Meisoindigo (Natura-α) is a derivative of indigo natural, might induces apoptosis and myeloid differentiation of acute myeloid leukemia (AML).

GSK3 Scintillation Proximity Assay: The competition experiments are carried out in duplicate with 10 concentrations of the inhibitor in clear-bottomed microtiter plates. The biotinylated peptide substrate, biotin-AAEELDSRAGS(PO3H2)PQL, is added at a final concentration of 2 μM in an assay buffer containing 6 milliunits of recombinant human GSK3 (equal mix of both α and β), 12 mM MOPS, pH 7.0, 0.3 mM EDTA, 0.01% β-mercaptoethanol, 0.004% Brij 35, 0.5% glycerol, and 0.5 μg of bovine serum albumin/25 μl and preincubated for 10-15 min. The reaction is initiated by the addition of 0.04 μCi of [γ-33P]ATP and unlabeled ATP in 50 mM Mg(Ac)2 to a final concentration of 1 μM ATP and assay volume of 25 μl. Blank controls without peptide substrate are used. After incubation for 20 min at room temperature, each reaction is terminated by the addition of 25 μl of stop solution containing 5 mM EDTA, 50 μM ATP, 0.1% Triton X-100, and 0.25 mg of streptavidin-coated SPA beads corresponding to ～35 pmol of binding capacity. After 6 h the radioactivity is determined in a liquid scintillation counter. Inhibition curves are analyzed by non-linear regression using GraphPad Prism.