Biodistribution of a 153Gd-folate dendrimer, generation=4, in mice with folate-receptor positive and negative ovarian tumor xenografts

RATIONALE AND OBJECTIVES. An important characteristic of targeted contrast agents is how they are tolerated in a biologic environment and their localization in the surrounding tissues in addition to target tissue. We evaluate the biodistribution of a gadolinium Gd 153-folate-dendrinier in high affinity folate-receptor (hFR) positive and negative ovarian tumor xenografts. METHODS. The Gd-foIate-dendrinjer chelate was prepared by exchanging Gd-153 with nonradioactive gadolinium for 1 week, followed by extensive filtration. Athymic mice with hFR-positive (n = 3) and negative tumors (n = 3) were injected intravenously and counted using a whole-body counting system with a 80 to 150 keV counting window. RESULTS. The hFR-positive tumors accumulate 3.6% +/- 2.8% injected dose/g, whereas only background counts were found in hFR-negative tumors. The folate-dendrimer's tumor-to-blood ratio of 12.6, in hFR-positive tumors, was similar to5.7 to 17.0 fold better than those obtained with monoclonal antibodies targeted to the folate receptor. CONCLUSIONS. Biodistribution studies confirm previous MRI findings and show that the accumulation of the folate-dendrimer requires the expression of the hFR.