Mutational hotspot in the p53 gene in human hepatocellular carcinomas

Establishment of a prognostic model for predicting short-term disease-free survival in cases of hepatitis B-related hepatocellular carcinoma with the TP53 249Ser mutation in southern China

Background

Hepatitis B virus (HBV) infection and dietary aflatoxin exposure are two major and synergistic carcinogenic factors of hepatocellular carcinoma (HCC) in southern China. Mutation of the TP53 gene at codon 249 (TP53 249Ser) is recognized as a fingerprint of aflatoxin B1 (AFB1) exposure.

Methods

A total of 485 HCC patients positive for serum hepatitis B surface antigen were enrolled. The clinicopathological information and survival time were collected. TP53 249Ser mutations in HCC were detected by Sanger DNA sequencing after PCR amplification. Immunohistochemical staining was used to evaluate TP53 expression. Propensity score matching (PSM) and Cox proportional hazards regression (CPHR) were conducted to identify independent risk factors for prognosis that were incorporated into the nomogram. Univariate logistic regression analysis was used to compare differences in clinical factors between the TP53 249Ser mutation group and the non-mutation group. A Kaplan-Meier plot, univariate and multivariate Cox proportional hazards models were used to assess the association between clinicopathological characteristics and survival outcomes.

Results

After PSM, a total of 322 cases were included in the analysis of clinical prognosis. Results of CPHR showed that the mutation group had a relatively higher risk of tumor recurrence within 2 years after undergoing hepatectomy (P=0.039, HR =1.47, 95% CI: 1.02–2.18). The prognostic model performed better in terms of 2-year DFS prediction than BCLC stage. Patients who had a nomogram score of more than 160 were considered to have a higher risk of recurrence within 2 years.

Conclusions

Our study found that the TP53 249Ser mutation may be a high risk factor of HBV-related HCC recurrence in the short term. And we initially established a nomogram scoring system for predicting 2-year recurrence in HBV-related HCC patients in southern China.

The Inhibitory Effect of Validamycin A on Aspergillus flavus

Aspergillus flavus is one of the most common isolates from patients with fungal infections. Aspergillus infection is usually treated with antifungal agents, but side effects of these agents are common. Trehalase is an essential enzyme involved in fungal metabolism, and the trehalase inhibitor, validamycin A, has been used to prevent fungal infections in agricultural products. In this study, we observed that validamycin A significantly increased trehalose levels in A. flavus conidia and delayed germination, including decreased fungal adherence. In addition, validamycin A and amphotericin B showed a combinatorial effect on A. flavus ATCC204304 and clinical isolates with high minimum inhibitory concentrations (MICs) of amphotericin B using checkerboard assays. We observed that validamycin A and amphotericin B had a synergistic effect on A. flavus strains resistant to amphotericin B. The MICs in the combination of validamycin A and amphotericin B were at 0.125 μg/mL and 2 μg/mL, respectively. The FICI of validamycin A and amphotericin B of these clinical isolates was about 0.25-0.28 with synergistic effects. No drug cytotoxicity was observed in human bronchial epithelial cells treated with validamycin A using LDH-cytotoxicity assays. In conclusion, this study demonstrated that validamycin A inhibited the growth of A. flavus and delayed conidial germination. Furthermore, the combined effect of validamycin A with amphotericin B increased A. flavus killing, without significant cytotoxicity to human bronchial epithelial cells. We propose that validamycin A could potentially be used in vivo as an alternative treatment for A. flavus infections.

Biochemical and molecular aspects of 1,2-dimethylhydrazine (DMH)-induced colon carcinogenesis: a review

1,2-dimethylhydrazine (DMH) is a member in the class of hydrazines, strong DNA alkylating agent, naturally present in cycads. DMH is widely used as a carcinogen to induce colon cancer in animal models. Exploration of DMH-induced colon carcinogenesis in rodent models provides the knowledge to perceive the biochemical, molecular, and histological mechanisms of different stages of colon carcinogenesis. The procarcinogen DMH, after a series of metabolic reactions, finally reaches the colon, there produces the ultimate carcinogen and reactive oxygen species (ROS), which further alkylate the DNA and initiate the development of colon carcinogenesis. The preneolpastic lesions and histopathological observations of DMH-induced colon tumors may provide typical understanding about the disease in rodents and humans. In addition, this review discusses about the action of biotransformation and antioxidant enzymes involved in DMH intoxication. This understanding is essential to accurately identify and interpret alterations that occur in the colonic mucosa when evaluating natural or pharmacological compounds in DMH-induced animal colon carcinogenesis.

Epidemiology and surveillance for hepatocellular carcinoma: New trends

The burden of hepatocellular carcinoma (HCC) is highest in East Asia and Africa, although its incidence and mortality are rapidly rising in the United States and Europe. With the implementation of hepatitis B vaccination and hepatitis C treatment programmes worldwide, the epidemiology of HCC is shifting away from a disease predominated by viral hepatitis - an increasing proportion of cases are now attributable to non-alcoholic steatohepatitis. Surveillance using ultrasound, with or without alpha-fetoprotein, every 6 months has been associated with improved early detection and improved overall survival; however, limitations in implementation lead to a high proportion of HCC being detected at late stages in clinical practice. Herein, we review the current state of HCC surveillance and highlight areas for future research, including improved risk stratification of at-risk patients, surveillance tools with higher sensitivity and specificity for early HCC, and interventions to increase surveillance utilisation.

Molecular Analysis of Mutations in the Human HPRT Gene

The HPRT assay uses incorporation of toxic nucleotide analogues to select for cells lacking the purine scavenger enzyme hypoxanthine-guanine phosphoribosyl transferase. A major advantage of this assay is the ability to isolate mutant cells and determine the molecular basis for their functional deficiency. Many types of analyses have been performed at this locus: the current protocol involves generation of a cDNA and multiplex PCR of each exon, including the intron/exon junctions, followed by direct sequencing of the products. This analysis detects point mutations, small deletions and insertions within the gene, mutations affecting RNA splicing, and the products of illegitimate V(D)J recombination within the gene. Establishment of and comparisons with mutational spectra hold the promise of identifying exposures to mutation-inducing genotoxicants from their distinctive pattern of gene-specific DNA damage at this easily analyzed reporter gene.

Overexpression of p62/IMP2 can Promote Cell Migration in Hepatocellular Carcinoma via Activation of the Wnt/β-Catenin Pathway

p62/IMP2 is an oncofetal protein that was first reported as a tumor-associated antigen in hepatocellular carcinoma (HCC). In our previous studies, we demonstrated a high frequency of p62/IMP2 autoantibodies appearing in various types of cancer. Therefore, we hypothesize that p62/IMP2 plays an important role in the progression of HCC, although the mechanism remains to be explored. In this study, we evaluated the expression of p62/IMP2 protein both in human tissues and liver cancer cell lines by immunohistochemistry and western blotting analysis and found that p62/IMP2 protein is overexpressed in human HCC tissue in comparison to normal human liver tissue. To explore the role that p62/IMP2 plays in HCC, p62/IMP2 was knocked out in two p62/IMP2-positive liver cancer cell lines (SNU449 and HepG2). Due to the low expression level of p62/IMP2 in SNU449, we overexpressed p62/IMP2 in this cell line. We subsequently demonstrated that high expression of p62/IMP2 in both cell lines can promote cell migration and invasion abilities in vitro by activating the Wnt/β-catenin pathway. We also used the Wnt/β-catenin pathway inhibitor, XAV 939, and a phosphoproteome assay to confirm our findings. Conclusion: Our results suggest that p62/IMP2 is an essential regulator of Wnt signaling pathways and plays an important role in HCC progression and metastasis.

