Specific mutations in the HIV-1 G-tract of the 3 '-polypurine tract cause resistance to integrase strand transfer inhibitors

Background In vitro selection experiments identified viruses resistant to integrase strand transfer inhibitors (INSTIs) carrying mutations in the G-tract (six guanosines) of the 3 '-polypurine tract (3 '-PPT). A clinical study also reported that mutations in the 3 '-PPT were observed in a patient receiving dolutegravir monotherapy. However, recombinant viruses with the 3 '-PPT mutations that were found in the clinical study were recently shown to be susceptible to INSTIs. Objectives To identify the specific mutation(s) in the G-tract of the 3 '-PPT for acquiring INSTI resistance, we constructed infectious clones bearing single or multiple mutations and systematically characterized the susceptibility of these clones to both first- and second-generation INSTIs. Methods The infectious clones were tested for their infectivity and susceptibility to INSTIs in a single-cycle assay using TZM-bl cells. Results A single mutation of thymidine (T) at the fifth position (GGG GTG) in the G-tract of the 3 '-PPT had no effect on INSTI resistance. A double mutation, cytidine (C) or 'T' at the second position and 'T' at the fifth position (GCG GTG and GTG GTG), increased resistance to INSTIs, with the appearance of a plateau in the maximal percentage inhibition (MPI) of the dose-response curves, consistent with a non-competitive mechanism of inhibition. Conclusions Mutations at the second and fifth positions in the G-tract of the 3 '-PPT may result in complex resistance mechanism(s), rather than simply affecting INSTI binding at the IN active site.