The compound
3-amino-1,2,4-benzotriazine 1,4-dioxide (
tirapazamine, TPZ) is a clinically promising
anticancer agent that selectively kills the
oxygen-poor (hypoxic) cells found in solid
tumors. It has long been known that, under hypoxic conditions, TPZ causes
DNA strand damage that is initiated by the abstraction of
hydrogen atoms from the
deoxyribose phosphate backbone of duplex
DNA, but exact chemical mechanisms underlying this process remain unclear. Here we describe detailed characterization of
sugar-derived products arising from TPZ-mediated strand damage. We find that the action of TPZ on duplex
DNA under hypoxic conditions generates
5-methylene-2-furanone (6),
oligonucleotide 3'-phosphoglycolates (7),
malondialdehyde equivalents (8 or 9), and
furfural (10). These results provide evidence that TPZ-mediated strand damage arises via
hydrogen atom abstraction from both the most hindered (C1') and least hindered (C4' and C5') positions of the
deoxyribose sugars in the double helix. The products observed are identical to those produced by
hydroxyl radical. Additional experiments were conducted to better understand the chemical pathways by which TPZ generates the observed DNA-damage products. Consistent with previous work showing that TPZ can substitute for molecular
oxygen in DNA damage reactions, it is found that, under anaerobic conditions, reaction of TPZ with a discrete, photogenerated C1'-radical in
a DNA 2'-oligodeoxynucleotide cleanly generates the
2-deoxyribonolactone lesion (5) that serves as the precursor to
5-methylene-2-furanone (6). Overall, the results provide insight regarding the chemical structure of the DNA lesions that confront cellular repair, transcription, and replication machinery following exposure to TPZ and offer new information relevant to the chemical mechanisms underlying TPZ-mediated strand cleavage.