Graham Cotton

Synthetic peptides representing discontinuous CD4 binding epitopes of HIV-1 gp120 that induce T cell apoptosis and block cell death induced by gp120

A vaccine against HIV‐1 virus would block initial infection and must target conserved residues. Since initial infection depends on binding of the viral envelope protein gp120 to CD4 on the cell surface, the CD4 binding site of gp120 is a target for vaccine design. To identify the optimal biologically active site, we synthesized a series of 32‐mer peptides, based on conserved residues in the C3 and C4 regions of gp120. These included three of five sequence discontinuous residues known to be involved in CD4 binding, one or two of which were substituted with alanine. We also synthesized a 44‐mer peptide with an additional branch to incorporate an extra C4 region sequence including a fourth CD4 binding residue. All these peptides used an oxidized Cys‐X‐Cys bridge to link the discontinuous sequence elements in a manner suggested by the known conserved disulfide bridges in gp120. Polyclonal sera raised to these peptides indicate that they all contain both B and T lymphocyte epitopes. Binding of the peptides to CD4‐transfected HeLa cells reveals a hierarchy dependent on the number of relevant CD4 binding residues present. Furthermore, antibody cross‐linking of peptides bound to the surface of human T cells results in apoptosis that is similar to the known properties of gp120. The peptide incorporating three CD4 binding residues competitively inhibited gp120‐induced T lymphocyte apoptosis. Thus, we have synthesized novel, branched peptides incorporating conserved discontinuous sequences from two different conserved domains of HIV‐1 gp120 that contain T and B lymphocyte epitopes and mimic biological functions of the native protein. These synthetic peptides are candidates for future vaccine development.—Howie, S. E. M., Cotton, G. J., Heslop, I., Martin, N. J., Harrison, D. J., Ramage, R. Synthetic peptides representing discontinuous CD4 binding epitopes of HIV‐1 gp120 that induce T cell apoptosis and block cell death induced by gp120. FASEB J. 12, 991–998 (1998)

9-Aminoacridine peptide derivatives as versatile reporter systems for use in fluorescence lifetime assays

A novel long lifetime fluorescence reporter based on 9-aminoacridine was designed, the lifetime of which can be modulated in a defined manner when in proximity to a tryptophan residue enabling fluorescence lifetime based biochemical assays to be configured.

Treatment of inflammatory bowel disease by chemokine receptor-targeted leukapheresis

Leukapheresis removes circulating leukocytes en route to the target organ. Hitherto unspecific matrixes have been used to remove leukocytes in inflammatory bowel disease (IBD). This report describes a novel selective leukapheresis column based on chemokine-chemokine receptor interaction. We found an increased expression of the gut homing chemokine receptor CCR9 on CD14(+) monocytes and on CD3(+) T lymphocytes from IBD patients. Biologically active CCL25 was coupled to a Sepharose matrix and demonstrated to selectively remove CCR9-expressing cells leaving other cell populations largely unaffected. A patient with active ulcerative colitis, was subjected to CCL25-column leukapheresis. Four days after treatment, he experienced clinical improvement and stable disease improvement ensued. The study illustrates that specific cells can be targeted using high affinity interactions, i.e., CCL25-CCR9 interactions to remove pathogenic gut-homing cells. Leukapheresis using the bCCL25 column should be investigated in a clinical phase I trial of patients with inflammatory bowel disease.

A functional, discontinuous HIV-1 gp120 C3/C4 domain-derived, branched, synthetic peptide that binds to CD4 and inhibits MIP-1α chemokine binding

This paper describes a branched synthetic peptide [3.7] that incorporates sequence discontinuous residues of HIV‐1 gp120 constant regions. The approach was to bring together residues of gp120 known to interact with human cell membranes such that the peptide could fold to mimic the native molecule. The peptide incorporates elements of both the conserved CD4 and CCR5 binding sites. The 3.7 peptide, which cannot be produced by conventional genetic engineering methods, is recognized by antiserum raised to native gp120. The peptide also binds to CD4 and competitively inhibits binding of QS4120 an antibody directed against the CDR2 region of CD4. When preincubated with the CD4+ve MM6 macrophage cell line, which expresses mRNA for the CCR3 and CCR5 chemokine receptors, both 3.7 and gp120 inhibit binding of the chemokine MIP‐1α. The peptide also inhibits infection of primary macrophages by M‐tropic HIV‐1. Thus, 3.7 is a prototype candidate peptide for a vaccine against HIV‐1 and represents a novel approach to the rational design of peptides that can mimic complex sequence discontinuous ligand binding sites of clinically relevant proteins.—Howie, S. E. M., Fernandes, M. L., Heslop, I., Hewson, T. J., Cotton, G. J., Moore, M. J., Innes, D., Ramage, R., Harrison, D. J. A discontinuous HIV‐1 gp120 C3/C4 domain‐derived, branched, synthetic peptide that binds to CD4 and inhibits MIP‐1α chemokine binding. FASEB J. 13, 503–511 (1999)

DESIGN AND SYNTHESIS OF A HIGHLY IMMUNOGENIC, DISCONTINUOUS EPITOPE OF HIV-1 GP120 WHICH BINDS TO CD4+VE TRANSFECTED CELLS

Here we report the design and synthesis of a novel 32-mer peptide, Lys364-378Val445-459.oxidized (named GC-1), which represents a discontinuous epitope from the C3 and C4 domains of gp120 from the HIV-1 IIIB isolate. This peptide induces high titre IgG antibody responses in mice, indicating that it has both B and T cell epitopes. Epitope mapping using reduced GC-1 and appropriate linear peptides demonstrated that a large proportion of the antibodies raised in mice were directed against discontinuous epitope(s). Furthermore, antibodies to GC-1 peptide cross-reacted with purified HIV-1 strain IIIB gp120, indicating the GC-1 mimicked at least one epitope of the native protein. The peptide, which incorporates three gp120 residues Asp 368, Glu 370 and Asp 457, previously shown to be critical for CD4 ligation, bound to the surface of a CD4 transfected human epithelial cell line HeLa, but not to the parent cell line and inhibited binding of recombinant HIV-1 gp120 to recombinant soluble CD4. We have synthesized the first of a series of discontinuous peptides which will be useful for the probing of interactions of HIV-1 gp120 with the CD4 molecule.

A Comparative Study of Fluorescence Assays in Screening for BRD4

Fluorescence assay technologies are commonly used in high-throughput screening because of their sensitivity and ease of use. Different technologies have their characteristics and the rationale for choosing one over the other can differ between projects because of factors such as availability of reagents, assay performance, and cost. Another important factor to consider is the assay susceptibility to artifacts, which is almost as important as the ability of the assay to pick up active compounds. Spending time and money on false positives or missing the opportunity to build chemistry around false negatives is something that every drug project tries to avoid. We used a BET family Bromodomain, BRD4(1), to explore the outcome of a screening campaign using three fluorescent assay technologies as primary assays. A diverse 7,038 compound set was screened in fluorescence lifetime, fluorescence polarization, and homogeneous time-resolved fluorescence to look at primary hit rates, compound overlap, and hit confirmation rates. The results show a difference between the fluorescence assay technologies with three separate hit lists and some overlap. The confirmed hits from each assay were further evaluated for translation into cells (NanoBRET™). Most of the actives confirmed in cells originated from compounds that overlapped between the assays. In addition, a well-annotated set of compounds with undesirable mechanism of inhibition was screened against BRD4(1) to compare the ability to discriminate true hits from artifact compounds. The results indicate a difference between the assays in their ability to generate false positives and negatives.