Neutralising properties of peptides derived from CXCR4 extracellular loops towards CXCL12 binding and HIV-1 infection.

The chemokine receptor CXCR4 interacts with a single endogenous chemokine, CXCL12, and regulates a wide variety of physiological and pathological processes including inflammation and metastasis development. CXCR4 also binds the HIV-1 envelope glycoprotein, gp120, resulting in viral entry into host cells. Therefore, CXCR4 and its ligands represent valuable drug targets. In this study, we investigated the inhibitory properties of synthetic peptides derived from CXCR4 extracellular loops (ECL1-X4, ECL2-X4 and ECL3-X4) towards HIV-1 infection and CXCL12-mediated receptor activation. Among these peptides, ECL1-X4 displayed anti-HIV-1 activity against X4, R5/X4 and R5 viruses (IC50=24 to 76µM) in cell viability assay without impairing physiological CXCR4-CXCL12 signalling. In contrast, ECL2-X4 only inhibited X4 and R5/X4 strains, interfering with HIV-entry into cells. At the same time, ECL2-X4 strongly and specifically interacted with CXCL12, blocking its binding to CXCR4 and its second receptor, CXCR7 (IC50=20 and 100µM). Further analysis using mutated and truncated peptides showed that ECL2 of CXCR4 forms multiple contacts with the gp120 protein and the N-terminus of CXCL12. Chemokine neutralisation was mainly driven by four aspartates and the C-terminal residues of ECL2-X4. These results demonstrate that ECL2 represents an important structural determinant in CXCR4 activation. We identified the putative site for the binding of CXCL12 N-terminus and provided new structural elements to explain the recognition of gp120 and dimeric CXCR4 ligands.

Cell-penetrating Alphabody protein scaffolds for intracellular drug targeting.

The therapeutic scope of antibody and nonantibody protein scaffolds is still prohibitively limited against intracellular drug targets. Here, we demonstrate that the Alphabody scaffold can be engineered into a cell-penetrating protein antagonist against induced myeloid leukemia cell differentiation protein MCL-1, an intracellular target in cancer, by grafting the critical B-cell lymphoma 2 homology 3 helix of MCL-1 onto the Alphabody and tagging the scaffold's termini with designed cell-penetration polypeptides. Introduction of an albumin-binding moiety extended the serum half-life of the engineered Alphabody to therapeutically relevant levels, and administration thereof in mouse tumor xenografts based on myeloma cell lines reduced tumor burden. Crystal structures of such a designed Alphabody in complex with MCL-1 and serum albumin provided the structural blueprint of the applied design principles. Collectively, we provide proof of concept for the use of Alphabodies against intracellular disease mediators, which, to date, have remained in the realm of small-molecule therapeutics.

Non-immunized natural human heavy chain CDR3 repertoires allow the isolation of high affinity peptides mimicking a human influenza hemagglutinin epitope.

In this study we constructed two phage libraries displaying non-immunized natural human IgM derived HCDR3 repertoires. One library was structurally constrained by a Gly to Cys substitution at position 104 enabling the formation of a disulfide bridge with the Cys at position 92. Panning of these libraries on an anti-human influenza hemagglutinin (HA) antibody resulted in the selection of 16 different HCDR3 loops displaying different degrees of sequence homology with the HA epitope. The specificity of the HCDR3 loops recovered from the structurally constrained library was confirmed by competition assays using the HA epitope. Only one of these HCDR3 peptides contained Cys104. Structural analysis of these sequences revealed that the loss of Cys104 was associated with an increased preference for the formation of the type I beta-turn required for high affinity binding to the antibody. Affinity studies confirmed that the HCDR3 peptides containing the sequence YDVPDY and Gly104 had affinities in the nanomolar range (K(d)=7.6 nM) comparable to the HA epitope. These findings provided evidence that the recovered HCDR3 sequences may bind to their target in a conformation that is unreachable by the parental antibody from which the HCDR3 was derived. Furthermore, the isolation of target-specific and high affinity binders demonstrates the value of HCDR3 libraries as a source of 'biologically randomized' sequences of human origin for the identification of peptidic lead molecules.

