Targeted molecular imaging of VEGF receptors overexpressed in ischemic microvasculature using chitosan-DC101 conjugates.

Expression of vascular endothelial growth factor receptors (VEGFRs) increases in ischemic muscles, and thus, VEGFR could potentially be used as marker to detect ischemia. Here, we investigated whether (99m)Tc or Cy5.5-labeled chitosan-DC101 conjugates could identify VEGFR-2 overexpressed in ischemia. To this end, chitosan was conjugated with the DC101 antibody and Cy5.5, FITC, or the HYNIC chelator for (99m)Tc-labeling. Targeting of the conjugate was evaluated in vitro and in vivo through cell-binding studies and gamma/optical imaging, respectively. A hindlimb ischemic mouse model was surgically created by femoral artery occlusion. The chitosan-DC101 conjugates exhibited VEGFR-selective cell binding properties as determined by both confocal microscopy and flow cytometry. At postoperative times of 2, 12, and 24 h, (99m)Tc or Cy5.5-labeled chitosan-DC101 conjugates were intravenously injected into the mice, and gamma/optical imaging studies were conducted at 1 or 3 h. Both the gamma and optical imaging results indicated a significantly higher uptake in ischemic muscles when compared with the contralateral nonischemic muscle. Further, semiquantitative analysis of scintigraphic imaging data revealed that the ischemic to contralateral limb ratio was 4.5 +/- 0.25 at 24 h postoperation. Western blotting analysis confirmed VEGFR expression in the ischemic muscle. In conclusion, we believe that (99m)Tc or Cy5.5-labeled chitosan-DC101 conjugates have the potential to be useful as VEGFR-2-targeted imaging agents for monitoring ischemia.