The evolution of juvenile animal testing for small and large molecules

Dose range finding approach for rodent preweaning juvenile animal studies

OBJECTIVES

Strategies for conducting juvenile dose ranging studies before definitive toxicity juvenile animal studies (JAS) have evolved, but the aim of demonstrating study design robustness and efficient animal use remains the same. The objective of dose selection is to identify a strategy to achieve consistent systemic exposure for the duration of the JAS while maintaining exposure separation between dose groups. For preweaning rodents this can prove challenging, as these studies typically treat animals over a broad period of considerable organ development.

MATERIALS AND METHODS

In our experience, over 45 rodent juvenile studies (dose range, definitive or investigative) were conducted over 20 years to support pediatric medicine development. In most cases (86%, 12/14), preweaning rodents required decreased doses of test articles than adult rodents; the majority (83%, 10/12) were due to increased systemic exposures in immature animals at the same doses. Thus, extrapolating tolerability and exposure data from adults is not ideal and should not take the place of well-designed juvenile dose range studies.

RESULTS/DISCUSSION/CONCLUSION

We propose a phased dose-range-finding approach by first conducting a tolerability phase with a few animals at a starting age corresponding to the youngest clinical starting age, spanning a wide range of doses, then a dose range phase with larger group sizes and fewer doses; both phases incorporate toxicokinetics. Often, exposure was higher in preweaning animals and decreased as animals matured postweaning (postnatal day, PND 21 and older), supporting an age-based dose adjustment strategy. Case studies demonstrate dose adjustment approaches incorporating dose increases or decreases or changes in dose frequency.

Juvenile Animal Testing: Assessing Need and Use in the Drug Product Label

BACKGROUND

Juvenile animal testing has become an established part of drug development to support safe clinical use in the human pediatric population and for eventual drug product label use.

METHODS AND RESULTS

A review of European Paediatric Investigation Plan decisions showed that from 2007 to mid-2017, 229 drugs had juvenile animal work requested, almost exclusively incorporating general toxicology study designs, in rat (57.5%), dog (8%), mouse (4.5%), monkey (4%), pig (2%), sheep (1%), rabbit (1%), hamster (0.5%), and species not specified (21.5%). A range of therapeutic areas were found, but the most common areas were infectious diseases (15%), endocrinology (13.5%), oncology (13%), neurology (11%), and cardiovascular diseases (10%). Examination of major clinical indications within these therapeutic areas showed some level of consistency in the species of choice for testing and the pediatric age that required support. Examination of juvenile animal study findings presented in product labels raises questions around how useful the data are to allow prescribing the drug to a child.

CONCLUSION

It is hopeful that the new ICH S11 guideline "Nonclinical Safety Testing in Support of Development of Pediatric Medicines" currently in preparation will aid drug developers in clarifying the need for juvenile animal studies as well as in promoting a move away from toxicology studies with a conventional design. This would permit more focused testing to examine identified areas of toxicity or safety concerns and clarify the presentation/interpretation of juvenile animal study findings for proper risk assessment by a drug prescriber.

An integrated approach to the safety assessment of food additives in early life

During the development of international standards by the Codex Alimentarius Commission, infant foods and their constituent ingredients are subject to rigorous risk analysis and are strictly regulated by many authorities. Various jurisdictions have approved only a limited number of additives specifically with regard to infant foods to fulfill specific technical requirements of quality. As part of the approval process, a rigorous safety assessment is essential to confirm that the use of additives does not pose any health risk for the consumer. An acceptable daily intake (ADI) may be derived from the toxicological databases. However, the ADI may not be applicable to infants because of the possible developmental sensitivities and potentially high exposure scenarios, leading to possible lower margins of safety than would often be determined for adult populations. There is interest in defining better food safety assessment approaches for pre-weaned infants aged less than 12–16 weeks. To confirm safe use in infants, we reviewed the suitability of the existing safety databases of six additives with historical uses in infant nutrition products. To determine further toxicity testing strategies, it is necessary to understand whether the chemical used in the additives is identical to endogenous physiological metabolites and/or whether immature organs of infants are targets of toxicity. Combined with an in-depth review of the existing relevant toxicological and nutritional studies, this integrated approach will facilitate decision-making. We propose a decision tree as a tool within this approach to help guide appropriate data requirements and identify data gaps. In cases of reasonable uncertainty, studies of targeted juvenile should be considered to investigate the safe use levels in food products.

Points to Consider in Designing and Conducting Juvenile Toxicology Studies

In support of a clinical trial in the pediatric population, available nonclinical and clinical data provide input on the study design and safety monitoring considerations. When the existing data are lacking to support the safety of the planned pediatric clinical trial, a juvenile animal toxicity study is likely required. Usually a single relevant species, preferably a rodent, is chosen as the species of choice, while a nonrodent species can be appropriate when scientifically justified. Juvenile toxicology studies, in general, are complicated both conceptually and logistically. Development in young animals is a continuous process with different organs maturing at different rates and time. Structural and functional maturational differences have been shown to affect drug safety. Key points to consider in conducting a juvenile toxicology study include a comparative development of the organ systems, differences in the pharmacokinetics/absorption, distribution, metabolism, excretion (PK/ADME) profiles of the drug between young animal and child, and logistical requirement in the juvenile study design. The purpose of this publication is to note pertinent points to consider when designing and conducting juvenile toxicology studies and to aid in future modifications and enhancements of these studies to enable a superior predictability of safety of medicines in the pediatric population.

