Biological consequences of ionizing radiation primarily arise when energy deposited within cell nuclei ultimately affects the DNA. Initially, the deposited energy creates ionized species at random. If ionization occurs away from the DNA, the radical ions may diffuse to and react with the DNA; if it occurs within a chromosome, the DNA is affected directly by the ionization. Electron-loss and electron-gain centers formed directly within DNA, molecular free-radical intermediates, are an important link connecting the initial event of energy deposition and the biological endpoints. This is an important health-related issue as direct ionization of DNA and its hydration shell is estimated to cause about half the cellular effects. Consequently, it is important to arrive at unambiguous identification of DNA radicals stabilized sufficiently long to undergo subsequent chemical reactions, and to understand the possible reactions in which these radicals may participate as may be dictated by their immediate surroundings. Thus, long-range objectives of this project are to identify unambiguously the possible radical products of directly ionized DNA, the factors which can control their stabilization, and the ways in which they may transform or react chemically within their surrounding. To meet the long-range objectives, specific aims for this project are: (1) to refine and further develop models describing the role of molecule-molecule associations, such as hydrogen bonding, in controlling the stabilization of DNA radical products; (2) to identify the mechanisms in which radicals from direct ionization may lead to strand breaks; (3) to further develop techniques for using oligonucleotides to extend these studies to well-defined, DNA-like systems. The approach is to use crystals of selected molecular systems and to apply the high-resolution, radical-specific, methods of electron paramagnetic resonance spectroscopy (EPR) with its companion, electron-nuclear double resonance (ENDOR) spectroscopy. Use of crystals permits taking advantage of the full, atomic-coordinate-level, characterization of these systems available from diffraction studies. To meet the aims, spectroscopic parameters and radical yields will be measured in a selected set of model systems containing hydrogen-bonding and other molecular associations reasonably like those in DNA. From this information and details of the crystal structure, patterns of behavior will be sought and related to specific elements of molecular associations. Final transfer of the results to DNA will be made by carefully selecting and employing the well-defined, DNA-like, systems provided by oligonucleotides.

Agency
National Institute of Health (NIH)
Institute
National Cancer Institute (NCI)
Type
Research Project (R01)
Project #
5R01CA036810-16
Application #
6375701
Study Section
Radiation Study Section (RAD)
Program Officer
Pelroy, Richard
Project Start
1986-04-01
Project End
2003-08-31
Budget Start
2001-09-01
Budget End
2002-08-31
Support Year
16
Fiscal Year
2001
Total Cost
$155,050
Indirect Cost
Name
Georgia State University
Department
Physics
Type
Schools of Arts and Sciences
DUNS #
837322494
City
Atlanta
State
GA
Country
United States
Zip Code
30302
Jackson, Christopher M; Kochel, Christina M; Nirschl, Christopher J et al. (2016) Systemic Tolerance Mediated by Melanoma Brain Tumors Is Reversible by Radiotherapy and Vaccination. Clin Cancer Res 22:1161-72
Jayatilaka, Nayana; Nelson, William H (2007) Structure of radicals from X-irradiated guanine derivatives: an experimental and computational study of sodium guanosine dihydrate single crystals. J Phys Chem B 111:800-10
Jayatilaka, Nayana; Nelson, William H (2007) Structure of radicals from X-irradiated guanine derivatives. 2. An experimental and computational study of 9-ethylguanine single crystals. J Phys Chem B 111:7887-96
Tokdemir, Sibel; Nelson, William H (2006) EPR and ENDOR study of radiation-induced radical formation in purines: sodium inosine crystals X-irradiated at 10 K. J Phys Chem A 110:6552-62
Sagstuen, Einar; Close, David M; Vagane, Randi et al. (2006) Electron transfer in amino acid.nucleic acid base complexes: EPR, ENDOR, and DFT study of X-irradiated N-formylglycine.cytosine complex crystals. J Phys Chem A 110:8653-62
Nelson, William H (2005) Dose-response relationships for radicals trapped in irradiated solids. Radiat Res 163:673-80
Tokdemir, Sibel; Nelson, William H (2005) Radiation-induced hydroxyl addition to purine molecules: EPR and ENDOR study of hypoxanthine hydrochloride monohydrate single crystals. Radiat Res 163:663-72
Tokdemir, Sibel; Nelson, William H (2005) EPR and ENDOR study of radiation-induced radical formation in purines: hypoxanthine hydrochloride monohydrate crystals X-irradiated at 10 K. J Phys Chem A 109:8732-44
Sagstuen, Einar; Sanderud, Audun; Hole, Eli O (2004) The solid-state radiation chemistry of simple amino acids, revisited. Radiat Res 162:112-9
Malinen, Eirik; Sagstuen, Einar (2003) Radical formation in pyrimidine bases after X, proton and alpha-particle irradiation. Radiat Res 160:186-97

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