DNA Adducts Research Articles

A High-Affinity and Selective DNA Aptamer for the N-Linked C8-Deoxyguanosine Adduct Produced by the Arylamine Carcinogen 4-Aminobiphenyl.

4-Aminobiphenyl (4-ABP) is a known human carcinogen that is implicated in the development of bladder cancers in smokers. The amine substituent undergoes bioactivation to generate nitrenium ions capable of covalently modifying DNA nucleobases. The primary adduct of 4-ABP, N-(deoxyguanosin-8-yl)-4-aminobiphenyl (dG-C8-ABP), is a bulky N-linked C8-dG adduct that serves as a biomarker for assessing the cancer risk associated with aromatic amine exposure. In this study, the capture-SELEX method was utilized to isolate DNA aptamers for dG-C8-ABP with high affinity and specificity. Using thioflavin T fluorescence spectroscopy and isothermal titration calorimetry, the parent aptamer PdG-1 has a Kd value below 100 nM and over 50-fold selectivity for dG-C8-ABP against competing analytes. A turn-on fluorescent sensor for dG-C8-ABP diagnostics, developed using a strand displacement assay, is also presented with a limit of detection of 68 nM. Our work represents the first selection of a DNA aptamer for a bulky DNA adduct produced by a known human carcinogen and sets the stage for the creation of ultrasensitive aptasensor platforms to meet the challenge of dG-C8-ABP detection in clinical settings.

Stir-fried Semen Armeniacae Amarum Suppresses Aristolochic Acid I-Induced Nephrotoxicity and DNA Adducts.

To investigate the protective effects of stir-fried Semen Armeniacae Amarum (SAA) against aristolochic acid I (AAI)-induced nephrotoxicity and DNA adducts and elucidate the underlying mechanism involved for ensuring the safe use of Asari Radix et Rhizoma. In vitro, HEK293T cells overexpressing Flag-tagged multidrug resistance-associated protein 3 (MRP3) were constructed by Lentiviral transduction, and inhibitory effect of top 10 common pairs of medicinal herbs with Asari Radix et Rhizoma in clinic on MRP3 activity was verified using a self-constructed fluorescence screening system. The mRNA, protein expressions, and enzyme activity levels of NAD(P)H quinone dehydrogenase 1 (NQO1) and cytochrome P450 1A2 (CYP1A2) were measured in differentiated HepaRG cells. Hepatocyte toxicity after inhibition of AAI metabolite transport was detected using cell counting kit-8 assay. In vivo, C57BL/6 mice were randomly divided into 5 groups according to a random number table, including: control (1% sodium bicarbonate), AAI (10 mg/kg), stir-fried SAA (1.75 g/kg) and AAI + stir-fried SAA (1.75 and 8.75 g/kg) groups, 6 mice in each group. After 7 days of continuous gavage administration, liver and kidney damages were assessed, and the protein expressions and enzyme activity of liver metabolic enzymes NQO1 and CYP1A2 were determined simultaneously. In vivo, combination of 1.75 g/kg SAA and 10 mg/kg AAI suppressed AAI-induced nephrotoxicity and reduced dA-ALI formation by 26.7%, and these detoxification effects in a dose-dependent manner (P<0.01). Mechanistically, SAA inhibited MRP3 transport in vitro, downregulated NQO1 expression in vivo, increased CYP1A2 expression and enzymatic activity in vitro and in vivo, respectively (P<0.05 or P<0.01). Notably, SAA also reduced AAI-induced hepatotoxicity throughout the detoxification process, as indicated by a 41.3% reduction in the number of liver adducts (P<0.01). Stir-fried SAA is a novel drug candidate for the suppression of AAI-induced liver and kidney damages. The protective mechanism may be closely related to the regulation of transporters and metabolic enzymes.

Wintering loons in South Korea face an ongoing threat from polycyclic aromatic hydrocarbons: Shifting sources and potential DNA damage.

