In vitro selection of HIV-1 variants resistant to GRL-216, GRL-246, GRL-286, and GRL-396. HIV-1NL4-3 was propagated in MT-4 cells in the presence of increasing concentrations of APV (•), GRL-216 (▴), GRL-246 (▪), GRL-286 (□), or GRL-396 (○). Each passage of HIV-1 was conducted in a cell-free fashion. APV was employed as a reference compound.