A comparative study of n.c.a. sodium [¹⁸F]fluoroacetate and sodium [¹¹C]acetate in xenotransplanted tumor bearing mice

Objectives :

This study describes the radiosynthesis of [18F]fluoroacetate (18F-FAC), radiopharmacological characterization, and molecular imaging of oxidative metabolism in tumor bearing mice using 18F-FAC in comparison with 11C-ACE.

Methods :

The radiosynthesis of n.c.a. sodium 18F-FAC was performed in two step reaction sequence and subsequent SPE purification in a remotely controlled synthesis module.
Biodistribution, metabolism and small animal PET studies of 18F-FAC and 11C-ACE were carried out in rats and HT-29 tumor-bearing mice.

Results :

18F-FAC was obtained in radiochemical yields of 20-25% within 50 min. Biodistribution data showed higher initial radioactivity uptake in most organs and tissues for 18F-FAC; the initial brain uptake of 0.67 %ID/g at 5 min p.i. followed by a 22% clearance at 60 min p.i. Both radiotracers can clearly delineate the tumor. The tumor-to-muscle ration was 1.8 for 18F-FAC and 1.5 for 11C-ACE. Unlike 11C-ACE, 18F-FAC shows a slow transport of the free radiotracer from the blood pool into the tumor, and 10% of the free fraction of 18FFAC is trapped in tumor tissue.

Conclusions :

The highly reproducible remotely-controlled two step/one pot synthesis of 18FFAC represents an alternative to previously published synthesis routes. The successful PET imaging of xenotransplanted human colorectal adenocarcinoma tumor HT-29 by means of 18F-FAC shows that the radiotracer may not only be restricted for imaging of previously reported prostate cancer tumors. However, the exact mechanism of 18F-FAC tissue uptake remains unclear and should be subject of further studies.

Research Support : Supported in part by the EU FP6 ‘‘BioCare’’, proposal #505785.