Diving birds, particularly those sharing coastal habitats with fishing grounds, are at risk from oil pollution. Despite documented cases of bird mortality, the specific role of oil pollution in these death remains unclear. To address this knowledge gap, this study examined polycyclic aromatic hydrocarbon (PAH) contamination, its sources, and its impact on loon health. An analysis of 86 carcasses from three species of loons revealed drowning as the leading cause of death, followed by oil pollution and unknown debilitation. While liver concentrations of 16 PAHs (∑PAHs) showed no significant variation by sex, location, species, or cause of death, it was evident that wintering loons were exposed to PAH pollution along South Korea's eastern coast. The ratio of low (di- and tri-cyclic) to high (tetra-, penta-, and hexa-cyclic) molecular weight PAHs was approximately 3-5 across all three loon species. From 2010 to 2017, the composition of PAHs shifted, with a decline in low molecular weight PAHs (indicative of petrogenic sources) and a concerning increase in high molecular weight PAHs (associated with pyrogenic sources). This trend coincided with a tenfold increase in the toxic equivalency quotient of benzo[a]pyrene (TEQBaP), despite a decrease in overall ∑PAH concentrations. The detection of benzo[a]pyrene diol epoxide (BPDE)-DNA adducts in some loons further suggests potential genotoxic effects from PAH exposure. These findings underscore the persistent PAH contamination affecting wintering loons. Continued research is crucial to understand the evolving threats posed by PAHs and to support the conservation of these migratory birds along the North America-Asia flyway.

P-Phenylenediamines and their derived quinones: A review of their environmental fate, human exposure, and biological toxicity.

p-Phenylenediamines (PPDs) are widely used as antioxidants in numerous rubber products to prevent or delay oxidation and corrosion. However, their derived quinones (PPD-Qs), generated through reactions with ozone, are ubiquitous in the environment and raise significant health and toxicity concerns. This review summarizes the current state of knowledge on environmental distribution and fate, human exposure, and biological toxicity of PPDs and PPD-Qs, and makes recommendations for future research directions. Although PPDs and PPD-Qs have been monitored in a variety of environmental matrices, studies on soil, sediment, and organisms remain limited. This shortcoming hinders our understanding of their distribution patterns and migration mechanisms in these specific environments. These contaminants can enter the human body through various exposure routes, but toxicological studies have not yielded sufficient results to derive risk thresholds for the assessment of human health. Most studies examining biological and toxicological effects have focused on acute exposure scenarios, which do not accurately reflect the long-term interactions that occur in natural settings. The toxic effects of PPDs and PPD-Qs on zebrafish, nematodes, and mammals include neurobehavioral changes, reproductive dysfunction, and digestive damage, which are linked to mitochondrial stress, DNA adduct formation, and disrupted lipid metabolism, respectively. However, the underlying toxicological mechanisms remain poorly understood. Future research should prioritize the investigation of the impacts of PPDs and PPD-Qs on various organizational levels within biota to provide a scientific basis for developing effective risk management measures.

Impacts of amino acid-linked platinum(II) complexes on DNA structure.

The discovery of cisplatin (cisPt) as an effective anticancer agent was a milestone in the health industry. Despite its success, undesired side effects and acquired resistance still limit the therapeutic usefulness of cisPt. Intrastrand adduct formation at consecutive purines and structural modifications of DNA caused by platinum(II) complexes are important factors for antitumor efficacy. In this study, we examined amino acid-linked platinum(II) complexes, collectively referred to as AAPt, for antiproliferative activity and ability to induce DNA bending. The antiproliferative activity of one AAPt complex tested against a prostate cancer cell line was comparable to that of cisPt, whereas only activity of the AAPt complex was lower in a normal human prostate cell line. Various AAPt analogues were examined for impact on the structures of DNAs with four different purine dinucleotide target sites (GG, AG, GA, and AA) and compared to the parent cisPt. The roles of side-chain identity, chirality, and coordination type (e.g., (N,O) vs. (N,N)) of AAPt complexes are discussed with respect to DNA adduct formation and ability to induce DNA bending. Although the AAPt complexes display different nucleotide preferences (A for AAPt vs. G for cisPt), DNAs containing GG-platinum adducts display a greater degree of bending compared to DNAs with AA-platinum adducts.

