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.
Crofts
F
F
Department of Drug Safety Evaluation, Aventis Inc., Bridgewater, New Jersey 08807, USA. Frances.Crofts@aventis.com
Rohatagi
S
S
Pino
M
M
DeLise
B
B
Zhang
J
J
Nguyen
M
M
Guittin
P
P
Barbellion
S
S
Brunel
P
P
Hofmann
T
T
Schmidt
J
J
Wong
M
M
Lockey
P
P
Lerman
S
S
Clark
R
R
D000014:Abnormalities, Drug-Induced; D000818:Animals; D001011:Aorta / Q000187:drug effects / Q000196:embryology; D019540:Area Under Curve; D001555:Benzene Derivatives; D002448:Cell Adhesion; D002460:Cell Line; D002823:Chorion / Q000187:drug effects; D004305:Dose-Response Relationship, Drug; D064420:Drug-Related Side Effects and Adverse Reactions; D004622:Embryo, Mammalian / Q000187:drug effects*; D047108:Embryonic Development / Q000187:drug effects*; D005260:Female; D006321:Heart / Q000187:drug effects; D006801:Humans; D007093:Imidazoles / Q000633:toxicity*; D020128:Inhibitory Concentration 50; D039041:Integrin alpha4beta1 / Q000037:antagonists & inhibitors* / Q000378:metabolism; D018811:Maternal Exposure; D008431:Maternal-Fetal Exchange; D008956:Models, Chemical; D010649:Phenylalanine / Q000031:analogs & derivatives* / Q000633:toxicity*; D010671:Phenylurea Compounds / Q000633:toxicity*; D011247:Pregnancy; D011270:Pregnancy, Animal; D011422:Propionates / Q000633:toxicity*; D011485:Protein Binding; D011817:Rabbits; D051381:Rats; D017207:Rats, Sprague-Dawley; D016029:Receptors, Very Late Antigen / Q000378:metabolism; D013045:Species Specificity; D013723:Teratogens; D013997:Time Factors
C483465:(3S)-3-(((2S)-2-(4,4-dimethyl-3-(4-((((2-methylphenyl)amino)carbonyl)amino)benzyl)-2,5-dioxoimidazolidin-1-yl)-4-methylpentanoyl)amino)-3-phenylpropanoic acid; C487626:3-(N-(3,4-dimethoxybenzyl)-2-(2-(3-methoxy-4-(3-o-tolylureido)phenyl)acetylamino)acetamido)propanoic acid; D001555:Benzene Derivatives; C493781:IVL 984; D007093:Imidazoles; D039041:Integrin alpha4beta1; D010671:Phenylurea Compounds; D011422:Propionates; D016029:Receptors, Very Late Antigen; D013723:Teratogens; D010649:Phenylalanine