Annual Meeting of the Japanese Society of Toxicology

As changes to carcinogenicity assessment of pharmaceuticals are being considered through ICH S1 modification, the weight-of-evidence approach being proposed opens up much broader opportunity for alternative short term mouse models to play a more expansive role in the future of pharmaceutical carcinogenicity testing. Recent experience with alternative transgenic mouse models in pharmaceutical development will be summarized, and the heightened value of using these animals from a scientific and business perspective will be described. The focus will be on the p53+/- and rasH2 mouse models, with which the pharmaceutical industry has the greatest experience and which have the highest level of acceptance by Regulatory Authorities. The p53+/- mouse model may be the preferred model for compounds with direct or equivocal evidence of genotoxicity, while the rasH2 mouse model developed by the Central Institute for Experimental Animals in Japan, is the only model acceptable for compounds with positive, equivocal or negative genotoxicity findings. The rasH2 model is becoming the choice of pharmaceutical companies that have adopted an alternative mouse model into their carcinogenicity risk assessment paradigm. The proposed modification of the ICH S1 guideline addresses the elimination or replacement of a 2-year rat study based on a weight-of-evidence argument to improve human risk assessment while reducing, refining, and replacing animal testing. In case-by-case situations, the alternative mouse models have the potential to contribute to this weight-of-evidence, and may be the only carcinogenicity study needed to adequately assess carcinogenic risk.

View full abstract

Show abstractHide abstract

The impact of testing in a second species for embryofetal developmental toxicity was discussed during a 2010 ICH Workshop in Tallinn, Estonia. It was proposed to review the frequency with which the results from studies in the rat versus rabbit have driven the lowest observed adverse effects level (LOAEL) and exposure margins in risk assessment for pharmaceuticals. The goal of this retrospective analysis is to better understand the implications of either postponing the testing in one of the two required species or waiving the need for one of the two embryofetal toxicity testing in specific circumstances. The ILSI Health and Environmental Sciences Institute’s Developmental and Reproductive Toxicology Technical Committee (HESI-DART) organized a cross-industry data survey in which anonymized embryofetal development and toxicokinetic study data from marketed and unmarketed drugs were submitted for analysis.
Additionally, compounds for which rat and rabbit data were derived from the files of the Medicines Evaluation Board. The two sources have accumulated data from more than 800 studies spanning more than 400 compounds which have been entered in US EPA’s ToxRefDB database. Fetal and maternal effect levels are being determined to address species sensitivity based on dose and internal exposure. In addition, the nature and severity of embryofetal findings in the rat and rabbit is being reviewed to establish which differences of embryofetal effects between species are driving risk assessment. Results will be discussed in the presentation. This comprehensive data survey will support integrated testing strategy for developmental toxicity testing of pharmaceuticals.

View full abstract

Download PDF (800K)

Nonhuman primate (NHP) models play an important role in the development and safety assessment of (bio)pharmaceuticals depending on the particular properties of the drug candidate. In many instances, the experimental use of NHPs is subject to special regulations and animal welfare considerations among which the 3R principles are of pivotal importance. Since NHP models will unlikely be replaced by alternatives in the near future, 3R efforts should focus on reduction and refinement. For reduction, some guideline changes related to biologics –ICH M3(R2) and ICH S6(R1) – can provide an option for using lesser NHPs. ICH S6(R1) makes specific recommendations on how many live infants are required per group for a NHP pre- and postnatal development study. This recommendation in conjunction with the use of reference data and normogram data can be used to reduce the number of NHPs needed for developmental toxicity testing. Also, under certain circumstances, the conduct of dedicated reproductive toxicity evaluation as per ICH S5(R2) can be incorporated in chronic toxicity studies thus further lowering the demand for NHPs. Importantly, refinement should be a key focus of any 3R efforts in order to optimize the use of NHP models. Recent work has provided statistical power estimates for some fertility parameters relative to group size that will aid developing appropriate study designs. Also, the potential of combining pre- and postnatal testing with juvenile toxicity testing has been raised. In summary, various options are available to optimize NHP DART testing in the spirit of 3R.

View full abstract

Previously we described that prenatal rat exposure to di(n-butyl) phthalate (DBP) induced Leydig cells (LC) hyperplasia after 9-week-old, while the number of LC was similar to that of vehicle group until 7- week-old. Nuclear pleomorphism of hyperplastic LCs is ordinary, and is considered as continuous progressive degeneration. Then the computer-assisted image cell nuclear analysis of LCs was performed for 5- and 7- week-old SD (srl) rats whose dams had been administered DBP (i.g.) at 100 mg/kg/day or vehicle (corn oil) from days 12 to 21 post-conception. The analysis results of 5- week-old DBP group were similar to those of vehicle group. While, compared to vehicle group, LCs nuclei of 7- week-old DBP group showed normal ploidy and similar amount of DNA; but the size, elongation, and peripheral chromatin aggregation parameters were significantly higher; and the chromatin reticular distribution and the isolated chromatin aggregation parameters were significantly lower. The present study quantitatively demonstrated that rats LCs nuclear morphological alteration by the prenatal DBP exposure revealed at 7- week-old puberty when apparent LCs hyperplasia was not developed.

View full abstract

Register with J-STAGE for free!