Mode of action of dieldrin-induced liver tumors: application to human risk assessment

Dieldrin is an organochlorine insecticide that was widely used until 1970 when its use was banned because of its liver carcinogenicity in mice. Several long-term rodent bioassays have reported dieldrin to induce liver tumors in in several strains of mice, but not in rats. This article reviews the available information on dieldrin liver effects and performs an analysis of mode of action (MOA) and human relevance of these liver findings. Scientific evidence strongly supports a MOA based on CAR activation, leading to alterations in gene expression, which result in increased hepatocellular proliferation, clonal expansion leading to altered hepatic foci, and ultimately the formation of hepatocellular adenomas and carcinomas. Associative events include increased liver weight, centrilobular hypertrophy, increased expression of Cyp2b10 and its resulting increased enzymatic activity. Other associative events include alterations of intercellular gap junction communication and oxidative stress. Alternative MOAs are evaluated and shown not to be related to dieldrin administration. Weight of evidence shows that dieldrin is not DNA reactive, it is not mutagenic, and it is not genotoxic in general. Furthermore, activation of other pertinent nuclear receptors, including PXR, PPARα, AhR, and estrogen are not related to dieldrin-induced liver tumors nor is there liver cytotoxicity. In previous studies, rats, dogs, and non-human primates did not show increased cell proliferation or production of pre-neoplastic or neoplastic lesions following dieldrin treatment. Thus, the evidence strongly indicates that dieldrin-induced mouse liver tumors are due to CAR activation and are specific to the mouse, which are qualitatively not relevant to human hepatocarcinogenesis. Thus, there is no carcinogenic risk to humans. This conclusion is also supported by a lack of positive epidemiologic findings for evidence of liver carcinogenicity. Based on current understanding of the mode of action of dieldrin-induced liver tumors in mice, the appropriate conclusion is that dieldrin is a mouse specific liver carcinogen and it does not pose a cancer risk to humans.

Causality between six psychiatric disorders and digestive tract cancers risk: a two-sample Mendelian randomization study

Associations between psychiatric disorders and digestive tract cancers have been proposed. However, the causal link between these factors remains unclear. This study pioneers Mendelian randomization (MR) analysis to explore the genetic link between psychiatric disorders and digestive tract cancers risk. We analysed data on six psychiatric disorders [schizophrenia, bipolar disorder, major depressive disorder (MDD), attention deficit hyperactivity disorder, autism spectrum disorder, and panic disorder (PD)] and digestive tract cancers [esophagus cancer (EC), gastric cancer (GC), and colorectal cancer (CRC)] from genome-wide association studies databases. Using instrumental variables identified from significant single nucleotide polymorphism associations, we employed the inverse variance weighted (IVW) method alongside the weighted median (WM) method and MR-Egger regression. The results revealed no causal link between psychiatric disorders and the risk of EC or GC. Psychiatric disorders were not identified as risk factors for CRC. Notably, PD demonstrated a lower CRC risk (OR = 0.79, 95% CI 0.66-0.93, P = 0.01). This MR analysis underscores the lack of a causal association between psychiatric disorders and digestive tract cancers risk while suggesting a potential protective effect of PD against CRC.

Cell proliferation and carcinogenesis: an approach to screening for potential human carcinogens

Cancer arises from multiple genetic errors occurring in a single stem cell (clonality). Every time DNA replicates, mistakes occur. Thus, agents can increase the risk of cancer either by directly damaging DNA (DNA-reactive carcinogens) or increasing the number of DNA replications (increased cell proliferation). Increased cell proliferation can be achieved either by direct mitogenesis or cytotoxicity with regenerative proliferation. Human carcinogens have a mode of action of DNA reactivity, immunomodulation (mostly immunosuppression), increased estrogenic activity (mitogenesis), or cytotoxicity and regeneration. By focusing on screening for these four effects utilizing in silico, in vitro, and short-term in vivo assays, a biologically based screening for human chemical carcinogens can be accomplished with greater predictivity than the traditional 2-year bioassay with considerably less cost, less time, and the use of fewer animals.

ICH S1 prospective evaluation study and weight of evidence assessments: commentary from industry representatives

Industry representatives on the ICH S1B(R1) Expert Working Group (EWG) worked closely with colleagues from the Drug Regulatory Authorities to develop an addendum to the ICH S1B guideline on carcinogenicity studies that allows for a weight-of-evidence (WoE) carcinogenicity assessment in some cases, rather than conducting a 2-year rat carcinogenicity study. A subgroup of the EWG composed of regulators have published in this issue a detailed analysis of the Prospective Evaluation Study (PES) conducted under the auspices of the ICH S1B(R1) EWG. Based on the experience gained through the Prospective Evaluation Study (PES) process, industry members of the EWG have prepared the following commentary to aid sponsors in assessing the standard WoE factors, considering how novel investigative approaches may be used to support a WoE assessment, and preparing appropriate documentation of the WoE assessment for presentation to regulatory authorities. The commentary also reviews some of the implementation challenges sponsors must consider in developing a carcinogenicity assessment strategy. Finally, case examples drawn from previously marketed products are provided as a supplement to this commentary to provide additional examples of how WoE criteria may be applied. The information and opinions expressed in this commentary are aimed at increasing the quality of WoE assessments to ensure the successful implementation of this approach.

Retrospective analysis of carcinogenicity assessments within FDA-notified GRAS determinations

Frameworks have been developed to standardize the assessment of carcinogenic potential in the pharmaceutical and agrochemical industries, building upon decades of research. Carcinogenicity is also evaluated during the safety evaluation of food substances, using a comprehensive approach unique to each substance. To better understand these approaches, a retrospective assessment was conducted on the publicly available database of substances notified to the United States Food and Drug Administration (US FDA) as being Generally Recognized As Safe (GRAS). The data contained within these GRAS notifications (GRNs) were reviewed for the methods used to evaluate carcinogenic potential (genotoxicity studies, 2-year bioassays, other pre-clinical animal studies) to identify patterns that could provide an understanding of how this assessment has been conducted for different categories of food substances. While different approaches to the safety evaluation were required to adapt to the unique food substances, the data in all notifications supported the conclusion of safety. The evaluation of food substances for carcinogenic potential must consider all available data, including identifying the need for when more data must be generated to support an evaluation. Due to the complexity of substances used in food, ranging from defined chemical entities to minimally processed agricultural commodities to live microorganisms, the approach to conducting the safety evaluation of food substances must be able to adapt to the most relevant scientifically supported approach. This paper illustrates the data commonly used to support the safety of different types of food substances and proposes an approach familiar to other product sectors.

Early detection of genotoxic hepatocarcinogens in rats using γH2AX and Ki-67: prediction by machine learning

Direct DNA double-strand breaks result in phosphorylation of H2AX, a variant of the histone H2 protein. Phosphorylated H2AX (γH2AX) may be a potential indicator in the evaluation of genotoxicity and hepatocarcinogenicity. In this study, γH2AX and Ki-67 were detected in the short-term responses (24 h after chemical administration) to classify genotoxic hepatocarcinogens (GHs) from non-GH chemicals. One hundred and thirty-five 6-week-old Crl: CD(SD) (SPF) male rats were treated with 22 chemicals including 11 GH and 11 non-GH, sacrificed 24 h later, and immunostained with γH2AX and Ki-67. Positivity rates of these markers were measured in the 3 liver ZONEs 1-3; portal, lobular, and central venous regions. These values were input into 3 machine learning models-Naïve Bayes, Random Forest, and k-Nearest Neighbor to classify GH and non-GH using a 10-fold cross-validation method. All 11 and 10 out of 11 GH caused significant increase in γH2AX and Ki-67 levels, respectively (P < .05). Of the 3 machine learning models, Random Forest performed the best. GH were identified with 95.0% sensitivity (76/80 GH-treated rats), 90.9% specificity (50/55 non-GH-treated rats), and 90.0% overall correct response rate using γH2AX staining, and 96.2% sensitivity (77/80), 81.8% specificity (45/55), and 90.4% overall correct response rate using Ki-67 labeling. Random Forest model using γH2AX and Ki-67 could independently predict GH in the early stage with high accuracy.

