• Exploring the Role of Selenocysteine Biosynthesis Enzyme SEPHS2 in Cancer

      Carlisle, Anne E. (2020-11-06)
      Selenium is a micronutrient that is used by the selenocysteine biosynthesis pathway to produce the amino acid selenocysteine, which is required in selenoproteins. Many of the 25 human selenoproteins, such as glutathione peroxidases and thioredoxin reductases, play important roles in maintaining cellular redox homeostasis. In this study we characterize how this metabolic pathway is upregulated in cancer cells and how this increase in activity creates a unique vulnerability. We have outlined the evidence and underlying mechanisms for how many metabolites normally produced in cells are highly toxic, and we describe this concept as illustrated in selenocysteine metabolism. My thesis explores how SEPHS2, an enzyme in the selenocysteine biosynthesis pathway, is essential for survival of cancer, but not normal cells. SEPHS2 is required in cancer cells to detoxify selenide, an intermediate that is formed during selenocysteine biosynthesis. Breast and other cancer cells are selenophilic, owing to a secondary function of the cystine/glutamate antiporter SLC7A11 that promotes selenium uptake and selenocysteine biosynthesis, which, by allowing production of selenoproteins such as GPX4, protects cells against ferroptosis. However, this activity also becomes a liability for cancer cells because selenide is poisonous and must be processed by SEPHS2. These results show that SEPHS2 is a cancer specific target and indicates the therapeutic potential of SEPHS2 inhibition in the treatment of cancer. Collectively, this thesis identifies SEPHS2 as a targetable vulnerability of cancer cells, defines the role of selenium metabolism in cancer, and outlines a roadmap for future studies regarding toxic metabolites and cancer.
    • Theoretical and Experimental Analysis of the Antioxidant and Anti-amyloid Features of Synthetic Resveratrol Mimics

      Horton, William; Kokel, Anne; Török, Fanni; Tran, Chris; Török, Marianna; Török, Bela (2016-05-20)
      Diaryl hydrazones, possessing similar structure to the popular red wine antioxidant resveratrol, have been previously identified as multitarget compounds interfering with several processes associated with the pathogenesis of Alzheimer’s disease (AD). These compounds exhibited particularly strong inhibition of the amyloid beta (A) peptide self-assembly, including blocking the formation of fibrils and oligomers, species that are widely accepted to be neurotoxic. The molecules were also powerful free radical scavengers and thus have a potential to defend against oxidative stress. In order to learn more about the mode of action of the compounds, theoretical and experimental studies have been carried out. First, the structural, energetic and electronic features of the core structure have been elucidated by density funtional theory (DFT) calculations. The DFT results identified the most likely form of the compounds, which was applied to a broad range of calculations using substituted derivates. Based on the structural information several characteristics such as logP, H-binding energy, HOMO-LUMO energies and band gap and electron densities were calculated. The compounds were subjected to three different antioxidant assays (DPPH, ABTS and ORAC). The % radical scavenging has been analyzed as a function of the above determined structural parameters in order to identify the role of the energetic and electronic features in the antioxidant activity. The analysis of the same parameters as potential markers to the anti-amyloid activity has also been carried out. Isotope labeling via H-D exchange and in situ hydrazone-radicals as well as hydrazone-A complex formation, applying 1H-NMR and HRMS, have also been used to experimentally observe the potential role of various tautomeric forms and the partially delocalized electron structure of the hydrazones.