The hydrophobic pocket in the HIV-1 gp41 N-terminal heptad repeat (NHR) domain name plays an important role in viral fusion and entry into the host cell Carboxypeptidase G2 (CPG2) Inhibitor and serves as a stylish Carboxypeptidase G2 (CPG2) Inhibitor target for development of HIV-1 fusion/entry inhibitors. longer half-life and more potent antiviral activity against a broad spectrum of HIV-1 strains including the T-20-resistant variants. Nonetheless the clinical application of these peptides is still limited by the lack of oral availability and the high cost of production. Thus development of small molecule compounds targeting the gp41 pocket with oral availability has been promoted. This review explains the main methods for identification of HIV fusion/access inhibitors targeting the gp41 pocket and summarizes the latest progress in developing these inhibitors as a new class of anti-HIV drugs. and studies have exhibited that T1249 is effective against T-20-resistant HIV-1 strains and it exhibits a longer half-life than T-20 in non-human primates. In addition T-1249 was well tolerated without dose-limiting toxicity in phase I/II clinical trials. Unfortunately further development of T1249 was terminated because of insufficient improvements around the bioavailability and tolerability characteristics of T-20 [26 27 Based on the results of T1249 experts at Trimeris further developed a series of peptides made up of PBD such as T2635 and T1144 as the third-generation peptide fusion inhibitors which showed longer half-life more potent antiviral activity against a broad spectrum of HIV-1 strains including T-20-resistant variants and a stronger genetic barrier to drug resistance . Clinical application of T-20 has shown that it can quickly induce mutations in the GIV motif (residues 547-556) in the viral gp41 NHR domain name resulting in high resistance . Since T-1249 and other PBD-containing C-peptides also contain the GIV motif-binding domain name they are less susceptible to T-20-resistant HIV-1 strains . To overcome this problem we designed two peptides CP32 and CP32M which contain only the PBD but no motif-binding domain name. We found that these peptides are highly effective against T-20-resistant strains [31 32 However the viruses with mutations in the gp41 pocket region are resistant to CP32M confirming that this C-peptides with PBD do indeed target the gp41 hydrophobic pocket . Sifuvirtide a C-peptide also made up of PBD was designed on the basis of the structure of C34 and the three-dimensional structure of the HIV-1 gp41 fusogenic core conformation [34 35 36 It shows much higher potency longer half-life and better drug resistance than T-20. The data from the phase IIb clinical trial in China show that Sifuvirtide could substantially improve efficacy over traditional treatment and the rate of undetectable viral loads while the rate of CD4 cell count increments for the Sifuvirtide group was 59% which is about 89% Carboxypeptidase G2 (CPG2) Inhibitor better than that for the control group. Furthermore the injection site reaction is usually 7% for Sifuvirtide compared to 98% for T-20. 2.3 Rational Design of Peptides Targeting gp41 CHR-Helices Unlike the C-peptides most of the N-peptides such as DP107 (also known as T21 residues 553-590)  and N36 (residues 546-581)  inhibit HIV-1 fusion by interacting with the viral Carboxypeptidase G2 (CPG2) Inhibitor gp41 CHR-helices to form heterologous 6-HB core . However their anti-HIV-1 activity is generally 100- to 1000-fold lower than the C-peptides  possibly because most N-peptides have a tendency to aggregate under physiological condition . To solve this problem a polypeptide named 5-Helix was designed as an HIV-1 fusion inhibitor targeting the gp41 CHR region . Five-Helix was designed by linking three N-peptides (N40 residues 543-582) and two C-peptides (C38 residues 625-662) with a GGSGG linker forming a single polypeptide. Unlike the 6-HB 5 contains five of six α-helical coils and exposes one of the three grooves to attract a C-helix or C-peptide to fill in the gap and prevent 6-HB core formation thus blocking HIV-1-mediated Mouse monoclonal to ALPP membrane fusion. It inhibits HIV-1 fusion and replication at low nanomolar level; Carboxypeptidase G2 (CPG2) Inhibitor thus it is much more potent than most CHR-targeting N-peptides probably because 5-helix is usually well folded soluble and extremely stable. Although most N-peptides inhibit HIV-1 access by targeting the gp41 CHR domain name some mutant N-peptides such as N36Mut(e g) inhibit viral fusion by interacting with the viral gp41 NHR to form a heterotrimer thus disrupting the formation of homotrimers. Therefore N36Mut(e g) is about 50-fold more potent than its parent peptide N36 in inhibiting HIV-1 Env-mediated cell-cell fusion [38 41.