Exposure-disease continuum for 2-chloro-2'-deoxyadenosine, a prototype ocular teratogen. 1. Dose-response analysis

Area of Science:

• Developmental toxicology
• Pharmacokinetics and pharmacodynamics
• Molecular biology and genetics

Background:

• 2-chloro-2'-deoxyadenosine (2CdA) exposure during gestation in mice causes microphthalmia.
• The teratogenic mechanism involves the p53 tumor suppressor gene.
• This study aims to establish 2CdA dosimetry correlating exposure, p53 induction, and microphthalmia.

Purpose of the Study:

• To define 2CdA dosimetry in pregnant mice.
• To correlate 2CdA pharmacokinetics with p53 protein induction.
• To establish the relationship between 2CdA exposure and the incidence of microphthalmia.

Main Methods:

• Pregnant CD-1 mice were administered varying doses of 2CdA on day 8 of gestation.
• 2CdA levels were quantified in maternal antimesometrium via HPLC.
• Embryonic p53 protein levels were assessed using immunostaining.
• 5'-/3'-RACE was employed to identify the gene responsible for 2CdA bioactivation.

Main Results:

• Microphthalmia incidence correlated with 2CdA dose, with a NOAEL of 1.5 mg/kg and BMD(5) of 2.5 mg/kg.
• Pharmacokinetic parameters (Cmax, AUC) were determined for doses around the teratogenic threshold.
• p53 induction was observed only at doses exceeding the benchmark dose lower confidence limit (BMDL), with a delayed response.
• A novel splice variant of mitochondrial deoxyguanosine kinase, dGK-3, was identified as the likely mediator of 2CdA bioactivation.

Conclusions:

• Microphthalmia is the critical malformation associated with 2CdA exposure.
• A mitochondrial pathway for 2CdA bioactivation is proposed.
• Embryonic p53 response occurs post-2CdA elimination, suggesting pharmacodynamic coupling to the exposure-disease continuum.