The Role of Polymorphisms at Position 89 in the HIV-1 Protease Gene in the Development of Drug Resistance to HIV-1 Protease Inhibitors

Objectives: Relatively little is known about the development of resistance to protease inhibitors (PIs) in non-B subtypes. In subtype B viruses, L89 is commonly found at position 89 in the HIV protease (PR) gene, whereas M89 is commonly observed as a polymorphism in other subtypes. We compared the frequencies of substitutions at position 89 in PR in tissue culture selections and in clinical databases of PI-naive and PI-experienced populations.

Methods: Representative subtype A/CRF01_AE (n = 2 and 3) and subtype C (n = 5) isolates were cultured in MT-2 cells and cord blood mononuclear cells (CBMCs), respectively, under increasing drug pressure with PIs, and drug resistance mutations were identified.

Results: The M89 natural polymorphism in non-B subtypes commonly led to the appearance of an M89T mutation in selections with atazanavir in subtypes A/AE and C, and was accompanied by other previously recognized atazanavir mutations. The M89T mutation contributed to phenotypic resistance to atazanavir and cross-resistance to lopinavir and nelfinavir, but not to other PIs. A shift from a L89 natural polymorphism to L89I/M arose in two of five subtype C selections with PIs. M89I/V/T mutations were acquired by 10%-11% of individuals harbouring non-B subtypes who were failing PI-based regimens, but were rarely observed in drug-naive persons and in patients failing non-PI-based regimens.

Conclusions: The M/L89 natural polymorphism present in non-B subtypes may lead to the M89T mutational pathway conferring resistance to atazanavir, lopinavir and nelfinavir.