Ferrocene is an organometallic compound that consists of an iron(II) ion linked to two cyclopentadienyl rings in a sandwich structure. This unique arrangement gives ferrocene remarkable stability and properties that make it valuable for various applications, including bioorganometallic chemistry. Several ferrocenyl-containing pharmacophores have been studied, such as ferrocifens, analogues of the anticancer tamoxifen, and ferroquine, an analogue of antimalarial chloroquine. Besides the specific activity of the organic portion of the ferrocene derivatives, such molecules are able to generate reactive oxygen species (ROS): Fe(II)/Fe(III) + H2O2 → Fe(III)/Fe(II) + HO•/HOO• + H2O.
ROS play a paradoxical role in disease progression: while elevated ROS levels are implicated in the onset of various pathologies, they act as tumor-suppressive agents involved in the mechanism of action of many chemotherapeutics. ROS generation is involved in many forms of programmed cell death, a group of self-protective cellular mechanisms triggered by external stimuli. Therefore, a fragile equilibrium is operating in healthy cells, where ROS can either promote or inhibit tumor development.
The activation of cell death pathways (i.e., apoptosis, necroptosis and ferroptosis) by ferrocene (Fc) and its monopositive cation ferrocenium (Fc+) has been investigated in triple-negative breast cancer MCF-7 cells using immunofluorescence, flow cytometry, and transmission electron microscopy.
The distinct capabilities of Fc and Fc+ to generate ROS and trigger oxidative stress were evident through the activation of apoptosis, along with morphological changes following treatment of MCF-7 cells, particularly with Fc+. Fc+ induced ferroptosis within 2 h exposure, whereas Fc did not. Conversely, the more stable Fc initiated necroptosis after prolonged treatment.
Differences in cell death mechanisms and timing of Fc and Fc+ may arise from the rapid interconversion between Fe(II) and Fe(III). Fc and Fc+ can be promising candidates to address the limitations of conventional apoptosis-based cancer therapies.
