Design and Evaluation of Sifuvirtide, a Novel HIV-1 Fusion Inhibitor

Abstract

Enfuvirtide (T20) is the first and only HIV-1 fusion inhibitor approved for clinical use, but it can easily induce drug resistance limiting its practical application. A novel anti-HIV peptide, termed sifuvirtide, was designed based on the three-dimensional structure of the HIV-1 gp41 fusogenic core conformation. Here we report its in vitro anti-HIV potency, its mechanism of action, as well as the results from Phase Ia clinical studies. We demonstrated that sifuvirtide inhibited HIV-1-mediated cellcell fusion in a dose-dependent manner and exhibited high potency against infections by a wide range of primary and laboratory-adapted HIV-1 isolates from multiple genotypes with R5 or X4 phenotypes. Notably, sifuvirtide was also highly effective against T20-resistant strains. Unlike T20, sifuvirtide could efficiently block six-helix bundle formation in a dominant negative fashion. These results suggest that sifuvirtide has a different mechanism of action from that of T20. Phase Ia clinical studies of sifuvirtide (FS0101) in 60 healthy individuals demonstrated good safety, tolerability, and pharmacokinetic profiles. A single dose regimen (5, 10, 20, 30, and 40 mg) by subcutaneous injection once daily at abdominal sites was well tolerated without serious adverse events. Pharmacokinetic studies of single and multiple administration of sifuvirtide showed that its decay half-lives were 20.0 ؎ 8.6 h and 26.0 ؎ 7.9 h, respectively. In summary, sifuvirtide has potential to become an ideal fusion inhibitor for treatment of HIV/AIDS patients, including those with HIV-1 strains resistant to T20.

Addition of a cholesterol group to an HIV-1 peptide fusion inhibitor dramatically increases its antiviral potency

“…Such is indeed the case for C34, T20 (4), which spans part of the HR2 region and the sequence downstream (Fig. 1), and several other FI-targeting HR1 or HR2, including peptides, proteins, and small molecules (7)(8)(9)(10)(11)(12)(13)(14)(15)(16)(17)(18)(19)(20)(21).…”

“…Because C34 shows essentially no helical structure before folding onto HR1 to form the 6-helix bundle, HR2-derived peptides have been designed with enhanced helical structure in solution, which translates into greater strength of association with the HR1 coiled-coil and greater antiviral potency (8)(9)(10)24). Hybrids between C34 and T20 have also been pursued because the membrane-proximal region of gp41, included in T20, is beneficial for half-life (11). Although these peptides form 6-helix bundles with much increased stability with respect to C34, there appears to be a limit to the increase in potency that can be achieved by this route, with antiviral activity reaching a plateau over a wide range of bundle stability (8).…”

Broad Antiviral Activity and Crystal Structure of HIV-1 Fusion Inhibitor Sifuvirtide

“…In this fusion-active gp41 core structure, three N-terminal heptad repeat regions (NHR) form a central trimeric coiled coil, whereas three C-terminal heptad repeat regions (CHR) around the NHR pack as antiparallel helices into hydrophobic grooves (3)(4)(5)(6). A number of synthetic peptides derived from the NHR and CHR of gp41 can efficiently inhibit HIV-1 infection by competitively binding to the exposed NHR or CHR in the gp41 pre-hairpin state, hence blocking 6-HB formation in a dominant-negative manner (7)(8)(9)(10)(11)(12)(13)(14)(15). Among them, T20 (Enfuvirtide, Fuzeon) has been approved for clinical use as the first member of a new class of anti-HIV drugs, HIV fusion inhibitors (9,16,17).…”

“…In succession to T20, the second-generation peptide fusion inhibitor T1249 was developed with increased antiviral potency, but its clinical development was halted due to the drug formulation problem (14,22,23). Among a series of more potent third generation fusion inhibitors (10,(12)(13)(14)(15), sifuvirtide (SFT) is one in advance stages. It has been evaluated by the phase I clinical trials and is currently under phase II clinical studies (13,24).…”

“…Among a series of more potent third generation fusion inhibitors (10,(12)(13)(14)(15), sifuvirtide (SFT) is one in advance stages. It has been evaluated by the phase I clinical trials and is currently under phase II clinical studies (13,24). This peptide inhibitor was originally designed with different sequence and/or location in relationship to CHR peptides C34, T20, and T1249 on the basis of three-dimensional structural information of gp41 (13).…”