Regression of Human Breast Carcinoma in Nude Mice After Ad sflt Gene Therapy is Mediated by Tumor Vascular Endothelial Cell Apoptosis

Two vascular endothelial growth factor (VEGF) receptors, FLT-1 and KDR, are expressed preferentially in proliferating endothelium. There is increasing evidence that recombinant, soluble VEGF receptor domains interfering with VEGF signaling may inhibit neoangiogenesis, tumor growth and metastatic spread. We hypothesized that a soluble form of FLT-1 receptor (sFLT-1) could inhibit the growth of pre-established tumors via an anti-angiogenic mechanism. A replication-deficient adenovirus (Ad) vector carrying the sflt-1 cDNA (Ad) was used to overexpress the sFLT-1 receptor in a breast cancer animal model. MCF-7 cells, which produce VEGF, were used to establish solid tumors in the mammary fat pads of female nude mice. After six weeks tumors were injected either with Ad, or a negative control virus (AdCMV.βgal). After six months, average tumor volume in the Adinfected group (33 ± 22 mm3) was decreased by 91% relative to that of the negative control group (388 ± 94 mm3; <0.05). Moreover, 10 of 15 Adinfected tumors exhibited complete regression. The vascular density in Adinfected tumors was reduced by 50% relative to that of negative controls (<0.05), consistent with sFLT-1-mediated tumor regression through an anti-angiogenic mechanism. Moreover, cell necrosis and fibrosis associated with long-term regression of Ad–infected tumors were preceded by apoptosis of tumor vascular endothelial cells. Mice treated with Ad intratumorally showed no delay in the healing of cutaneous wounds, providing preliminary evidence that Ad-mediated sFLT-1 overexpression may be an effective anti-angiogenic therapy for cancer without the risk of systemic anti-angiogenic effects.