factor are associated with increased nitric oxide synthase activity and inhibition of apoptosis in human breast carcinoma xenografts

Previously, we demonstrated the significance of vascular endothelial growth factor (VEGF) in promoting the growth of tetracycline-regulated human VEGF165 retroviral vector transduced T47-D breast carcinoma cells, particularly at the early stages of tumor development (Cancer Res. 57 (1997) 3924). Here, we showed histologically that the VEGF overexpressing (VEGF (+)) T47-D cells formed a distinct tumor nodule at day 11, while control cells showed no evidence of replication. The VEGF (+) tumors contained large avascular cavities at days 11 and 21, which were replaced by basement membrane-lined channels at day 30. The number of proliferating tumor cells was not significantly different between the VEGF (+) and control tumors, but the number of apoptotic cells was significantly decreased in the VEGF (+) tumors. Increased nitric oxide synthase (NOS) activity was also observed in the VEGF (+) tumors. These findings indicate that VEGF contributes to tumor growth through inhibition of apoptosis and increased NOS activity, which may be critical during pre-vascular stages of tumor development.