Identifying Hepatocellular Carcinoma Driver Genes by Integrative Pathway Crosstalk and Protein Interaction Network

In this study, we mined out hepatocellular carcinoma (HCC) driver genes from MEDLINE literatures by bioinformatics methods of pathway crosstalk and protein interaction network. Furthermore, the relationship between driver genes and their clinicopathological characteristics, as well as classification effectiveness was verified in the public databases. We identified 560 human genes reported to be associated with HCC in 1074 published articles. Functional analysis revealed that biological processes and biochemical pathways relating to tumor pathogenesis, cancer disease, tumor cell molecule, and hepatic disease were enriched in these genes. Pathway crosstalk analysis indicated that significant pathways could be divided into three modules: cancer disease, virus infection, and tumor signaling pathway. The HCC-related protein-protein interaction network comprised 10,212 nodes, and 56,400 edges were mined out to identify 18 modules corresponding to 14 driver genes. We verified that these 14 driver genes have high classification effectiveness to distinguish cancer samples from normal samples and the classification effectiveness was better than that of randomly selected genes. Present study provided pathway crosstalk and protein interaction network for understanding potential tumorigenesis genes underlying HCC. The 14 driver genes identified from this study are of great translational value in HCC diagnosis and treatment, as well as in clinical study on the pathogenesis of HCC.

Achievements in Cancer Research and its Therapeutics in Hundred Years

Cancer research has progressed leaps and bounds over the years. This review is a brief overview of the cancer research, milestone achievements and therapeutic studies on it over the one hundred ten years which would give us an insight into how far we have come to understand and combat this fatal disease leading to millions of deaths worldwide. Modern biology has proved that cancer is a very complex disease as still we do not know precisely how it triggers. It involves several factors such as protooncogene, oncogene, kinase, tumor suppressor gene, growth factor, signalling cascade, micro RNA, immunity, environmental factors and carcinogens. However, modern technology now helps the cancer patient on the basis of acquired and established knowledge in the last hundred years to save human lives.

Analysis of TP53 gene in uterine myomas: No mutations but P72R polymorphism is associated with myoma development

AIM

The aim of the present study was to investigate the familial and somatic mutations as well as polymorphisms of TP53 gene in patients with uterine leiomyoma.

METHODS

The study included 35 women with histologically diagnosed as uterine leiomyomas at the Gynecology Department of Adnan Menderes University Faculty of Medicine. Tissue and blood samples were analyzed for mutations and polymorphisms of TP53 gene by next generation sequencing (Miseq-Illumina). Acquired data was compared with the normal data in Ensembl database. Data from 1000 genome project and data from exome sequencing analyses in Intergen Genetic Diagnosis Center (Ankara) were used as controls for polymorphism analyses.

RESULTS

There were no mutations in tissue and blood samples. However, when the polymorphisms were evaluated, a significant difference was found in NM_000546.5(TP53):c.215C > G (p.Pro72Arg) polymorphism between the study and control groups. The results indicated that P72R/P72R genotype increased the risk of leiomyoma development by 6.3 fold (95% confidence interval [CI]: 2.880-13.793). There was a negative correlation between P72R/WT genotype and leiomyoma development (OR = 0.261, 95% CI: 0.114-0.596). P72R/P72R genotype was statistically higher in the patients with leiomyoma compared with the controls and 1000 genomes from Asian, European and World populations.

CONCLUSION

The results of the present study suggested that P72R/P72R genotype may be associated with development of uterine leiomyoma in the Turkish population in the Western part of the country.

p53-Mediated PI3K/AKT/mTOR Pathway Played a Role in PtoxDpt-Induced EMT Inhibition in Liver Cancer Cell Lines

Epithelial-mesenchymal transition (EMT) involves metastasis and drug resistance; thus, a new EMT reversing agent is required. It has shown that wild-type p53 can reverse EMT back to epithelial characteristics, and iron chelator acting as a p53 inducer has been demonstrated. Moreover, recent study revealed that etoposide could also inhibit EMT. Therefore, combination of etoposide with iron chelator might achieve better inhibition of EMT. To this end, we prepared di-2-pyridineketone hydrazone dithiocarbamate S-propionate podophyllotoxin ester (Ptox^Dpt) that combined the podophyllotoxin (Ptox) structural unit (etoposide) with the dithiocarbamate unit (iron chelator) through the hybridization strategy. The resulting Ptox^Dpt inherited characteristics from parent structural units, acting as both the p53 inducer and topoisomerase II inhibitor. In addition, the Ptox^Dpt exhibited significant inhibition in migration and invasion, which correlated with downregulation of matrix metalloproteinase (MMP). More importantly, Ptox^Dpt could inhibit EMT in the absence or presence of TGF-β1, concomitant to the ROS production, and the additional evidence revealed that Ptox^Dpt downregulated AKT/mTOR through upregulation of p53, indicating that Ptox^Dpt induced EMT inhibition through the p53/PI3K/AKT/mTOR pathway.

Mechanisms underlying aflatoxin-associated mutagenesis - Implications in carcinogenesis

Chronic dietary exposure to aflatoxin B1 (AFB1), concomitant with hepatitis B infection is associated with a significant increased risk for hepatocellular carcinomas (HCCs) in people living in Southeast Asia and sub-Saharan Africa. Human exposures to AFB1 occur through the consumption of foods that are contaminated with pervasive molds, including Aspergillus flavus. Even though dietary exposures to aflatoxins constitute the second largest global environmental risk factor for cancer development, there are still significant questions concerning the molecular mechanisms driving carcinogenesis and what factors may modulate an individual's risk for HCC. The objective of this review is to summarize key discoveries that established the association of chronic inflammation (most commonly associated with hepatitis B viral (HBV) infection) and environmental exposures to aflatoxin with increased HCC risk. Special emphasis will be given to recent investigations that have: 1) refined the aflatoxin-associated mutagenic signature, 2) expanded the DNA repair mechanisms that limit mutagenesis via adduct removal prior to replication-induced mutagenesis, 3) implicated a specific DNA polymerase in the error-prone bypass and resulting mutagenesis, and 4) identified human polymorphic variants that may modulate individual susceptibility to aflatoxin-induced cancers. Collectively, these investigations revealed that specific sequence contexts are differentially resistant against, or prone to, aflatoxin-induced mutagenesis and that these associations are remarkably similar between in vitro and in vivo analyses. These recent investigations also established DNA polymerase ζ as the major polymerase that confers the G to T transversion signature. Additionally, although the nucleotide excision repair (NER) pathway has been previously shown to repair aflatoxin-induced DNA adducts, recent murine data demonstrated that NEIL1-initiated base excision repair was significantly more important than NER relative to the removal of the highly mutagenic AFB1-Fapy-dG adducts. These data suggest that inactivating polymorphic variants of NEIL1 could be a potential driver of HCCs in aflatoxin-exposed populations.

