A mass spectrometry study of tirapazamine and its metabolites: Insights into the mechanism of metabolic transformations and the characterization of reaction intermediates

Zagorevskii, Dmitri V.; Song, Minghu; Breneman, Curt M.; Yang, Yuan; Fuchs, Tarra; Gates, Kent S.; Greenlief, C. Michael

doi:10.1016/s1044-0305(03)00334-9

Cited by 36 publications

(38 citation statements)

References 17 publications

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“…Redox-activated DNA cleavage by 5 is substantially inhibited (60–90%) by classical radical-scavenging agents15 such as ethanol, methanol, t -butanol, DMSO, and mannitol (500 mM, Figure 4). Overall, the data indicate that one-electron reduction of 5 under anoxic conditions leads to direct DNA strand cleavage via radical mechanisms such as those characterized previously for TPZ 22–24,26,29…”

Section: Resultssupporting

confidence: 71%

Initiation of DNA Strand Cleavage by 1,2,4-Benzotriazine 1,4-Dioxide Antitumor Agents: Mechanistic Insight from Studies of 3-Methyl-1,2,4-benzotriazine 1,4-Dioxide

et al. 2008

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The antitumor agent 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine, TPZ, 1) gains medicinal activity through its ability to selectively damage DNA in the hypoxic cells found inside solid tumors. This occurs via one-electron enzymatic reduction of TPZ to yield an oxygen-sensitive drug radical (2) that leads to oxidatively generated DNA damage under hypoxic conditions. Two possible mechanisms have been considered to account for oxidatively generated DNA damage by TPZ. First, homolysis of the N-OH bond in 2 may yield the well known DNA-damaging agent, hydroxyl radical. Alternatively, it has been suggested that elimination of water from 2 generates a benzotriazinyl radical (4) as the ultimate DNA-damaging species. In the studies described here, the TPZ analogue 3-methyl-1,2,4-benzotriazine 1,4-dioxide (5) was employed as a tool to probe the mechanism of DNA damage within this new class of antitumor drugs. Initially, it was demonstrated that 5 causes redoxactivated, hypoxia-selective oxidation of DNA and small organic substrates in a manner that is completely analogous to TPZ. This suggests that 5 and TPZ damage DNA by the same chemical mechanism. Importantly, the methyl substituent in 5 provides a means for assessing whether the putative benzotriazinyl intermediate 7 is generated following one-electron reduction. Two complementary isotopic labeling experiments provide evidence against the formation of the benzotriazinyl radical intermediate. Rather, a mechanism involving the release of hydroxyl radical from the activated drug radical intermediates can explain the DNA-cleaving properties of this class of antitumor drug candidates.The compound 3-amino-1,2,4-benzotriazine 1,4-dioxide (tirapazamine, TPZ, 1, Scheme 1) is currently undergoing a variety of phase I, II, and III clinical trials for the treatment of human cancers. 1 TPZ gains medicinal activity from its ability to selectively damage DNA in the oxygen-poor (hypoxic) cells found inside solid tumors. [2][3][4][5][6][7][8] This DNA-damage process begins with intracellular enzymatic reduction of TPZ to yield the drug radical intermediate (2 , Scheme 1). [9][10][11][12] In normally-oxygenated cells, 2 undergoes relatively harmless oxidation back to the parent drug (Scheme 1), 9,10,13 while, under hypoxic conditions, the drug radical intermediate 2 leads to oxidatively generated DNA damage including hydroxylation of the nucleobases 22,23 and strand breaks initiated by the abstraction of hydrogen atoms from the sugar-phosphate backbone of DNA. [7][8][9][24][25][26][27][28] In the recent literature, two mechanisms have been considered to explain TPZ-mediated DNA damage. We have presented evidence [22][23][24]26,29 supporting a mechanism involving homolysis of the N-OH bond in the neutral drug radical (2) to yield the mono-N-oxide metabolite 3 and the well known DNA-damaging agent hydroxyl radical (Scheme 1, upper branch). 30 This *To whom correspondence should be addressed: gatesk@missouri.edu; phone: (573) FAX: (573) NIH-PA Author ManuscriptNIH-PA ...

