INTRACELLULAR METABOLISM AND MECHANISM OF ANTIRETROVIRUS ACTION OF 9-(2-PHOSPHONYLMETHOXYETHYL)ADENINE, A POTENT ANTI-HUMAN-IMMUNODEFICIENCY-VIRUS COMPOUND

9-(2-Phosphonylmethoxyethyl)adenine (PMEA) is a potent and selective inhibitor of retrovirus (i.e., human immunodeficiency virus) replication in vitro and in vivo. Uptake of PMEA by human MT-4 cells and subsequent conversion to the mono- and diphosphorylated metabolites (PMEAp and PMEApp) are dose-dependent and occur proportionally with the initial extracellular PMEA concentrations. Adenylate kinase is unable to phosphorylate PMEA. However, 5-phosphoribosyl-1-pyrophosphate synthetase directly converts PMEA to PMEApp with a K(m) of 1.47 mM and a V(max) that is 150-fold lower than the V(max) for AMP. ATPase, 5'-phosphodiesterase, and nucleoside diphosphate kinase are able to dephosphorylate PMEApp to PMEAp, albeit to a much lower extent than the dephosphorylation of ATP. PMEApp has a relatively long intracellular half-life (16-18 hr) and has a much higher affinity for the human immunodeficiency virus-specified reverse transcriptase than for the cellular DNA polymerase-alpha (K(i)/K(m): 0.01 and 0.60, respectively). PMEApp is at least as potent an inhibitor of human immunodeficiency virus reverse transcriptase as 2', 3'-dideoxyadenosine 5'-triphosphate. Being an alternative substrate to dATP, PMEApp acts as a potent DNA chain terminator, and this may explain its anti-retrovirus activity.