Enfuvirtide

Overview

Enfuvirtide (brand name Fuzeon; development code T-20) is a 36-amino-acid peptide antiretroviral that blocks HIV-1 entry into CD4+ host cells by inhibiting membrane fusion. Approved by the FDA in 2003, it was the first-in-class fusion inhibitor and the first peptide antiretroviral brought to market. Developed by Trimeris and commercialized by Roche, enfuvirtide transformed treatment options for heavily treatment-experienced patients with multidrug-resistant HIV during the early 2000s.

Although use has declined with the emergence of integrase inhibitors and long-acting injectables like cabotegravir, enfuvirtide remains a milestone in antiviral peptide therapeutics and a proof of concept for rationally designed mimics of viral fusion intermediates.

Structure / Sequence

Enfuvirtide is a synthetic 36-mer with the sequence Ac-YTSLIHSLIEESQNQQEKNEQELLELDKWASLWNWF-NH2, derived from the heptad repeat 2 (HR2) region of HIV-1 gp41. The acetylated N-terminus and amidated C-terminus enhance stability, but enfuvirtide still requires subcutaneous administration due to oral proteolysis.

Mechanism of Action

HIV entry proceeds through gp120 binding to CD4 and a coreceptor (CCR5 or CXCR4), exposing gp41. gp41 then forms a prehairpin intermediate in which HR1 and HR2 must assemble into a six-helix bundle that drives viral-host membrane fusion. Enfuvirtide mimics HR2 and binds the exposed HR1 groove of the prehairpin intermediate, preventing six-helix bundle formation and blocking fusion.

Because enfuvirtide targets a transient extracellular intermediate, it is unaffected by intracellular drug efflux mechanisms and retains activity against reverse-transcriptase and protease inhibitor-resistant strains.

Research Summary

Resistance develops through HR1 mutations at gp41 positions 36 to 45, which reduce enfuvirtide binding affinity.

Pharmacokinetics

Subcutaneous enfuvirtide at 90 mg reaches peak concentrations in 4 to 8 hours with an elimination half-life of approximately 3.8 hours. It is highly protein bound (92 percent) and primarily degraded to its constituent amino acids via catabolism, with no meaningful CYP450 involvement and therefore few drug interactions. Oral bioavailability is negligible.

Dosing Protocols

• Adults: 90 mg subcutaneously twice daily
• Pediatric (6 to 16 years): 2 mg/kg twice daily, maximum 90 mg
• Administration: Rotate injection sites (abdomen, thigh, upper arm) to limit injection site reactions
• Storage: Lyophilized powder reconstituted with sterile water before dosing

Common Discussion Topics

• Injection site reactions are the most frequent adverse event and drive discontinuation
• Reservoir role for salvage therapy despite largely superseded status
• Resistance pathway through HR1 mutations
• Peptide manufacturing complexity and the historically high cost per year
• Comparisons with newer attachment and maturation inhibitors

Related Compounds

• Bortezomib — peptide-based drug in another class
• Daptomycin — cyclic lipopeptide antibiotic
• Ziconotide — conotoxin-derived peptide analgesic
• Conotoxins — venom-derived peptide class
• Bivalirudin — synthetic peptide anticoagulant