Escape of HIV-1 from a Small Molecule CCR5 Inhibitor Is Not Associated with a Fitness Loss

Open Access
Publisher Website
Google Scholar
Abstract
Fitness is a parameter used to quantify how well an organism adapts to its environment; in the present study, fitness is a measure of how well strains of human immunodeficiency virus type 1 (HIV-1) replicate in tissue culture. When HIV-1 develops resistance in vitro or in vivo to antiretroviral drugs such as reverse transcriptase or protease inhibitors, its fitness is often impaired. Here, we have investigated whether the development of resistance in vitro to a small molecule CCR5 inhibitor, AD101, has an associated fitness cost. To do this, we developed a growth-competition assay involving dual infections with molecularly cloned viruses that are essentially isogenic outside the env genes under study. Real-time TaqMan quantitative PCR (QPCR) was used to quantify each competing virus individually via probes specific to different, phenotypically silent target sequences engineered within their vif genes. Head-to-head competition assays of env clones derived from the AD101 escape mutant isolate, the inhibitor-sensitive parental virus, and a passage control virus showed that AD101 resistance was not associated with a fitness loss. This observation is consistent with the retention of the resistant phenotype when the escape mutant was cultured for a total of 20 passages in the absence of the selecting compound. Amino acid substitutions in the V3 region of gp120 that confer complete AD101 resistance cause a fitness loss when introduced into an AD101-sensitive, parental clone; however, in the resistant isolate, changes elsewhere in env that occurred prior to the substitutions within V3 appear to compensate for the adverse effect of the V3 changes on replicative capacity. These in vitro studies may have implications for the development and management of resistance to other CCR5 inhibitors that are being evaluated clinically for the treatment of HIV-1 infection. When human immunodeficiency virus type 1 (HIV-1) develops resistance in vitro or in vivo to antiretroviral drugs such as reverse transcriptase or protease inhibitors, its replicative fitness is often impaired (i.e., it grows at a lower rate or to a lesser extent than the parental, inhibitor-sensitive virus). Here, we investigated whether resistance development in vitro to a new class of antiretroviral drugs, the CCR5 inhibitors, has an associated fitness cost. These inhibitors, exemplified by the AD101 compound, are small molecules that bind CCR5, a cell surface protein that HIV-1 uses as a co-receptor during the process of cellular entry. We performed direct-competition assays using sequence-labeled, clonal viruses derived from an AD101 escape mutant, the AD101-sensitive parental isolate, and a passage control isolate, and found that AD101 resistance was not associated with a fitness loss. Furthermore, when the escape mutant was cultured for 20 passages without AD101, it remained resistant. Specific amino acid substitutions conferring AD101 resistance did cause a fitness loss when experimentally introduced into a sensitive clone, but in the naturally selected escape mutant they are probably compensated for by other changes. This work may help understand the development and management of resistance to CCR5 inhibitors now being evaluated clinically to treat HIV-1 infection.

This publication has 50 references indexed in Scilit: