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 mM 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.

hTERT: a novel endogenous inhibitor of the mitochondrial cell death pathway

“…This applies to rapamycin (Zhou et al, 2003), histone deacetylase inhibitors (Wu et al, 2005), imatinib mesylate (Gleevec) (Uziel et al, 2005), the Bcl-2/Bcl-XL-specific antisense oligonucleotide 4625 (Del Bufalo et al, 2005), as well as vitamin D3 (Jiang et al, 2004). It remains to be determined, however, to which extent hTERT downmodulation may explain the cytotoxic and chemosensitizing effects of such drugs.…”

Immunodetection of human telomerase reverse-transcriptase (hTERT) re-appraised: nucleolin and telomerase cross paths

“…However, we were not able to identify any amino-acid sequence similarity between the two proteins that could have the immunological properties of NCL-hTERT, and the question of this misrecognition remains non-elucidated. Nevertheless, the identification of nucleolin as the protein recognized by NCL-hTERT antibody should lead to an urgent re-evaluation of the results obtained with this antibody and that are already published (Brustmann, 2005;Dalerba et al, 2005;Domont et al, 2005;Dutu et al, 2005;Elkak et al, 2005;Falchetti et al, 2003;Fullen et al, 2005;Gulmann et al, 2005;Kraemer et al, 2003;Lantuejoul et al, 2005;Lantuejoul et al, 2004;Luzar et al, 2005a;Luzar et al, 2005b;Maes et al, 2005;Sabah et al, 2004;Sato et al, 2004;Smith et al, 2004;Uziel et al, 2005;Yan et al, 2004).…”

“…The most salient points are herein reported. A new mouse monoclonal antibody (Novocastra, NCL-hTERT, clone 44F12) has been widely used, based on the assumption that this antibody correctly recognizes the protein peptide against which it has been claimed to be developed (Brustmann, 2005;Dalerba et al, 2005;Domont et al, 2005;Dutu et al, 2005;Elkak et al, 2005;Falchetti et al, 2003;Fullen et al, 2005;Gulmann et al, 2005a;Kraemer et al, 2003;Lantuejoul et al, 2005;Lantuejoul et al, 2004;Luzar et al, 2005a;Luzar et al, 2005b;Maes et al, 2005;Sabah et al, 2004;Sato et al, 2004;Smith et al, 2004;Uziel et al, 2005;Yan et al, 2004). Using this antibody, we confirmed on western blots, as previously shown, the labelling of a unique protein band in the 100 kDa area, which is generally thought consistent with the estimated molecular weight of telomerase of 127 kDa (Wick et al, 1999).…”

Carvedilol in glioma treatment alone and with imatinib in vitro

“…Imatinib mesylate (IM; STI-571, Gleevec ® ) an ATP analogue, potently and selectively inhibits several protein tyrosine kinase receptors for platelet-derived growth factor (PDGF), including breakpoint cluster regionabelson (Bcr-Abl) and c-kit by interacting with their ATPbinding site (2,3). Mitochondria and telomerase are also targets of IM (4,5). IM was primarily designed to treat chronic myelogenous leukemia (CML), and is currently the drug of choice for metastatic gastrointestinal stromal tumors (6,7).…”