Studies Toward the Biological Efficacy of 99mTc-Labeled Dextran-Cysteine-Mannose ([99mTc(CO)3]DCM20) for Sentinel Lymph Node Detection

The aim of this work was to determine the potential of [sup]99mTc carbonyl-labeled dextran-cysteine-mannose (DCM20) as a mannose receptor targeting agent for sentinel lymph node (SLN) detection using biological in vitro and in vivo assays. [sup]99mTc labeling of the previously reported DCM20 ligand was carried out via the [[sup]99mTc(H[sub]2O)[sub]3(CO)[sub]3][sup]+ synthon. High-performance liquid chromatography (HPLC) showed >99% radiolabeling yield using 50 μg of the ligand. In vitro cell uptake studies performed in RAW 264.7 mouse macrophage precursor cells showed a specific uptake of the preparation. In vivo distribution and scintigraphic imaging were studied in the Wistar rat model. Appreciable uptake and retention of the radiolabeled conjugate was observed in the SLN (4.53%±0.29% at 15 minutes and 3.35%±0.72% at 180 minutes postinjection [p.i.] for 2.5 μg/animal) with a high percentage of popliteal extraction (≥98% at all time points studied), and negligible activity in other nodes as well as blood and nontarget organs. The radiolabeled conjugate also exhibited rapid clearance from the injection site (from ∼39.1% clearance at 15 minutes to ∼56.5% clearance at 180 minutes p.i.), comparable to current clinically employed agents for SLN detection. These results suggest that [[sup]99mTc(CO)[sub]3]DCM20 could be a potentially useful receptor-based SLN detection agent.