WR1065 conjugated to thiol-PEG polymers as novel anticancer prodrugs: broad spectrum efficacy, synergism, and drug resistance reversal

The lack of anticancer agents that overcome innate/acquired drug resistance is the single biggest barrier to achieving a durable complete response to cancer therapy. To address this issue, a new drug family was developed for intracellular delivery of the bioactive aminothiol WR1065 by conjugating it to discrete thiol-PEG polymers: 4-star-PEG-S-S-WR1065 (4SP65) delivers four WR1065s/molecule and m-PEG6-S-S-WR1065 (1LP65) delivers one. Infrequently, WR1065 has exhibited anticancer effects when delivered via the FDA-approved cytoprotectant amifostine, which provides one WR1065/molecule extracellularly. The relative anticancer effectiveness of 4SP65, 1LP65, and amifostine was evaluated in a panel of 15 human cancer cell lines derived from seven tissues. Additional experiments assessed the capacity of 4SP65 co-treatments to potentiate the anticancer effectiveness and overcome drug resistance to cisplatin, a chemotherapeutic, or gefitinib, a tyrosine kinase inhibitor (TKI) targeting oncogenic EGFR mutations. The CyQUANT®-NF proliferation assay was used to assess cell viability after 48-h drug treatments, with the National Cancer Institute COMPARE methodology employed to characterize dose-response metrics. In normal human epithelial cells, 4SP65 or 1LP65 enhanced or inhibited cell growth but was not cytotoxic. In cancer cell lines, 4SP65 and 1LP65 induced dose-dependent cytostasis and cytolysis achieving 99% cell death at drug concentrations of 11.2 ± 1.2 µM and 126 ± 15.8 µM, respectively. Amifostine had limited cytostatic effects in 11/14 cancer cell lines and no cytolytic effects. Binary pairs of 4SP65 plus cisplatin or gefitinib increased the efficacy of each partner drug and surmounted resistance to cytolysis by cisplatin and gefitinib in relevant cancer cell lines. 4SP65 and 1LP65 were significantly more effective against TP53-mutant than TP53-wild-type cell lines, consistent with WR1065-mediated reactivation of mutant p53. Thus, 4SP65 and 1LP65 represent a unique prodrug family for innovative applications as broad-spectrum anticancer agents that target p53 and synergize with a chemotherapeutic and an EGFR-TKI to prevent or overcome drug resistance.

DNA damage in cetaceans: A mini review

DNA damage has long been known to play an essential role in tumorigenesis induced by chemical carcinogen exposure. The preponderance of data generated during the past approximately 50 years of cancer research indicates that DNA damage and DNA adduct formation are necessary but not sufficient for tumor induction by chemical carcinogenesis. This is true for all of the species studied, including experimental animals, some animals in the wild, and humans. Cetaceans, which include whales, dolphins and porpoises, are a challenge to evaluate because tissues are difficult to obtain, and cancer rates, with a single exception, are low (0.7-2.0 %). However, both non-specific (chromosomal aberrations, DNA strand breaks, 8-hydroxy-2^'-deoxyguanosine, mitochondrial DNA damage), and chemical-specific (aromatic DNA adducts, and carcinogenic polycyclic aromatic hydrocarbon [PAH]-DNA adducts) DNA damage have been found in cetaceans. For some types of DNA damage, cetaceans may carry a burden similar to that seen in many other species, including humans, but linking DNA damage to cancer rates in cetaceans has been largely impossible. The one exception is a population of beluga whales in the St. Lawrence Estuary (SLE) in Quebec, Canada, where correlations have been found between long-term PAH exposure, PAH-DNA adducts in small intestinal crypt cells, and a high rate (7%) of gastrointestinal cancers. Taken together, the current literature demonstrates that cetaceans may carry a burden of many types of DNA damage and, given the example of the SLE beluga, cetaceans may sustain a potential susceptibility to pollution-induced tumorigenesis. Knowledge of DNA damage and cancer rates in whales is critically important for understanding and predicting the health of marine life, human life, and the aquatic environment of our planet.

Polycyclic Aromatic Hydrocarbon-DNA Adducts in Gulf of Mexico Sperm Whale Skin Biopsies Collected in 2012

The northern Gulf of Mexico has a long history of polycyclic aromatic hydrocarbon (PAH) contamination from anthropogenic activities, natural oil seepages, and the 2010 Deepwater Horizon explosion and oil spill. The continental shelf of the same area is a known breeding ground for sperm whales (Physeter macrocephalus). To evaluate PAH-DNA damage, a biomarker for potential cancer risk, we compared skin biopsies collected from Gulf of Mexico sperm whales in 2012 with skin biopsies collected from sperm whales in areas of the Pacific Ocean in 1999-2001. All samples were obtained by crossbow and comprised both epidermis and subcutaneous blubber. To evaluate exposure, 7 carcinogenic PAHs were analyzed in lipids extracted from Pacific Ocean sperm whale blubber, pooled by sex, and location. To evaluate PAH-DNA damage, portions of all tissue samples were formalin-fixed, paraffin-embedded, sectioned, and examined for PAH-DNA adducts by immunohistochemistry (IHC) using an antiserum elicited against benzo[a]pyrene-modified DNA, which crossreacts with several high molecular weight carcinogenic PAHs bound to DNA. The IHC showed widespread epidermal nuclear localization of PAH-DNA adducts in the Gulf of Mexico whales (n = 15) but not in the Pacific Ocean whales (n = 4). A standard semiquantitative scoring system revealed significantly higher PAH-DNA adducts in the Gulf of Mexico whales compared to the whales from the Pacific Ocean study (p = .0002).

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.

In vivo localization and postmortem stability of benzo[a]pyrene-DNA adducts

DNA adducts of carcinogenic polycyclic aromatic hydrocarbons (PAHs) play a critical role in the etiology of gastrointestinal tract cancers in humans and other species orally exposed to PAHs. Yet, the precise localization of PAH-DNA adducts in the gastrointestinal tract, and the long-term postmortem PAH-DNA adduct stability are unknown. To address these issues, the following experiment was performed. Mice were injected intraperitoneally with the PAH carcinogen benzo[a]pyrene (BP) and euthanized at 24 h. Tissues were harvested either at euthanasia (0 time), or after 4, 8, 12, 24, 48, and 168 hr (7 days) of storage at 4°C. Portions of mouse tissues were formalin-fixed, paraffin-embedded, and immunohistochemically (IHC) evaluated by incubation with r7,t8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA antiserum and H-scoring. The remaining tissues were frozen, and DNA was extracted and assayed for the r7,t8,t9-trihydroxy-c-10-(N ² -deoxyguanosyl)-7,8,9,10-tetrahydrobenzo[a]pyrene (BPdG) adduct using two quantitative assays, the BPDE-DNA chemiluminescence immunoassay (CIA), and high-performance liquid chromatography electrospray ionization tandem mass spectrometry (HPLC-ES-MS/MS). By IHC, which required intact nuclei, BPdG adducts were visualized in forestomach basal cells, which included gastric stem cells, for up to 7 days. In proximal small intestine villus epithelium BPdG adducts were visualized for up to 12 hr. By BPDE-DNA CIA and HPLC-ES-MS/MS, both of which used DNA for analysis and correlated well (P= 0.0001), BPdG adducts were unchanged in small intestine, forestomach, and lung stored at 4°C for up to 7 days postmortem. In addition to localization of BPdG adducts, this study reveals the feasibility of examining PAH-DNA adduct formation in wildlife species living in colder climates. Environ. Mol. Mutagen. 61:216-223, 2020. © 2019 Wiley Periodicals, Inc.

