BackgroundTriple-negative breast cancer (TNBC) is defined by the absence of expression of estrogen receptor, progesterone receptor and human epidermal growth factor receptor 2. Breast cancers with a BRCA1 mutation are also frequently triple-negative. Currently, there is a lack of effective therapies and known specific molecular targets for this aggressive breast cancer subtype. To address this concern, we have explored the cellular responses of BRCA1-defective and triple-negative breast cancer cells, and in vitro BRCA1 interactions induced by the ruthenium(II) complexes containing the bidentate ligand, 5-chloro-2-(phenylazo)pyridine.MethodsTriple-negative MDA-MB-231, BRCA1-defective HCC1937 and BRCA1-competent MCF-7 breast cancer cell lines were treated with ruthenium(II) complexes. The cytoxoxicity of ruthenium-induced breast cancer cells was evaluated by a real time cellular analyzer (RTCA). Cellular uptake of ruthenium complexes was determined by ICP-MS. Cell cycle progression and apoptosis were assessed using propidium iodide and Annexin V flow cytometry. The N-terminal BRCA1 RING protein was used for conformational and functional studies using circular dichroism and in vitro ubiquitination.ResultsHCC1937 cells were significantly more sensitive to the ruthenium complexes than the MDA-MB-231 and MCF-7 cells. Treatment demonstrated a higher degree of cytotoxicity than cisplatin against all three cell lines. Most ruthenium atoms were retained in the nuclear compartment, particularly in HCC1937 cells, after 24 h of incubation, and produced a significant block at the G2/M phase. An increased induction of apoptotic cells as well as an upregulation of p53 mRNA was observed in all tested breast cancer cells. It was of interest that BRCA1 mRNA and replication of BRCA1-defective cells were downregulated. Changes in the conformation and binding constants of ruthenium-BRCA1 adducts were observed, causing inactivation of the RING heterodimer BRCA1/BARD1-mediated E3 ubiquitin ligase activity.ConclusionsThis study has revealed the ability of ruthenium complexes to inhibit cell proliferation, induce cell cycle progression and apoptosis. Ruthenium treatment upregulated the marker genes involved in apoptosis and cell cycle progression while it downregulated BRCA1 mRNA and replication of HCC1937 cells. Our results could provide an alternative approach to finding effective therapeutic ruthenium-based agents with promising anticancer activity, and demonstrated that the BRCA1 RING domain protein was a promising therapeutic target for breast cancers.

The interaction of two ruthenium-arene-1,3,5-triaza-7-phosphaadamantane compounds ([Ru(eta(6)-p-cymene)Cl(2)(pta)] and [Ru(eta(6)-p-cymene)(C(6)H(6)O(4))(pta)], termed RAPTA-C (3) and carboRAPTA-C (4), resp.) with the DNA sequence of the human breast-cancer suppressor gene 1 (BRCA1) has been studied using a range of techniques that probe conformation, cross-linking, base specificity, restriction analysis, and in vitro inhibition of DNA polymerization. The study demonstrates that substitution of the two labile chloride ligands in 3 by the more stable cyclobutane-1,1-dicarboxylate ligand onto the RAPTA framework reduces the rate of reaction with DNA in a similar manner to the analogous Pt-based drug pair cisplatin (1) and carboplatin (2), suggesting that hydrolysis may be a prerequisite to DNA binding with the Ru compounds. Moreover, the rate of DNA interaction for 3 is in a similar range to that of 2, despite the fact that these compounds have a different therapeutic profile. The similar rates of reaction contrasting with the different modes of activity suggests that the RAPTA compounds may be clinically useful against cancer cells that have developed resistance to Pt-based therapies, particularly involving excision-repair mechanisms.

No abstract

No abstract

No abstract