18F-5-FPN: A Specific Probe for Monitoring Photothermal Therapy Response in Malignant Melanoma

Background: The increasing global burden and the significant breakthroughs in malignant melanoma therapy make urgent demands on efficient response evaluation and surveillance of adverse events. Though there have been a few probes explored for early diagnosis or staging of malignant melanoma, but rare for response assessment investigations except for common 18 F-deoxyglucose ( 18 F-FDG). Thus, this research would further explore the feasibility and ability of 18 F-5-fluoro-N-(2-(diethylamino)ethyl)picolinamide ( 18 F-5-FPN)PET imaging to evaluate photothermal therapy (PTT) response of malignant melanoma, simultaneously comparing with 18 F-FDG. Methods B16F10 and MDA-MB-231subcutaneous tumor models were irradiated with an 808 nm laser for PTT. 18 F-5-FPN and 18 F-FDG PET imaging were adopted to estimate the therapy response. B16F10, inflammatory, and MDA-MB-231 models were subjected to 18 F-FDG and 18 F-5-FPN PET static acquisitions and compared by quantitative data for assessing the specificity of different agents to different diseases. Furthermore, B16F10 and 231 models were exploited for survival analysis to observe the efficacy and response feature of PTT. Results Melanin in B16F10 tumors successfully transformed the optical energy into heat for PTT. H&E staining at 24 h discovered framework destruction of tumor tissue and extensive necrosis. The mean tumor uptakes of 18 F-5-FPN on Day 2 (7.52 ± 3.65%ID/g) and Day 6 (10.22 ± 6.00%ID/g) were much lower than before treatment (p < 0.01). However, no significant difference of the 18 F-FDG uptakes was found between Day 1 after PTT and before treatment. 18 F-5-FPN PET scanning only manifested B16F10 tumor strikingly, while they all accumulated 18 F-FDG highly. PTT contributed to suppressing B16F10 tumors’ growth rapidly in a short time and prolonged the median survival of B16F10 models to some extent. Whereas, both of the temperature and growth of 231 tumors were not distinctly influenced. Conclusions Compared with 18 F-FDG PET scanning, 18 F-5-FPN PET imaging was capable of estimating PTT efficacy in malignant melanoma, successfully monitored the occult recurrence after therapy, and distinguished malignant melanoma from inflammation and other carcinomas well by high affinity to melanin. This potential probe may provide a new approach for precise and useful response evaluation, timely therapeutic regimen management, and sensitive follow-up.