Myeloperoxidase-Dependent Oxidation of Etoposide in Human Myeloid Progenitor CD34⁺Cells

Abstract

Etoposide is a widely used anticancer drug successfully used for the treatment of many types of cancer in children and adults. Its use, however, is associated with an increased risk of development of secondary acute myelogenous leukemia involving the mixed-lineage leukemia (MLL) gene (11q23) translocations. Previous studies demonstrated that the phenoxyl radical of etoposide can be produced by action of myeloperoxidase (MPO), an enzyme found in developing myeloid progenitor cells, the likely origin for myeloid leukemias. We hypothesized, therefore, that one-electron oxidation of etoposide by MPO to its phenoxyl radical is important for converting this anticancer drug to genotoxic and carcinogenic species in human CD34ϩ myeloid progenitor cells. In the present study, using electron paramagnetic resonance spectroscopy, we provide conclusive evidence for MPO-dependent formation of etoposide phenoxyl radicals in growth factor-mobilized CD34 ϩ cells isolated from human umbilical cord blood and demonstrate that MPO-induced oxidation of etoposide is amplified in the presence of phenol. Formation of etoposide radicals resulted in the oxidation of endogenous thiols, thus providing evidence for etoposide-mediated MPO-catalyzed redox cycling that may play a role in enhanced etoposide genotoxicity. In separate studies, etoposide-induced DNA damage and MLL gene rearrangements were demonstrated to be dependent in part on MPO activity in CD34 ϩ cells. Together, our results are consistent with the idea that MPO-dependent oxidation of etoposide in human hematopoietic CD34 ϩ cells makes these cells especially prone to the induction of etoposide-related acute myeloid leukemia.

Myeloperoxidase Enhances Etoposide and Mitoxantrone-Mediated DNA Damage: A Target for Myeloprotection in Cancer Chemotherapy

“…MPO activity can be efficiently reduced in cell culture systems by the heme biosynthesis inhibitor succinylacetone (SA) (Pinnix et al, 1994; Kagan et al, 2001; Vlasova et al, 2011). By using NB4 cells, an acute promyleocytic leukemia line that express MPO at a high level (Hu et al, 1993), we found that incubation with 200 μ M SA for 48 hours reduced MPO enzymatic activity to below the detection level of the assay employed, and as reported previously (Pinnix et al, 1994), it significantly depleted mature MPO protein (Fig.…”

“…Myeloperoxidase is expressed exclusively in cells of the myeloid lineage; it is present at high levels in neutrophils where it exerts its antimicrobial action but is also expressed in myeloid precursor/progenitor cells, including human and mouse common myeloid progenitor and granulocyte/macrophage progenitor cells (Strobl et al, 1993; Mori et al, 2009; Goardon et al, 2011) and is readily detectable in ex vivo normal human bone marrow CD34 + cells (Supplemental Fig. 1) (Strobl et al, 1993; Vlasova et al, 2011). Thus, MPO is likely to be present in the cells in which t-AML arises.…”

“…This occurs by one-electron oxidation of the etoposide E-ring, yielding a phenoxy radical species and by O -demethylation to the reactive orthoquinone (Supplemental Fig. 2A) (Haim et al, 1986; Kalyanaraman et al, 1989; Kagan et al, 2001; Fan et al, 2006; Jacob et al, 2011; Vlasova et al, 2011). Additionally, CYP3A4 and/or CYP3A5 can oxidize etoposide to etoposide catechol, a metabolite found in patient plasma (Zheng et al, 2004; Zhuo et al, 2004), and oxidation of etoposide by CYP3A4 has been implicated in the incidence of t-AMLs (Felix et al, 1998).…”

Effect of Nitric Oxide on the Anticancer Activity of the Topoisomerase-Active Drugs Etoposide and Adriamycin in Human Melanoma Cells

“…It has been reported that VP-16 metabolites increase Topo II-dependent cleavage near leukemia-associated MLL translocation breakpoints (Lovett et al, 2001). Furthermore, Vlasova et al (2011) have shown that the VP-16 radical formed from 1-electron oxidation can redox cycle, leading to enhanced Topo II-mediated strand breaks and MLL gene translocation. Our previous studies have shown that VP-16 is readily oxidized by × NO chemistry to its phenoxyl radical, an obligatory intermediate in the formation of the VP-16-oquinone (Sinha et al, 2013).…”

Mangiferin activates the Nrf2-ARE pathway and reduces etoposide-induced DNA damage in human umbilical cord mononuclear blood cells

“…Moreover, previous studies have explored the association of etoposide with acute myeloid leukemia (AML) by using human umbilical cord blood (hUCB) cells (Libura et al, 2005;Vlasova et al, 2011). In the present study, we investigated the effects of mangiferin on the Nrf-ARE signaling pathway and etoposide-induced DNA damage in mononuclear cells (MNCs) from hUCB.…”