It takes a team: a gain-of-function story of p53-R249S

Gain-of-function (GOF), the most malicious oncogenic activity of a cancer-promoting protein, is well illustrated to three hotspot p53 mutations at R248, R175, and R273 with distinct molecular mechanisms. Yet, less is known about another hotspot p53 mutant, R249S (p53-R249S). p53-R249S is the sole hotspot mutation in hepatocellular carcinoma (HCC) that is highly associated with chronic hepatitis B virus (HBV) infection and dietary exposure to aflatoxin B1 (AFB1). Its GOF is suggested by the facts that this mutant is associated with earlier onset of HCC and poorer prognosis of cancer patients and that its overexpression drives HCC proliferation and tumorigenesis. By contrast, simply knocking in this mutant in normal mice did not show apparent GOF activity. Hence, the GOF activity for p53-R249S and its underlying mechanisms have been elusive until recent findings offered some new insights. This review will discuss these findings as well as their clinical significance and implications for the development of a strategy to target multiple molecules as a therapy for p53-R249S-harboring HCC.

tRNA modification and cancer: potential for therapeutic prevention and intervention

Transfer RNAs (tRNAs) undergo extensive chemical modification within cells through the activity of tRNA methyltransferase enzymes (TRMs). Although tRNA modifications are dynamic, how they impact cell behavior after stress and during tumorigenesis is not well understood. This review discusses how tRNA modifications influence the translation of codon-biased transcripts involved in responses to oxidative stress. We further discuss emerging mechanistic details about how aberrant TRM activity in cancer cells can direct programs of codon-biased translation that drive cancer cell phenotypes. The studies reviewed here predict future preventative therapies aimed at augmenting TRM activity in individuals at risk for cancer due to exposure. They further predict that attenuating TRM-dependent translation in cancer cells may limit disease progression while leaving noncancerous cells unharmed.

Mutation profiling in the PIK3CA, TP53, and CDKN2A genes in circulating free DNA and impalpable breast lesions

Breast impalpable lesions have become a clinical dilemma because they are small, presenting a heterogeneous cellular phenotype. The aim of this study was to evaluate the mutational profile of the PIK3CA, TP53, and CDKN2A genes, comparing the mammary tissue with the respective circulating free DNA (cfDNA). The PIK3CA, TP53, and CDKN2A genes were sequenced (PCR-Sanger) in 58 women with impalpable lesions (49 malignant and 9 benign) with the respective cfDNA. The chi-square or Fisher's exact test was used to evaluate statistical significance between the clinical variables and mutational profile. A total of 51 out of 58 samples generated successful mutation profiles in both breast lesion and cfDNA. Of the 37 mutations detected, 10 (27%) and 16 (43%) mutations were detected in benign and malignant breast lesions, respectively, while 2 (5%) and 9 (24%) were found in cfDNA of women with benign and malignant lesions, respectively. The lymph node involvement with mutations in the PIK3CA in malignant lesions (P = 0.001), and the relationship between mutations in PIK3CA, comparing ductal tumors with benign lesions (P = 0.05), were statistically significant. This study detected different mutations in PIK3CA, TP53, and CDKN2A genes, which represent, in part, the heterogeneity of impalpable lesions. The results confirm that more studies should be conducted on the functional role of cfDNA in the impalpable lesions.

Aflatoxin B₁⁻Formamidopyrimidine DNA Adducts: Relationships between Structures, Free Energies, and Melting Temperatures

Thermal stabilities of DNA duplexes containing Gua (g), α- (a) or β-anomer of formamidopyrimidine-N7-9-hydroxy-aflatoxin B₁ (b) differ markedly (T_m: a<g<b), but the underlying molecular origin of this experimentally observed phenomenon is yet to be identified and determined. Here, by employing explicit-solvent molecular dynamics simulations coupled with free-energy calculations using a combined linear-interaction-energy/linear-response-approximation approach, we explain the quantitative differences in Tm in terms of three structural features (bulkiness, order, and compactness) and three energetical contributions (non-polar, electrostatic, and preorganized-electrostatic), and thus advance the current understanding of the relationships between structures, free energies, and thermal stabilities of DNA double helices.

Genomic Medicine and Implications for Hepatocellular Carcinoma Prevention and Therapy

The pathogenesis of hepatocellular carcinoma (HCC) is poorly understood, but recent advances in genomics have increased our understanding of the mechanisms by which hepatitis B virus, hepatitis C virus, alcohol, fatty liver disease, and other environmental factors, such as aflatoxin, cause liver cancer. Genetic analyses of liver tissues from patients have provided important information about tumor initiation and progression. Findings from these studies can potentially be used to individualize the management of HCC. In addition to sorafenib, other multi-kinase inhibitors have been approved recently for treatment of HCC, and the preliminary success of immunotherapy has raised hopes. Continued progress in genomic medicine could improve classification of HCCs based on their molecular features and lead to new treatments for patients with liver cancer.

Aflatoxin-Guanine DNA Adducts and Oxidatively Induced DNA Damage in Aflatoxin-Treated Mice in Vivo as Measured by Liquid Chromatography-Tandem Mass Spectrometry with Isotope Dilution

Dietary exposure to aflatoxin B₁ (AFB₁) is a significant contributor to the incidence of hepatocellular carcinomas globally. AFB₁ exposure leads to the formation of AFB₁-N⁷-guanine (AFB₁-N⁷-Gua) and two diastereomers of the imidazole ring-opened 8,9-dihydro-8-(2,6-diamino-4-oxo-3,4-dihydropyrimid-5-yl-formamido)-9-hydroxyaflatoxin B₁ (AFB₁-FapyGua) in DNA. These adducts lead to G → T transversion mutations with the ring-opened adduct being more mutagenic than the cationic species. Accurate measurement of these three adducts as biomarkers in DNA and urine will help identify dietary exposure to AFB₁ as a risk factor in the development of hepatocellular carcinoma worldwide. Herein, we report an improved methodology for the measurement of AFB₁-N⁷-Gua and the two diastereomers of AFB₁-FapyGua using liquid chromatography-tandem mass spectrometry with isotope dilution. We measured the levels of these compounds in liver DNA of six control mice and six AFB₁-treated mice. Levels varying from 1.5 to 45 lesions/10⁶ DNA bases in AFB₁-treated mice were detected depending on the compound and animal. No background levels of these adducts were detected in control mice. We also tested whether the AFB₁ treatment caused oxidatively induced DNA base damage using gas chromatography-tandem mass spectrometry with isotope dilution. Although background levels of several pyrimidine- and purine-derived lesions were detected, no increases in these levels were found upon AFB₁ treatment of mice. On the other hand, significantly increased levels of (5' R)- and (5' S)-8,5'-cyclo-2'-deoxyadenosines were observed in liver DNA of AFB₁-treated mice. The impact of this work is expected to achieve the accurate measurement of three AFB₁-DNA adducts and oxidatively induced DNA lesions as biomarkers of AFB₁ exposure as germane to investigations designed for the prevention of aflatoxin-related hepatocellular carcinomas and for determining the effects of genetic deficiencies in human populations.

