Effects of the W153L substitution in HIV reverse transcriptase on viral replication and drug resistance to multiple categories of reverse transcriptase inhibitors

Resistance to reverse transcriptase inhibitors used in the treatment and prevention of HIV-1 infection

Inhibitors that target the retroviral enzyme reverse transcriptase (RT) have played an indispensable role in the treatment and prevention of HIV-1 infection. They can be grouped into two distinct therapeutic groups, namely the nucleoside and nucleotide RT inhibitors (NRTIs), and the non-nucleoside RT inhibitors (NNRTIs). NRTIs form the backbones of most first- and second-line antiretroviral therapy (ART) regimens formulated for the treatment of HIV-1 infection. They are also used to prevent mother-to-child transmission, and as pre-exposure prophylaxis in individuals at risk of HIV-1 infection. The NNRTIs nevirapine (NVP), efavirenz and rilpivirine also used to form part of first-line ART regimens, although this is no longer recommended, while etravirine can be used in salvage ART regimens. A single-dose of NVP administered to both mother and child has routinely been used in resource-limited settings to reduce the rate of HIV-1 transmission. Unfortunately, the development of HIV-1 resistance to RT inhibitors can compromise the efficacy of these antiviral drugs in both the treatment and prevention arenas. Here, we provide an up-to-date review on drug-resistance mutations in HIV-1 RT, and discuss their cross-resistance profiles, molecular mechanisms and clinical significance.

Subtype-specific analysis of the K65R substitution in HIV-1 that confers hypersusceptibility to a novel nucleotide-competing reverse transcriptase inhibitor

Compound A is a novel nucleotide-competing HIV-1 reverse transcriptase (RT) inhibitor (NcRTI) that selects for a unique W153L substitution that confers hypersusceptibility to tenofovir, while the K65R substitution in RT confers resistance against tenofovir and enhances susceptibility to NcRTIs. Although the K65R substitution is more common in subtype C viruses, the impact of subtype variability on NcRTI susceptibility has not been studied. In the present study, we performed experiments with compound A by using purified recombinant RT enzymes and viruses of subtypes B and C and circulating recombinant form CRF_A/G. We confirmed the hypersusceptibility of K65R substitution-containing RTs to compound A for subtype C, CRF_A/G, and subtype B. Steady-state kinetic analysis showed that K65R RTs enhanced the susceptibility to compound A by increasing binding of the inhibitor to the nucleotide binding site of RT in a subtype-independent manner, without significantly discriminating against the natural nucleotide substrate. These data highlight the potential utility of NcRTIs, such as compound A, for treatment of infections with K65R substitution-containing viruses, regardless of HIV-1 subtype.