Perinatal genotoxicity and carcinogenicity of anti-retroviral nucleoside analog drugs
ABSTRACT The current worldwide spread of the human immunodeficiency virus-1 (HIV-1) to the heterosexual population has resulted in approximately 800,000 children born yearly to HIV-1-infected mothers. In the absence of anti-retroviral intervention, about 25% of the approximately 7,000 children born yearly to HIV-1-infected women in the United States are HIV-1 infected. Administration of zidovudine (AZT) prophylaxis during pregnancy reduces the rate of infant HIV-1 infection to approximately 7%, and further reductions are achieved with the addition of lamivudine (3TC) in the clinical formulation Combivir. Whereas clinically this is a remarkable achievement, AZT and 3TC are DNA replication chain terminators known to induce various types of genotoxicity. Studies in rodents have demonstrated AZT-DNA incorporation, HPRT mutagenesis, telomere shortening, and tumorigenicity in organs of fetal mice exposed transplacentally to AZT. In monkeys, both AZT and 3TC become incorporated into the DNA from multiple fetal organs taken at birth after administration of human-equivalent protocols to pregnant dams during gestation, and telomere shortening has been found in monkey fetuses exposed to both drugs. In human infants, AZT-DNA and 3TC-DNA incorporation as well as HPRT and GPA mutagenesis have been documented in cord blood from infants exposed in utero to Combivir. In infants of mice, monkeys, and humans, levels of AZT-DNA incorporation were remarkably similar, and in newborn mice and humans, mutation frequencies were also very similar. Given the risk-benefit ratio, these highly successful drugs will continue to be used for prevention of vertical viral transmission, however evidence of genotoxicity in mouse and monkey models and in the infants themselves would suggest that exposed children should be followed well past adolescence for early detection of potential cancer hazard.
- SourceAvailable from: Ofelia A Olivero
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- "Zidovudine (AZT or 3′-azido-2′,3′-dideoxythymidine) was the first nucleoside reverse transcriptase inhibitor (NRTI) used to treat HIV-1 infection and to reduce vertical transmission of the virus during pregnancy, and the largest body of data showing the potential for NRTIs to induce long-term side effects pertains to AZT (reviewed in [IARC, 2000; Wutzler and Thust, 2001; Dagan et al., 2002; Poirier et al., 2004; NTP, 2006; Kohler and Lewis, 2007; Walker and Poirier, 2007]). Phillips et al.  reported that in vivo exposure of mice to AZT caused significant increases in micronucleated cells in bone marrow; since then additional studies have described the DNA damaging effects, clastogenicity, mutagenicity, and carcinogenicity of AZT and other NRTIs in animal models and humans [Olivero et al., 1997, 1999; Bonnet et al., 2004; Poirier et al., 2004; Brock et al. 2006; NTP, 2006; Escobar et al., 2007; Meng et al., 2007; Walker et al., 2007; Witt et al., 2007]. Previous work showed that in vitro and in vivo exposure of cells to AZT caused significant increases in mutations in reporter genes and in genes associated with neoplastic transformation (reviewed in [Walker and Poirier, 2007]). "
ABSTRACT: The success of nucleoside reverse transcriptase inhibitors (NRTIs) in treating HIV-1 infection and reducing mother-to-child transmission of the virus during pregnancy is accompanied by evidence that NRTIs cause long-term health risks for cancer and mitochondrial disease. Thus, agents that mitigate toxicities of the current combination drug therapies are needed. Previous work had shown that the NRTI-drug pair zidovudine (AZT)-didanosine (ddI) was highly cytotoxic and mutagenic; thus, we conducted preliminary studies to investigate the ability of the active moiety of amifostine, WR1065, to protect against the deleterious effects of this NRTI-drug pair. In TK6 cells exposed to 100 muM AZT-ddI (equimolar) for 3 days with or without 150 muM WR1065, WR1065 enhanced long-term cell survival and significantly reduced AZT-ddI-induced mutations. Follow-up studies were conducted to determine if coexposure to AZT and WR1065 abrogated the antiretroviral efficacy of AZT. In human T-cell blasts infected with HIV-1 in culture, inhibition of p24 protein production was observed in cells treated with 10 muM AZT in the absence or presence of 5-1,000 muM WR1065. Surprisingly, WR1065 alone exhibited dose-related inhibition of HIV-1 p24 protein production. WR1065 also had antiviral efficacy against three species of adenovirus and influenza A and B. Intracellular levels of unbound WR1065 were measured following in vitro/in vivo drug exposure. These pilot study results indicate that WR1065, at low intracellular levels, has cytoprotective and antimutagenic activities against the most mutagenic pair of NRTIs and has broad spectrum antiviral effects. These findings suggest that the activities have a possible common mode of action that merits further investigation.Environmental and Molecular Mutagenesis 07/2009; 50(6):460-72. DOI:10.1002/em.20482 · 2.55 Impact Factor
