Since nanocarriers such as
liposomes are known to accumulate in
tumors of
tumor-bearing animals, and those that have entrapped a positron emitter can be used to image a
tumor by PET, we applied (18)F-labeled 100-nm-sized
liposomes for the imaging of
brain tumors.
Polyethylene glycol (PEG)-modified
liposomes, which are known to accumulate in
tumors by passive targeting and those modified with
Ala-Pro-Arg-Pro-Gly, which are known to home into angiogenic sites were used. Those
liposomes labeled with DiI fluorescence accumulated in a
glioma implanted in a rat brain 1h after the injection, although they did not accumulate in the normal brain tissues due to the protection afforded by the blood-brain barrier. Preformed
liposomes were easily labeled with 1-[(18)F]fluoro-3,6-dioxatetracosane, and enabled the imaging of
gliomas by PET with higher contrast than that obtained with [(18)F]deoxyfluoroglucose. In addition, the smallest
tumor among those tested, having a diameter of 1mm was successfully imaged by the liposomal (18)F. Therefore, nanocarrier-based imaging of
brain tumors is promising for the diagnosis of
brain cancer and possible
drug delivery-based
therapy.