Transplacental effects of 3'-azido-2',3'-dideoxythymidine (AZT): tumorigenicity in mice and genotoxicity in mice and monkeys

In-utero exposure to zidovudine-containing antiretroviral therapy and clonal hematopoiesis in HIV-exposed uninfected newborns

OBJECTIVE

Zidovudine (ZDV) has been extensively used in pregnant women to prevent vertical transmission of HIV but few studies have evaluated potential mutagenic effects of ZDV during fetal development.

DESIGN

Our study investigated clonal hematopoiesis in HIV-exposed uninfected (HEU) newborns, 94 of whom were ZDV-exposed and 91 antiretroviral therapy (ART)-unexposed and matched for potential confounding factors.

METHODS

Utilizing high depth sequencing and genotyping arrays, we comprehensively examined blood samples collected during the first week after birth for potential clonal hematopoiesis associated with fetal ZDV exposure, including clonal single nucleotide variants (SNVs), small insertions and deletions (indels), and large structural copy number or copy neutral alterations.

RESULTS

We observed no statistically significant difference in the number of SNVs and indels per person in ZDV-exposed children (adjusted ratio [95% confidence interval, CI] for expected number of mutations = 0.79 [0.50--1.22], P = 0.3), and no difference in the number of large structural alterations. Mutations in common clonal hematopoiesis driver genes were not found in the study population. Mutational signature analyses on SNVs detected no novel signatures unique to the ZDV-exposed children and the mutational profiles were similar between the two groups.

CONCLUSION

Our results suggest that clonal hematopoiesis at levels detectable in our study is not strongly influenced by in-utero ZDV exposure; however, additional follow-up studies are needed to further evaluate the safety and potential long-term impacts of in-utero ZDV exposure in HEU children as well as better investigate genomic aberrations occurring late in pregnancy.

Azidothymidine "Clicked" into 1,2,3-Triazoles: First Report on Carbonic Anhydrase-Telomerase Dual-Hybrid Inhibitors

Cancer cells rely on the enzyme telomerase (EC 2.7.7.49) to promote cellular immortality. Telomerase inhibitors (i.e., azidothymidine) can represent promising antitumor agents, although showing high toxicity when administered alone. Better outcomes were observed within a multipharmacological approach instead. In this context, we exploited the validated antitumor targets carbonic anhydrases (CAs; EC 4.2.1.1) IX and XII to attain the first proof of concept on CA–telomerase dual-hybrid inhibitors. Compounds 1b, 7b, 8b, and 11b showed good in vitro inhibition potency against the CAs IX and XII, with K_I values in the low nanomolar range, and strong antitelomerase activity in PC-3 and HT-29 cells (IC₅₀ values ranging from 5.2 to 9.1 μM). High-resolution X-ray crystallography on selected derivatives in the adduct with hCA II as a model study allowed to determine their binding modes and thus to set the structural determinants necessary for further development of compounds selectively targeting the tumoral cells.

Association between zidovudine-containing antiretroviral therapy exposure in utero and leukocyte telomere length at birth

OBJECTIVES

Zidovudine (ZDV) is a nucleoside reverse transcriptase inhibitor that could cause telomere shortening through inhibition of telomerase. We examined the association between in utero exposure to ZDV and telomere length at birth in HIV-exposed-uninfected (HEU) newborns.

METHODS

We selected 94 ZDV-exposed HEU children and 85 antiretroviral therapy (ART)-unexposed HEU children from the Surveillance Monitoring for ART Toxicities Study and the Women and Infants Transmission Study. We assessed relative telomere length in stored peripheral blood mononuclear cells taken in the first 7 days of life using quantitative polymerase chain reaction. We used linear regression to compare relative telomere length between ZDV-exposed and ART-unexposed children. We additionally evaluated relative telomere length according to maternal and infant characteristics.

RESULTS

Relative telomere length was longer in ZDV-exposed children compared with ART-unexposed individuals (adjusted mean ratio difference 0.21, 95% confidence interval 0.15-0.28, P < 0.001). We found an inverse correlation between maternal HIV RNA levels and infant relative telomere length (-0.06 per log10 copies, 95% confidence interval -0.08 to -0.03, P < 0.001). Relative telomere length was not associated with maternal CD4 cell count, maternal age, gestational age, sex, sample storage time, or maternal substance use (P > 0.05).

CONCLUSION

Relative telomere length was longer in ZDV-exposed infants. This difference may reflect beneficial health effects of ART during pregnancy, as we observed an inverse association with maternal HIV RNA levels.

Risk of cancer in children exposed to antiretroviral nucleoside analogues in utero: The french experience

All nucleoside analogues for treating HIV infection, due to their capacity to integrate into and alter human DNA, are experimentally genotoxic to some extent. The long-term oncogenic risk after in utero exposure remains to be determined. Cancer incidence in uninfected children exposed to nucleos(t)ide reverse transcriptase inhibitors (NRTIs) was evaluated, by cross-checking against the National Cancer Registry, in the French perinatal study of children born to HIV⁺ mothers. Twenty-one cancers were identified in 15,163 children (median age: 9.9 years [interquartile range (IQR): 5.8-14.2]) exposed to at least one NRTI in utero between 1990 and 2014. Five of these children were exposed to zidovudine monotherapy, and 15 to various combinations, seven of which included didanosine. Overall, the total number of cases was not significantly different from that expected for the general population (SIR = 0.8[0.47-1.24]), but the number of cases after didanosine exposure was twice that expected (SIR = 2.5 [1.01-5.19]). Didanosine accounted for only 10% of prescriptions but was associated with one-third of cancers. In multivariate analysis, didanosine exposure was significantly associated with higher risk (HR = 3.0 [0.9-9.8]). This risk was specifically linked to first-trimester exposure (HR = 5.5 [2.1-14.4]). Three cases of pineoblastoma, a very rare cancer, were observed, whereas 0.03 were expected. Two were associated with didanosine exposure. Despite reassuring data overall, there is strong evidence to suggest that didanosine displays transplacental oncogenicity. These findings cannot be extrapolated to other NRTIs, but they highlight the need for comprehensive evaluations of the transplacental genotoxicity of this antiretroviral class. Environ. Mol. Mutagen., 60:404-409, 2019. © 2017 Wiley Periodicals, Inc.

Mesoporous silica nanoparticle is comparatively safer than zinc oxide nanoparticle which can cause profound steroidogenic effects on pregnant mice and male offspring exposed in utero

The increasing use of nanomaterials has naturally caused heightened concerns about their potential risks to human and animal health. We investigated the effect of zinc oxide nanoparticles (ZnO NPs) and mesoporous silica nanoparticles (MSN) on steroidogenesis in the corpus luteum (CL) of pregnant mice and testis of male offspring. Pregnant albino mice were exposed to ZnO NPs and MSN for 2 days on alternate days, gestation days 15–19. Hepatic injury marker enzymes increased in the higher concentration of NM-exposed mother mice, but histological examination revealed no changes in the placenta of pregnant mice, whereas testis of male offspring showed gross pathological changes. The expression pattern of progesterone biosynthesis-related genes was also altered in the CL of NP-exposed pregnant mice. In utero exposure of ZnO NPs increased the relative expression of StAR in 100 mg/kg body weight (BW) ZnO NP-treated and bulk ZnO-treated groups and P450 side-chain cleavage enzyme (P450scc) in 50 mg/kg BW ZnO NP-treated and 100 mg/kg of bulk ZnO-treated male offspring. Serum testosterone concentration significantly increased in the 100 mg/kg of bulk ZnO-treated group and decreased in the 250 mg/kg of MSN-treated group and a single dose of 300 mg/Kg BW of ZnO NPs caused miscarriages and adversely affected the developing foetus in mice.

