Maternal embryonic leucine zipper kinase (MELK) is a serine/threonine kinase that regulates signaling central to cell cycling, stem cell renewal, apoptosis, and other cellular processes. MELK is overexpressed in some forms of cancer, particularly those with aggressive undifferentiated tumors. OTSSP167 is a potent inhibitor of MELK (IC50 = 0.41 nM). It suppresses the growth of diverse cancer cell lines at low nanomolar concentrations. It also blocks the phosphorylation of MELK-specific substrates and reduces the ability of MCF-7 breast cancer cells to invade and form spheroids in Matrigel. OTSSP167 is also effective in vivo when delivered either orally or intravenously, suppressing the growth of xenograft tumors in mice.
