Metabolizable Near-Infrared-II Nanoprobes for Dynamic Imaging of Deep-Seated Tumor-Associated Macrophages in Pancreatic Cancer

Tumor-associated macrophages (TAMs) play a crucial part in cancer evolution. Dynamic imaging of TAMs is of great significance for treatment outcome evaluation and precision tumor therapy. Currently, most fluorescence nanoprobes tend to accumulate in the liver and are difficult to metabolize, which leads to strong background signals and inadequate imaging quality of TAMs nearby the liver such as pancreatic cancer. Herein, we aim to develop metabolizable dextran-indocyanine green (DN-ICG) nanoprobes in the second near-infrared window (NIR-II, 1 000-1 700 nm) for dynamic imaging of TAMs in pancreatic cancer. Compared to free ICG, the NIR-II fluorescence intensity of DN-ICG nanoprobes increased by 279% with significantly improved stability. We demonstrated that DN-ICG nanoprobes could specifically target TAMs through the interaction of dextran with specific ICAM-3-grabbing nonintegrin related 1 (SIGN-R1), which were highly expressed in TAMs. Subsequently, DN-ICG nanoprobes gradually metabolized in the liver yet remained in pancreatic tumor stroma in mouse models, achieving a high signal-to-background ratio (SBR = 7) in deep tissue (∼0.5 cm) NIR-II imaging of TAMs. Moreover, DN-ICG nanoprobes could detect dynamic changes of TAMs induced by low-dose radiotherapy and zoledronic acid. Therefore, the highly biocompatible and biodegradable DN-ICG nanoprobes harbor great potential for precision therapy in pancreatic cancer.