Novel 18F-labeled α-methyl-phenylalanine derivative with high tumor accumulation and ideal pharmacokinetics for tumor specific imaging

Positron emission tomography (PET) imaging with 18F-labeled α-methyl-substituted amino acids exerts significant influence on differential diagnosis of malignant tumors and tumor-like lesions. Exclusive uptake via L-type amino acid transporter 1 (LAT1), a tumor-specific transporter, accounts for their excellent tumor specificity and low background accumulation. However, further refinement and optimization in their tumor accumulation and pharmacokinetics are sorely needed. To address these issues, we newly designed 18F-labeled α-methyl-phenylalanine (18F-FAMP) regioisomers (2-, 3-, or 4-18F-FAMP) and stereoisomers (L- or D-form), and we comprehensively evaluated their potential as tumor-imaging agents. 18F-FAMPs were prepared from α-methyl phenylalanine by electrophilic radiofluorination and purified by reversed-phase HPLC. In biodistribution studies on normal mice, L-2-18F-FAMP and the three D-18F-FAMPs showed faster blood clearance and lower renal accumulation than L-3-18F-FAMP or L-4-18F-FAMP. In LS180 h...