title: A critical subset model provides a conceptual basis for the high antiviral activity of major HIV drugs.
abstract: Control of HIV-1 replication was first achieved with regimens that included a nonnucleoside reverse transcriptase inhibitor (NNRTI) or a protease inhibitor (PI); however, an explanation for the high antiviral activity of these drugs has been lacking. Indeed, conventional pharmacodynamic measures like IC(50) (drug concentration causing 50% inhibition) do not differentiate NNRTIs and PIs from less active nucleoside reverse transcriptase inhibitors (NRTIs). Drug inhibitory potential depends on the slope of the dose-response curve (m), which represents how inhibition increases as a function of increasing drug concentration and is related to the Hill coefficient, a measure of intramolecular cooperativity in ligand binding to a multivalent receptor. Although NNRTIs and PIs bind univalent targets, they unexpectedly exhibit cooperative dose-response curves (m > 1). We show that this cooperative inhibition can be explained by a model in which infectivity requires participation of multiple copies of a drug target in an individual life cycle stage. A critical subset of these target molecules must be in the unbound state. Consistent with experimental observations, this model predicts m > 1 for NNRTIs and PIs and m = 1 in situations where a single drug target/virus mediates a step in the life cycle, as is the case with NRTIs and integrase strand transfer inhibitors. This model was tested experimentally by modulating the number of functional drug targets per virus, and dose-response curves for modulated virus populations fit model predictions. This model explains the high antiviral activity of two drug classes important for successful HIV-1 treatment and defines a characteristic of good targets for antiviral drugs in general, namely, intermolecular cooperativity.
authors.affiliation: Department of Medicine, Johns Hopkins University School of Medicine, Baltimore, MD 21205, USA.
authors.forename: Lin
authors.initials: L
authors.lastname: Shen
authors.forename: S Alireza
authors.initials: SA
authors.lastname: Rabi
authors.forename: Ahmad R
authors.initials: AR
authors.lastname: Sedaghat
authors.forename: Liang
authors.initials: L
authors.lastname: Shan
authors.forename: Jun
authors.initials: J
authors.lastname: Lai
authors.forename: Sifei
authors.initials: S
authors.lastname: Xing
authors.forename: Robert F
authors.initials: RF
authors.lastname: Siliciano
mesh_terms: D019380:Anti-HIV Agents / Q000494:pharmacology*; D004305:Dose-Response Relationship, Drug; D006678:HIV / Q000187:drug effects*; D017320:HIV Protease Inhibitors / Q000494:pharmacology; D019429:Integrase Inhibitors / Q000494:pharmacology; D008954:Models, Biological; D010641:Phenotype; D015203:Reproducibility of Results; D018894:Reverse Transcriptase Inhibitors / Q000494:pharmacology; D014771:Virion / Q000187:drug effects
chemical_list: D019380:Anti-HIV Agents; D017320:HIV Protease Inhibitors; D019429:Integrase Inhibitors; D018894:Reverse Transcriptase Inhibitors