The value of juvenile animal studies "What have we learned from preclinical juvenile toxicity studies? II".

Recent changes in the regulations from the FDA and EMA have shifted the focus of juvenile toxicity studies more to the safe use of all pharmaceuticals and the absence of label or safety information for the pediatric population. Unlike other regulatory guidance, the need or design of these animal studies is not specified. Ideally these should be decided "case-by-case" based on the patient population, pharmacology, existing toxicological and clinical data, dosing regimen, and developing system impact. Following the publishing of a small intercompany survey (Bailey and Mariën, 2009), a more extensive survey was commissioned by the ILSI/HESI DART Technical Committee to clarify what has been learned for the safety assessment for pediatrics. Contributions from 24 companies totaling 241 studies (84% rat and 14% dog) were received. In 12 of 82 programs (15%) were the existing adult preclinical or clinical data considered a sufficient safety prediction for pediatric trials. Clinical/preclinical correlates were observed in 17.2% (rat) and 42.9% (dog) of the studies and a lack of predictability from the pharmacology or the adult toxicity data was seen in 25% of rat and 14.3% of dog studies. Many of the studies were large, lengthy, complex, included parameters that mirrored the adult studies and yielded no new or useful information. We should avoid conducting complex or inappropriate studies and Contract Research Organisations and regulatory agencies have a role in encouraging more targeted designs. Only with appropriate designs can we adequately identify safety or pharmacokinetic issues, suggest clinical endpoints, and contribute to the product label.

Pre- and postnatal developmental toxicity study design for pharmaceuticals.

Assessment of potential developmental and reproductive toxicity of human pharmaceuticals is currently guided by the ICH S5(R2) document. The studies that assess the hazard of both pre- and postnatal exposure are predominantly conducted in rodents (rat and mouse). Utilizing the collective experience of the authors, acceptable designs for both the range-finding and definitive studies are presented with detailed descriptions for the presentation of data. In addition, the suggested initiation and then total duration of these studies in relation to clinical studies are described. Optional parameters that may be included in the studies, as well as possible combination with other study designs are discussed. The details described herein will assist all laboratories performing these studies, individuals who need to plan for the studies, and regulatory agencies that ultimately review these studies.

Juvenile animal toxicity study designs to support pediatric drug development.

The objective of juvenile animal toxicity studies of pharmaceuticals is to obtain safety data, including information on the potential for adverse effects on postnatal growth and development. Studies in juvenile animals may assist in identifying postnatal developmental toxicities or other adverse effects that are not adequately assessed in the routine toxicity evaluations and that cannot be safely or adequately measured in pediatric clinical trials. Unlike the traditional reproductive and developmental toxicology studies that have been discussed in the accompanying reports, the design requirements for toxicity studies in juvenile animals are not explicitly defined in regulatory guidance. However, studies in juvenile animals can be useful in providing safety information necessary to enable pediatric clinical trials in pediatric patients or when there are special concerns for toxicities that cannot be safely or adequately measured in clinical trials. These juvenile animal toxicity studies are designed on a case-by-case basis. General design considerations and examples of study designs for assessment of juvenile animal toxicity are discussed.

Real life juvenile toxicity case studies: the good, the bad and the ugly.

With the growing experience in the conduct of juvenile toxicity studies for multiple classes of compound, the 'case-by-case' approach has become under much more pressure. Instead, a general screen or 'standard design' is now commonly expected by regulatory authorities with more routine inclusion of neurological and reproductive assessments. Minor modifications or additions can be made to the design to address specific questions according to the class of drug or intended clinical use. This drift from a 'case-by-case' approach to a 'standard design' approach is present within certain reviewing divisions of the FDA, often requesting by default a rodent and non-rodent juvenile animal study. However, juvenile animal studies should be designed thoughtfully to fulfil a purpose based on scientific rationale, with each endpoint carefully considered in terms of practicality and interpretability of data generated. Only when using the appropriate strategy and design may juvenile studies add value by (1) identifying potential safety or pharmacokinetic issues for drugs intended for paediatric use, (2) suggesting additional clinical endpoints and (3) adding new information to the product label. As the knowledge from juvenile animal studies in various species grows, a better understanding of the significance/relevance of findings will be achieved.

The ontogeny of drug metabolizing enzymes and transporters in the rat.

Knowledge of the ontogeny of the various systems involved in distribution and elimination of drugs is important for adequate interpretation of the findings during safety studies in juvenile animals. The present study was designed to collect information on plasma concentrations of total protein and albumin, enzyme activity and mRNA expression of cytochrome P450 isoenzymes (CYP1A1/2, CYP2B1/2, CYP2E1, CYP3A1/2, and CYP4A1), carboxylesterase and thyroxin glucuronidation (T4-GT) activity in liver microsomes, and mRNA expression of transporters (Mdr1a/b, Mrp1-3 and 6, Bsep and Bcrp, Oct1-2, Oat1-3 and Oatp1a4) in liver, kidney and brain tissue during development in Sprague-Dawley rats. Enzyme activities were determined by measuring the metabolism of marker substrates; expression of mRNAs was assessed using RTq-PCR. There were considerable differences in the ontogeny of the individual cytochrome P450 isoenzymes. In addition, ontogeny patterns of enzyme activity did not always parallel ontogeny patterns of mRNA expression. Ontogeny of the transporters depended on the transporter and the organ studied. Changes in mRNA expression of the various transporters during development are likely to result in altered elimination and/or tissue distribution of substrates, with concomitant changes in hepatic metabolism, renal excretion and passage through the blood-brain barrier. Consideration of the ontogeny of metabolizing enzymes and transporters may improve the design and interpretation of results of toxicity studies in juvenile animals.

Timing is everything for sperm assessment in fertility studies.

The fertility study design recommended in the ICH S5(R2) Harmonised Guideline for Detection of Toxicity to Reproduction for Medicinal Products emphasizes the importance of histopathological endpoints next to a pairing assessment in evaluating male fertility. However, in a male rat fertility study with JNJ-26489112, a CNS-active agent, while there were no effects on histological endpoints, mating performance or pregnancy outcomes, sperm assessment was included. The high dose males presented with reversible decreases in epididymal, but not testicular, sperm concentration and motility and an increase in abnormal sperm morphology. In view of the differences in fertility between rats and humans, these types of sperm effects in rats suggest the potential for an impact on human male fertility that would be undetected if not for the sperm assessment. Therefore, the current example suggests that including semenology as a standard endpoint in nonclinical fertility studies may be warranted.

What have we learned from pre-clinical juvenile toxicity studies?

Juvenile toxicity studies have assumed a higher priority within the pharmaceutical industry following recent changes in regulations. The requirement and designs of these studies should be on a 'case-by-case' basis. Discussions have suggested that recently the regulatory agencies have requested a more standard design incorporating multiple parameters, despite the disparity in the data available and the mode of action and indication of the respective drugs. In addition, the general perception was that studies were generating nothing new; there was no clear indication of novel toxicity or sensitivity; and the findings observed were predictable from what was already known. Clarity was therefore required both in terms of the study designs used and their usefulness and ability to generate meaningful data. This paper discusses the contributions from 10 pharmaceutical companies of 39 studies to clarify what has been learned and whether this has contributed to our greater understanding. Juvenile toxicity studies should be designed to fulfil a scientific rationale, only after first deciding what useful toxicological information might be obtained. Should a study be conducted, the endpoints must be assessed for both practicality and interpretability. Only when using appropriately designed studies can we adequately identify potential safety or pharmacokinetic issues, suggest additional clinical endpoints and/or contribute to the product label.