Evaluation of bioreductive activation of anticancer drugs idarubicin and mitomycin C by NADH-cytochrome b5 reductase and cytochrome P450 2B4

DNA damage induced by NADPH cytochrome P450 reductase-activated idarubicin in sensitive and multidrug resistant MCF7 breast cancer cells

BACKGROUND

Idarubicin (IDA) is one of clinically important anticancer drugs belonging to the anthracycline antibiotic family. The aim of this study was to examine DNA damage induced by NADPH cytochrome P450 reductase (CPR)-activated IDA in human sensitive MCF7 and multidrug resistant MCF7/DOX₅₀₀ (overexpressing P-gp) breast adenocarcinoma cells.

METHODS

The evaluation of DNA fragmentation caused by single strand breaks (SSB) and double strand breaks (DSB) was performed using terminal deoxynucleotidyl transferase-mediated dUTP nick end labelling (TUNEL) test. Additionally, DSB formation was examined using H2AX histone phosphorylation assays.

RESULTS

It was found that IDA alone and CPR-activated used at IC₉₀ caused a higher level of DNA strand breaks in sensitive MCF7 cells detected by TUNEL assessments (p=0.0011 for IDA alone and p=0.0109 for IDA reductively activated, Kruskal-Wallis test) and γ-H2AX-positive staining (p=0.0003 for IDA alone and p=0.0193 for IDA reductively activated, Kruskal-Wallis test) than in multidrug resistant MCF7/DOX₅₀₀ cells. However, no changes were observed in the percentage of TUNEL-positive and DSB-positive cells for MCF7 as well as MCF7/DOX₅₀₀ cells in the case of IDA alone and the drug pretreated in the presence of the activating system.

CONCLUSIONS

The obtained results suggest that CPR-activation of IDA does not significantly change the cellular DNA damage response of studied sensitive MCF7 and multidrug resistant MCF7/DOX₅₀₀ breast cancer cells, even if the results concerning the interaction of IDA undergoing CPR activation with naked DNA showed the important differences in comparison with the drug alone (non-activated).

In vitro effects of myricetin, morin, apigenin, (+)-taxifolin, (+)-catechin, (-)-epicatechin, naringenin and naringin on cytochrome b5 reduction by purified NADH-cytochrome b5 reductase

The microsomal NADH-dependent electron transport system consisting of cytochrome b5 reductase and cytochrome b5 participates in a number of physiologically important processes including lipid metabolism as well as is involved in the metabolism of various drug and xenobiotics. In the present study, we assessed the inhibitory effects of eight dietary flavonoids representing five distinct chemical classes on cytochrome b5 reduction by purified cytochrome b5 reductase. From the flavonoids tested, myricetin was the most potent in inhibiting cytochrome b5 reduction with an IC50 value of 0.35μM. Myricetin inhibited b5 reductase noncompetitively with a Ki of 0.21μM with respect to cofactor NADH, and exhibited a non-linear relationship indicating non-Michaelis-Menten kinetic binding with respect to cytochrome b5. In contrast to the potent inhibitory activity of myricetin, (+)-taxifolin was found to be a weak inhibitor (IC50=9.8μM). The remaining flavonoids were inactive within the concentration range tested (1-50μM). Analysis of structure-activity data suggested that simultaneous presence of three OH groups in ring B is a primary structural determinant for a potent enzyme inhibition. Our results suggest that inhibition of the activity of this system by myricetin or myricetin containing diets may influence the metabolism of therapeutic drugs as well as detoxification of xenobiotics.