title: Imatinib mesylate (Gleevec) downregulates telomerase activity and inhibits proliferation in telomerase-expressing cell lines.
abstract: Imatinib mesylate (IM) is a tyrosine kinase inhibitor, which inhibits phosphorylation of downstream proteins involved in BCR-ABL signal transduction. It has proved beneficial in treating patients with chronic myeloid leukaemia (CML). In addition, IM demonstrates activity against malignant cells expressing c-kit and platelet-derived growth factor receptor (PDGF-R). The activity of IM in the blastic crisis of CML and against various myeloma cell lines suggests that this drug may also target other cellular components. In the light of the important role of telomerase in malignant transformation, we evaluated the effect of IM on telomerase activity (TA) and regulation in various malignant cell lines. Imatinib mesylate caused a dose-dependent inhibition of TA (up to 90% at a concentration of 15 microM IM) in c-kit-expressing SK-N-MC (Ewing sarcoma), SK-MEL-28 (melanoma), RPMI 8226 (myeloma), MCF-7 (breast cancer) and HSC 536/N (Fanconi anaemia) cells as well as in ba/F3 (murine pro-B cells), which do not express c-kit, BCR-ABL or PDGF-R. Imatinib mesylate did not affect the activity of other DNA polymerases. Inhibition of TA was associated with 50% inhibition of proliferation. The inhibition of proliferation was associated with a decrease in the S-phase of the cell cycle and an accumulation of cells in the G2/M phase. No apoptosis was observed. Inhibition of TA was caused mainly by post-translational modifications: dephosphorylation of AKT and, to a smaller extent, by early downregulation of hTERT (the catalytic subunit of the enzyme) transcription. Other steps of telomerase regulation were not affected by IM. This study demonstrates an additional cellular target of IM, not necessarily mediated via known tyrosine kinases, that causes inhibition of TA and cell proliferation.
authors.affiliation: Felsenstein Medical Research Center, Beilinson Campus, Sackler School of Medicine, Tel Aviv University, Petah-Tikva, Israel.
authors.forename: O
authors.initials: O
authors.lastname: Uziel
authors.forename: E
authors.initials: E
authors.lastname: Fenig
authors.forename: J
authors.initials: J
authors.lastname: Nordenberg
authors.forename: E
authors.initials: E
authors.lastname: Beery
authors.forename: H
authors.initials: H
authors.lastname: Reshef
authors.forename: J
authors.initials: J
authors.lastname: Sandbank
authors.forename: M
authors.initials: M
authors.lastname: Birenbaum
authors.forename: M
authors.initials: M
authors.lastname: Bakhanashvili
authors.forename: R
authors.initials: R
authors.lastname: Yerushalmi
authors.forename: D
authors.initials: D
authors.lastname: Luria
authors.forename: M
authors.initials: M
authors.lastname: Lahav
mesh_terms: D000818:Animals; D000970:Antineoplastic Agents / Q000494:pharmacology*; D001549:Benzamides; D001943:Breast Neoplasms / Q000473:pathology*; D049109:Cell Proliferation; D004305:Dose-Response Relationship, Drug; D015536:Down-Regulation; D005199:Fanconi Anemia / Q000473:pathology; D006801:Humans; D000068877:Imatinib Mesylate; D008545:Melanoma / Q000473:pathology*; D051379:Mice; D009101:Multiple Myeloma / Q000473:pathology*; D010879:Piperazines / Q000494:pharmacology*; D011505:Protein-Tyrosine Kinases / Q000037:antagonists & inhibitors / Q000494:pharmacology; D011743:Pyrimidines / Q000494:pharmacology*; D012512:Sarcoma, Ewing / Q000473:pathology*; D012878:Skin Neoplasms / Q000473:pathology*; D019098:Telomerase / Q000096:biosynthesis / Q000494:pharmacology*; D014407:Tumor Cells, Cultured
chemical_list: D000970:Antineoplastic Agents; D001549:Benzamides; D010879:Piperazines; D011743:Pyrimidines; D000068877:Imatinib Mesylate; D011505:Protein-Tyrosine Kinases; D019098:Telomerase