Background An in vitro rat whole embryo culture study investigated whether direct exposure to dolutegravir (TivicayTM) during the critical period for neural tube development would result in abnormal development. Methods Dolutegravir (DTG), and HIV integrase inhibitor, was administered at 0 (vehicle), 5.3 μg/mL and 9.3 μg/mL on Gestation Day (GD) 9 through 11 (approximate 40 hour exposure period) along with positive (Valproic Acid) and negative (Penicillin G) controls. The DTG concentrations tested were selected based on clinical exposure at the maximum human recommended dose and maximum feasible concentration that could be formulated under the experimental conditions. Results Approximately 6% of DTG present in the culture media was absorbed into the embryos, demonstrating embryonic exposure at a similar level to that observed in a rat DTG placental transfer study. There was no effect in either the DTG or Penicillin G groups on visceral yolk sac size/morphology, embryo size, somite number and embryo morphology at any concentration tested. Valproic Acid, by contrast, produced statistically significant decreases in visceral yolk sac size, embryo size and somite number along with defects in visceral yolk sac and embryonic morphology, including neural tube defects (NTDs), in all embryos. Conclusion DTG at the maximum human recommended dose administered to rats in a whole embryo culture assay did not produce any abnormal effects, while the positive control Valproic Acid produced abnormal effects, including neural tube defects.

Micro-CT imaging is an accurate, reliable and robust method that can be used as an alternative to stain when examining fetal rabbit skeletons in developmental toxicity studies.

ObjectivesThe objective of this study was to examine the fetal skeletons using both alizarin red stain and micro‐computed tomography (CT) images; investigate differences, and to determine if the conclusions of the study were the same regardless of the examination method.MethodsA candidate drug was given orally by gavage to pregnant New Zealand White rabbits on gestation day (GD) 7 to GD 19 (mating = GD 0) at doses of 0 (control), 0.02, 0.5, 5, and 15 mg/kg/day. Maternal toxicity was evident at ≥0.02 mg/kg/day. The 199 fetal skeletons (totaling 50,546 skeletal elements) obtained at cesarean delivery on GD29 were first stained with Alizarin Red S, then imaged by a Siemens Inveon micro‐CT scanner. All fetal skeletons were examined by both methods, without knowledge of dose group, and the results were compared.ResultsIn total, 33 types of skeletal abnormalities were identified. There was 99.8% concordance of results comparing stain to micro‐CT. Ossification of the middle phalanx of the forepaw digit 5 showed the greatest difference between the two methods.ConclusionOverall, micro‐CT imaging is a realistic, and robust alternative to skeletal staining to examine fetal rabbit skeletons in developmental toxicity studies.