Intestinal polycyclic aromatic hydrocarbon-DNA adducts in a population of beluga whales with high levels of gastrointestinal cancers

Carcinogenic polycyclic aromatic hydrocarbons (PAHs) were disposed directly into the Saguenay River of the St. Lawrence Estuary (SLE) by local aluminum smelters (Quebec, Canada) for 50 years (1926-1976). PAHs in the river sediments are likely etiologically related to gastrointestinal epithelial cancers observed in 7% of 156 mature (>19-year old) adult beluga found dead along the shorelines. Because DNA adduct formation provides a critical link between exposure and cancer induction, and because PAH-DNA adducts are chemically stable, we hypothesized that SLE beluga intestine would contain PAH-DNA adducts. Using an antiserum specific for DNA modified with several carcinogenic PAHs, we stained sections of paraffin-embedded intestine from 51 SLE beluga (0-63 years), 4 Cook Inlet (CI) Alaska beluga (0-26 years), and 20 beluga (0-46 years) living in Arctic areas (Eastern Beaufort Sea, Eastern Chukchi Sea, Point Lay Alaska) and aquaria, all with low PAH contamination. Stained sections showed nuclear light-to-dark pink color indicating the presence of PAH-DNA adducts concentrated in intestinal crypt epithelial lining cells. Scoring of whole tissue sections revealed higher values for the 51 SLE beluga, compared with the 20 Arctic and aquarium beluga (P = 0.003). The H-scoring system, applied to coded individual photomicrographs, confirmed that SLE beluga and CI beluga had levels of intestinal PAH-DNA adducts significantly higher than Arctic and aquarium beluga (P = 0.003 and 0.02, respectively). Furthermore, high levels of intestinal PAH-DNA adducts in four SLE beluga with gastrointestinal cancers, considered as a group, support a link of causality between PAH exposure and intestinal cancer in SLE beluga. Environ. Mol. Mutagen. 60:29-41, 2019. Published 2018. This article is a U.S. Government work and is in the public domain in the USA.

Carcinogens and DNA damage

Humans are variously and continuously exposed to a wide range of different DNA-damaging agents, some of which are classed as carcinogens. DNA damage can arise from exposure to exogenous agents, but damage from endogenous processes is probably far more prevalent. That said, epidemiological studies of migrant populations from regions of low cancer risk to high cancer risk countries point to a role for environmental and/or lifestyle factors playing a pivotal part in cancer aetiology. One might reasonably surmise from this that carcinogens found in our environment or diet are culpable. Exposure to carcinogens is associated with various forms of DNA damage such as single-stand breaks, double-strand breaks, covalently bound chemical DNA adducts, oxidative-induced lesions and DNA-DNA or DNA-protein cross-links. This review predominantly concentrates on DNA damage induced by the following carcinogens: polycyclic aromatic hydrocarbons, heterocyclic aromatic amines, mycotoxins, ultraviolet light, ionising radiation, aristolochic acid, nitrosamines and particulate matter. Additionally, we allude to some of the cancer types where there is molecular epidemiological evidence that these agents are aetiological risk factors. The complex role that carcinogens play in the pathophysiology of cancer development remains obscure, but DNA damage remains pivotal to this process.

Linking DNA adduct formation and human cancer risk in chemical carcinogenesis

Over two centuries ago, Sir Percival Pott, a London surgeon, published a pioneering treatise showing that soot exposure was the cause of high incidences of scrotal cancers occurring in young men who worked as chimney sweeps. Practicing at a time when cellular pathology was not yet recognized, Sir Percival nonetheless observed that the high incidence and short latency of the chimney sweep cancers, was fundamentally different from the rare scrotal cancers typically found in elderly men. Furthermore, his diagnosis that the etiology of these cancers was related to chimney soot exposure, was absolutely accurate, conceptually novel, and initiated the field of "occupational cancer epidemiology." After many intervening years of research focused on mechanisms of chemical carcinogenesis, briefly described here, it is clear that DNA damage, or DNA adduct formation, is "necessary but not sufficient" for tumor induction, and that many additional factors contribute to carcinogenesis. This review includes a synopsis of carcinogen-induced DNA adduct formation in experimental models and in the human population, with particular attention paid to molecular dosimetry and molecular cancer epidemiology. Environ. Mol. Mutagen. 57:499-507, 2016. © 2016 Wiley Periodicals, Inc.

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.

Use of Ciliogenesis to Detect Aneugens: The Role of Primary Cilia

Primary cilia arise from the centrosomes of quiescent or post-mitotic cells, and serve as sensory organelles that communicate mechanical and chemical stimuli from the environment to the interior of the cell. Cilium formation may, therefore, become a useful end point signaling exposure to genotoxins or aneugens. Here we have used the aneugen, zidovudine (AZT), an antiretroviral drug that induces DNA replication arrest and centrosomal amplification (>2 centrosomes per quiescent cell), to evaluate cilia formation in retinal epithelial (pigmented) cells. Since cilia are derived from centrosomes, and aneugens can induce centrosomal amplification, the production of multiple cilia arising from multiple centrosomes may reveal the aneugenic nature of the agents. Cells were exposed to AZT to induce centrosomal amplification, cultured without serum to allow the centrioles to develop cilia, and immunostained to visualize cilia and centrosomes. Nuclear DNA was stained with DAPI. Preliminary observations suggest that cells with multiple centrosomes are able to generate extra cilia.

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.

Correlation between CYP1A1 transcript, protein level, enzyme activity and DNA adduct formation in normal human mammary epithelial cell strains exposed to benzo[a]pyrene

The polycyclic aromatic hydrocarbon (PAH) benzo(a)pyrene (BP) is thought to bind covalently to DNA, through metabolism by cytochrome P450 1A1 (CYP1A1) and CYP1B1, and other enzymes, to form r7, t8, t9-trihydroxy-c-10-(N(2)-deoxyguanosyl)-7,8,9,10-tetrahydro-benzo[a]-pyrene (BPdG). Evaluation of RNA expression data, to understand the contribution of different metabolic enzymes to BPdG formation, is typically presented as fold-change observed upon BP exposure, leaving the actual number of RNA transcripts unknown. Here, we have quantified RNA copies/ng cDNA (RNA cpn) for CYP1A1 and CYP1B1, as well as

NAD(P)H

quinone oxidoreductase 1 (NQO1), which may reduce formation of BPdG adducts, using primary normal human mammary epithelial cell (NHMEC) strains, and the MCF-7 breast cancer cell line. In unexposed NHMECs, basal RNA cpn values were 58-836 for CYP1A1, 336-5587 for CYP1B1 and 5943-40112 for NQO1. In cells exposed to 4.0 µM BP for 12h, RNA cpn values were 251-13234 for CYP1A1, 4133-57078 for CYP1B1 and 4456-55887 for NQO1. There were 3.5 (mean, range 0.2-15.8) BPdG adducts/10(8) nucleotides in the NHMECs (n = 16), and 790 in the MCF-7s. In the NHMECs, BP-induced CYP1A1 RNA cpn was highly associated with BPdG (P = 0.002), but CYP1B1 and NQO1 were not. Western blots of four NHMEC strains, chosen for different levels of BPdG adducts, showed a linear correlation between BPdG and CYP1A1, but not CYP1B1 or NQO1. Ethoxyresorufin-O-deethylase (EROD) activity, which measures CYP1A1 and CYP1B1 together, correlated with BPdG, but NQO1 activity did not. Despite more numerous levels of CYP1B1 and NQO1 RNA cpn in unexposed and BP-exposed NHMECs and MCF-7cells, BPdG formation was only correlated with induction of CYP1A1 RNA cpn. The higher level of BPdG in MCF-7 cells, compared to NHMECs, may have been due to a much increased induction of CYP1A1 and EROD. Overall, BPdG correlation was observed with CYP1A1 protein and CYP1A1/1B1 enzyme activity, but not with CYP1B1 or NQO1 protein, or NQO1 enzyme activity.

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.