Processing of N5-substituted formamidopyrimidine DNA adducts by DNA glycosylases NEIL1 and NEIL3

A variety of agents cause DNA base alkylation damage, including the known hepatocarcinogen aflatoxin B₁ (AFB₁) and chemotherapeutic drugs derived from nitrogen mustard (NM). The N7 site of guanine is the primary site of alkylation, with some N7-deoxyguanosine adducts undergoing imidazole ring-opening to stable mutagenic N⁵-alkyl formamidopyrimidine (Fapy-dG) adducts. These adducts exist as a mixture of canonical β- and unnatural α-anomeric forms. The β species are predominant in double-stranded (ds) DNA. Recently, we have demonstrated that the DNA glycosylase NEIL1 can initiate repair of AFB₁-Fapy-dG adducts both in vitro and in vivo, with Neil1^-/- mice showing an increased susceptibility to AFB₁-induced hepatocellular carcinoma. Here, we hypothesized that NEIL1 could excise NM-Fapy-dG and that NEIL3, a closely related DNA glycosylase, could excise both NM-Fapy-dG and AFB₁-Fapy-dG. Product formation from the reaction of human NEIL1 with ds oligodeoxynucleotides containing a unique NM-Fapy-dG followed a bi-component exponential function under single turnover conditions. Thus, two adduct conformations were differentially recognized by hNEIL1. The excision rate of the major form (∼13.0 min^-1), presumed to be the β-anomer, was significantly higher than that previously reported for 5-hydroxycytosine, 5-hydroxyuracil, thymine glycol (Tg), and AFB₁-Fapy-dG. Product generation from the minor form was much slower (∼0.4 min^-1), likely reflecting the rate of conversion of the α anomer into the β anomer. Mus musculus NEIL3 (MmuNEIL3Δ324) excised NM-Fapy-dG from single-stranded (ss) DNA (turnover rate of ∼0.4 min^-1), but not from ds DNA. Product formation from ss substrate was incomplete, presumably because of a substantial presence of the α anomer. MmuNEIL3Δ324 could not initiate repair of AFB₁-Fapy-dG in either ds or ss DNA. Overall, the data suggest that both NEIL1 and NEIL3 may protect cells against cytotoxic and mutagenic effects of NM-Fapy-dG, but NEIL1 may have a unique role in initiation of base excision repair of AFB₁-Fapy-dG.

Mutational processes shape the landscape of TP53 mutations in human cancer

Unlike most tumor suppressor genes, the most common genetic alterations in TP53 are missense mutations^1,2. Mutant p53 protein is often abundantly expressed in cancers, and specific allelic variants exhibit dominant-negative or gain-of-function activities in experimental models^3–8. To gain a systematic view of p53 function, we interrogated loss-of-function screens conducted in hundreds of human cancer cell lines and performed TP53 saturation mutagenesis screens in an isogenic pair of TP53-wild-type and -null cell lines. We found that loss or dominant-negative inhibition of p53 function reliably enhanced cellular fitness. By integrating these data with the COSMIC mutational signatures database^9,10, we developed a statistical model that describes the TP53 mutational spectrum as a function of the baseline probability of acquiring each mutation and the fitness advantage conferred by attenuation of p53 activity. Collectively, these observations show that widely-acting and tissue-specific mutational processes combine with phenotypic selection to dictate the frequencies of recurrent TP53 mutations.

N6-(2-Deoxy-d- erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-(2-hydroxy-3-buten-1-yl)-formamidopyrimidine Adducts of 1,3-Butadiene: Synthesis, Structural Identification, and Detection in Human Cells

1,3-Butadiene (BD) is an environmental and occupational toxicant classified as a human carcinogen. BD is metabolically activated by cytochrome P450 monooxygenases to 3,4-epoxy-1-butene (EB), which alkylates DNA to form a range of nucleobase adducts. Among these, the most abundant are the hydrolytically labile N7-guanine adducts such as N7-(2-hydroxy-3-buten-1-yl)-guanine (N7-EB-dG). We now report that N7-EB-dG can be converted to the corresponding ring open N⁶-(2-deoxy-d- erythro-pentofuranosyl)-2,6-diamino-3,4-dihydro-4-oxo-5- N-(2-hydroxy-3-buten-1-yl)-formamidopyrimidine (EB-Fapy-dG) adducts. EB-Fapy-dG lesions were detected in EB-treated calf thymus DNA and in EB-treated mammalian cells using quantitative isotope dilution nanoLC-ESI⁺-MS/MS. EB-Fapy-dG adduct formation in EB-treated calf thymus DNA was concentration dependent and was greatly accelerated at an increased pH. EB-FAPy-dG adduct amounts were 2-fold higher in base excision repair-deficient NEIL1^-/- mouse embryonic fibroblasts (MEF) as compared to isogenic controls (NEIL1^+/+), suggesting that this lesion may be a substrate for NEIL1. Furthermore, NEIL1^-/- cells were sensitized to EB treatment as compared to NEIL1^+/+ fibroblasts. Overall, our results indicate that ring-opened EB-FAPy-dG adducts form under physiological conditions, prompting future studies to determine their contributions to genotoxicity and mutagenicity of BD.

Comprehensive review of Hepatitis B Virus-associated hepatocellular carcinoma research through text mining and big data analytics

PubMed was text mined to glean insights into the role of Hepatitis B virus (HBV) in hepatocellular carcinoma (HCC) from the massive number of publications (9249) available to date. Reports from ∼70 countries identified >1300 human genes associated with either the Core, Surface or X gene in HBV-associated HCC. One hundred and forty-three of these host genes, which can potentially yield 1180 biomolecular interactions, each were reported in at least three different publications to be associated with the same HBV. These 143 genes function in 137 pathways, involved mainly in the cell cycle, apoptosis, inflammation and signalling. Fourteen of these molecules, primarily transcriptional regulators or kinases, play roles in several pathways pertinent to the hallmarks of cancers. 'Chronic' was the most frequent word used across the 9249 abstracts. A key event in chronic HBV infection is the integration of HBV into the host genome. The advent of cost-effective, next-generation sequencing technology facilitated the employment of big-data analytics comprehensively to characterize HBV-host integration within HCC patients. A total of 5331 integration events were reported across seven publications, with most of these integrations observed between the Core/X gene and the introns of genes. Nearly one-quarter of the intergenic integrations are within repeats, especially long interspersed nuclear elements (LINE) repeats. Integrations within 13 genes were each reported by at least three different studies. The human gene with the most HBV integrations observed is the TERT gene where a total of 224 integrations, primarily at its promoter and within the tumour tissue, were reported by six of seven publications. This unique review, which employs state-of-the-art text-mining and data-analytics tools, represents the most complete, systematic and comprehensive review of nearly all the publications associated with HBV-associated HCC research. It provides important resources to either focus future research or develop therapeutic strategies to target key molecules reported to play important roles in key pathways of HCC, through the systematic analyses of the commonly reported molecules associated with the various HBV genes in HCC, including information about the interactions amongst these commonly reported molecules, the pathways in which they reside as well as detailed information regarding the viral and host genes associated with HBV integration in HCC patients. Hence this review, which highlights pathways and key human genes associated with HBV in HCC, may facilitate the deeper elucidation of the role of HBV in hepato-carcinogenesis, potentially leading to timely intervention against this deadly disease.

Participation of liver stem cells in cholangiocarcinogenesis after aflatoxin B1 exposure of glutathione S-transferase A3 knockout mice

Aflatoxin B1, arguably the most potent human carcinogen, induces liver cancer in humans, rats, trout, ducks, and so on, but adult mice are totally resistant. This resistance is because of a detoxifying enzyme, mouse glutathione S-transferase A3, which binds to and inactivates aflatoxin B1 epoxide, preventing the epoxide from binding to DNA and causing mutations. Glutathione S-transferase A3 or its analog has not been detected in any of the sensitive species, including humans. The generation of a glutathione S-transferase A3 knockout (represented as KO or -/-) mice has allowed us to study the induction of liver cancer in mice by aflatoxin B1. In contrast to the induction of hepatocellular carcinomas in other species, aflatoxin B1 induces cholangiocarcinomas in GSTA3-/- mice. In other species and in knockout mice, the induction of liver cancer is preceded by extensive proliferation of small oval cells, providing additional evidence that oval cells are bipolar stem cells and may give rise to either hepatocellular carcinoma or cholangiocarcinoma depending on the nature of the hepatocarcinogen and the species of animal. The recent development of mouse oval cell lines in our laboratory from aflatoxin B1-treated GSTA3-/- mice should provide a new venue for study of the properties and potential of putative mouse liver stem cells.