Paediatric HIV-1 infection: updated strategies of prevention mother-to-child transmission

INTRODUCTION

HIV-1 epidemiology is changing and prevention of mother-to-child transmission (PMTCT) strategies have been continuously optimized over time. However, the correct management of infected women during pregnancy is crucial for PMTCT and cases of vertical transmission continue to occur.

OBJECTIVE

To review the most recent evidence regarding the prevention of MTCT in resource-rich and resource-limited settings, focalizing on new possible approaches.

RESULTS

New issues regard the optimal antiretroviral therapy regimen for pregnant women with good immunological control, the use of intrapartum zidovudine (ZDV) in pregnant women with low viral load, the optimization of prophylaxis in the settings where breastfeeding is recommended and use of combined neonatal prophylaxis (CNP) in infants at high-risk for MTCT. Complete viral control, in recent years, has been achieved in most infected pregnant women, has led to change the recommended mode of delivery, since vaginal birth has become a safe option and is now largely recommended. Recent data reported a large use of CNP in preterm infants: this practice may be dangerous, due to the lack of safety data, and its efficacy and effectiveness is unproven.

CONCLUSION

Data are accumulating on efficacy, effectiveness and safety of different PMTCT strategies in various possible clinical scenarios, however further researches are needed in order to optimize the management of infants at extremely low risk for MTCT as well as in those presenting with high risk for infection.

Incidence of cancer and overall risk of mortality in individuals treated with raltegravir-based and non-raltegravir-based combination antiretroviral therapy regimens

Objectives

There are currently few data on the long‐term risk of cancer and death in individuals taking raltegravir (RAL). The aim of this analysis was to evaluate whether there is evidence for an association.

Methods

The EuroSIDA cohort was divided into three groups: those starting RAL‐based combination antiretroviral therapy (cART) on or after 21 December 2007 (RAL); a historical cohort (HIST) of individuals adding a new antiretroviral (ARV) drug (not RAL) to their cART between 1 January 2005 and 20 December 2007, and a concurrent cohort (CONC) of individuals adding a new ARV drug (not RAL) to their cART on or after 21 December 2007. Baseline characteristics were compared using logistic regression. The incidences of newly diagnosed malignancies and death were compared using Poisson regression.

Results

The RAL cohort included 1470 individuals [with 4058 person‐years of follow‐up (PYFU)] compared with 3787 (4472 PYFU) and 4467 (10 691 PYFU) in the HIST and CONC cohorts, respectively. The prevalence of non‐AIDS‐related malignancies prior to baseline tended to be higher in the RAL cohort vs. the HIST cohort [adjusted odds ratio (aOR) 1.31; 95% confidence interval (CI) 0.95–1.80] and vs. the CONC cohort (aOR 1.89; 95% CI 1.37–2.61). In intention‐to‐treat (ITT) analysis (events: RAL, 50; HIST, 45; CONC, 127), the incidence of all new malignancies was 1.11 (95% CI 0.84–1.46) per 100 PYFU in the RAL cohort vs. 1.20 (95% CI 0.90–1.61) and 0.83 (95% CI 0.70–0.99) in the HIST and CONC cohorts, respectively. After adjustment, there was no evidence for a difference in the risk of malignancies [adjusted rate ratio (RR) 0.73; 95% CI 0.47–1.14 for RALvs. HIST; RR 0.95; 95% CI 0.65–1.39 for RALvs. CONC] or mortality (adjusted RR 0.87; 95% CI 0.53–1.43 for RALvs. HIST; RR 1.14; 95% CI 0.76–1.72 for RALvs. CONC).

Conclusions

We found no evidence for an oncogenic risk or poorer survival associated with using RAL compared with control groups.

Toxicity of Nanoparticles on the Reproductive System in Animal Models: A Review

In the last two decades, nanotechnologies demonstrated various applications in different fields, including detection, sensing, catalysis, electronics, and biomedical sciences. However, public concerns regarding the well-being of human may hinder the wide utilization of this promising innovation. Although, humans are exposed to airborne nanosized particles from an early age, exposure to such particles has risen dramatically within the last century due to anthropogenic sources of nanoparticles. The wide application of nanomaterials in industry, consumer products, and medicine has raised concerns regarding the potential toxicity of nanoparticles in humans. In this review, the effects of nanomaterials on the reproductive system in animal models are discussed. Females are particularly more vulnerable to nanoparticle toxicity, and toxicity in this population may affect reproductivity and fetal development. Moreover, various types of nanoparticles have negative impacts on male germ cells, fetal development, and the female reproductive system. These impacts are associated with nanoparticle modification, composition, concentration, route of administration, and the species of the animal. Therefore, understanding the impacts of nanoparticles on animal growth and reproduction is essential. Many studies have examined the effects of nanoparticles on primary and secondary target organs, with a concentration on the in vivo and in vitro effects of nanoparticles on the male and female reproductive systems at the clinical, cellular, and molecular levels. This review provides important information regarding organism safety and the potential hazards of nanoparticle use and supports the application of nanotechnologies by minimizing the adverse effects of nanoparticles in vulnerable populations.

Zidovudine use in pregnancy and congenital malformations

OBJECTIVE

There is inconsistent evidence that zidovudine use during pregnancy increases overall, cardiac, and male genital malformations.

DESIGN

We conducted a systematic review and meta-analysis of zidovudine use and malformations and, using Bayesian methods, combined it with data from a cohort study of mother-infant pairs in the nationwide Medicaid Analytic eXtract (MAX).

METHODS

Using MAX data (2000-2010), we identified pregnant women with HIV treated with antiretroviral therapy (ART). Women with at least one zidovudine dispensing during the first trimester were compared to women receiving ART without zidovudine in the first trimester. Malformation outcomes were defined using diagnosis/procedure codes. To adjust for confounding, we performed 1 : 1 propensity score matching. Bayesian methods require specification of a prior, which we developed in the meta-analysis. Logistic regression models combined MAX data with the prior, estimating odds ratios (ORs) and 95% credible intervals.

RESULTS

Fourteen articles contributed information on overall malformations, seven on cardiac malformations, and five on male genital malformations. In MAX, matching led to a sample of 735 women each in the zidovudine and comparator groups. When comparing first trimester zidovudine use to other ART, the Bayesian procedure yielded OR estimates slightly above the null for overall [OR = 1.11, 95% credible interval (0.80-1.55)] and cardiac [OR = 1.30 (0.63-2.71)] malformations. There were no zidovudine-exposed cases of male genital malformations in MAX, but the meta-analysis yielded elevated OR estimates [OR = 2.57 (1.26-5.24)].

CONCLUSION

For most malformations, first-trimester zidovudine was not associated with increased risk. The potential increase in male genital malformations was small in absolute terms, and should be evaluated further.