Development of Mimokines, chemokine N terminus-based CXCR4 inhibitors optimized by phage display and rational design.

The chemokine receptor CXCR4 (C-X-C chemokine receptor type 4 also known as fusin or CD184 (cluster of differentiation 184)) is implicated in various biological and pathological processes of the hematopoietic and immune systems. CXCR4 is also one of the major coreceptors for HIV-1 entry into target cells and is overexpressed in many cancers, supporting cell survival, proliferation, and migration. CXCR4 is thus an extremely relevant drug target. Among the different strategies to block CXCR4, chemokine-derived peptide inhibitors hold great therapeutic potential. In this study, we used the N-terminus of vCCL2/vMIPII, a viral CXCR4 antagonist chemokine, as a scaffold motif to engineer and select CXCR4 peptide inhibitors, called Mimokines, which imitate the chemokine-binding mode but display an enhanced receptor affinity, antiviral properties, and receptor selectivity. We first engineered a Mimokine phage displayed library based on the first 21 residues of vCCL2, in which cysteine 11 and 12 were fully randomized and screened it against purified CXCR4 stabilized in liposomes. We identified Mimokines displaying up to 4-fold higher affinity for CXCR4 when compared to the reference peptide and fully protected MT-4 cells against HIV-1 infection. These selected Mimokines were then subjected to dimerization, D-amino acid, and aza-ß3-amino acid substitution to further enhance their potency and selectivity. Optimized Mimokines exhibited up to 120-fold enhanced CXCR4 binding (range of 20 nM) and more than 200-fold improved antiviral properties (≤ 1 µM) compared to the parental Mimokines. Interestingly, these optimized Mimokines also showed up to 25-fold weaker affinity for ACKR3/CXCR7 and may therefore serve as lead compounds for further development of more selective CXCR4 peptide inhibitors and probes.

A new recombinant virus system for the study of HIV-1 entry and inhibition.

The construction is described of a HIV-1 proviral, eGFP-tagged plasmid that allows for the recombination of any selected env gene without the use of restriction enzymes and for the quantitation of the infection by the recombinant virus using flow cytometry. The system was tested showing that an isoleucine to valine substitution at residue position 37 of the HIV-1 gp41 impairs the fitness of the virus but does not lead by itself to T-20 resistance.

Isolation of an HIV-1 neutralizing peptide mimicking the CXCR4 and CCR5 surface from the heavy-chain complementary determining region 3 repertoire of a viremic controller.

OBJECTIVES: The recent identification of neutralizing antibodies able to prevent viral rebound reemphasized the interest in humoral immune responses to control HIV-1 infection. In this study, we characterized HIV-1-inhibiting sequences from heavy-chain complementary determining region 3 (HCDR3) repertoires of a viremic controller. DESIGN AND METHODS: IgM and IgG-derived HCDR3 repertoires of a viremic controller presenting plasma-neutralizing activity and characterized by over 20 years of infection with a stable CD4 T-cell count were displayed on filamentous phage to identify HCDR3 repertoire-derived peptides inhibiting HIV-1 entry. RESULTS: Screening of phage libraries against recombinant gp120 led to the identification of an HCDR3-derived peptide sequence (LRTV-1) displaying antiviral properties against both X4 and R5 viruses. The interaction of LRTV-1 with gp120 was enhanced upon CD4 binding and sequence comparison revealed homology between LRTV-1 and the second extracellular loop of C-X-C chemokine receptor type 4 (CXCR4) (11/23) and the N-terminus of C-C chemokine receptor type 5 (CCR5) (7/23). Alanine scanning experiments identified different clusters of residues critical for interaction with the viral envelope protein. CONCLUSIONS: LRTV-1 peptide is to date the smallest human HCDR3 repertoire-derived peptide identified by phage display inhibiting HIV entry of R5 and X4 viruses. This peptide recognizes a CD4-dependent gp120 epitope critical for coreceptor binding and mimics the surface of CXCR4 and CCR5. Our data emphasize the potential of human HCDR3 immune repertoires as sources of small biologically active peptides for HIV cure.

