Evaluation of LAT1 tracer ¹⁸F-FAMT in the inflammatory lesions -comparison study with ¹⁸F-FDG PET

Objectives: ¹⁸F-FDG is mainly used as an oncology PET-tracer. However, ¹⁸F-FDG can show false positive findings because it also accumulates in the inflammatory lesion. L-[3-¹⁸F]-α-methyl tyrosine (¹⁸F-FAMT) is reported as a tumor specific tracer as a substrate of L-type amino acid transporter 1 (LAT1), which is expressed in major cancer cells but not in normal tissue. The purpose of this study was to evaluate ¹⁸F-FAMT as a next oncology PET tracer by comparing with ¹⁸F-FDG. [Method] Four mice with inflammation (NOD mouse, body weight = 22.3 ± 0.3 g, 8 weeks old) were investigated in this study. Mouse model of inflammation was established by subcutaneous injection of turpentine oil (0.05 ml) in the bilateral flank regions. Static PET scans were performed 50min after the intravenous injection of ¹⁸F-FDG at day 4 (20.8 ± 2.4 MBq), and ¹⁸F-FAMT at day 5 (20.1 ± 1.2 MBq) under isoflurane anesthesia. Volumes of interest were placed on the inflammatory lesion to measure SUV using Pmod software (ver 3.6). Uptakes of the lesions were compared between ¹⁸F-FAMT and ¹⁸F-FDG by paired t-test. [Result] Visual analysis showed that uptakes of ¹⁸F-FAMT in the inflammatory lesions were almost as low as the background level. To the contrary, moderate uptakes were observed on ¹⁸F-FDG PET. The SUVmax of the inflammatory lesions were 1.37 ± 0.11 in the ¹⁸F-FDG PET and 0.37 ± 0.05 in the ¹⁸F-FAMT PET. The SUVmax of ¹⁸F-FAMT was significantly lower than that of ¹⁸F-FDG (p<0.01 by paired t-test). [Conclusion] ¹⁸F-FDG showed high uptakes on inflammatory lesions as previously reported. ¹⁸F-FAMT showed lower accumulation in inflammation compared to ¹⁸F-FDG and it is expected to be a tumor specific PET tracer to reduce false positive findings in the clinical oncology.