Combination antiretroviral therapy and cancer risk

PURPOSE OF REVIEW

To review the newest research about the effects of combination antiretroviral therapy (cART) on cancer risk.

RECENT FINDINGS

HIV+ persons are at increased risk of cancer. As this risk is higher for malignancies driven by viral and bacterial coinfections, classifying malignancies into infection-related and infection-unrelated has been an emerging trend. Cohorts have detected major reductions in the incidence of Kaposi sarcoma and non-Hodgkin lymphoma (NHL) following cART initiation among immunosuppressed HIV+ persons. However, recent randomized data indicate that cART reduces risk of Kaposi sarcoma and NHL also during early HIV infection before overt immunosuppression occurs. Long-term effects of cART exposure on cancer risk are not well defined; according to basic and epidemiological research, there might be specific associations of each cART class with distinct patterns of cancer risk.

SUMMARY

The relationship between cART exposure and cancer risk is complex and nuanced. It is an intriguing fact that, whether initiated during severe immunosuppression or not, cART reduces risk of Kaposi sarcoma and NHL. Further research should identify mediators of the benefit of immediate cART initiation in reducing cancer risk, understand the relationship between long-term cART exposure and cancer incidence and assess whether adjuvant anti-inflammatory therapies can reduce cancer risk during treated HIV infection.

Mitochondrial compromise in 3-year old patas monkeys exposed in utero to human-equivalent antiretroviral therapies

Antiretroviral (ARV) drug therapy, given during pregnancy for prevention of mother-to-child transmission of human immunodeficiency virus 1 (HIV-1), induces fetal mitochondrial dysfunction in some children. However, the persistence/reversibility of that dysfunction is unclear. Here we have followed Erythrocebus patas (patas) monkey offspring for up to 3 years of age (similar in development to a 15-year old human) after exposure of the dams to human-equivalent in utero ARV exposure protocols. Pregnant patas dams (3-5/exposure group) were given ARV drug combinations that included zidovudine (AZT)/lamivudine (3TC)/abacavir (ABC), or AZT/3TC/nevirapine (NVP), for the last 10 weeks (50%) of gestation. Infants kept for 1 and 3 years also received drug for the first 6 weeks of life. In offpsring at birth, 1 and 3 years of age mitochondrial morphology, examined by electron microscopy (EM), was compromised compared to the unexposed controls. Mitochondrial DNA (mtDNA), measured by hybrid capture chemiluminescence assay (HCCA) was depleted in hearts of patas exposed to AZT/3TC/NVP at all ages (P < 0.05), but not in those exposed to AZT/3TC/ABC at any age. Compared to unexposed controls, mitochondrial reserve capacity oxygen consumption rate (OCR by Seahorse) in cultured bone marrow mesenchymal fibroblasts from 3-year-old patas offspring was ∼50% reduced in AZT/3TC/ABC-exposed patas (P < 0.01), but not in AZT/3TC/NVP-exposed patas. Overall the data show that 3-year-old patas sustain persistent mitochondrial dysfunction as a result of perinatal ARV drug exposure. Environ. Mol. Mutagen. 57:526-534, 2016. © 2016 Wiley Periodicals, Inc.

Fetal consequences of maternal antiretroviral nucleoside reverse transcriptase inhibitor use in human and nonhuman primate pregnancy

PURPOSE OF REVIEW

Here we present fetal genotoxicity and mitochondrial toxicity, induced by nucleoside reverse transcriptase inhibitors (NRTIs), in HIV-1-infected pregnant women treated to prevent mother-to-child HIV-1 transmission, and in virus-free pregnant patas monkeys.

RECENT FINDINGS

In the offspring of pregnant patas monkeys given human-equivalent NRTI protocols, aneuploidy was found in cultured bone marrow cells taken at birth, 1, and 3 years of age. In some newborn human infants, the offspring of HIV-1-infected mothers given zidovudine (AZT) therapy, aneuploidy, mitochondrial DNA (mtDNA) depletion, morphologically damaged mitochondria, and reduction in cardiac left ventricular muscle were observed. NRTI-exposed human and patas umbilical cords had similar levels of mtDNA depletion and mitochondrial morphological damage. NRTI-exposed patas offspring showed a compensatory increase in heart mtDNA, and a 50% loss of brain mtDNA at 1 year of age. Mitochondrial morphological damage and mtDNA loss were persistent in blood cells of NRTI-exposed infants up to 2 years of age, and in heart and brain from NRTI-exposed patas up to 3 years of age (human equivalent of 15 years).

SUMMARY

Whereas use of NRTIs in human pregnancy protects many thousands of children worldwide, some HIV-1-uninfected infants born to HIV-1-infected mothers receiving antiretroviral drug therapy sustain toxicities that may have adverse consequences later in life.

Neurotoxic effects of AZT on developing and adult neurogenesis

Azidothymidine (AZT) is a synthetic, chain-terminating nucleoside analog used to treat HIV-1 infection. While AZT is not actively transported across the blood brain barrier, it does accumulate at high levels in cerebrospinal fluid, and subsequently diffuses into the overlying parenchyma. Due to the close anatomical proximity of the neurogenic niches to the ventricular system, we hypothesize that diffusion from CSF exposes neural stem/progenitor cells and their progeny to biologically relevant levels of AZT sufficient to perturb normal cell functions. We employed in vitro and in vivo models of mouse neurogenesis in order to assess the effects of AZT on developing and adult neurogenesis. Using in vitro assays we show that AZT reduces the population expansion potential of neural stem/progenitor cells by inducing senescence. Additionally, in a model of in vitro neurogenesis AZT severely attenuates neuroblast production. These effects are mirrored in vivo by clinically-relevant animal models. We show that in utero AZT exposure perturbs both population expansion and neurogenesis among neural stem/progenitor cells. Additionally, a short-term AZT regimen in adult mice suppresses subependymal zone neurogenesis. These data reveal novel negative effects of AZT on neural stem cell biology. Given that the sequelae of HIV infection often include neurologic deficits—subsumed under AIDS Dementia Complex (Brew, 1999)—it is important to determine to what extent AZT negatively affects neurological function in ways that contribute to, or exacerbate, ADC in order to avoid attributing iatrogenic drug effects to the underlying disease process, and thereby skewing the risk/benefit analysis of AZT therapy.

Role of nucleotide excision repair and p53 in zidovudine (AZT)-induced centrosomal deregulation

The nucleoside reverse transcriptase inhibitor zidovudine (AZT) induces genotoxic damage that includes centrosomal amplification (CA > 2 centrosomes/cell) and micronucleus (MN) formation. Here we explored these end points in mice deficient in DNA repair and tumor suppressor function to evaluate their effect on AZT-induced DNA damage. We used mesenchymal-derived fibroblasts cultured from C57BL/6J mice that were null and wild type (WT) for Xpa, and WT, haploinsufficient and null for p53 (6 different genotypes). Dose-responses for CA formation, in cells exposed to 0, 10, and 100 μM AZT for 24 hr, were observed in all genotypes except the Xpa((+/+)) p53((+/-)) cells, which had very low levels of CA, and the Xpa((-/-)) p53((-/-)) cells, which had very high levels of CA. For CA there was a significant three-way interaction between Xpa, p53, and AZT concentration, and Xpa((-/-)) cells had significantly higher levels of CA than Xpa((+/+)) cells, only for p53((+/-)) cells. In contrast, the MN and MN + chromosomes (MN + C) data showed a lack of AZT dose response. The Xpa((-/-)) cells, with p53((+/+)) or ((+/-)) genotypes, had levels of MN and MN + C higher than the corresponding Xpa((+/+)) cells. The data show that CA is a major event induced by exposure to AZT in these cells, and that there is a complicated relationship between AZT and CA formation with respect to gene dosage of Xpa and p53. The loss of both genes resulted in high levels of damage, and p53 haploinsufficicency strongly protected Xpa((+/+)) cells from AZT-induced CA damage.

