Initial evaluation of (4S)-4-(3-[ 18 F]fluoropropyl)-L-glutamate (FSPG) PET/CT imaging in patients with head and neck cancer, colorectal cancer, or non-Hodgkin lymphoma.

Purpose: (4S)-4-(3-[ ¹⁸ F]Fluoropropyl)-L-glutamic acid ([ ¹⁸ F]FSPG) measures system x _C ^- transporter activity and shows promise for oncologic imaging. We present data on tumor uptake of this radiopharmaceutical in human subjects with head and neck cancer (HNC), colorectal cancer (CRC), and non-Hodgkin lymphoma (NHL).
Methods: A total of 15 subjects with HNC (n = 5), CRC (n = 5), or NHL (n = 5) were recruited (mean age 66.2 years, range 44-87 years). 301.4 ± 28.1 MBq (8.1 ± 0.8 mCi) of [ ¹⁸ F]FSPG was given intravenously to each subject, and 3 PET/CT scans were obtained 0-2 h post-injection. All subjects also had a positive [ ¹⁸ F]FDG PET/CT scan within 1 month prior to the [ ¹⁸ F]FSPG PET scan. Semi-quantitative and visual comparisons of the [ ¹⁸ F]FSPG and [ ¹⁸ F]FDG scans were performed.
Results: [ ¹⁸ F]FSPG showed strong uptake in all but one HNC subject. The lack of surrounding brain uptake facilitated tumor delineation in the HNC patients. [ ¹⁸ F]FSPG also showed tumor uptake in all CRC subjects, but variable uptake in the NHL subjects. While the absolute [ ¹⁸ F]FDG SUV values were comparable or higher than [ ¹⁸ F]FSPG, the tumor-to-background SUV ratios were greater with [ ¹⁸ F]FSPG than [ ¹⁸ F]FDG.
Conclusions: [ ¹⁸ F]FSPG PET/CT showed promising results across 15 subjects with 3 different cancer types. Concordant visualization was mostly observed between [ ¹⁸ F]FSPG and [ ¹⁸ F]FDG PET/CT images, with some inter- and intra-individual uptake variability potentially reflecting differences in tumor biology. The tumor-to-background ratios were greater with [ ¹⁸ F]FSPG than [ ¹⁸ F]FDG in the cancer types evaluated. Future studies based on larger numbers of subjects and those with a wider array of primary and recurrent or metastatic tumors are planned to further evaluate the utility of this novel tracer.