SLC38A7 and glioblastoma: Additionally, several <i>N</i><sub>in</sub>-[<sup>18</sup>F]SAF-substituted tryptophan analogues showed up to 2-3-fold higher cellular uptake than the current gold standard [<sup>18</sup>F]FET in U87 MG glioblastoma cells, and their accumulation was sensitive to inhibition of amino acid transporters.