Blood Trihalomethanes and Human Cancer: A Systematic Review and Meta-Analysis.

The control of waterborne diseases through water disinfection is a significant advancement in public health. However, the disinfection process generates disinfection by-products (DBPs), including trihalomethanes (THMs), which are considered to influence the occurrence of cancer. This analysis aims to quantitatively evaluate the relationship between blood concentrations of THMs and cancer. Additionally, the relationship between blood chloroform concentration and cancer is analyzed separately. Following PRISMA guidelines, we conducted a thorough search in the PubMed, Web of Science, and CNKI databases. Statistical analysis was performed using Review Manager 5.4 software. After screening, seven studies meeting the evaluation criteria were included. A total of 1027 blood samples from patients with cancer and 7351 blood samples from the control group were collected. The average concentration of THMs in the blood of the experimental group was 46.71 pg/mL, while it was 36.406 pg/mL in the control group. The difference between the two groups was statistically significant (SMD = -0.36, 95% CI: -0.45 to -0.27, p < 0.00001). However, due to the limited research data on the relationship between blood THMs and cancer, the conclusions drawn exhibit high heterogeneity. Additionally, we discussed the carcinogenic mechanisms of THMs, which involve multiple biological pathways such as oxidative stress, DNA adduct formation, and endocrine disruption, with variations in accumulation and target sites potentially leading to different cancer types, for which evidence is currently lacking. In the future, further epidemiological and animal model studies on THMs should be conducted to obtain more accurate conclusions.

Absorptivity Is an Important Determinant in the Toxicity Difference between Aristolochic Acid I and Aristolochic Acid II.

Inadvertent exposure to aristolochic acids (AAs) is causing chronic renal disease worldwide, with aristolochic acid I (AA-I) identified as the primary toxic agent. This study employed chemical methods to investigate the mechanisms underlying the nephrotoxicity and carcinogenicity of AA-I. Aristolochic acid II (AA-II), which has a structure similar to that of AA-I, was investigated with the same methods for comparison. Despite their structural similarities, findings from cultured human cells and gut sac experiments showed that AA-I is absorbed more effectively than AA-II (∼3 times greater for AA-I than for AA-II; p < 0.001). This increased absorption, along with the previously observed higher activity of reductive activation enzymes for AA-I, results in greater DNA damage and oxidative stress, both of which are key factors in AA-related toxicity. The similar patterns of cell mortality (34.4 ± 2.3% vs 9.7 ± 0.1% for AA-I and AA-II at 80 μM; p < 0.0001), DNA adduct formation (∼3 times greater for AA-I than for AA-II; p < 0.001), and oxidative stress levels in relation to the concentrations of AA-I and AA-II indicate that the higher absorption rate of AA-I is a significant contributor to its greater toxicity. The toxicity of AA-I was also found to be further enhanced by its (natural) coexistence with AA-II. Since AA-I and AA-II differ only by a methoxy group, future research on reducing risks associated with AA exposure should focus on strategies to lower the absorption of these compounds.

Investigating the origins of the mutational signatures in cancer.

Most of the risk factors associated with chronic and complex diseases, such as cancer, stem from exogenous and endogenous exposures experienced throughout an individual's life, collectively known as the exposome. These exposures can modify DNA, which can subsequently lead to the somatic mutations found in all normal and tumor tissues. Understanding the precise origins of specific somatic mutations has been challenging due to multitude of DNA adducts (i.e. the DNA adductome) and their diverse positions within the genome. Thus far, this limitation has prevented researchers from precisely linking exposures to DNA adducts and DNA adducts to subsequent mutational outcomes. Indeed, many common mutations observed in human cancers appear to originate from error-prone endogenous processes. Consequently, it remains unclear whether these mutations result from exposure-induced DNA adducts, orarise indirectly from endogenous processes or are a combination of both. In this review, we summarize approaches that aim to bridge our understanding of the mechanism by which exposure leads to DNA damage and then to mutation and highlight some of the remaining challenges and shortcomings to fully supporting this paradigm. We emphasize the need to integrate cellular DNA adductomics, long read-based mapping, single-molecule duplex sequencing of native DNA molecules and advanced computational analysis. This proposed holistic approach aims to unveil the causal connections between key DNA modifications and the mutational landscape, whether they originate from external exposures, internal processes or a combination of both, thereby addressing key questions in cancer biology.

