title: Kinetic analysis of inhibition of human immunodeficiency virus type-1 reverse transcriptase by calanolide A.
abstract: Calanolide A, first isolated from the tropical rain forest tree Calophyllum lanigerum, is a potent human immunodeficiency virus type-1 (HIV-1) specific reverse transcriptase (RT) inhibitor, broadly active against diverse HIV-1 strains, including nucleoside and nonnucleoside-resistant variants. We examined the biochemical mechanism of inhibition of HIV-1 RT by calanolide A. Two template/primer systems were examined: ribosomal RNA and homopolymeric rA-dT 12-18. Calanolide A inhibited HIV-1 RT by a complex mechanism involving two calanolide A binding sites. With respect to either deoxynucleotide triphosphate (dNTP) or template/primer binding, one site was competitive and the other was uncompetitive. The data indicated that calanolide A bound near the active site of the enzyme and interfered with dNTP binding. Calanolide A inhibited HIV-1 RT in a synergistic fashion with nevirapine, further distinguishing it from the general class of nonnucleoside RT inhibitors. At certain concentrations, calanolide A bound HIV-1 RT in a mutually exclusive fashion with respect to both the pyrophosphate analog, phosphonoformic acid and the acyclic nucleoside analog 1-ethoxymethyl-5-ethyl-6-phenylthio-2-thiouracil. This indicates that calanolide A shares some binding domains with both phosphonoformic acid and 1-ethoxymethyl-5-ethyl-6-phenylthio-2-thiouracil, presumably reflecting that it interacts with RT near both the pyrophosphate binding site and the active site of the enzyme.
authors.affiliation: Laboratory of Drug Discovery Research and Development, National Cancer Institute, Frederick, Maryland, USA.
authors.forename: M J
authors.initials: MJ
authors.lastname: Currens
authors.forename: J M
authors.initials: JM
authors.lastname: Mariner
authors.forename: J B
authors.initials: JB
authors.lastname: McMahon
authors.forename: M R
authors.initials: MR
authors.lastname: Boyd
mesh_terms: D019380:Anti-HIV Agents / Q000494:pharmacology*; D001665:Binding Sites; D003374:Coumarins / Q000494:pharmacology*; D054303:HIV Reverse Transcriptase / Q000037:antagonists & inhibitors*; D006801:Humans; D007700:Kinetics; D039681:Pyranocoumarins; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology*
chemical_list: D019380:Anti-HIV Agents; D003374:Coumarins; D039681:Pyranocoumarins; D018894:Reverse Transcriptase Inhibitors; D054303:HIV Reverse Transcriptase; C075959:calanolide A