Murine Model Study of a New Receptor-Targeted Tracer for Sentinel Lymph Node in Breast Cancer

Abstract

Purpose: Sentinel lymph node biopsy (SLNB), a critical staging and treatment step, has replaced axillary lymph node (LN) dissection as the standard staging procedure for early stage breast cancer patients with clinically negative axillary LNs. Hence, using a murine sentinel lymph node (SLN) model, we investigated the localization effect of the new receptor-targeted tracer, indocyanine green (ICG)-rituximab, on breast cancer SLNB.

Methods: After establishing the murine SLN model, different doses of ICG-rituximab were subcutaneously injected into the hind insteps of BALB/c mice to determine the optimal dose and imaging time using continuous (> 3 hours) MDM-I fluorescence vasculature imaging. To explore the capacity of ICG-rituximab for sustained SLN localization with the optimal dose, MDM-I imaging was monitored at 6, 12, and 24 hours.

Results: The popliteal LN was defined as the SLN for hindlimb lymphatic drainage, the iliac LN as the secondary, and the para-aortic or renal LN as the tertiary LNs. The SLN initial imaging and optimal imaging times were shortened with increased ICG-rituximab doses, and the imaging rates of the secondary and tertiary LNs increased accordingly. The optimal ICG dose was 0.12 μg, and its optimal imaging time was 34 minutes. After 24 hours, the SLN imaging rate remained 100%, while those of the secondary and the tertiary LNs increased from 0% (6 hours) and 0% (6 hours) to 10% (12 hours) and 10% (12 hours) to 20% (24 hours) and 10% (24 hours), respectively.

Conclusion: ICG-rituximab localized to the SLN without imaging from the secondary or tertiary LNs within 6 hours. The optimal ICG dose was 0.12 μg, and the optimal interval for SLN detection was 34 minutes to 6 hours post-injection. This novel receptor-targeted tracer is of great value to clinical research and application.

Keywords: Animal model; Indocyanine green; Rituximab; Sentinel lymph node; Synthetic imaging agent.

Figure 1. Lymphatic drainage system in the mouse hindlimb. (A) popliteal lymph node (a); iliac lymph node (b); lumbar aortic lymph nodes (c); and renal lymph node (d). (B) Each mouse was placed under a Cyclone phosphor screen imager to record an image popliteal lymph node (e); injection point (f).

Figure 2. Comparison between a high and low dose of the new tracer. (A, B) High dose of ICG-rituximab (0.48 μg); (C, D) low dose of ICG-rituximab (0.12 μg); and (E, F) ICG (0.12 μg).

ICG = indocyanine green.

Figure 3. Lymph node imaging at secondary and tertiary LN levels after 12-hr post ICG-rituximab injection. (A) ICG-rituximab (0.12 μg); (B) ICG (0.12 μg).

LN = lymph node; ICG = indocyanine green.

Figure 4. Continual mapping of the LNs post ICG-rituximab (0.12 μg) injection. SLN imaging rate was maintained at 100%. The imaging rates of the secondary and tertiary LNs increased with time, respectively.

SLN = sentinel lymph node, LNs = lymph nodes; ICG = indocyanine green.

Figure 5. Continual mapping of the LNs post IGC (0.12 μg) injection. The imaging rates of LNs at all levels decreased with time.

SLN = sentinel lymph node, LNs = lymph nodes; ICG = indocyanine green.