Bracken Fern Carcinogen, Ptaquiloside, Forms a Guanine O6-Adduct in DNA.

Bracken fern (Pteridium sp.) is a viable and vigorous plant with invasive potential, ingestion of which causes chronic illness and cancers in farm animals. Bracken is a suspected human carcinogen, and exposure can result from ingestion of bracken-contaminated water, dairy products, or meat derived from livestock grazing on bracken fern. Bracken is also consumed in the diets of some communities. Ptaquiloside (PTQ), a known bracken carcinogen, is an illudane-type glycoside that forms a highly reactive electrophile, PTQ dienone, known to produce N7-guanine and N3-adenine adducts in DNA. Here, we demonstrate for the first time that PTQ dienone also produces an O6-alkylguanine (O6-PTBguanine) in DNA. Since O6-alkylguanines in DNA can be mutagenic, this work provides a potential mechanistic link between PTQ exposure and carcinogenicity. O6-PTBguanine is poorly repaired by O6-methylguanine-DNA methyltransferase that acts on other O6-alkylguanines, further highlighting the potential risk of exposure to bracken and PTQ.

Synthesis of N6-dA Damaged DNAs to Probe the Replication Ability of Human Translesion Polymerases.

The DNA adducts formed by the alkenylbenzene natural products, safrole (SF) and methyleugenol (MEG) are primarily attributed to their reported carcinogenic properties. Herein, we report a concise strategy to access N6-Ac-SF/MEG-dA phosphoramidites, which were selectively incorporated into DNA oligonucleotides by solid-phase DNA synthesis. The replication studies using human polymerases hpolκ and hpolη showed that both polymerases replicate these adducts error-free, which indicates that these polymerases do not contribute to the adduct-induced mutagenicity.

Aflatoxin B1-induced DNA adduct formation in murine kidney and liver.

Aflatoxicosis is a life-threatening nephrotoxic condition arising from eating foods highly contaminated with aflatoxin-producing molds. Additionally, chronic aflatoxin exposures are linked to enhanced hepatocellular carcinomas. Using recent advances in mass spectrometry for the detection of aflatoxin B1 (AFB1) DNA adducts, we present data which show generation of these adducts in the kidney, albeit at ≈ 100-fold lower levels than in the liver of the same animal. This result is consistent with tissue-specific differences in the expression of cytochrome P450s implicated in the activation of AFB1. Although the mechanisms underlying aflatoxin-induced nephrotoxicity had been postulated to be driven by the generation of high levels of reactive oxygen species, measurement of oxidatively-induced DNA base damage did not reveal evidence for genotoxic induction of these lesions. Overall, this investigation provides evidence of the formation of aflatoxin-specific adducts in kidney tissue and challenges the hypothesis of acute aflatoxin exposures generating reactive oxygen-mediated DNA damage.

Yatakemycin biosynthesis requires two deoxyribonucleases for toxin self-resistance.

The highly active natural product yatakemycin (YTM) from Streptomyces sp. TP-A0356 is a potent DNA damaging agent with antimicrobial and antitumor properties. The YTM biosynthesis gene cluster (ytk) contains several toxin self-resistance genes. Of these, ytkR2 encodes a DNA glycosylase that is important for YTM production and host survival by excising lethal YTM-adenine lesions from the genome, presumably initiating a base excision repair (BER) pathway. However, the genes involved in repair of the resulting apurinic/apyrimidinic (AP) site as the second BER step have not been identified. Here, we show that ytkR4 and ytkR5 are essential for YTM production and encode deoxyribonucleases related to other known DNA repair nucleases. Purified YtkR4 and YtkR5 exhibit AP endonuclease activity specific for YtkR2-generated AP sites, providing a basis for BER of the toxic AP intermediate produced from YTM-adenine excision and consistent with co-evolution of ytkR2, ytkR4, and ytkR5. YtkR4 and YtkR5 also exhibit 3'-5' exonuclease activity with differing substrate specificities. The YtkR5 exonuclease is capable of digesting through a YTM-DNA lesion and may represent an alternative repair mechanism to BER. We also show that ytkR4 and ytkR5 homologs are often clustered together in putative gene clusters related to natural product production, consistent with non-redundant roles in repair of other DNA adducts derived from genotoxic natural products.

