Compensatory PI3-kinase/Akt/mTor activation regulates imatinib resistance development

Leukemia. 2005 Oct;19(10):1774-82. doi: 10.1038/sj.leu.2403898.


BCR/ABL-kinase mutations frequently mediate clinical resistance to the selective tyrosine kinase inhibitor Imatinib mesylate (IM, Gleevec). However, mechanisms that promote survival of BCR/ABL-positive cells before clinically overt IM resistance occurs have poorly been defined so far. Here, we demonstrate that IM-treatment activated the phosphatidylinositol 3-kinase (PI3K)/Akt/mammalian target of rapamycin (mTor)-pathway in BCR/ABL-positive LAMA-cells and primary leukemia cells in vitro, as well as in a chronic phase CML patient in vivo. In fact, PI3K/Akt-activation critically mediated survival during the early phase of IM resistance development before manifestation of BCR/ABL-dependent strong IM resistance such as through a kinase mutation. Accordingly, inhibition of IM-induced Akt activation using mTor inhibitors and Akt-specific siRNA effectively antagonized development of incipient IM-resistance in vitro. In contrast, IM-resistant chronic myeloid leukemia (CML) patients with BCR/ABL kinase mutations (n=15), and IM-refractory BCR/ABL-positive acute lymphatic leukemia patients (n=2) displayed inconsistent and kinase mutation-independent autonomous patterns of Akt-pathway activation, and mTor-inhibition overcame IM resistance only if Akt was strongly activated. Together, an IM-induced compensatory Akt/mTor activation may represent a novel mechanism for the persistence of BCR/ABL-positive cells in IM-treated patients. Treatment with mTor inhibitors may thus be particularly effective in IM-sensitive patients, whereas Akt-pathway activation variably contributes to clinically overt IM resistance.

Publication types

  • Research Support, Non-U.S. Gov't

MeSH terms

  • Antineoplastic Agents / therapeutic use*
  • Apoptosis / drug effects*
  • Benzamides
  • Blotting, Western
  • Cell Cycle / drug effects
  • Drug Resistance, Neoplasm*
  • Enzyme Activation / drug effects
  • Everolimus
  • Fusion Proteins, bcr-abl / genetics
  • Fusion Proteins, bcr-abl / metabolism
  • Humans
  • Imatinib Mesylate
  • Immunosuppressive Agents / pharmacology
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / drug therapy*
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / metabolism
  • Leukemia, Myelogenous, Chronic, BCR-ABL Positive / pathology
  • Mutagenesis
  • Phosphatidylinositol 3-Kinases / metabolism*
  • Phosphorylation / drug effects
  • Piperazines / therapeutic use*
  • Protein Kinases / chemistry
  • Protein Kinases / metabolism*
  • Protein Serine-Threonine Kinases / genetics
  • Protein Serine-Threonine Kinases / metabolism*
  • Proto-Oncogene Proteins / genetics
  • Proto-Oncogene Proteins / metabolism*
  • Proto-Oncogene Proteins c-akt
  • Pyrimidines / therapeutic use*
  • RNA, Messenger / genetics
  • RNA, Messenger / metabolism
  • RNA, Small Interfering / pharmacology
  • Reverse Transcriptase Polymerase Chain Reaction
  • Ribosomal Protein S6 Kinases, 70-kDa / metabolism
  • Sirolimus / analogs & derivatives
  • Sirolimus / pharmacology
  • TOR Serine-Threonine Kinases
  • Tumor Cells, Cultured


  • Antineoplastic Agents
  • Benzamides
  • Immunosuppressive Agents
  • Piperazines
  • Proto-Oncogene Proteins
  • Pyrimidines
  • RNA, Messenger
  • RNA, Small Interfering
  • Imatinib Mesylate
  • Everolimus
  • Protein Kinases
  • MTOR protein, human
  • Fusion Proteins, bcr-abl
  • AKT1 protein, human
  • Protein Serine-Threonine Kinases
  • Proto-Oncogene Proteins c-akt
  • Ribosomal Protein S6 Kinases, 70-kDa
  • TOR Serine-Threonine Kinases
  • Sirolimus