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Section: Resultssupporting

confidence: 71%

Initiation of DNA Strand Cleavage by 1,2,4-Benzotriazine 1,4-Dioxide Antitumor Agents: Mechanistic Insight from Studies of 3-Methyl-1,2,4-benzotriazine 1,4-Dioxide

et al. 2008

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“…Under hypoxic conditions TZP undergoes intracellular one-electron reduction to a radical anion that is converted to either a highly toxic hydroxyl radical or to an oxidizing radical by the elimination of water [94][95][96]. These radicals cause DNA-ssbs, base damage and DPCs which stall and collapse replication forks, which in turn are repaired by the HR pathway [91].…”

Section: Consequences For Tumor Resistance and Treatmentmentioning

confidence: 99%

Tumor Hypoxia as a Modifier of DNA Strand Break and Cross-Link Repair

Chan

Koch

Bristow

2009

CMM

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Hypoxia is a common characteristic of many solid tumors and is associated with poor prognosis. Cells with low oxygen levels can have altered sensitivity to radiotherapy and chemotherapy secondary to changes in the incidence of DNA single- and double-strand breaks (DNA-ssb, DNA-dsb), DNA base damage, DNA-DNA cross-links and DNA-protein cross-links. Recent evidence also supports that cells exposed to chronic hypoxia have a decreased capacity of DNA-dsb repair. This review will examine the influence of short-term and prolonged hypoxia on the two major pathways of DNA-dsb repair: homologous recombination (HR) and non-homologous end-joining (NHEJ). Novel treatment strategies designed to exploit the hypoxic tumor microenvironment are also discussed. Modification of DNA damage sensing and repair due to fluctuating oxygen levels within a dynamic tumor microenvironment may have profound implications for tumor progression and treatment.

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“…There is evidence that TPZ is reduced under hypoxic conditions via a one electron enzymic reduction to a reactive intermediate (TPZ • ), which produces hydroxyl radicals (HO • ) [73][74][75] or benzotriazinyl radicals (BTZ • ) [76]. These radicals are then able to abstract a hydrogen atom from DNA and cause DNA fragmentation [24,77].…”

Section: N-oxide-based Bioreductive Agentsmentioning

confidence: 99%

Sensor/Effector Drug Design with Potential Relevance to Cancer

Fry¹,

Jacob

2006

CPD

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Many cancer cells exhibit a disturbed intracellular redox balance, making them distinctively different from their 'healthy' counterparts. Some tumors, such as solid lung carcinoma, are hypoxic, and its cells are therefore more reducing than normal, while others, such as the ones of breast and prostate cancer, proliferate under oxidative stress (OS). These biochemical differences between normal and tumor tissue are significant, and can be used to design effective, yet selective redox drugs. The resulting drug design can follow different avenues. The bioreductive approach is perhaps the most advanced, and uses changes in intracellular redox enzyme concentrations to activate otherwise inactive pro-drug molecules inside cancer cells by a reductive step, often followed by further chemical transformations, such as hydrolysis. Related anti-cancer compounds, such as varacin, employ an intricate combination of reduction and oxidation processes to develop their therapeutic potential inside cells. Another, just emerging approach considers the use of pro-oxidants and catalysts, taking advantage of the inherent efficiency and selectivity associated with OS-induced cell death. Even more complex tactics, such as chelator-assisted photodynamic therapy, exploit the intracellular metal homeostasis to target cancer cells. Together, all of these avenues try to endow molecules with a combination of sensor and effector properties, which might allow them to single out and selectively kill cancer cells without the need for cell-selective drug delivery systems. In the long term, such agents could be associated with high efficiency, good selectivity and dramatically reduced drug side effects.

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A mass spectrometry study of tirapazamine and its metabolites: Insights into the mechanism of metabolic transformations and the characterization of reaction intermediates

Cited by 36 publications

References 17 publications

Initiation of DNA Strand Cleavage by 1,2,4-Benzotriazine 1,4-Dioxide Antitumor Agents: Mechanistic Insight from Studies of 3-Methyl-1,2,4-benzotriazine 1,4-Dioxide

Initiation of DNA Strand Cleavage by 1,2,4-Benzotriazine 1,4-Dioxide Antitumor Agents: Mechanistic Insight from Studies of 3-Methyl-1,2,4-benzotriazine 1,4-Dioxide

Tumor Hypoxia as a Modifier of DNA Strand Break and Cross-Link Repair

Sensor/Effector Drug Design with Potential Relevance to Cancer

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