Electrochemical Determination of Enzymes Metabolizing Ellipticine in Thyroid Cancer Cells - a Tool to Explain the Mechanism of Ellipticine Toxicity to these Cells

Abstract

The antineoplastic alkaloid ellipticine is a prodrug, the pharmacological efficiency of which is dependent on its cytochrome P450 (CYP)- and/or peroxidase-mediated activation to species forming DNA adducts in target tissues. Here, we found that this compound is cytotoxic to human BHT-101, B-CPAP and 8505-C thyroid cancer cells and blocks one or more phases of cell cycle in these cancer cells.

Ellipticine toxicity to the thyroid cancer cells corresponded to levels of DNA adducts generated by the CYP- and/or peroxidase-mediated ellipticine metabolites, 12-hydroxy- and 13-hydroxyellipticine, in these cells. Cultivation of all tested cells under hypoxic conditions (1 % oxygen) led to a decrease in ellipticine toxicity.

Such a lower sensitivity of cells to ellipticine correlates with a decrease in the formation of ellipticine-derived DNA adducts in these cells. Using Western blotting, the expression of CYP1A1, 1B1, 3A4, thyroid peroxidase (TPO), cyclooxygenase-1 (COX-1) and cytochrome b(5), the enzymes that catalyze, and/or influence ellipticine metabolism, was investigated in the cancer cells.

Furthermore, the effects of ellipticine treatment on the expression levels of these proteins in thyroid cancer cells were also examined. The results indicate that the highest expression levels of cytochrome b(5) together with CYP1A1 and 3A4 determine the highest DNA adduct formation and cytotoxicity of ellipticine in B-CPAP cells.

They also demonstrate that formation of covalent DNA adducts by ellipticine is the predominant mechanism responsible for its cytotoxicity in studied cells.