Critical period for a teratogenic VLA-4 antagonist: Developmental effects and comparison of embryo drug concentrations of teratogenic and non-teratogenic VLA-4 antagonists

BACKGROUND

Integrins such as VLA-4 (Very late antigen 4, integrin alpha4beta1) play key roles in cell-cell interactions that are critical for development. Homozygous null knockouts of the VLA-4 alpha4-subunit or VCAM-1 (VLA-4 cell surface ligand) in mice result in failure of the allantois and chorion to fuse leading to interrupted placentation and cardiac development and embryo lethality. Embryo-fetal studies of three VLA-4 antagonists, IVL745, IVL984, and HMR1031 [Crofts et al., Birth Defects Res B 71:55-68 (this issue), 2004] with exposure on gestation days (GD) 6-17 (rat), 6-18 (rabbit) or 6-15 (mouse) showed that only IVL984 treatment resulted in embryo lethality and cardiac defects. Objectives of the current study were to determine the critical period for inducing IVL984-related embryo-fetal effects, and to test the hypothesis that these effects were due to higher embryo drug concentrations.

METHODS

IVL984 was administered at 40 mg/kg/day to pregnant rats on GD 4 and 5, GD 6 and 7, GD 8 and 9, GD 10 and 11, or GD 12 and 13. Animals were euthanized on GD 21 and uteri and fetuses were examined. A treatment period of GD 10-12 was selected for subsequent toxicokinetic (TK) studies in which IVL984, HMR1031, or IVL745 was administered to pregnant rats and rabbits. On GD 12, maternal plasma, extra-embryonic tissue (placenta and amniotic fluid), and embryonic tissue were collected and analyzed for drug concentrations.

RESULTS

In the IVL984 critical period study in pregnant rats, treatment on GD 10 and 11 resulted in increased post-implantation loss, skeletal variations, and spiral septal defects similar to those observed in standard embryo-fetal development studies with treatment throughout organogenesis. There were no embryo-fetal effects after treatment on GD 4 and 5, GD 6 and 7, or GD 8 and 9. There was a single aorta malformation after treatment on GD 12 and 13. In the TK studies, IVL745, HMR1031, and IVL984 were all detectable in embryonic tissue and there was no evidence for accumulation. Rat and rabbit embryo exposures (AUC or dose-adjusted AUC) on GD 12 could not explain the observed teratology (IVL984<HMR1031<IVL745). Further analyses incorporating pharmacological activity, clearance, and protein binding data provided a positive correlation between embryonic exposure and teratogenic potency.

CONCLUSIONS

The critical period for IVL984 in the rat, GD 10 to 11, corresponds to the expression of alpha-4 integrin on the chorion and VCAM-1 on the allantois and myocardium as well as chorioallantoic fusion and formation of the spiral septum. Embryo drug levels adjusted for pharmacological activity, clearance, and protein binding provide a possible explanation for the differing teratogenic potency of IVL984, HMR1031, and IVL745.

Different embryo-fetal toxicity effects for three VLA-4 antagonists

BACKGROUND

VLA-4 (Very late antigen 4, integrin alpha4beta1) plays an important role in cell-cell interactions that are critical for development. Homozygous null knockouts of the alpha4 subunit of VLA-4 or VCAM-1 (cell surface ligand to VLA-4) in mice result in abnormal placental and cardiac development and embryo lethality. Objectives of the current study were to assess and compare the teratogenic potential of three VLA-4 antagonists.

METHODS

IVL745, HMR1031, and IVL984 were each evaluated by the subcutaneous route in standard embryo-fetal developmental toxicity studies in rats and rabbits. IVL984 was also evaluated in mice. Fetuses were examined externally, viscerally, and skeletally.

RESULTS

IVL745 did not cause significant maternal or fetal effects at doses up to 100 or 250 mg/kg/day in rats or rabbits, respectively. HMR1031 treatment resulted in marked maternal toxicity and slight fetal toxicity at the highest tested doses of 200 and 75 mg/kg/day in rats and rabbits, respectively. HMR1031 embryo-fetal effects consisted of slightly lower body weight and crown-rump length in rats and minor sternebral defects in rabbits. IVL984 treatment resulted in minimal maternal effects at doses up to 40, 15, and 100 mg/kg/day in rats, rabbits, and mice, respectively (excluding abortions in rabbits). However, marked developmental effects were observed at the lowest tested IVL984 doses, 1, 0.2, and 3 mg/kg/day in rats, rabbits, and mice, respectively. IVL984 embryo-fetal effects consisted of increased total post-implantation loss due to early resorptions and high incidences of cardiac malformations and skeletal malformations and/or variations. Notably, spiral septal defects were observed in up to 76% of rat fetuses and up to 58% of rabbit fetuses.