Achieving professional success in US government, academia, and industry: an EMGS commentary

One of the goals of the EMGS is to help members achieve professional success in the fields they have trained in. Today, there is greater competition for jobs in genetic toxicology, genomics, and basic research than ever before. In addition, job security and the ability to advance in one's career is challenging, regardless of whether one works in a regulatory, academic, or industry environment. At the EMGS Annual Meeting in Monterey, CA (September, 2013), the Women in EMGS Special Interest Group held a workshop to discuss strategies for achieving professional success. Presentations were given by three speakers, each representing a different employment environment: Government (Miriam C. Poirier), Academia (Jeffrey L. Schwartz), and Industry (Marilyn J. Aardema). Although some differences in factors or traits affecting success in the three employment sectors were noted by each of the speakers, common factors considered important for advancement included networking, seeking out mentors, and developing exceptional communication skills.

Exposure of Allium cepa root cells to zidovudine or nevirapine induces cytogenotoxic changes

Antiretroviral drugs have proved useful in the clinical management of HIV-infected persons, though there are concerns about the effects of exposure to these DNA-reactive drugs. We investigated the potential of the plant model Allium cepa root tip assay to demonstrate the cytogenotoxicity of zidovudine and nevirapine and as a replace-reduce-refine programme amenable to resource-poor research settings. Cells mitotic index were determined in squashed root cells from Allium cepa bulbs exposed to zidovudine or nevirapine for 48 hr. The concentration of zidovudine and nevirapine inhibiting 50% root growth after 96 hr exposure was 65.0 µM and 92.5 µM respectively. Root length of all antiretroviral-exposed roots after 96 hr exposure was significantly shorter than the unexposed roots while additional root growth during a subsequent 48 hr recovery period in the absence of drug was not significantly different. By ANOVA, there was a significant association between percentage of cells in mitosis and zidovudine dose (p=0.004), but not nevirapine dose (p=0.68). Chromosomal aberrations such as sticky chromosomes, chromatin bridges, multipolar mitoses and binucleated cells were observed in root cells exposed to zidovudine and nevirapine for 48 hr. The most notable chromosomal aberration was drug-related increases in sticky chromosomes. Overall, the study showed inhibition in root length growth, changes in the mitotic index, and the induction of chromosomal aberrations in Allium bulbs treated for 96 hr or 48 hr with zidovudine and nevirapine. The study reveals generalized cytogenotoxic damage induced by exposure to zidovudine and nevirapine, and further show that the two compounds differ in their effects on mitosis and the types of chromosomal aberrations induced.

Tempol protects cardiomyocytes from nucleoside reverse transcriptase inhibitor-induced mitochondrial toxicity

Nucleoside reverse transcriptase inhibitors (NRTIs), essential components of combinational therapies used for treatment of human immunodeficiency virus-1, damage heart mitochondria. Here, we have shown mitochondrial compromise in H9c2 rat cardiomyocytes exposed for 16 passages (P) to the NRTIs zidovudine (AZT, 50μM) and didanosine (ddI, 50μM), and we have demonstrated protection from mitochondrial compromise in cells treated with 200μM 1-oxyl-2,2,6,6-tetramethyl-4-hydroxypiperidine (Tempol) or 200μM 1-hydroxy-4-[2-triphenylphosphonio)-acetamido]-2,2,6,6-tetramethylpiperidine (Tempol-H), along with AZT/ddI, for 16P. Exposure to AZT/ddI caused a moderate growth inhibition at P3, P5, P7, and P13, which was not altered by addition of Tempol or Tempol-H. Mitochondrial oxidative phosphorylation capacity was determined as uncoupled oxygen consumption rate (OCR) by Seahorse XF24 Analyzer. At P5, P7, and P13, AZT/ddI-exposed cells showed an OCR reduction of 8.8-57.2% in AZT/ddI-exposed cells, compared with unexposed cells. Addition of Tempol or Tempol-H, along with AZT/ddI, resulted in OCR levels increased by about 300% above the values seen with AZT/ddI alone. The Seahorse data were further supported by electron microscopy (EM) studies in which P16 cells exposed to AZT/ddI/Tempol had less mitochondrial pathology than P16 cells exposed to AZT/ddI. Western blots of P5 cells showed that Tempol and Tempol-H upregulated expression of mitochondrial uncoupling protein-2 (UCP-2). However, Complex I activity that was reduced by AZT/ddI, was not restored in the presence of AZT/ddI/Tempol. Superoxide levels were increased in the presence of AZT/ddI and significantly decreased in cells exposed to AZT/3TC/Tempol at P3, P7, and P10. In conclusion, Tempol protects against NRTI-induced mitochondrial compromise, and UCP-2 plays a role through mild uncoupling.

Tamoxifen-DNA adduct formation in monkey and human reproductive organs

The estrogen analog tamoxifen (TAM), used for adjuvant therapy of breast cancer, induces endometrial and uterine tumors in breast cancer patients. Proliferation stimulus of the uterine endometrium is likely involved in tumor induction, but genotoxicity may also play a role. Formation of TAM-DNA adducts in human tissues has been reported but remains controversial. To address this issue, we examined TAM-DNA adducts in uteri from two species of monkeys, Erythrocebus patas (patas) and Macaca fascicularis (macaque), and in human endometrium and myometrium. Monkeys were given 3-4 months of chronic TAM dosing scaled to be equivalent to the daily human dose. In the uteri, livers and brains from the patas (n = 3), and endometrium from the macaques (n = 4), TAM-DNA adducts were measurable by TAM-DNA chemiluminescence immunoassay. Average TAM-DNA adduct values for the patas uteri (23 adducts/10(8) nucleotides) were similar to those found in endometrium of the macaques (19 adducts/10(8) nucleotides). Endometrium of macaques exposed to both TAM and low-dose estradiol (n = 5) averaged 34 adducts/10(8) nucleotides. To examine TAM-DNA persistence in the patas, females (n = 3) were exposed to TAM for 3 months and to no drug for an additional month, resulting in low or non-detectable TAM-DNA in livers and uteri. Human endometrial and myometrial samples from women receiving (n = 8) and not receiving (n = 8) TAM therapy were also evaluated. Women receiving TAM therapy averaged 10.3 TAM-DNA adducts/10(8) nucleotides, whereas unexposed women showed no detectable TAM-DNA. The data indicate that genotoxicity, in addition to estrogen agonist effects, may contribute to TAM-induced human endometrial cancer.

The influence of age on serum concentrations of cardiac troponin I: results in rats, monkeys, and commercial sera

Cardiac troponins serve as serum biomarkers of myocardial injury. The current study examined the influence of age on serum concentrations of cardiac troponin I (cTnI). An ultrasensitive immunoassay was used to monitor cTnI concentrations in Sprague-Dawley (SD) rats and Erythrocebus patas monkeys of different ages. The mean cTnI concentrations were highest in 10-day-old rats compared to 25-, 40-, and 80-day-old SD rats. Cardiomyocyte remodeling was apparent in hearts from 10-day-old SD rats as evident by hypercellularity, irregularly shaped nuclei, and moderate numbers of myocytes undergoing mitosis and apoptosis. The mean concentration of cTnI in 5 newborn monkeys was considerably higher than that of three 1-year-old monkeys. Evidence of cardiomyocyte remodeling was also observed in these newborn hearts (loss of myofibrils and cytoplasmic vacuolation). Commercial animal serum samples were also analyzed. The concentrations of cTnI detected in fetal equine and porcine serum were considerably higher than that found in adult equine and porcine serum samples Likewise, fetal bovine serum had higher cTnI concentrations (>2,400 pg/ml) than did adult caprine and laprine samples (2.5-2.7 pg/ml). The present study found age-related differences in cTnI concentrations, with higher levels occurring at younger ages. This effect was consistent across several animal species.

