Relationships between DNA incorporation, mutant frequency, and loss of heterozygosity at the TK locus in human lymphoblastoid cells exposed to 3'- azido-3'-deoxythymidine

Quanxin Meng, Ting Su, Ofelia A. Olivero, Miriam C. Poirier, Xiaochu Shi, Xinxin Ding, Vernon E. Walker

Research output: Contribution to journalArticle

38 Scopus citations

Abstract

3'-Azido-3'-deoxythymidine (AZT), a thymidine analogue widely used in the treatment of AIDS patients and for prevention of the onset of AIDS in HIV-seropositive individuals, causes tumors in mice exposed as adults or in utero. The purpose of this study was to investigate the potential mechanisms of AZT mutagenicity and carcinogeniCity by quantifying the incorporation of AZT into cellula DNA, measuring AZT-induced thymidine kinase (TK) mutant frequencies (Mfs), and determining the percentage of loss of heterozygosity (LOH) in spontaneous or AZT-induced TK mutants in the human lymphoblastoid cell line, TK6. Cells were exposed to 300 μM AZT for 0, 1, 3, or 6 days, or to 0, 33, 100, 300, or 900 μM AZT for 3 days (n = 5 flasks/group). The effects of exposure concentration on incorporation of AZT into cellular DNA were evaluated by an AZT radioimmunoassay, and the effects of duration and concentration of AZT exposure on the TK Mfs were assessed by a cell-cloning assay. AZT was incorporated into DNA in a dose-related manner at concentrations up to 300 μM, above which no further increase was observed. TK Mf increased with the extended duration and with incremental concentrations of AZT exposure. There was a positive correlation (P = 0.036, coefficient = 0.903) between AZT-DNA incorporation and AZT-induced TK Mfs, suggesting that AZT incorporation into cellular DNA has a direct role in the genotoxicity of AZT. Southern blot analyses indicated that 84% (6.2 x 10- 6/7.4 x 10-6) of AZT-induced mutants were attributable to LOH, consistent with the known mechanism of AZT as a DNA chain terminator. Considering the importance of LOH in human carcinogenesis, AZT-induced LOH warrants further study.

Original languageEnglish (US)
Pages (from-to)322-329
Number of pages8
JournalToxicological Sciences
Volume54
Issue number2
DOIs
StatePublished - 2000

Keywords

  • 3'-azido-3'-deoxythymidine
  • DNA incorporation
  • Human lymphoblastoid cells
  • Loss of heterozygosity
  • Mutant frequency
  • Thymidine kinase

ASJC Scopus subject areas

  • Toxicology

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