Prosurvival kinase PIM2 is a therapeutic target for eradication of chronic myeloid leukemia stem cells

Proc Natl Acad Sci U S A. 2019 May 21;116(21):10482-10487. doi: 10.1073/pnas.1903550116. Epub 2019 May 8.

Abstract

A major obstacle to curing chronic myeloid leukemia (CML) is the intrinsic resistance of CML stem cells (CMLSCs) to the drug imatinib mesylate (IM). Prosurvival genes that are preferentially expressed in CMLSCs compared with normal hematopoietic stem cells (HSCs) represent potential therapeutic targets for selectively eradicating CMLSCs. However, the discovery of such preferentially expressed genes has been hampered by the inability to completely separate CMLSCs from HSCs, which display a very similar set of surface markers. To overcome this challenge, and to minimize confounding effects of individual differences in gene expression profiles, we performed single-cell RNA-seq on CMLSCs and HSCs that were isolated from the same patient and distinguished based on the presence or absence of BCR-ABL. Among genes preferentially expressed in CMLSCs is PIM2, which encodes a prosurvival serine-threonine kinase that phosphorylates and inhibits the proapoptotic protein BAD. We show that IM resistance of CMLSCs is due, at least in part, to maintenance of BAD phosphorylation by PIM2. We find that in CMLSCs, PIM2 expression is promoted by both a BCR-ABL-dependent (IM-sensitive) STAT5-mediated pathway and a BCR-ABL-independent (IM-resistant) STAT4-mediated pathway. Combined treatment with IM and a PIM inhibitor synergistically increases apoptosis of CMLSCs, suppresses colony formation, and significantly prolongs survival in a mouse CML model, with a negligible effect on HSCs. Our results reveal a therapeutically targetable mechanism of IM resistance in CMLSCs. The experimental approach that we describe can be generally applied to other malignancies that harbor oncogenic fusion proteins or other characteristic genetic markers.

Keywords: BCR-ABL; CML stem cells; PIM2; imatinib resistance; targeted therapy.

Publication types

  • Research Support, N.I.H., Extramural

MeSH terms

  • Animals
  • Biphenyl Compounds / therapeutic use*
  • Drug Resistance, Neoplasm*
  • Drug Screening Assays, Antitumor
  • Fusion Proteins, bcr-abl / metabolism
  • Humans
  • Imatinib Mesylate
  • Leukemia, Experimental / drug therapy
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / drug therapy*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / metabolism
  • Mice
  • Molecular Targeted Therapy
  • Neoplastic Stem Cells / metabolism*
  • Phosphorylation
  • Protein Kinase Inhibitors
  • Protein-Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins / metabolism*
  • STAT Transcription Factors / metabolism
  • Thiazolidines / therapeutic use*
  • bcl-Associated Death Protein / metabolism

Substances

  • AZD1208
  • Biphenyl Compounds
  • PIM2 protein, human
  • Protein Kinase Inhibitors
  • Proto-Oncogene Proteins
  • STAT Transcription Factors
  • Thiazolidines
  • bcl-Associated Death Protein
  • Imatinib Mesylate
  • Fusion Proteins, bcr-abl
  • Protein-Serine-Threonine Kinases