Foetal loss and enhanced fertility observed in mice treated with Zidovudine or Nevirapine

BACKGROUND

Health concerns for HIV-infected persons on antiretroviral therapy (ART) have moved from morbidity to the challenges of long-term ART. We investigated the effect of Zidovudine or Nevirapine on reproductive capacity across two mouse generations.

METHODS

A prospective mouse study with drugs administered through one spermatogenic cycle. Mouse groups (16 males and 10 females) were given Zidovudine or Nevirapine for 56 days. Males were mated to untreated virgin females to determine dominant lethal effects. Twenty females (10 treated and 10 untreated) mated with the treated males per dose and gave birth to the F1 generation. Parental mice were withdrawn from drugs for one spermatogenic cycle and mated to the same dams to ascertain if effects are reversible. The F1 generation were exposed for another 56 days and mated to produce the F2 generation.

RESULTS

Foetal loss was indicated in the dominant lethal assay as early as four weeks into drug administration to the males. At the first mating of the parental generation to produce the F1 generation, births from 10 dams/dose when the 'father-only' was exposed to Zidovudine (10, 100 and 250 mg/kg) was 3, 2 and 1 while it was 7, 1 and 4 respectively when 'both-parents' were exposed. Similarly births from the parental generation first mating when the 'father-only' was exposed to Nevirapine (5, 50 and 150 mg/kg) was 2, 2 and 0 while it was 6, 5 and 9 respectively when 'both-parents' were exposed. However, fertility was not significantly different neither by dose nor by the parental exposure. The F1 mice mated to produce the F2 generation recorded only one birth.

CONCLUSION

The dominant lethal analysis showed foetal loss occurred when the "fathers-only" were treated while fertility was enhanced when "both-parents" were on therapy at the time of mating.

Selective protection of zidovudine-induced DNA-damage by the antioxidants WR-1065 and tempol

The cytokinesis-block micronucleus cytome (CBMN) assay, introduced by Fenech, was used to demonstrate different types of DNA damage in MOLT-3 human lymphoblastoid cells exposed to 10 μM zidovudine (AZT). In addition, we explored the cytoprotective potential of two antioxidants, WR-1065 and Tempol, to decrease AZT-induced genotoxicity. Binucleated cells, arrested by Cytochalasin B (Cyt B), were evaluated for micronuclei (MN), caused by DNA damage or chromosomal loss, and chromatin nucleoplasmic bridges (NPBs), caused by telomere attrition. Additionally, nuclear buds (NBUDs), caused by amplified DNA, and apoptotic and necrotic (A/N) cells were scored. We hypothesized that AZT exposure would increase the frequency of genotoxic end points, and that the antioxidants Tempol and WR-1065 would protect against AZT-induced genotoxicity. MOLT-3 cells were exposed to 0 or 10 µM AZT for a total of 76 hr. After the first 24 hr, 0 or 5 µM WR-1065 and/or 0 or 200 µM Tempol were added for the remainder of the experiment. For the last 28 hr (of 76 hr), Cyt B was added to arrest replication after one cell division, leaving a predominance of binucleated cells. The nuclear division index (NDI) was similar for all treatment groups, indicating that the exposures did not alter cell viability. MOLT-3 cells exposed to AZT alone had significant (P < 0.05) increases in MN and NBs, compared to unexposed cells. Both Tempol and WR-1065 protected against AZT-induced MN formation (P < 0.003 for both), and WR-1065, but not Tempol, reduced the levels of A/N (P = 0.041). In cells exposed to AZT/Tempol there were significantly reduced levels of NBUDs, compared to cells exposed to AZT alone (P = 0.015). Cells exposed to AZT/WR-1065 showed reduced levels of NPBs, compared to cells exposed to AZT alone (P = 0.037). Thus WR-1065 and Tempol protected MOLT-3 cells against specific types of AZT-induced DNA damage.

Factors contributing to risk for cancer among HIV-infected individuals, and evidence that earlier combination antiretroviral therapy will alter this risk

PURPOSE OF REVIEW

To critically appraise recent published literature about factors associated with cancer risk likely to be influenced by combination antiretroviral therapy (cART) in HIV-infected individuals, and the potential of earlier cART initiation to reduce this risk.

RECENT FINDINGS

Factors leading to increased risk of non-AIDS-defining malignancies (NADMs) in particular remain poorly understood. Immunodeficiency appears to be key, whereas evidence is emerging that a direct pro-oncogenic effect of HIV, activated inflammatory and coagulation pathways, and cART toxicity may also contribute. By reducing HIV replication, improving immune function, and limiting chronic inflammation, cART initiation at higher CD4 cell counts may, therefore, reduce NADM risk. However, cART only partly normalizes enhanced inflammation and coagulation seen during HIV infection and conflicting laboratory and epidemiological data have been reported as to whether (and how) cART affects NADM risk. Furthermore, secondary analyses of randomized controlled trials comparing early versus delayed cART initiation were inconclusive.

SUMMARY

Continuous epidemiological surveillance is warranted to monitor trends in cancer incidence among HIV-infected individuals and to better understand the impact of earlier cART on NADM risk. The role of adjuvant anti-inflammatory or antithrombotic therapies to reduce cancer risk deserves further investigation.

Differential gene expression in human hepatocyte cell lines exposed to the antiretroviral agent zidovudine

Zidovudine (3'-azido-3'-deoxythymidine; AZT) is the most widely used nucleoside reverse transcriptase inhibitor for the treatment of AIDS patients and prevention of mother-to-child transmission of HIV-1. Previously, we demonstrated that AZT had significantly greater growth inhibitory effects upon the human liver carcinoma cell line HepG2 as compared to the immortalized human liver cell line THLE2. We have now used gene expression profiling to determine the molecular pathways associated with toxicity in both cell lines. HepG2 cells were incubated with 0, 2, 20, or 100 μM AZT for 2 weeks; THLE2 cells were treated with 0, 50, 500, or 2,500 μM AZT, concentrations that were equi-toxic to those used in the HepG2 cells. After the treatment, total RNA was isolated and subjected to microarray analysis. Global analysis of gene expression, with a false discovery rate ≤0.01 and a fold change ≥1.5, indicated that 6- to 70-fold more genes were differentially expressed in a significant concentration-dependent manner in HepG2 cells when compared to THLE2 cells. Comparative analysis indicated that 7 % of these genes were common to both cell lines. Among the common differentially expressed genes, 70 % changed in the same direction, most of which were associated with cell death and survival, cell cycle, cell growth and proliferation, and DNA replication, recombination, and repair. As determined by the uptake of [methyl-(3)H]AZT, the intracellular levels of total AZT were approximately twofold higher in THLE2 cells than in HepG2 cells. The expression of thymidine kinase 1 (TK1) and UDP-glucuronosyltransferase 2B7 (UGT2B7) genes that regulate the metabolic activation and deactivation of AZT, respectively, was increased in HepG2 cells but decreased in THLE2 cells after treatment with AZT. This differential response in AZT metabolism was confirmed by real-time PCR, western blotting, and/or enzymatic assays. These data indicate that molecular pathways involved with cell death and survival, cell cycle, cell growth and proliferation, and DNA replication, recombination, and repair are involved in the toxicities associated with AZT in both human cell lines, and that the difference in expression of TK1 and UGT2B7 in response to AZT treatment in HepG2 cells and THLE2 cells might explain why HepG2 cells are more sensitive than THLE2 cells to the toxicity of AZT.

