Enfuvirtide Resistance Mutations: Impact on Human Immunodeficiency Virus Envelope Function, Entry Inhibitor Sensitivity, and Virus Neutralization

Abstract

Enfuvirtide (ENF/T-20/Fuzeon), the first human immunodeficiency virus (HIV) entry inhibitor to be licensed, targets a structural intermediate of the entry process. ENF binds the HR1 domain in gp41 after Env has bound CD4, preventing conformational changes needed for membrane fusion. Mutations in HR1 that confer ENF resistance can arise following ENF therapy. ENF resistance mutations were introduced into an R5-and X4-tropic Env to examine their impact on fusion, infection, and sensitivity to different classes of entry inhibitors and neutralizing antibodies. HR1 mutations could reduce infection and fusion efficiency and also delay fusion kinetics, likely accounting for their negative impact on viral fitness. HR1 mutations had minimal effect on virus sensitivity to other classes of entry inhibitors, including those targeting CD4 binding (BMS-806 and a CD4-specific monoclonal antibody [MAb]), coreceptor binding (CXCR4 inhibitor AMD3100 and CCR5 inhibitor TAK-779), or fusion (T-1249), indicating that ENF-resistant viruses can remain sensitive to other entry inhibitors in vivo. Some HR1 mutations conferred increased sensitivity to a subset of neutralizing MAbs that likely target fusion intermediates or with epitopes preferentially exposed following receptor interactions (17b, 48D, 2F5, 4E10, and IgGb12), as well as sera from some HIV-positive individuals. Mechanistically, enhanced neutralization correlated with reduced fusion kinetics, indicating that, in addition to steric constraints, kinetics may also limit virus neutralization by some antibodies. Therefore, escape from ENF comes at a cost to viral fitness and may confer enhanced sensitivity to humoral immunity due to prolonged exposure of epitopes that are not readily accessible in the native Env trimer. Resistance to other entry inhibitors was not observed.

Increased HIV-1 sensitivity to neutralizing antibodies by mutations in the Env V3-coding region for resistance to CXCR4 antagonists

“…As previous reports for other entry inhibitors (Berro et al, 2009;Pugach et al, 2008;Reeves et al, 2005; Yoshimura et al, 2014), we showed that CXCR4 inhibitor-resistant Env altered neutralization sensitivity to some NAbs (Fig. 3, Table S2).…”

Cross-resistance mechanism of respiratory syncytial virus against structurally diverse entry inhibitors

“…Different escape pathways were also identified for HIV resistance to the peptidic entry inhibitor Fuzeon (52,53). However, Fuzeon escape did not coincide with resistance to other entry inhibitors (54). Broad cross-resistance against a structurally highly diverse panel of entry inhibitors appears unique to RSV F and may amount to a substantial obstacle in the clinic.…”

Complex interplay of kinetic factors governs the synergistic properties of HIV-1 entry inhibitors

“…In addition to gp120-coreceptor interactions, substitutions in the gp41 N-HR and C-HR regions can influence the lifetime of the PHI (54,55). How such mutations impact the fusion …”