¹¹C-labeling DAPT a small-molecular inhibitor of the Notch signaling pathway, and preliminary imaging study of dynamic distribution in a normal rabbit

Objective: To label N-[N-(3, 5-difluorophenacetyl)-L-alanyl]-S-phenylglycine t-butyl ester (DAPT), an inhibitor of the Notch signaling pathway, with ¹¹C and perform preliminarily dynamic imaging in normal rabbit. Methods: Proliferation of human pancreatic cancer cell line MiaPaCa-2 were assessed by cell counting kit-8 method after treatment with various concentrations of DAPT and CH₃-DAPT. Half-maximal inhibitory concentration (IC₅₀) was calculated. DAPT was then used as a precursor to prepare ¹¹C-N-methyl-DAPT (¹¹C-DAPT) with a fully automatic synthesizer. The final product was purified through semipreparative high performance liquid chromatography (HPLC). After intravenous injection of 125.8 MBq (3.4 mCi) ¹¹C-DAPT, a normal New Zealand rabbit was subjected to dynamic whole-body PET/CT scanning. The dynamic changes in radioactivity were measured by drawing regions of interest over different organs. Results: DAPT and CH₃-DAPT concentration-dependently inhibited the growth of the human pancreatic cancer cell line MiaPaCa-2. The IC₅₀ values were 64.2 and 180.0 μmol/L at 72 h after administration, respectively. ¹¹C-DAPT was synthesized for approximately 30 min. The uncorrected radiochemical yield was 25%-35%. Radiochemical purity was above 95%. ¹¹C-DAPT was mainly excreted through the kidney, the highest uptake was in the kidneys, and the uptake in the liver, intestine, lung, and brain was relatively low. The tracer uptake in the kidneys and liver peaked at 7 min after injection and decreased to > 50% at 28 min. Conclusions: ¹¹C-DAPT can be easily and rapidly synthesized with high radiochemical purity. Preliminary PET/CT imaging can lay a foundation for further investigating ¹¹C-DAPT as a novel molecular probe. (authors)