Mechanism of UVA-dependent DNA damage induced by an antitumor drug dacarbazine in relation to its photogenotoxicity.
OBJECTIVE
It has been reported that dacarbazine (DTIC) is photogenotoxic. The purpose of this study is to clarify the mechanism of photogenotoxicity induced by DTIC.


METHODS
We examined DNA damage induced by UVA-irradiated DTIC using 32P-5'-end-labeled DNA fragments obtained from human genes. Formation of 8-oxo-7,8-dihydro-2'-deoxyguanosine (8-oxodG) in calf thymus DNA was measured by high performance liquid chromatograph with an electrochemical detector. Electron spin resonance (ESR) spin-trapping experiments were performed to detect radical species generated from UVA-irradiated DTIC.


RESULTS
UVA-irradiated DTIC caused DNA damage at guanine residues, especially at the 5'-GGT-3' sequence in the presence of Cu(II) and also induced 8-oxodG generation in calf thymus DNA. DTIC-induced photodamage to DNA fragments was partially inhibited by catalase, whereas 8-oxodG formation was significantly increased by catalase. NaN3, a carbene scavenger, inhibited DNA damage and 8-oxodG formation in a dose-dependent manner, suggesting that carbene intermediates are involved. The ESR spin-trapping experiments demonstrated the generation of aryl radicals in the process of photodegradation of DTIC.


CONCLUSIONS
Photoactivated DTIC generates the carbene and aryl radicals, which may induce both DNA adduct and 8-oxodG formation, resulting in photogenotoxicity. This study could provide an insight into the safe usage of DTIC.
Iwamoto
Takuya
T
Department of Pharmacy, Mie University Hospital, Tsu, Mie 514-8507, Japan.
Hiraku
Yusuke
Y
Okuda
Masahiro
M
Kawanishi
Shosuke
S
D000080242:8-Hydroxy-2'-Deoxyguanosine; D000818:Animals; D018906:Antineoplastic Agents, Alkylating / Q000737:chemistry / Q000528:radiation effects / Q000633:toxicity*; D002417:Cattle; D002614:Chelating Agents / Q000494:pharmacology; D003300:Copper / Q000737:chemistry; D004247:DNA / Q000737:chemistry / Q000187:drug effects*; D018736:DNA Adducts; D004249:DNA Damage; D003606:Dacarbazine / Q000737:chemistry / Q000528:radiation effects / Q000633:toxicity*; D003849:Deoxyguanosine / Q000031:analogs & derivatives / Q000737:chemistry; D004305:Dose-Response Relationship, Drug; D004578:Electron Spin Resonance Spectroscopy; D016166:Free Radical Scavengers / Q000494:pharmacology; D005609:Free Radicals / Q000737:chemistry; D006801:Humans; D015394:Molecular Structure; D009153:Mutagens / Q000737:chemistry / Q000528:radiation effects / Q000633:toxicity*; D009690:Nucleic Acid Conformation; D010618:Phenanthrolines / Q000494:pharmacology; D010777:Photochemistry; D014466:Ultraviolet Rays
D018906:Antineoplastic Agents, Alkylating; D002614:Chelating Agents; D018736:DNA Adducts; D016166:Free Radical Scavengers; D005609:Free Radicals; D009153:Mutagens; D010618:Phenanthrolines; D003300:Copper; D003606:Dacarbazine; D000080242:8-Hydroxy-2'-Deoxyguanosine; D004247:DNA; C427203:calf thymus DNA; C002478:bathocuproine; D003849:Deoxyguanosine
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