Etoposide Quinone Is a Redox-Dependent Topoisomerase II Poison

Abstract

Etoposide is a topoisomerase II poison that is used to treat a variety of human cancers. Unfortunately, 2–3% of patients treated with etoposide develop treatment-related leukemias characterized by 11q23 chromosomal rearrangements. The molecular basis for etoposide-induced leukemogenesis is not understood, but is associated with enzyme-mediated DNA cleavage. Etoposide is metabolized by CYP3A4 to etoposide catechol, which can be further oxidized to etoposide quinone. A CYP3A4 variant is associated with a lower risk of etoposide-related leukemias, suggesting that etoposide metabolites may be involved in leukemogenesis. Although etoposide acts at the enzyme-DNA interface, several quinones poison topoisomerase II via redox-dependent protein adduction. The effects of etoposide quinone on topoisomerase IIα-mediated DNA cleavage have been examined previously. Although findings suggest that the activity of the quinone is slightly greater than that of etoposide, these studies were carried out in the presence of significant levels of reducing agents (which should reduce etoposide quinone to the catechol). Therefore, we examined the ability of etoposide quinone to poison human topoisomerase IIα in the absence of reducing agents. Under these conditions, etoposide quinone was ~5–fold more active than etoposide at inducing enzyme-mediated DNA cleavage. Consistent with other redox-dependent poisons, etoposide quinone inactivated topoisomerase IIα when incubated with the protein prior to DNA and lost activity in the presence of dithiothreitol. Unlike etoposide, the quinone metabolite did not require ATP for maximal activity and induced a high ratio of double-stranded DNA breaks. Our results support the hypothesis that etoposide quinone contributes to etoposide-related leukemogenesis.

Proteolytic Degradation of Topoisomerase II (Top2) Enables the Processing of Top2·DNA and Top2·RNA Covalent Complexes by Tyrosyl-DNA-Phosphodiesterase 2 (TDP2)

“…Yet, while doing so, Top2 enzymes can be trapped on DNA by endogenous DNA modifications, protein oxidation, food products, and anticancer drugs (1,6,7,20,34,35), which explains why human cells have evolved mechanisms to remove such Top2-associated lesions. Previous reports have linked the proteasome pathway to the degradation of Top2 in response to Top2 inhibitors (28,29).…”

Etoposide Quinone Is a Covalent Poison of Human Topoisomerase IIβ

“…27,56,57 The purity was determined to be >99% by liquid chromatography–mass spectrometry analysis at 220 and 254 nm, and the final yield of etoposide quinone was 72%.…”

“…57 Ligation was initiated by cooling samples from 37 to 0 °C. Reactions were stopped at time points ranging from 0 to 30 s by the addition of 2 μL of 5% SDS followed by 1 μL of 375 mM Na 2 EDTA (pH 8.0).…”

Podophyllotoxin derivatives: a patent review (2012 – 2014)

“…From brief biological investigations it was hypothesized that b rather than a isoform of topoisomerase II is involved in etoposide-induced carcinogenesis. These findings highlighted the significance of topoisomerase IIa thereby leading to the development of PPT derivatives more specifically targeting topoisomerase IIa [15,16]. Therefore, over the past two decades, several structurally modified PPT derivatives have been developed as topoisomerase II inhibitors ( Figure 2).…”

“…In their subsequent invention, the same group has patented a series of thioacyl-PPT ester derivatives as potential antitumor agents [35]. From this series compound 16 …”