Abstract 4418: Overexpression of PGC-1α in rat cardiomyocytes protects against nucleoside reverse transcriptase inhibitor (NRTI)-induced mitochondrial toxicity

The NRTIs Zidovudine (AZT) and Didanosine (ddI) are components of the antiretroviral combination therapies in widespread use for treatment of HIV-1 infection. However, AZT, a carcinogen in mice, is a DNA replication chain terminator that damages heart, skeletal muscle, brain and liver during long-term clinical use. In addition, both drugs are known to cause treatment-limiting mitochondrial compromise. In order to elucidate the mechanisms resulting in cardiac mitochondrial toxicity in patients using these drugs, we have evaluated rat cardiomyocyte H9c2 cells exposed for &gt;30 passages (P) to 50 μM AZT or 50 μM AZT/50 μM ddI, doses allowing for ≥80% survival. Mitochondrial integrity, evaluated as Oxygen Consumption Rate (OCR, by Seahorse Analyzer) was reduced by ≥50% (p&lt;0.05) in NRTI-exposed cells at most P compared to unexposed controls. Progressive abnormal mitochondrial morphology was observed, with time of exposure, by electron microscopy (EM). In addition, in AZT/ddI-exposed cells there were reductions (about 50%) in protein levels of PGC-1α, a master regulator of mitochondrial function and biogenesis, and its downstream effector NRF-1, compared to unexposed cells. Hypothesizing that up-regulation of PGC-1α might protect cells from AZT/ddI-induced mitochondrial damage, H9c2 cells were infected with lentivirus carrying PGC-1α, and shown by Western blot to overexpress PGC-1α. When both the H9c2 cells and the H9c2/ PGC-1α cells were exposed to 50 μM AZT/50 μM ddI, significantly-increased (20-50%) OCR levels were observed at P 2, 6, 8, 12 and 15 in the H9c2/ PGC-1α cells, compared to the H9c2 cells (p&lt;0.05 for all P). In addition, Western blot showed about 50% higher levels of NRF-1 in AZT/ddI-exposed H9c2/ PGC-1α cells, compared to AZT/ddI-exposed H9c2 cells. These studies support our hypothesis that PGC-1α overexpression protects cardiomyocytes from NRTI-induced mitochondrial compromise, and suggest that the AZT/ddI-induced reduction in protein levels of PGC-1α is a major mechanism contributing to AZT/ddI induced toxicity. We plan to search for natural products that offer similar protection and evaluate their effect on genotoxicity and mitochondrial toxicity of the antiretroviral NRTIs.

Citation Format: Eunwoo Shim, Daniel Liu, Alexander Gibbons, Miriam C. Poirier, Yongmin Liu. Overexpression of PGC-1α in rat cardiomyocytes protects against nucleoside reverse transcriptase inhibitor (NRTI)-induced mitochondrial toxicity. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 4418. doi:10.1158/1538-7445.AM2013-4418

Abstract 3603: Zidovudine (AZT)-induced aneuploidy, mediated by Stathmin 1 (STMN1), involves a loss of polymerized β-tubulin

The nucleoside reverse transcriptase inhibitor AZT induces multiple manifestations of genotoxicity, among which aneuploidy, observed as micronuclei containing whole chromosomes, has been reported (Borojerdi et al., Mut Res, 2009). We have seen a loss of β-tubulin polymerization in about 23% of normal human mammary epithelial cells (NHMECs) exposed for 24 hr to 200 μM AZT, and demonstrated down-regulation of hsa-miR-770-5p, a microRNA known to target STMN1, in the same AZT-exposed cells. STMN1 prevents microtubule polymerization, resulting in destabilization of the mitotic spindle and chromosome misalignment. We therefore hypothesized that, if AZT exposure downregulates hsa-miR-770-5p, there should be increased expression of STMN1, which would result in loss of microtubule polymerization leading to aneuploidy. In this study we exposed cells of the human breast line MCF-10A to 100 μM AZT continuously for 1 to 3 passages (P). By Western Blot we showed that total STMN1 was 3.5-fold increased at P1, in AZT-exposed cells, compared to the unexposed controls. Using the same STMN1 antiserum, by immunohistochemistry (IHC), we observed that some cells stained heavily for STMN1, while others had virtually no staining, and that the overall STMN1 fluorescence was increased in AZT-exposed cells, compared to unexposed controls. When tubulin polymerization was evaluated by IHC, using β-tubulin antiserum, 10.1% of AZT-exposed cells showed a loss of tubulin polymerization, while only 0.7% of unexposed cells showed the same effect (p=0.004). The data suggest that AZT induced aneuploidy may be mediated by inhibition of hsa-miR-770-5p, upregulation of STMN1, impaired polymerization of β-tubulin, aberrant mitotic spindle formation and consequent chromosome misalignment resulting in aneuploidy. If confirmed, this will constitute a novel mechanism of AZT-induced genotoxicity that may or may not be related to AZT-DNA incorporation. Ongoing experiments will explore these relationships further by localizing STMN1 and β-tubulin in specific cells, and examining the same cultures for spindle aberrations at mitosis.

Citation Format: Andrea V. Rivera, Vanesa C. Sanchez, Miriam C. Poirier, Ofelia A. Olivero. Zidovudine (AZT)-induced aneuploidy, mediated by Stathmin 1 (STMN1), involves a loss of polymerized β-tubulin. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 3603. doi:10.1158/1538-7445.AM2013-3603

Abstract 5367: Comparison of global DNA methylation in uterine tissue from different species of monkeys and humans exposed to tamoxifen

Tamoxifen (TAM) is a selective estrogen receptor modulator used worldwide for adjuvant therapy and chemoprevention of breast cancer. However, women receiving TAM therapy have an increased risk of endometrial and myometrial cancer, which may be due to genotoxicity and/or estrogen receptor-related mechanisms. It is now accepted that cancer can be both a genetic and an epigenetic disease, with these components participating at all stages of cancer development. DNA methylation at the 5-position of cytosine silences gene expression. Aberrant global DNA 5-methylcytosine (5-mC) levels may produce critical changes in the expression of genes that regulate cell growth and invasiveness. In order to study the effect of TAM exposure on uterine 5-mC levels, we examined uterine tissues taken from aging Erythrocebus patas (patas) and Macaca fascicularis (macaque) monkeys given oral TAM dosing for 3-4 months. In addition, we evaluated endometrial and myometrial samples from breast cancer survivors, who typically receive adjuvant TAM therapy for 5 years. The percentage of 5-mC in DNA was determined by an ELISA that employed a highly-specific 5-mC antibody. Of 5 female patas, 2 were unexposed and 3 were given oral dosing with 1.7 mg TAM/kg bw/day for 3 months. Of 12 female macaques, 6 were unexposed and 6 were given 1.3 mg TAM/kg bw/day for 4 months. Also, uterine tissue was taken at surgery or autopsy from normal-appearing areas and malignant-appearing areas, from women who received 20 mg TAM/day (n=9) and unexposed women (n=6). The patas monkeys given TAM had significantly increased levels of uterine 5-mC compared to the controls (2.9±0.13% vs. 1.9±0.26%, mean ± SE, respectively, p=0.03). However, the macaques showed no significant differences in uterine 5-mC between unexposed and TAM-exposed animals (0.93%±0.1 vs. 1.07%±0.05, mean ± SE, respectively). In human patients, TAM treatment did not alter the global 5-mC levels in either normal-appearing or malignant-appearing endometrium. However, global 5-mC levels in normal-appearing endometrium from the combined TAM-treated and untreated women (n=6) were significantly lower than those found in malignant-appearing uterine tissue from the combined TAM-treated and untreated (n=9) group (0.33%±0.01 vs. 0.70%±0.09, mean ± SE, respectively, p=0.006). Therefore, changes in uterine global DNA 5-mC are not altered consistently within primate species as a result of long-term TAM exposure, suggesting that 5-mC alterations are not major contributors to TAM-induced endometrial cancer. Continuing studies will evaluate 5-mC levels in the promoter regions of specific genes that are modulated in expression level during TAM therapy.

