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.

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