The 2-year rodent bioassay in drug and chemical carcinogenesis testing: Sensitivity, according to the framework of carcinogenic action.

The long-term rodent bioassay (RCB) has been the gold-standard for the pre-marketing prediction of chemical and drug carcinogenicity to humans. Nonetheless, the validity of this toxicity test has remained elusive for several decades. In the quest to uncover the performance of the RCB, its sensitivity (SEN) was charted as the first step. This appraisal was based on (a) chemicals with sufficient epidemiological evidence of carcinogenicity, and (b) other substances with limited epidemiological evidence, or remarkable classifications of carcinogenicity based on mechanistic or pharmacological data. In the present study, chemicals evaluated for their carcinogenicity to humans in IARC Monographs volumes 1-123, U.S. EPA IRIS Assessments, and U.S. NTP RoC were considered. This investigation gathered additional evidence supporting that, in hazard identification, the RCB is unwarranted for mutagenic or direct-acting genotoxicants. However, for purposes of risk assessment or management, the RCB might be justified whenever there is a lack of reliable and/or comprehensive epidemiological data. The RCB exhibited a significantly different SEN for threshold-based human carcinogens compared to non-threshold-based ones. With threshold-based chemicals, to increase the SEN of the testing from 80% (rat-RCB) to 90%, the 2-species RCB might be warranted. Nevertheless, the resolve would depend on the viewpoint, and on the future analysis of the overall performance of the RCB. In terms of SEN, and cancer hazard identification, the comparison between the RCB and alternative methods (e.g. rasH2 mouse, Tg.AC mouse) is now enabled.

Drug excipients, food additives, and cosmetic ingredients probably not carcinogenic to humans reveal a functional specificity for the 2-year rodent bioassay.

Regarding carcinogenicity testing, the long-term rodent bioassay (RCB) has been the test required by most regulatory agencies across the world. Nonetheless, due to the lack of knowledge about its specificity, it has been argued that the RCB is unspecific or even invalid. Because of the substantial limitations of epidemiology to identify chemicals probably not carcinogenic to humans (PNCH), it has been very difficult to address the specificity of the RCB. Nevertheless, because mechanistic/pharmacological data are currently recognized as a valid stream of evidence for the identification of chemical hazards, the road is now open to gain insight into the specificity of the RCB. Based on sound mechanistic/pharmacological data that support the classification of chemicals as PNCH, 100 PNCH substances were gathered in this investigation. Contrary to what was previously forecast, in this study, the RCB exhibited a functional specificity that ranged from 83% to 91%, depending on the settings of the testing (2-species vs. rats only, and the nominal maximum tolerated dose). Other contributions of this work were: (a) enabling the comparison, in terms of specificity, between the RCB and the alternative methods that could replace it (eg, Tg.AC mouse, rasH2 mouse); (b) disclosing what the specificity is for alternative methods that were developed using the RCB as the reference standard; and (c) expanding the previous narrow (only seven substances) set of chemicals identified as not likely to be carcinogenic to humans by hazard identification programs.

The predictivity of the -alert performance- functionality of the OECD QSAR-Toolbox (c/w further issues on the predictivity of nonclinical testing).

The OECD QSAR-Toolbox can be considered a milestone in predictive toxicology. Because of the reliability of its supporting institutions (OECD and ECHA), its broadness in terms of feeder databases, and its predictive capacity, the QSAR-Toolbox is called to have a major role in regulatory toxicology. Recently, a novel functionality was built for the QSAR-Toolbox: the alert performance (AP). This prompted us to analyze the strengths, potentialities, and limitations of this new functionality, especially in the light of a pivotal framework recently discussed in the literature for the predictive use of nonclinical screening and testing. After meticulous analysis, and through some worked examples, high predictive capacity and applicability were found for the AP in both predictive and regulatory toxicology. For a specified chemical, the AP is useful in (a) anticipating its overall results in a given nonclinical test; (b) predicting its overall results regarding a selected toxicological endpoint in humans, and (c) facilitating post- to pre-test probabilities approaches that may support regulatory authorization for waiving the conduction of selected tests in laboratory animals. Furthermore, if a QSAR-Toolbox initiative is developed in or extended to pharmacology (e.g., safety pharmacology, drug abuse potential), it could represent another milestone; one that would give rise to the field of predictive pharmacology.

[Identificación de fármacos reguladores de la actividad del promotor Egr-1 en fibroblastos humanos transducidos con AdΔegr-1-Luc7]. / Identification of drugs as regulators on the activity of Egr-1 promoter in human fibroblasts transduced with AdΔegr-1-Luc7.

INTRODUCCIÓN: La proteína de respuesta temprana a crecimiento 1 (EGR-1) es un factor de transcripción involucrado en la diferenciación y la proliferación celulares, cuya expresión es regulada por su promotor en respuesta a diversos factores físicos y químicos, y a fármacos. Aquí se describen algunos de los principales efectos de los fármacos esteroides y del factor de crecimiento epitelial 1 (EGF-1) sobre la actividad del promotor, mediante un sistema reportero transducido por el adenovirus AdΔegr-1-Luc7 en fibroblastos primarios humanos. MÉTODO: Los fibroblastos primarios humanos fueron cultivados en pase 5, transducidos con AdΔegr-1-Luc7 y expuestos a betametasona, hidrocortisona, dexametasona, testosterona, beta-estradiol y EGF-1 durante 1, 3 y 6 horas. La actividad de reportero fue cuantificada por luminometría y ajustada a la concentración de proteínas totales. RESULTADOS: La actividad del promotor en presencia de betametasona, hidrocortisona, dexametasona, testosterona y beta-estradiol fue similar a la actividad basal del promotor a las 1, 3 y 6 horas. El control positivo mostró una actividad 17.8 veces mayor a las 6 horas (p ≤ 0.05). De manera similar, las células expuestas a EGF-1 mostraron una actividad 22.07 veces mayor que las células sin fármaco. CONCLUSIÓN: La actividad del promotor Egr-1 en fibroblastos humanos es regulada negativamente por los fármacos esteroides y positivamente por el EGF-1. INTRODUCTION: The early growth response protein (EGR-1) is a transcription factor involved in cell differentiation and proliferation, whose expression is regulated by its promoter in response to various physical, chemical and drug factors. Hereby, we describe some of the main effects of steroid drugs and EGF-1 on promoter activity, through a reporter system transduced by AdΔegr-1-Luc7 in human primary fibroblasts (HPF). METHODS: Human primary fibroblasts transduced with AdΔegr-1-Luc7 were exposed to betamethasone, hydrocortisone, dexamethasone, testosterone, beta-estradiol, and EGF-1 during 1, 3 and 6 h. Reporter assay was quantified by luminometry. RESULTS: The activity of the promoter in presence of betamethasone, hydrocortisone, dexamethasone, testosterone and beta-estradiol were similar to the basal activity of the promoter at 1, 3 and 6 h. The positive control showed an activity 17.8 folds higher (p ≤ 0.05) at 6 h. EGF-1 showed activity of 22.07 folds greater than cells without drug. CONCLUSION: The activity of the EGR-1 promoter in human fibroblasts is negatively regulated by steroid drugs and positively by the EGF-1.