SKLB4771 (FLT3-IN-1)

SKLB4771 just weakly inhibits Aurora A, FMS, FLT4, and c-Kit (IC50s: 1.5 μM, 2.8 μM, 3.7 μM, and 6.8 μM, respectively). SKLB4771 displays almost no inhibitory activity against the other 13 selected protein kinases. SKLB4771 potently inhibits the growth of MV4-11 cells that express FLT3-ITD, with an IC50 value of 0.006 μM. SKLB4771 just exhibits 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).^[1].

The leukemia cells are seeded in a 96-well plate at 1−4 × 10⁴ cells per well, and an equal volume of medium containing increasing concentrations of inhibitors is added to each well. At the end of the incubation period (72 h at 37 °C), 20 μL of 5 mg/mL MTT reagent is added per well for 2−4 h of incubation, and 50 μL of 20% acidified SDS per well is used to lyse the cells. The other cell lines are seeded in 96-well plates at a density of 2−5 × 10³ cells/well for 24 h followed by replacement of the medium with serial dilutions of inhibitors in culture medium. Following a 72-h incubation, the MTT reagent is added for a 2−4-h incubation, and 100% DMSO is used to dissolve the cells.

Treatment with SKLB4771 at 100 mg/ kg/d results in rapid and complete tumor regression in all mice of this group in the MV4-11 xenograft model. SKLB4771 treatment at 20 mg/kg/d and 40 mg/kg/d significantly slows 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 are observed for all of the SKLB4771-treated mice. The tumor tissues from the SKLB4771-treated groups show significantly fewer Ki67(tumor mitotic index)-positive cells. The TUNEL data shows an obvious increase in the percentage of apoptotic cells in a time-dependent manner.^[1]