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The ICH S1B carcinogenicity global testing guideline has been recently revised with a novel addendum that describes a comprehensive integrated Weight of Evidence (WoE) approach to determine the need for a 2-year rat carcinogenicity study. In the present work, experts from different organizations have joined efforts to standardize as much as possible a procedural framework for the integration of evidence associated with the different ICH S1B(R1) WoE criteria. The framework uses a pragmatic consensus procedure for carcinogenicity hazard assessment to facilitate transparent, consistent, and documented decision-making and it discusses best-practices both for the organization of studies and presentation of data in a format suitable for regulatory review. First, it is acknowledged that the six WoE factors described in the addendum form an integrated network of evidence within a holistic assessment framework that is used synergistically to analyze and explain safety signals. Second, the proposed standardized procedure builds upon different considerations related to the primary sources of evidence, mechanistic analysis, alternative methodologies and novel investigative approaches, metabolites, and reliability of the data and other acquired information. Each of the six WoE factors is described highlighting how they can contribute evidence for the overall WoE assessment. A suggested reporting format to summarize the cross-integration of evidence from the different WoE factors is also presented. This work also notes that even if a 2-year rat study is ultimately required, creating a WoE assessment is valuable in understanding the specific factors and levels of human carcinogenic risk better than have been identified previously with the 2-year rat bioassay alone. [ABSTRACT FROM AUTHOR]

Timed-pregnant CD® outbred albino Sprague-Dawley rats received formamide (50, 100, or 200 mg/kg/day) or vehicle (5 ml/kg deionized/distilled water, po) on gestational days (gd) 6 through 19. Maternal food and water consumption (absolute and relative), body weight, and clinical signs were monitored at regular intervals throughout gestation. At termination (gd 20), confirmed-pregnant females (21–23 per group) were evaluated for clinical status and gestational outcome; live fetuses were examined for external, visceral, and skeletal malformations and variations. There were no maternal deaths and no dose-related clinical signs. At 200 mg/kg/day, maternal body weight on gd 20, weight gain, and gravid uterine weight were significantly decreased. Maternal weight gain, corrected for gravid uterine weight, liver weight (absolute or relative), and food and water consumption (absolute or relative), were not affected. Formamide did not affect prenatal viability or incidences of fetal malformations or variations. Average fetal body weight/litter was decreased at 100 and 200 mg/kg/day. Fetal body weight was affected at lower daily doses than in previously published studies, possibly due to the longer total exposure period and/or lack of a recovery period between cessation of exposure and termination. In summary, the maternal toxicity no-observed-adverse-effect level (NOAEL) was 100 mg/kg/day and the low observed adverse effect level (LOAEL) was 200 mg/kg/day under the conditions of this study. Similarly, the developmental toxicity NOAEL was 50 mg/kg/day and the LOAEL was 100 mg/kg/day. [ABSTRACT FROM PUBLISHER]

The susceptibility of the rodent mammary gland to known chemical carcinogens can vary with the stage of gland development. Full-term pregnancy (parity) can confer permanent structural and functional changes in the gland that are associated with decreased breast cancer risk in humans and protection from mammary carcinogenesis in rodents. In this study, the formation and persistence of benzo[]pyrene (B[]P)-derived DNA adducts was determined in the abdominal mammary organs of adult nulliparous and parous BALB/c mice treated orally with the carcinogen. Mammary DNA isolated from animals in both groups revealed only one major adduct on TLC maps by P1-nuclease P-postlabeling analysis. The major adduct co-migrated with the (+)-enantiomer of -BPDE-dGp. Much lower levels of the (−)-enantiomer were detected. Most of the adduct quantitated was probably contributed by cells of the stromal compartment, since the gland-free organ (cleared fat pad) generated essentially equivalent profiles and level of adduct by P-postlabeling. Comparable levels of the B[]P-derived adduct were observed in the intact mammary organ of both nulliparous and parous mice during a time course from 1 to 28 days after treatment. In both cases, adduct removal occurred exponentially with a half-life of ∼16 days. The capacity for formation of reactive metabolites by the mammary organ was demonstrated : digests of DNA from mammary mince exposed to B[]P generated an adduct on TLC maps that also co-migrated with the (+)--BPDE-dGp standard. Thus, our cumulative findings confirm the capacity of mammary cells to form potentially carcinogenic DNA adducts; however, the functional changes that occur in the mouse mammary gland as a result of parity did not influence the profile, level or persistence of adduct following exposure to a known carcinogen. Other factors, such as changes in mammary cell cycle kinetics or responsiveness to promotional stimuli may be more causally related to reduction in incidence of neoplasia observed in parous animals. [ABSTRACT FROM PUBLISHER]

