Synthesis, Preclinical Toxicity, and Biodistribution of [ ¹⁸ F]AVT-011 to Assess the P-Glycoprotein Function

<b><i>Introduction:</i></b> Many studies have reported the role of P-glycoprotein (Pgp) in chemoresistance in various pathological conditions such as cancer and neurodegenerative diseases, such as Alzheimer's. In this study, we are reporting the high-performance liquid chromatography (HPLC)-based purification of fluorine-18 [¹⁸F]AVT-011 and its preclinical evaluation. <b><i>Methods:</i></b> AVT-011 was labeled with ¹⁸F using the nucleophilic substitution method by heating the reaction mixture at 110°C for 10 min, followed by purification using preparative HPLC and C18ec cartridge. The <i>in vitro</i> cell uptake study was carried out in U87 cells with and without an inhibitor. The preclinical toxicity was carried out in CD1 mice in three groups, including control, AVT-011 treated, and [¹⁸F]AVT-011 treated. The biodistribution study was done in CD1 mice (<i>n</i> = 12) after intravenous injection of 4-6 MBq [¹⁸F]AVT-011, and mice were sacrificed at various time intervals. A dose of 3.7 ± 0.7 MBq of [¹⁸F]AVT-011 was injected intravenously in the healthy Swiss albino mice, and the whole-body micro-positron emission tomography was acquired at 0-, 30-, 60-, and 120-min postinjection. <b><i>Results:</i></b> The radiochemical purity of [¹⁸F]AVT-011 was 97 ± 1.5% as evaluated by radio-HPLC with a yield of 14 ± 2% and was stable up to 95% under <i>in vitro</i> conditions in blood and <i>in vivo</i> conditions up to 4 h. The <i>in vitro</i> cell uptake study showed a significant difference in control (27.4 ± 2.1%) and blocked U987 cells (73.2 ± 3.2%) after incubation of 120 min. The tissue distribution in mice showed the highest uptake in the liver (17.3 ± 2.4%), kidneys (16.6 ± 3.1%), lungs (10.4 ± 2.9%), and spleen (5.6 ± 0.8%) at 15 min, and the activity was washed out with time. The radioactivity cleared through the hepatorenal pathway. The animal imaging study also demonstrates a similar biodistribution pattern. <b><i>Conclusions:</i></b> [¹⁸F]AVT-011 showed higher specific activity than the cartridge-based method but showed similar biological activity.