Imatinib inhibits proliferation of Ewing tumor cells mediated by the stem cell factor/KIT receptor pathway, and sensitizes cells to vincristine and doxorubicin-induced apoptosis.
OBJECTIVE
The stem cell factor/KIT receptor loop may represent a novel target for molecular-based therapies of Ewing tumor. We analyzed the in vitro impact of KIT blockade by imatinib in Ewing tumor cell lines.


RESULTS
KIT expression was detected in 4 of 4 Ewing tumor cell lines and in 49 of 110 patient samples (44.5%) by immunohistochemistry and/or Western blot analysis. KIT expression was stronger in Ewing tumors showing EWS-FLI1 nontype 1 fusions. Despite absence of c-kit mutations, constitutive and ligand-inducible phosphorylation of KIT was found in all tumor cell lines, indicating an active receptor. Treatment with KIT tyrosine kinase inhibitor imatinib (0.5-20 micro M) induced down-regulation of KIT phosphorylation and dose response inhibition of cell proliferation (IC(50), 12-15 micro M). However, imatinib administered alone at doses close to IC(50) for growth inhibition (10 micro M) did not induce a significant increase in apoptosis. We then analyzed if blockade of KIT loop through imatinib (10 micro M) was able to increase the antitumor in vitro effect of doxorubicin (DXR) and vincristine (VCR), drugs usually used in Ewing tumor treatment. Addition of imatinib decreased in 15-20 and 15-36% of the proliferative rate of Ewing tumor cells exposed to DXR and VCR, respectively, and increased in 15 and 30% of the apoptotic rate of Ewing tumor cells exposed to the same drugs.


CONCLUSIONS
Inhibition of Ewing tumor cell proliferation by imatinib is mediated through blockade of KIT receptor signaling. Inhibition of KIT increases sensitivity of these cells to DXR and VCR. This study supports a potential role for imatinib in the treatment of Ewing tumor.
González
Iranzu
I
Department of Histology and Pathology, School of Medicine-Universidad de Navarra, Pamplona, Spain.
Andreu
Enrique J
EJ
Panizo
Angel
A
Inogés
Susana
S
Fontalba
Ana
A
Fernández-Luna
José Luis
JL
Gaboli
Mirella
M
Sierrasesúmaga
Luis
L
Martín-Algarra
Salvador
S
Pardo
Javier
J
Prósper
Felipe
F
de Alava
Enrique
E
D000903:Antibiotics, Antineoplastic / Q000494:pharmacology; D000970:Antineoplastic Agents / Q000494:pharmacology; D000972:Antineoplastic Agents, Phytogenic / Q000494:pharmacology; D017209:Apoptosis; D001549:Benzamides; D015153:Blotting, Western; D001859:Bone Neoplasms / Q000188:drug therapy*; D002455:Cell Division; D045744:Cell Line, Tumor; D004305:Dose-Response Relationship, Drug; D004317:Doxorubicin / Q000494:pharmacology*; D004791:Enzyme Inhibitors / Q000494:pharmacology; D005434:Flow Cytometry; D006801:Humans; D000068877:Imatinib Mesylate; D007150:Immunohistochemistry; D007202:Indicators and Reagents / Q000494:pharmacology; D020128:Inhibitory Concentration 50; D008024:Ligands; D019950:Mitogen-Activated Protein Kinase 1 / Q000378:metabolism; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases / Q000378:metabolism; D010766:Phosphorylation; D010879:Piperazines / Q000494:pharmacology*; D011233:Precipitin Tests; D011419:Propidium / Q000494:pharmacology; D019009:Proto-Oncogene Proteins c-kit / Q000378:metabolism; D011743:Pyrimidines / Q000494:pharmacology*; D012333:RNA, Messenger / Q000378:metabolism; D020133:Reverse Transcriptase Polymerase Chain Reaction; D012512:Sarcoma, Ewing / Q000188:drug therapy*; D015398:Signal Transduction; D019089:Stem Cell Factor / Q000096:biosynthesis*; D014750:Vincristine / Q000494:pharmacology*
D000903:Antibiotics, Antineoplastic; D000970:Antineoplastic Agents; D000972:Antineoplastic Agents, Phytogenic; D001549:Benzamides; D004791:Enzyme Inhibitors; D007202:Indicators and Reagents; D008024:Ligands; D010879:Piperazines; D011743:Pyrimidines; D012333:RNA, Messenger; D019089:Stem Cell Factor; D011419:Propidium; D014750:Vincristine; D004317:Doxorubicin; D000068877:Imatinib Mesylate; D019009:Proto-Oncogene Proteins c-kit; D019950:Mitogen-Activated Protein Kinase 1; D048052:Mitogen-Activated Protein Kinase 3; D020928:Mitogen-Activated Protein Kinases