2000•The Japanese Journal of PharmacologyOpen access

Reversal of Multidrug Resistance in Human Leukemia K562 by Tamolarizine, a Novel Calcium Antagonist

Norihisa Miyake, Ryousuke Fujita, Masaaki Ishikawa, Motoaki Takayanagi, Yoshio Takayanagi, Ken‐ichi Sasaki

Abstract

A new type of organic Ca2+ channel blocker, tamolarizine, was examined for its reversing effect on multidrug-resistant tumor cells. Tamolarizine synergistically potentiated the cytotoxicity of doxorubicin for doxorubicin-resistant K562 cells (K562/DXR) at a concentration of 0.1-10 microM, but had hardly any synergistic effects in the parental cell line (K562) at the same concentration. Moreover, tamolarizine inhibits the P-glycoprotein pump-efflux activity in a dose-related manner and reduces the expression of the immunoreactive P-glycoprotein in K562/DXR cells as evaluated by cytofluorimetric assay. These results indicate that tamolarizine reverses the multidrug-resistance phenotype through direct interaction with P-glycoprotein.

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Key concepts: K562 cells, P-glycoprotein, Efflux, Doxorubicin, Multiple drug resistance, Pharmacology, Cytotoxicity, Antagonist