Article Text

  1. B. W. Parcells,
  2. A. K. Ikeda,
  3. T. B. Moore,
  4. K. B. Glaser,
  5. K. M. Sakamoto
  1. Department of Pediatrics, David Geffen School of Medicine at UCLA, Los Angeles, CA, and Abbott Laboratories, Chicago, IL


Purpose of Study Constitutive activation of the FMS-tyrosine kinase 3 (FLT3) receptor has been identified as the most frequent genetic abnormality in acute myeloid leukemia (AML) and also confers a poor prognosis. FLT3 receptor signaling is deregulated due to internal tandem duplications (ITD) in the juxtamembrane domain or point mutations in the activation loop of the kinase domain (TKD. ABT-869 is a novel multitargeted small-molecule inhibitor of receptor tyrosine kinases in the type III subfamily that includes FLT3, c-FMS, c-KIT, and all VEGF and PDGF receptors. ABT-869 inhibits the growth of a human myeloid leukemia cell line MV-411 that expresses the FLT3-ITD mutation both in vitro and in vivo. To determine the effects of ABT-869 on other mutant FLT3-expressing cell lines, we treated murine lymphoid BaF3 cells stably expressing FLT3-ITD or FLT3-D835V and wild-type Baf3 cells at varying concentrations of the drug.

Methods The viability of BaF3 cells treated with ABT-869 at concentrations ranging from 1 pM to 10 μM was determined using trypan-blue exclusion method. The effect of ABT-869 on apoptosis was examined using annexin V-FITC or propidium iodide staining and FACs analysis. The effect of ABT-869 on subcutaneous tumors in SCID mice was examined by injecting 5 × 106 of FLT3-ITD, FLT3-D835V, or wild-type cells (n = 15/group). Tumor growth was measured by vernier caliper. Three weeks after inoculation, mice received daily oral doses of vehicle or ABT-869 (20 mg/kg or 40 mg/kg).

Results ABT-869 inhibited the growth of FLT3-ITD-expressing cells at an IC50 of 10 nM and of FLT3-D835V cells at an IC50 of 100 nM. Growth of wild-type BaF3 cells was inhibited by ABT-869 at an IC50 of 10 μM. Apoptosis was observed in BaF3 cells expressing FLT3-ITD 24 hours after ABT-869 treatment at a concentration of 10 nM but not in BaF3-D835V or wild-type cells. Preliminary in vivo data suggest that ABT-869 induced significant tumor regression in FLT3-ITD-injected mice and increased survival. ABT-869 did not significantly affect tumor growth or survival in FLT3-D835V or wild-type injected mice.

Conclusions Baf3 cells expressing the FLT3-ITD are more susceptible to the proapoptotic effects of ABT-869 compared to cells expressing the D835V mutation or wild-type cells. Our results suggest that ABT-869 may be effective in AML patients who have blasts harboring the FLT3-ITD mutation.

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