A global pharmaceutical company initiative: an evidence-based approach to define the upper limit of body weight loss in short term toxicity studies.

Short term toxicity studies are conducted in animals to provide information on major adverse effects typically at the maximum tolerated dose (MTD). Such studies are important from a scientific and ethical perspective as they are used to make decisions on progression of potential candidate drugs, and to set dose levels for subsequent regulatory studies. The MTD is usually determined by parameters such as clinical signs, reductions in body weight and food consumption. However, these assessments are often subjective and there are no published criteria to guide the selection of an appropriate MTD. Even where an objective measurement exists, such as body weight loss (BWL), there is no agreement on what level constitutes an MTD. A global initiative including 15 companies, led by the National Centre for the Replacement, Refinement and Reduction of Animals in Research (NC3Rs), has shared data on BWL in toxicity studies to assess the impact on the animal and the study outcome. Information on 151 studies has been used to develop an alert/warning system for BWL in short term toxicity studies. The data analysis supports BWL limits for short term dosing (up to 7days) of 10% for rat and dog and 6% for non-human primates (NHPs).

The utility of the minipig as an animal model in regulatory toxicology.

In this article we review the value and utility of the minipig as an animal model in regulatory toxicity testing. Our review is based on detailed consideration of the comparative biology of the minipig, and of the practical features of toxicity testing in the minipig. The minipig presents a favourable profile as a non-rodent toxicology model, in terms of the similarity to man and also in terms of applicability to different study types. Studies of general toxicology can be performed in the minipig by oral, cutaneous, parenteral and inhalation routes. For reproductive toxicology studies the minipig offers numerous advantages as a non-rodent model although the lack of placental transfer of macromolecules may limit the role of the minipig in reproductive testing of biotechnology products. For safety pharmacology studies the minipig is an advantageous model, particularly as regards the cardiovascular system. The immune system of the pig is better characterized than that of the dog, making the pig an interesting alternative model to the nonhuman primate for therapeutic approaches based on manipulation of the immune system. Overall, this review leads us to believe that the minipig might be a better non-rodent toxicology model than the dog. At the present time, however, insufficient comparative data is available to permit a rigorous evaluation of the predictivity of the minipig for human drug-induced toxicities and research is urgently needed to provide experimental data for evaluation of the hypothesis that minipig studies may better reflect human drug-induced toxicities than studies performed in traditional non-rodent toxicology models. It would be of particular value to gain a better vision of the potential utility of the minipig as a model for the safety testing of new biologics, where the minipig could potentially replace the use of non-human primates in the testing of some new products.

A European pharmaceutical company initiative challenging the regulatory requirement for acute toxicity studies in pharmaceutical drug development.

Regulatory guidelines indicate acute toxicity studies in animals are considered necessary for pharmaceuticals intended for human use. This is the only study type where lethality is mentioned as an endpoint. The studies are carried out, usually in rodents, to support marketing of new drugs and to identify the minimum lethal dose. A European initiative including 18 companies has undertaken an evidence-based review of acute toxicity studies and assessed the value of the data generated. Preclinical and clinical information was shared on 74 compounds. The analysis indicated acute toxicity data was not used to (i) terminate drugs from development (ii) support dose selection for repeat dose studies in animals or (iii) to set doses in the first clinical trials in humans. The conclusion of the working group is that acute toxicity studies are not needed prior to first clinical trials in humans. Instead, information can be obtained from other studies, which are performed at more relevant doses for humans and are already an integral part of drug development. The conclusions have been discussed and agreed with representatives of regulatory bodies from the US, Japan and Europe.

GLC756 decreases TNF-alpha via an alpha2 and beta2 adrenoceptor related mechanism.

GLC756, a polyvalent anti-glaucoma drug showed in an endotoxin-induced-uveitis model (EIU) in rats a significant tumor necrosis factor-alpha (TNF-alpha) decrease in serum, indicating an additional anti-inflammatory potential of this compound. The receptors on which GLC756 binds (D1, D2, D4, alpha-1, alpha-2, 5-HT1A, 5-HT2C, 5-HT1D, 5-HT2 A, beta-1, and beta-2) were suggested to play a role. In order to identify a receptor type mediating the TNF-alpha lowering response, GLC756 was combined with various counteracting compounds (CP). For EIU, 8-week-old Lewis rats were intravenously injected at 160 microg lipopolysaccharide (LPS) from Salmonella typhimurium. Before EIU-induction animals received either one of the CP's or GLC756 alone, or GLC756 in combination with one of the CP's. TNF-alpha was determined in serum 2h post EIU-induction. Treatment with CP's alone indicated that agonistic effects on beta-2 adrenoceptors and antagonistic effects on alpha-2, 5-HT1A and 5-HT1D receptors resulted in statistically significant decreased TNF-alpha levels in comparison to the LPS-control group. In combination with GLC756, the counteracting CP's domitor (alpha-2 adrenoceptor agonist) and ICI 118551 (beta-2 adrenoceptor antagonist) inhibited completely the TNF-alpha decreasing effect of GLC756. Counteracting the 5-HT1A receptor with the 5-HT1A agonist 8-OH-DPAT could not prevent the TNF-alpha decreasing effect of GLC756. In conclusion, the antagonistic effect on alpha-2 adrenoceptors and the agonistic effect on beta-2 adrenoceptors were identified as mechanism for the TNF-alpha decreasing effect of GLC756.

The minipig in dermatotoxicology: methods and challenges.

In view of more morphological and physiological similarities between human and porcine skin than for other laboratory animal species, the minipig is a preferred model to evaluate the safety profile of dermally applied xenobiotics. Different methods of dermal administration and examples of non-invasive and invasive investigations during the in-life phase of the studies are described. Routine and special post-mortem examinations in dermal studies are presented to assess responses to the topical treatment of minipig skin. Challenges in dermal minipig studies are discussed with respect to animal welfare and husbandry, test formulations, application methods and different types of investigations. One of the most significant issues for dermal minipig studies is the extensive measures required to prevent cross-contamination of blood and tissue samples taken to monitor local and systemic exposure to the test item.