Increased Cell Proliferation as a Key Event in Chemical Carcinogenesis: Application in an Integrated Approach for the Testing and Assessment of Non-Genotoxic Carcinogenesis

In contrast to genotoxic carcinogens, there are currently no internationally agreed upon regulatory tools for identifying non-genotoxic carcinogens of human relevance. The rodent cancer bioassay is only used in certain regulatory sectors and is criticized for its limited predictive power for human cancer risk. Cancer is due to genetic errors occurring in single cells. The risk of cancer is higher when there is an increase in the number of errors per replication (genotoxic agents) or in the number of replications (cell proliferation-inducing agents). The default regulatory approach for genotoxic agents whereby no threshold is set is reasonably conservative. However, non-genotoxic carcinogens cannot be regulated in the same way since increased cell proliferation has a clear threshold. An integrated approach for the testing and assessment (IATA) of non-genotoxic carcinogens is under development at the OECD, considering learnings from the regulatory assessment of data-rich substances such as agrochemicals. The aim is to achieve an endorsed IATA that predicts human cancer better than the rodent cancer bioassay, using methodologies that equally or better protect human health and are superior from the view of animal welfare/efficiency. This paper describes the technical opportunities available to assess cell proliferation as the central gateway of an IATA for non-genotoxic carcinogenicity.

An exploration of the correlations between seven psychiatric disorders and the risks of breast cancer, breast benign tumors and breast inflammatory diseases: Mendelian randomization analyses

Background

Previous observational studies have showed that certain psychiatric disorders may be linked to breast cancer risk, there is, however, little understanding of relationships between mental disorders and a variety of breast diseases. This study aims to investigate if mental disorders influence the risks of overall breast cancer, the two subtypes of breast cancer (ER+ and ER-), breast benign tumors and breast inflammatory diseases.

Methods

During our research, genome-wide association study (GWAS) data for seven psychiatric disorders (schizophrenia, major depressive disorder, bipolar disorder, post-traumatic stress disorder, panic disorder, obsessive-compulsive disorder and anorexia nervosa) from the Psychiatric Genomics Consortium (PGC) and the UK Biobank were selected, and single-nucleotide polymorphisms (SNPs) significantly linked to these mental disorders were identified as instrumental variables. GWAS data for breast diseases came from the Breast Cancer Association Consortium (BCAC) as well as the FinnGen consortium. We performed two-sample Mendelian randomization (MR) analyses and multivariable MR analyses to assess these SNPs' effects on various breast diseases. Both heterogeneity and pleiotropy were evaluated by sensitivity analyses.

Results

When the GWAS data of psychiatric disorders were derived from the PGC, our research found that schizophrenia significantly increased the risks of overall breast cancer (two-sample MR: OR 1.05, 95%CI [1.03-1.07], p = 3.84 × 10^-6; multivariable MR: OR 1.06, 95%CI [1.04-1.09], p = 2.34 × 10^-6), ER+ (OR 1.05, 95%CI [1.02-1.07], p = 5.94 × 10^-5) and ER- (two-sample MR: OR 1.04, 95%CI [1.01-1.07], p = 0.006; multivariable MR: OR 1.06, 95%CI [1.02-1.10], p = 0.001) breast cancer. Nevertheless, major depressive disorder only showed significant positive association with overall breast cancer (OR 1.12, 95%CI [1.04-1.20], p = 0.003) according to the two-sample MR analysis, but not in the multivariable MR analysis. In regards to the remainder of the mental illnesses and breast diseases, there were no significant correlations. While as for the data from the UK Biobank, schizophrenia did not significantly increase the risk of breast cancer.

Conclusions

The correlation between schizophrenia and breast cancer found in this study may be false positive results caused by underlying horizontal pleiotropy, rather than a true cause-and-effect relationship. More prospective studies are still needed to be carried out to determine the definitive links between mental illnesses and breast diseases.

Quantification of Hepatocellular Mitoses in a Toxicological Study in Rats Using a Convolutional Neural Network

Convolutional neural networks (CNNs) have been recognized as valuable tools for rapid quantitative analysis of morphological changes in toxicologic histopathology. We have assessed the performance of CNN-based (Halo-AI) mitotic figure detection in hepatocytes in comparison with detection by pathologists. In addition, we compared with Ki-67 and 5-bromodesoxyuridin (BrdU) immunohistochemistry labeling indices (LIs) obtained by image analysis. Tissues were from an exploratory toxicity study with a glycogen synthase kinase-3 (GSK-3) inhibitor. Our investigations revealed that (1) the CNN achieved similarly accurate but faster results than pathologists, (2) results of mitotic figure detection were comparable to Ki-67 and BrdU LIs, and (3) data from different methods were only moderately correlated. The latter is likely related to differences in the cell cycle component captured by each method. This highlights the importance of considering the differences of the available methods upon selection. Also, the pharmacology of our test item acting as a GSK-3 inhibitor potentially reduced the correlation. We conclude that hepatocyte cell proliferation assessment by CNNs can have several advantages when compared with the current gold standard: it relieves the pathologist of tedious routine tasks and contributes to standardization of results; the CNN algorithm can be shared and iteratively improved; it can be performed on routine histological slides; it does not require an additional animal experiment and in this way can contribute to animal welfare according to the 3R principles.

Evaluation of the human hazard of the liver and lung tumors in mice treated with permethrin based on mode of action

The non-genotoxic synthetic pyrethroid insecticide permethrin produced hepatocellular adenomas and bronchiolo-alveolar adenomas in female CD-1 mice, but not in male CD-1 mice or in female or male Wistar rats. Studies were performed to evaluate possible modes of action (MOAs) for permethrin-induced female CD-1 mouse liver and lung tumor formation. The MOA for liver tumor formation by permethrin involves activation of the peroxisome proliferator-activated receptor alpha (PPARα), increased hepatocellular proliferation, development of altered hepatic foci, and ultimately liver tumors. This MOA is similar to that established for other PPARα activators and is considered to be qualitatively not plausible for humans. The MOA for lung tumor formation by permethrin involves interaction with Club cells, followed by a mitogenic effect resulting in Club cell proliferation, with prolonged administration producing Club cell hyperplasia and subsequently formation of bronchiolo-alveolar adenomas. Although the possibility that permethrin exposure may potentially result in enhancement of Club cell proliferation in humans cannot be completely excluded, there is sufficient information on differences in basic lung anatomy, physiology, metabolism, and biologic behavior of tumors in the general literature to conclude that humans are quantitatively less sensitive to agents that increase Club cell proliferation and lead to tumor formation in mice. The evidence strongly indicates that Club cell mitogens are not likely to lead to increased susceptibility to lung tumor development in humans. Overall, based on MOA evaluation it is concluded that permethrin does not pose a tumorigenic hazard for humans, this conclusion being supported by negative data from permethrin epidemiological studies.

