MR imaging of tumor angiogenesis using sterically stabilized Gd-DTPA liposomes targeted to CD105

Aim: To depict tumor angiogenesis via the expression of CD105 in tumor-bearing rats using Gd-DTPA liposomes targeted to CD105 (CD105-Gd-SLs) on MR imaging. Materials and methods: Three Gd-DTPA liposomal nanoparticles were prepared in our trial: liposomes entrapping Gd-DTPA (Gd-SLs), Gd-SLs conjugated to immunoglobulins (IgG-Gd-SLs) and CD105-Gd-SLs. Forty glioma-bearing rats were randomized into four groups: (a) Gd-DTPA; (b) Gd-SLs; (c) IgG-Gd-SLs; (d) CD105-Gd-SLs. Axial TIWI MRI images were collected at baseline and repeated at 5, 30, 60 and 120 min post-intravenous injection of Gd-DTPA or liposome. Enhancement features and contrast-to-noise ratio of each group were analyzed. After imaging, tumors were resected for immunohistochemistry and immunofluorescence staining to assess vascularity and angiogenesis. Results: The four groups showed different enhancement features. The enhancement area was restricted for group CD105-Gd-SLs, while diffused for the other three. The degree of enhancement over time varied: group Gd-DTPA showed an early contrast enhancement at instant after injection with a peak at 30 min and a decline to baseline values at 60 min, In group CD105-Gd-SLs, the signal intensity (SI) continuously increased over 120 min. In groups IgG-Gd-SLs and Gd-SLs the SI peaked at 60 min, followed by a minor decrease for IgG-Gd-SLs and a rapid decrease for Gd-SLs almost to baseline. Immunohistochemistry and immunofluorescence showed that the enhancement in the CD105-Gd-SLs group resulted mainly from new microvessels. While in the other three groups, mature microvessels and new microvasculature resulted in the enhancement of the tumor. Conclusion: CD105-Gd-SLs can be used to detect early tumor angiogenesis on MR images. This might provide a means to non-invasively reveal a malignant phenotype of extracerebral F98 tumor and evaluate its progression. (C) 2008 Elsevier Ireland Ltd. All rights reserved.