Tumor-Trackable NIRF Nanoprobes for Gastric Cancer Metastasis

Gastric cancer (GC) is the second most common malignant gastrointestinal tumor and the fourth leading cause of cancer death, with approximately 1.1 million new cases and 760,000 deaths globally in 2020. Due to a lack of specific symptoms in the early stages, about 70% of GC patients are diagnosed at an advanced stage, often accompanied by lymph node (LN) metastasis. Although LN metastasis is an important adverse prognostic factor closely related to survival rates, its dissemination pathways in GC remain poorly understood. Non-invasive imaging techniques, such as positron emission tomography (PET), computed tomography (CT), and magnetic resonance imaging (MRI), have been used for preoperative staging but lack sensitivity in detecting early lymphatic metastasis. The lymphoscintigraphy with 99m-technetium (99 mTc) is a gold-standard clinical method for detecting and excising sentinel LNs, but it poses radioactive risks. Despite the effectiveness of sentinel LN biopsy (SLNB), identifying metastatic LNs within fibrofatty tissue remains challenging, with a relatively high false-negative rate of 13-52%. Therefore, there is an urgent need for alternative methods for non-invasive early detection of metastatic LNs and guiding surgeons for precise excision.

Fluorescence imaging enables real-time, non-invasive visualization of dynamic biological pathological processes in live subjects with high sensitivity.Clinically, indocyanine green (ICG) is used as a signal-to-background ratio (SBR) tracer for intraoperative real-time visualization of lymphatic vessels and sentinel LNs. However, due to non-specific interactions in the human body, its “always-on” fluorescence may lead to false-positive results, hindering accurate tracking of cancer metastasis. Although other probes with passive (such as polymer-coated nanoprobes, gold nanoclusters, or quantum dots) or active (such as IRDye800CW-conjugated bevacizumab, cetuximab, or panitumumab) tumor-targeting capabilities have been explored, they exhibit non-specific biodistribution, resulting in low signal-to-noise ratios and insufficient differentiation between macro/micro metastatic LNs and benign LNs. In contrast, activatable probes that generate specific responses to tumor biomarkers (such as overexpressed enzymes or abnormal acidity) provide higher sensitivity for the precise excision of metastatic foci. However, few studies have reported activatable probes for early detection of disseminated cancer cells within metastatic LNs. Furthermore, the patterns of lymphatic metastasis in GC are highly complex, with abnormal lymphatic drainage patterns frequently leading to skipping LN metastasis. Previous studies primarily focused on investigating the frequency of sentinel LN metastasis, and the temporal dynamics (time-dependent manner) of tumor cell dissemination within the lymphatic network and the anatomical locations (spatial-dependent manner) of metastatic LNs remain unclear.

Figure 1 Schematic diagram of tumor-trackable and enzyme-activatable NIRF nanoprobes for spatiotemporal localization of metastatic LNs (adapted from ACS Nano)

This study reports a tumor-trackable and enzyme-activatable NIRF nanoprobes (MLR) for spatiotemporal localization of metastatic LNs.MLRs are self-assembled nanocomplexes that consist of two chemically modified 1,2-distearoyl-sn-glycero-3-phosphoethanolamine-poly(ethylene glycol) (DSPE-PEG) derivatives. Each derivative has a lipophilic DSPE tail for efficient LN delivery and is functionalized at the other end with a cyclic arginine-glycine-aspartic acid peptide (cRGDyC) targeting integrins, which is overexpressed as a tumor recognition motif in cancer, or d-galactose residues that lock the half-cyanine NIRF fluorophore, which can be cleaved by the tumor biomarker β-galactosidase (β-Gal) as a sensing motif. Because the cage-like phenolic groups inhibit the electron donor capability, MLRs are essentially non-fluorescent. They emit fluorescence only in the presence of increased β-Gal in disseminated tumor cells, thus able to specifically identify lymph node metastasis. Meanwhile, the authors described the construction and screening of MLR1-3 in a subcutaneous gastric tumor model. MLR1 exhibited the best performance in tumor targeting and sensing, further optimized in an in situ gastric tumor model for spatiotemporal localization of metastatic LNs, distinguishing macro and micro metastatic LNs from benign LNs, and able to early detect skipping LN metastasis patterns in a spatially dependent manner.Finally, the authors demonstrated the application of this probe in identifying cancerous tissues and metastatic LNs in collected specimens during radical gastrectomy, showcasing the potential of this probe in assisting early diagnosis of metastatic LNs clinically.

Reference:

https://pubs.acs.org/doi/10.1021/acsnano.4c12915