In vitro and in vivo Stability and the Octanol–Water Partition Coefficient Study (logP)

For the stability tests in vivo, mice were injected with 11.1 MBq (300 μCi) of the [¹⁸F]AlF-NOTA-NSC-GLU (0.2 ml) via the tail vein. The mice were sacrificed at 1 h post-injection. Blood samples were collected from the eyeballs and then centrifuged (6,000 rpm for 4 min) to separate plasma and were used for the HPLC analysis.

Additionally, a sample of [¹⁸F]AlF-NOTA-NSC-GLU (1.48 MBq, 20 μl) dissolved in normal saline was incubated with 200 μl of fetal bovine serum at 37°C for 120 min. An aliquot of the serum sample was filtered through a 0.22-μm Millipore filter and was used for the HPLC analysis.

For the octanol–water partition coefficient study, 20 μl of [¹⁸F]AlF-NOTA-NSC-GLU (740 KBq, 20 μCi) in saline was added to an equal volume [octanol/phosphate buffered saline (PBS): 5/5 ml] mixture. The mixture was allowed to stand for complete phase separation prior to use by stirring in a vortex mixer for 2 min and centrifuging at 3,000 rpm for 5 min. Samples of 300 μl were taken from each layer and radioactivity was measured with a γ-counter. The logP value was calculated [logP = log10 (counts of octanol/counts of PBS)].