P4C-2 Contrast Enhanced US for Monitoring the Effect of VEGF Trap on Melanoma Tumor Vascularity

The purpose of this study was to use contrast enhanced ultrasound (US) to monitor tumor angiogenesis in vivo in a human melanoma xenograft model and to study the effects of an anti-angiogenic therapy on tumor blood flow. Thirty nude mice (3 groups of 10) were implanted with a human melanoma cell line (DB-1). The active group received VEGF Trap (dose: 4times25 mg/kg over 2 weeks; Regeneron Pharmaceuticals, Tarrytown, NY), which binds vascular endothelial growth factor (VEGF) with high-affinity. One control group received human Fc protein and one was untreated. The contrast agent Optison (GE Healthcare, Princeton, NJ) was injected in a tail vein (dose: 0.4-0.6 ml/kg). Power Doppler (PDI) and pulse inversion harmonic imaging (PIHI regular and intermittent) was performed with an Elegra scanner (Siemens Medical Solutions, Issaquah, WA). Specimens were stained for endothelial cells (CD31), VEGF, and cyclooxygenase-2 (COX-2). Image-processing software was used to calculate fractional tumor neovascularity for US and specimens. Of the 30 mice, 11 failed for technical reasons. Linear regression showed correlations between US and percent area stained with CD31 and COX-2 (r>0.40; p<0.04). Tumor volumes were smaller (656plusmn225 mm
³
) in the active group than in the control groups (1160plusmn605 mm
³
Fc; p=0.099 & 1634plusmn1117 mm
³
untreated; p=0.009). Differences in fractional vascularity between groups were found for PIHI, intermittent-PIHI, CD31 and COX-2 (p<0.02). Even though CD31 decreased markedly from the sham control to the treated group, there was a significant increase in tumor blood flow (p<0.001). This may be due to a transient normalization of the vasculature following elimination of immature tumor vessels. In conclusion, contrast enhanced US appear to allow in vivo monitoring of the anti-angiogenic effects of VEGF Trap in the DB-1 human melanoma xenograft model. There are indications of vascular normalization following treatment with VEGF Trap. However, the current data set is limited and further investigations are required.