| Assay Method Information | |
| | HTRF PI3K Biochemical Assay |
| Description: | The PI3-Kinase biochemical assays were developed to measure the intrinsic potency and compound dependent inhibition of the alpha, beta, delta, and gamma PI3K isoform enzymes. This assay was developed and further optimized from a kit produced by Upstate (Millipore catalog #33-047) and has been configured for HTS and SAR screening. Briefly, this procedure exploits the exquisite specificity and high affinity binding of enzyme reaction substrate phosphatidyl(3,4,5)triphosphate (PIP3) to the GRP1 pleckstrin homology (PH) domain to generate the signal. In the absence of PIP3, an HTRF (Homogeneous Time-Resolved Fluorescence energy transfer) complex is formed consisting of europium (Eu)-labeled anti-GST, GSTtagged GRP1-PH domain, biotin-PIP3 and streptavidin conjugated APC. The native PIP3 produced by PI3-Kinase activity disrupts, in a competitive manner, the biotin-PIP3 from the PH domain, resulting in the loss of energy transfer (HTRF complex) and a decrease in the signal. The format of this assay is the same for all 4 isoforms of PI3K; the differences lie in the concentration of enzyme used to achieve robust assay window. The alpha, beta, and delta assays are run at 0.5, 1, and 0.3 nM enzymes and the gamma assay is run at 5 nM enzyme. The ATP concentration is 100 uM in the alpha, beta, and delta assays and 50 uM ATP in the gamma assay. All reactions are run at 50 uM PIP2.Assay ProtocolCompounds are serially diluted (3-fold in 100% DMSO) across a 384-well polypropylene source plated from column 3 to column 12 and column 13 to column 22, to yield 10 concentration dose response for each test compound. Columns 1, 2, 23 and 24 contain either only DMSO or pharmacological known control inhibitor. Once titrations are made, 2.5 nL of the compounds on 384 well plates are reformatted and transferred by acoustic dispense in quadruplicates to a 1536 assay plate (Greiner) to assay across all four PI3K isoform enzymes.The PI3-Kinase biochemical assay was optimized using the HTRF kit provided by Upstate (Millipore). The assay kit contains six reagents: 1) 4× Reaction Buffer; 2) native PIP2 (substrate); 3) Stop (EDTA); 4) Detection Mix A (Streptavidin-APC); 5) Detection Mix B (Eu-labeled Anti-GST plus GST-tagged PH-domain); 6) Detection Mix C. In addition, the following items were obtained or purchased; PI3Kinase (alpha 14-602, beta 14-603, gamma 14-558 and delta 14-604 from Upstate; Millipore), dithiothreitol (Sigma, D-5545), Adenosine-5′ triphosphate (InVitrogen, Cat # AS001A), native PIP3 (PI(3,4,5)P3, diC8, H+, CELLSIGNALS, INC. Cat #907) DMSO (Sigma, 472301).PI3Kinase Reaction Buffer was prepared by dilution the stock 1:4 with de-ionized water. DTT, PIP2 and Biotin-PIP3 were added to 1536 assay plate at a final concentration of 5 mM, 5 mM and 25 nM on the day of use. Enzyme addition and compound pre-incubation were initiated by the addition of 1.25 ul of PI3K (at twice its final concentration) in the 1× reaction buffer to all wells using a BioRaptor. Plates were incubated at room temperature for 15 minutes. Reactions are initiated by addition of 1.25 ul of 2× substrate solution (PIP2 and ATP in 1× reaction buffer) using BioRaptor. Plates were incubated in humidified chamber at room temperature for one hour. Reactions were quenched by addition of 0.625 uL of stop solution to all wells using the BioRaptor. The quenched reactions are then processed to detect product formation by adding 0.625 uL of Detection Solution to all wells using the BioRaptor (Detection mix C, Detection Mix A, and Detection Mix B combined together in an 18:1:1 ratio prepared 2 hours prior to use). Following a one hour incubation in the dark, the HTRF signal was measured on the Envision plate reader set for 330 nm excitation and dual emission detection at 620 nM (Eu) and 665 nM (APC).Data AnalysisThe loss of the HTRF signal is due to the displacement of biotinylated-PIP3 from the PH domain by the PI3K-dependent conversion of PIP2 to PIP3. |
| Affinity data for this assay | |
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