An HIV reverse transcriptase inhibitor (Kis = 0.022 and 1.55 μM for RNA and DNA, respectively); an HBV polymerase inhibitor (Ki = 0.18 μM); selective over DNA polymerase α and β, as well as mitochondrial DNA polymerase γ (Kis = 5.2, 81.7, and 59.5 μM, respectively); increased levels in isolated PBMCs correlate with a decrease in the risk of SHIV acquisition in a macaque model of rectal SHIV transmission