AlkA Glycosylase and AlkB Dioxygenase Constitute an Effective Protective System for Endogenously Arising Acrolein: E. coli AlkA Glycosylase Excises Acrolein Adduct to Adenine.

Acrolein (ACR) is a ubiquitous environmental pollutant but also formed endogenously as a metabolite in oxidative stress conditions. Its adduct to adenine 1,N6-α-hydroxypropanoadenine (HPA) is a mutagenic lesion effectively repaired by the AlkB dioxygenase. Here, we provide in vivo, in vitro, and in silico evidence that it is also the substrate for the AlkA glycosylase. We studied the role of AlkA and AlkB in E. coli cells under conditions of induced adaptive response. Both alkA and alkB defective strains were not more sensitive to exogenous ACR than the wild type was. To simulate endogenously arising adducts, we used acrolein-modified plasmids, allowing monitoring of all kinds of substitutions originating from the acrolein modification of adenine. Both the AlkA and AlkB proteins were engaged in alleviating HPA-induced mutagenesis. Moreover, HPA was effectively repaired by AlkA and AlkB in vivo, even without induction of adaptive response. These findings suggest that the main contribution to acrolein mutagenicity comes from its endogenous sources, whereas AlkA and AlkB can play an additional role in controlling the level of DNA adducts of endogenous origin. Acrolein does not induce the adaptive response. HPA contains an asymmetric carbon atom in the hydroxypropano ring and exists as two stereoisomers. AlkA excises both of them in vitro. Molecular modelling demonstrated how dsDNA carrying both HPA stereoisomers could be properly bound at the AlkA catalytic centre. So, in contrast to the reaction catalyzed by AlkB, the HPA repair by AlkA is not expected to be stereoselective.

Novel factors of cisplatin resistance in epithelial ovarian tumours.

Ovarian tumours are these days one of the biggest oncogynecological problems. In addition to surgery, the treatment of ovarian cancer includes also chemotherapy in which platinum preparations are one of the most used chemotherapeutic drugs. The principle of antineoplastic effects of cisplatin (cis-diamminedichloroplatinum(II), CDDP) is its binding to the DNA and the formation of adducts. While DNA adducts induce the process of apoptosis, or inhibit the process of DNA replication, which prevents further division of tumour cells, various molecular mechanisms can reverse this process. On the other hand, with increasing scientific knowledge, it is becoming clearer that chemotherapy resistance is a very complex process. In this regard, factors and the amount of their expression may regulate the effect of resistance to chemotherapy. This review focuses on new molecular mechanisms and factors such as mitochondrial dynamics, epithelial-mesenchymal transition (EMT), cluster of differentiation, exosomes and others, that could be involved in the emergence of CDDP resistance.

Genotoxic effects of NDMA-contaminated ranitidine on Allium cepa cells and unveiling carcinogenic mechanisms via DFT and molecular dynamics simulation study

This study investigated the potential genotoxic and carcinogenic effects of N-nitrosodimethylamine (NDMA), a hazardous compound found in ranitidine formulations that are used to treat excessive stomach acid. The study first examined the effects of NDMA-contaminated ranitidine formulation on Allium cepa root growth and mitotic activity. The results demonstrated dose-dependent decreases in both root growth and mitotic index indicating genotoxicity and cell division disruption. Elevated concentrations of ranitidine correlated with increased chromosomal aberrations indicating genotoxic capabilities. These outcomes underscored that NDMA contaminated ranitidine exposure triggers genotoxicity hampering cell division and inducing chromosomal aberrations. Electronic characteristics of NDMA revealed its electrophilic nature suggesting its capability to create covalent adducts with DNA bases fostering genotoxic and carcinogenic characteristics. Molecular docking analysis showed the interactions of NDMA with DNA including hydrogen bonds and carbon-hydrogen interactions with nucleotide bases forming DNA adducts. Molecular dynamics simulations showcased the dynamic behavior of the DNA-NDMA complex over time with structural fluctuations. Dynamic hydrogen bond fluctuations implied interactive intricacies between solute and solvent molecules. Overall, this study illuminates how NDMA-contaminated ranitidine could trigger DNA damage and potentially contribute to carcinogenesis. It emphasizes the urgency of minimizing exposure to this perilous and hazardous compound.

