Tirapazamine is a bioreductively activated
DNA-damaging agent that selectively kills the hypoxic cells found in solid
tumors. This compound shows clinical promise and is currently being examined in a variety of clinical trials, including several phase III studies. It is well established that
DNA is an important cellular target for
tirapazamine; however, the structural nature of the DNA damage inflicted by this
drug remains poorly understood. As part of an effort to understand the chemical events responsible for the
hypoxia-selective cytotoxicity of this
drug, the studies reported here are designed to characterize
tirapazamine-mediated damage to the genetic information stored in the heterocyclic base residues of
double-stranded DNA. Here, we used gas chromatography/mass spectrometry and liquid chromatography/mass spectrometry to characterize and quantify oxidative
DNA base damage mediated by
tirapazamine. A multiplicity of modified bases including 8,5'-cyclopurine-2'-deoxynucleoside tandem lesions were identified and quantified. The results provide the first detailed insight regarding the structural identity of the
DNA base lesions caused by this
drug. Interestingly, it appears that the hypoxic conditions under which
tirapazamine operates, along with the unique chemical properties of the
drug, yield a unique variety of
DNA base damage that is dominated by formamidopyrimidine and 5-hydroxy-6-hydropyrimidine lesions. Importantly, the results suggest that
tirapazamine may generate a set of poorly repaired, potentially cytotoxic
DNA base lesions that block
DNA transcription and replication. Overall, the results indicate that
DNA base damage may contribute to the
biological effects of
tirapazamine in vivo.