Citation Format: Elena E. Hernandez Ramon, Nancy Si, Mark J. Cline, Charles E. Wood, Ruth Woodward, Miriam C. Poirier. Comparison of global DNA methylation in uterine tissue from different species of monkeys and humans exposed to tamoxifen. [abstract]. In: Proceedings of the 104th Annual Meeting of the American Association for Cancer Research; 2013 Apr 6-10; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2013;73(8 Suppl):Abstract nr 5367. doi:10.1158/1538-7445.AM2013-5367

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.

Chemical-induced DNA damage and human cancer risk

For more than 200 years human cancer induction has been known to be associated with a large variety of chemical exposures. Most exposures to chemical carcinogens occur as a result of occupation, pollution in the ambient environment, lifestyle choices, or pharmaceutical use. Scientific investigations have revealed that the majority of cancer causing chemicals, or chemical carcinogens, act through "genotoxic" or DNA damaging mechanisms, which involve covalent binding of the chemical to DNA (DNA adduct formation). Cancer-inducing exposures are typically frequent and/or chronic over years, and the accumulation of DNA damage or DNA adduct formation is considered to be a necessary requirement for tumor induction. Studies in animal models have indicated that the ability to reduce DNA damage will also result in reduction of tumor risk, leading to the hypothesis that individuals having the highest levels of DNA adducts may have an increased cancer risk, compared to individuals with the lowest levels of DNA adducts. Here we have reviewed twelve investigations showing 2- to 9-fold increased Relative Risks (RR) or Odds Ratios (OR) for cancer in (the 25% of) individuals having the highest DNA adduct levels, compared to (the 25% of) matched individuals with the lowest DNA adducts. These studies also provided preliminary evidence that multiple types of DNA adducts combined, or DNA adducts combined with other risk factors (such as infection or inflammation), may be associated with more than 10-fold higher cancer risks (RR = 34-60), compared to those found with a single carcinogen. Taken together the data suggest that a reduction in human DNA adduct level is likely to produce a reduction in human cancer risk.

Exposure to benzo[a]pyrene of Hepatic Cytochrome P450 Reductase Null (HRN) and P450 Reductase Conditional Null (RCN) mice: Detection of benzo[a]pyrene diol epoxide-DNA adducts by immunohistochemistry and 32P-postlabelling

Benzo[a]pyrene (BaP) is a widespread environmental carcinogen activated by cytochrome P450 (P450) enzymes. In Hepatic P450 Reductase Null (HRN) and Reductase Conditional Null (RCN) mice, P450 oxidoreductase (Por) is deleted specifically in hepatocytes, resulting in the loss of essentially all hepatic P450 function. Treatment of HRN mice with a single i.p. or oral dose of BaP (12.5 or 125mg/kg body weight) resulted in higher DNA adduct levels in liver (up to 10-fold) than in wild-type (WT) mice, indicating that hepatic P450s appear to be more important for BaP detoxification in vivo. Similar results were obtained in RCN mice. We tested whether differences between hepatocytes and non-hepatocytes in P450 activity may underlie the increased liver BaP-DNA binding in HRN mice. Cellular localisation by immunohistochemistry of BaP-DNA adducts showed that HRN mice have ample capacity for formation of BaP-DNA adducts in liver, indicating that the metabolic process does not result in the generation of a reactive species different from that formed in WT mice. However, increased protein expression of cytochrome b(5) in hepatic microsomes of HRN relative to WT mice suggests that cytochrome b(5) may modulate the P450-mediated bioactivation of BaP in HRN mice, partially substituting the function of Por.

Benzo[a]pyrene (BP) DNA adduct formation in DNA repair-deficient p53 haploinsufficient [Xpa(-/-)p53(+/-)] and wild-type mice fed BP and BP plus chlorophyllin for 28 days

We have evaluated DNA damage (DNA adduct formation) after feeding benzo[a]pyrene (BP) to wild-type (WT) and cancer-susceptible Xpa(-/-)p53(+/-) mice deficient in nucleotide excision repair and haploinsufficient for the tumor suppressor p53. DNA damage was evaluated by high-performance liquid chromatography/electrospray ionization tandem mass spectrometry (HPLC/ES-MS/MS), which measures r7,t8,t9-trihydroxy-c-10-(N (2)-deoxyguanosyl)-7,8,9,10-tetrahydrobenzo[a]pyrene (BPdG), and a chemiluminescence immunoassay (CIA), using anti-r7,t8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA antiserum, which measures both BPdG and the other stable BP-DNA adducts. When mice were fed 100 ppm BP for 28 days, BP-induced DNA damage measured in esophagus, liver and lung was typically higher in Xpa(-/-)p53(+/-) mice, compared with WT mice. This result is consistent with the previously observed tumor susceptibility of Xpa(-/-)p53(+/-) mice. BPdG, the major DNA adduct associated with tumorigenicity, was the primary DNA adduct formed in esophagus (a target tissue in the mouse), whereas total BP-DNA adducts predominated in higher levels in the liver (a non-target tissue in the mouse). In an attempt to lower BP-induced DNA damage, we fed the WT and Xpa(-/-)p53(+/-) mice 0.3% chlorophyllin (CHL) in the BP-containing diet for 28 days. The addition of CHL resulted in an increase of BP-DNA adducts in esophagus, liver and lung of WT mice, a lowering of BPdG in esophagi of WT mice and livers of Xpa(-/-)p53(+/-) mice and an increase of BPdG in livers of WT mice. Therefore, the addition of CHL to a BP-containing diet showed a lack of consistent chemoprotective effect, indicating that oral CHL administration may not reduce PAH-DNA adduct levels consistently in human organs.

Development and validation of a direct sandwich chemiluminescence immunoassay for measuring DNA adducts of benzo[a]pyrene and other polycyclic aromatic hydrocarbons

We have developed and validated a sandwich chemiluminescence immunoassay (SCIA) which measures polycyclic aromatic hydrocarbon (PAH)-DNA adducts combining high throughput and adequate sensitivity, appropriate for evaluation of adduct levels in human population studies. Fragmented DNA is incubated with rabbit antiserum elicited against DNA modified with r7,t8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE) and subsequently trapped by goat anti-rabbit IgG bound to a solid surface. Anti-single-stranded (ss) DNA antibodies binds in a quantity proportional to the adduct levels and is detected by chemiluminescence. The BPDE-DNA SCIA has a limit of detection of 3 adducts per 10(9) nucleotides with 5 μg DNA per well. We have validated the BPDE-DNA SCIA using DNA modified in vitro, DNA from benzo[a]pyrene (BP)-exposed cultured cells and mice. The levels of adduct measured by SCIA were lower (30-60%) than levels of bulky DNA adducts measured in the same samples by (32)P-postlabelling. The BPDE-DNA SCIA also detected adducts produced in vivo by PAHs other than BP. When blood DNA samples from maternal/infant pairs were assayed by BPDE-DNA SCIA, the adduct levels obtained were significantly correlated. However, there was no correlation between (32)P-postlabelling and SCIA values for the same samples. The SCIA can be extended to any DNA adduct and is expected to provide, when fully automated, a valuable high-throughput approach in large-scale population studies.

