Preclinical uPAR-targeted multimodal imaging of locoregional head-and-neck cancers

Objectives: Establishing adequate resection margins and lymphatic mapping are crucial for the prognosis of oral cancer patients. Novel targeted imaging modalities are needed, enabling preand intraoperative detection of tumour cells, in combination with improved post-surgical examination by the pathologist. The urokinase-receptor (uPAR) is overexpressed in head and neck cancer, where it is associated with tumour progression and metastasis. Material and methods: To determine suitability of uPAR for molecular imaging of oral cancer surgery, human head and neck tumours were sectioned and stained for uPAR to evaluate the expression pattern compared to normal mucosa. Furthermore, metastatic oral squamous carcinoma cell line OSC-19 was used for targeting uPAR in in vivo mouse models. Using anti-uPAR antibody ATN-658, equipped with a multimodal label, the in vivo specificity was investigated and the optimal dose and time-window were evaluated. Results: All human oral cancer tissues expressed uPAR in epithelial and stromal cells. Hybrid ATN-658 clearly visualized tongue tumours in mice using either NIRF or SPECT imaging. Mean fluorescent TBRs over time were 4.3 ± 0.7 with the specific tracer versus 1.7 ± 0.1 with a control antibody. A significant difference in TBRs could be seen between 1 nmol (150 μg) and 0.34 nmol (50 μg) dose groups (n = 4, p < 0.05). Co-expression between BLI, GFP and the NIR fluorescent signals were seen in the tongue tumour, whereas human cytokeratin staining confirmed presence of malignant cells in the positive cervical lymph nodes. Conclusion: This study shows the applicability of an uPAR specific multimodal tracer in an oral cancer model, combining SPECT with intraoperative guidance. Preclinical uPAR-targeted multimodal imaging in oral cancer 219 Highlights – Novel tumour-specific multimodal imaging agent that will aid in surgical procedures. – Recognizing both neoplastic as well as tumour surrounding stromal cells. – Antibody-based, providing large imaging windows and high specific signals. – One administration sufficient for pre-, intraand postoperative imaging. – The agent can be applied in low doses and visualizes millimetre sized metastases.