Ferrocenes as new anticancer drug candidates: Determination of the mechanism of action.

Chemotherapy plays an essential role in the management of cancer worldwide. However, it is a non-specific treatment limited by major drawbacks, thus identification and testing of new promising molecular structures representing potential drug candidates are urgently needed. In this work, ferrocene complexes as potential antitumor drugs that display cytotoxicity in low micromolar concentrations against ovarian cancer cells A2780 and SK-OV-3 were investigated to identify their mode of action. Their mechanism of cellular accumulation was studied using differential pulse voltammetry and inductively coupled plasma - mass spectrometry. Their mode of cell death induction was determined by changes in the mitochondrial membrane potential, production of reactive oxygen species and by Annexin V staining. Transferrin receptors were identified as key mediators of intracellular accumulation of ferrocenes and the extent of cellular uptake reflected the anticancer activity of individual compounds. Functional analysis revealed activation of intrinsic apoptosis as a dominant mechanism leading to regulated cell death induced in ovarian cancer cells by ferrocenes. Ferrocenes represent a group of promising sandwich organometallic complexes exerting cytotoxic activity. We suggest their application not only as standalone chemotherapeutics but also as modifying substituents of known drugs to improve their antitumor effects.

Ferroptosis as a New Type of Cell Death and its Role in Cancer Treatment.

BACKGROUND: Ferroptosis is a recently discovered type of cell death. It is genetically, morphologically, and biochemically distinct from other types of programmed cell death, such as necrosis, apoptosis, and autophagy. The level of intracellular free iron and reactive oxygen species formation are important for ferroptosis activation, which can occur through either of two key inhibitory processes. The first one involves inhibition of cystine transfer into cells by the cystine/glutamate antiporter system (Xc-). Cystine serves as a precursor for the synthesis of glutathione, a major cellular antioxidant. The second one involves the inhibition of glutathione peroxidase 4, which protects cells from lipid peroxidation. Ferroptosis is associated with many metabolic disorders, including neurological diseases and cancer. Molecules involved in the activation of ferroptotic pathways are involved in protecting cells against stress conditions, and in the maintenance of nicotinamide adenine dinucleotide phosphate and glutathione levels, as well as iron homeostasis. Also important is the connection with autophagy, so called ferritinophagy, in which iron is released from lysosomes into the cytosol. Cascade reactions of free unstable iron atoms with other molecules result in the production of reactive oxygen species that initiate the cellular stress that triggers ferroptosis. In diseases such as cancer where cell death inducing mechanisms, including apoptosis, are usually suppressed by genetic changes, the induction of alternative pathways leading to cell death could provide an attractive treatment strategy. CONCLUSION: In recent years, research into new antimetastatic drugs has focused on the activation of alternative cell death pathways that might overcome disturbed metabolic processes inside cancer cells or the chemotherapy resistance acquired in the course of routine treatment. A number of molecules have been found to induce ferroptosis in tumor cells, suggesting that they may offer new alternatives for anticancer treatment. Key words: cell death - cancer - autophagy - ferroptosis - ferritinophagy - cellular stress - ROS This work was supported by the projects GAČR 17-05838S, MEYS - NPS I - LO1413 and MH CZ- -DRO (MMCI, 00209805). The authors declare they have no potential conflicts of interest concerning drugs, products, or services used in the study. The Editorial Board declares that the manuscript met the ICMJE recommendation for biomedical papers. Accepted: 31. 8. 2018.

Tamoxifen-Dependent Induction of AGR2 Is Associated with Increased Aggressiveness of Endometrial Cancer Cells.

Tamoxifen treatment in breast cancer patients is associated with increased risk of endometrial malignancies. Significantly, higher AGR2 expression was found in endometrial cancers that developed in women previously treated with tamoxifen compared to those who had not been exposed to tamoxifen. An association of elevated AGR2 level with myometrial invasion occurrence and invasion depth was also found. In vitro analyses identified a stimulatory effect of AGR2 on cellular proliferation. Although adverse tamoxifen effects on endometrial cells remain elusive, our work identifies elevated AGR2 as a candidate tamoxifen-dependent mechanism of action responsible for increased incidence of endometrial cancer.

Titanocenes as anticancer agents: recent insights.

BACKGROUND: Enormous success of antitumor agent cisplatin initiated interest in other organometallic complexes. A subclass of organometallic compounds termed metallocenes, characterized by a transition metal central atom (M) bound to cyclopentadienide (Cp-/[C5H5]-) ligands with the basic formula Cp2M, has gained increasing interest as promising anticancer agents. OBJECTIVES: This review is aimed at a progress in the development of organometallic titanium-based compounds focusing primarily on the evaluation of their cytotoxic activity and mechanism of action in relation to potential utilization as anticancer drugs. RESULTS: Metallocenes bearing titanium as central atom were sorted according to their structure and modifications and their anticancer activity is further discussed. CONCLUSION: Titanocenes represent family of promising compounds exerting cytostatic activity. We suggest that their application not only as separate agents, but also in combination with newly developed carriers, e.g. nanomaterials, may lead to improvement of their delivery into tumor cells and following utilization in cancer treatment.

Chromatin association of the SMC5/6 complex is dependent on binding of its NSE3 subunit to DNA.

SMC5/6 is a highly conserved protein complex related to cohesin and condensin, which are the key components of higher-order chromatin structures. The SMC5/6 complex is essential for proliferation in yeast and is involved in replication fork stability and processing. However, the precise mechanism of action of SMC5/6 is not known. Here we present evidence that the NSE1/NSE3/NSE4 sub-complex of SMC5/6 binds to double-stranded DNA without any preference for DNA-replication/recombination intermediates. Mutations of key basic residues within the NSE1/NSE3/NSE4 DNA-binding surface reduce binding to DNA in vitro. Their introduction into the Schizosaccharomyces pombe genome results in cell death or hypersensitivity to DNA damaging agents. Chromatin immunoprecipitation analysis of the hypomorphic nse3 DNA-binding mutant shows a reduced association of fission yeast SMC5/6 with chromatin. Based on our results, we propose a model for loading of the SMC5/6 complex onto the chromatin.