HIV-1 subtypes in Luxembourg, 1983-2000.

OBJECTIVES: To study the prevalence of HIV-1 subtypes in Luxembourg between 1983 and 2000. To compare the drug susceptibility of non-B and B clade viruses and the prevalence of resistance-associated mutations and polymorphisms before antiretroviral treatment. DESIGN: A retrospective study on plasma samples of HIV-infected patients registered at the National Service of Infectious Diseases, Luxembourg, between 1983 and 2000. METHODS: Genotyping was performed by sequencing of the reverse transcriptase (RT) and protease coding region of the pol gene. Drug susceptibility was assessed in a recombinant virus assay. RESULTS: A total of 20.1% of the HIV-positive patients were infected with non-B subtypes, and since 1990 the proportion of non-B viruses has increased ninefold. Eleven out of 14 F1 subtypes occurred in patients native to Luxembourg. Major resistance mutations related to protease inhibitors (PI), nucleoside reverse transcriptase inhibitors (NRTI) and non-nucleoside reverse transcriptase inhibitors (NNRTI) occurred in less than 3% of treatment-naive viruses; however, 87% of the viruses had at least one PI-associated mutation. Natural polymorphism of the protease and RT coding region was observed more frequently among non-B than B viruses. Significantly more B viruses displayed resistance to the tested PI, NRTI and NNRTI (P = 0.044). CONCLUSION: The proportion of non-B viruses has increased dramatically since 1990. Non-B subtypes showed no decreased susceptibility to antiretroviral drugs, but displayed minor mutations and polymorphisms at higher frequency in their protease and RT coding region. In contrast, a significantly higher proportion of B viruses showed resistance to a range of antiretroviral drugs.

Structural basis of IL-23 antagonism by an Alphabody protein scaffold.

Protein scaffolds can provide a promising alternative to antibodies for various biomedical and biotechnological applications, including therapeutics. Here we describe the design and development of the Alphabody, a protein scaffold featuring a single-chain antiparallel triple-helix coiled-coil fold. We report affinity-matured Alphabodies with favourable physicochemical properties that can specifically neutralize human interleukin (IL)-23, a pivotal therapeutic target in autoimmune inflammatory diseases such as psoriasis and multiple sclerosis. The crystal structure of human IL-23 in complex with an affinity-matured Alphabody reveals how the variable interhelical groove of the scaffold uniquely targets a large epitope on the p19 subunit of IL-23 to harness fully the hydrophobic and hydrogen-bonding potential of tryptophan and tyrosine residues contributed by p19 and the Alphabody, respectively. Thus, Alphabodies are suitable for targeting protein-protein interfaces of therapeutic importance and can be tailored to interrogate desired design and binding-mode principles via efficient selection and affinity-maturation strategies.

Engineering and screening the N-terminus of chemokines for drug discovery.

Chemokines are small chemoattractive proteins involved in many important physiological and pathological processes such as leukocyte mobilisation, inflammation, cancer and HIV-1 infection. The N-terminus of chemokines was shown to be crucial for interaction and activation with their cognate receptors. Therefore, multiple strategies including elongation, truncation, mutagenesis or chemical modifications of chemokine N-terminus were developed to identify analogues with modified selectivity displaying antagonist or enhanced agonist activities. Library approaches allowed fast screening of a large number of such chemokine variants and led to the identification of promising therapeutic candidates. Additional studies were able to reduce the chemokine to the size of a peptide while retaining its receptor affinity and selectivity. In analogy to full length chemokines, peptides derived from the chemokine N-terminal sequence were improved by mutagenesis, elongation and truncation approaches to develop potential therapeutic molecules used in various clinical trials. Altogether these studies demonstrated the pharmacophore potential of the chemokine N-terminus and its vast modulation properties to develop analogues with great therapeutic value for a large set of pathologies.

Selection of a CXCR4 antagonist from a human heavy chain CDR3-derived phage library.

