Detection of melanoma metastases with PET-Comparison of 18F-5-FPN with 18F-FDG

Introduction18F-5-fluoro-N-(2-(Diethylamino)ethyl)picolinamide (18F-5-FPN) is a new positron-emission tomography (PET) radiopharmaceutical with potential for the detection of lymph node (LN) and pulmonary metastatic lesions of melanoma. We compared its performance with that of 18F-deoxyglucose (18F-FDG).MethodsCervical LN and lung melanoma metastasis models were established in C57BL/6 mice. Primary tumors were created by injection of melanoma cells into the pinna, and the resulting cervical LN metastases were evaluated. Lung metastases were created by intravenous injection of melanoma cells. The mice underwent 18F-FDG and 18F-5-FPN positron emission tomography (PET) imaging. A biodistribution study was conducted after imaging. Histopathologic evaluation of the tumors was also performed.ResultsLN metastases with a diameter < 1 cm were more visible on 18F-5-FPN PET imaging than 18F-FDG imaging. Quantitative analysis showed that the uptake of 18F-5-FPN was significantly higher than that of 18F-FDG, with values of 13.29 ± 3.80% ID/g and 7.24 ± 1.95% ID/g (n = 5, P < 0.05), respectively. LN-to-muscle ratios were 21.23 ± 6.02 and 4.50 ± 2.11 (n = 5, P < 0.01) for 18F-5-FPN and 18F-FDG, respectively. Biodistribution results were similar, with high uptake of 18F-5-FPN in the LN. 18F-5-FPN imaging manifested the pulmonary lesions clearly, while the 18F-FDG imaging showed no uptake in lesions <2 mm. The related uptakes of 18F-5-FPN and 18F-FDG were 3.12 ± 1.17% ID/g and 1.48 ± 0.15% ID/g, respectively (n = 5, P < 0.05), with lung metastasis-to-muscle ratios of 8.16 ± 3.12 and 1.28 ± 0.18 (n = 5, P < 0.01), respectively. H&E and Prussian blue staining displayed pluri nucleated or mega nucleus cells and dark brown granules in the metastatic tissues, characteristic of melanoma.Conclusions18F-5-FPN targeted small metastatic lesions with a higher target-to-normal ratio of uptake than those of 18F-FDG, which suggests its ability to detect metastatic lesions earlier than 18F-FDG. Further studies with a wide range of melanoma cell lines should be needed to confirm the similar performance.