Role of the Envelope Genetic Context in the Development of Enfuvirtide Resistance in Human Immunodeficiency Virus Type 1-Infected Patients

Abstract

Acquired human immunodeficiency virus type 1(HIV-1) resistance to the fusion inhibitor enfuvirtide (ENF)is primarily associated with mutations within the highly conserved first heptad repeat (HR1) region of gp41. Viral env sequences, however, are remarkably variable, and the envelope genetic background could have an important impact on optimal expression of HR1 mutations. We have examined the genetic evolution of env sequences, ENF susceptibility, and Env replicative capacity in patients failing ENF treatment. Sequential plasma-derived virus populations, obtained from six patients initiating ENF treatment as part of a salvage therapy, were studied using a recombinant phenotypic assay evaluating the entire gp120 and the gp41 ectodomains. Regardless of major differences in the baseline ENF susceptibilities, viral populations with similar phenotypic ENF resistance (50% inhibitory concentration, >3,000 ng/ml) were selected under treatment in four of six patients. As expected, in all patients ENF-resistant viruses harbored one or more HR1 mutations (positions 36, 38, and 43). Interestingly, in five patients the emergence of resistance mutations was not associated with reduced Env replicative capacity. Phylogenetic analysis of env sequences in sequential samples from two patients showed that the HR1 mutations had emerged in the context of env quasi-species that were different from those prevalent at baseline. Thus, the envelope genetic context appears to play a critical role in the selection of HR1 mutations and the expression of ENF resistance, thereby conditioning the evolution of HIV-1 under fusion inhibitor selective pressure.Considerable effort is currently being devoted to the development of antiviral agents able to prevent human immunodeficiency virus type 1 (HIV-1) entry into target cells. The HIV-1 entry process is mediated by the trimeric viral envelope glycoproteins (Env) exposed at the surface of the virion (45). The HIV-1 entry is a multistep process (11,14,45). The sequential interaction of the surface subunit, gp120, with CD4 and a chemokine receptor (CCR5 or CXCR4) exposed on the cell membrane triggers conformational changes in the ectodomain of the transmembrane subunit, gp41, which ultimately lead to fusion between the viral and host cell membranes. Like most of the retroviral transmembrane proteins, the ectodomain of gp41 contains an N-terminal fusion peptide followed by two heptad repeat domains (HR1 and HR2), which are connected by a non-helical loop region of 25 to 30 amino acids. Membrane fusion is currently thought to result from the insertion of the fusion peptide into the cellular membrane, and the formation of a six-helix bundle in which the central trimeric HR1 coiled-coil forms three hydrophobic grooves onto which three HR2 domains pack in reverse orientation (4,5,40,43).Although several HIV-1 entry inhibitors have been evaluated in clinical trials and have shown promising prospects for therapy (1, 28), the only entry inhibitor licensed to date is the fusion inhibitor enfuvirtide (ENF; als...

RNA Structures Facilitate Recombination-Mediated Gene Swapping in HIV-1

“…Recombination between closely related strains, including viruses belonging to the same quasispecies present in an infected individual, is certainly frequent and important for the generation and emergence of antiviral resistance and immune escape variants (17,27,34). However, a critical feature of the recombination process as an evolutionary force is that of…”

“…The net effect is to facilitate both the combination of advantageous mutations within individual highly fit genomes and the removal of deleterious mutations from viral populations. In the case of human immunodeficiency virus (HIV), these processes contribute to the dynamic evasion of immune responses and to the evolution of drug resistance (20,27,34,45).In addition to encoding information necessary for protein production, the genomes of RNA viruses, including HIV, convey functional information through their secondary and tertiary structures. These structures regulate many stages of the viral replication cycle, including genome replication, genome packaging into new viral particles, and intracellular trafficking (5,6,30,36,42).…”

“…The net effect is to facilitate both the combination of advantageous mutations within individual highly fit genomes and the removal of deleterious mutations from viral populations. In the case of human immunodeficiency virus (HIV), these processes contribute to the dynamic evasion of immune responses and to the evolution of drug resistance (20,27,34,45).…”

Vicriviroc Resistance Decay and Relative Replicative Fitness in HIV-1 Clinical Isolates under Sequential Drug Selection Pressures

“…The N43D-containing env genes became the majority clones from week 42 to 48, and it seems likely that regions outside the gp120 V3 loop or the HR-1 gp41 domain contributed to these observed fitness differences. The presence of compensatory changes in env has been previously described for both V3 loop and HR-1 mutations (19,25,41,47,64).…”

“…The fitness cost of the enfuvirtide-associated G36D mutation, a substitution in the first heptad repeat (HR-1) of gp41, results from reduced viral fusion kinetics (30,49). The particular enfuvirtide mutation selected during therapy is a function of the total env genetic context, suggesting that sequences outside gp41 influence resistance development (25). Env context is also important in the development of CCR5 antagonist resistance mutations (24).…”