Structure-activity relationships of the Human Immunodeficiency Virus type 1 maturation inhibitor PF-46396

HIV-1 maturation inhibitors are a novel class of antiretroviral compounds, which consist of two structurally distinct chemical classes; betulinic acid derivatives and the pyridone-based compound PF-46396. It is currently believed that both classes act by a similar mode of action to generate aberrant non-infectious particles via inhibition of CA-SP1 cleavage during Gag proteolytic processing. In this study we utilized a series of novel analogues, with decreasing similarity to PF-46396, to determine the chemical groups within PF-46396 that contribute to antiviral activity, Gag binding and the relationship between these essential properties. A spectrum of antiviral activity (active, intermediate, inactive) was observed across the analogue series with respect to CA-SP1 cleavage and HIV-1 (NL4-3) replication kinetics in Jurkat T cells. We demonstrate that selected inactive analogues are incorporated into WT immature particles and that one inactive analogue is capable of interfering with PF-46396 inhibition of CA-SP1 cleavage. Mutations that confer PF-46396 resistance can impose a defective phenotype on HIV-1 that can be rescued in a compound-dependent manner. Some inactive analogues retained the capacity to rescue PF-46396-dependent mutants (SP1-A3V, SP1-A3T, CA-P157S), implying that they can also interact with mutant Gag. The structure-activity relationships observed in this study demonstrate that (i) the tert-butyl group is essential for antiviral activity, but not an absolute requirement for Gag binding, (ii) the trifluromethyl group is optimal but not essential for antiviral activity and (iii) the 2-aminoindan group is important for antiviral activity and Gag binding but not essential as its replacement is tolerated.