Relationship between drought and preharvest aflatoxin contamination in groundnut (Arachis hypogaea L.)

Groundnut is a commercial oilseed crop that is prone to infection by Aspergillus flavus or Aspergillus parasiticus. Drought impairs the defence mechanism of the plant and favours the production of aflatoxin by the fungus. Aflatoxin is a carcinogen and its presence in food and feed causes significant economic loss. The answer to the question, ‘how drought tolerance and aflatoxin resistance are related?’ is not clear. In this review paper, the relationship of drought and preharvest aflatoxin contamination (AC), the relationship of drought tolerance traits and AC, and the approaches to enhance resistance to AC are discussed using up-to-date literature. Factors leading to AC are drought, high geocarposphere temperature, kernel/pod damage, and reduced phytoalexin synthesis by the plant. If the fungus colonises a kernel with reduced water activity, the plant cannot synthesise phytoalexin and then, the fungus synthesises aflatoxin. Breeding for resistance to AC is complicated because aflatoxin concentration is costly to measure, highly variable, and influenced by the environment. Since drought tolerant cultivars have resistance to AC, traits of drought tolerance have been used as indirect selection tools for reduced AC. The genetics of aflatoxin resistance mechanisms have not been made clear as the environment influences the host-pathogen relationship. Host-pathogen interactions under the influence of environment should be studied at molecular level to identify plant resistant factors using the tools of genomics, proteomics, and metabolomics in order to develop cultivars with durable resistance. Many candidate genes involved in host-pathogen interactions have been identified due to improvements in fungal expressed sequence tags, microarrays, and genome sequencing techniques. Moreover, research projects are underway on identifying genes coding for antifungal compounds, resistance associated proteins and quantitative trait loci associated with aflatoxin resistance. This review is expected to help those who wish to work on reducing AC in groundnuts.

MDM2-p53 Interactions in Human Hepatocellular Carcinoma: What Is the Role of Nutlins and New Therapeutic Options?

Human hepatocellular carcinoma (HCC) is the fifth most common cancer and is associated with poor prognosis worldwide. The molecular mechanisms underlying the pathogenesis of HCC have been an area of continuing interest, and recent studies using next generation sequencing (NGS) have revealed much regarding previously unsettled issues. Molecular studies using HCC samples have been mainly targeted with the aim to identify the fundamental mechanisms contributing to HCC and identify more effective treatments. In response to cellular stresses (e.g., DNA damage or oncogenes), activated p53 elicits appropriate responses that aim at DNA repair, genetic stability, cell cycle arrest, and the deletion of DNA-damaged cells. On the other hand, the murine double minute 2 (MDM2) oncogene protein is an important cellular antagonist of p53. MDM2 negatively regulates p53 activity through the induction of p53 protein degradation. However, current research has shown that the mechanisms underlying MDM2-p53 interactions are more complex than previously thought. Microarray data have added new insight into the transcription changes in HCC. Recently, Nutlin-3 has shown potency against p53-MDM2 binding and the enhancement of p53 stabilization as well as an increment of p53 cellular accumulation with potential therapeutic effects. This review outlines the molecular mechanisms involved in the p53-MDM2 pathways, the biological factors influencing these pathways, and their roles in the pathogenesis of HCC. It also discusses the action of Nutlin-3 treatment in inducing growth arrest in HCC and elaborates on future directions in research in this area. More research on the biology of p53-MDM2 interactions may offer a better understanding of these mechanisms and discover new biomarkers, sensitive prognostic indicators as well as new therapeutic interventions in HCC.

Development of an adverse outcome pathway for chemically induced hepatocellular carcinoma: case study of AFB1, a human carcinogen with a mutagenic mode of action

Adverse outcome pathways (AOPs) are frameworks starting with a molecular initiating event (MIE), followed by key events (KEs) linked by KE relationships (KERs), ultimately resulting in a specific adverse outcome. Relevant data for the pathway and each KE/KER are evaluated to assess biological plausibility, weight-of-evidence, and confidence. We aimed to describe an AOP relevant to chemicals directly inducing mutation in cancer critical gene(s), via the formation of chemical-specific pro-mutagenic DNA adduct(s), as an early critical step in tumor etiology. Such chemicals have mutagenic modes-of-action (MOA) for tumor induction. To assist with developing this AOP, Aflatoxin B1 (AFB1) was selected as a case study because it has a rich database and is considered to have a mutagenic MOA. AFB1 information was used to define specific KEs, KERs, and to inform development of a generic AOP for mutagen-induced hepatocellular carcinoma (HCC). In assessing the AFB1 information, it became clear that existing data are, in fact, not optimal and for some KEs/KERs, the definitive data are not available. In particular, while there is substantial information that AFB1 can induce mutations (based on a number of mutation assays), the definitive evidence - the ability to induce mutation in the cancer critical gene(s) in the tumor target tissue - is not available. Thus, it is necessary to consider the patterns of results in the weight-of-evidence for KEs and KERs. It was important to determine whether there was sufficient evidence that AFB1 can induce the necessary critical mutations early in the carcinogenic process, which was the case.

Genomic Analysis Revealed New Oncogenic Signatures in TP53-Mutant Hepatocellular Carcinoma

The TP53 gene is the most commonly mutated gene in human cancers and mutations in TP53 have been shown to have either gain-of-function or loss-of-function effects. Using the data generated by The Cancer Genome Atlas, we sought to define the spectrum of TP53 mutations in hepatocellular carcinomas (HCCs) and their association with clinicopathologic features, and to determine the oncogenic and mutational signatures in TP53-mutant HCCs. Compared to other cancer types, HCCs harbored distinctive mutation hotspots at V157 and R249, whereas common mutation hotspots in other cancer types, R175 and R273, were extremely rare in HCCs. In terms of clinicopathologic features, in addition to the associations with chronic viral infection and high Edmondson grade, we found that TP53 somatic mutations were less frequent in HCCs with cholestasis or tumor infiltrating lymphocytes, but were more frequent in HCCs displaying necrotic areas. An analysis of the oncogenic signatures based on the genetic alterations found in genes recurrently altered in HCCs identified four distinct TP53-mutant subsets, three of which were defined by CTNNB1 mutations, 1q amplifications or 8q24 amplifications, respectively, that co-occurred with TP53 mutations. We also found that mutational signature 12, a liver cancer-specific signature characterized by T>C substitutions, was prevalent in HCCs with wild-type TP53 or with missense TP53 mutations, but not in HCCs with deleterious TP53 mutations. Finally, whereas patients with HCCs harboring deleterious TP53 mutations had worse overall and disease-free survival than patients with TP53-wild-type HCCs, patients with HCCs harboring missense TP53 mutations did not have worse prognosis. In conclusion, our results highlight the importance to consider the genetic heterogeneity among TP53-mutant HCCs in studies of biomarkers and molecular characterization of HCCs.