Aging and HIV/AIDS: pathogenetic role of therapeutic side effects

The intersection of aging and HIV/AIDS is a looming 'epidemic within an epidemic.' This paper reviews how HIV/AIDS and its therapy cause premature aging or contribute mechanistically to HIV-associated non-AIDS illnesses (HANA). Survival with HIV/AIDS has markedly improved by therapy combinations containing nucleoside reverse transcriptase inhibitors (NRTIs), non-nucleoside reverse transcriptase inhibitors, and protease inhibitors (PIs) called HAART (highly active antiretroviral therapy). Because NRTIs and PIs together prevent or attenuate HIV-1 replication, and prolong life, the population of aging patients with HIV/AIDS increases accordingly. However, illnesses frequently associated with aging in the absence of HIV/AIDS appear to occur prematurely in HIV/AIDS patients. Theories that help to explain biological aging include oxidative stress (where mitochondrial oxidative injury exceeds antioxidant defense), chromosome telomere shortening with associated cellular senescence, and accumulation of lamin A precursors (a nuclear envelop protein). Each of these has the potential to be enhanced or caused by HIV/AIDS, antiretroviral therapy, or both. Antiretroviral therapy has been shown to enhance events seen in biological aging. Specifically, antiretroviral NRTIs cause mitochondrial dysfunction, oxidative stress, and mitochondrial DNA defects that resemble features of both HANA and aging. More recent clinical evidence points to telomere shortening caused by NRTI triphosphate-induced inhibition of telomerase, suggesting telomerase reverse transcriptase (TERT) inhibition as being a pathogenetic contributor to premature aging in HIV/AIDS. PIs may also have a role in premature aging in HIV/AIDS as they cause prelamin A accumulation. Overall, toxic side effects of HAART may both resemble and promote events of aging and are worthy of mechanistic studies.

Effect of antiretroviral drugs on the DNA damage in mice

In order to investigate the effects of two non-nucleoside reverse transcriptase inhibitors (NNRTIs) on the DNA damage in vivo, nevirapine (NVP; 3.3 mg/kg), efavirenz (EFV; 10 mg/kg) or saline were administered orally. Acute effects were analyzed 24 h after the administration of a single NNRTI dose, and subchronic effects 24 h after the last dose. Peripheral blood, brain, heart and liver samples were subjected to genotoxicity analyses and polychromatic erythrocytes from the bone marrow to micronucleus test. The micronucleus test did not reveal any significant differences between animals from the acute or subchronic groups. Comet assay showed that acute and subchronic NNRTI treatment did not cause any significant DNA damage in heart, liver or peripheral blood cells. However, increased damage indexes and frequencies were observed in the brain of mice, subchronically treated with EFV. This result suggests for the first time that this drug might induce genotoxicity in the brain.

Telomerase inhibition may contribute to accelerated mitochondrial aging induced by anti-retroviral HIV treatment

HIV-infected individuals undergoing long-term anti-retroviral treatment tend to show premature senescence. Accelerated mitochondrial aging induced by nucleoside reverse transcriptase inhibitors (NRTIs) has been implicated as a part of this phenomenon. Traditionally, this has been attributed to inhibition of mtDNA polymerase γ by these drugs, but alternative explanations have been proposed. It is known that NRTIs can not only inhibit viral reverse transcriptase, but also human telomerase. A number of extratelomeric roles of telomerase, including protection of mitochondrial DNA and function, have emerged recently. In this paper, I propose that inhibition of mitochondrial telomerase activity by NRTI drugs contributes to the mitochondrial toxicity and premature aging seen in treated HIV patients, and discuss objections and experimental testing of the hypothesis.

Effects of nanotoxicity on female reproductivity and fetal development in animal models

The extensive application of nanomaterials in industry, medicine and consumer products has raised concerns about their potential toxicity. The female population is particularly vulnerable and deserves special attention because toxicity in this group may impact both female reproductivity and fetal development. Mouse and zebrafish models each have their own unique features and studies using these models to examine the potential toxicity of various nanoparticles are compared and summarized in this review. Several nanoparticles exhibit detrimental effects on female reproductivity as well as fetal development, and these adverse effects are related to nanoparticle composition, surface modification, dose, exposure route and animal species. Limited studies on the mechanisms of nanotoxicity are also documented and reviewed herein.

Perinatal exposure of patas monkeys to antiretroviral nucleoside reverse-transcriptase inhibitors induces genotoxicity persistent for up to 3 years of age

BACKGROUND

Erythrocebus patas (patas) monkeys were used to model antiretroviral (ARV) drug in human immunodeficiency virus type 1-infected pregnant women.

METHODS

Pregnant patas dams were given human-equivalent doses of ARVs daily during 50% of gestation. Mesenchymal cells, cultured from bone marrow of patas offspring obtained at birth and at 1 and 3 years of age, were examined for genotoxicity, including centrosomal amplification, micronuclei, and micronuclei containing whole chromosomes.

RESULTS

Compared with controls, statistically significant increases (P < .05) in centrosomal amplification, micronuclei, and micronuclei containing whole chromosomes were found in mesenchymal cells from most groups of offspring at the 3 time points.

CONCLUSIONS

Transplacental nucleoside reverse-transcriptase inhibitor exposures induced fetal genotoxicity that was persistent for 3 years.