CONCLUSIONS

Dramatic differences in teratogenic potential were observed: IVL745 was not teratogenic, HMR1031 caused slight embryo-fetal effects at maternally-toxic doses, and IVL984 was a potent teratogen at doses where direct maternal toxicity was limited to abortions in rabbits. Prominent effects of IVL984 included embryo lethality and cardiac malformations including spiral septal defects in three species.

Harmonisation of rat fetal skeletal terminology and classification. Report of the Third Workshop on the Terminology in Developmental Toxicology. Berlin, 14-16 September 2000

The initial efforts of the Federal Institute for Health Protection of Consumers and Veterinary Medicine (BgVV) and the Free University of Berlin to standardise terminology in the field of developmental toxicology began in 1995. Procedures were undertaken to harmonise the terminology used by the International Federation of Teratology Societies (IFTS) and the International Programme on Chemical Safety (IPCS). This article reflects these activities and is a report on the Third Workshop on the Terminology in Developmental Toxicology held in September 2000. This Workshop served as a forum to discuss the results of a survey on the classification of skeletal anomalies that had been previously sent to scientists active in the field. Although high agreement was reached among the evaluators for several terms, the use of a number of terms was rather variable. Therefore, the discussions at the workshop among the experts from research institutions, regulatory agencies, and industry were mainly focussed on those terms for which there was disagreement and/or uncertainties and the possible reasons. Pictures provided by the participants for the illustration of "grey zone" anomalies constituted the basis for detailed discussions. In many of the cases with lower agreement, decisions were facilitated by the provision of the corresponding picture. The main reasons for lower agreement were imprecise terms, insufficient knowledge on postnatal consequences, theoretical terms that are unlikely to occur in isolation, and the possibility of observing a range of severity that might be decisive for the classification of either a malformation or variation. The attendees concluded that "grey-zone" anomalies will never disappear completely and that for the assessment, the grade of severity and/or the frequency of the observation can be decisive for the terminology chosen. A Joint IPCS/IFTS Project was proposed to further consensus of terminology and classification and to link these anomalies to pictures at different skeletal sites. In order to support the harmonisation of regulatory decisions, it was proposed to establish a "Clearinghouse" System under the umbrella of the IPCS. The Clearinghouse could be contacted either by the regulatory authorities or by any company to clarify their queries, particularly with regard to registration or authorisation processes. Finally, it was recommended to also carry out a similar survey on "soft tissue anomalies" and "external findings." The results of this survey will be discussed at a Joint IPCS/IFTS Workshop in Berlin in 2002.

[Education and role of the toxicologist]

Toxicology covers a very large scientific area, needing specialists in the main basic disciplines involved, and generalists with a large and practical overview. Academic education, consequently, should take this necessity into account. This education is presently satisfactory in France, even if some adjustments are necessary, for the specialists but is inadequate for the generalists, whereas an important need exists in industry. It should be emphasized that toxicology is a profession and consequently practical experience is essential, as well as continuing education. In view of this situation, an evaluation of toxicologists in the course of their professional activities is necessary. In the USA, this evaluation is devolved to the American Board of Toxicology and in Europe to the Eurotox Accreditation. In conclusion of the Round Table, 8 recommendations are proposed.

Changes in clinical pathology parameters during gestation in the New Zealand white rabbit

Hematology and serum chemistry parameters were analyzed in 2 groups of pregnant rabbits to assess changes in these parameters over the course of gestation. These data were used to generate a historical control reference range for embryofetal development regulatory toxicology studies. During the 28-day gestation period, the following major changes were observed. Red blood cell counts, hemoglobin, and hematocrit increased slightly up to day 13 and subsequently decreased progressively to a nadir for all parameters on day 25. Reticulocyte counts increased maximally by day 16 and then decreased to a minimum value on day 28. White blood cell counts progressively declined after day 7. Platelet counts increased slightly by day 10, were relatively stable until day 13, then progressively decreased to a nadir on day 25. Aspartate aminotransferase and alanine aminotransferease values increased steadily throughout the study to reach a maximum value on day 25. Triglycerides increased to their maximum value by day 19 and then steadily decreased until day 28, whereas cholesterol decreased progressively to reach a nadir on day 25. Urea and total protein decreased steadily from day 13 onward. Calcium values decreased throughout the study to reach a minimum value on day 28. Phosphorus values increased slightly on days 7 and 13 and then progressively decreased to reach a nadir on day 28. With a few exceptions, changes that occur in clinical pathology parameters during pregnancy in the rabbit are similar to those observed in pregnant women. Therefore, the rabbit can be considered a suitable species for embryofetal development toxicity studies with regard to clinical pathology.

