Modulation by verapamil of doxorubicin induced expression of multidrug resistance gene (mdr-1p-glycoprotein)‎ in murine tumor cells

الملخص EN

Overexpression of the transmembrane drug efflux pump p-glycoprotein (p-gp) is one of the major mechanisms by which cancer cells develop multidrug resistance (MDR) against natural product anticancer drugs including Doxorubicin (DOX).

In this study, the effects of DOX And / or DOX plus the calcium channel blocker, Verapamil, on mdr-1 / p-gp expression in Ehrlich ascites carcinoma cells (EAC-cells) were studied using Rhodamine 123 (RD 123), Western blotting and Reverse Transcriptase- Polymerase Chain Reaction (RT-PCR).

Tumor-bearing mice treated with DOX (2 mg / kg I.P.

every other day for a total of 3 doses) showed 34.1 days median survival time with 20 % long-term survivors.

However, pretreatment with Verapamil (20 mg / kg I.P.

daily for 5 days), before DOX increased the long-term survivors to 60 % with median survival time of 44.4 days.

Verapamil pretreatment increased the cellular levels of DOX at all time points tested with maximum level appeared at 6 hours after treatment (5.5 μg / 108 cells compared to 3.4 μg / 108 for DOX alone).

The expression of mdr-1 / p-gp was significantly increased 6 hours after treatment with DOX.

Verapamil pretreatment (20 mg / kg) for 5 days before DOX significantly decreased mdr-1 / p-gp expression and decreased p-gp function from 37 % to 16 %.

On the basis of our findings we may conclude : (1) DOX induced mdr-1 / p-gp expression in sensitive EAC-cells at both transcriptional and translational levels at only 6 hours post treatment.

(2) Verapamil block DOX-induced mdr-1 / p-gp expression with the consequent increase in DOX cellular uptake and cytotoxicity.

(3) Verapamil can potentiate the cytotoxic activity of DOX against the growth of EAC cells by mdr-1/p-gp independent mechanism.