In vitro and ex vivo inhibition of human telomerase by anti-HIV nucleoside reverse transcriptase inhibitors (NRTIs) but not by non-NRTIs

Telomerase is a specialized reverse transcriptase responsible for the de novo synthesis of telomeric DNA repeats. In addition to its established reverse transcriptase and terminal transferase activities, recent reports have revealed unexpected cellular activities of telomerase, including RNA-dependent RNA polymerization. This telomerase characteristic, distinct from other reverse transcriptases, indicates that clinically relevant reverse transcriptase inhibitors might have unexpected telomerase inhibition profiles. This is particularly important for the newer generation of RT inhibitors designed for anti-HIV therapy, which have reported higher safety margins than older agents. Using an in vitro primer extension assay, we tested the effects of clinically relevant HIV reverse transcriptase inhibitors on cellular telomerase activity. We observed that all commonly used nucleoside reverse transcriptase inhibitors (NRTIs), including zidovudine, stavudine, tenofovir, didanosine and abacavir, inhibit telomerase effectively in vitro. Truncated telomere synthesis was consistent with the expected mode of inhibition by all tested NRTIs. Through dose-response experiments, we established relative inhibitory potencies of NRTIs on in vitro telomerase activity as compared to the inhibitory potencies of the corresponding dideoxynucleotide triphosphates. In contrast to NRTIs, the non-nucleoside reverse transcriptase inhibitors (NNRTIs) nevirapine and efavirenz did not inhibit the primer extension activity of telomerase, even at millimolar concentrations. Long-term, continuous treatment of human HT29 cells with select NRTIs resulted in an accelerated loss of telomere repeats. All tested NRTIs exhibited the same rank order of inhibitory potencies on telomerase and HIV RT, which, according to published data, were orders-of-magnitude more sensitive than other DNA polymerases, including the susceptible mitochondria-specific DNA polymerase gamma. We concluded that telomerase activity could be inhibited by common NRTIs, including currently recommended RTI agents tenofovir and abacavir, which warrants large-scale clinical and epidemiological investigation of the off-target effects of long-term highly active antiretroviral therapy (HAART) with these agents.

Leukocyte telomere length in HIV-infected pregnant women treated with antiretroviral drugs during pregnancy and their uninfected infants

OBJECTIVES

HIV disease can lead to accelerated telomere attrition, although certain drugs used as part of antiretroviral therapy (ART) can inhibit telomerase reverse transcriptase activity. This could in turn lead to shorter telomeres. We hypothesized that HIV and ART exposure would be associated with shorter leukocyte telomere length (TL) in exposed mother/infant pairs compared with controls.

METHODS

In these retrospective and prospective observational cohort studies, TL was evaluated in peripheral blood leukocytes obtained from HIV-infected pregnant women treated with ART and their uninfected infants, and compared with HIV untreated (retrospective cohort) or HIV mothers and their infants (prospective cohort).

RESULTS

In HIV-infected ART-exposed mothers, leukocyte TL was not significantly shorter than that in HIV untreated mothers or HIV controls, nor was their infants' TL significantly different. Cord blood of ART-exposed infants exhibited TL shorter than that from infants born to HIV-negative mothers. Placenta also showed evidence of shorter TL after adjustment for relevant covariates. Factors associated with shorter maternal and infant TL included smoking and the use of drugs of addiction in pregnancy.

CONCLUSIONS

These results suggest that maternal HIV infection or exposure to ART has minimal effect on infant leukocyte TL, a reassuring finding. In contrast, tissues that express higher telomerase activity such as umbilical cord blood and placenta appear comparatively more affected by ART. Smoking and the use of drugs of addiction have a negative impact on maternal and infant leukocyte TL, possibly through oxidative telomere damage.

AZT as a telomerase inhibitor

Telomerase is a highly specialized reverse transcriptase (RT) and the maintenance of telomeric length is determined by this specific enzyme. The human holoenzyme telomerase is a ribonucleoprotein composed by a catalytic subunit, hTERT, an RNA component, hTR, and a group of associated proteins. Telomerase is normally expressed in embryonic cells and is repressed during adulthood. The enzyme is reexpressed in around 85% of solid tumors. This observation makes it a potential target for developing drugs that could be developed for therapeutic purposes. The identification of the hTERT as a functional catalytic RT prompted studies of inhibiting telomerase with the HIV RT inhibitor azidothymidine (AZT). Previously, we have demonstrated that AZT binds preferentially to telomeres, inhibits telomerase and enhances tumor cell senescence, and apoptosis after AZT treatment in breast mammary adenocarcinoma cells. Since then, several studies have considered AZT for telomerase inhibition and have led to potential clinical strategies for anticancer therapy. This review covers present thinking of the inhibition of telomerase by AZT and future treatment protocols using the drug.

An unusual phenotypic and genotypic expression in F2 generation following one stage zidovudine exposure during pregnancy and lactation- an experiment in mice

Zidovudine (3'-Azido-2', 3'-dideoxythymidine, AZT, ZDV) is routinely used as one of the component of antiretroviral therapy to prevent transmission of the HIV infection from mother to child. The drug, when given during pregnancy can give rise to myriad toxicities as reported in previous studies on human, animal and in-vitro experiments. The present study was an attempt to explore the Zidovudine teratogenesis in F1 and F2 generation of mice following initial maternal exposure to Zidovudine during pregnancy, through delivery and lactation. The F1 generation actually would have got the exposure during embryonic development and infant stages. Pregnant Swiss mice were treated orally with ZDV 50 mg/kg/day or distilled water (control), from day eighth of gestation, through delivery and continued for first ten days of lactation. The F1 generation litters were raised and mated to produce F2 generation mice. An interesting phenotype of "healthy" and "sick" was noted in F2 generation but not in the F1 generation. In F2 generation 35% died on different postnatal day during 120 days of follow up period. Chromosomal study from bone marrow of F1 and F2 showed various chromosomal aberrations. Lipodystrophy and hepatotoxicity was observed in "sick" mice. The study generated a hypothesis of recessive mutation and concludes that Zidovudine is a transplacental genotoxic agent. The result of present study therefore suggests the need to study the effect of zidovudine in human subjects for a longer period of time to rule out similar genotoxic effect.

Effects of in utero antiretroviral exposure on mitochondrial DNA levels, mitochondrial function and oxidative stress

OBJECTIVES

HIV and antiretroviral (ART) exposure in utero may have deleterious effects on the infant, but uncertainty still exists. The objective of this study was to evaluate aspects of mitochondrial DNA (mtDNA) content, mitochondrial function and oxidative stress simultaneously in placenta, umbilical cord blood and infant blood in HIV/ART-exposed infants compared with uninfected controls.

METHODS

HIV-1-infected pregnant women and HIV-1-uninfected healthy pregnant controls were enrolled in the study prospectively. Placenta and umbilical cord blood were obtained at delivery and infant blood was obtained within 48 h of delivery. mtDNA content was determined for each specimen. Nuclear [subunit IV of cytochrome c-oxidase (COX IV)]- and mitochondrial (COX II)-encoded polypeptides of the oxidative phosphorylation enzyme cytochrome c-oxidase were quantified in cord and infant blood. Placental mitochondria malondialdehyde (MDA) concentrations were measured as a marker of oxidative stress.

RESULTS

Twenty HIV-positive/HIV-exposed and 26 control mother-infant pairs were enrolled in the study. All HIV-infected women and their infants received ART. Placental MDA concentration and mtDNA content in placenta and cord blood were similar between groups. The cord blood COX II:IV ratio was lower in the HIV-positive group than in the controls, whereas the infant peripheral blood mtDNA content was higher in the HIV-exposed infants, but the infant peripheral blood COX II:IV ratio was similar. No infant had clinical evidence of mitochondrial disease or acquired HIV infection. In multivariable regression analyses, the significant findings in cord and infant blood were both most associated with HIV/ART exposure.

CONCLUSIONS

HIV-exposed infants showed reduced umbilical cord blood mitochondrial enzyme expression with increased infant peripheral blood mitochondrial DNA levels, the latter possibly reflecting a compensatory mechanism to overcome HIV/ART-associated mitochondrial toxicity.

