Structure-based design of mimetics for granulocyte-macrophage colony stimulating factor (GM-CSF).

Granulocyte-macrophage colony stimulating factor (GM-CSF) activity has been linked to pro-inflammatory effects in autoimmune syndromes, such as rheumatoid arthritis. Thus GM-CSF mimetics with antagonist activity might play a therapeutic role in these diseases. The human GM-CSF core structure consists of a four alpha-helix bundle, and GM-CSF activity is controlled by its binding to a two-subunit receptor. A number of residues located on the B and C helices of GM-CSF are postulated to interact with the alpha chain of the GM-CSF receptor (GM-CSFR). Several approaches have been successfully utilized to develop peptide mimetics of this site, including peptides from the native sequence, a peptide derived from a recombinant antibody (rAb) light chain which mimicked GM-CSF receptor binding activity, and structurally guided de novo design. Analysis of the rAb light chain had suggested mimicry of GM-CSF with residues mostly contributed by the CDR I region. Key residues involved in CDR I peptide/GM-CSFR binding were identified by truncation and alteration of individual residues, while the structural elements required to antagonize the biological action of GM-CSF were separately tested in binding and inhibitory activity assays of multiple cyclic analogues. A peptide designed to retain the loop conformation of the CDR I region of the rAb light chain competed with GM-CSF for both antibody and receptor binding, but the role of specific residues in antibody versus receptor binding differed markedly. These studies suggest that structural analysis of peptide mimetics can reveal differences in receptor and antibody binding, perhaps including key interactions that impact binding kinetics. Peptide mimetics of other four-helix bundle cytokines are reviewed, including helical and reverse turn mimetics of helical structures. Use of peptide mimetics coupled with structural and kinetic analysis provides a powerful approach to identifying important receptor-ligand interactions, which implications for rational design of novel therapeutics.

Adoptive protection from experimental myasthenia gravis with T cells from mice treated nasally with acetylcholine receptor epitopes.

Nasal administration of synthetic CD4(+) epitopes of the acetylcholine receptor (AChR) prevents experimental myasthenia gravis (EMG) in C57Bl/6 mice, but not in IL4-deficient C57Bl/6 (IL4(-/-)) mice. Here we verify that nasal tolerance requires IL4, by showing that CD4(+) cells from C57Bl/6 mice treated nasally with a pool of AChR CD4(+) epitopes protected IL4(-/-) mice from EMG and caused a reduced production of anti-AChR antibody. CD4(+) cells from C57Bl/6 mice treated with unrelated peptides or sham-treated did not induce protection. CD4(+) cells from C57Bl/6 mice treated with just one AChR peptide protected IL4(-/-) mice from EMG without affecting antibody synthesis.

Selective alkylation and acylation of alpha and epsilon amino groups with PEG in a somatostatin analogue: tailored chemistry for optimized bioconjugates.

The effects of the type and location of polymer grafting on the biological activity of different mono-PEG derivatives of the somatostatin analogue RC160 were evaluated. A chemical strategy to obtain mono-PEG alkylation or acylation of the peptide's alpha-terminal or lysil-epsilon primary amines was devised. Selective BOC protection of the two available primary amines, followed by reaction with two different PEG reagents and removal of the protecting group, was carried out. Chemical characterization, structural studies, and the evaluation of the biological activity of the bioconjugates synthesized allowed the identification of the one having characteristics more suitable for therapeutic application. This corresponds to the mono-epsilon-lysil-pegylated form, obtained by reductive alkylation, where the amine's positive charge is preserved. The results obtained suggest the importance of preliminary studies in the development of new polymer-peptide conjugates with improved pharmacological properties.