Mutant p53 Gains Its Function via c-Myc Activation upon CDK4 Phosphorylation at Serine 249 and Consequent PIN1 Binding

TP53 missense mutations significantly influence the development and progression of various human cancers via their gain of new functions (GOF) through different mechanisms. Here we report a unique mechanism underlying the GOF of p53-R249S (p53-RS), a p53 mutant frequently detected in human hepatocellular carcinoma (HCC) that is highly related to hepatitis B infection and aflatoxin B1. A CDK inhibitor blocks p53-RS's nuclear translocation in HCC, whereas CDK4 interacts with p53-RS in the G1/S phase of the cells, phosphorylates it, and enhances its nuclear localization. This is coupled with binding of a peptidyl-prolyl cis-trans isomerase NIMA-interacting 1 (PIN1) to p53-RS, but not the p53 form with mutations of four serines/threonines previously shown to be crucial for PIN1 binding. As a result, p53-RS interacts with c-Myc and enhances c-Myc-dependent rDNA transcription key for ribosomal biogenesis. These results unveil a CDK4-PIN1-p53-RS-c-Myc pathway as a novel mechanism for the GOF of p53-RS in HCC.

Prevalence of Aflatoxin-Associated TP53R249S Mutation in Hepatocellular Carcinoma in Hispanics in South Texas

We aimed to determine whether aflatoxin dietary exposure plays a role in the high incidence of hepatocellular carcinoma (HCC) observed among Hispanics in South Texas. We measured TP53R249S somatic mutation, hallmark of aflatoxin etiology in HCC, using droplet digital PCR and RFLP. TP53R249S mutation was detected in 3 of 41 HCC tumors from Hispanics in South Texas (7.3%). We also measured TP53R249S mutation in plasma cell-free DNA (cfDNA) from 218 HCC patients and 96 Hispanic subjects with advanced fibrosis or cirrhosis, from South Texas. The mutation was detected only in Hispanic and Asian HCC patients, and patients harboring TP53R249S mutation were significantly younger and had a shorter overall survival. The mutation was not detected in any Hispanic subject with advanced fibrosis or cirrhosis. Genes involved in cell-cycle control of chromosomal replication and in BRCA1-dependent DNA damage response were enriched in HCCs with TP53R249S mutation. The E2F1 family members, E2F1 and E2F4, were identified as upstream regulators. TP53R249S mutation was detected in 5.7% to 7.3% of Hispanics with HCC in South Texas. This mutation was associated with a younger age and worse prognosis. TP53R249S was however not detected in Hispanics in South Texas with cirrhosis or advanced fibrosis. Aflatoxin exposure may contribute to a small number of HCCs in Hispanics in South Texas, but the detection of TP53R249S mutation in plasma cfDNA is not a promising biomarker of risk assessment for HCC in subjects with cirrhosis or advanced fibrosis in this population. Cancer Prev Res; 11(2); 103-12. ©2017 AACR.

Engaging One Health for Non-Communicable Diseases in Africa: Perspective for Mycotoxins

The role of mycotoxins-e.g., aflatoxins, ochratoxins, trichothecenes, zearalenone, fumonisins, tremorgenic toxins, and ergot alkaloids-has been recognized in the etiology of a number of diseases. In many African countries, the public health impact of chronic (indoor) and/or repeated (dietary) mycotoxin exposure is largely ignored hitherto, with impact on human health, food security, and export of African agricultural food products. Notwithstanding, African scientific research reached milestones that, when linked to findings gained by the international scientific community, make the design and implementation of science-driven governance schemes feasible. Starting from Nigeria as leading African Country, this article (i) overviews available data on mycotoxins exposure in Africa; (ii) discusses new food safety issues, such as the environment-feed-food chain and toxic exposures of food producing animals in risk assessment and management; (iii) identifies milestones for mycotoxins risk management already reached in West Africa; and (iv) points out preliminary operationalization aspects for shielding communities from direct (on health) and indirect (on trade, economies, and livelihoods) effects of mycotoxins. An African science-driven engaging of scientific knowledge by development actors is expected therefore. In particular, One health/One prevention is suggested, as it proved to be a strategic and sustainable development framework.

Innovative Disease Model: Zebrafish as an In Vivo Platform for Intestinal Disorder and Tumors

Colorectal cancer (CRC) is one of the world’s most common cancers and is the second leading cause of cancer deaths, causing more than 50,000 estimated deaths each year. Several risk factors are highly associated with CRC, including being overweight, eating a diet high in red meat and over-processed meat, having a history of inflammatory bowel disease, and smoking. Previous zebrafish studies have demonstrated that multiple oncogenes and tumor suppressor genes can be regulated through genetic or epigenetic alterations. Zebrafish research has also revealed that the activation of carcinogenesis-associated signal pathways plays an important role in CRC. The biology of cancer, intestinal disorders caused by carcinogens, and the morphological patterns of tumors have been found to be highly similar between zebrafish and humans. Therefore, the zebrafish has become an important animal model for translational medical research. Several zebrafish models have been developed to elucidate the characteristics of gastrointestinal diseases. This review article focuses on zebrafish models that have been used to study human intestinal disorders and tumors, including models involving mutant and transgenic fish. We also report on xenograft models and chemically-induced enterocolitis. This review demonstrates that excellent zebrafish models can provide novel insights into the pathogenesis of gastrointestinal diseases and help facilitate the evaluation of novel anti-tumor drugs.

Chemotherapy for Hepatocellular Carcinoma: Current Evidence and Future Perspectives

Hepatocarcinogenesis is a multistep process, heralded by abnormalities in cell differentiation and proliferation and sustained by an aberrant neoangiogenesis. Understanding the underlying molecular pathogenesis leading to hepatocellular carcinoma is a prerequisite to develop new drugs that will hamper or block the steps of these pathways. As hepatocellular carcinoma has higher arterial vascularization than normal liver, this could be a good target for novel molecular therapies. Introduction of the antiangiogenic drug sorafenib into clinical practice since 2008 has led to new perspectives in the management of this tumor. The importance of this drug lies not only in the modest gain of patients' survival, but in having opened a roadmap towards the development of new molecules and targets. Unfortunately, after the introduction of sorafenib, during the last years, a wide number of clinical trials on antiangiogenic therapies failed in achieving significant results. However, many of these trials are still ongoing and promise to improve overall survival and progression-free survival. A recent clinical trial has proven regorafenib effective in patients showing tumor progression under sorafenib, thus opening new interesting therapeutic perspectives. Many other expectations have been borne from the discovery of the immune checkpoint blockade, already known in other solid malignancies. Furthermore, a potential role in hepatocellular carcinoma therapy may derive from the use of branched-chain amino acids and of nutritional support. This review analyses the biomolecular pathways of hepatocellular carcinoma and the ongoing studies, the actual evidence and the future perspectives concerning drug therapy in this open field.

Serum and tissue markers in hepatocellular carcinoma and cholangiocarcinoma: clinical and prognostic implications

HCC represents the sixth most common cancer worldwide and the second leading cause of cancer-related death. Despite the high incidence, treatment options for advanced HCC remain limited and unsuccessful, resulting in a poor prognosis. Despite the major advances achieved in the diagnostic management of HCC, only one third of the newly diagnosed patients are presently eligible for curative treatments. Advances in technology and an increased understanding of HCC biology have led to the discovery of novel biomarkers. Improving our knowledge about serum and tissutal markers could ultimately lead to an early diagnosis and better and early treatment strategies for this deadly disease. Serum biomarkers are striking potential tools for surveillance and early diagnosis of HCC thanks to the non-invasive, objective, and reproducible assessments they potentially enable. To date, many biomarkers have been proposed in the diagnosis of HCC. Cholangiocarcinoma (CCA) is an aggressive malignancy, characterized by early lymph node involvement and distant metastasis, with 5-year survival rates of 5%-10%. The identification of new biomarkers with diagnostic, prognostic or predictive value is especially important as resection (by surgery or combined with a liver transplant) has shown promising results and novel therapies are emerging. However, the relatively low incidence of CCA, high frequency of co-existing cholestasis or cholangitis (primary sclerosing cholangitis –PSC- above all), and difficulties with obtaining adequate samples, despite advances in sampling techniques and in endoscopic visualization of the bile ducts, have complicated the search for accurate biomarkers. In this review, we attempt to analyze the existing literature on this argument.

