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Updated: May 22, 2026
HPLC Measurement of the DNA Oxidation Biomarker, 8-oxo-7,8-dihydro-2’-deoxyguanosine, in Cultured Cells and Animal Tissues
Published on: August 1, 2015
A strategy for selective O(6)-alkylguanine-DNA alkyltransferase depletion under hypoxic conditions
Philip G Penketh1, Krishnamurthy Shyam, Raymond P Baumann
1Department of Pharmacology, Yale University School of Medicine, New Haven, CT 06520, USA. philip.penketh@yale.edu
Abstract:
Cellular resistance to chemotherapeutics that alkylate the O-6 position of guanine residues in DNA correlates with their O(6)-alkylguanine-DNA alkyltransferase activity. In normal cells high [O(6)-alkylguanine-DNA alkyltransferase] is beneficial, sparing the host from toxicity, whereas in tumor cells high [O(6)-alkylguanine-DNA alkyltransferase] prevents chemotherapeutic response. Therefore, it is necessary to selectively inactivate O(6)-alkylguanine-DNA alkyltransferase in tumors. The oxygen-deficient compartment unique to solid tumors is conducive to reduction, and could be utilized to provide this selectivity. Therefore, we synthesized 2-nitro-6-benzyloxypurine, an analog of O(6)-benzylguanine in which the essential 2-amino group is replaced by a nitro moiety, and 2-nitro-6-benzyloxypurine is >2000-fold weaker than O(6)-benzylguanine as an O(6)-alkylguanine-DNA alkyltransferase inhibitor. We demonstrate oxygen concentration sensitive net reduction of 2-nitro-6-benzyloxypurine by cytochrome P450 reductase, xanthine oxidase, and EMT6, DU145, and HL-60 cells to yield O(6)-benzylguanine. We show that 2-nitro-6-benzyloxypurine treatment depletes O(6)-alkylguanine-DNA alkyltransferase in intact cells under oxygen-deficient conditions and selectively sensitizes cells to laromustine (an agent that chloroethylates the O-6 position of guanine) under oxygen-deficient but not normoxic conditions. 2-Nitro-6-benzyloxypurine represents a proof of concept lead compound; however, its facile reduction (E(1/2) - 177 mV versus Ag/AgCl) may result in excessive oxidative stress and/or the generation of O(6)-alkylguanine-DNA alkyltransferase inhibitors in normoxic regions in vivo.
Insights
Researchers developed 2-nitro-6-benzyloxypurine to selectively inhibit O(6)-alkylguanine-DNA alkyltransferase in tumors. This compound is reduced in low-oxygen tumor environments, sensitizing cancer cells to chemotherapy.
Area of Science:
- Medicinal Chemistry
- Cancer Biology
- Pharmacology
Background:
- Cellular resistance to DNA alkylating chemotherapeutics is linked to O(6)-alkylguanine-DNA alkyltransferase (MGMT) activity.
- High MGMT levels protect normal cells but reduce tumor cell sensitivity to chemotherapy.
- Selective inactivation of MGMT in tumors is crucial for effective cancer treatment.
Purpose of the Study:
- To develop a prodrug that selectively targets and inactivates MGMT in the hypoxic environment of solid tumors.
- To utilize the unique oxygen-deficient tumor microenvironment for targeted drug activation.
Main Methods:
- Synthesis of 2-nitro-6-benzyloxypurine, an analog of O(6)-benzylguanine.
- Assessment of 2-nitro-6-benzyloxypurine reduction by cellular reductases (cytochrome P450 reductase, xanthine oxidase) and cancer cell lines (EMT6, DU145, HL-60) under varying oxygen concentrations.
- Evaluation of MGMT depletion and chemosensitization to laromustine in intact cells under hypoxic versus normoxic conditions.
Main Results:
- 2-nitro-6-benzyloxypurine is a prodrug that is reduced to O(6)-benzylguanine, a potent MGMT inhibitor, in an oxygen-dependent manner.
- The compound effectively depletes MGMT in cancer cells under oxygen-deficient conditions.
- Treatment with 2-nitro-6-benzyloxypurine selectively sensitizes cells to laromustine in hypoxic, but not normoxic, environments.
Conclusions:
- 2-nitro-6-benzyloxypurine demonstrates proof of concept for hypoxia-activated MGMT inhibition.
- This approach offers selective targeting of MGMT in solid tumors, potentially overcoming chemotherapy resistance.
- Further optimization is needed to mitigate potential off-target effects like oxidative stress in normoxic tumor regions.