Breast cancer in schizophrenia could be interleukin-33-mediated

Recent epidemiological and genetic studies have revealed an interconnection between schizophrenia and breast cancer. The mutual underlying pathophysiological mechanisms may be immunologically driven. A new cluster of molecules called alarmins may be involved in sterile brain inflammation, and we have already reported the potential impact of interleukin-33 (IL-33) on positive symptoms onset and the role of its soluble trans-membranes full length receptor (sST2) on amelioration of negative symptoms in schizophrenia genesis. Furthermore, these molecules have already been shown to be involved in breast cancer etiopathogenesis. In this review article, we aim to describe the IL-33/suppressor of tumorigenicity 2 (ST2) axis as a crossroad in schizophrenia-breast cancer comorbidity. Considering that raloxifene could be tissue-specific and improve cognition and that tamoxifen resistance in breast carcinoma could be improved by strategies targeting IL-33, these selective estrogen receptor modulators could be useful in complementary treatment. These observations could guide further somatic, as well as psychiatric therapeutical protocols by incorporating what is known about immunity in schizophrenia.

Molecular alterations that precede the establishment of the hallmarks of cancer: An approach on the prevention of hepatocarcinogenesis

Chronic liver injury promotes the molecular alterations that precede the establishment of cancer. Usually, several decades of chronic insults are needed to develop the most common primary liver tumor known as hepatocellular carcinoma. As other cancer types, liver cancer cells are governed by a common set of rules collectively called the hallmarks of cancer. Although those rules have provided a conceptual framework for understanding the complex pathophysiology of established tumors, therapeutic options are still ineffective in advanced stages. Thus, the molecular alterations that precede the establishment of cancer remain an attractive target for therapeutic interventions. Here, we first summarize the chemopreventive interventions targeting the early liver carcinogenesis stages. After an integrative analysis on the plethora of molecular alterations regulated by anticancer agents, we then underline and discuss that two critical processes namely oxidative stress and genetic alterations, play the role of 'dirty work laborer' in the initial cell damage and drive the transformation of preneoplastic into neoplastic cells, respectively; besides, the activation of cellular senescence works as a key mechanism in attempting to prevent the onset and establishment of liver cancer. Whereas the detrimental effects of the binomial made up of oxidative stress and genetic alterations are either eliminated or reduced, senescence activation is promoted by anticancer agents. We argue that collectively, oxidative stress, genetic alterations, and senescence are key events that influence the fate of initiated cells and the establishment of the hallmarks of cancer.

In Silico Approaches In Carcinogenicity Hazard Assessment: Current Status and Future Needs

Historically, identifying carcinogens has relied primarily on tumor studies in rodents, which require enormous resources in both money and time. In silico models have been developed for predicting rodent carcinogens but have not yet found general regulatory acceptance, in part due to the lack of a generally accepted protocol for performing such an assessment as well as limitations in predictive performance and scope. There remains a need for additional, improved in silico carcinogenicity models, especially ones that are more human-relevant, for use in research and regulatory decision-making. As part of an international effort to develop in silico toxicological protocols, a consortium of toxicologists, computational scientists, and regulatory scientists across several industries and governmental agencies evaluated the extent to which in silico models exist for each of the recently defined 10 key characteristics (KCs) of carcinogens. This position paper summarizes the current status of in silico tools for the assessment of each KC and identifies the data gaps that need to be addressed before a comprehensive in silico carcinogenicity protocol can be developed for regulatory use.

Application of humanized mice to toxicology studies: Evaluation of the human relevance of the mode of action for rodent liver tumor formation by activators of the constitutive androstane receptor (CAR)

The constitutive androstane receptor (CAR)-mediated mode of action (MOA) for phenobarbital (PB)-induced rodent liver tumor formation has been established, with increased hepatocyte proliferation, which is a key event in tumor formation. Previous studies have demonstrated that PB and other CAR-activators stimulate proliferation in cultured rodent hepatocytes, but not in cultured human hepatocytes. However, in the genetically humanized CAR and pregnane X receptor (PXR) mouse (hCAR/hPXR mouse, downstream genes are still mouse), PB increased hepatocyte proliferation and tumor production in vivo. In contrast to the hCAR/hPXR mouse, studies with chimeric mice with human hepatocytes (PXB-mouse, both receptor and downstream genes are human) demonstrated that PB did not increase human hepatocyte proliferation in vivo. PB increased hepatocyte proliferation in a chimeric mouse model with rat hepatocytes, indicating that the lack of human hepatocyte proliferation is not due to any functional defect in the chimeric mouse liver environment. Gene expression analysis demonstrated that the downstream genes of CAR/PXR activation were similar in hCAR/hPXR and CD-1 mice, but differed from those observed in chimeric mice with human hepatocytes. These findings strongly support the conclusion that the MOA for CAR-mediated rodent liver tumor formation is qualitatively implausible for humans. Indeed, epidemiological studies have found no causal link between PB and human liver tumors. There are many similarities with respect to hepatic effects and species differences between rodent CAR and peroxisome proliferator-activated receptor α activators. Based on our research, the chimeric mouse with human hepatocytes (PXB-mouse) is reliable for human cancer risk assessment of test chemicals.

Dietary fibre to reduce colon cancer risk in Alaska Native people: the Alaska FIRST randomised clinical trial protocol

INTRODUCTION

Diet, shown to impact colorectal cancer (CRC) risk, is a modifiable environmental factor. Fibre foods fermented by gut microbiota produce metabolites that not only provide food for the colonic epithelium but also exert regulatory effects on colonic mucosal inflammation and proliferation. We describe methods used in a double-blinded, randomised, controlled trial with Alaska Native (AN) people to determine if dietary fibre supplementation can substantially reduce CRC risk among people with the highest reported CRC incidence worldwide.

METHODS AND ANALYSES

Eligible patients undergoing routine screening colonoscopy consent to baseline assessments and specimen/data collection (blood, urine, stool, saliva, breath and colon mucosal biopsies) at the time of colonoscopy. Following an 8-week stabilisation period to re-establish normal gut microbiota post colonoscopy, study personnel randomise participants to either a high fibre supplement (resistant starch, n=30) or placebo (digestible starch, n=30) condition, repeating stool sample collection. During the 28-day supplement trial, each participant consumes their usual diet plus their supplement under direct observation. On day 29, participants undergo a flexible sigmoidoscopy to obtain mucosal biopsy samples to measure the effect of the supplement on inflammatory and proliferative biomarkers of cancer risk, with follow-up assessments and data/specimen collection similar to baseline. Secondary outcome measures include the impact of a high fibre supplement on the oral and colonic microbiome and biofluid metabolome.

ETHICS AND DISSEMINATION

Approvals were obtained from the Alaska Area and University of Pittsburgh Institutional Review Boards and Alaska Native Tribal Health Consortium and Southcentral Foundation research review bodies. A data safety monitoring board, material transfer agreements and weekly study team meetings provide regular oversight throughout the study. Study findings will first be shared with AN tribal leaders, health administrators, providers and community members. Peer-reviewed journal articles and conference presentations will be forthcoming once approved by tribal review bodies.

TRIAL REGISTRATION NUMBER

NCT03028831.

Adversity Considerations for Thyroid Follicular Cell Hypertrophy and Hyperplasia in Nonclinical Toxicity Studies: Results From the 6th ESTP International Expert Workshop

The European Society of Toxicologic Pathology organized an expert workshop in May 2018 to address adversity considerations related to thyroid follicular cell hypertrophy and/or hyperplasia (FCHH), which is a common finding in nonclinical toxicity studies that can have important implications for risk assessment of pharmaceuticals, food additives, and environmental chemicals. The broad goal of the workshop was to facilitate better alignment in toxicologic pathology and regulatory sciences on how to determine adversity of FCHH. Key objectives were to describe common mechanisms leading to thyroid FCHH and potential functional consequences; provide working criteria to assess adversity of FCHH in context of associated findings; and describe additional methods and experimental data that may influence adversity determinations. The workshop panel was comprised of representatives from the European Union, Japan, and the United States. Participants shared case examples illustrating issues related to adversity assessments of thyroid changes. Provided here are summary discussions, key case presentations, and panel recommendations. This information should increase consistency in the interpretation of adverse changes in the thyroid based on pathology findings in nonclinical toxicity studies, help integrate new types of biomarker data into the review process, and facilitate a more systematic approach to communicating adversity determinations in toxicology reports.

