| In Vitro | In vitro activity: OTSSP167 inhibits A549, T47D, DU4475, and 22Rv1 cancer cells, in which MELK is highly expressed, with IC50 values of 6.7, 4.3, 2.3, and 6.0 nM, respectively. OTSSP167 inhibited the phosphorylation of PSMA1 (proteasome subunit alpha type 1) and DBNL (drebrin-like), which are novel MELK substrates and are important for stem-cell characteristics and invasiveness. OTSSP167 suppresses mammosphere formation of breast cancer cells through the inhibition of PSMA1 phosphorylation.
Kinase Assay: MELK recombinant protein (0.4 μg) is mixed with 5 μg of each substrate in 20 μL of kinase buffer containing 30 mM Tris-HCl (pH), 10 mM DTT, 40 mM NaF, 10 mM MgCl2, 0.1 mM EGTA with 50 μM cold-ATP and 10 Ci of [γ-32P]ATP for 30 min at 30 °C. The reaction is terminated by addition of SDS sample buffer and boiled for 5 min prior to SDS-PAGE. The gel is dried and autoradiographed with intensifying screens at room temperature. OTSSP167 (final concentration of 10 nM) is dissolved in DMSO and added to kinase buffer before the incubation.
Cell Assay: OTSSP167 inhibits cell proliferation of a variety of cancer cell lines including A549, T47D, DU4475 and 22Rv1. The IC50 values are 6.7nM, 4.3nM, 2.3nM and 6nM, respectively. |
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