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Purpose: 68Ga-labeled fibroblast activation protein inhibitors, such as [68Ga]Ga-DOTA-FAPI-04 and [68Ga]Ga-DOTA-FAPI-46, have been successfully applied in positron emission tomography imaging of various tumor types. To broaden the PET tracers of different positron nuclides for imaging studies of FAP-dependent diseases, we herein report the radiosynthesis and preclinical evaluation of two 11C-labeled FAP inhibitors, 11C-RJ1101 and 11C-RJ1102. Methods: Two phenolic hydroxyl precursors based on a quinoline amide core coupled with a 2-cyanopyrrolidine moiety were coupled with [11C]CH3I to synthesize 11C-RJ1101 and 11C-RJ1102. In vivo small-animal PET and biological distribution studies of 11C-RJ1101 and 11C-RJ1102 compared to [68Ga]Ga-DOTA-FAPI-04 were conducted in nude mice bearing U87MG tumor xenografts at 30, 60, and 90min, respectively. Results: 11C-RJ1101 and 11C-RJ1102 were synthesized in over 15% radiochemical yields, with specific activities of 67 GBq/μmol and 34 GBq/μmol, respectively, at the end of synthesis and radiochemical purities greater than 99%. In U87MG tumor xenograft PET studies, the three tracers experienced higher specific uptake at the tumor site. However, because of significant differences in metabolism and clearance, [68Ga]Ga-DOTA-FAPI-04 experienced high uptake in the kidney, whereas 11C-RJ1101 and 11C-RJ1102 showed high uptake in the liver and intestine. Biodistribution studies revealed significant hepatobiliary excretion of 11C-RJ1101 and 11C-RJ1102. 11C-RJ1102 showed higher specific tumor uptake in U87MG xenografts (1.71 ± 0.08% injected dose per Gram of tissue [ID/g]) than 11C-RJ1101 (1.34 ± 0.10%ID/g) and [68Ga]Ga-DOTA-FAPI-04 (1.29 ± 0.04%ID/g) after 30 min p. i. In orthotopic glioma models, the uptake values were 0.07 ± 0.03% ([68Ga]Ga-DOTA-FAPI-04) and 0.16 ± 0.03% (11C-RJ1102), respectively. Conclusion: 11C-RJ1101 and 11C-RJ1102 are interesting candidates for translation to the clinic, taking advantage of the shorter half-life and physical imaging properties of C-11.

Purpose: Translocator protein (TSPO), an outer mitochondrial membrane protein, is regarded as a key biomarker for neuroinflammation in a variety of neurodegenerative diseases. In this study, we aim to evaluate two highly specific TSPO radiotracers [18F]VUIIS1009A and [18F]VUIIS1009B in a mild cerebral ischemic rat model, and to compare their in vivo performance to the well-established TSPO probe [18F]DPA-714 for neuroinflammation imaging. With multiple graphic analytical methods tested and macro parameters determined, we propose to find a suitable and best quantification method to profile neuroinflammation and measure TSPO density with the three TSPO radiotracers.Methods: Cerebral ischemia rat model was created and imaged using [18F]VUIIS1009A, [18F]VUIIS1009B and [18F]DPA-714. Displacement studies using non-radioactive analogs were performed to evaluate the binding specificities of [18F]VUIIS1009A and [18F]VUIIS1009B individually. Imaging analysis using arterial plasma input functions (AIFs) was employed to generate Logan plots and parametric images of total distribution volume (VT) for each radiotracer. Reference Logan model using contralateral brain as a reference region was introduced to generate parametric images for binding potential (BPND). Results: When compared to [18F]DPA-714, [18F]VUIIS1009B demonstrated higher binding potential (BPND) and distribution volume ratio (DVR). Parameter images of BPND and VT also indicate [18F]VUIIS1009B has a superior imaging profile with higher BPND and DVR when compared with other two radiotracers in TSPO imaging. Correlation analysis between BPND for [18F]VUIIS1009B and [18F]DPA-714 also indicates [18F]VUIIS1009B is more sensitive than [18F]DPA-714 in TSPO density measurement.Conclusions: This study demonstrates the superiority of [18F]VUIIS1009B to [18F]VUIIS1009A and [18F]DPA-714 in the neuroinflammation imaging. It also demonstrates that [18F]VUIIS1009B PET imaging coupled with parameter mapping (VT and BPND) and graphic analysis using Logan analysis and reference Logan analysis holds great promise for neuroinflammation characterization and TSPO density measurement.

Abstract Purpose Translocator protein (TSPO), an out-mitochondrial membrane protein, is regarded as a key biomarker for neuroinflammation in a variety of neurodegenerative diseases. In this study, we aim to evaluate two highly specific TSPO radiotracers 18F-VUIIS1009A and 18F-VUIIS1009B in a mild cerebral ischemic rat model, and to compare their in vivo performance to the well-established TSPO probe 18F-DPA-714 for neuroinflammation imaging. With multiple graphic analytical methods tested and macro parameters determined, we propose to find a suitable and best quantification method to profile neuroinflammation and measure TSPO density with the three TSPO radiotracers. Methods Cerebral ischemia rat model was created and imaged using 18F-VUIIS1009A, 18F-VUIIS1009B and 18F-DPA-714. Displacement studies using cold analogs were performed to evaluate the binding specificities of 18F-VUIIS1009A and 18F-VUIIS1009B individually. Imaging analysis using arterial plasma input functions (AIFs) was employed to generate Logan plots and parametric images of total distribution volume (VT) for each radiotracer. Reference Logan model using healthy brain as a reference region was introduced to generate parametric images for binding potential (BPND). Results When compared to 18F-DPA-714, 18F-VUIIS1009B demonstrated higher in vitro binding specificity, binding potential (BPND) and distribution volume ratio (DVR). Parameter images of BPND and VT also indicate 18F-VUIIS1009B has a superior imaging profile when compared with other two radiotracers in TSPO imaging. Correlation analysis between BPND for 18F-VUIIS1009B and 18F-DPA-714 also indicates 18F-VUIIS1009B is more sensitive than 18F-DPA-714 in TSPO density measurement. Conclusions This study demonstrates the superiority of 18F-VUIIS1009B to 18F-VUIIS1009A and 18F-DPA-714 in the neuroinflammation imaging. It also demonstrates that 18F-VUIIS1009B PET imaging coupled with parameter mapping (VT and BPND) and graphic analysis holds great promise for neuroinflammation characterization and TSPO density measurement.