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Myeloperoxidase oxidizes mitoxantrone to metabolites which bind covalently to DNA and RNA
C Panousis1, A J Kettle, D R Phillips
1School of Biochemistry, La Trobe University, Bundoora, Victoria, Australia.
Abstract:
The anticancer agent mitoxantrone is readily oxidized by the human haem enzyme myeloperoxidase and hydrogen peroxide. Intercalation of mitoxantrone with DNA inhibited oxidation of the drug by myeloperoxidase. However, at a physiological ionic strength, significant oxidation of the drug was evident. At a H2O2:mitoxantrone ratio of 1.0, myeloperoxidase oxidized mitoxantrone to a metabolite (product B) which associated reversibly with DNA. At greater hydrogen peroxide concentrations, two further metabolites were produced (products C and D), neither of which associated reversibly with DNA, as indicated by the absence of any spectral change in the presence of DNA. Long exposure of the products derived from the oxidation of [14C]mitoxantrone by myeloperoxidase resulted in a time-dependent covalent binding of the activated drug to both DNA and RNA. The amount of DNA adduct increased linearly with the extent of oxidation of mitoxantrone (up to a H2O2:mitoxantrone ratio of 5.0). No adducts resulted from exposure of the oxidized product B to DNA, but adducts formed following further oxidation of B by myeloperoxidase. The myeloperoxidase-catalysed oxidation of mitoxantrone to products capable of interacting covalently and non-covalently with nucleic acids may represent an important mode of action of mitoxantrone against acute myeloid leukemias since these cells (including neutrophils, monocytes and their precursors) contain high levels of myeloperoxidase.
Insights
The anticancer drug mitoxantrone is oxidized by myeloperoxidase, forming metabolites that bind to DNA and RNA. This myeloperoxidase-mediated activation is a potential mechanism of action for mitoxantrone in acute myeloid leukemias.
Area of Science:
- Biochemistry
- Pharmacology
- Molecular Biology
Background:
- Mitoxantrone is an anticancer agent.
- Myeloperoxidase (MPO) is a human enzyme involved in oxidative processes.
- Acute myeloid leukemias (AML) often exhibit high MPO levels.
Purpose of the Study:
- To investigate the oxidation of mitoxantrone by myeloperoxidase.
- To characterize the metabolites of mitoxantrone oxidation.
- To determine the interaction of these metabolites with nucleic acids.
Main Methods:
- In vitro oxidation of mitoxantrone using myeloperoxidase and hydrogen peroxide.
- Spectroscopic analysis to assess metabolite-DNA interactions.
- Radiolabeling ([14C]mitoxantrone) to quantify covalent binding to DNA and RNA.
Main Results:
- Myeloperoxidase oxidized mitoxantrone to various metabolites (products B, C, D).
- Product B associated reversibly with DNA, while products C and D did not.
- Oxidized mitoxantrone metabolites covalently bound to DNA and RNA over time, with binding increasing with oxidation extent.
- Adduct formation required further oxidation of product B.
Conclusions:
- Myeloperoxidase-catalyzed oxidation generates mitoxantrone metabolites that interact with nucleic acids.
- These interactions include both reversible and irreversible covalent binding.
- This activation pathway may contribute to mitoxantrone's efficacy in MPO-rich acute myeloid leukemias.