Objective:To explore the binding characteristics of N, N-diethyl-2-(2-(4-(2- 18F-fluoroethoxy)phenyl)-5, 7-dimethylpyrazolo[1, 5-a]pyrimidin-3-yl)acetamide ( 18F-DPA-714) and ( R)- N-sec-butyl- N-methyl-4-(3-( 18F-trifluoromethyl)phenyl)quinazoline-2-carboxamide ( 18F-TFQC) to the single nucleotide polymorphisms of the 18×10 3 translocator protein (TSPO), and to evaluate the imaging efficacy and feasibility of those 2 molecular probes in neuroinflammation rat models. Methods:To test the selectivity of 18F-DPA-714 and 18F-TFQC for TSPO polymorphisms, the wild-type (high-affinity binding, HAB) and mutant (low-affinity binding, LAB) sequences of the human TSPO gene were transfected into 293T cells respectively. A competitive inhibition assay was carried out with N-methyl- N-(1-methylpropyl)-1-(2-chlorophenyl)-3-isoquinoline carboxamide (PK11195) as an inhibitor to determine the binding affinities of 2 probes to TSPO polymorphisms. Rat neuroinflammation models ( n=6) were established using lipopolysaccharide. Three days after modeling, small animal PET/CT imaging was performed using 18F-DPA-714 and 18F-TFQC, respectively, to observe and compare the uptake of the tracers, and the ratio of SUV mean of the right striatum to SUV mean of the left striatum (SUVR) was calculated. After the imaging, the expression and distribution of microglia and TSPO were detected by tissue immunofluorescence. Repeated-measures analysis of variance was used to analyze the SUVR data of different groups. Results:The inhibition constants ( Ki) of 18F-TFQC on 293T-LAB and 293T-HAB cells were 23.51 and 14.60 nmol/L, respectively, with a Ki LAB/ Ki HAB ratio of 1.61, indicating low sensitivity to TSPO single nucleotide polymorphisms. The Ki of 18F-DPA-714 for binding to 293T-LAB and 293T-HAB cells were 45.23 and 6.47 nmol/L, respectively, with a Ki LAB/ Ki HAB ratio of 6.99. Small animal PET/CT imaging demonstrated that specifically uptake of both probes could be found in neuroinflammatory lesions. The overall SUVR of 18F-DPA-714 in the lesions within 60minutes was slightly higher than that of 18F-TFQC, but no significant difference was observed ( F values: inter-group 0.40, time effect 0.30, cross-effect 0.03; all P>0.05). Conclusions:Compared with 18F-DPA-714, 18F-TFQC is less sensitive to TSPO gene polymorphisms, thus being more suitable for clinical application and promotion. It holds promise for the early identification of neuroinflammation and the efficacy monitoring of anti-inflammatory drug treatments.

The translocator protein (TSPO) positron emission tomography (PET) can noninvasively detect neuroinflammation associated with epileptogenesis and epilepsy. This study explored the role of the TSPO-targeting radioligand [¹⁸F]F-TFQC, an m-trifluoromethyl ER176 analog, in the PET neuroimaging of epileptic rats. Initially, [¹⁸F]F-TFQC was synthesized with a radiochemical yield of 8%-10% (EOS), a radiochemical purity of over 99%, and a specific activity of 38.21 ± 1.73 MBq/nmol (EOS). After determining that [¹⁸F]F-TFQC exhibited good biochemical properties, [¹⁸F]F-TFQC PET neuroimaging was performed in epileptic rats at multiple time points in various stages of disease progression. PET imaging showed specific [¹⁸F]F-TFQC uptake in the right hippocampus (KA-injected site, i.e., epileptogenic zone), which was most pronounced at 1 week (T/NT 1.63 ± 0.21) and 1 month (T/NT 1.66 ± 0.20). The PET results were further validated using autoradiography and pathological analysis. Thus, [¹⁸F]F-TFQC can reflect the TSPO levels and localize the epileptogenic zone, thereby offering the potential for monitoring neuroinflammation and guiding anti-inflammatory treatment in patients with epilepsy.

