Discovery of an HIV inhibitor in human blood points to new type of fusion inhibitor
Jan Münch (33), in cooperation with IPF Pharmaceuticals GmbH based in Hannover, succeeded in identifying an HIV inhibitor known as VIRIP. Viro Pharmaceuticals GmbH & Co. KG was subsequently established in Hannover in order to test an improved version of this inhibitor clinically.
The research done by Münch is based on two factors. It has been known for a long time that endogenous retroviruses constitute an integral part of the human genome (approx. 8%). The young researcher was also aware of the fact that specific substances were able to inhibit HIVin the blood. In cooperation with IPF Pharmaceuticals GmbH, Germany, Münch specialised in identifying peptides in human blood and other body fluids and develop them further into antiviral substances.
Jan Münch. (Photo: BioRegionUlm)
IPF Pharmaceuticals GmbH developed a large scale chromatography method with which it was possible to produce peptide libraries from large amounts of body fluids (blood, sperm, saliva). ”High molecularproteins were removed, leaving behind a library of an estimated one million peptide substances,” explained Münch.
According to Münch, these peptide mixtures are a unique source of bioactive substances that might lead the researchers to the identification of antiviral peptides. In cooperation with IPF Pharmaceuticals GmbH, the virologist screened peptide libraries for substances that are able to prevent HIV-1, HSV-2 and HCV infections in vitro. Where possible, substances from active fractions were purified, the sequence of the active peptide and the mechanism of action were determined and then evaluated to determine whether it was possible to develop the peptide into a drug.
At a symposium organised by the Drug Commission on 14 January 2006, the German Medical Association discussed the growing importance of new AIDS drugs in light of the observation that around ten percent of all new HIV infections are the result of resistant viruses. To date, approximately 40 different drugs of different classes are approved for the treatment of viral infections in humans, including approximately 50% for the treatment of AIDS.
Human immunodeficiency viruses possess specific proteins on their surface (receptors) with which they intrude the host cells. For example, to enter human cells, HIV-1 uses CD4 and CCR5 molecules that are expressed on T cells. These proteins transfer signals from or into cells. In many cases, the signals are triggered by peptide ligands such as cytokines, chemokines and peptide hormones. By binding to the viral receptors, some of these messenger substances are capable of preventing the virus from intruding into the cells and thus represent specific targets for the development of new therapeutics. In addition, peptides like defensins are believed to play an important role in innate immune response.
The efficacy of an improved derivate of the natural VIRIP peptide (virus inhibitory peptide) will now be tested in clinical trials. The VIRIP peptide is an α1 antitrypsin fragment consisting of 20 amino acids that was isolated from a blood peptide library. Jan Münch is confident about the likelyhood of success as the molecule has proved to be capable of inhibiting all HIV-1 variants tested so far, including patient isolates and HI viruses that have already become resistant to other drugs.
Frank Kirchhoff (Photo: BioRegionUlm)
Over the last two years, the researchers have succeeded in increasing the peptide’s antiviral activity by several orders of magnitude by specifically altering its structure. Haemolysis tests and NMR spectroscopy revealed that VIRIP was able to inhibit HIV-1 by way of a new mechanism of action. Münch explained: “VIRIP binds to the fusion peptide (FP), which is a sequence in the gp41 envelope protein of HIV-1 mediating the fusion of viral and cellular membranes. The FP represents the first point of contact between viral and human cell membranes. By binding to FP, VIRIP thus prevents this essential step of the infection process and hence blocks infection.”
Due to their enormous variability, the HI viruses are able to develop resistance against any drug available. Mutation and FP sequence analyses suggest, however, that it might be difficult for the viruses to becoming resistant to VIRIP. These findings were decisive for VIRO Pharmaceuticals GmbH & Co., KG in their decision to submit the substance to clinical Phase I trials and test the peptide’s efficacy on humans.
Münch also told us that the screening of the human peptidome will certainly also lead to the identification of other interesting substances like SEVI (semen enhancer of viral infection). SEVI was isolated from human sperm fluid and surprisingly enhances HIV-1 infection dramatically in vitro. SEVI also leads to HIV infection in cases when the amount of viral material is too low to lead to a productive infection. Münch and his colleagues are currently investigating the virus’ mechanism of action.
In parallel, the researchers are carrying out experiments in order to determine the physiological concentrations of SAVI (sperm activator of virus infection) in human sperm. An HIV activating factor in human semen might potentially play an important part in the sexual transmission of HIV and, according to Münch, might present an interesting target for the development of new HIV therapies.
Cell. 2007 Apr 20;129(2):263-75.
Discovery and optimization of a natural HIV-1 entry inhibitor targeting the gp41 fusion peptide.
Institute of Virology, University of Ulm, 89081 Ulm, Germany.
A variety of molecules in human blood have been implicated in the inhibition of HIV-1. However, it remained elusive which circulating natural compounds are most effective in controlling viral replication in vivo. To identify natural HIV-1 inhibitors we screened a comprehensive peptide library generated from human hemofiltrate. The most potent fraction contained a 20-residue peptide, designated VIRUS-INHIBITORY PEPTIDE (VIRIP), corresponding to the C-proximal region of alpha1-antitrypsin, the most abundant circulating serine protease inhibitor. We found that VIRIP inhibits a wide variety of HIV-1 strains including those resistant to current antiretroviral drugs. Further analysis demonstrated that VIRIP blocks HIV-1 entry by interacting with the gp41 fusion peptide and showed that a few amino acid changes increase its antiretroviral potency by two orders of magnitude. Thus, as a highly specific natural inhibitor of the HIV-1 gp41 fusion peptide, VIRIP may lead to the development of another class of antiretroviral drugs.
PMID: 17448989 [PubMed – indexed for MEDLINE]
J Virol. 2007 Jun 6; [Epub ahead of print]
Proline 35 of HIV-1 Vpr regulates the integrity of the N-terminal helix, the incorporation of Vpr into virus particles, and supports the replication of R-5 tropic HIV-1 in human lymphoid tissue ex vivo.
Institute of Virology, University of Erlangen-Nuremberg, Erlangen, Germany, Institute of Virology, University of Ulm, Ulm, Germany, Department of Otolaryngology, University Hospitals Erlangen-Nuremberg, Erlangen, Germany, Institute of Biochemistry, Humboldt University, Berlin, Germany, Department of Chemistry, University of Bergen, Bergen, Norway, Department of Structural Biology, Helmholtz Centre for Infection Research, Braunschweig, Germany.
Mutational analysis of the four conserved proline residues in HIV-1 Vpr reveals that only Pro-35 is required for efficient replication of R5-tropic, but not of X4-tropic viruses in human lymphoid tissue (HLT) cultivated ex vivo. While the Vpr-mediated apoptosis and G2-cell-cycle arrest as well as the expression and sub-cellular localization of Vpr was independent, the capacity for encapsidation of Vpr into budding virions was dependent on Pro-35. (1)H-NMR data suggest that mutation of Pro-35 causes a conformational change in the hydrophobic core of the molecule, whose integrity is required for encapsidation of Vpr, and thus supports replication of R5-tropic HIV-1 in HLT.
PMID: 17553868 [PubMed – as supplied by publisher]