Kendra Vann, Ph.D.
Department: Biochemistry, 2016
Faculty Mentor: Neil Osheroff, Ph.D.
Dissertation Title: Effects of natural products on the activity of human topoisomerase II
Dissertation Abstract: Topoisomerase II plays many essential roles in genome maintenance. To carry out its physiological functions, the enzyme generates transient double-stranded breaks in the DNA to help resolve topological problems that occur naturally. Thus, while essential to cell survival, topoisomerase II has the potential to fragment the genome. Beyond its critical cellular functions, human topoisomerase II is the target for a number of widely prescribed anticancer drugs that are used in the treatment of solid tumors and hematological malignancies. Drugs that target topoisomerase II act by increasing levels of enzyme-mediated DNA strand breaks. Many of these “topoisomerase II poisons” are derived from natural sources.
Identification and characterization of topoisomerase II poisons from natural sources can potentially provide novel drug scaffolds or chemopreventative agents. The goals of my research were to identify naturally derived compounds that alter human topoisomerase II? activity and characterize their mechanism of action. I examined compounds that were originally derived from natural sources or synthesized based on a natural parent compound for activity against topoisomerase II?. Naturally occurring polyphenols from the olive plant, such as oleuropein, hydroxytyrosol, and verbascoside, and the soil fungi Septofusidium berolinense, 3,6-dihydroxy-2-propylbenzaldehyde (GE-1) and 2-hydroxymethyl-3-propylcyclohexa-2,5-diene-1,4-dione (GE-2), enhanced human topoisomerase IIalpha-mediated DNA cleavage. The presence of an oxidant increased the potency of catechol- and hydroquinone-based covalent poisons, and was able to convert a reduced quinone that inhibited topoisomerase II activity into a topoisomerase poison. The olive and fungal metabolites were covalent topoisomerase IIalpha poisons and appeared to act at sites outside of the catalytic core.
Ellipticine, a natural product first isolated from the Australian evergreen tree, is an antineoplastic agent that intercalates into DNA and alters topoisomerase II activity. Two novel C5-demethylated derivatives, ET-1 and ET-2, were catalytic inhibitors of human topoisomerase II?. The potency of ET-1 and ET-2 appeared to be related to their ability to intercalate into the double helix. The results of these studies may provide a cellular target for some chemopreventative therapies and a platform for developing new anticancer drugs.