Abstract B31: Delineation of sentinel lymph nodes in athymic nude mice by systemically administered ultra-pH-sensitive micelles shows fluorescence intensity in metastatic nodes

Introduction: Prognosis and overall survival in head and neck cancer patients is inversely correlated with the number of metastatic lymph nodes. Lymph node dissections prevent recurrence and improve survival outcomes. However, associated morbidity—such as lymphedema—decreases quality of life in surviving patients. Therefore, targeted, exogenous agents have the ability to improve intraoperative discrimination of cancer-involved lymph nodes and limit the extent of nodal dissection, reducing both patient mortality and morbidity. Procedures: A pH-responsive micellar agent, poly(ethylene glycol)-poly(2-dibutylamino ethyl methacrylate-indocyanine green) (PEG-b-PDBA-r-ICG), is delivered intravenously to an athymic nude murine model with orthotopic oral squamous cell carcinoma. Lymph node metastasis (LNM) is observed from the primary tumor—grown intramuscularly in the distal tongue—to cervical lymph nodes after 5 weeks. Circulation of PEG-b-PDBA-r-ICG for 24 hours allows for accumulation in the tumor vasculature and lymph nodes. The animal is sacrificed and dissected to expose the superficial nodes. ICG fluorescence is excited with near-infrared (NIR) light (Hamamatsu PDE C9830). Resulting NIR fluorescent emission is filtered with an 850 ± 8 nm bandpass filter at a 45-cm working distance and detected at 5.86 μm pixel resolution. The lymph node fluorescence intensity is quantified using Image Studio software to calculate the contrast to noise ratio (CNR) —defined as the difference of mean signal between lymph node and skeletal muscle divided by the muscle signal standard deviation. Results: NIR fluorescence imaging shows delineation of all superficial lymph nodes at high resolution. Critically in cases of LNM, the extracellular metastatic microenvironment shows accumulation of protonated polymer, delineating occult LNM. Cervical lymph nodes in tumor-bearing animals show a mean CNR of 45.4 ± 16.8. Pathologically normal lymph nodes from tumor-naive mice display a dimmer—but observable—fluorescence intensity (mean CNR = 12.1 ± 2.7). Conclusions: Systemically administered PEG-b-PDBA-r-ICG illuminates occult LNM microenvironments as well as lymph node resident macrophage, enabling high-resolution discrimination of sentinel nodes in an intraoperative setting. Previously reported nanoscale LNM detection techniques rely on only the disruption of macrophage accumulation in metastatic lesions. Therefore, other techniques display a negative signal in presence of LNM. Conversely, PEG-b-PDBA-r-ICG positively identifies cancer-involved sentinel nodes, offering potential to improve lymph node staging and to remove metastatic sentinel nodes at high sensitivity. Future work will include technology development to eliminate intracellular activation of the nanoprobe in macrophages, improving the specificity of this lymph node metastasis detection. Citation Format: Zachary Bennett, Qiang Feng, Joel Thibodeaux, Gang Huang, Jinming Gao, Baran Sumer. Delineation of sentinel lymph nodes in athymic nude mice by systemically administered ultra-pH-sensitive micelles shows fluorescence intensity in metastatic nodes [abstract]. In: Proceedings of the AACR-AHNS Head and Neck Cancer Conference: Optimizing Survival and Quality of Life through Basic, Clinical, and Translational Research; 2019 Apr 29-30; Austin, TX. Philadelphia (PA): AACR; Clin Cancer Res 2020;26(12_Suppl_2):Abstract nr B31.