The genetic toxicity effects of lamivudine and stavudine antiretroviral agents

IMPORTANCE OF THE FIELD

The nucleoside reverse transcriptase inhibitors (NRTIs) are used in antiretroviral therapy worldwide for the treatment of HIV infections. These drugs act by blocking reverse transcriptase enzyme activity, causing pro-viral DNA chain termination. As a consequence, NRTIs could cause genomic instability and loss of heterozygosity.

AREAS COVERED IN THIS REVIEW

This review highlights the toxic and genotoxic effects of NRTIs, particularly lamivudine (3TC) and stavudine (d4T) analogues. In addition, a battery of short-term in vitro and in vivo systems are described to explain the potential genotoxic effects of these NRTIs as a single drug or a complexity of highly active antiretroviral therapy.

WHAT THE READER WILL GAIN

The readers will gain an understanding of a secondary effect that could be induced by 3TC and d4T treatments.

TAKE HOME MESSAGE

Considering that AIDS has become a chronic disease, more comprehensive toxic genetic studies are needed, with particular attention to the genetic alterations induced by NRTIs. These alterations play a primary role in carcinogenesis and are also involved in secondary and subsequent steps of carcinogenesis.

XPC is essential for nucleotide excision repair of zidovudine-induced DNA damage in human hepatoma cells

Zidovudine (3'-azido-3'-dexoythymidine, AZT), a nucleoside reverse transcriptase inhibitor, can be incorporated into DNA and cause DNA damage. The mechanisms underlying the repair of AZT-induced DNA damage are unknown. To investigate the pathways involved in the recognition and repair of AZT-induced DNA damage, human hepatoma HepG2 cells were incubated with AZT for 2 weeks and the expression of DNA damage signaling pathways was determined using a pathway-based real-time PCR array. Compared to control cultures, damaged DNA binding and nucleotide excision repair (NER) pathways showed significantly increased gene expression. Further analysis indicated that AZT treatment increased the expression of genes associated with NER, including XPC, XPA, RPA1, GTF2H1, and ERCC1. Western blot analysis demonstrated that the protein levels of XPC and GTF2H1 were also significantly up-regulated. To explore further the function of XPC in the repair of AZT-induced DNA damage, XPC expression was stably knocked down by 71% using short hairpin RNA interference. In the XPC knocked-down cells, 100 μM AZT treatment significantly increased [³H]AZT incorporation into DNA, decreased the total number of viable cells, increased the release of lactate dehydrogenase, induced apoptosis, and caused a more extensive G2/M cell cycle arrest when compared to non-transfected HepG2 cells or HepG2 cells transfected with a scrambled short hairpin RNA sequence. Overall, these data indicate that XPC plays an essential role in the NER repair of AZT-induced DNA damage.

Micronuclei induced by reverse transcriptase inhibitors in mononucleated and binucleated cells as assessed by the cytokinesis-block micronucleus assay

This study evaluated the clastogenic and/or aneugenic potential of three nucleoside reverse transcriptase inhibitors (zidovudine - AZT, lamivudine - 3TC and stavudine - d4T) using the cytokinesis-block micronucleus (CBMN) assay in human lymphocyte cultures. All three inhibitors produced a positive response when tested in binucleated cells. The genotoxicity of AZT and 3TC was restricted to binucleated cells since there was no significant increase in the frequency of micronuclei in mononucleated cells. This finding indicated that AZT and 3TC caused chromosomal breakage and that their genotoxicity was related to a clastogenic action. In addition to the positive response observed with d4T in binucleated cells, this drug also increased the frequency of micronuclei in mononucleated cells, indicating clastogenic and aneugenic actions. Since the structural differences between AZT and 3TC and AZT and d4T involve the 3' position in the 2'-deoxyribonucleoside and in an unsaturated 2',3',dideoxyribose, respectively, we suggest that an unsaturated 2', 3', dideoxyribose is responsible for the clastogenic and aneugenic actions of d4T.

In utero exposure of female CD-1 mice to AZT and/or 3TC: II. Persistence of functional alterations in cardiac tissue

To delineate temporal changes in the integrity and function of mitochondria/cardiomyocytes in hearts from mice exposed in utero to commonly used nucleoside analogs (NRTIs), CD-1 mice were exposed in utero to 80 mg AZT/kg, 40 mg 3TC/kg, 80 mg AZT/kg plus 40 mg 3TC/kg, or vehicle alone during days 12-18 of gestation and hearts from female mouse offspring were examined at 13 and 26 weeks postpartum. Alterations in cardiac mitochondrial DNA (mtDNA) content, oxidative phosphorylation (OXPHOS) enzyme activities, mtDNA mutations, and echocardiography of NRTI-exposed mice were assessed and compared with findings in vehicle-exposed control mice. A hybrid capture-chemiluminescence assay showed significant twofold increases in mtDNA levels in hearts from AZT- and AZT/3TC-exposed mice at 13 and 26 weeks postpartum, consistent with near doubling in mitochondrial numbers over time compared with vehicle-exposed mice. Echocardiographic measurements at 13 and 26 weeks postpartum indicated progressive thinning of the left ventricular posterior wall in NRTI-exposed mice, relative to controls, with differences becoming statistically significant by 26 weeks. Overall, progressive functional changes occurred in mouse mitochondria and cardiac tissue several months after in utero NRTI exposures; AZT and 3TC acted in concert to cause additive cardiotoxic effects of AZT/3TC compared with either drug alone.

In utero exposure of female CD-1 Mice to AZT and/or 3TC: I. Persistence of microscopic lesions in cardiac tissue

The current study was designed to delineate temporal changes in cardiomyocytes and mitochondria at the light and electron microscopic levels in hearts of mice exposed transplacentally to commonly used nucleoside analogs (NRTIs). Pregnant CD-1 mice were given 80 mg AZT/kg, 40 mg 3TC/kg, 80 mg AZT/kg plus 40 mg 3TC/kg, or vehicle alone during the last 7 days of gestation, and hearts from female mouse pups were examined at 13 and 26 weeks postpartum for histopathological or ultrastructural changes in cross-sections of both the ventricles and the interventricular septum. Using light microscopy and special staining techniques, transplacental exposure to AZT, 3TC, or AZT/3TC was shown to induce significant histopathological changes in myofibrils; these changes were more widespread at 13 weeks than at 26 weeks postpartum. While most light microscopic lesions resolved, some became more severe between 13 and 26 weeks postpartum. Transplacental NRTI exposure also resulted in progressive drug-specific changes in the number and ultrastructural integrity of cardiac mitochondria. These light and electron microscopic findings show that a subset of changes in cardiac mitochondria and myofibrils persisted and progressed months after transplacental exposure of an animal model to NRTIs, with combined AZT/3TC exposure yielding additive effects compared with either drug alone.