Identification of DNA adducts in peripheral lymphocytes could serve as a means of monitoring human exposure to potential genotoxic agents. In this study, DNA from peripheral lymphocytes of smokers and nonsmokers was examined for adducts by the P1 nuclease P-postlabeling technique. Thin layer chromatography (TLC) maps from both groups revealed multiple DNA adducts which ranged from no adducts for one individual to six adducts for a different individual. The total DNA adduct concentrations were approximately one adduct in 10- 10 normal nucleotides. Comparison of the adduct TLC profiles revealed individual variation in both pattern and level of DNA adducts. The type and amount of adduct was not influenced by smoking history and remained unchanged in four out of six subjects who were resampled after a 1 month interval. The capacity of lymphocytes to form BaP-derived DNA adducts after a 72 h incubation with 10 M [H]BaP was measured by both high-performance liquid chromatography (HPLC) and P-postlabeling analysis. The adduct values detected by [H]nucleoside concentrations on HPLC ranged from 1 to 7 fmol adduct per μg DNA (3.3–23.3 adducts per 10 nucleotides). The[H] nucleoside values were consistent with values obtained by P-postlabeling of the same sample (correlation coefficient of 0.88). No relationship was apparent between the capacity of lymphocytes to form a [H] BaP- derived adduct and the concentration of any adduct, or total adducts present in untreated lymphocytes. These results suggest that multiple DNA adducts are present in lymphocytes from nonsmokers as well as smokers, although the profile and extent of these adducts can vary among individuals. The relationship of the lymphocyte DNA adducts detected in this study to human cancer susceptibility remains to be determined. [ABSTRACT FROM PUBLISHER]

In silico toxicology protocols are meant to support computationally-based assessments using principles that ensure that results can be generated, recorded, communicated, archived, and then evaluated in a uniform, consistent, and reproducible manner. We investigated the availability of in silico models to predict the carcinogenic potential of pregabalin using the ten key characteristics of carcinogens as a framework for organizing mechanistic studies. Pregabalin is a single-species carcinogen producing only one type of tumor, hemangiosarcomas in mice via a nongenotoxic mechanism. The overall goal of this exercise is to test the ability of in silico models to predict nongenotoxic carcinogenicity with pregabalin as a case study. The established mode of action (MOA) of pregabalin is triggered by tissue hypoxia, leading to oxidative stress (KC5), chronic inflammation (KC6), and increased cell proliferation (KC10) of endothelial cells. Of these KCs, in silico models are available only for selected endpoints in KC5, limiting the usefulness of computational tools in prediction of pregabalin carcinogenicity. KC1 (electrophilicity), KC2 (genotoxicity), and KC8 (receptor-mediated effects), for which predictive in silico models exist, do not play a role in this mode of action. Confidence in the overall assessments is considered to be medium to high for KCs 1, 2, 5, 6, 7 (immune system effects), 8, and 10 (cell proliferation), largely due to the high-quality experimental data. In order to move away from dependence on animal data, development of reliable in silico models for prediction of oxidative stress, chronic inflammation, immunosuppression, and cell proliferation will be critical for the ability to predict nongenotoxic compound carcinogenicity., Competing Interests: DK, LB, GJ and RT are independent contractors. AB is employed by Innovatune. AA is employed by Sanofi. JC, KC and FH are employed by Instem. AL is employed by Medline Industries. SM is employed by Nestle Research. JM is employed by Chemotargets SL. Amy Mihalchik-Burhans is employed by ToxStrategies, LLC. David Wooley is employed by ForthTox. The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest., (Copyright © 2023 Keller, Bassan, Amberg, Burns Naas, Chambers, Cross, Hall, Jahnke, Luniwal, Manganelli, Mestres, Mihalchik-Burhans, Woolley and Tice.)