Effects of Olive Metabolites on DNA Cleavage Mediated by Human Type II Topoisomerases

Abstract

Several naturally occurring dietary polyphenols with chemopreventive or anticancer properties are topoisomerase II poisons. To identify additional phytochemicals that enhance topoisomerase II-mediated DNA cleavage, a library of 341 Mediterranean plant extracts was screened for activity against human topoisomerase IIα. An extract from Phillyrea latifolia L., a member of the olive tree family, displayed high activity against the human enzyme. On the basis of previous metabolomics studies, we identified several polyphenols (hydroxytyrosol, oleuropein, verbascoside, tyrosol, and caffeic acid) as potential candidates for topoisomerase II poisons. Of these, hydroxytyrosol, oleuropein, and verbascoside enhanced topoisomerase II-mediated DNA cleavage. The potency of these olive metabolites increased 10–100-fold in the presence of an oxidant. Hydroxytyrosol, oleuropein, and verbascoside displayed hallmark characteristics of covalent topoisomerase II poisons. (1) The activity of the metabolites was abrogated by a reducing agent. (2) Compounds inhibited topoisomerase II activity when they were incubated with the enzyme prior to the addition of DNA. (3) Compounds were unable to poison a topoisomerase IIα construct that lacked the N-terminal domain. Because hydroxytyrosol, oleuropein, and verbascoside are broadly distributed across the olive family, extracts from the leaves, bark, and fruit of 11 olive tree species were tested for activity against human topoisomerase IIα. Several of the extracts enhanced enzyme-mediated DNA cleavage. Finally, a commercial olive leaf supplement and extra virgin olive oils pressed from a variety of Olea europea subspecies enhanced DNA cleavage mediated by topoisomerase IIα. Thus, olive metabolites appear to act as topoisomerase II poisons in complex formulations intended for human dietary consumption.

Evidence to Support the Anti-Cancer Effect of Olive Leaf Extract and Future Directions

“…Topoisomerase IIα is an enzyme essential for cell survival, catalysing the breaking and re-joining of the DNA helix to remove tangles and playing an important role in cell replication. Acting as Topoisomerase IIα poisons the polyphenols increased DNA cleavage, this effect was 10–100 times stronger in the presence of an oxidant [149]. This is consistent with the idea that the polyphenols have been transformed into quinone electrophiles, which are then able to bind to cysteine residues.…”

Effects of Secondary Metabolites from the Fungus Septofusidium berolinense on DNA Cleavage Mediated by Human Topoisomerase IIα

“…31 Presumably, oxidation converts the catechols to more reactive quinone-based species 45 that can more readily adduct the type II enzyme. Oxidation had no effect on the activity of GE-2, which already was a quinone (Figure 7).…”

Novel trifluoromethylated 9-amino-3,4-dihydroacridin-1(2H)-ones act as covalent poisons of human topoisomerase IIα

“…20,21 Covalent poisons display several hallmark characteristics that distinguish them from interfacial poisons. 16,20,22–26 Because covalent poisons are reactive and require redox cycling as part of the adduction reaction, their activities are abrogated by the presence of reducing agents. Furthermore, because covalent poisons act by altering the N-terminal portion of the enzyme, they do not enhance DNA cleavage by topoisomerase II constructs that lack this domain.…”