Investigation of the substituent effect of indocyanine green derivatives for lymph imaging

Fluorescence lymph imaging with indocyanine green (ICG) is widely utilized as diagnostic tool for lymphatic diseases. While this technique offers numerous advantages, the kinetics of ICG at the injection site can pose challenges for a detailed diagnosis. In this study, we synthesized various ICG derivatives possessing cationic, anionic, or uncharged substituents and examined their photochemical properties, binding affinity to human serum albumin, as well as their correlation to pharmacokinetics in mice. The introduction of different substituents not only affected certain physiochemical properties, but also impacted the pharmacokinetics within the lymph nodes. Immunofluorescence imaging suggested that the extent of uptake of the ICG derivatives by phagocytic cells may affect the retention of the contrast ratios in the lymph nodes. These findings can provide new insights in the pharmacokinetics in lymphatic tissues, which could be useful for the development of novel fluorescent agents for lymph imaging.