3-O-methyl-6[18F]Fluor-L-DOPA (OMFD) - First experiences in brain tumor imaging

F-18 labelled amino acid 3-O-methyl-6[18F]Fluor-L-DOPA (OMFD), not used for diagnostics until now, was synthesized, tested in cell cultures as well as in animals and studied in patients (pts) with recurrences of low differentiated brain tumors. Synthesis is based on a new precursor (N-formyl-3-O-methyl-4-O-Boc-6-trimethylstannyl-L-DOPA-ethyl-ester). Biologic behavior was tested HAT 29 and RBE-4-cell cultures and tumor bearing nude mice. First clinical studies we carried out in recurrent glioblastoma multiforme (4 pts.) with inconclusive MRT and CT. The application of OMFD was based on an individual decision. The aim was to detect localization and extent of recurrent tumor for planning of stereotactic radiotherapy. After 50 min synthesis time a radiochemical yield of 20 - 25% was reached. A high tracer uptake in tumor cells via L-amino-transporter was seen. However there was no evidence for metabolism or incorporation into proteins. Biodistribution in mice showed 60 min p.i. high intratumoral uptake (12.4 ± 1.8% ID/g) and a tumor/blood ratio of 9.5 ± 0.8. Increased radioactivity uptake was found in all pts. 60 min p.i. in the region of the suspected recurrences (lesion/nonlesion 2.2 ± 0.5), only little tracer uptake was found in the whole body scans in muscle, thorax and abdomen. Suspected recurrences were clearly seen in on PET images. Preliminary diagnostic studies in pts. With low differentiated tumor suggest that the new F-18 labelled amino acid is a valuable PET-tracer for tumor imaging.