TMEM88, CCL14 and CLEC3B as prognostic biomarkers for prognosis and palindromia of human hepatocellular carcinoma

Hepatocellular carcinoma is one of the most mortal and prevalent cancers with increasing incidence worldwide. Elucidating genetic driver genes for prognosis and palindromia of hepatocellular carcinoma helps managing clinical decisions for patients. In this study, the high-throughput RNA sequencing data on platform IlluminaHiSeq of hepatocellular carcinoma were downloaded from The Cancer Genome Atlas with 330 primary hepatocellular carcinoma patient samples. Stable key genes with differential expressions were identified with which Kaplan-Meier survival analysis was performed using Cox proportional hazards test in R language. Driver genes influencing the prognosis of this disease were determined using clustering analysis. Functional analysis of driver genes was performed by literature search and Gene Set Enrichment Analysis. Finally, the selected driver genes were verified using external dataset GSE40873. A total of 5781 stable key genes were identified, including 156 genes definitely related to prognoses of hepatocellular carcinoma. Based on the significant key genes, samples were grouped into five clusters which were further integrated into high- and low-risk classes based on clinical features. TMEM88, CCL14, and CLEC3B were selected as driver genes which clustered high-/low-risk patients successfully (generally, p = 0.0005124445). Finally, survival analysis of the high-/low-risk samples from external database illustrated significant difference with p value 0.0198. In conclusion, TMEM88, CCL14, and CLEC3B genes were stable and available in predicting the survival and palindromia time of hepatocellular carcinoma. These genes could function as potential prognostic genes contributing to improve patients' outcomes and survival.

Genetic Features of Aflatoxin-Associated Hepatocellular Carcinoma

BACKGROUND & AIMS

Dietary exposure to aflatoxin is an important risk factor for hepatocellular carcinoma (HCC). However, little is known about the genomic features and mutations of aflatoxin-associated HCCs compared with HCCs not associated with aflatoxin exposure. We investigated the genetic features of aflatoxin-associated HCC that can be used to differentiate them from HCCs not associated with this carcinogen.

METHODS

We obtained HCC tumor tissues and matched non-tumor liver tissues from 49 patients, collected from 1990 through 2016, at the Qidong Liver Cancer Hospital Institute in China-a high-risk region for aflatoxin exposure (38.2% of food samples test positive for aflatoxin contamination). Somatic variants were identified using GATK Best Practices Pipeline. We validated part of the mutations from whole-genome sequencing and whole-exome sequencing by Sanger sequencing. We also analyzed genomes of 1072 HCCs, obtained from 5 datasets from China, the United States, France, and Japan. Mutations in 49 aflatoxin-associated HCCs and 1072 HCCs from other regions were analyzed using the Wellcome Trust Sanger Institute mutational signatures framework with non-negative matrix factorization. The mutation landscape and mutational signatures from the aflatoxin-associated HCC and HCC samples from general population were compared. We identified genetic features of aflatoxin-associated HCC, and used these to identify aflatoxin-associated HCCs in datasets from other regions. Tumor samples were analyzed by immunohistochemistry to determine microvessel density and levels of CD34 and CD274 (PD-L1).

RESULTS

Aflatoxin-associated HCCs frequently contained C>A transversions, the sequence motif GCN, and strand bias. In addition to previously reported mutations in TP53, we found frequent mutations in the adhesion G protein-coupled receptor B1 gene (ADGRB1), which were associated with increased capillary density of tumor tissue. Aflatoxin-associated HCC tissues contained high-level potential mutation-associated neoantigens, and many infiltrating lymphocytes and tumors cells that expressed PD-L1, compared to HCCs not associated with aflatoxin. Of the HCCs from China, 9.8% contained the aflatoxin-associated genetic features, whereas 0.4%-3.5% of HCCs from other regions contained these genetic features.

CONCLUSIONS

We identified specific genetic and mutation features of HCCs associated with aflatoxin exposure, including mutations in ADGRB1, compared to HCCs from general populations. We associated these mutations with increased vascularization and expression of PD-L1 in HCC tissues. These findings might be used to identify patients with HCC due to aflatoxin exposure, and select therapies.

Aflatoxin B1-induced epigenetic alterations: An overview

Aflatoxin B1 (AFB1) is widely distributed in nature, especially in a variety of food commodities. It is confirmed to be the most toxic of all the aflatoxins. The toxicity of AFB1 has been well investigated, and it may result in severe health problems including carcinogenesis, mutagenesis, growth retardation, and immune suppression. Epigenetic modifications including DNA methylation, histone modifications and regulation of non-coding RNA play an important role in AFB1-induced disease and carcinogenesis. To better understand the evidence for AFB1-induced epigenetic alterations and the potential mechanisms of the toxicity of AFB1, we conducted a review of published studies of AFB1-induced epigenetic alterations.

Innovative technologies to manage aflatoxins in foods and feeds and the profitability of application - A review

Aflatoxins are mainly produced by certain strains of Aspergillus flavus, which are found in diverse agricultural crops. In many lower-income countries, aflatoxins pose serious public health issues since the occurrence of these toxins can be considerably common and even extreme. Aflatoxins can negatively affect health of livestock and poultry due to contaminated feeds. Additionally, they significantly limit the development of international trade as a result of strict regulation in high-value markets. Due to their high stability, aflatoxins are not only a problem during cropping, but also during storage, transport, processing, and handling steps. Consequently, innovative evidence-based technologies are urgently required to minimize aflatoxin exposure. Thus far, biological control has been developed as the most innovative potential technology of controlling aflatoxin contamination in crops, which uses competitive exclusion of toxigenic strains by non-toxigenic ones. This technology is commercially applied in groundnuts maize, cottonseed, and pistachios during pre-harvest stages. Some other effective technologies such as irradiation, ozone fumigation, chemical and biological control agents, and improved packaging materials can also minimize post-harvest aflatoxins contamination in agricultural products. However, integrated adoption of these pre- and post-harvest technologies is still required for sustainable solutions to reduce aflatoxins contamination, which enhances food security, alleviates malnutrition, and strengthens economic sustainability.

Frequency and geographic distribution of TERT promoter mutations in primary hepatocellular carcinoma

Primary hepatocellular carcinoma (HCC) mainly develops in subjects chronically infected with hepatitis B (HBV) and C (HCV) viruses through a multistep process characterized by the accumulation of genetic alterations in the human genome. Nucleotide changes in coding regions (i.e. TP53, CTNNB1, ARID1A and ARID2) as well as in non-coding regions (i.e. TERT promoter) are considered cancer drivers for HCC development with variable frequencies in different geographic regions depending on the etiology and environmental factors. Recurrent hot spot mutations in TERT promoter (G > A at-124 bp; G > A at -146 bp), have shown to be common events in many tumor types including HCC and to up regulate the expression of telomerases. We performed a comprehensive review of the literature evaluating the differential distribution of TERT promoter mutations in 1939 primary HCC from four continents. Mutation rates were found higher in Europe (56.6%) and Africa (53.3%) than America (40%) and Asia (42.5%). In addition, HCV-related HCC were more frequently mutated (44.8% in US and 69.7% in Asia) than HBV-related HCC (21.4% in US and 45.5% in Africa). HCC cases associated to factors other than hepatitis viruses are also frequently mutated in TERT promoter (43.6%, 52.6% and 57.7% in USA, Asia and Europe, respectively). These results support a major role for telomere elongation in HCV-related and non-viral related hepatic carcinogenesis and suggest that TERT promoter mutations could represent a candidate biomarker for the early detection of liver cancer in subjects with HCV infection or with metabolic liver diseases.

