In vitro activity: SGI-1027 inhibits DNA methylation by directly inhibiting DNMTs, and results in selective degradation of DNMT1 in a wide variety of human cancer cell lines. SGI-1027 exhibits minimal or no cytotoxic effect in rat hepatoma H4IIE cells. SGI-1027 (0-100 μM) exhibits a moderate pro-apoptotic effect on U937 human leukemia cell line with no relevant changes on the cell cycle.

Kinase Assay: DNA methylase activity is assayed by measuring the incorporation of 3H1-methyl group from Ado-Met into DNA using DE-81 ion exchange filter binding assay with some modifications. Human recombinant DNMT1, recombinant mouse Dnmt3a/ Dnmt3b (500 ng) is incubated with 500 ng of poly(dI-dC) or hemimethylated DNA duplex and 75 or 150 nM (0.275μCi or 0.55μCi) of [methyl-3H]-Sadenosylmethionine (Ado-Met) in a total volume of 50 μl at 37°C for 1hr. or M. Sss I is assayed in the supplier’s buffer. SGI-1027 or decitabine is added at indicated concentrations. Each reaction is performed in duplicate and included controls with no inhibitor or no DNA. The reaction is stopped by soaking reaction mixture onto a Whatman DE-81 ion exchange filter disc, washed (five times, 10 min each, with 0.5M Na-phosphate buffer; pH 7.0) dried and counted in a scintillation counter. The background radioactivity (no DNA control) is subtracted from the values obtained with reaction mixtures containing DNA and the radioactivity obtained in the reaction without any inhibitor is considered as 100% activity. IC50 is determined by interpolation from the plot of percent activity versus inhibitor concentration. To determine the nature of inhibition of DNMTase activity by SGI-1027, DNMT1 enzyme activityis measured in presence of a fixed concentration of inhibitor (0, 2.5, 5, and 10μM) while one of the two (Ado-Met or DNA) was varied in a particular reaction mixture. At a fixed concentration of DNA (500 ng) varying concentrations of Ado-Met used are from 25-500 nM, respectively. Similarly, final DNA concentrations are varied from (25-500ng) at 75 nM Ado-Met. 

Cell Assay: Rat hepatoma H4IIE cells are used as the test system. These cells are grown in DMEM supplemented with fetal bovine serum (10%) and calf serum (10%). Cells are seeded into 96-well plates and after 48 h exposed to SGI-1027 at concentrations ranging from 0 to 300 µmol/L. The solubility is determined by Nephalometry techniques immediately after dosing and before harvesting the cells at 24 h. Following the exposure period, the cells or their supernatant (culture medium) are analyzed for changes in cell proliferation (propidium iodide), membrane leakage (α-GST), mitochondrial function [3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide and cellular ATP], oxidative stress (intracellular GSH and 8-isoprostane), and apoptosis. The half-maximal toxic concentration (TC50) is determined from the dose-response curves.