초록
<P><B>Purpose</B></P><P>(<I>S</I>)-4-(3-[<SUP>18</SUP>F]Fluoropropyl)-L-glutamic acid ([<SUP>18</SUP>F]FSPG) is an L-glutamate derivative used as a PET biomarker to assess intracellular redox status in vivo through targeting of the cystine/glutamate antiporter protein, x<SUB>c</SUB><SUP>−</SUP> transporter. In this report, we describe a radiosynthesis of [<SUP>18</SUP>F]FSPG for use in PET studies that address specific challenges in relation to the radiotracer purity, molar activity, and quality control testing methods.</P><P><B>Procedures</B></P><P>The radiosynthesis of [<SUP>18</SUP>F]FSPG was performed using a customised RNPlus Research automated radiosynthesis system (Synthra GmbH, Hamburg, Germany). [<SUP>18</SUP>F]FSPG was labelled in the 3-fluoropropylmoiety at the 4-position of the glutamic acid backbone with fluorine-18 via substitution of nucleophilic [<SUP>18</SUP>F]fluoride with a protected naphthylsulfonyloxy-propyl-L-glutamate derivative. Radiochemical purity of the final product was determined by radio HPLC using a new method of direct analysis using a Hypercarb C<SUB>18</SUB> column.</P><P><B>Results</B></P><P>The average radioactivity yield of [<SUP>18</SUP>F]FSPG was 4.2 GBq (range, 3.4–4.8 GBq) at the end of synthesis, starting from 16 GBq of [<SUP>18</SUP>F]fluoride at the end of bombardment (<I>n</I> = 10) in a synthesis time of 50 min. The average molar activity and radioactivity volumetric concentration at the end of synthesis were 66 GBq µmol<SUP>−1</SUP> (range, 48–73 GBq µmol<SUP>−1</SUP>) and 343–400 MBq mL<SUP>−1</SUP>, respectively.</P><P><B>Conclusion</B></P><P>Stability tests using a 4.6 GBq dose with a radioactivity volumetric concentration of 369 MBq mL<SUP>−1</SUP> at the end of synthesis showed no observable radiolysis 3 h after production. The formulated product is of high radiochemical purity (> 95%) and higher molar activity compared to previous methods and is safe to inject into mice up to 3 h after production.</P>