Hormesis Effect of Methyl Triclosan on Cell Proliferation and Migration in Human Hepatocyte L02 Cells

Methyl triclosan (mTCS) is a methylated derivative of triclosan (TCS), which is extensively used as an antimicrobial component of various nursing products and disinfectants. Current research studies of mTCS mainly focused on the environmental persistence and bioaccumulation potential. Knowledge regarding the toxicity and carcinogenicity of mTCS is limited until now. In this study, the human hepatocyte L02 cells were used to investigate the cellular effects of mTCS under different concentrations (0.1-60 μM). The hormesis effect was observed where a low dose of mTCS (≤5 μM) exposure stimulated the cell proliferation ability, while high-dose exposure (≥20 μM) inhibited cell proliferation. In the same time, low doses of mTCS (0.5 and 1 μM) induced enhanced anchorage-independent proliferation ability and cell migration ability, indicating a positive effect on malignant transformation in L02 cells. Moreover, reactive oxygen species productions were significantly increased after mTCS exposure (≥1 μM), as compared with the control group. Furthermore, expressions of tumor-related genes, mouse double minute 2 (MDM2), matrix metalloproteinase 9 (MMP9), and proliferating cell nuclear antigen (PCNA), and proto-oncogene MYC (c-Myc), Jun, and FosB were significantly upregulated, while no significant changes were observed on expressions of apoptosis-related and cell cycle-related genes in L02 cells after exposure of low-dose mTCS. In conclusion, these results indicated that a low dose of mTCS had a hormesis effect in L02 cells on cell proliferation and malignant transformation in vitro, which might be mediated through oxidative stress response.

Comparison of the Hepatic Effects of Phenobarbital in Chimeric Mice Containing Either Rat or Human Hepatocytes With Humanized Constitutive Androstane Receptor and Pregnane X Receptor Mice

Using a chimeric mouse humanized liver model, we provided evidence that human hepatocytes are refractory to the mitogenic effects of rodent constitutive androstane receptor (CAR) activators. To evaluate the functional reliability of this model, the present study examined mitogenic responses to phenobarbital (PB) in chimeric mice transplanted with rat hepatocytes, because rats are responsive to CAR activators. Treatment with 1000 ppm PB for 7 days significantly increased replicative DNA synthesis (RDS) in rat hepatocytes of the chimeric mice, demonstrating that the transplanted hepatocyte model is functionally reliable for cell proliferation analysis. Treatment of humanized CAR and pregnane X receptor (PXR) mice (hCAR/hPXR mice) with 1000 ppm PB for 7 days significantly increased hepatocyte RDS together with increases in several mitogenic genes. Global gene expression analysis was performed with liver samples from this and from previous studies focusing on PB-induced Wnt/β-catenin signaling and showed that altered genes in hCAR/hPXR mice clustered most closely with liver tumor samples from a diethylnitrosamine/PB initiation/promotion study than with wild-type mice. However, different gene clusters were observed for chimeric mice with human hepatocytes for Wnt/β-catenin signaling when compared with those of hCAR/hPXR mice, wild-type mice, and liver tumor samples. The results of this study demonstrate clear differences in the effects of PB on hepatocyte RDS and global gene expression between human hepatocytes of chimeric mice and hCAR/hPXR mice, suggesting that the chimeric mouse model is relevant to humans for studies on the hepatic effects of rodent CAR activators whereas the hCAR/hPXR mouse is not.

Chimeric Mouse With Humanized Liver Is an Appropriate Animal Model to Investigate Mode of Action for Porphyria-Mediated Hepatocytotoxicity

Porphyrinogenic compounds are known to induce porphyria-mediated hepatocellular injury and subsequent regenerative proliferation in rodents, ultimately leading to hepatocellular tumor induction. However, an appropriate in vivo experimental model to evaluate an effect of porphyrinogenic compounds on human liver has not been fully established. Recently, the chimeric mouse with humanized liver (PXB mice) became widely used as a humanized model in which human hepatocytes are transplanted. In the present study, we examined the utility of PXB mice as an in vivo experimental model to evaluate the key events of the porphyria-mediated cytotoxicity mode of action (MOA) in humans. The treatment of PXB mice with 5-aminolevulinic acid, a representative porphyrinogenic compound, for 28 days caused protoporphyrin IX accumulation, followed by hepatocyte necrosis, increased mitosis, and an increase in replicative DNA synthesis in human hepatocytes, indicative of cellular injury and regenerative proliferation, similar to findings in patients with porphyria or experimental porphyria models and corresponding to the key events of the MOA for porphyria-mediated hepatocellular carcinogenesis. We conclude that the PXB mouse is a useful model to evaluate the key events of the porphyria-mediated cytotoxicity MOA in humans and suggest the utility of PXB mice for clarifying the human relevancy of findings in mice.

An updated mode of action and human relevance framework evaluation for Formaldehyde-Related nasal tumors

Formaldehyde is a reactive aldehyde naturally present in all plant and animal tissues and a critical component of the one-carbon metabolism pathway. It is also a high production volume chemical used in the manufacture of numerous products. Formaldehyde is also one of the most well-studied chemicals with respect to environmental fate, biology, and toxicology-including carcinogenic potential, and mode of action (MOA). In 2006, a published MOA for formaldehyde-induced nasal tumors in rats concluded that nasal tumors were most likely driven by cytotoxicity and regenerative cell proliferation, with possible contributions from direct genotoxicity. In the past 15 years, new research has better informed the MOA with the publication of in vivo genotoxicity assays, toxicogenomic analyses, and development of ultra-sensitive methods to measure endogenous and exogenous formaldehyde-induced DNA adducts. Herein, we review and update the MOA for nasal tumors, with particular emphasis on the numerous studies published since 2006. These new studies further underscore the involvement of cytotoxicity and regenerative cell proliferation, and further inform the genotoxic potential of inhaled formaldehyde. The data lend additional support for the use of mechanistic data for the derivation of toxicity criteria and/or scientifically supported approaches for low-dose extrapolation for the risk assessment of formaldehyde.

Critical evaluation of the human relevance of the mode of action for rodent liver tumor formation by activators of the constitutive androstane receptor (CAR)

Many nongenotoxic chemicals have been shown to produce liver tumors in mice and/or rats by a mode of action (MOA) involving activation of the constitutive androstane receptor (CAR). Studies with phenobarbital (PB) and other compounds have identified the key events for this MOA: CAR activation; increased hepatocellular proliferation; altered foci formation; and ultimately the development of adenomas/carcinomas. In terms of human relevance, the pivotal species difference is that CAR activators are mitogenic agents in mouse and rat hepatocytes, but they do not stimulate increased hepatocellular proliferation in humans. This conclusion is supported by substantial in vitro studies with cultured rodent and human hepatocytes and also by in vivo studies with chimeric mice with human hepatocytes. Examination of the literature reveals many similarities in the hepatic effects and species differences between activators of rodent CAR and the peroxisome proliferator-activated receptor alpha (PPARα), with PPARα activators also not being mitogenic agents in human hepatocytes. Overall, a critical analysis of the available data demonstrates that the established MOA for rodent liver tumor formation by PB and other CAR activators is qualitatively not plausible for humans. This conclusion is supported by data from several human epidemiology studies.