Phage display technology is a powerful selection approach to identify strong and specific binders to a large variety of targets. In this study, we compared the efficacy of a phage library displaying human heavy chain complementarity determining region 3 (HCDR3) repertoires with a set of conventional random peptide libraries for the identification of CXCR4 antagonists using a peptide corresponding to the second extracellular loop of the receptor CXCR4 as target. A total of 11 selection campaigns on this target did not result in any specific ligand from the random peptide libraries. In contrast, a single selection campaign with an HCDR3 library derived from the IgM repertoire of a nonimmunized donor resulted in nine specific peptides with lengths ranging from 10 to 19 residues. Four of these HCDR3 sequences interacted with native receptor and the most frequently isolated peptide displayed an affinity of 5.6 µm and acted as a CXCR4 antagonist (IC(50) = 23 µm). To comprehend the basis of the highly efficient HCDR3 library selection, its biochemical properties were investigated. The HCDR3 length varied from 3 to 21 residues and displayed a biased amino acid content with a predominant proportion of Tyr, Gly, Ser and Asp. Repetitive and conserved motifs were observed in the majority of the HCDR3 sequences. The strength and efficacy of the HCDR3 libraries reside in the combination of multiple size peptides and a naturally biased sequence variation. Therefore, HCDR3 libraries represent a powerful and versatile alternative to fully randomized peptide libraries, in particular for difficult targets.

Synthesis of 4-[2-aminoethyl(nitrosamino)]-1-pyridin-3-yl-butan-1-one, a new NNK hapten for the induction of N-nitrosamine-specific antibodies.

4-(Methylnitrosamino)-1-(3-pyridyl)-1-butanone (NNK) is one of the most abundant and potent procarcinogens in tobacco smoke. In order to induce a strong and substained antibody response against NNK, we developed a functionalized derivative that closely mimicked its structural features, in particular, the pyridyloxobutyl moiety, the adjacent ketone, and the N-nitrosamino group. This hapten was conjugated via a C 2 linker to the highly immunogenic diphteria toxoid licensed as a vaccine in humans to induce polyclonal and monoclonal antibodies. Two monoclonal antibodies were obtained with Kd values of 45.8 nM (P9D5) and 37.6 nM (P7H3), respectively, for NNK-C 2. Both the monoclonal (P9D5 and P7H3) and polyclonal antibodies reacted strongly with NNK (IC 50 = 80 microM or 160 microM) and NNAL (IC 50 = 29 microM or 93 microM) and to a lesser extent with some of the metabolites of NNK. Interestingly, the mAbs did not react with the metabolites of the detoxification pathways such as NNK-N-Oxide and NNAL-N-Oxide (IC 50 > 512 microM). Therefore, such antibodies detect NNK and NNAL and may have the potential to modulate their redistribution in vivo, perhaps reducing some detrimental effects of smoking.

Uncommon mutations at residue positions critical for enfuvirtide (T-20) resistance in enfuvirtide-naive patients infected with subtype B and non-B HIV-1 strains.

Enfuvirtide (T-20) is the lead compound of the new class of antiretroviral drugs called fusion inhibitors. T-20 resistance-associated mutations located in the heptad repeat 1 (HR-1) domain of gp41 have been described in vitro and in clinical trials. In this study, the authors investigated the primary genotypic T-20 resistance in subtype B and non-B HIV-1 strains from patients at the beginning of their follow-up in the Luxembourg HIV Cohort as well as the emergence of primary resistance to T-20 in patients who had long-term infection with subtype B HIV-1 strains. HR-1 fragments including the gp41 amino acid 36-45, T-20-sensitive region were screened for amino acid variation. No classic T-20 resistance-associated mutations were identified in subtype B or non-B isolates. However, several uncommon mutations were found at residues 37, 39, and 42 for subtype B isolates and at residue 42 for a subtype non-B isolate. The results indicate that primary genotypic T-20 resistance seems to be rare in HIV-1, regardless of subtype or prior antiretroviral therapy (excluding fusion inhibitors). However, episodic variation within HR-1 can occur and needs further phenotypic evaluation in accurate fusion inhibitor resistance assays.