Chemical Modulation of Ferroptosis in Mammalian Cells by Synthetic Organoselenium and Gold-based Small Molecules

Abstract

Oxidative stress induced by reactive oxygen species (ROS) plays a crucial role in triggering various forms of cell death, including apoptosis, autophagy, and necrosis. In recent years, a distinct and regulated form of cell death, termed ferroptosis, has been discovered. Ferroptosis is an iron-dependent, non-apoptotic cell death mechanism characterized by the accumulation of lipid peroxides within the cell membranes, ultimately leading to irreversible membrane damage and cell death. Ferroptosis has been implicated in a wide range of pathological conditions. This thesis highlights the role of small molecules which can effectively modulate lipid peroxidation and ferroptosis in mammalian cells. These molecules can either prevent or induce these processes, offering potential therapeutic avenues for various diseases such as degenerative disorders including neurodegeneration and cancer.

The first part of this work focuses on the design and synthesis of small molecule organoselenium compounds that prevent ferroptosis by functionally mimicking the redox enzyme glutathione peroxidase 4 (GPX4), which is generally considered as a master regulator of ferroptosis. This work builds on the recent study from our laboratory that an isoform-specific synthetic GPX4 mimetic prevents ferroptosis in neuronal cells. We show here that an oxazoline-based organoselenium compound prevents ferroptosis in mammalian cells by catalytically reducing hydroperoxides including lipid peroxides using cellular reducing agents. We also show that another organoselenium compound effectively prevents ferroptosis, possibly through a mechanism independent of GPX4 activity. A structure-activity relationship (SAR) study reveals that the presence of a selenium atom is important for the anti-ferroptotic activity as the substitution with oxygen or sulfur completely abolishes the activity, suggesting a new mode of action for the selenium compound.

The second part of the thesis explores the development of N-heterocyclic carbene (NHC)-based gold(I) complexes that induce ferroptosis and other cell death processes. Ferroptosis-inducing small molecules may have therapeutic potential in targeting drug resistant cancers. Many of the Au(I)-NHC complexes with different leaving groups developed in this study induce significant cell death in cancer cell lines through modulation of the redox processes. Interestingly, the Au(I) complexes having two NHCs induce ferroptosis in cancer cell lines by increasing the level of lipid peroxidation. In contrast to the Au(I)-chloride and thiolate complexes, these bis-carbene complexes are essentially unreactive towards cellular thiols such as cysteine and glutathione. The activity of these complexes was found to be significantly higher than that of the well-known therapeutic Au(I) complex, auranofin, in many of the cell lines.