A Compendium of Mutational Signatures of Environmental Agents.

Whole-genome-sequencing (WGS) of human tumors has revealed distinct mutation patterns that hint at the causative origins of cancer. We examined mutational signatures in 324 WGS human-induced pluripotent stem cells exposed to 79 known or suspected environmental carcinogens. Forty-one yielded characteristic substitution mutational signatures. Some were similar to signatures found in human tumors. Additionally, six agents produced double-substitution signatures and eight produced indel signatures. Investigating mutation asymmetries across genome topography revealed fully functional mismatch and transcription-coupled repair pathways. DNA damage induced by environmental mutagens can be resolved by disparate repair and/or replicative pathways, resulting in an assortment of signature outcomes even for a single agent. This compendium of experimentally induced mutational signatures permits further exploration of roles of environmental agents in cancer etiology and underscores how human stem cell DNA is directly vulnerable to environmental agents. VIDEO ABSTRACT.

Differentiation-associated urothelial cytochrome P450 oxidoreductase predicates the xenobiotic-metabolizing activity of "luminal" muscle-invasive bladder cancers.

Extra-hepatic metabolism of xenobiotics by epithelial tissues has evolved as a self-defence mechanism but has potential to contribute to the local activation of carcinogens. Bladder epithelium (urothelium) is bathed in excreted urinary toxicants and pro-carcinogens. This study reveals how differentiation affects cytochrome P450 (CYP) activity and the role of NADPH:P450 oxidoreductase (POR). CYP1A1 and CYP1B1 transcripts were inducible in normal human urothelial (NHU) cells maintained in both undifferentiated and functional barrier-forming differentiated states in vitro. However, ethoxyresorufin O-deethylation (EROD) activity, the generation of reactive BaP metabolites and BaP-DNA adducts, were predominantly detected in differentiated NHU cell cultures. This gain-of-function was attributable to the expression of POR, an essential electron donor for all CYPs, which was significantly upregulated as part of urothelial differentiation. Immunohistology of muscle-invasive bladder cancer (MIBC) revealed significant overall suppression of POR expression. Stratification of MIBC biopsies into "luminal" and "basal" groups, based on GATA3 and cytokeratin 5/6 labeling, showed POR over-expression by a subgroup of the differentiated luminal tumors. In bladder cancer cell lines, CYP1-activity was undetectable/low in basal PORlo T24 and SCaBER cells and higher in the luminal POR over-expressing RT4 and RT112 cells than in differentiated NHU cells, indicating that CYP-function is related to differentiation status in bladder cancers. This study establishes POR as a predictive biomarker of metabolic potential. This has implications in bladder carcinogenesis for the hepatic versus local activation of carcinogens and as a functional predictor of the potential for MIBC to respond to prodrug therapies.

Review of the state of science and evaluation of currently available in silico prediction models for reproductive and developmental toxicity: A case study on pesticides.

BACKGROUND: In silico methods for toxicity prediction have increased significantly in recent years due to the 3Rs principle. This also applies to predicting reproductive toxicology, which is one of the most critical factors in pesticide approval. The widely used quantitative structure-activity relationship (QSAR) models use experimental toxicity data to create a model that relates experimentally observed toxicity to molecular structures to predict toxicity. Aim of the study was to evaluate the available prediction models for developmental and reproductive toxicity regarding their strengths and weaknesses in a pesticide database. METHODS: The reproductive toxicity of 315 pesticides, which have a GHS classification by ECHA, was compared with the prediction of different in silico models: VEGA, OECD (Q)SAR Toolbox, Leadscope Model Applier, and CASE Ultra by MultiCASE. RESULTS: In all models, a large proportion (up to 77%) of all pesticides were outside the chemical space of the model. Analysis of the prediction of remaining pesticides revealed a balanced accuracy of the models between 0.48 and 0.66. CONCLUSION: Overall, predictions were only meaningful in rare cases and therefore always require evaluation by an expert. The critical factors were the underlying data and determination of molecular similarity, which offer great potential for improvement.

Food grade safflower concentrate: No evidence for reproduction and early developmental toxicity.

Safflower (Carthamus tinctorius) petals have been used for centuries as a spice, in tea blends and in traditional Asian medicine. Aqueous extracts of Safflower petals have been used as a colouring food over the last 30 years due to their bright colour. Publications in the past raised concerns about fertility impairing, maternal toxicity, fetotoxic and teratogenic properties in rodents. As the tested extracts were poorly characterized and the studies were not performed according to guidelines, a need for further evaluation was seen. In silico predictions for the main pigments provided negative results for bacterial mutagenicity. Further, in vitro genotoxicity and in vivo reproductive toxicity studies of a well-characterized aqueous safflower concentrate generated more relevant data for risk assessment of its use in food. In vitro AMES tests and a mouse lymphoma cell assay were negative. An OECD guideline 421 screening study was performed in rats with oral daily doses of up to 1000 mg/kg bodyweight, applied via gavage to simulate a bolus effect. The highest dose reflected a toxicological limit test. The study did not give indications of general toxicity, did not show any effect on fertility and reproduction nor any effect on prenatal development and, also in contrast to previous results, treatment did not affect estradiol and FSH levels. Furthermore, pups raised until PND 14-16, developed normally with no adverse effects observed. With the established NOAEL of at least 1000 mg/kg/d, a considerable margin of exposure is achieved when compared with human intake estimates.