Abstract #4090: In vitro and in vivo evaluation of novel VEGF-binding proteins, sFLT01 and sFLT02

AACR Annual Meeting-- Apr 18-22, 2009; Denver, CO Vascular endothelial growth factor (VEGF) is essential for promoting the growth of blood vessels. Anti-angiogenic agents targeting VEGF or its receptors have shown clinical value in combination with chemotherapy. In the current study we have compared two novel engineered soluble hybrid forms of VEGFR1, sFLT01 (80 KD) and sFLT02 (52 KD). sFLT01 and sFLT02 bind to both human and murine VEGF. sFLT01 and sFLT02 were evaluated in vitro in VEGF binding assays whereby the free or unbound VEGF is quantified by ELISA and the activity of sFLT01 and sFLT02 were compared in endothelial cell-based proliferation assays. sFLT01 and sFLT02 were also evaluated for anti-tumor activity in vivo in the A673 sarcoma xenograft model. sFLT01 and sFLT02 were delivered by intraperitoneal injection twice a week at doses that were matched on a molar basis, ranging from 3-5 mg/kg. Microvessel density (MVD) and vessel integrity were analyzed by immunohistochemical methods with antibodies against CD31 for endothelial cells and against NG2 or smooth muscle actin for pericytes. The results indicate that sFLT01 and sFLT02 bound to human VEGF with affinities comparable to other known high affinity VEGF binders and equally inhibited VEGF-driven HUVEC proliferation with IC90 values of approximately 1-3 nM. In vivo however, when dosed at equivalent molar amounts, sFLT01 was more effective than sFLT02. Subcutaneous A673 tumors were inhibited more effectively with sFLT01 than with sFLT02. sFLT01 was also efficacious when treatment began when the A673 tumors were larger, 400-500 mm3 in size, whereas sFLT02 was not. MVD was reduced by 10-fold in the A673 model after three doses of sFLT01 compared to control. The blood vessels of these tumors were more immature demonstrating less pericyte involvement. The effect of sFLT02 on MVD was less pronounced. The discrepancy between the in vitro and in vivo performance of the two molecules may be due to the shorter half-life of the smaller size sFLT02 (4.1 hrs vs. 6.3 days for sFLT01) and it may be that higher, more frequent doses are required to achieve similar efficacy. sFLT01 in combination with cyclophosphamide prolonged survival compared with either agent delivered as a single agent in the A673 tumor model. Direct comparisons between sFLT01 and sFLT02 in combination with cyclophosphamide are ongoing. Citation Information: In: Proc Am Assoc Cancer Res; 2009 Apr 18-22; Denver, CO. Philadelphia (PA): AACR; 2009. Abstract nr 4090.