SKLB4771 (FLT3-IN-1)

SKLB4771 (FLT3-IN-1) 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). It displays almost no inhibitory activity against the other 13 selected protein kinases. This compound potently inhibits the growth of MV4-11 cells that express FLT3-ITD, with an IC50 value of 0.006 μM. It 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].

SKLB4771 (FLT3-IN-1) is evaluated by seeding leukemia cells in a 96-well plate at 1–4 × 10⁴ cells per well, with an equal volume of medium containing increasing concentrations of this compound 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 the inhibitor 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.

In the MV4-11 xenograft model, treatment with SKLB4771 (FLT3-IN-1) at 100 mg/kg/d results in rapid and complete tumor regression in all mice of this group. At doses of 20 mg/kg/d and 40 mg/kg/d, it significantly slows down tumor growth, with inhibition rates of 66% and 84%, respectively. Throughout the experiment, no significant weight loss or other obvious signs of toxicity were observed in any of the treated mice. Tumor tissues from groups receiving this compound showed significantly fewer Ki67 (tumor mitotic index)-positive cells. TUNEL data indicated a time-dependent increase in the percentage of apoptotic cells.^[1]