SKLB4771 is a novel potent and selective Flt3 inhibitor with IC50 of 10 nM; against FLT3-ITD-expressing MV4-11 cells with IC50 of 6 nM.IC50 value: 10 nM (in vitro) [1]Target: in vitro: SKLB4771 inhibited FLT3 phosphorylation in a dose-dependent manner. Consistent with the downregulation of the phosphorylation of FLT3, the phosphorylation of the downstream signaling proteins STAT5 and ERK1/2 was also significantly inhibited at concentrations >0.1 μM. SKLB4771 potently inhibited the growth of MV4-11 cells that express FLT3-ITD, with an IC50 value of 0.006 μM. It just exhibited very weak inhibitory activity against human T lymphoma Jurkat cells, human Burkitt's lymphoma Ramos cells, human lung cancer PC-9 and H292 cells, and human epithelial carcinoma A431 cells (IC50: 3.05 μM, 6.25 μM, 3.72 μM, 6.94 μM, and 8.91 μM, respectively). For other leukemia and solid tumor cell lines, including K562, U937, Karpas299, HCC827, A549, H2228, H820, MDA-MB-231, BT474, MCF-7, HCT116, SW480, LoVo, HeLa, SKOV-3, SK, DU145, PC-3, A431, and SH-SY5Y [1].in vivo: Treatment with SKLB4771 at 100 mg/kg/d resulted in rapid and complete tumor regression in all mice of this group. SKLB4771 treatment at 20 mg/kg/d and 40 mg/kg/d significantly slowed down the tumor growth; the tumor inhibition rates are 66% and 84%, respectively. Moreover, during the whole experiment, no significant weight loss or any other obvious signs of toxicity were observed for all of the SKLB4771 treated mice.

[1]. Li WW, et al. Discovery of the novel potent and selective FLT3 inhibitor 1-{5-[7-(3- morpholinopropoxy)quinazolin-4-ylthio]-[1,3,4]thiadiazol-2-yl}-3-p-tolylurea and its anti-acute myeloid leukemia (AML) activities in vitro and in vivo. J Med Chem. 2012 Apr 26;55(8):3852-66.