An in vitro system for measuring genotoxicity mediated by human CYP3A4 in Saccharomyces cerevisiae

P450 activity is required to metabolically activate many chemical carcinogens, rendering them highly genotoxic. CYP3A4 is the most abundantly expressed P450 enzyme in the liver, accounting for most drug metabolism and constituting 50% of all hepatic P450 activity. CYP3A4 is also expressed in extrahepatic tissues, including the intestine. However, the role of CYP3A4 in activating chemical carcinogens into potent genotoxins is unclear. To facilitate efforts to determine whether CYP3A4, per se, can activate carcinogens into potent genotoxins, we expressed human CYP3A4 in the DNA-repair mutant (rad4 rad51) strain of budding yeast Saccharomyces cerevisiae and tested the novel, recombinant yeast strain for ability to report CYP3A4-mediated genotoxicity of a well-known genotoxin, aflatoxin B1 (AFB1 ). Yeast microsomes containing human CYP3A4, but not those that do not contain CYP3A4, were active in hydroxylation of diclofenac, a known CYP3A4 substrate drug, a result confirming CYP3A4 activity in the recombinant yeast strain. In cells exposed to AFB1 , the expression of CYP3A4 supported DNA adduct formation, chromosome rearrangements, cell death, and expression of the large subunit of ribonucleotide reductase, Rnr3, a marker of DNA damage. Expression of CYP3A4 also conferred sensitivity in rad4 rad51 mutants exposed to colon carcinogen, 2-amino-3,8-dimethylimidazo[4,5-f]quinoxaline (MeIQx). These data confirm the ability of human CYP3A4 to mediate the genotoxicity of AFB1 , and illustrate the usefulness of the CYP3A4-expressing, DNA-repair mutant yeast strain for screening other chemical compounds that are CYP3A4 substrates, for potential genotoxicity. Environ. Mol. Mutagen. 58:217-227, 2017. © 2017 Wiley Periodicals, Inc.

NEIL1 protects against aflatoxin-induced hepatocellular carcinoma in mice

Global distribution of hepatocellular carcinomas (HCCs) is dominated by its incidence in developing countries, accounting for >700,000 estimated deaths per year, with dietary exposures to aflatoxin (AFB₁) and subsequent DNA adduct formation being a significant driver. Genetic variants that increase individual susceptibility to AFB₁-induced HCCs are poorly understood. Herein, it is shown that the DNA base excision repair (BER) enzyme, DNA glycosylase NEIL1, efficiently recognizes and excises the highly mutagenic imidazole ring-opened AFB₁-deoxyguanosine adduct (AFB₁-Fapy-dG). Consistent with this in vitro result, newborn mice injected with AFB₁ show significant increases in the levels of AFB₁-Fapy-dG in Neil1^-/- vs. wild-type liver DNA. Further, Neil1^-/- mice are highly susceptible to AFB₁-induced HCCs relative to WT controls, with both the frequency and average size of hepatocellular carcinomas being elevated in Neil1^-/- The magnitude of this effect in Neil1^-/- mice is greater than that previously measured in Xeroderma pigmentosum complementation group A (XPA) mice that are deficient in nucleotide excision repair (NER). Given that several human polymorphic variants of NEIL1 are catalytically inactive for their DNA glycosylase activity, these deficiencies may increase susceptibility to AFB₁-associated HCCs.

Mutational spectra of aflatoxin B1 in vivo establish biomarkers of exposure for human hepatocellular carcinoma

Aflatoxin B₁ (AFB₁) and/or hepatitis B and C viruses are risk factors for human hepatocellular carcinoma (HCC). Available evidence supports the interpretation that formation of AFB₁-DNA adducts in hepatocytes seeds a population of mutations, mainly G:C→T:A, and viral processes synergize to accelerate tumorigenesis, perhaps via inflammation. Responding to a need for early-onset evidence predicting disease development, highly accurate duplex sequencing was used to monitor acquisition of high-resolution mutational spectra (HRMS) during the process of hepatocarcinogenesis. Four-day-old male mice were treated with AFB₁ using a regimen that induced HCC within 72 wk. For analysis, livers were separated into tumor and adjacent cellular fractions. HRMS of cells surrounding the tumors revealed predominantly G:C→T:A mutations characteristic of AFB₁ exposure. Importantly, 25% of all mutations were G→T in one trinucleotide context (CGC; the underlined G is the position of the mutation), which is also a hotspot mutation in human liver tumors whose incidence correlates with AFB₁ exposure. The technology proved sufficiently sensitive that the same distinctive spectrum was detected as early as 10 wk after dosing, well before evidence of neoplasia. Additionally, analysis of tumor tissue revealed a more complex pattern than observed in surrounding hepatocytes; tumor HRMS were a composite of the 10-wk spectrum and a more heterogeneous set of mutations that emerged during tumor outgrowth. We propose that the 10-wk HRMS reflects a short-term mutational response to AFB₁, and, as such, is an early detection metric for AFB₁-induced liver cancer in this mouse model that will be a useful tool to reconstruct the molecular etiology of human hepatocarcinogenesis.

Aflatoxin B1 inhibits the type 1 interferon response pathway via STAT1 suggesting another mechanism of hepatocellular carcinoma

BACKGROUND

Aflatoxin B1 (AFB1) contamination of food is very high in most sub-Saharan African countries. AFB1 is known to cause hepatocellular carcinoma (HCC) by inducing mutation in the tumour suppressor gene TP53. The number of new HCC cases is high in West Africa with an accompanying high mortality. The type I interferon (IFN) pathway of the innate immune system limits viral infections and exerts its anti-cancer property by up-regulating tumour suppressor activities and pro-apoptotic pathways. Indeed, IFN-α is reported to show significant protective effects against hepatic fibrogenesis and carcinogenesis. However, the mechanism behind AFB1 deregulation of the type I interferon (IFN) signalling pathway, with consequent HCC is largely unknown. This current study seeks to test the hypothesis that AFB1 inhibits the type I IFN response by directly interfering with key signalling proteins and thus increase the risk of HCC in humans.

METHODS

We evaluated the effects of AFB1 on the type I IFN signalling pathway using IFN stimulated response element (ISRE)-based luciferase reporter gene assay. In addition, the effects of AFB1 on the transcript levels of JAK1, STAT1 and OAS3 were assessed by real-time quantitative polymerase chain reaction (RT-qPCR) and confirmed by immunoblot assay.

RESULTS

Our results indicated that AFB1 inhibited the type I IFN signalling pathway in human hepatoma cell line HepG2 cells by suppressing the transcript levels of JAK1, STAT1 and OAS3. AFB1 also decreased the accumulation of STAT1 protein.

CONCLUSION

The inhibition of the type I IFN anti-cancer response pathway by AFB1 suggest a novel mechanism by which AFB1 may induce hepatocellular carcinoma in humans.