Abstract
The 2-phenylaminopyrimidine derivative imatinib-mesylate, a powerful protein tyrosine kinase (PTK) inhibitor that targets abl, c-kit, and the platelet-derived growth factor receptors, is rapidly gaining a relevant role in the treatment of several types of neoplasms. Because first generation PTK inhibitors affect the activity of a large number of voltage-dependent ion channels, the present study explored the possibility that imatinib-mesylate could interfere with the activity of T-type channels, a class of voltage-dependent Ca2+ channels that take part in the chain of events elicited by PTK activation. The effect of the drug on T-type channel activity was examined using the whole-cell patch-clamp technique with Ba2+ (10 mM) as the permeant ion in human embryonic kidney-293 cells, stably expressing the rat CaV3.3 channels. Imatinib-mesylate concentrations, ranging from 30 to 300 μM, reversibly decreased CaV3.3 current amplitude with an IC50 value of 56.9 μM. By contrast, when imatinib-mesylate (500 μM) was intracellularly dialyzed with the pipette solution, no reduction in Ba2+ current density was observed. The 2-phenylaminopyrimidine derivative modified neither the voltage dependence of activation nor the steady-state inactivation of CaV3.3 channels. The decrease in extracellular Ba2+ concentration from 10 to 2 mM and the substitution of Ca2+ for Ba2+ increased the extent of 30 μM imatinib-mesylate-induced percentage of channel blockade from 25.9 ± 2.4 to 36.3 ± 0.9% in 2 mM Ba2+ and 44.2 ± 2.3% in 2 mM Ca2+. In conclusion, imatinib-mesylate blocked the cloned CaV3.3 channels by a PTK-independent mechanism. Specifically, the drug did not affect the activation or the inactivation of the channel but interfered with the ion permeation process.
Footnotes
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This work was supported by the following grants to L.A.: MIUR COFIN 2001, from the Ministero Italiano per l' Università e la Ricerca Scientifica; FIRB 2002 RBNE01E7YX_007, POP, and Legge 41 from Regione Campania; Programma Speciale art. 12bis comma 6, d. Igs 502/92 modificato 229/99 from Ministero della Salute and Regione Campania. M.R. is a Ph.D. student recipient of a fellowship grant from Ente Italiano Tabacchi.
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Article, publication date, and citation information can be found at http://jpet.aspetjournals.org.
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DOI: 10.1124/jpet.103.061184.
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ABBREVIATIONS: PTK, protein tyrosine kinase; PDGF, platelet-derived growth factor; PDGFr, platelet-derived growth factor receptor; VDCC, voltage-dependent calcium channel; HEK, human embryonic kidney; I/V, current to voltage.
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↵1 Present address: Section of Pharmacology, Department of Neuroscience, University of Aneona, Italy.
- Received October 7, 2003.
- Accepted December 10, 2003.
- The American Society for Pharmacology and Experimental Therapeutics
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