KIT signaling governs differential sensitivity of mature and primitive CML progenitors to tyrosine kinase inhibitors

Cancer Res. 2013 Sep 15;73(18):5775-86. doi: 10.1158/0008-5472.CAN-13-1318. Epub 2013 Jul 25.

Abstract

Imatinib and other BCR-ABL1 inhibitors are effective therapies for chronic myelogenous leukemia (CML), but these inhibitors target additional kinases including KIT, raising the question of whether off-target effects contribute to clinical efficacy. On the basis of its involvement in CML pathogenesis, we hypothesized that KIT may govern responses of CML cells to imatinib. To test this, we assessed the growth of primary CML progenitor cells under conditions of sole BCR-ABL1, sole KIT, and dual BCR-ABL1/KIT inhibition. Sole BCR-ABL1 inhibition suppressed mature CML progenitor cells, but these effects were largely abolished by stem cell factor (SCF) and maximal suppression required dual BCR-ABL1/KIT inhibition. In contrast, KIT inhibition did not add to the effects of BCR-ABL1 inhibition in primitive progenitors, represented by CD34(+)38(-) cells. Long-term culture-initiating cell assays on murine stroma revealed profound depletion of primitive CML cells by sole BCR-ABL1 inhibition despite the presence of SCF, suggesting that primitive CML cells are unable to use SCF as a survival factor upon BCR-ABL1 inhibition. In CD34(+)38(+) cells, SCF strongly induced pAKT(S473) in a phosphoinositide 3-kinase (PI3K)-dependent manner, which was further enhanced by inhibition of BCR-ABL1 and associated with increased colony survival. In contrast, pAKT(S473) levels remained low in CD34(+)38(-) cells cultured under the same conditions. Consistent with reduced response to SCF, KIT surface expression was significantly lower on CD34(+)38(-) compared with CD34(+)38(+) CML cells, suggesting a possible mechanism for the differential effects of SCF on mature and primitive CML progenitor cells.

Publication types

  • Research Support, N.I.H., Extramural
  • Research Support, Non-U.S. Gov't

MeSH terms

  • Animals
  • Antigens, CD34 / metabolism
  • Apoptosis / drug effects
  • Benzamides / pharmacology*
  • Blotting, Western
  • Cell Differentiation / drug effects
  • Cell Proliferation / drug effects
  • Drug Resistance, Neoplasm*
  • Flow Cytometry
  • Fluorescent Antibody Technique
  • Fusion Proteins, bcr-abl / antagonists & inhibitors*
  • Fusion Proteins, bcr-abl / genetics
  • Fusion Proteins, bcr-abl / metabolism
  • Humans
  • Imatinib Mesylate
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / drug therapy*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / metabolism
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / pathology
  • Mice
  • Neoplastic Stem Cells / drug effects*
  • Neoplastic Stem Cells / metabolism
  • Neoplastic Stem Cells / pathology
  • Phosphatidylinositol 3-Kinases / genetics
  • Phosphatidylinositol 3-Kinases / metabolism
  • Phosphoinositide-3 Kinase Inhibitors
  • Piperazines / pharmacology*
  • Protein Kinase Inhibitors / pharmacology
  • Proto-Oncogene Proteins c-kit / antagonists & inhibitors*
  • Proto-Oncogene Proteins c-kit / genetics
  • Proto-Oncogene Proteins c-kit / metabolism
  • Pyrimidines / pharmacology*
  • RNA, Messenger / genetics
  • Real-Time Polymerase Chain Reaction
  • Reverse Transcriptase Polymerase Chain Reaction
  • Stem Cell Factor / genetics
  • Stem Cell Factor / metabolism
  • Stromal Cells / drug effects
  • Stromal Cells / metabolism
  • Stromal Cells / pathology
  • Tumor Cells, Cultured

Substances

  • Antigens, CD34
  • Benzamides
  • Phosphoinositide-3 Kinase Inhibitors
  • Piperazines
  • Protein Kinase Inhibitors
  • Pyrimidines
  • RNA, Messenger
  • Stem Cell Factor
  • Imatinib Mesylate
  • Proto-Oncogene Proteins c-kit
  • Fusion Proteins, bcr-abl