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- "For ethical reasons, the current study did not include a treatment-control group of drug-naïve infants born to untreated HIV-1-infected mothers to assess the mutagenic potential of the fetal environment in the presence of maternal HIV-1 infection. In the United States, women are routinely treated with ARVs upon diagnosis of HIV-1 infection, making it problematic to address the degree to which fetal responses to " HIV-1 exposure, " in the absence of maternal ARV treatment, contributes to perinatal toxicities and long-term health risks in the offspring [Poirier et al., 2003, 2004; Funk et al., 2007]. Consequently, there is limited evidence that fetal responses and/or " HIV-1 exposure " damage mitochondria of fetal cells/ tissues, perhaps increasing the risk for mtDNA mutations. "
ABSTRACT: A sensitive vertical denaturing gradient gel electrophoresis (DGGE) method, using 13 unipolar psoralen-clamped PCR primer pairs, was developed for detecting sequence variants in the 22 tRNA genes and flanking regions (together spanning approximately 21%) of the human mitochondrial genome. A study was conducted to determine (i) if mitochondrial DNA (mtDNA) polymorphisms and/or mutations were detectable in healthy newborns and (ii) if prepartum 3'-azido-2',3'-dideoxythymidine (AZT) based HIV-1 prophylaxis was associated with significant increases in mtDNA mutations and changes in the degree of heteroplasmy of sequence variants in uninfected infants born to HIV-1-infected mothers. DGGE analysis of umbilical cord tissue (where vascular endothelium and smooth muscle cells are the major source of mtDNA) showed that mtDNA sequence variants were significantly elevated by threefold in AZT-treated infants compared with unexposed controls (P < 0.001), with 24 changes observed in 19/52 (37%) treated newborns (averaging 0.46 changes/subject) versus only eight changes found in 7/55 (13%) unexposed newborns (averaging 0.15 changes/subject). Six distinct sequence variants occurring in unexposed controls were predominately synonymous and homoplasmic, representing previously reported polymorphisms. Uninfected infants exposed to a combination of AZT and 2',3'-dideoxy-3'-thiacytidine and "maternal HIV-1" had a significant shift in the spectrum of mutations (P = 0.04) driven by increases in nonsynonymous heteroplasmic sequence variants at polymorphic sites (10 distinct variants) and novel sites (four distinct variants). While the weight of evidence suggests that prepartum AZT-based prophylaxis produces mtDNA mutations, additional research is needed to determine the degree to which fetal responses to maternal HIV-1 infection, in the absence of antiretroviral treatment, contribute to prenatal mtDNA mutagenesis.Environmental and Molecular Mutagenesis 01/2009; 50(1):10-26. DOI:10.1002/em.20433 · 2.55 Impact Factor
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- "The nucleoside reverse transcriptase inhibitor (NRTI), 3′-azido-3′-deoxythymidine (AZT) comprises part of the first-line therapy for HIV-1 infection worldwide (DHHS, 2006), and is specifically recommended by the Centers for Disease Control for inhibition of mother-to-child HIV-1 transmission (Centers for Disease Control and Prevention, 2003) and post-exposure prophylaxis in health care, laboratory and rescue workers (Cardo et al., 1997; Centers for Disease Control and Prevention, 1999). The genotoxicity of this drug has been studied extensively, and numerous reports indicate that incorporation of the drug into DNA, clastogenicity and mutagenicity are consequences of AZT exposure in cultured cells, animal models and humans (IARC, 2000; Poirier et al., 2004; Escobar et al., 2007; Olivero, 2007) Transplacental carcinogenesis in mouse offspring exposed to AZT during the last week of gestation was documented in multiple organs at 1–2 years of age (Olivero et al., 1997; Diwan et al., 1999; NTP, 1996; Walker et al., 2007). The studies revealed dose-related increases in incidences of liver, lung and reproductive organ tumors, and raised some concerns regarding potential cancer risk in human infants exposed to the NRTI drugs during development. "
ABSTRACT: A mainstay of the antiretroviral drugs used for therapy of HIV-1, zidovudine (AZT) is genotoxic and becomes incorporated into DNA. Here we explored host inter-individual variability in AZT-DNA incorporation, by AZT radioimmunoassay (RIA), using 19 different strains of normal human mammary epithelial cells (NHMECs) exposed for 24 h to 200 microM AZT. Twelve of the 19 NHMEC strains showed detectable AZT-DNA incorporation levels (16 to 259 molecules of AZT/10(6) nucleotides), while 7 NHMEC strains did not show detectable AZT-DNA incorporation. In order to explore the basis for this variability, we compared the 2 NHMEC strains that showed the highest levels of AZT-DNA incorporation (H1 and H2) with 2 strains showing no detectable AZT-DNA incorporation (L1 and L2). All 4 strains had similar (> or =80%) cell survival, low levels of accumulation of cells in S-phase, and no relevant differences in response to the direct-acting mutagen bleomycin (BLM). Finally, when levels of thymidine kinase 1 (TK1), the first enzyme in the pathway for incorporation of AZT into DNA, were determined by Western blot analysis in all 19 NHMEC strains at 24 h of AZT exposure, higher TK1 protein levels were found in the 12 strains showing AZT-DNA incorporation, compared to the 7 showing no incorporation (p=0.0005, Mann-Whitney test). Furthermore, strains L1 and L2, which did not show AZT-DNA incorporation at 24 h, did have measurable incorporation by 48 and 72 h. These data suggest that variability in AZT-DNA incorporation may be modulated by inter-individual differences in the rate of induction of TK1 in response to AZT exposure.Toxicology and Applied Pharmacology 05/2008; 228(2):158-64. DOI:10.1016/j.taap.2007.12.005 · 3.63 Impact Factor