PET imaging of glutamate transporter EAAC1 using N-(2-¹⁸F-fluoropropionyl)-L-glutamate

Objectives N-(2-¹⁸F-fluoropropionyl)-L-glutamate(¹⁸F-FPGLU) was a recently developed potential amino acid tracer for tumor imaging with positron emission tomography (PET) imaging. In vitro cell experiments showed that ¹⁸F-FPGLU was primarily transported through the X_AG^- system. The aim of this study was to investigate the relationship between glutamate transporter excitatory amino acid carrier 1 (EAAC1) expression and ¹⁸F-FPGLU uptake and to perform PET imaging of the model mice with shRNA-mediated EAAC1 knock down SPC-A-1 xerography.

Methods EAAC1 mRNA and protein expression was measured by quantitative reverse transcription polymerase chain reaction (qRT-PCR) and western blot. The uptake of ¹⁸F-FPGLU was assessed in ATRA-treated and untreated C6 cells lines, and also in shRNA-mediated EAAC1 knock down SPC-A-1 cells and the non-targeted (NT) control cells in vitro. PET imaging of the human lung adenocarcinoma SPC-A-1-bearing mice and the model mice with EAAC1 knock down xerography was performed with ¹⁸F-FPGLU.

Results Compared with untreated C6 cells, after 72 hours the EAAC1 mRNA expression was increased to 246±17% or 160±10% and ¹⁸F-FPGLU uptake was significantly increased to 340±28% or 212±26% in ATRA-treated C6 cells cultured with 0.1% or 10% fetal bovine serum (FBS) respectively. Compared with non-targeted control cells, expression of EAAC1 mRNA and protein was strongly inhibited to 28% and 40.4% in stable shRNA-mediated EAAC1 knockdown SPC-A-1 cells, and the uptake of ¹⁸F-FPGLU was decreased to 64.0±0.5% in EAAC1 shRNA knockdown cells. PET imaging showed that the uptake of ¹⁸F-FPGLU in the SPCA-1 human lung adenocarcinoma was significantly higher than that in model with EAAC1 shRNA knockdown cells at 60 min, with Tumor/Muscle ratio of 3.01 ±0.8 and 1.67±0.2(n-=3) respectivly.

Conclusions The transport mechanism of ¹⁸F-FPGLU in glioma C6 and lung adenocarcinoma SPC-A-1 cells lines is involved in glutamate transporter EAAC1, which may be a hallmark of tumor glutamate metabolism PET imaging.

Research Support This work was supported by the National Natural Science Foundation of China (81371584), and Science and Technology Planning Project Foundation of Guangzhou (No.2011J5200025).