Transcriptomic analyses of livers from mice exposed to 1,4-dioxane for up to 90 days to assess potential mode(s) of action underlying liver tumor development.

1,4-Dioxane is a volatile organic compound with industrial and commercial applications as a solvent and in the manufacture of other chemicals. 1,4-Dioxane has been demonstrated to induce liver tumors in chronic rodent bioassays conducted at very high doses. The available evidence for 1,4-dioxane-induced liver tumors in rodents aligns with a threshold-dependent mode of action (MOA), with the underlying mechanism being less clear in the mouse than in rats. To gain a better understanding of the underlying molecular mechanisms related to liver tumor development in mice orally exposed to 1,4-dioxane, transcriptomics analysis was conducted on liver tissue collected from a 90-day drinking water study in female B6D2F1/Crl mice (Lafranconi et al., 2020). Using tissue samples from female mice exposed to 1,4-dioxane in the drinking water at concentrations of 0, 40, 200, 600, 2,000 or 6,000 ppm for 7, 28, and 90 days, transcriptomic analyses demonstrate minimal treatment effects on global gene expression at concentrations below 600 ppm. At higher concentrations, genes involved in phase II metabolism and mitotic cell cycle checkpoints were significantly upregulated. There was an overall lack of enrichment of genes related to DNA damage response. The increase in mitotic signaling is most prevalent in the livers of mice exposed to 1,4-dioxane at the highest concentrations for 90 days. This finding aligns with phenotypic changes reported by Lafranconi et al. (2020) after 90-days of exposure to 6,000 ppm 1,4-dioxane in the same tissues. The transcriptomics analysis further supports overarching study findings demonstrating a non-mutagenic, threshold-based, mitogenic MOA for 1,4-dioxane-induced liver tumors.

Lack of potential carcinogenicity for steviol glycosides - Systematic evaluation and integration of mechanistic data into the totality of evidence.

Steviol glycosides are present in the leaves of the Stevia rebaudiana plant, have a sweet taste, and have been used as a sweetener for centuries. To build on previous authoritative safety assessments of steviol glycosides, a systematic assessment of mechanistic data related to key characteristics of carcinogens (KCCs) was conducted. Over 900 KCC-relevant endpoints from peer-reviewed literature and high-throughput screening data (ToxCast/Tox21) were identified across individual steviol glycosides and derivatives, metabolites, and whole leaf extracts. Most data (both in vivo and in vitro, including human cells), showed inactivity. Studies were weighted according to quality and relevance. Although data were available for eight of the ten KCC, genotoxicity, oxidative stress, inflammation, and cell proliferation/cell death represent the KCCs with the most data. The data for these KCC primarily show beneficial activity (anti-inflammatory, antioxidant, and anti-proliferative). Following integration across all data, and accounting for study quality and relevance, the totality of the evidence demonstrated an overall lack of genotoxic and carcinogenic activity for steviol glycosides. This is in agreement with previous regulatory decisions, and is consistent with the lack of tumor response in two-year rodent cancer bioassays. The findings support prior conclusions that steviol glycosides are unlikely to be carcinogenic in humans.

Lack of potential carcinogenicity for acesulfame potassium - Systematic evaluation and integration of mechanistic data into the totality of the evidence.

The safety of low- and no-calorie sweeteners remains a topic of general interest. Substantial evidence exists demonstrating a lack of carcinogenicity of the no-calorie sweetener acesulfame potassium (Ace K). The objective of this evaluation was to conduct a systematic assessment of available mechanistic data using a framework that quantitatively integrates proposed key characteristics of carcinogens (KCCs) into the totality of the evidence. Over 800 KCC-relevant endpoints from a variety of in vitro and in vivo assays were assessed for quality, relevance, and activity, and integrated to determine the overall strength of the evidence for plausibility that Ace K acts through the KCC. Overall, there was a lack of activity across the KCCs (overall integrated score <0 and no "strong" categorization for evidence of activity) in which data were identified. Together with the absence of treatment-related tumor effects in rodent bioassays, these results support the conclusion that Ace K is unlikely to induce a carcinogenic response. This assessment employed a weight of the evidence analysis that includes the consideration of factors such as reliability, strength of the model system, activity, and dose in a complex and heterogeneous dataset, and the ultimate integration of multiple data streams in the cancer hazard evaluation.

