The stem cell factor-c-KIT pathway must be inhibited to enable apoptosis induced by BCR-ABL inhibitors in chronic myelogenous leukemia cells.
Imatinib is an effective first-line therapy for chronic myelogenous leukemia (CML) that acts by targeting the tyrosine kinase activity of BCR-ABL. To overcome resistance, second-generation inhibitors of BCR-ABL have been developed. Among these, nilotinib is more potent against BCR-ABL than imatinib, and is effective against many imatinib-resistant BCR-ABL mutants. In this study, an in vitro flow cytometry assay to analyze imatinib- and nilotinib-induced apoptosis in CML cells has been developed. Both the drugs induced significant apoptosis in CD34+ cells from 36 CML bone marrow samples (P<10(-4)), whereas CD34+ cells from BCR-ABL negative samples were unaffected. When the experiments were carried out in the presence of a cocktail of cytokines, nilotinib- but not imatinib-induced apoptosis was inhibited. This differential inhibition was confirmed on K562 cells. A blocking anti-CD117 antibody alleviated the antiapoptotic effect of cytokines against nilotinib. Moreover, using short hairpin RNA against BCR-ABL, we showed that K562 cells were not dependent on BCR-ABL signaling as long as the stem cell factor (SCF) receptor pathway was activated. We conclude that the c-KIT pathway may substitute for BCR-ABL tyrosine kinase to activate survival signals, and that c-KIT must be inhibited besides Bcr-Abl to allow apoptosis of CML cells.
Belloc
F
F
Laboratoire d'Hématopoïèse Leucémique et Cibles Thérapeutiques, INSERM U876, Université Victor Ségalen, Bordeaux Cedex, France. francis.belloc@chu-bordeaux.fr
Airiau
K
K
Jeanneteau
M
M
Garcia
M
M
Guérin
E
E
Lippert
E
E
Moreau-Gaudry
F
F
Mahon
F-X
FX
D017209:Apoptosis / Q000187:drug effects*; D001549:Benzamides; D016207:Cytokines / Q000494:pharmacology; D016044:Fusion Proteins, bcr-abl / Q000037:antagonists & inhibitors*; D006801:Humans; D000068877:Imatinib Mesylate; D015464:Leukemia, Myelogenous, Chronic, BCR-ABL Positive / Q000188:drug therapy* / Q000473:pathology*; D010879:Piperazines / Q000494:pharmacology; D047428:Protein Kinase Inhibitors / Q000494:pharmacology; D019009:Proto-Oncogene Proteins c-kit / Q000187:drug effects / Q000378:metabolism*; D011743:Pyrimidines / Q000494:pharmacology; D019089:Stem Cell Factor / Q000037:antagonists & inhibitors / Q000378:metabolism*; D014407:Tumor Cells, Cultured
D001549:Benzamides; D016207:Cytokines; D010879:Piperazines; D047428:Protein Kinase Inhibitors; D011743:Pyrimidines; D019089:Stem Cell Factor; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit; D016044:Fusion Proteins, bcr-abl; C498826:nilotinib