Near-infrared imaging system for the detection of sentinel lymph node using indocyanine green and pullulan nanoparticle fluorescent tracers in large animal models

Abstract

Introduction: The near-infrared (NIR) imaging system has been applied for the sentinel lymph node biopsy with a potential to overcome the limitation of current techniques. The purpose of this study was to design the NIR tracers and the large animal models, to develop and assess the NIR tracers for the clinical application in sentinel lymph node mapping in human malignant tumors. Methods: A new near-infrared-emitting polymer nanogel (NIR-PNG) was developed by conjugating IRDye800 organic dye to biodegradable pullulan-cholesterol polymer nanogels. Breast cancer, cutaneous malignancy, small intestine, and gastric cancer models were prepared using 40kgs of female pigs and 30kgs of female dogs. Indocyanine green (ICG), ICG/poly ɣ-glutamic acid(PGA) complex, ICG/hyaluronic acid(HA) mixture, and IRDye900-conjugated pullulan-cholesterol nanoprobe (NIR-PNG) were examined in different concentrations and dosages to assess the characteristics of tracers such as sensitivity, pattern of dispersion, and retention time using NIR imaging system. Results: The NIR-PNG nanoprobes had about 30nms diameter. It was more photostable and had higher signal intensity and longer retention time in the lymph node compared with those of IRDye800-free dye when injected into the front paw of mice. Breast cancer model in pigs were not a proper model because of unpredictable lymphatic flows. Breast and inguinal model in dogs and inguinal and small bowel model in pigs were found to be useful with highly sensitive NIR images of not only the sentinel lymph nodes but also lymphatic flows, however, they were not useful in examine the lymphatic flows after the sentinel nodes. A gastric cancer model to examine the movement of tracers from the lower body greater curvature side of the stomach via the infrapyloric nodes and to suprapancreatic nodes was useful to assess lymphatic flows after the sentinel nodes. NIR-PNG seemed to be the best candidate for NIR tracers with the highest selective to show only one sentinel lymph node and prolonged retention time, in contrast to dilute ICG and ICG/PGA complex that spread multi-directionally to numerous lymph nodes and beyond the sentinel nodes, although they could be also useful tracers to show the detailed lymphatic flows with high sensitivity. ICG and ICG/HA mixture showed applicability of endoscopic injection in marking method for early gastric cancer to localize the tumor and decide the resection line in gastrectomy Conclusions: NIR imaging system may provide superior visual sensitivity in sentinel lymph node biopsy for numerous malignancies. NIR-PNG, the best candidate, and also diluted ICG and ICG/PGA complex can be useful for sentinel node mapping of gastric cancer compared with conventional vital dye method using ICG in high concentration.

*This work about development of NIR-PNG was published in ACS Nano (Noh YW, Kong SH (co-first author), Choi DY, et al. Near-infrared emitting polymer nanogels for efficient sentinel lymph node mapping. ACS Nano. 2012 Sep 25

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