[Toxicology of reproduction: predictive value of experimental models. Round Table No 1 at Giens XIII]

The carrying out of clinical trials with a view to the marketing of drugs for human use is directly related to results of some animal studies. This workshop was devoted to evaluation of the quality and interest of these experimental models in reproductive toxicology. The predictive ability of preclinical trials to make extrapolations from animals to man decreases from foetotoxic to tetratogenic risks respectively and from the effects on fertility in both sexes to postnatal risks. As a result of this workshop, we propose the following improvements: (1) standardization and generalization of fertility test evaluations, especially the spermogram, in order to improve animal and human correlations; (2) development of knowledge and standardization of the follow up of the oestral cycle; (3) improvement of standardization, harmonization and diffusion of postnatal tests that prove relevant in animals; (4) increase in initiatives aimed at better mutual understanding of all drug partners; (5) creation of registers for new drugs, as soon as possible during clinical trials, to study their effects on the whole reproductive process; (6) recommendations for the creation of guidelines for International Conference on Harmonisation (ICH) to enable classification of observed effects in experimental models. This could lead to specific (potentially for each phase of the reproductive cycle) guidelines, precautions for use and/or contraindications which are listed in the summary of product characteristics.

Terminology of developmental abnormalities in common laboratory mammals (version 1)

This paper presents the first version of an internationally-developed glossary of terms for structural developmental abnormalities in common laboratory animals. The glossary is put forward by the International Federation of Teratology Societies (IFTS) Committee on International Harmonization of Nomenclature in Developmental Toxicology, and represents considerable progress toward harmonization of terminology in this area. The purpose of this effort is to provide a common vocabulary that will reduce confusion and ambiguity in the description of developmental effects, particularly in submissions to regulatory agencies worldwide. The glossary contains a primary term or phrase, a definition of the abnormality, and notes, where appropriate. Selected synonyms or related terms, which reflect a similar or closely related concept, are noted. Nonpreferred terms are indicated where their usage may be incorrect. Modifying terms used repeatedly in the glossary (e.g., absent, branched) are listed and defined separately, instead of repeating their definitions for each observation. Syndrome names are generally excluded from the glossary, but are listed separately in an appendix. The glossary is organized into broad sections for external, visceral, and skeletal observations, then subdivided into regions, structures, or organs in a general overall head to tail sequence. Numbering is sequential, and not in any regional or hierarchical order. Uses and misuses of the glossary are discussed. Comments, questions, suggestions, and additions from practitioners in the field of developmental toxicology are welcomed on the organization of the glossary as well as on the specific terms and definitions. Updates of the glossary are planned based on the comments received.

Mechanisms of pulmonary edema induced by an organophosphorus compound in anesthetized dogs

To determine the mechanism governing pulmonary edema induced by an organophosphorus compound, S-(2-diisopropylaminoethyl)-O-ethylmethyl phosphonothiolate (VX), lung lymph flow and lymph-to-plasma protein concentration ratio were measured in six anesthetized, open-chest, mechanically ventilated beagle dogs before and after intravenous injection of 6 micrograms/kg of VX. Systemic and pulmonary hemodynamic data (heart rate, aortic blood flow, and left atrial, systemic arterial, pulmonary arterial, and pulmonary capillary pressures) were continuously recorded. Arterial blood gases and pH were measured every 30 min. Histological examinations and lung water content measurements were also carried out. Following VX injection, lung lymph flow increased (from 109 +/- 38 to 179 +/- 66 microliters/min, p less than 0.05) while lymph-to-plasma protein concentration ratio remained unchanged (from 0.64 +/- 0.14 to 0.62 +/- 0.12, N.S.). Neither systemic nor pulmonary hemodynamics were changed. Lung water content expressed as blood-free wet-to-dry weight ratio increased from 4.31 +/- 0.23 to 5.35 +/- 0.26 (p less than 0.05). Histological examinations revealed in many cases diffuse congestion of lungs and interstitial edema. These results suggest that VX injection induces an increase in pulmonary capillary permeability which may lead to a high-permeability edema.

Effects of an organophosphorous compound on cardiac rhythm and haemodynamics in anaesthetized and conscious beagle dogs

Cardiac toxicity of S-(2-diisopropylaminoethyl)-O-ethylmethyl phosphonothiolate (VX) has been investigated in the dog. Conscious or open-chest anaesthetized animals were subcutaneously injected with VX (1.5, 3.0 or 6.0 micrograms/kg b.w.). Blood cholinesterase activity decreased to 60%, 20% and 18% respectively of initial values. Only in the 6.0 micrograms/kg-treated group, heart rate, arterial and left intraventricular pressures and contractility index slightly but significantly decreased. In some dogs, treated with either 3.0 micrograms/kg or 6.0 micrograms/kg b.w. of VX, the electrocardiogram was changed: the Q-T interval was lengthened and arrhythmias (atrioventricular blocks, ventricular premature complexes. 'Torsade de pointe') were observed. Plasma non-esterified fatty acid concentrations were identical in control and VX-poisoned dogs. This study shows that, besides the expected cardiac effects resulting from muscarinic stimulation, VX can affect ventricular function through a yet unknown mechanism.