Preparation of 99m Tc-Labeled Mannan-S-Cysteine and Effect of Molecular Size of Mannan on Its Biodistribution.

Macrophage mannose receptor (MMR/CD206) is a promising target for the detection and identification of sentinel lymph node (SLN). MMR-targeting probes have been developed using mannosylated dextran, however, impairment of efficient targeting of SLN was often caused because of retention of injection site in which macrophages and dendritic cells exist. In this study, we prepared new MMR-targeting probes from yeast mannan (85 kDa), and its bioditribution was investigated. In-vivo evaluation showed that 11.9% of injected dose of ^99m Tc-labeled mannan-S-cysteines ( ^99m Tc-MSCs) was accumulated in popliteal lymph node (the SLN in this model), however, significant level of radioactivity (approximately 80%) was remained in injection site. Interestingly, ^99m Tc-labeled low molecular weight mannan-S-cysteine mannan ( ^99m Tc-LSC) prepared from 50 and 25 kDa mannan showed a decreased specific accumulation of ^99m Tc-LSC in the popliteal lymph node, while the radioactivity at the injection site remained unchanged. These results suggest that the molecular size, or nature/shape of the sugar chain is important for the specific accumulation of ^99m Tc-MSC in popliteal lymph node.