Multiple DNA repair pathways prevent acetaldehyde-induced mutagenesis in yeast.

Acetaldehyde is the primary metabolite of alcohol and is present in many environmental sources including tobacco smoke. Acetaldehyde is genotoxic, whereby it can form DNA adducts and lead to mutagenesis. Individuals with defects in acetaldehyde clearance pathways have increased susceptibility to alcohol-associated cancers. Moreover, a mutation signature specific to acetaldehyde exposure is widespread in alcohol and smoking-associated cancers. However, the pathways that repair acetaldehyde-induced DNA damage and thus prevent mutagenesis are vaguely understood. Here, we used Saccharomyces cerevisiae to delete genes in each of the major DNA repair pathways to identify those that alter acetaldehyde-induced mutagenesis. We observed that loss of functional nucleotide excision repair (NER) had the largest effect on acetaldehyde mutagenesis. In addition, base excision repair (BER), as well as DNA protein crosslink (DPC) repair pathways were involved in modulating acetaldehyde mutagenesis, while mismatch repair (MMR), homologous recombination (HR) and post replication repair are dispensable for acetaldehyde mutagenesis. Acetaldehyde-induced mutations in an NER-deficient (Δrad1) background were dependent on translesion synthesis as well as DNA inter-strand crosslink (ICL) repair. Moreover, whole genome sequencing of the mutated isolates demonstrated an increase in C→A changes coupled with an enrichment of gCn→A changes which is diagnostic of acetaldehyde exposure in yeast and in human cancers. Finally, downregulation of the leading strand replicative polymerase Pol epsilon, but not the lagging strand polymerase, resulted in increased acetaldehyde mutagenesis, indicating that lesions are likely formed on the leading strand. Our findings demonstrate that multiple DNA repair pathways coordinate to prevent acetaldehyde-induced mutagenesis.

Repair of Retrorsine-Induced DNA Damage in Rat Livers: Insights Gained from Transcriptomic and Proteomic Studies.

Pyrrolizidine alkaloids (PAs) are common phytotoxins that are found worldwide. Upon hepatic metabolic activation, the reactive PA metabolites covalently bind to DNAs and form DNA adducts, causing mutagenicity and tumorigenicity in the liver. However, the molecular basis of the formation and removal of PA-derived DNA adducts remains largely unexplored. In the present study, Sprague Dawley (SD) rats were exposed to retrorsine (RTS), a representative PA, at a human-relevant dose of 3.3 mg/kg/day for 28 days. The rats were divided into three groups: control, RTS-28 (sacrificed after continuous RTS exposure), and RTS-161 (sacrificed at 133 days post-RTS-exposure). The multi-omics analyses demonstrated the involvement of homologous recombination (HR) and non-homologous end joining (NHEJ) repair pathways as a response to PA-induced DNA damage. Additionally, the characteristic guanine adducts induced by RTS exposure were in accordance with the higher expression of XPA and XPC, indicating that nucleotide excision repair (NER) and base excision repair (BER) also contributed to repairing RTS-induced DNA damage. Furthermore, we also showed that DNA damage persisted after PA exposure, and mutagenically related repair errors might occur due to the prolonged genotoxic effects. The present study lays the foundation for bridging PA-derived DNA adducts, DNA damage, DNA repair, and the follow-up mutagenesis and carcinogenesis associated with PA exposure.

Sulphotransferase-mediated toxification of chemicals in mouse models: effect of knockout or humanisation of SULT genes.

