Developing allantois is a primary site of 2'-deoxycoformycin toxicity.

In this study, an assessment of normal mouse allantoic development and its sensitivity to 2'-(R)-deoxycoformycin (dCF; Pentostatin) exposure were examined. Both dissecting microscopy and scanning electron microscopy were used to describe the normal growth and morphogenesis of the mouse allantois over gestational days 7-10 as a preliminary step in evaluating potential abnormal allantoic ontogeny and its effect on umbilical cord and placental development. Two abnormal allantoic/umbilical cord phenotypes were observed subsequent to injecting pregnant mice with 5 mg dCF/kg, i.p., on gestational day 7 (GD 7) and evaluating litters on GD 10, 11, and 12. Abnormal phenotypes included: (1) an allantois which extended approximately halfway across the exocoelom but failed to establish a functional contact with the chorion; and (2) a phenotype characterized by reduced expansion of the allantois across the chorionic surface, a very thin umbilical cord, and aberrant vascularization throughout the structure. Both abnormal phenotypes exhibited either an agenesis or hypogenesis of the umbilical cord and chorioallantoic plate, respectively. Neither abnormal phenotype, however, exhibited errors in the directionality of allantoic growth toward the chorion nor in the formation of aberrant contacts between allantois and adjacent yolk sac or amnionic mesenchyme. Statistical interpretation of the experimental data strongly suggested that abnormalities in allantoic/umbilical cord development were directly associated with embryolethality as evidenced by a decline in the frequency of abnormal allantoic/umbilical cord phenotypes over GD 10-12 (73, 36, and 4%; respectively) and a concomitant increase in the frequency of implantation site resorptions over the same time period (7, 47, and 78%). These results strongly suggest that the developing allantois is very sensitive to the effects of dCF exposure, and that interference with its development leads to embryolethality by GD 12.