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Zhou Z, Hu Z, Zhang X, Jia M, Wang X, Su H, Sun H, Chen J, Xu J. pH Controlled Intersystem Crossing and Singlet Oxygen Generation of 8-Azaadenine in Aqueous Solution. Chemphyschem 2019; 20:757-765. [PMID: 30702794 DOI: 10.1002/cphc.201800969] [Citation(s) in RCA: 5] [Impact Index Per Article: 1.0] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/16/2018] [Revised: 01/30/2019] [Indexed: 01/01/2023]
Abstract
Azabases are intriguing DNA and RNA analogues and have been used as effective antiviral and anticancer medicines. However, photosensitivity of these drugs has also been reported. Here, pH-controlled intersystem crossing (ISC) process of 9H 8-azaadenine (8-AA) in aqueous solution is reported. Broadband transient absorption measurements reveal that the hydrogen atom at N9 position can greatly affect ISC of 8-AA and ISC is more favorable when 8-AA is in its neutral form in aqueous solution. The initial excited ππ* (S2 ) state evolves through ultrafast internal conversion (IC) (4.2 ps) to the lower-lying nπ* state (S1 ), which further stands as a door way state for ISC with a time constant of 160 ps. The triplet state has a lifetime of 6.1 μs. On the other hand, deprotonation at N9 position promotes the IC from the ππ* (S2 ) state to the ground state (S0 ) and the lifetime of the S2 state is determined to be 10 ps. The experimental results are further supported by time-dependent density functional theory (TDDFT) calculations. Singlet oxygen generation yield is measured to be 13.8 % for the neutral 8-AA while the deprotonated one exhibit much lower yield (<2 %), implying that this compound could be a potential pH-sensitized photodynamic therapy agent.
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Affiliation(s)
- Zhongneng Zhou
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Zhubin Hu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Xianwang Zhang
- College of Chemistry, Beijing Normal University, Beijing, 100875, China
| | - Menghui Jia
- Shanghai Institute of Optics and Fine Mechanics, Shanghai, 201800, China
| | - Xueli Wang
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Hongmei Su
- College of Chemistry, Beijing Normal University, Beijing, 100875, China
| | - Haitao Sun
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China
| | - Jinquan Chen
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China.,Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi, 030006, China
| | - Jianhua Xu
- State Key Laboratory of Precision Spectroscopy, East China Normal University, Shanghai, 200062, China.,Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan, Shanxi, 030006, China
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Folkes LK, O'Neill P. DNA damage induced by nitric oxide during ionizing radiation is enhanced at replication. Nitric Oxide 2013; 34:47-55. [PMID: 23623927 DOI: 10.1016/j.niox.2013.04.005] [Citation(s) in RCA: 21] [Impact Index Per Article: 1.9] [Reference Citation Analysis] [What about the content of this article? (0)] [Affiliation(s)] [Abstract] [Key Words] [MESH Headings] [Grants] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Received: 10/17/2012] [Revised: 02/28/2013] [Accepted: 04/16/2013] [Indexed: 01/08/2023]
Abstract
Nitric oxide (NO) is a very effective radiosensitizer of hypoxic mammalian cells, at least as efficient as oxygen in enhancing cell death in vitro. NO may induce cell death through the formation of base lesions which are difficult to repair, and if they occur within complex clustered damage common to ionizing radiation, they may lead to replication-induced DNA strand breaks. It has previously been shown that 8-azaguanine and xanthine result from the reaction of guanine radicals with nitric oxide. We have now shown that adenine radicals also react with NO to form hypoxanthine and 8-azaadenine. Cells irradiated in exponential growth in the presence of NO are twice as radiosensitive compared to those irradiated in anoxia alone, whereas confluent cells are less radiosensitive to (•)NO. In addition, the numbers of DNA double strand breaks observed as γH2AX staining following radiosensitization by NO, are higher in exponential cells than in confluent cells. DNA damage, detected as 53BP1 foci, is also higher in HF-19 cells expressing Cyclin A, a marker for cells in S and G2 phases of the cell cycle, following radiosensitization by NO. RAD51 foci are highest in V79-4 cells irradiated in the presence of NO compared to in anoxia, 24h after radiolysis. This work presents evidence that radiosensitization of cells by NO is in part through the formation of specific DNA damage, difficult to repair, which in dividing cells may induce the formation of stalled replication forks and as a consequence replication-induced DNA strand breaks which may lead to cell death.
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Affiliation(s)
- Lisa K Folkes
- Gray Institute for Radiation Oncology and Biology, Department of Oncology, University of Oxford, Old Road Campus Research Building, Roosevelt Drive, Oxford OX3 7DQ, UK.
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