Molecular imaging of tumor angiogenesis with VEGFR2 targeting microbubbles in colon cancer bearing nude mice

Objective: To evaluate the effect of tumor neovascularization imaging in a nude mouse model of colon cancer by contrast ultrasound molecular imaging (UMI) of VEGF receptor 2 (kinase insert domain receptor, KDR). Methods: Targeted microbubbles (MBt) were built by conjugating K237, a small peptide with high affinity for KDR, to liposome microbubbles through a biotin-avidin bridge. Control microbubbles (MBc) with control peptide were prepared by the same method. Nude mice models of LS174T human colon cancer were established. MBt and MBc were injected intravenously in twelve mice in random order with an interval of 30 min. MBt were injected in another six mice after K237-peptide blocking. UMI was performed in all mice at 5 min postinjection to observe the imaging difference and measure the video intensity (Ⅵ) of tumor tissues in different groups. One-way analysis of variance and the least significant difference t test were performed to analyze the difference of tumor Ⅵ in the groups with MBt, MBc and K237 blocking. Immunohistochemistry was applied to detect the expression and distribution of KDR in tumor tissue and adjacent tumor tissues. Results: K237 peptide was successfully conjugated to the surface of microbubbles through biotin-avidin mediation. Ultrasound imaging signal of the tumor was high in the MBt group, while there were no significant enhancement in the groups of K237 blocking and MBc. The Ⅵ in MBt, MBc and K237 blocking groups was significantly different (F=39.130, P<0.01). There was a significant difference of Ⅵ in the MBt group compared to the MBc group (30.18 ± 9.56 vs 8.28 ± 4.74, t=6.91, P<0.01). In the K237 blocking group Ⅵ was significantly lower than that in the MBt group (9.23 ± 3.44 vs 30.18 ± 9.56, t=4.91, P<0.01). Immunohistochemistry results showed that KDR was highly expressed in tumor tissue. Conclusions: KDR-targeting liposome contrast microbubbles may specifically and efficiently link to tumor vascular endothelial cells in vivo. Thus it may be used for UMI of tumor angiogenesis. (authors)