Remdesivir impairs mouse preimplantation embryo development at therapeutic concentrations.

Remdesivir (RDV) is the first antiviral drug to be approved by the US Food and Drug Administration for the treatment of COVID-19. While the general safety of RDV has been studied, its reproductive risk, including embryotoxicity, is largely unknown. Here, to gain insights into its embryotoxic potential, we investigated the effects of RDV on mouse preimplantation embryos cultured in vitro at the concentrations comparable to the therapeutic plasma levels. Exposure to RDV (2-8 µM) did not affect the initiation of blastocyst formation, although the maintenance of the cavity failed at 8 µM due to increased cell death. While exposure to 2-4 µM permitted the cavity maintenance, expressions of developmental regulator genes associated with the inner cell mass (ICM) lineage were significantly diminished. Adverse effects of RDV depended on the duration and timing of exposure, as treatment between the 8-cell to early blastocyst stage most sensitively affected cavity expansion, gene expressions, and cell proliferation, particularly of the ICM than the trophectoderm lineage. GS-441524, a major metabolite of RDV, did not impair blastocyst formation or cavity expansion, although it altered gene expressions in a manner differently from RDV. Additionally, RDV reduced the viability of human embryonic stem cells, which were used as a model for the human ICM lineage, more potently than GS-441524. These findings suggest that RDV is potentially embryotoxic to impair the pluripotent lineage, and will be useful for designing and interpreting further in vitro and in vivo studies on the reproductive toxicity of RDV.