Exposure-disease continuum for 2-chloro-2'-deoxyadenosine, a prototype ocular teratogen. 1. Dose-response analysis.
BACKGROUND
Treatment of pregnant mice with 2-chloro-2'-deoxyadenosine (2CdA) on day 8 of gestation induces microphthalmia through a mechanism coupled to the p53 tumor suppressor gene. The present study defines 2CdA dosimetry with respect to exposure (pharmacokinetics), p53 protein induction, and disease (microphthalmia).


METHODS
Pregnant CD-1 mice dosed with 0.5-10.0 mg/kg 2CdA on day 8 provided fetuses for teratological evaluation; 2CdA was measured by HPLC in the antimesometrium through 180 min postexposure, and p53 was assessed with immunostaining of the embryo through 270 min. 5'-/3'-RACE was used to sequence the candidate gene for 2CdA bioactivation from target cells.


RESULTS
Microphthalmia appeared first in the dose-response curve. The highest 2CdA dose having no observable adverse effect (NOAEL) was 1.5 mg/kg; the benchmark dose that produced an extra 5% risk of microphthalmia (BMD(5)) was 2.5 mg/kg, and the lower confidence limit (BMDL) was 2.0 mg/kg. Pharmacokinetic parameters for doses encompassing the threshold (1.5-2.5 mg/kg) were modeled at 1.0-1.8 microM (C(max)) and 30-80 microM-min (AUC). The p53 response was not detected below the BMDL; however, a low-grade response appeared 4.5 hr after a teratogenic dose (5.0 mg/kg), and high-grade induction followed an embryolethal dose (10.0 mg/kg). RACE identified a novel splice variant of mitochondrial deoxyguanosine kinase, dGK-3, as the likely candidate for 2CdA bioactivation in the embryo.


CONCLUSIONS
Microphthalmia represented the critical effect malformation of 2CdA. The findings suggest a mitochondrial mechanism for 2CdA bioactivation, leading to an embryonic p53 response only after 2CdA elimination and implying pharmacodynamic coupling to the exposure-disease continuum. Published 2001 Wiley-Liss, Inc.
Wubah
J A
JA
Department of Pathology, Anatomy and Cell Biology, Jefferson Medical College, Philadelphia, Pennsylvania 19107, USA.
Setzer
R W
RW
Lau
C
C
Charlap
J H
JH
Knudsen
T B
TB
D000595:Amino Acid Sequence; D000818:Animals; D001483:Base Sequence; D002851:Chromatography, High Pressure Liquid; D017338:Cladribine / Q000009:adverse effects* / Q000493:pharmacokinetics*; D018076:DNA, Complementary / Q000378:metabolism; D004305:Dose-Response Relationship, Drug; D004622:Embryo, Mammalian / Q000002:abnormalities; D005123:Eye / Q000196:embryology / Q000473:pathology; D016158:Genes, p53; D007150:Immunohistochemistry; D007166:Immunosuppressive Agents / Q000009:adverse effects* / Q000493:pharmacokinetics*; D051379:Mice; D008850:Microphthalmos / Q000139:chemically induced*; D008969:Molecular Sequence Data; D009154:Mutation; D017853:Phosphotransferases (Alcohol Group Acceptor) / Q000378:metabolism; D017422:Sequence Analysis, DNA; D013723:Teratogens; D013997:Time Factors; D016159:Tumor Suppressor Protein p53 / Q000096:biosynthesis
D018076:DNA, Complementary; D007166:Immunosuppressive Agents; D013723:Teratogens; D016159:Tumor Suppressor Protein p53; D017338:Cladribine; D017853:Phosphotransferases (Alcohol Group Acceptor); C019165:deoxyguanosine kinase