An adverse outcome pathway for small intestinal tumors in mice involving chronic cytotoxicity and regenerative hyperplasia: a case study with hexavalent chromium, captan, and folpet

Small intestinal (SI) tumors are relatively uncommon outcomes in rodent cancer bioassays, and limited information regarding chemical-induced SI tumorigenesis has been reported in the published literature. Herein, we propose a cytotoxicity-mediated adverse outcome pathway (AOP) for SI tumors by leveraging extensive target species- and site-specific molecular, cellular, and histological mode of action (MOA) research for three reference chemicals, the fungicides captan and folpet and the transition metal hexavalent chromium (Cr(VI)). The gut barrier functions through highly efficient homeostatic regulation of SI epithelial cell sloughing, regenerative proliferation, and repair, which involves the replacement of up to 10¹¹ cells per day. This dynamic turnover in the SI provides a unique local environment for a cytotoxicity mediated AOP/MOA. Upon entering the duodenum, cytotoxicity to the villous epithelium is the molecular initiating event, as indicated by crypt elongation, villous atrophy/blunting, and other morphologic changes. Over time, the regenerative capacity of the gut epithelium to compensate declines as epithelial loss accelerates, especially at higher exposures. The first key event (KE), sustained regenerative crypt proliferation/hyperplasia, requires sufficient durations, likely exceeding 6 or 12 months, due to extensive repair capacity, to create more opportunities for the second KE, spontaneous mutation/transformation, ultimately leading to proximal SI tumors. Per OECD guidance, biological plausibility, essentiality, and empirical support were assessed using modified Bradford Hill considerations. The weight-of-evidence also included a lack of induced mutations in the duodenum after up to 90 days of Cr(VI) or captan exposure. The extensive evidence for this AOP, along with the knowledge that human exposures are orders of magnitude below those associated with KEs in this AOP, supports its use for regulatory applications, including hazard identification and risk assessment.

Chemical carcinogen safety testing: OECD expert group international consensus on the development of an integrated approach for the testing and assessment of chemical non-genotoxic carcinogens

While regulatory requirements for carcinogenicity testing of chemicals vary according to product sector and regulatory jurisdiction, the standard approach starts with a battery of genotoxicity tests (which include mutagenicity assays). If any of the in vivo genotoxicity tests are positive, a lifetime rodent cancer bioassay may be requested, but under most chemical regulations (except plant protection, biocides, pharmaceuticals), this is rare. The decision to conduct further testing based on genotoxicity test outcomes creates a regulatory gap for the identification of non-genotoxic carcinogens (NGTxC). With the objective of addressing this gap, in 2016, the Organization of Economic Cooperation and Development (OECD) established an expert group to develop an integrated approach to the testing and assessment (IATA) of NGTxC. Through that work, a definition of NGTxC in a regulatory context was agreed. Using the adverse outcome pathway (AOP) concept, various cancer models were developed, and overarching mechanisms and modes of action were identified. After further refining and structuring with respect to the common hallmarks of cancer and knowing that NGTxC act through a large variety of specific mechanisms, with cell proliferation commonly being a unifying element, it became evident that a panel of tests covering multiple biological traits will be needed to populate the IATA. Consequently, in addition to literature and database investigation, the OECD opened a call for relevant assays in 2018 to receive suggestions. Here, we report on the definition of NGTxC, on the development of the overarching NGTxC IATA, and on the development of ranking parameters to evaluate the assays. Ultimately the intent is to select the best scoring assays for integration in an NGTxC IATA to better identify carcinogens and reduce public health hazards.

Anillin facilitates cell proliferation and induces tumor growth of hepatocellular carcinoma via miR-138/SOX4 axis regulation

Actin-binding protein Anillin plays a pivotal role in regulating cytokinesis during the cell cycle, and involves in tumorigenesis and progress. However, the exact regulation mechanism of Anillin in human hepatocellular carcinoma (HCC) remains largely unknown. In this study, we examined and verified the anomalous high expression of Anillin in both HCC patients' specimens and HCC cell lines. High expression of Anillin is associated with dismal clinicopathologic features of HCC patients and poor prognosis. We conducted loss-of and gain-of function studies in HCC Hep3B cells. Anillin presented a significantly facilitating effect on cell proliferation in vitro and induced remarkable tumor growth in vivo. We found that the over-expression of Anillin was driven by a potential axis of miR-138/SOX4. Transcription factor SOX4 presented a high expression profile positive correlated with Anillin, and ChIP assay validated the interaction between SOX4 and the specific sequence of the promoter region of Anillin gene. While, we verified miR-138 as an upstream regulator of SOX4, which is abrogated in HCC cells and exerts degenerating effect on SOX4 mRNA. In our conclusion, Anillin facilitates the cell proliferation and enhances tumor growth of HCC, and is modulated by miR-138/SOX4 axis which regulates the transcriptional activity of Anillin. Findings above demonstrate us a probable axis for HCC diagnosis and treatment.

Summary of the main point

Anillin facilitates the cell proliferation and enhances tumor growth in HCC. The transcriptional activity of Anillin is modulated by miR-138/SOX4 axis. Findings above demonstrate us a probable axis for HCC diagnosis and treatment.

Cell proliferation analysis is a reliable predictor of lack of carcinogenicity: Case study using the pyrethroid imiprothrin on lung tumorigenesis in mice

In the mouse carcinogenicity study, an apparent increase in lung adenocarcinoma was observed in male mice at 7000 ppm. Based on the overall evaluation of toxicology, oncology, pathology and statistics, we concluded that the apparent increase in lung tumors is not relevant for evaluation of carcinogenicity of imiprothrin (Regul Toxicol Pharmacol, 105, 1-14, 2019). To investigate whether imiprothrin has any mitogenic effect on mouse Club cells, the present study examined its effects on replicative DNA synthesis of Club cells and lung histopathology in male mice treated with imiprothrin for 7 days at 3500 and 7000 ppm in the diet. Isoniazid, a known mouse lung mitogen and tumor inducer, was also examined at 1000 ppm in the diet as a positive control of Club cell mitogenesis and morphological changes. Neither imiprothrin nor isoniazid caused any necrotic changes in lung by light or electron microscopy. There were no increases observed in the bromodeoxyuridine (BrdU) labeling index in the imiprothrin groups, while there was a statistically significant increase in the BrdU labeling index in the isoniazid group. These findings demonstrate that imiprothrin does not induce mouse Club cell proliferation or morphologic changes, supporting our previous conclusion described above. Thus, imiprothrin should not be classified as a carcinogen. Furthermore, this study indicates that short-term studies focusing on cell proliferation can be reliable for predicting a lack of carcinogenic potential of test chemicals.

Development and Validation of an Image Analysis System for the Measurement of Cell Proliferation in Mammary Glands of Rats

Reliable detection and measurement of cell proliferation are essential in the preclinical assessment of carcinogenic risk of therapeutics. In this context, the assessment of mitogenic potential on mammary glands is crucial in the preclinical safety evaluation of novel insulins. The existing manual counting is time-consuming and subject to operator bias. To standardize the processes, make it faster, and resistant to errors, we developed a semiautomated image analysis system (CEPA software, which is open-source) for counting of proliferating cells in photomicrographs of mammary gland sections of rats labeled with Ki-67. We validated the software and met the predefined targets for specificity, accuracy, and reproducibility. In comparison to manual counting, the respective mean differences in absolute labeling indices (LIs) for CEPA software were 3.12% for user 1 and 3.05% for user 2. The respective regression analysis revealed a good correlation between the CEPA software user and manual counting. Moreover, the CEPA software showed enhanced reproducibility between independent users. The interuser variability is centered around 0 and the absolute difference was about 0.53% LI. Based on validation data, our software has superiority to the manual counting and is a valid and reliable tool for the routine analysis of cell proliferation in mammary glands from rats exposed to insulin analogs.

