Genotoxicity of 3′-azido-3′-deoxythymidine in the human lymphoblastoid cell line, TK6: relationships between DNA incorporation, mutant frequency, and spectrum of deletion mutations in HPRT

Sussman, Hillary E.; Olivero, Ofelia A.; Meng, Quanxin; Pietras, Sara M.; Poirier, Miriam C.; O’Neill, J. Patrick; Finette, Barry A.; Bauer, Michael J.; Walker, Vernon E.

doi:10.1016/s0027-5107(99)00111-6

Cited by 61 publications

(64 citation statements)

References 19 publications

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“…The plating efficiencies and mutant frequencies for all groups are shown in Figure 1. Our spontaneous hprt mutant frequency was similar to that described by other authors, who reported spontaneous mutation frequencies ranging from 1.3 to 3.8 x 10 -6 (Giver et al, 1993;Nelson et al, 1994;Sussman et al, 1999;Tomita-Mitchel et al, 2000). The hprt mutant frequencies for the groups exposed to 0.2 and 0.5 Gy were closer to the mutant frequencies of TK6 cells exposed to 0.3 and 0.5 Gy described elsewhere (Grosovsky and Little, 1985).…”

supporting

confidence: 90%

Low doses of gamma ionizing radiation increase hprt mutant frequencies of TK6 cells without triggering the mutator phenotype pathway

et al. 2006

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The TK6 lymphoblastoid cell line is known to be mismatch repair (MMR) and p53 proficient. Deficiency in MMR results in a mutator phenotype characterized by microsatellite instability (MSI) and increased hprt mutant frequency (MF). Increased hprt MF is also a biomarker of effect for exposure to ionizing radiation. In order to test if a mutator phenotype could be induced by low doses of gamma ionizing radiation, an hprt cloning assay and a MSI investigation were performed after radiation exposure. The spontaneous MF was 1.6 x 10 -6 . The groups exposed to 0.2, 0.5 and 1.0 Gy had hprt MFs of 2.3, 3.3 and 2.2 x 10 -6 , respectively. The spontaneous MSI frequency per allele in non-selected cells was 5.4 x 10 -3 , as evidenced at the loci D11S35, nm23-H1, D8S135 and p53. MSI frequencies in the groups exposed to 0.2, 0.5 and 1.0 Gy were found to be < 4.7, < 7.7 and < 12 x 10 -3 , respectively. The frequencies of hprt mutants and MSI found in this study suggest that low doses of ionizing radiation increase hprt mutant frequency without triggering the mutator phenotype pathway.

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supporting

confidence: 90%

Low doses of gamma ionizing radiation increase hprt mutant frequencies of TK6 cells without triggering the mutator phenotype pathway

et al. 2006

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“…Therefore, we cannot conclude with certainty that the elevated reticulocyte micronucleus frequencies observed in ZDV-exposed infants in our study will be associated with a higher risk of future disease in these infants compared with healthy, non-exposed individuals. However, we are concerned about the long-term health implications for these infants because the MN increases noted in this study add to the growing body of evidence that ZDV readily induces genetic damage (mutational and clastogenic) in both nuclear and mitochondrial DNA in a variety of in vitro and in vivo test systems (Sussman et al, 1999;Poirier et al, 2004;Chan et al, in press;Von Tunglen et al, 2004;Meng et al, 2002;Olivero et al, 2002;Bishop et al, 2004;Witt et al, 2004;Meng et al, 2000;Hong et al, in press;Olivero, in press). …”

Section: Discussionmentioning

confidence: 89%

“…Thus, HIV-uninfected infants born to mothers with HIV may be exposed to ZDV both transplacentally during gestation, and directly during the postpartum treatment period. Although ZDV is tremendously effective in preventing vertical transmission of HIV, ZDV has been shown to be carcinogenic in animals (Ayers et al, 1996;National Toxicology Program, 1999Olivero et al, 1997;Diwan et al, 1999), genotoxic in numerous in vitro and in vivo test systems (Phillips et al, 1991;Sussman et al, 1999;Poirier et al, 2004;Chan et al, in press;von Tungeln et al, 2004;Meng et al, 2002), and incorporated into DNA of primates and humans after transplacental or direct exposure (Poirier et al, 2004Olivero et al, 2000Olivero et al, ,2002.…”

Section: Introductionmentioning

confidence: 99%

Elevated frequencies of micronucleated erythrocytes in infants exposed to zidovudine in utero and postpartum to prevent mother‐to‐child transmission of HIV

