Influence of blood-brain barrier permeability on O-(2-[F-18]fluoroethyl)-L-tyrosine uptake in rat gliomas.

Objectives PET using O-(2-[F-18]Fluoroethyl)-L-tyrosine (FET) is a powerful method for the diagnostics of brain tumors. The influence of blood-brain barrier (BBB) disruption on FET uptake is controversial. This study investigates FET uptake kinetics in rat gliomas by influencing the permeability of the BBB by dexamethasone (Dex) treatment.

Methods Tumor cells of F98 glioma or 9L gliosarcoma were implanted in the striatum of Fischer rats. Ten animals (F98: n=5; 9L: n=5) remained untreated and an identical group was injected with Dex (8 mg/kg 2 d, 4 mg/kg 24h and 1h before sacrifice). After 10-12 days of tumor growth BBB-permeability was quantified histologically 30 min after i.v. injection of Evans Blue (EB). FET PET (0-60 min post injection, p.i.) was performed in 18 untreated animals (F98: n=10; 9L: n=8) and in 13 Dex treated animals (F98: n=6; 9L: n=7) by Inveon PET. Tumor to brain ratios (TBR) (18-60 min p.i.) and the slope of a linear fit of the time activity curve (15 to 60 min p.i.) were determined.

Results Dex treated tumors showed significantly lower EB staining than untreated tumors (F98: -44 ± 20.9 %, 9L: - 82 ± 6.5 %; p < 0.01) indicating reduced BBB-permeability. PET-analysis revealed no significant difference in FET uptake in untreated and Dex treated animals (F98: SUV 1.32 ± 0.14 vs. 1.35 ± 0.12; 9L: 1.44 ± 0.06 vs. 1.48 ± 0.07, n.s.) and no change of FET kinetics. Normal brain tissue showed a slight increase of FET uptake after Dex treatment (SUV: 0.80 ± 0.05 vs. 0.72 ± 0.06, p < 0.001).

Conclusions FET uptake and tracer kinetics in rat gliomas are not significantly influenced by changes of BBB permeability in the tumors.