Differential Cytotoxicity, Cellular Uptake, Apoptosis and Inhibition of BRCA1 Expression of BRCA1-Defective and Sporadic Breast Cancer Cells Induced by an Anticancer Ruthenium(II)-Arene Compound, RAPTA-EA1.

Abstract

The RAPTA-EA1 complex [ruthenium(II)-arene 1,3,5-triaza-7-phosphaadamantane (pta) complex with an arene-tethered ethacrynic acid ligand] has been reported to overcome drug resistance that developed due to the current use of platinum-based treatments. However, the exact mechanism of action of RAPTA-EA1 remains largely unexplored and unknown. Here we have further studied the effect of RAPTA-EA1 on BRCA1-defective HCC1937 breast cancer cells and compared its effects on BRCA1-competent MCF-7 breast cancer cells. HCC1937 and MCF-7 breast cancer cells were treated with the RAPTA-EA1 complex. The cytotoxicity of ruthenium-induced cells was evaluated by a MTT assay. Cellular uptake of ruthenium was determined by ICP-MS. Cell cycle and apoptosis were assessed using a flow cytometer. Expression of BRCA1 mRNA and its encoded protein was quantitated by a real-time RT-PCR and Western blotting. Differences in cytotoxicity were correlated with the differential accumulations of ruthenium and the induction of apoptosis. The ruthenium complex caused dramatically more damage to the BRCA1 gene in the BRCA1-defective HCC1937 cells than to the BRCA1-competent MCF-7 cells. It decreased the expression of BRCA1 mRNA in the BRCA1-competent cells, while in contrast, its expression increased in the BRCA1-defective cells. However, the expression of the BRCA1 protein was significantly reduced in both types of breast cancer cells. The results presented here have demonstrated a differential cellular response for the BRCA1-defective and BRCA1-competent breast cancer cells to RAPTA-EA1. These findings have provided more insight into the actions and development of the ruthenium-based compounds for use for the treatment of breast cancer.