The resveratrol analogue, 2,3',4,5'-tetramethoxystilbene, does not inhibit CYP gene expression, enzyme activity and benzo[a]pyrene-DNA adduct formation in MCF-7 cells exposed to benzo[a]pyrene

Exposure to carcinogenic polycyclic aromatic hydrocarbons (PAHs) induces cytochrome P450 (CYP) 1A1 and 1B1 enzymes, which biotransform PAHs resulting in the formation of DNA adducts. We hypothesised that 2,3',4,5'-tetramethoxystilbene (TMS), an analogue of resveratrol and a potent CYP1B1 inhibitor, may inhibit r7, t8, t9-trihydroxy-c-10-(N(2)deoxyguanosyl)-7,8,9,10-tetrahydro-benzo[a]pyrene (BPdG) adduct formation in cells exposed to benzo[a]pyrene (BP). To address this, MCF-7 cells were cultured for 96 h in the presence of 1 μM BP, 1 μM BP + 1 μM TMS or 1 μM BP + 4 μM TMS. Cells were assayed at 2-12 h intervals for: BPdG adducts by r7, t8-dihydroxy-t-9,10-epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA chemiluminescence immunoassay; CYP1A1 and 1B1 gene expression changes by relative real-time polymerase chain reaction; and CYP1A1/1B1 enzyme activity by ethoxyresorufin-O-deethylase (EROD) assay. Whereas maximal BPdG levels were similar for all exposure groups, the times at which the maxima were reached increased by 16 and 24 h with the addition of 1 and 4 μM TMS, respectively. The maximal expression of CYP1A1 and CYP1B1 occurred at 16, 24 and 48 h, but the maximal level for EROD-specific activity was reached at 24, 48 and 60 h, in cells exposed to 1 μM BP, 1 μM BP + 1 μM TMS or 1 μM BP + 4 μM TMS, respectively. The area under the curve from 4 to 96 h of exposure (AUC(4-)(96 h)) for BPdG adduct formation was not increased in the presence of TMS, but for CYP1A1 and CYP1B1 expression fold increase AUC(4-)(96 h) and EROD-specific activity AUC(4-)(96 h), there were significant (P < 0.05) increases in the presence of 4 μM TMS. Therefore, during 96 h of exposure in MCF-7 cells, the combination of BP plus TMS caused a slowing of BP biotransformation, with an increase in CYP1A1 and CYP1B1 expression and EROD activity, and a slowing, but no change in magnitude of BPdG formation.

Assessment of multiple types of DNA damage in human placentas from smoking and nonsmoking women in the Czech Republic

Three classes of DNA damage were assessed in human placentas collected (2000-2004) from 51 women living in the Teplice region of the Czech Republic, a mining area considered to have some of the worst environmental pollution in Europe in the 1980s. Polycyclic aromatic hydrocarbon (PAH)-DNA adducts were localized and semiquantified using immunohistochemistry (IHC) and the Automated Cellular Imaging System (ACIS). More generalized DNA damage was measured both by (32)P-postlabeling and by abasic (AB) site analysis. Placenta stained with antiserum elicited against DNA modified with 7β,8α-dihydroxy-9α,10α-epoxy-7,8,9,10-tetrahydro-benzo[a]pyrene (BPDE) revealed PAH-DNA adduct localization in nuclei of the cytotrophoblast (CT) cells and syncytiotrophoblast (ST) knots lining the chorionic villi. The highest levels of DNA damage, 49-312 PAH-DNA adducts/10(8) nucleotides, were found by IHC/ACIS in 14 immediately fixed placenta samples. An additional 37 placenta samples were stored frozen before fixation and embedding, and because PAH-DNA adducts were largely undetectable in these samples, freezing was implicated in the loss of IHC signal. The same placentas (n = 37) contained 1.7-8.6 stable/bulky DNA adducts/10(8) nucleotides and 0.6-47.2 AB sites/10(5) nucleotides. For all methods, there was no correlation among types of DNA damage and no difference in extent of DNA damage between smokers and nonsmokers. Therefore, the data show that DNA from placentas obtained in Teplice contained multiple types of DNA damage, which likely arose from various environmental exposures. In addition, PAH-DNA adducts were present at high concentrations in the CT cells and ST knots of the chorionic villi.

Seasonal variations in the levels of PAH-DNA adducts in young adults living in Mexico City

Polycyclic aromatic hydrocarbons (PAHs) are ubiquitous components of polluted air. The Mexico City Metropolitan Area (MCMA), one of the most densely populated areas in the world, is 2240 m above sea level. At this altitude, less oxygen is available, making combustion less efficient and therefore producing more PAH pollutants. According to the Automatic Monitoring Network in Mexico City (RAMA, for its Spanish initials; http://www.sma.df.gob.mx/simat2/informaciontecnica/index.php?opcion=5&opciondifusion_bd=90), which performs environmental monitoring, the critical air pollutants in Mexico City are ozone and particulate matter (PM). PM emissions increase during the dry season (winter to spring) and decrease during the rainy season (summer to autumn). The bioactivation of some PAHs produces reactive metabolites that bind to DNA, and the presence of elevated levels of PAH-DNA adducts in tissues such as blood lymphocytes represents an elevated risk for the development of cancer. We have compared the levels of PAH-DNA adducts and the percentage of cells with chromosomal aberrations (CWAs) using a matched set of peripheral blood lymphocytes obtained on two separate occasions from young non-smoking inhabitants of the MCMA (n = 92) during the 2006 dry season and the following rainy season. PAH-DNA adducts were analysed using the r7, t8-dihydroxy-t-9, 10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA chemiluminescence immunoassay (CIA). The percentages of CWA were determined in cultured lymphocytes from the same individuals. Both DNA adduct levels and chromosomal aberrations were tested for correlation with lifestyle and the polymorphisms of cytochromes P450 CYP1A1 and CYP1B1 as well as glutathione-S-transferases GSTM1 and GSTT1. The levels of PAH-DNA adducts were significantly higher (P < 0.001) in the dry season (10.66 ± 3.05 per 10(9) nt, n = 92) than during the rainy season (9.50 ± 2.85 per 10(9) nt, n = 92) and correlated with the seasonal levels of particulate matter with a diameter of ≤ 10 μm (PM(10)). The percentage of CWA was not seasonally related; however, significant associations between the number of risk alleles and adduct levels in the dry (R = 0.298, P = 0.048) and in the wet seasons (R = 0.473, P = 0.001) were observed.

Progressive mitochondrial compromise in brains and livers of primates exposed in utero to nucleoside reverse transcriptase inhibitors (NRTIs)

Mitochondrial compromise has been documented in infants born to women infected with the human immunodeficiency virus (HIV-1) who received nucleoside reverse transcriptase inhibitor (NRTI) therapy during pregnancy. To model these human exposures, we examined mitochondrial integrity at birth and 1 year in brain cortex and liver from offspring of retroviral-free Erythrocebus patas dams-administered human-equivalent NRTI doses for the last half (10 weeks) of gestation. Additional infants, followed for 1 year, were given the same drugs as their mothers for the first 6 weeks of life. Exposures included: no drug, Zidovudine (AZT), Lamivudine (3TC), AZT/3TC, AZT/Didanosine (ddI), and Stavudine (d4T)/3TC. In brain and liver, oxidative phosphorylation (OXPHOS) enzyme activities (complexes I, II, and IV) showed minimal differences between unexposed and NRTI-exposed offspring at both times. Brain and liver mitochondria from most NRTI-exposed patas, both at birth and 1 year of age, contained significant (p < 0.05) morphological damage observed by electron microscopy (EM), based on scoring of coded photomicrographs. Brain and liver mitochondrial DNA (mtDNA) levels in NRTI-exposed patas were depleted significantly in the 3TC and d4T/3TC groups at birth and were depleted significantly (p < 0.05) at 1 year in all NRTI-exposed groups. In 1-year-old infants exposed in utero to NRTIs, mtDNA depletion was 28.8-51.8% in brain and 37.4-56.5% in liver. These investigations suggest that some NRTI-exposed human infants may sustain similar mitochondrial compromise in brain and liver and should be followed long term for cognitive integrity and liver function.

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.

