Time-Resolved Fluorescence Resonance Energy Transfer (TR-FRET) Assay: The test detects the phosphorylation of the substrate GFP-4EBP1 using a terbium-labelled antibody that is specific for the phospho-Thr46 epitope. Binding of the Tb-antibody to the phosphorylated GFP peptide allows the transfer of energy from Tb, excited at 340 nm, to GFP with an increase in the fluorescence emission of the GFP at 520 nm. The test is performed in 96-well format (Corning/Costar 96 black flat-bottomed half-wells plate, ref. 3694) in a total volume of 30 ul. To 1 ul of inhibitor in 100% DMSO are added (final concentrations) 400 nM of GFP-4EBP1 (Invitrogen PV4759), 8 uM of ATP, 200 ng/ml of enzyme (human recombinant aa mTOR 1360-2549, Invitrogen PV4753) in a buffer of HEPES 50 mM pH 7.5, EGTA 1 mM, MnCl2 10 mM, BSA 0.1 mg/ml, glycerol 0.5%, NV-10 0.1 mg/ml, DTT 2 mM. The mixture is incubated for 30 minutes at room temperature. 10 ul of solution are taken up and the reaction is quenched by adding 10 ul of Tb-antibody solution (Invitrogen PV4757)/EDTA.
Enzyme Assay: The test uses a lucifeurerin/luciferase system to measure the concentration of ATP and its consumption during the enzymatic reaction. The test is performed in 96-well format (Corning/Costar 96 black flat-bottomed half-wells plate, ref. 3694) in a total volume of 30 μl. To 1 μl of inhibitor in 100% DMSO are added (final concentrations) 50 μM of the substrate PIP2 ((L-α-phosphatidyl-D-myoinositol 4,5-bisphosphate, Echelon 117P-4516-0500), 2 μM of ATP and 1.7 μg/ml of PI3Kα, (p110α/p85α, Invitrogen PV4788) in a buffer of Tris/HCl 50 mM pH 7.5, EGTA 1 mM, MgCl2 10 mM, Chaps 0.03%, 1 mM DTT). After 90 minutes, the reaction is quenched by adding 20 μl/well of KinaseGlo reagent (Promega V6713). After 10 minutes in the dark, the luminescence is read on the PHERAStar microplate reader (reading at 0.8 sec/well).