Systematic assessment of mechanistic data for FDA-certified food colors and neurodevelopmental processes.

Seven US FDA-batch certified synthetic food colors are approved for use as food additives in the United States. Perceived neurodevelopmental concerns for these colors persist. This study assessed the plausibility of such an association through the evaluation of mechanistic evidence collected from in vitro assays or other alternative models. Mechanisms and molecular targets underlying neurodevelopmental processes associated with attention deficit and hyperactivity disorder (ADHD) and other neurodevelopmental-related symptoms (e.g., cognitive function, learning and memory disorder, etc.) were identified. Publicly available data from the ToxCast/Tox21 high-throughput screening (HTS) program and peer-reviewed literature that measure activity of the colors for such molecular targets were analyzed and reviewed. Erythrosine (Red No. 3) was active in several assays mapped to neurodevelopmental processes - specifically, HTS assays that measure signals in neurotransmitter pathways. The remaining six colors do not appear to alter signaling pathways related to neurodevelopmental processes on the molecular or cellular level. This assessment provides an approach for systematically identifying and mapping mechanistic data to putative neurodevelopmental processes as a means to prioritize substances for possible further investigation. The assessment also provides insights into the lack of activity of synthetic food colors for key events in neurodevelopmental signaling pathways.

Lack of potential carcinogenicity for sucralose - Systematic evaluation and integration of mechanistic data into the totality of the evidence.

Sucralose is widely used as a sugar substitute. Many studies and authoritative reviews have concluded that sucralose is non-carcinogenic, based primarily on animal cancer bioassays and genotoxicity data. To add to the body of knowledge on the potential carcinogenicity of sucralose, a systematic assessment of mechanistic data was conducted. This entailed using a framework developed for the quantitative integration of data related to the proposed key characteristics of carcinogens (KCCs). Data from peer-reviewed literature and the ToxCast/Tox21 database were evaluated using an algorithm that weights data for quality and relevance. The resulting integration demonstrated an overall lack of activity for sucralose across the KCCs, with no "strong" activity observed for any KCC. Almost all data collected demonstrated inactivity, including those conducted in human models. The overall lack of activity in mechanistic data is consistent with findings from animal cancer bioassays. The few instances of activity across the KCC were generally accompanied by limitations in study design in the context of either quality and/or dose and model relevance, highlighted upon integration of the totality of the evidence. The findings from this comprehensive and integrative evaluation of mechanistic data support prior conclusions that sucralose is unlikely to be carcinogenic in humans.

Lack of potential carcinogenicity for aspartame - Systematic evaluation and integration of mechanistic data into the totality of the evidence.

Despite repeated confirmation of aspartame safety in a variety of foods and beverages, there continues to be interest in researching the potential carcinogenic risk associated with its consumption. The objective of this evaluation was to conduct a systematic assessment of available mechanistic data using a framework for quantitatively integrating the key characteristics of carcinogens (KCCs). For aspartame, 1332 endpoints were appraised for quality and relevance and quantitatively integrated using an algorithm to determine the potential for individual KCC activity based on all available evidence, and subsequently assessed in the context of human and animal evidence streams. An overall lack of activity (integrated scores <0 and no "strong" categorizations) was observed for all KCCs except oxidative stressor (#5), for which activity was determined to be unlikely to be related to a carcinogenic response. Overall, the KCC-based analysis, together with the lack of consistent evidence of carcinogenicity in experimental animals, continue to support lack of carcinogenicity from aspartame consumption. This comprehensive evaluation of available mechanistic data demonstrates the need for a systematic approach to identify and appraise all avaialble data as part of weight-of-evidence determinations related use of KCC in evaluations of potential human carcinogenicity.