Nuclear bud formation: a novel manifestation of Zidovudine genotoxicity

Normal diploid somatic mammalian cell division generates 2 daughter cells as a result of a strict and well-controlled mitotic process. However, some defects during the progression of that process could generate an unbalanced distribution of chromosomes, aneuploidy and eventually, a malignant phenotype. Previous observations using a transgenic mouse model with diminished DNA repair capacity revealed the presence of nuclear buds (NBs) induced in vitro by the nucleoside analog zidovudine (Retrovir(R), 3'-azido-3'-deoxythymidine, AZT). Here we used bone marrow mesenchymal cells, taken from mice with the Xpa(-/-)Trp53(+/-) genotype, that were cultured and exposed to 0 and 100 muM AZT for 24 hours. Fixed and denatured cells were processed by fluorescence in situ hybridization (FISH) with whole chromosome painting probes used to identify chromosomes in cells growing on glass chamber slides (2 probes/slide). A variety of sizes and shapes of NBs were observed. Some NBs had a large connection with the main nucleus (>(1/4) of the NB diameter), others hada smaller connection (<(1/4) of the NB diameter), some were circular and positioned close to the nucleus, while some resided in the cytoplasm separated from the nucleus or connected by a thin chromatin strand. We had hypothesized that NBs would progress in the process of budding until separation occurred, but this was not proven by time-lapse photography studies performed for 20 hours. From 1,126 cells scored in the unexposed cultures, 10.39 % of cells carried NBs, while from 1,108 cells scored in the AZT-exposed cultures 29.16% of cells carried NBs (p = 0.001). In AZT-exposed cells there were a total of 322 NBs scored; 46.6% or 150 NBs contained positive signals for one or both probes used, while 53% or 172 NBs had no probe signal. In addition, FISH analysis showed no preferential localization of any chromosome within the NBs. Among the NBs that carried no probe signal, the presence of positive signals with inversion of DAPI imaging demonstrated centromeric content. It has been hypothesized that NBs occur as a result of expulsion of amplified DNA from the main nucleus; however, this data demonstrates that NBs may contain any chromosome, suggesting that NBs do not consist of just amplified DNA.

Abstract 3458: Benzo[a]pyrene (BP)-induced DNA damage is elevated in mice lacking Xeroderma pigmentosum complementation group A (Xpa) and heterozygous for the tumor suppressor gene p53

In developing countries, esophageal cancer is the third most common cancer in men. We have employed a mouse model of esophageal cancer using DNA repair deficient mice. Unlike their wild type counterparts, C57BL/6J mice lacking Xpa and heterozygous for p53 [Xpa(−/−) p53(+/−)] have previously been shown to develop forestomach and esophageal tumors when fed BP (Hoogervorst et al., Carcinogenesis, 2003). Two methodologies were employed to examine BP-induced steady-state levels of DNA damage in esophagi of male mice fed 0 or 100 ppm BP for 4 weeks. HPLC, in conjunction with tandem mass spectrometry (HPLC-MS/MS), was used to measure 10-(deoxyguanosin-N2-yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydro-benzo[a]pyrene (BPdG) and a chemiluminiscence immunoassay (CIA), using antiserum elicited against r7,t8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-modified DNA was used to evaluate BP-DNA adducts. In the esophagi of Xpa(−/−) p53(+/−) mice, there were 38.7 ± 4.8 BPdG adducts/108 nucleotides (mean ± SE, n=5), as measured by HPLC-MS/MS, while in the wild type mice there were 28.0 ± 1.8 BPdG adducts/108 nucleotides (mean ± SE, n=5). Furthermore, complete loss of p53 resulted in the greatest accumulation of BPdG adducts, with 58.1 ± 8.6 BPdG adducts/108 nucleotides (n=5) in Xpa(−/−) p53(−/−) mice (p&lt;0.05 vs. wild type mice). Esophageal BP-DNA adduct values, as measured by CIA, were 23.3 ± 1.7 adducts/108 nucleotides (n=3) in the Xpa(−/−) p53(+/−) mice, compared to 14.6 ± 3.0 adducts/108 nucleotides (n=3) in the wild type mice. Since similar adduct levels were determined using both HPLC-MS/MS and CIA, this indicates that BPdG is the major adduct resulting from BP in mouse esophagus. The higher levels of DNA damage in DNA repair-deficient p53-deficient mice, compared to their wild type counterparts, may contribute to the enhanced susceptibility of these mice to esophageal tumor induction by BP. Currently we are examining the role of chlorophyllin, a chemopreventive agent, in reducing BP-induced DNA damage levels and tumor formation in this model.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 3458.

Abstract 2980: Role of XPA and p53 genes in the induction of centrosomal amplification in mice exposed to Zidovudine (AZT)

In cultured cells, exposure to the highly-effective nucleoside reverse transcriptase inhibitor (NRTI) Zidovudine (AZT) induces genomic instability, causing cell cycle arrest, micronuclei, sister chromatid exchanges, and shortened telomeres. In previous studies, we demonstrated for the first time that AZT induced centrosomal amplification (defined as &gt; 2 centrosomes /cell), a novel manifestation of genotoxicity. Here, bone marrow cells from wild type C57BL/6J mice and their transgenic counterparts with genotypes XPA −/− p53 +/+, XPA−/−p53 +/− and XPA−/−p53 −/−, were cultured in vitro to obtain homogeneous populations of mesenchymal-derived fibroblasts. Wild type, and DNA repair- / p53-deficient cells (n=3/group) were exposed to 0, 10 or 100 μM AZT for 24 hr, and centrosomal amplification was examined by immunohistochemical (IHC) staining with an anti-pericentrin antibody. Values for centrosomal amplification (% of cells with ≥2 centrosomes/cell) were 12.2, 15.2 and 19.7% in wild type (XPA +/+ p53 +/+) cells exposed to 0, 10 or 100 μM AZT, respectively. Values for centrosomal amplification were 18.0, 28.7 and 33.9 % for XPA −/− p53 +/+cells, and 21.6, 29.3 and 39.5% for XPA−/−p53 +/− cells, after exposure to 0, 10 and 100 μM AZT, respectively. For XPA−/−p53 −/− cells there were 18.4, 22.9 and 29.0% of cells with centrosomal amplification after exposure to 0, 10 and 100 µM AZT, respectively. Statistical analysis (by ANOVA) showed significance between each of the three transgenic groups, when compared to the wild type cells (p= 0.0025). The data suggest that loss of both XPA alleles confers genomic instability, but that additional loss of p53 does not further enhance instability. Whereas nucleotide excision repair is not considered to impact NRTI intracellular processing, these data would argue that lack of intact nucleotide excision repair enhances genomic instability in AZT-exposed cells.

Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2980.

CYP1A1 and CYP1B1 gene expression and DNA adduct formation in normal human mammary epithelial cells exposed to benzo[a]pyrene in the absence or presence of chlorophyllin

Benzo[a]pyrene (BP) is a potent pro-carcinogen and ubiquitous environmental pollutant. Here, we examined the induction and modulation of CYP1A1 and CYP1B1 and 10-(deoxyguanosin-N(2)-yl)-7,8,9-trihydroxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPdG) adduct formation in DNA from 20 primary normal human mammary epithelial cell (NHMEC) strains exposed to BP (4muM) in the absence or presence of chlorophyllin (5muM). Real-time polymerase chain reaction (RT-PCR) analysis revealed strong induction of both CYP1A1 and CYP1B1 by BP, with high levels of inter-individual variability. Variable BPdG formation was found in all strains by r7, t8-dihydroxy-t-9, 10 epoxy-7,8,9,10-tetrahydrobenzo[a]pyrene (BPDE)-DNA chemiluminescence assay (CIA). Chlorophyllin mitigated BP-induced CYP1A1 and CYP1B1 gene expression in all 20 strains when administered with BP. Chlorophyllin, administered prior to BP-exposure, mitigated CYP1A1 expression in 18/20 NHMEC strains (p<0.005) and CYP1B1 expression in 17/20 NHMEC strains (p<0.005). Maximum percent reductions of CYP1A1 and CYP1B1 gene expression and BPdG adduct formation were observed when cells were pre-dosed with chlorophyllin followed by administration of the carcinogen with chlorophyllin (p<0.005 for CYP1A1 and CYP1B1 expression and p<0.0005 for BPdG adducts). Therefore, chlorophyllin is likely to be a good chemoprotective agent for a large proportion of the human population.