Cytosolic sulphotransferase (SULT) enzymes catalyse reactions involved in xenobiotic elimination and hormone regulation. However, SULTs can also generate electrophilic reactive intermediates from certain substrates, including the activation of carcinogens. Here, we review toxicological studies of mouse strains with SULT status altered by genetic modification. Knockout mouse strains have been constructed for the enzymes Sult1a1, 1d1, 1e1, 2b1 and 4a1. In addition, transgenic strains are available for human SULT1A1/2. Among SULT knockout mouse strains, reduced fertility (Sult1e1) and early postnatal death (Sult4a1) were observed. In contrast, Sult1a1 or Sult1d1 knockouts and SULT1A1/2 transgenics were healthy and showed no obvious deficiencies. These strains were used in toxicological studies with 13 chemicals. Manipulation of the SULT system altered dramatically the adverse effects of many compounds; thus, very large differences in levels of DNA adducts formed in the liver or other tissues were seen with some chemicals - up to 99.2% decreases in knockouts and 83-fold increases in SULT1A1/2 transgenics. In many cases, these changes were restricted to the tissues in which the corresponding enzymes are expressed, arguing for local activation. However, with some compounds, the kidney was an important target tissue, due to the active transfer to that organ, via the circulation, of reactive sulphuric acid esters.

Transcription factors, nucleotide excision repair, and cancer: A review of molecular interplay.

Bulky DNA adducts are mostly formed by external factors such as UV irradiation, smoking or treatment with DNA crosslinking agents. If such DNA adducts are not removed by nucleotide excision repair, they can lead to formation of driver mutations that contribute to cancer formation. Transcription factors (TFs) may critically affect both DNA adduct formation and repair efficiency at the binding site to DNA. For example, "hotspot" mutations in melanoma coincide with UV-induced accumulated cyclobutane pyrimidine dimer (CPD) adducts and/or inhibited repair at the binding sites of some TFs. Similarly, anticancer treatment with DNA cross-linkers may additionally generate DNA adducts leading to secondary mutations and the formation of malignant subclones. In addition, some TFs are overexpressed in response to UV irradiation or chemotherapeutic treatment, activating oncogenic and anti-oncogenic pathways independently of nucleotide excision repair itself. This review focuses on the interplay between TFs and nucleotide excision repair during cancer development and progression.

Genome-modified Caenorhabditis elegans expressing the human cytochrome P450 (CYP1A1 and CYP1A2) pathway: An experimental model for environmental carcinogenesis and pharmacological research.

Polycyclic aromatic hydrocarbons (PAHs), including the Group 1 human carcinogen benzo[a]pyrene (BaP), are produced by the incomplete combustion of organic matter and thus are present in tobacco smoke, charbroiled food and diesel exhaust. The nematode Caenorhabditis elegans is an established model organism, however it lacks the genetic components of the classical mammalian cytochrome P450 (CYP)-mediated BaP-diol-epoxide metabolism pathway. We therefore introduced human CYP1A1 or CYP1A2 together with human epoxide hydrolase (EPHX) into the worm genome by Mos1-mediated Single Copy Insertion (MosSCI) and evaluated their response to BaP exposure via toxicological endpoints. Compared to wild-type control, CYP-humanised worms were characterised by an increase in pharyngeal pumping rate and a decrease in volumetric surface area. Furthermore, BaP exposure reduced reproductive performance, as reflected in smaller brood size, which coincided with the downregulation of the nematode-specific major sperm protein as determined by transcriptomics (RNAseq). BaP-mediated reproductive toxicity was exacerbated in CYP-humanised worms at higher exposure levels. Collagen-related genes were downregulated in BaP-exposed animals, which correlate with the reduction in volumetric size. Whole genome DNA sequencing revealed a higher frequency of T>G (A>C) base substitution mutations in worms expressing human CYP1A1;EPHX which aligned with an increase in DNA adducts identified via an ELISA method (but not classical 32P-postlabelling). Overall, the CYP-humanised worms provided new insights into the value of genome-optimised invertebrate models by identifying the benefits and limitations within the context of the (3Rs) concept which aims to replace, reduce and refine the use of animals in research.