In vitro efficacy of brincidofovir against variola virus

Brincidofovir (CMX001), a lipid conjugate of the acyclic nucleotide phosphonate cidofovir, is under development for smallpox treatment using "the Animal Rule," established by the FDA in 2002. Brincidofovir reduces mortality caused by orthopoxvirus infection in animal models. Compared to cidofovir, brincidofovir has increased potency, is administered orally, and shows no evidence of nephrotoxicity. Here we report that the brincidofovir half-maximal effective concentration (EC50) against five variola virus strains in vitro averaged 0.11 μM and that brincidofovir was therefore nearly 100-fold more potent than cidofovir.