Long-term AZT exposure alters the metabolic capacity of cultured human lymphoblastoid cells

The antiretroviral efficacy of 3′-azido-3′-deoxythymidine (AZT) is dependent upon intracellular mono-, di-, and triphosphorylation and incorporation into DNA in place of thymidine. Thymidine kinase 1 (TK-1) catalyzes the first step of this pathway. MOLT-3, human lymphoblastoid cells, were exposed to AZT continuously for 14 passages (P₁–P₁₄) and cultured for an additional 14 passages (P₁₅–P₂₈) without AZT. Progressive and irreversible depletion of the enzymatically active form of the TK-1 24-kDa monomer with loss of active protein was demonstrated during P₁–P₅ of AZT exposure. From P₁₅ to P₂₈, both the 24- and the 48-kDa forms of TK-1 were undetectable and a tetrameric 96-kDa form was present. AZT-DNA incorporation was observed with values of 150, 133, and 108 molecules of AZT/10⁶ nucleotides at the 10μM plasma-equivalent AZT dose at P₁, P₅, and P₁₄, respectively. An exposure-related increase in the frequency of micronuclei (MN) was observed in cells exposed to either 10 or 800μM AZT during P₁–P₁₄. Analysis of the cell cycle profile revealed an accumulation of S-phase cells and a decrease in G₁-phase cells during exposure to 800μM AZT for 14 passages. When MOLT-3 cells were grown in AZT-free media (P₁₅–P₂₉), there was a reduction in AZT-DNA incorporation and MN formation; however, TK-1 depletion and the persistence of S-phase delay were unchanged. These data suggest that in addition to known mutagenic mechanisms, cells may become resistant to AZT partially through inactivation of TK-1 and through modulation of cell cycle components.

Antiretroviral activity of the aminothiol WR1065 against Human Immunodeficiency virus (HIV-1) in vitro and Simian Immunodeficiency virus (SIV) ex vivo

Background

WR1065 is the free-thiol metabolite of the cytoprotective aminothiol amifostine, which is used clinically at very high doses to protect patients against toxicity induced by radiation and chemotherapy. In an earlier study we briefly reported that the aminothiol WR1065 also inhibits HIV-1 replication in phytohemagglutinin (PHA)-stimulated human T-cell blasts (TCBs) infected in culture for 2 hr before WR1065 exposure. In this study we expanded the original observations to define the dose-response curve for that inhibition, and address the question of additive effects for the combination of WR1065 plus Zidovudine (AZT). Here we also explored the effect of WR1065 on SIV by examining TCBs taken from macaques with well-established infections several months with SIV.

Results

TCBs from healthy human donors were infected for 2 hr with HIV-1, and viral replication (p24) was measured after 72 hr of incubation with or without WR1065, AZT, or both drugs. HIV-1 replication, in HIV-1-infected human TCBs, was inhibited by 50% at 13 μM WR1065, a dose at which 80% of the cells were viable. Cell cycle parameters were the same or equivalent at 0, 9.5 and 18.7 μM WR1065, showing no drug-related toxicity. Combination of AZT with WR1065 showed that AZT retained antiretroviral potency in the presence of WR1065. Cultured CD8⁺ T cell-depleted PHA-stimulated TCBs from Macaca mulatta monkeys chronically infected with SIV were incubated 17 days with WR1065, and viral replication (p27) and cell viability were determined. Complete inhibition (100%) of SIV replication (p27) was observed when TCBs from 3 monkeys were incubated for 17 days with 18.7 μM WR1065. A lower dose, 9.5 μM WR1065, completely inhibited SIV replication in 2 of the 3 monkeys, but cells from the third macaque, with the highest viral titer, only responded at the high WR1065 dose.

Conclusion

The study demonstrates that WR1065 and the parent drug amifostine, the FDA-approved drug Ethyol, have antiretroviral activity. WR1065 was active against both an acute infection of HIV-1 and a chronic infection of SIV. The data suggest that the non-toxic drug amifostine may be a useful antiretroviral agent given either alone or in combination with other drugs as adjuvant therapy.

Centrosome amplification induced by the antiretroviral nucleoside reverse transcriptase inhibitors lamivudine, stavudine, and didanosine

In cultured cells, exposure to the nucleoside reverse transcriptase inhibitor (NRTI) zidovudine (AZT) induces genomic instability, cell cycle arrest, micronuclei, sister chromatid exchanges, and shortened telomeres. In previous studies, we demonstrated AZT-induced centrosome amplification (>2 centrosomes/cell). Here, we investigate centrosome amplification in cells exposed to other commonly used NRTIs. Experiments were performed using Chinese Hamster ovary (CHO) cells, and two normal human mammary epithelial cell (NHMEC) strains: M99005 and M98040, which are high and low incorporators of AZT into DNA, respectively. Cells were exposed for 24 hr to lamivudine (3TC), stavudine (d4T), didanosine (ddI), and thymidine, and stained with anti-pericentrin antibody. Dose response curves were performed to determine cytotoxicity and a lower concentration at near plasma levels and a 10 fold higher concentration were chosen for the experiments. In CHO cells, there was a concentration-dependent, significant (P < 0.05) increase in centrosome amplification for each of the NRTIs. In NHMEC strain M99005, an NRTI-induced increase (P < 0.05) in centrosome amplification was observed for the high concentrations of each NRTI and the low doses of 3TC and ddI. In NHMEC strain M98040, the high doses of ddI and d4T showed significant increases in centrosome amplification. Functional viability of amplified centrosomes was assessed by arresting microtubule nucleation with nocodazole. In cells with more than two centrosomes, the ability to recover microtubule nucleation was similar to that of unexposed cells. We conclude that centrosome amplification is a consequence of exposure to NRTIs and that cells with centrosome amplification are able to accomplish cell division.

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.

Quantification of phase I/II metabolizing enzyme gene expression and polycyclic aromatic hydrocarbon-DNA adduct levels in human prostate

BACKGROUND

Studies of migrant populations suggest that dietary and/or environmental factors play a crucial role in the etiology of prostatic adenocarcinoma (CaP). The human prostate consists of the peripheral zone (PZ), transition zone (TZ), and central zone (CZ); CaP occurs most often in the PZ.

METHODS

To investigate the notion that an underlying differential expression of phase I/II genes, and/or the presence of polycyclic aromatic hydrocarbon (PAH)-DNA adducts might explain the elevated PZ susceptibility, we examined prostate tissues (matched tissue sets consisting of PZ and TZ) from men undergoing radical retropubic prostatectomy for CaP (n = 26) or cystoprostatectomy (n = 1). Quantitative gene expression analysis was employed for cytochrome P450 (CYP) isoforms CYP1A1, CYP1B1, and CYP1A2, as well as N-acetyltransferase 1 and 2 (NAT1 and NAT2) and catechol-O-methyl transferase (COMT).

RESULTS

CYP1B1, NAT1, and COMT were expressed in all tissue sets; levels of CYP1B1 and NAT1 were consistently higher in the PZ compared to TZ. Immunohistochemistry confirmed the presence of CYP1B1 (nuclear-associated and primarily in basal epithelial cells) and NAT1. Normal tissue from 23 of these aforementioned 27 matched tissue sets was analyzed for PAH-DNA adduct levels using antiserum elicited against DNA modified with r7,t8-dihydroxy-t-9,10-oxy-7,8,9,10-tetrahydro-benzo[a]pyrene (BPDE). PAH-DNA adduct levels were highest in glandular epithelial cells, but a comparison of PZ and TZ showed no significant differences.

CONCLUSION

Although expression of activating and/or detoxifying enzymes may be higher in the PZ, PAH-DNA adduct levels appear to be similar in both zones. Therefore, factors other than PAH-DNA adducts may be responsible for promotion of tumor formation in the human prostate.