GM-CSF Inhibitory Peptides

Definition
GM-CSF inhibitory peptides are short peptides based on the sequence of human granulocyte macrophage-colony stimulating factor (GM-CSF) exhibited inhibition of GM-CSF binding and direct biological antagonist activity.

Discovery
Linear peptide analogs of GM-CSF were produced by dividing the human GM-CSF sequence into six peptides. This strategy led to the identification of two peptides with receptor binding and antagonist activity by VonFeldt, JM et al., in 19951. One peptide corresponding to residues 17-31 (the A helix of GM-CSF) inhibited high affinity receptor binding, while a second peptide corresponding to residues 54-78 (the B and C helices of GM-CSF) inhibited low affinity receptor binding. This implicates these sites in intermolecular interactions with the GM-CSFR2.

Structural Characteristics
GM-CSF inhibitory peptides are generally derivatives of GM-CSF with amino residue 21 substituted by a basic amino acid. Preferably, the basic amino acid residue is Arg or Lys. The most preferred antagonist comprises Arg at position 21 of GM-CSF and is referred to herein as E21R.

Mostly GM-CSF antagonists are
(i) in unglycosylated form;
(ii) lack post-translational modification;
(iii) produced in prokaryotic microorganisms; and/or
(iv) produced by chemical synthesis.

GM-CSF antagonists carrying a substitution of amino acid 21 (Glu) of human GM-CSF by Arg or Lys are designated "E21R" and "E21K", respectively, based on a single letter designation of the amino acids involved in the substitution and the position of the substitution3.

Two cyclic peptide GM-CSF mimics (1785 and 1786) were designed from structural analysis of the GM-CSF region mimicked by rAb 23.2. The cyclized peptides specifically bind to polyclonal anti-GM-CSF antibody (stronger for 1786 than for 1785). 1786 competes with GM-CSF for binding to the GM-CSF receptor present on HL-60 cells and reverses GM-CSF's prevention of apoptosis of MO7E cells. Thus, 1786 represents a structurally designed biological and receptor antagonist of GM-CSF. Important residues in the GM-CSF structure mimicked by similar residues on 23.2 are postulated to be: Thr-57, Glu-60, Lys-63, Lys-74, Thr-78, Ser-82, and Lys-854.

Mode of Action
The GM-CSF antagonist either blocks the action of wild-type GM-CSF by interacting selectively with the receptor a-chain or induces apoptosis by interacting with the a- and ß-chains of the receptor in a manner that leads to abnormal stimulation of the ß-chain either qualitatively or quantitatively .GM-CSF antagonist E21R binds to the GM-CSF-specific a-chain of the GM-CSF receptor and that such binding directly induces apoptosis of normal and malignant myeloid cells expressing the GM-CSF receptor. 1786 competes with GM-CSF for binding to the GM-CSF receptor4.

Functions
E21R acts as a specific GM-CSF receptor antagonist on human leukemic cells and neutrophils. E21R significantly accelerated apoptosis of eosinophils. The effect of E21R on eosinophil survival was selectively mediated through the GM-CSF receptor complex and not by nonspecific toxicity. The introduction of the GM-CSF analogue E21R may offer a novel therapy in inflammatory diseases associated with eosinophil infiltration of different etiologies5. E21R and E21K are effective antagonists of both nonglycosylated and glycosylated wild-type GM-CSF and have potential clinical significance for the management of inflammatory diseases and certain leukemias where GM-CSF plays a pathogenic role6. Antagonists of GM-CSF are disclosed that comprise antibodies and anti-idiotypic antibodies specific for the carboxyl terminus of GM-CSF. These antagonists are useful for treating various diseases, the symptoms of which are increased by GM-CSF, and for lessening the effects of chemotherapy7.

References
1.VonFeldt JM, Monfardini C, Fish S, Rosenbaum H, Kieber-Emmons T, Williams RM, Khan SA, Weiner DB, Williams WV (1995). Development of GM-CSF antagonist peptides. Pept Res., 8(1):20-27, 30-32.
2.Monfardini C, Kieber-Emmons T, VonFeldt JM, O'Malley B, Rosenbaum H, Godillot AP, Kaushansky K, Brown CB, Voet D, McCallus DE (1995) Recombinant Antibodies in Bioactive Peptide Design. J Biol Chem., 270(12):6628-6638.
3.http://www.patentstorm.us/patents/6322791/description.html
4.Monfardini C, Kieber-Emmons T, Voet D, Godillot AP, Weiner DB, Williams WV (1996). Rational Design of Granulocyte-Macrophage Colony-stimulating Factor Antagonist Peptides. J. Biol. Chem., 271(6):2966-71.
5.Iversen PO, Robinson D, Ying S, Meng Q, Kay AB, Clark-Lewis I, Lopez AF (1997). The GM-CSF Analogue E21R Induces Apoptosis of Normal and Activated Eosinophils. Am. J. Respir. Crit. Care Med, 156(5):1628-1632.
6.Hercus TR, Bagley CJ, Cambareri B, Dottore M, Woodcock JM, Vadas MA, Shannon MF, Lopez AF(1994). Specific human granulocyte-macrophage colony-stimulating factor antagonists. PNAS, 91(13):5838-5842.