Witt

Cunningham

Patterson

et al. 2007

Environ and Mol Mutagen

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Zidovudine-based antiretroviral therapies (ART) for treatment of HIV-infected pregnant women have markedly reduced mother-to-child transmission of the human immunodeficiency virus (HIV-1) from ~25% to <1%. However, zidovudine (ZDV; AZT), a nucleoside analogue, induces chromosomal damage, gene mutations, and cancer in animals following direct or transplacental exposures. To determine if chromosomal damage is induced by ZDV in infants exposed transplacentally, we evaluated micronucleated reticulocyte frequencies (%MN-RET) in 16 HIVinfected ART-treated mother-infant pairs. Thirteen women received prenatal ART containing ZDV; 3 received ART without ZDV. All infants received ZDV for 6 weeks postpartum. Venous blood was obtained from women at delivery, and from infants at 1-3 days, 4-6 weeks, and 4-6 months of life; cord blood was collected immediately after delivery. Ten cord blood samples (controls) were obtained from infants of HIV-uninfected women who did not receive ART. %MN-RET was measured using a single laser 3-color flow cytometric system. Ten-fold increases in %MN-RET were seen in women and infants who received ZDV-containing ART prenatally; no increases were detected in 3 women and infants who received prenatal ART without ZDV. Specifically, mean %MN-RET in cord blood of ZDV-exposed infants was 1.67±0.34 compared with 0.16±0.06 in non-ZDV ARTexposed infants (P=0.006) and 0.12±0.02 in control cord bloods (p<0.0001). %MN-RET in ZDVexposed newborns decreased over the first 6 months of life to levels comparable to cord blood controls. These results demonstrate that transplacental ZDV exposure is genotoxic in humans. Longterm monitoring of HIV-uninfected ZDV-exposed infants is recommended to ensure their continued health.

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“…However, this shared locus of toxicity belies the apparent complexity of NRTI toxicity. Suggested mechanisms of toxicity include, but are not limited to, the inhibition of DNA Pol-␥ (23,24,32), inhibition of endogenous nucleotide kinases (30,35,49), direct inhibition of oxidative phosphorylation (4,5,29,40), reactive oxygen species (ROS) generation (31,44,46), and mtDNA and nuclear DNA mutagenesis (1,10,45), yet mtDNA abundance is commonly employed as the hallmark of NRTI toxicity. The results of this investigation demonstrate that inhibition of DNA Pol-␥ is but one of many possible cytotoxic mechanisms of the different NRTIs to alter the metabolic status of the cell and that the essences of mtDNA depletion in the mechanism of cytotoxicity differ among the different cell lines.…”

Section: Discussionmentioning

confidence: 99%

Absence of a Universal Mechanism of Mitochondrial Toxicity by Nucleoside Analogs

Lund

Peterson

Wallace

2007

Antimicrob Agents Chemother

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Nucleoside analogs are associated with various mitochondrial toxicities, and it is becoming increasingly difficult to accommodate these differences solely in the context of DNA polymerase gamma inhibition. Therefore, we examined the toxicities of zidovudine (AZT) (10 and 50 M; 2.7 and 13.4 g/ml), didanosine (ddI) (10 and 50 M; 2.4 and 11.8 g/ml), and zalcitabine (ddC) (1 and 5 M; 0.21 and 1.1 g/ml) in HepG2 and H9c2 cells without the presumption of mitochondrial DNA (mtDNA) depletion. Ethidium bromide (EtBr) (0.5 g/ml; 1.3 M) was used as a positive control. AZT treatment resulted in metabolic disruption (increased lactate and superoxide) and increased cell mortality with decreased proliferation, while mtDNA remained unchanged or increased (HepG2 cells; 50 M AZT). ddC caused pronounced mtDNA depletion in HepG2 cells but not in H9c2 cells and increased mortality in HepG2 cells, but no significant metabolic disruption in either cell type. ddI caused a moderate depletion of mtDNA in both cell types but showed no other effects. EtBr exposure resulted in metabolic disruption, increased cell mortality with decreased cell proliferation, and mtDNA depletion in both cell types. We conclude that nucleoside analogs display unique toxicities within and between culture models, and therefore, care should be taken when generalizing about the mechanisms of nucleoside reverse transcriptase inhibitor toxicity. Additionally, mtDNA abundance does not necessarily correlate with metabolic disruption, especially in cell culture; careful discernment is recommended in this regard.Nucleoside reverse transcriptase inhibitors (NRTIs) as a class represent one of the primary options for the treatment and prevention of human immunodeficiency virus infection. Despite the vast amount of clinical and experimental data demonstrating their toxicity, NRTIs remain at the forefront of human immunodeficiency virus chemotherapy. This dominance is due to several factors, namely, their efficacy, lack of effective alternatives, and an accepted but imperfect risk-benefit approach (i.e., toxicity versus viral inhibition). The future prospects for their use over extended periods inspire an urgency to better understand the toxic mechanisms of these drugs in order to minimize further patient risk.By design, NRTIs share structural similarities with each other and with the endogenous nucleosides they mimic. Structure-activity assumptions would normally suggest that these compounds share similar mechanisms of toxicity; however, a survey of the literature involving NRTI research shows that the evidence paints a much more convoluted picture (34, 52). The distinctiveness and tissue specificities of NRTI toxicities suggests that unintended targets are varied among individual compounds within this family of drugs. Much of the variation in NRTI toxicity has been attributed to differing levels of prodrug activation in different tissues (reviewed in reference 21). The activities of NRTIs against viral reverse transcriptase and incorporation/termination of endogenous DNA b...

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Genotoxicity of 3′-azido-3′-deoxythymidine in the human lymphoblastoid cell line, TK6: relationships between DNA incorporation, mutant frequency, and spectrum of deletion mutations in HPRT

Cited by 61 publications

References 19 publications

Low doses of gamma ionizing radiation increase hprt mutant frequencies of TK6 cells without triggering the mutator phenotype pathway

Low doses of gamma ionizing radiation increase hprt mutant frequencies of TK6 cells without triggering the mutator phenotype pathway

Elevated frequencies of micronucleated erythrocytes in infants exposed to zidovudine in utero and postpartum to prevent mother‐to‐child transmission of HIV

Absence of a Universal Mechanism of Mitochondrial Toxicity by Nucleoside Analogs

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