Development of a Novel AOP for Cyp2F2-Mediated Lung Cancer in Mice

Traditional methods for carcinogenicity testing rely heavily on the rodent bioassay as the standard for identification of tumorigenic risk. As such, identification of species-specific outcomes and/or metabolism are a frequent argument for regulatory exemption. One example is the association of tumor formation in the mouse lung after exposure to Cyp2F2 ligands. The adverse outcome pathway (AOP) framework offers a theoretical platform to address issues of species specificity that is consistent, transparent, and capable of integrating data from new approach methodologies as well as traditional data streams. A central premise of the AOP concept is that pathway progression from the molecular initiating event (MIE) implies a definable “response-response” (R-R) relationship between each key event (KE) that drives the pathway towards a specific adverse outcome (AO). This article describes an AOP for lung cancer in the mouse from an MIE of Cyp2F2-specific reactive metabolite formation, advancing through KE that include protein and/or nucleic acid adducts, diminished Club Cell 10 kDa (CC10) protein expression, hyperplasia of CC10 deficient Club cells, and culminating in the AO of mixed-cell tumor formation in the distal airways. This tumor formation is independent of route of exposure and our AOP construct is based on overlapping mechanistic events for naphthalene, styrene, ethyl benzene, isoniazid, and fluensulfone in the mouse. This AOP is intended to accelerate the explication of an apparent mouse-specific outcome and serve as a starting point for a quantitative analysis of mouse-human differences in susceptibility to the tumorigenic effects of Cyp2F2 ligands.

Sedaxane-Use of Nuclear Receptor Transactivation Assays, Toxicogenomics, and Toxicokinetics as Part of a Mode of Action Framework for Rodent Liver Tumors

Experimental data demonstrate a mode of action (MOA) for liver tumors in male rats and mice treated with sedaxane that starts with activation of CAR, followed by altered expression of CAR-responsive genes, increased cell proliferation, and eventually clonal expansion of preneoplastic cells, leading to the development of altered foci and tumors. This MOA is nonrelevant to human risk assessments. Methods and results in the MOA work for sedaxane illustrate promising directions that future MOA studies may be able to employ, in the spirit of "Tox21" and reduction of in vivo animal use: (1) currently available in vitro CAR and PXR reporter assays demonstrated that sedaxane is a direct CAR activator in mice and rats, and a weak PXR activator in rats; (2) mouse liver microarray results compared with a published CAR biomarker signature (based on 83 genes) showed a clear, statistical match, and a lack of correlation to similar biomarker signatures for AhR, PPARα, and STAT5B; (3) Ki67 immunohistochemistry and zonal image analysis showed significant increases in this marker of cell proliferation in mouse liver, without the need to dose a DNA labeling agent; and (4) toxicokinetic analysis of Cmax levels of sedaxane in blood showed a marked species difference between mice and rats that helps to explain differences in sensitivity to sedaxane. Incorporating these tools into the study plan for a new agrochemical or drug during development offers a promising alternative to the traditional need to conduct later, specialized MOA studies after the results of chronic bioassays are known.

Case examples of an evaluation of the human relevance of the pyrethroids/pyrethrins-induced liver tumours in rodents based on the mode of action

Rodent carcinogenicity studies are useful for screening for human carcinogens but they are not perfect. Some modes of action (MOAs) lead to cancers in both experimental rodents and humans, but others that lead to cancers in rodents do not do so in humans. Therefore, analysing the MOAs by which chemicals produce tumours in rodents and determining the relevance of such tumour data for human risk are critical. Recently, experimental data were obtained as case examples of an evaluation of the human relevance of pyrethroid (metofluthrin and momfluorothrin)- and pyrethrins-induced liver tumours in rats based on MOA. The MOA analysis, based on the International Programme on Chemical Safety (IPCS) framework, concluded that experimental data strongly support that the postulated MOA for metofluthrin-, momfluorothrin- and pyrethrins-produced rat hepatocellular tumours is mediated by constitutive androstane receptor (CAR) activation. Since metofluthrin and momfluorothrin are close structural analogues, reproducible outcomes for both chemicals provide confidence in the MOA findings. Furthermore, cultured human hepatocyte studies and humanized chimeric mouse liver studies demonstrated species difference between human hepatocytes (refractory to the mitogenic effects of these compounds) and rat hepatocytes (sensitive to their mitogenic effects). These data strongly support the hypothesis that the CAR-mediated MOA for liver tumorigenesis is of low carcinogenic risk for humans. In this research, in addition to cultured human hepatocyte studies, the usefulness of the humanized chimeric liver mouse models was clearly demonstrated. These data substantially influenced decisions in regulatory toxicology. In this review I comprehensively discuss the human relevance of the CAR-mediated MOA for rodent liver tumorigenesis based on published information, including our recent molecular research on CAR-mediated MOA.

Screening for human urinary bladder carcinogens: two-year bioassay is unnecessary

Screening for carcinogens in general, and for the urinary bladder specifically, traditionally involves a two-year bioassay in rodents, the results of which often do not have direct relevance to humans with respect to mode of action (MOA) and/or dose response. My proposal describes a multi-step short-term (90 day) screening process that characterizes known human urinary bladder carcinogens, and identifies those reported in rodent two-year bioassays. The initial step is screening for urothelial proliferation, by microscopy or by increased Ki-67 labeling index. If these are negative, the agent is not a urinary bladder carcinogen. If either of these is positive, an MOA and dose response analysis are performed. DNA reactivity is evaluated. If the chemical is non-DNA reactive, evaluation for cytotoxicity is performed. This involves examination of the urothelium and urine, the latter to identify the generation of urinary solids (e.g. calculi). If urinary solids are the cause of cytotoxicity, the MOA is not relevant to human cancer, but dose response becomes essential for evaluating potential toxicity to humans. If cytotoxicity occurs but no urinary solids are detected, urinary concentrations of the chemical and its metabolites are evaluated, and compared to in vitro cytotoxicity against rodent and human immortalized urothelial cell lines. Based on this process, a screen for urinary bladder carcinogenicity is reliable, and more importantly, can be based on MOA and dose response analyses useful in the overall risk assessment for possible human bladder cancer. The proposed procedure is shorter, less expensive and more relevant than the two-year bioassay.

Human relevance of rodent liver tumour formation by constitutive androstane receptor (CAR) activators

A large number of nongenotoxic chemicals have been shown to increase the incidence of liver tumours in rats and/or mice by a mode of action (MOA) involving activation of the constitutive androstane receptor (CAR). Studies with the model CAR activator phenobarbital (PB) and its sodium salt (sodium phenobarbital; NaPB) have demonstrated that the key and associative events for rat and mouse liver tumour formation include CAR activation, increased hepatocyte replicative DNA synthesis (RDS), induction of cytochrome P450 CYP2B subfamily enzymes, liver hypertrophy, increased altered hepatic foci and hepatocellular adenomas/carcinomas. The key species difference between the rat and mouse compared to humans, is that human hepatocytes are refractory to the mitogenic effects of PB/NaPB and other CAR activators. While PB/NaPB and other CAR activators stimulate RDS in rat and mouse hepatocytes in both in vitro and in vivo studies, such compounds do not stimulate RDS in cultured human hepatocytes and in in vivo studies performed in chimeric mice with humanised livers. In terms of species differences in RDS, unlike the rat and mouse, humans are similar to other species such as the Syrian hamster and guinea pig in being nonresponsive to the mitogenic effects of CAR activators. Overall, the MOA for rat and mouse liver tumour formation by PB/NaPB and other CAR activators is considered qualitatively not plausible for humans. This conclusion is supported by data from a number of epidemiological studies, which demonstrate that chronic treatment with PB does not increase the incidence of liver cancer in humans.

