Synthesis and evaluation of an N-[18F]fluorodeoxyglycosyl amino acid for PET imaging of tumor metabolism

Abstract

IntroductionThe limitations of [18F]fluorodeoxyglucose ([18F]FDG), including producing false-positive or -negative results, low image contrast in brain tumor diagnosis and poor differentiation of tumor and inflammatory, necessitate the development of new radiopharmaceuticals. In the present study, a novel [18F]fluoroglycoconjugate tracer, [18F]FDGly-NH-Phe, for tumor metabolism imaging was prepared and evaluated. Methods[18F]FDGly-NH-Phe was prepared by condensing [18F]FDG with L-4-aminophenylalanine in an acidic condition, and purified with semi-preparative-high performance liquid chromatography (HPLC). The in vitro stability study was conducted in phosphate-buffered saline (PBS, pH 4.0–9.18) at room temperature (RT) and in fetal bovine serum (FBS) at 37 °C. The preliminary cellular uptake studies were performed using Hep-2 cell. The bio-distribution studies, PET/CT imaging and metabolism studies were performed and compared with [18F]FDG on ICR or BALB/c nude model mice. Results[18F]FDGly-NH-Phe was derived from a direct condensation of [18F]FDG with L-4-aminophenylalanine with high stability in FBS and PBS (pH of 6.5–9.18). In vitro cell experiments showed that [18F]FDGly-NH-Phe uptake in Hep-2 cells was primarily transported through amino acid transporters including Na+-dependent A system, ASC system, and system B0,+ system. The bio-distribution of [18F]FDGly-NH-Phe in normal ICR mice showed faster blood radioactivity clearance, and lower uptake in brain and heart than [18F]FDG. The performance of PET/CT imaging for [18F]FDGly-NH-Phe in the mice model manifested excellent tumor visualization, high tumor-to-background ratios, and low accumulation in inflammatory lesions. Metabolism studies for [18F]FDGly-NH-Phe indicated high in vivo stability in plasma and urine and decomposition into [18F]FDG in the tumor microenvironment. ConclusionThe results demonstrated that [18F]FDGly-NH-Phe as a novel amino acid PET tracer showed the capability to differentiate tumor from inflammation, and the potentials for future clinical applications.