The novel use of a heterozygous knockout mouse for embryofetal development assessment of a glucokinase activator.

Glucokinase activators (GKAs), such as AZD1656, are designed as antihyperglycemic agents for diabetics and can cause dose-limiting hypoglycemia in normal animals used in embryofetal development studies. Genetically modified heterozygous GK knockout (gkdel/wt) mice are less susceptible to severe GKA-induced hypoglycemia than wild-type mice due to their elevated baseline glucose levels. In this study, the gkdel/wt mouse was used as an alternative rodent strain for embryofetal development studies with AZD1656. Heterozygous global knockout gkdel/wt females were dosed with 20, 50, or 130 mg/kg/day of AZD1656 or vehicle for a minimum of 14 consecutive days before mating with wild-type males and throughout organogenesis. Maternal effects were confined to slightly reduced food consumption, reduced body weight gain, and the pharmacologic effect of decreased plasma glucose. Fetuses were genotyped. Fetal weights at the high dose were slightly reduced but there was no effect on fetal survival. There were two specificmajormalformations, omphalocele and right-sided aortic arch, with increased fetal incidence in mid- and high-dose fetuses (e.g., omphalocele fetal incidence of 0.6, 0.7, 4.6, and 2% across the dose groups) plus increased incidences of minor abnormalities and variants indicative of either delayed or disturbed development. Fetal weight and abnormalities were unaffected by fetal genotype. The fetal effects are considered hypoglycemia related. There was no effect on embryofetal survival in the gkdel/wt mouse at AZD1656 exposures, which were 70× higher than those causing 75% fetal death in rabbits. This illustrates the value of genetically modified animals in unraveling target versus chemistry-related effects.