From the Cover: Genomic Effects of Androstenedione and Sex-Specific Liver Cancer Susceptibility in Mice

Current strategies for predicting carcinogenic mode of action for nongenotoxic chemicals are based on identification of early key events in toxicity pathways. The goal of this study was to evaluate short-term key event indicators resulting from exposure to androstenedione (A4), an androgen receptor agonist and known liver carcinogen in mice. Liver cancer is more prevalent in men compared with women, but androgen-related pathways underlying this sex difference have not been clearly identified. Short-term hepatic effects of A4 were compared with reference agonists of the estrogen receptor (ethinyl estradiol, EE) and glucocorticoid receptor (prednisone, PRED). Male B6C3F1 mice were exposed for 7 or 28 days to A4, EE, or PRED. EE increased and PRED suppressed hepatocyte proliferation, while A4 had no detectable effects. In a microarray analysis, EE and PRED altered >3000 and >670 genes, respectively, in a dose-dependent manner, whereas A4 did not significantly alter any genes. Gene expression was subsequently examined in archival liver samples from male and female B6C3F1 mice exposed to A4 for 90 days. A4 altered more genes in females than males and did not alter expression of genes linked to activation of the mitogenic xenobiotic receptors AhR, CAR, and PPARα in either sex. A gene expression biomarker was used to show that in female mice, the high dose of A4 activated the growth hormone-regulated transcription factor STAT5b, which controls sexually dimorphic gene expression in the liver. These findings suggest that A4 induces subtle age-related effects on STAT5b signaling that may contribute to the higher risk of liver cancer in males compared with females.

Epithelium Lining Rat Renal Papilla: Nomenclature and Association with Chronic Progressive Nephropathy (CPN)

Chronic progressive nephropathy (CPN) occurs commonly in rats, more frequently and severely in males than females. High-grade CPN is characterized by increased layers of the renal papilla lining, designated as urothelial hyperplasia in the International Harmonization of Nomenclature and Diagnostic Criteria classification. However, urothelium lining the pelvis is not equivalent to the epithelium lining the papilla. To evaluate whether the epithelium lining the renal papilla is actually urothelial in nature and whether CPN-associated multicellularity represents proliferation, kidney tissues from aged rats with CPN, from rats with multicellularity of the renal papilla epithelium of either low-grade or marked severity, and from young rats with normal kidneys were analyzed and compared. Immunohistochemical staining for uroplakins (urothelial specific proteins) was negative in the papilla epithelium in all rats with multicellularity or not, indicating these cells are not urothelial. Mitotic figures were rarely observed in this epithelium, even with multicellularity. Immunohistochemical staining for Ki-67 was negative. Papilla lining cells and true urothelium differed by scanning electron microscopy. Based on these findings, we recommend that the epithelium lining the papilla not be classified as urothelial, and the CPN-associated lesion be designated as vesicular alteration of renal papilla instead of hyperplasia and distinguished in diagnostic systems from kidney pelvis urothelial hyperplasia.

Simvastatin exerts anticancer effects in osteosarcoma cell lines via geranylgeranylation and c-Jun activation

Osteosarcoma is the leading primary bone cancer in young adults and exhibits high chemoresistance rates. Therefore, characterization of both alternative treatment options and the underlying mechanisms is essential. Simvastatin, a cholesterol-lowering drug, has among its pleiotropic effects anticancer potential. Characterizing this potential and the underlying mechanisms in osteosarcoma is the subject of the present study. Human osteosarcoma cells (SaOS-2 and U2OS) were treated with simvastatin (4-66 µM) for 48 or 72 h. The effects of downstream substrate mevalonate (MA) or substrates for isoprenylation farnesyl pyrophosphate (FPP) and geranylgeranyl-pyrophosphate (GGPP) were evaluated using add-back experiments. Tumour growth using MTT assay, apoptosis, cell cycle and signalling cascades involved in simvastatin-induced manipulation were analysed. The results revealed that simvastatin dose-dependently inhibited cell growth. Simvastatin significantly induced apoptosis, increased the Bax/Bcl-2 ratio, and cleavage of caspase-3 and PARP protein. Simvastatin impaired cell cycle progression as shown by significantly increased percentages of cells in the G0/G1 phase and lower percentages of cells in the S phase. Gene expression levels of cell cycle-regulating genes (TP53, CDKN1A and CDK1) were markedly altered. These effects were not completely abolished by FPP, but were reversed by MA and GGPP. JNK and c-Jun phosphorylation was enhanced after simvastatin treatment, while those were abolished when either MA or GGPP were added. In conclusion, simvastatin acts primarily by reducing prenylation to induce apoptosis and reduce osteosarcoma cell growth. Particularly enhanced activation of c-Jun seems to play a pivotal role in osteosarcoma cell death.

Toll-like receptor 2 induces adenosine receptor A2a and promotes human squamous carcinoma cell growth via extracellular signal regulated kinases ½

Patient treatment for oral squamous cell carcinoma (OSCC) not associated with Human papillomavirus remains problematic. OSCC microenvironment is typically inflamed and colonized by microorganisms, providing ligands for toll-like receptors (TLR). In immune cells TLR2 and TLR4 activate NF-kB and extracellular signal regulated kinase (ERK)1/2 pathways, leading to upregulation of inhibitory adenosine receptors A2a and A2b, and reduction in stimulatory A1 and A3. How TLR and adenosine receptors function in SCC cells is not understood. To address this gap, we evaluated TLR and adenosine receptor expression and function in human OSCC cells and keratinocytes. TLR2 and A2a were co-expressed in pre-cancer and SCC cells of 17 oral specimens. In vitro, 5/6 OSCC lines expressed more TLR2 than TLR1, 4 or 6 mRNA. TLR2 ligands stimulated A2a expression in TLR2-high cell lines, but no A1 or A3 was detected with or without stimuli. In TLR2-high OSCC, TLR2/1, 2/6 and adenosine receptor agonists activated ERK1/2. TLR2-mediated ERK1/2 phosphorylation resulted in accumulation of c-FOS, ERK-dependent cell proliferation and reduced caspase-3 activity. Similar ERK1/2-dependent proliferation and decreased caspase-3 activity were caused by combined TLR2 and adenosine receptor stimuli. We conclude that TLR2 and adenosine receptor agonists, known to be present in the tumor microenvironment, may contribute to OSCC progression in part via direct effects on the ERK1/2 pathway in squamous carcinoma cells.

Candidate genes responsible for early key events of phenobarbital-promoted mouse hepatocellular tumorigenesis based on differentiation of regulating genes between wild type mice and humanized chimeric mice

Phenobarbital (PB) is a nongenotoxic hepatocellular carcinogen in rodents. PB induces hepatocellular tumors by activating the constitutive androstane receptor (CAR). Some previous research has suggested the possible involvement of epigenetic regulation in PB-promoted hepatocellular tumorigenesis, but the details of its molecular mechanism are not fully understood. In the present study, comprehensive analyses of DNA methylation, hydroxymethylation and gene expression using microarrays were performed in mouse hepatocellular adenomas induced by a single 90 mg kg-1 intraperitoneal injection dose of diethylnitrosamine (DEN) followed by 500 ppm PB in the diet for 27 weeks. DNA modification and expression of hundreds of genes are coordinately altered in PB-induced mouse hepatocellular adenomas. Of these, gene network analysis showed alterations of CAR signaling and tumor development-related genes. Pathway enrichment analysis revealed that differentially methylated or hydroxymethylated genes belong mainly to pathways involved in development, immune response and cancer cells in contrast to differentially expressed genes belonging primarily to the cell cycle. Furthermore, overlap was evaluated between the genes with altered expression levels with 5-methylcytosine (5mC) and 5-hydroxymethylcytosine (5hmC) alterations in mouse hepatocellular adenoma induced by DEN/PB and the genes with altered expression levels in the liver of CD-1 mice or humanized chimeric mice treated with PB for 7 days. With the integration of transcriptomic and epigenetic approaches, we detected candidate genes responsible for early key events of PB-promoted mouse hepatocellular tumorigenesis. Interestingly, these genes did not overlap with genes altered by the PB treatment of humanized chimeric mice, thus suggesting a species difference between the effects of PB in mouse and human hepatocytes.

