Macrophage-Targeted Indocyanine Green-Neomannosyl Human Serum Albumin for Intraoperative Sentinel Lymph Node Mapping in Porcine Esophagus

Background The sentinel lymph node (SLN) concept has been proposed to avoid unnecessary invasive LN dissection in surgery for esophageal cancer. This study evaluated a new macrophage-targeting fluorescent agent, indocyanine green-neomannosyl human serum albumin (ICG:MSA), for SLN mapping using a custom-made intraoperative color and fluorescence-merged imaging system (ICFIS) in porcine esophagus. Methods The LN targeting ability of ICG:MSA, indocyanine green-human serum albumin (ICG:HSA), and ICG was examined in vitro using the U937 differentiated monocyte cell line and in vivo in a mouse footpad model using fluorescence imaging. SLN identification in rabbit esophagus was then performed using ICG:MSA, ICG:HSA, and ICG. Finally, intraoperative SLN detection was conducted in porcine esophagus after esophagoscopic injection of ICG:MSA. Results The fluorescence signal of U937 cells treated by ICG:MSA was significantly higher than that of ICG or ICG:HSA (ICG: 1.0 ± 0.37; ICG:HSA: 3.4 ± 0.28, ICG:MSA: 6.8 ± 1.61; ICG to ICG:HSA, p = 0.03; ICG:HSA to ICG:MSA, p = 0.04; ICG to ICG:MSA, p = 0.0009). ICG:MSA was retained in popliteal LNs as long as 3 h, while ICG rapidly diffused through the entire mouse lymphatic system within 5 min. Esophageal SLN was detected within 15 min after injection of either ICG or ICG:MSA, but ICG:MSA provided more distinguishable images of LNss than ICG in rabbit esophagus. The SLN was also successfully detected in all porcine esophagus; the mean number of SLNs identified per esophagus was 1.6 ± 0.55. Conclusions ICG:MSA has more specific macrophage-targeting properties, which could overcome the limitation of the low SLN retention of ICG, and could provide more precise real-time SLN detection during esophageal cancer surgery.