1 research outputs found
Cytotoxicity of Tirapazamine (3-Amino-1,2,4-benzotriazine-1,4-dioxide)-Induced DNA Damage in Chicken DT40 Cells
Tirapazamine (TPZ)
is an anticancer drug with highly selective
cytotoxicity toward hypoxic cells. TPZ is converted to a radical intermediate
under hypoxic conditions, and this intermediate interacts with intracellular
macromolecules, including DNA. TPZ has been reported to indirectly
induce DNA double-strand breaks (DSBs) through the formation of various
intermediate DNA lesions under hypoxic conditions. Although the topoisomerase
II–DNA complex has been identified as one of these intermediates,
other lesions have not yet been defined. In order to obtain a deeper
understanding of the mechanisms responsible for the selective cytotoxicity
of TPZ toward hypoxic cells, its cellular sensitivity was systematically
examined with genetically isogenic DNA-repair-deficient mutant DT40
cell lines. Our results showed that <i>tdp1</i><sup>–/–</sup>, <i>tdp2</i><sup>–/–</sup>, <i>parp1</i><sup>–/–</sup>, and <i>aptx1</i><sup>–/–</sup> cells displayed hypersensitivity to TPZ only under hypoxic conditions.
These results strongly suggest that the accumulation of the topoisomerase
I-trapped DNA complex, topoisomerase II-trapped DNA complex, and abortive
ligation products with 5′-AMP are the potential causes of TPZ-induced
hypoxic cell death. Furthermore, our genetic analysis revealed that
under normoxic conditions (as well as hypoxic conditions), TPZ exhibited
significant cytotoxicity toward cell lines deficient in homologous
recombination, nonhomologous end joining, base excision repair, and
translesion synthesis. Ascorbic acid, a radical scavenger, suppressed
TPZ-induced cytotoxicity toward normoxic cells. These results suggest
the involvement of oxidative DNA damage and DSBs produced by reactive
oxygen species generated from superoxide, a byproduct of the oxidation
of TPZ radical intermediates in normoxic cells. Collectively, our
results demonstrate that TPZ induces oxidative DNA damage under normoxic
and hypoxic conditions and selectively introduces abortive topoisomerase–DNA
complexes and unligatable DNA ends under hypoxic conditions