Metabolic Disruption Early in Life is Associated With Latent Carcinogenic Activity of Dichloroacetic Acid in Mice

Early-life environmental factors can influence later-life susceptibility to cancer. Recent evidence suggests that metabolic pathways may mediate this type of latency effect. Previously, we reported that short-term exposure to dichloroacetic acid (DCA) increased liver cancer in mice 84 weeks after exposure was stopped. Here, we evaluated time course dynamics for key events related to this effect. This study followed a stop-exposure design in which 28-day-old male B6C3F1 mice were given the following treatments in drinking water for up to 93 weeks: deionized water (dH2O, control); 3.5 g/l DCA continuously; or 3.5 g/l DCA for 4-52 weeks followed by dH2O. Effects were evaluated at eight interim time points. A short-term biomarker study was used to evaluate DCA effects at 6, 15, and 30 days. Liver tumor incidence was higher in all DCA treatment groups, including carcinomas in 82% of mice previously treated with DCA for only 4 weeks. Direct effects of DCA in the short-term study included decreased liver cell proliferation and marked mRNA changes related to mitochondrial dysfunction and altered cell metabolism. However, all observed short-term effects of DCA were ultimately reversible, and prior DCA treatment did not affect liver cell proliferation, apoptosis, necrosis, or DNA sequence variants with age. Key intermediate events resulting from transient DCA exposure do not fit classical cytotoxic, mitogenic, or genotoxic modes of action for carcinogenesis, suggesting a distinct mechanism associated with early-life metabolic disruption.

Renal tubular and adrenal medullary tumors in the 2-year rat study with canagliflozin confirmed to be secondary to carbohydrate (glucose) malabsorption in the 15-month mechanistic rat study

During preclinical development of canagliflozin, an SGLT2 inhibitor, treatment-related pheochromocytomas, renal tubular tumors (RTT), and testicular Leydig cell tumors were reported in the 2-year rat toxicology study. In a previous 6-month rat mechanistic study, feeding a glucose free diet prevented canagliflozin effects on carbohydrate malabsorption as well as the increase in cell proliferation in adrenal medulla and kidneys, implicating carbohydrate malabsorption as the mechanism for tumor formation. In this chronic study male Sprague-Dawley rats were dosed orally with canagliflozin at high dose-levels (65 or 100 mg/kg/day) for 15 months and received either a standard diet or a glucose-free diet. Canagliflozin-dosed rats on standard diet showed presence of basophilic renal tubular tumors (6/90) and an increased incidence of adrenal medullary hyperplasia (35/90), which was fully prevented by feeding a glucose-free diet (no RTT's; adrenal medullary hyperplasia in ≤5/90). These data further confirm that kidney and adrenal medullary tumors in the 2-year rat study were secondary to carbohydrate (glucose) malabsorption and were not due to a direct effect of canagliflozin on these target tissues.

Effects of low doses of glyphosate on DNA damage, cell proliferation and oxidative stress in the HepG2 cell line

We studied the toxic effects of glyphosate in vitro on HepG2 cells exposed for 4 and 24 h to low glyphosate concentrations likely to be encountered in occupational and residential exposures [the acceptable daily intake (ADI; 0.5 μg/mL), residential exposure level (REL; 2.91 μg/mL) and occupational exposure level (OEL; 3.5 μg/mL)]. The assessments were performed using biomarkers of oxidative stress, CCK-8 colorimetric assay for cell proliferation, alkaline comet assay and cytokinesis-block micronucleus (CBMN) cytome assay. The results obtained indicated effects on cell proliferation, both at 4 and 24 h. The levels of primary DNA damage after 4-h exposure were lower in treated vs. control samples, but were not significantly changed after 24 h. Using the CBMN assay, we found a significantly higher number of MN and nuclear buds at ADI and REL after 4 h and a lower number of MN after 24 h. The obtained results revealed significant oxidative damage. Four-hour exposure resulted in significant decrease at ADI [lipid peroxidation and glutathione peroxidase (GSH-Px)] and OEL [lipid peroxidation and level of total antioxidant capacity (TAC)], and 24-h exposure in significant decrease at OEL (TAC and GSH-Px). No significant effects were observed for the level of reactive oxygen species (ROS) and glutathione (GSH) for both treatment, and for 24 h for lipid peroxidation. Taken together, the elevated levels of cytogenetic damage found by the CBMN assay and the mechanisms of primary DNA damage should be further clarified, considering that the comet assay results indicate possible cross-linking or DNA adduct formation.

Glyphosate toxicity and carcinogenicity: a review of the scientific basis of the European Union assessment and its differences with IARC

Glyphosate is the most widely used herbicide worldwide. It is a broad spectrum herbicide and its agricultural uses increased considerably after the development of glyphosate-resistant genetically modified (GM) varieties. Since glyphosate was introduced in 1974, all regulatory assessments have established that glyphosate has low hazard potential to mammals, however, the International Agency for Research on Cancer (IARC) concluded in March 2015 that it is probably carcinogenic. The IARC conclusion was not confirmed by the EU assessment or the recent joint WHO/FAO evaluation, both using additional evidence. Glyphosate is not the first topic of disagreement between IARC and regulatory evaluations, but has received greater attention. This review presents the scientific basis of the glyphosate health assessment conducted within the European Union (EU) renewal process, and explains the differences in the carcinogenicity assessment with IARC. Use of different data sets, particularly on long-term toxicity/carcinogenicity in rodents, could partially explain the divergent views; but methodological differences in the evaluation of the available evidence have been identified. The EU assessment did not identify a carcinogenicity hazard, revised the toxicological profile proposing new toxicological reference values, and conducted a risk assessment for some representatives uses. Two complementary exposure assessments, human-biomonitoring and food-residues-monitoring, suggests that actual exposure levels are below these reference values and do not represent a public concern.

Quantification of epithelial cell proliferation, cell dynamics, and cell kinetics in vivo

The measurement of cell proliferation in vivo is usually carried out by the examination of static measures. These comprise the mitotic index or labeling indices using incorporation of DNA synthesis markers such as bromodeoxyuridine or tritiated thymidine, or intrinsic markers, such as Ki67 and proliferative cell nuclear antigen (PCNA). But static measures only provide a 'snapshot' of cell proliferation. Rate measures, including double labeling methods and the metaphase arrest method, can actually measure cell production rates but they are far less utilized at present. Transit times and migration rates can also be measured using pulse and chase labeling or by following the transit of labeled cells through the tissue. Simple indices of cell division can easily be confounded by concomitant changes in the compartment size and many alleged markers of proliferation have serious shortcomings, as the markers may be involved in multiple aspects of cell regulation. The complexities of studying proliferation in vivo are illustrated here with a focus on the gastrointestinal tract. Some of these methods can help elucidate the role of the stem cells and their relationship to label retaining cells. WIREs Dev Biol 2017, 6:e274. doi: 10.1002/wdev.274 For further resources related to this article, please visit the WIREs website.