Jensen, Andreas Tue Ingemann2; Binderup, Tina5; Andresen, Thomas Lars1; Kjær, Andreas5; Rasmussen, Palle3
1 Department of Micro- and Nanotechnology, Technical University of Denmark2 Center for Nuclear Technologies, Technical University of Denmark3 The Hevesy Laboratory, Center for Nuclear Technologies, Technical University of Denmark4 Colloids and Biological Interfaces, Department of Micro- and Nanotechnology, Technical University of Denmark5 Copenhagen University Hospital
A novel [F-18]-labeled cholesteryl ether lipid probe was prepared by synthesis of the corresponding mesylate, which was [F-18]-fluorinated by a [F-18]KF, Kryptofix-222, K2CO3 procedure. Fluorination was done for 10 minutes at 165 degrees C and took place with conversion between 3 and 17%, depending on conditions. Radiolabelling of the probe and subsequent in situ purification on SEP-Paks were done on a custom-built, fully automatic synthesis robot. Long-circulating liposomes were prepared by hydration (magnetic stirring) of a lipid film containing the radiolabeled probe, followed by fully automated extrusion through 100-nm filters. The [F-18]-labeled liposomes were injected into nude, tumor-bearing mice, and positron emission tomography (PET) scans were performed several times over 8 hours to investigate the in vivo biodistribution. Clear tumor accumulation, as well as hepatic and splenic uptake, was observed, corresponding to expected liposomal pharmacokinetics. The tumor accumulation 8 hours postinjection accounted for 2.25 +/- 0.23 (mean +/- standard error of the mean) percent of injected dose per gram (%ID/g), and the tumor-to-muscle ratio reached 2.20 +/- 0.24 after 8 hours, which is satisfactorily high for visualization of pathological lesions. Moreover, the blood concentration was still at a high level (13.9 +/- 1.5 %ID/g) at the end of the 8-hour time frame. The present work demonstrates the methodology for automated preparation of radiolabeled liposomes, and shows that [F-18]-labeled liposomes could be suitable as a methodology for visualization of tumors and obtaining short-term pharmacokinetics in vivo.
Journal of Liposome Research, 2012, Vol 22, Issue 4, p. 295-305