Juvenile Nonclinical Safety Studies in Support of Pediatric Drug Development

A pediatric assessment is now a required component of every drug marketing application in North America, Europe, and Japan, unless a waiver has been granted previously. Nonclinical juvenile toxicity studies are often required as part of this assessment. The protocols for juvenile toxicity studies are best devised in consultation with the regulatory authorities. It is important to submit the pediatric investigation plan (PIP) or pediatric study plan (PSP) early, in order not to delay the marketing authorization of the drug in adults. The choice of species and the design of juvenile toxicity studies are based on a series of complex considerations, including the therapeutic use of the drug, age at which children will be treated, duration of treatment, and potential age- or species-specific differences in efficacy, pharmacokinetics, or toxicity.

Current Topics in Postnatal Behavioral Testing

The study of developmental neurotoxicity (DNT) continues to be an important component of safety evaluation of candidate therapeutic agents and of industrial and environmental chemicals. Developmental neurotoxicity is considered to be an adverse change in the central and/or peripheral nervous system during development of an organism and has been primarily evaluated by studying functional outcomes, such as changes in behavior, neuropathology, neurochemistry, and/or neurophysiology. Neurobehavioral evaluations are a component of a wide range of toxicology studies in laboratory animal models, whereas neurochemistry and neurophysiology are less commonly employed. Although the primary focus of this article is on neurobehavioral evaluation in pre- and postnatal development and juvenile toxicology studies used in pharmaceutical development, concepts may also apply to adult nonclinical safety studies and Environmental Protection Agency/chemical assessments. This article summarizes the proceedings of a symposium held during the 2015 American College of Toxicology annual meeting and includes a discussion of the current status of DNT testing as well as potential issues and recommendations. Topics include the regulatory context for DNT testing; study design and interpretation; behavioral test selection, including a comparison of core learning and memory systems; age of testing; repeated testing of the same animals; use of alternative animal models; impact of findings; and extrapolation of animal results to humans. Integration of the regulatory experience and scientific concepts presented during this symposium, as well as from subsequent discussion and input, provides a synopsis of the current state of DNT testing in safety assessment, as well as a potential roadmap for future advancement.

Feasibility of repeated testing for learning ability in juvenile primates for pediatric safety assessment

Assessment of learning ability in nonhuman primate (NHP) models is sometimes requested by regulatory authorities. The double choice object discrimination task using a Wisconsin General Testing Apparatus (WGTA) approach is typically being applied. In this study, the WGTA approach was performed on 66 juvenile cynomolgus monkeys aged 8-9 months in the predose phase of juvenile toxicity assessment. In addition, reversal learning data of seven control animals/gender were obtained for the weeks 25 and 52 of dosing. Gender differences in the number of days required to pass the habituation, learning or reversal learning phases were statistically comparable, males and females may be combined for statistical analysis. At first instance, the habituation phase was passed on average after 6.4 days, and the learning test on average after 8.6 days with improvement to 2.0-2.6 days for habituation and 6.4-6.7 days for learning in weeks 52. Power analysis (α = 0.05, one-sided t-test) revealed a sample size of 8 and 41 to predict a 50% and 20% difference, respectively. In conclusion, examination for learning ability, but not for memory ability (during repeated testing) is feasible in juvenile NHPs using the WGTA approach.

Use of juvenile animal studies to support oncology medicine development in children

Childhood cancer has remained a challenge because of long-term effects in children. The need to extend access of children into new cancer therapies requires early prediction of specific safety aspects and juvenile animal studies (JAS) are being conducted to screen for age-related toxicities and differences occurring during postnatal development. This paper investigates oncology approved medicines in the EU (1995-2014) and PIP (Paediatric Investigation Plans - 2007-2014), regarding the usefulness of JAS in their non-clinical development by evaluating information on the medicines labelling. The retrospective review from medicines and PIPs revealed a steady use of JAS to better characterize safety: Approximately 1 in 3 oncology medicine or PIP has conducted JAS. For 6 of the cancer medicines with JAS the toxicity profile in adult and juvenile animals showed some differences in study findings. The discussion of these cases is illustrative of the potential significance that JAS have provided in oncology medicines.

Paediatric drug development: the impact of evolving regulations

Children deserve medicines that are adapted to their needs. The need to include children in drug development has been recognised increasingly over the past few decades. Legal and regulatory frameworks are well established in the EU and US. The amount of work done to study medicines for children is significantly greater than it was 10 years go. Proof-of-concept has been demonstrated for all segments of the paediatric drug development pipeline. It is now time to examine how the practice of developing medicines for children has evolved within those frameworks and to determine how that work should be generalised. This review describes the development of medicines for children and critically appraises the work that has been done within those frameworks. Significant effort is needed to realize the potential provided by the current regulatory framework. Using the work programme of the Global Research in Paediatrics (GRiP) Network of Excellence as a template we outline current work and future growing points.