A review of nucleoside reverse transcriptase inhibitor use to prevent perinatal transmission of HIV

Worldwide, women comprise > 50% of all people living with HIV and the vast majority of these women are of childbearing age. In fact, a significant proportion of these women are identified as HIV-infected during pregnancy. Preventing perinatal transmission has been one of the greatest prevention successes of the HIV epidemic with < 2% of live births resulting in an HIV-infected infant. The strategic use of combination antiretroviral therapy has been a critical component of this reduction. With more antiretroviral agents available for HIV, the appropriate selection of therapy is often based on provider familiarity with the various agents. Although benefits of antiretroviral use in pregnancy tremendously outweigh the risks, concerns regarding short- and long-term toxicity in mothers and their children, in addition to the risk of the development of HIV resistance, remain subjects of discussion. The choice of antiretroviral 'backbone' is supported by extensive data showing efficacy in the prevention of HIV vertical transmission. Co-formulated zidovudine/lamivudine is the most commonly used combination in pregnancy. Long-term consequences of in utero exposure to antiretroviral agents are not fully understood. In this article, we review the data regarding nucleoside reverse transcriptase inhibitors with a focus on tenofovir.

Neurodevelopment and in utero antiretroviral exposure of HIV-exposed uninfected infants

OBJECTIVE

Antiretroviral (ARV) drugs are routinely provided to HIV-infected pregnant women to prevent HIV mother-to-child transmission. Although ARV use has significantly reduced mother-to-child transmission to <2% in the United States, it remains crucial to monitor uninfected infants and children for adverse consequences of in utero ARV exposure.

METHODS

We studied neurodevelopmental function in HIV-exposed uninfected children who were enrolled in Pediatric AIDS Clinical Trials Group 219/219C, a multisite, prospective, cohort study. Mental and motor functioning were assessed with the Bayley Scales of Infant Development (BSID), first and second editions. ARV exposure information was collected during pregnancy or within the first years of life. Linear regression methods were used to evaluate the association of in utero ARV exposure on Mental Developmental Index and Psychomotor Developmental Index at 2 years of age, controlling for demographic factors (age, gender, and race/ethnicity) and potential confounders: test version, primary language, primary caregiver, caregiver education level, low birth weight, geographic and urban/rural location, birth year, and maternal illicit drug use.

RESULTS

Among 1840 infants who were born between 1993 and 2006, 1694 (92%) were exposed to ARV in utero and 146 (8%) were not exposed. After controlling for confounders, children who were exposed in utero to any ARV did not have lower Mental Developmental Index and Psychomotor Developmental Index scores than unexposed children. Among low birth weight infants, significantly higher BSID scores were observed for prenatally ARV-exposed than unexposed children. Maternal illicit drug use was reported for 17% of mothers but was not associated with BSID scores.

CONCLUSIONS

Mental and motor functioning scores were not lower for infants with in utero ARV exposure compared with no exposure. Although these results are reassuring, continued evaluation of uninfected children with in utero ARV exposure for long-term adverse outcomes is important.

A review of the molecular mechanisms of chemically induced neoplasia in rat and mouse models in National Toxicology Program bioassays and their relevance to human cancer

Tumor response in the B6C3F1 mouse, F344 rat, and other animal models following exposure to various compounds provides evidence that people exposed to these or similar compounds may be at risk for developing cancer. Although tumors in rodents and humans are often morphologically similar, underlying mechanisms of tumorigenesis are often unknown and may be different between the species. Therefore, the relevance of an animal tumor response to human health would be better determined if the molecular pathogenesis were understood. The underlying molecular mechanisms leading to carcinogenesis are complex and involve multiple genetic and epigenetic events and other factors. To address the molecular pathogenesis of environmental carcinogens, the authors examine rodent tumors (e.g., lung, colon, mammary gland, skin, brain, mesothelioma) for alterations in cancer genes and epigenetic events that are associated with human cancer. National Toxicology Program (NTP) studies have identified several genetic alterations in chemically induced rodent neoplasms that are important in human cancer. Identification of such alterations in rodent models of chemical carcinogenesis caused by exposure to environmental contaminants, occupational chemicals, and other compounds lends further support that they are of potential human health risk. These studies also emphasize the importance of molecular evaluation of chemically induced rodent tumors for providing greater public health significance for NTP evaluated compounds.

WR1065 mitigates AZT-ddI-induced mutagenesis and inhibits viral replication

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.

Long-term exposure to zidovudine delays cell cycle progression, induces apoptosis, and decreases telomerase activity in human hepatocytes

Zidovudine (3'-azido-3'-deoxythymidine; AZT), which is currently used in the treatment of acquired immunodeficiency syndrome, has been shown to have anticancer properties. In the present study, we examined the mechanisms contributing to increased sensitivity of cancer cells to the growth-inhibitory effects of AZT. This was accomplished by incubating a hepatoma cell line (HepG2) and a normal liver cell line (THLE2) with AZT in continuous culture for up to 4 weeks and evaluating the number of viable and necrotic cells, the induction of apoptosis, cell cycle alterations, and telomerase activity. In HepG2 cells, AZT (2-100 microM) caused significant dose-dependent decreases in the number of viable cells at exposures > 24 h. During a 1-week recover period, there was only a slight increase in the number of viable cells treated with AZT. The decrease in viable cells was associated with an induction of apoptosis, a decrease in telomerase activity, and S and G2/M phase arrest of the cell cycle. During the recovery period, the extent of apoptosis and telomerase activity returned to control levels, whereas the disruption of cell cycle progression persisted. Western blot analysis indicated that AZT caused a decrease in checkpoint kinase 1 (Chk1) and kinase 2 (Chk2) and an increase in phosphorylated Chk1 (Ser345) and Chk2 (Thr68). Similar effects, to lesser extent, were observed in THLE2 cells given much higher concentrations of AZT (50-2500 microM). These data show that HepG2 cells are much more sensitive than THLE2 cells to AZT. They also indicate that a combination of a delay of cell cycle progression, an induction of apoptosis, and a decrease in telomerase activity is contributing to the decrease in the number of viable cells from AZT treatment, and that checkpoint enzymes Chk1 and Chk2 may play an important role in the delay of cell cycle progression.

Centrosomal amplification and aneuploidy induced by the antiretroviral drug AZT in hamster and human cells

The centrosome directs chromosomal migration by a complex process of tubulin-chromatin binding. In this contribution centrosomal abnormalities, including centrosomal amplification, were explored in Chinese hamster ovary (CHO) and normal human mammary epithelial cells (NHMECs) exposed to the antiretroviral drug zidovudine (3'-azido-3'-deoxythymidine, AZT). Centrosomal amplification/fragmentation was observed in both cell types and kinetochore positive micronuclei were found in AZT-exposed CHO cells in correlation with dose. Normal human mammary epithelial cell (NMHEC) strain M99005, previously identified as a strain that incorporates high levels of AZT into DNA (high incorporator, HI), showed greater centrosomal amplification when compared with a second strain, NHMEC M98040, which did not incorporate AZT into DNA (low incorporator, LI). Additionally, an abnormal tubulin distribution was observed in AZT-exposed HI cells bearing multiple centrosomes. Immunofluorescent staining of human cells with Aurora A, a kinase involved in the maturation of the centrosome, confirmed the induction of centrosomal amplification and revealed multipolar mitotic figures. Flow cytometric studies revealed that cells bearing abnormal numbers of centrosomes and abnormal tubulin distribution had similar S-phase percentages suggesting that cells bearing unbalanced chromosomal segregation could divide. Therefore, AZT induces genomic instability and clastogenicity as well as alterations in proteins involved in centrosomal activation, all of which may contribute to the carcinogenic properties of this compound.