Preparation of Polymer-Based Magnetic Resonance Imaging Contrast Agent to Visualize Therapeutic Angiogenesis

The objective of this study was to design and prepare a new contrast agent of magnetic resonance (MR) imaging for the evaluation of therapeutic angiogenesis. Diethylenetriaminepentaacetic acid (DTPA) residue of a chelator was chemically introduced to dextran with a molecular weight of 74,000 (dextran-DTPA). Cyclic peptide containing an arginine-glycine-aspartic acid (RGD) sequence (cyclic RGD) with an inherent affinity for the alpha(v)beta(3) integrin was then introduced to dextran-DTPA (Cyclic RGD-dextran-DTPA). Gd3+ was added to cyclic RGD-dextran-DTPA to prepare a dextran-based MR contrast agent (Cyclic RGD-dextran-DTPA-Gd). Cyclic RGD-dextran-DTPA-Gd had affinity for cells expressing the alpha(v)beta(3) integrin and showed a higher longitudinal relaxivity compared with DTPA-Gd of an MR contrast agent clinically used. Right femoral, external iliac, and deep femoral and circumflex arteries and veins were surgically ligated to prepare a mouse model of hindlimb ischemia. A laser Doppler analysis and histological evaluation confirmed that hindlimb ischemia healed naturally and was accompanied by angiogenesis, while alpha(v)beta(3) integrin was expressed in the ischemic-angiogenic region without any treatment. Mice at 7 days after vascular ligation were used as an angiogenesis model. When intravenously injected into mice with hindlimb ischemia, cyclic RGD-dextran-DTPA accumulated in the ischemic-angiogenic region and showed the MR ability to detect the ischemic-angiogenic region. It is concluded that cyclic RGD-dextran-DTPA-Gd is a promising material for evaluation of therapeutic angiogenesis.