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The triple-negative breast cancer subtype (TNBC) is highly aggressive and metastatic and corresponds to 15–20% of diagnosed cases. TNBC treatment is hampered, because these cells usually do not respond to hormonal therapy, and they develop resistance to chemotherapeutic drugs. On the other hand, the severe side effects of cisplatin represent an obstacle for its clinical use. Ruthenium (Ru)-based complexes have emerged as promising antitumor and antimetastatic substitutes for cisplatin. In this study, we demonstrated the effects of a Ru/biphosphine complex, containing gallic acid (GA) as a ligand, [Ru­(GA)­(dppe)2]­PF6, hereafter called Ru­(GA), on a TNBC cell line, and compared them to the effects in a nontumor breast cell line. Ru­(GA) complex presented selective cytotoxicity against TNBC over nontumor cells, inhibited its migration and invasion, and induced apoptosis. These effects were associated with the increased amount of transferrin receptors (TfR) on tumor cells, compared to nontumor ones. Silencing of TfR decreased Ru­(GA) effects on TNBC cells, demonstrating that these receptors were at least partially responsible for Ru­(GA) delivery into tumor cells. The Ru­(GA) compound must be further studied in different in vivo assays in order to investigate its antitumor properties and its toxicity in complex biological systems.

Organometallic ruthenium complexes as potential anticancer agents have been explored due to their suitable properties, such as stability in the solid state and in solution, water solubility and low toxicity. In this study, eight metal complexes of this class were synthesized, characterized and their important biological activities against a human breast tumor cell line (MDA-MB-231) were studied. Complexes 1-8 were obtained in good yields and have been characterized by satisfactory elemental analyses, IR, 1D and 2D H andC{H} NMR, UV-Vis spectroscopy, cyclic voltammetry, ESI-MS and X-ray diffractometry (1, 2, 3 and 6). All complexes exhibit growth inhibition on human breast and lung tumor cell lines, with IC values ranging from 6.0 to 45.0 μM in 48 h. Four compounds were selected to evaluate the changes in the morphology, clonogenic, migration, cell cycle arrest and cell death in MDA-MB-231 cells. The complexes are able to induce morphological changes and inhibit the size, number of colonies and cell migration, and induce cell cycle arrest in the sub-G1 phase and apoptosis cell death. The interaction of the complexes with DNA was determined by performing spectroscopic titration, a competitive assay with thiazole orange, circular dichroism, gel electrophoresis and interactions with guanosine or guanosine monophosphate by H NMR, indicating the non-covalent interaction. The HSA binding affinity measured by spectrophotometric titration, revealed the hydrophobic and spontaneous association with the human protein. Overall, the studies indicated that these metal complexes are potential agents against MDA-MB-231 cells, encouraging us to continue studies of these types of compounds.

In this study, half-sandwich Ru(II) complexes containing acylthiourea ligands of the general type [Ru(η 6 -p-cymene)(PPh 3 )-(S)Cl]PF 6 (1m−6m) and [Ru(η 6 -p-cymene)(PPh 3 )(S−O)]PF 6 (1b− 6b) where S/S−O = N',N'-disubstituted acylthiourea were synthesized and characterized (via elemental analyses, IR spectroscopy, 1 H NMR spectroscopy, 13 C{ 1 H} NMR spectroscopy, and X-ray diffractometry), and their cytotoxic activity was evaluated. The different coordination modes of the acylthiourea ligands, monodentately via S (1m−6m) and bidentately via S,O (1b−6b), to ruthenium were modulated from different synthetic routes. The cytotoxicity of the complexes was evaluated in five human cell lines (DU-145, A549, MDA-MB-231, MRC-5, and MCF-10A) by MTT assay. The IC 50 values for prostate cancer cells (2.89−7.47 μM) indicated that the complexes inhibited cell growth, but that they were less cytotoxic than cisplatin (2.00 μM). Unlike for breast cancer cells (IC 50 = 0.28−0.74 μM) and lung cancer cells (IC 50 = 0.51−1.83 μM), the complexes were notably more active than the reference drug, and a remarkable selectivity index ) was observed for breast cancer cells. Based on both the activity and selectivity, complexes 5b and 6b, as well as their respective analogous complexes in the monodentate coordination 5m and 6m, were chosen for further investigation in the MDA-MB-231 cell line. These complexes not only induced morphology changes but also were able to inhibit colony formation and migration. In addition, the complexes promoted cell cycle arrest at the sub-G 1 phase inducing apoptosis. Interaction studies by viscosity measurements, gel electrophoresis, and fluorescence spectroscopy indicated that the complexes interact with the DNA minor groove and exhibit an HSA binding affinity.

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Triple negative breast cancer (TNBC) is very aggressive and lacks specific therapeutic targets, having limited treatment options and poor prognosis. [6]-gingerol is the most abundant and studied compound in ginger, presenting diverse biological properties such as antitumor activity against several types of cancer, including breast cancer. In this study, we show that the semi-synthetic analogue SSi6, generated after chemical modification of the [6]-gingerol molecule, using acetone-2,4-dinitrophenylhydrazone (2,4-DNPH) reagent, enhanced selective cytotoxic effects on MDA-MB-231 cells. Remarkably, unlike the original [6]-gingerol molecule, SSi6 enabled autophagy followed by caspase-independent apoptosis in tumor cells. We found a time-dependent association between SSi6-induced oxidative stress, autophagy and apoptosis. Initial SSi6-induced reactive oxygen species (ROS) accumulation (1h) led to autophagy activation (2-6h), which was followed by caspase-independent apoptosis (14h) in TNBC cells. Additionally, our data showed that SSi6 induction of ROS plays a key role in the promotion of autophagy and apoptosis. In order to investigate whether the observed cell death induction was dependent on preceding autophagy in MDA-MB-231 cells, we used siRNA to knock down LC3B prior to SSi6 treatment. Our data show that LC3B downregulation decreased the number of apoptotic cells after treatment with SSi6, indicating that autophagy is a key initial step on SSi6-induced caspase-independent apoptosis. Overall, the results of this study show that structural modifications of natural compounds can be an interesting strategy for developing antitumor drugs, with distinct mechanisms of actions, which could possibly be used against triple negative breast cancer cells that are resistant to canonical apoptosis-inducing drugs.