<sup>18</sup>F‑Alanine Derivative Serves as an ASCT2 Marker for Cancer Imaging

Amino acids derivative are well established molecular probes for diagnosis of a variety of cancer using positron emission tomography (PET). Recently, boramino acid (BAAs) was found as a prospective molecular platform for developing PET tracer. The objective of this study was to develop a <sup>18</sup>F-labeled alanine derivative through displacing its carboxylate by trifluoroborate as a selective ASCT2 marker for cancer imaging. <sup>18</sup>F-Ala-BF<sub>3</sub> was first evaluated in healthy FVB/N mice <i>in vivo</i>, exhibiting rapid renal clearance with almost negligible uptake in stomach (1.53 ± 0.31%ID/g). Notable uptake was observed in thyroid (3.71 ± 0.49%ID/g, 40 min post injection), of which the uptake was significantly inhibited by co-injection with natural L-alanine. In addition, we further established <sup>18</sup>F-Ala-BF<sub>3</sub> on a human gastric cancer cell (BGC-823) xenografts bearing mouse model. Dynamic PET-CT scan revealed the optimal time window for tumor imaging, it was between 40 and 60 min post injection, when the BGC-823 xenografts uptake was 5.49 ± 1.47%ID/g (<i>n</i> = 4), and the tumor-to-stomach, tumor-to-blood, tumor-to-muscle, and tumor-to-brain ratios were 3.27 ± 1.53, 3.80 ± 1.48, 3.47 ± 1.48, and 6.20 ± 1.47, respectively.