In vitro activity: MG-101 (ALLN) effectively inhibits cysteine proteinases with ID50 of 7 nM and 13 nM for cathepsins L and B, respectively. MG-101 (ALLN) shows very weak inhibitory activities towards cathepsin D (aspartic protease) and subtilisin (serine protease). MG-101 thus transforms NIH3T3 cells and also induces differentiation of PC12 pheochromocytoma cells. MG-101, as an inhibitor of Ca(2+)-dependent cysteine proteases, inhibits the degradation of HMG-CoA reductase and HMGal in cholesterol biosynthesis. In HCT116 cells, MG-101 decreases cell viability and tumor growth, and induces apoptosis response through Bax translocation from cytosol to mitochondria.

Kinase Assay: MG-101 is a potent inhibitor of cysteine proteases which inhibits calpain I, calpain II, cathepsin B and cathepsin L with Kis of 190, 220, 150 and 500 pM, respectively.

Cell Assay: Cells viability is assayed using Cell Counting Kit-8 following manufacturer’s protocol. All HCT116 cell typesare seeded into each well of 96-well plate, cultured to 80% density and treated with different doses of ALLN for 24 h. Medium is then replaced by 100 μl fresh McCoy’s 5A complete medium with 10% CCK-8 reagent and incubated for 1 h. Absorbance is measured at 450 nm using a microplate reader. Results are shown as death percentages.