AMG319 

A PI3K Alphascreen assay is used to measure the activity of a panel of four phosphoinositide 3-kinases: PI3Kα, PI3Kβ, PI3Kγ, and PI3Kδ. Enzyme reaction buffer is prepared using sterile water and 50 mM Tris-HCl, pH 7, 14 mM MgCl₂, 2 mM sodium cholate, and 100 mM NaCl. 2 mM DTT is added fresh on the day of the experiment. The Alphascreen buffer is made using sterile water and 10 mM Tris-HCl, pH 7.5, 150 mM NaCl, 0.10% Tween 20, and 30 mM EDTA. Then 1 mM DTT is added fresh on the day of the experiment. Compound source plates used for this assay are 384-well Greiner clear polypropylene plates containing test compounds at 5 mM and diluted 1:2 over 22 concentrations. Columns 23 and 24 contained only DMSO, as these wells comprised the positive and negative controls, respectively. Source plates are replicated by transferring 0.5 μL per well into 384-well Optiplates. Each PI3K isoform is diluted in enzyme reaction buffer to 2× working stocks. PI3Kα is diluted to 1.6 nM, PI3Kβ is diluted to 0.8 nM, PI3Kγ is diluted to 15 nM, and PI3Kδ is diluted to 1.6 nM. PI(4,5)P2 is diluted to 10 μM, and ATP is diluted to 20 μM. This 2× stock is used in the assays for PI3Kα and PI3Kβ. For assay of PI3Kγ and PI3Kδ, PI(4,5)P2 is diluted to 10 μM and ATP is diluted to 8 μM to prepare a similar 2× working stock. Alphascreen reaction solutions are made using beads from the anti-GST Alphascreen kit. Two 4× working stocks of the Alphascreen reagents are made in Alphascreen reaction buffer. In one stock, biotinylated-IP₄ is diluted to 40 nM and streptavadin-donor beads are diluted to 80 μg/mL. In the second stock, PIP₃-binding protein is diluted to 40 nM and anti-GST-acceptor beads are diluted to 80 μg/mL. The plates are incubated at room temperature for 30 min. Still in the dark, 10 μL/well of the acceptor bead solution is added to columns 1-24 of the plates. The plates are then incubated in the dark for 1.5 h. The plates are read on an Envision multimode plate reader using a 680 nm excitation filter and a 520-620 nm emission filter^[1].

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B cells are purified from human peripheral blood mononuclear cells (PBMCs) by negative selection. Approximately 3×10⁴ purified B cells per well are seeded into a 96-well plate. Compounds (e.g., AMG319) are dissolved in DMSO at a concentration of 10 mM, and a 10-point, 3-fold serial dilution of the compound is carried out in DMSO. Then 0.5 μL of compound is added to each well in duplicates so that the final DMSO concentration is 0.25% and the highest compound concentration is 10 μM. After preincubating for 30 min, B cells are treated with 2 μg/mL of anti-human IgM antibody plus 300 ng/mL human CD40L or 5 ng/mL human IL-4 plus 200 ng/mL of CD40L as a counterscreen to evaluate the off-target effects. The plates are incubated at 37°C and 5% CO₂ for 72 h, then pulsed with 0.5 μCi per well ³H thymidine for 18 h, and B cells are collected to count the incorporation of ³H thymidine^[1].

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Mice^[1]
IgM membrane only homozygous transgenic mice (6- to 12-week-old female) are orally dosed with AMG319 or vehicle control (n=5 per group). At 15 min after treatment, mice are tail iv injected with 50 μg of Endotoxin-free FITC-labeled μ chain specific anti-IgM or PBS only control. Blood and spleen tissue are collected after 30 min of stimulation for drug concentration and B cell pAKT analysis via flow cytometry. Briefly, blood and dispersed splenocytes are fixed with BD Phosflow lyse/fix buffer, pelleted, and permeabilized with cold 90% MeOH. Cells are then stained with pAKT and Alexa-647 secondary and B220-Pacific Blue for FACS analysis. Stimulated B220+/anti-IgM FITC+ B cells are analyzed for pAKT levels with B220+/FITC-B cells from anti-IgM untreated mice serving as a control. Mice are maintained and experiments are performed.
Rats^[1]
Female Lewis rats (N=8/dose group) are dosed po with AMG319 or vehicle (2% HPMC, 1% Pluronic F68, 10% Captisol, pH 2.0) once a day for 10 days at various doses. Two hours after the first dosing, 200 μL of PBS containing 60 μg of KLH is administered to each rat intravenously. Ten days after the KLH priming, rats are euthanized and blood is taken by cardiac puncture for the measurement of KLH specific IgG and IgM by ELISA.

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• [1]. Cushing TD, et al. Discovery and in vivo evaluation of (S)-N-(1-(7-fluoro-2-(pyridin-2-yl)quinolin-3-yl)ethyl)-9H-purin-6-amine (AMG319) and related PI3Kδ inhibitors for inflammation and autoimmune disease. J Med Chem. 2015 Jan 8;58(1):480-511.  [Content Brief]