Prenatal therapy in developmental disorders: drug targeting via intra-amniotic injection to treat X-linked hypohidrotic ectodermal dysplasia

Abstract

X-linked hypohidrotic ectodermal dysplasia (XLHED), the most common inherited disorder of ectoderm development, is caused by a lack of the signaling molecule EDA-A1. In the Tabby XLHED mouse model, prenatal EDA-A1 replacement via maternal injection corrected the developmental abnormalities to a far greater extent than postnatal administration to newborn pups. This approach, however, may not be optimal for achieving therapeutic levels of corrective protein in the human fetus, and additionally exposes the mother to high serum levels of the exogenous molecule. We hypothesized that direct injection of EDA-A1 replacement protein into the amniotic fluid (AF) could result in fetal uptake via lung and gut, leading to sustained drug exposure at levels sufficient for successful treatment of XLHED. Methods: EDI200, a human IgG1:EDA-A1 fusion protein, was tested for stability in AF using a binding ELISA. Subsequently, EDI200 was injected into amniotic sacs of pregnant wild-type mice to evaluate drug uptake and pharmacokinetics. Fetal and maternal serum levels were monitored. Based on these results, EDI200 at a dose of 100 mg/kg fetal weight was administered intra-amniotically to E15 Tabby mouse fetuses and phenotypic correction was assessed. Results: EDI200 was demonstrated to be stable in AF at 37° for one week without detectable loss of activity. Intra-amniotic administration to E15 wild-type mice (35 mcg EDI200/fetus) resulted in substantial fetal uptake with mean serum levels of 9.0 mcg/ml and 1.2 mcg/ml at 6 hours and 96 hours, respectively. Maternal serum levels remained <0.1mcg/ml. In Tabby mice, a single maternal injection of EDI200 at E15 proved to correct the XLHED phenotype in offspring only partially. The complete spectrum of hair, sweat gland and dentition response following E15 intra-amniotic administration of EDI200 is being evaluated through adulthood and will be presented along with statistics on fetal loss related to this therapeutic approach. Conclusions: Intra-amniotic protein application to mice may lead to rapid fetal uptake, sustained substantial serum levels, and efficacy comparable with intravenous injection. As amniocentesis is generally a low-risk procedure in humans, this route of delivery may be suitable for drug targeting with reduced drug exposure of the mother and longer bioavailability due to a reservoir function of AF. It may, thus, represent a novel paradigm for treatment of disorders in early human development.