Objective:To explore the binding characteristics of N, N-diethyl-2-(2-(4-(2- 18F-fluoroethoxy)phenyl)-5, 7-dimethylpyrazolo[1, 5-a]pyrimidin-3-yl)acetamide ( 18F-DPA-714) and ( R)- N-sec-butyl- N-methyl-4-(3-( 18F-trifluoromethyl)phenyl)quinazoline-2-carboxamide ( 18F-TFQC) to the single nucleotide polymorphisms of the 18×10 3 translocator protein (TSPO), and to evaluate the imaging efficacy and feasibility of those 2 molecular probes in neuroinflammation rat models. Methods:To test the selectivity of 18F-DPA-714 and 18F-TFQC for TSPO polymorphisms, the wild-type (high-affinity binding, HAB) and mutant (low-affinity binding, LAB) sequences of the human TSPO gene were transfected into 293T cells respectively. A competitive inhibition assay was carried out with N-methyl- N-(1-methylpropyl)-1-(2-chlorophenyl)-3-isoquinoline carboxamide (PK11195) as an inhibitor to determine the binding affinities of 2 probes to TSPO polymorphisms. Rat neuroinflammation models ( n=6) were established using lipopolysaccharide. Three days after modeling, small animal PET/CT imaging was performed using 18F-DPA-714 and 18F-TFQC, respectively, to observe and compare the uptake of the tracers, and the ratio of SUV mean of the right striatum to SUV mean of the left striatum (SUVR) was calculated. After the imaging, the expression and distribution of microglia and TSPO were detected by tissue immunofluorescence. Repeated-measures analysis of variance was used to analyze the SUVR data of different groups. Results:The inhibition constants ( Ki) of 18F-TFQC on 293T-LAB and 293T-HAB cells were 23.51 and 14.60 nmol/L, respectively, with a Ki LAB/ Ki HAB ratio of 1.61, indicating low sensitivity to TSPO single nucleotide polymorphisms. The Ki of 18F-DPA-714 for binding to 293T-LAB and 293T-HAB cells were 45.23 and 6.47 nmol/L, respectively, with a Ki LAB/ Ki HAB ratio of 6.99. Small animal PET/CT imaging demonstrated that specifically uptake of both probes could be found in neuroinflammatory lesions. The overall SUVR of 18F-DPA-714 in the lesions within 60minutes was slightly higher than that of 18F-TFQC, but no significant difference was observed ( F values: inter-group 0.40, time effect 0.30, cross-effect 0.03; all P>0.05). Conclusions:Compared with 18F-DPA-714, 18F-TFQC is less sensitive to TSPO gene polymorphisms, thus being more suitable for clinical application and promotion. It holds promise for the early identification of neuroinflammation and the efficacy monitoring of anti-inflammatory drug treatments.

Objective:To explore whether the specific synaptic vesicle glycoprotein 2A (SV2A) targeted imaging agent ( R)-4-(3-fluoro-5-(fluoro- 18F)phenyl)-1-((3-methylpyridin-4-yl)methyl)pyrrolidin-2-one ( 18F-SDM-8) can be used to detect epileptic foci. Methods:Twenty male Sprague-Dawley (SD) rats (8-9 weeks) were injected with 1.2 μl of kainic acid (16 rats in the epilepsy group) or saline (4 rats in the control group) into the right hippocampus. 18F-SDM-8 and 18F-FDG mircoPET/CT imaging were respectively performed at 1-2 d (acute phase), 6-7 d (incubation period) and 45-60 d (chronic phase) after the seizure. Asymmetric index (AI) was used to evaluate the epileptic foci identify ability of 18F-SDM-8. Paired t test, Mann-Whitney U test and Pearson correlation analysis were used to analyze data. Results:In the three periods of 18F-SDM-8 imaging, the differences of AI of hippocampus between the epilepsy group and control group were statistically significant ( z values: from -2.64 to 2.67, all P<0.05). Both imaging agents had asymmetric uptake in the epilepsy group (right was lower than left), and the decrease in the medial right temporal lobe was the most significant. The pathological staining results were consistent with the imaging results. In the chronic phase of the epilepsy group, the differences of 18F-SDM-8 SUV mean (right versus left) in each brain area of interest were statistically significant ( t value: from -33.40 to -5.60, all P<0.05). The asymmetric uptake of the two imaging agents in the hippocampus had a better correlation ( r=0.97, P=0.001), and the AI of 18F-SDM-8 ((34.2±8.4)%) in this area was 1.4 times higher than that of 18F-FDG ((24.6±4.7)%). Conclusions:18F-SDM-8 PET is a promising method to test the level of SV2A. It can reflect the changes of SV2A in the rat epilepsy model induced by intrahippocampal injection of kainic acid, and improve the sensitivity of molecular imaging for epileptic foci.