64Cu-cyclam-RAFT-c(-RGDfK-)4 is a novel multimeric positron emission tomography (PET) probe for αVβ3
integrin imaging. Its uptake and αVβ3 expression in
tumors showed a linear correlation. Since αVβ3
integrin is strongly expressed on activated endothelial cells during angiogenesis, we aimed to determine whether
64Cu-cyclam-RAFT-c(-RGDfK-)4 PET can be used to image
tumor angiogenesis and monitor the antiangiogenic effect of a novel multi-targeted
tyrosine kinase inhibitor,
TSU-68. Athymic nude mice bearing human
hepatocellular carcinoma HuH-7 xenografts, which expressed negligible αVβ3 levels on the
tumor cells, received
intraperitoneal injections of
TSU-68 or the vehicle for 14 days. Antiangiogenic effects were determined at the end of
therapy in terms of
64Cu-cyclam-RAFT-c(-RGDfK-)4 uptake evaluated using PET, biodistribution assay, and autoradiography, and they were compared with microvessel density (MVD) determined by CD31 immunostaining.
64Cu-cyclam-RAFT-c(-RGDfK-)4 PET enabled clear
tumor visualization by targeting the vasculature, and the biodistribution assay indicated high
tumor-to-blood and
tumor-to-muscle ratios of 31.6 ± 6.3 and 6.7 ± 1.1, respectively, 3 h after probe injection.
TSU-68 significantly slowed
tumor growth and reduced MVD; these findings were consistent with a significant reduction in the
tumor 64Cu-cyclam-RAFT-c(-RGDfK-)4 uptake. Moreover, a linear correlation was observed between
tumor MVD and the corresponding standardized uptake value (SUV) (r = 0.829, P = 0.011 for SUV(mean); r = 0.776, P = 0.024 for SUV(max)) determined by quantitative PET. Autoradiography and immunostaining showed that the distribution of intratumoral radioactivity and
tumor vasculature corresponded. We concluded that
64Cu-cyclam-RAFT-c(-RGDfK-)4 PET can be used for in vivo angiogenesis imaging and monitoring of
tumor response to antiangiogenic
therapy.