Amino-terminal dimerization of an erythropoietin mimetic peptide results in increased erythropoietic activity.
BACKGROUND
Erythropoietin (EPO), the hormone involved in red blood cell production, activates its receptor by binding to the receptor's extracellular domain and presumably dimerizing two receptor monomers to initiate signal transduction. EPO-mimetic peptides, such as EMP1, also bind and activate the receptor by dimerization. These mimetic peptides are not as potent as EPO, however. The crystal structure of the EPO receptor (EBP) bound to EMP1 reveals the formation of a complex consisting of two peptides bound to two receptors, so we sought to improve the biological activity of EPO-mimetic peptides by constructing covalent dimers of EMP1 and other peptide mimetics linked by polyethylene glycol (PEG).


RESULTS
The potency of the PEG-dimerized EPO peptide mimetics both in vitro and in vivo was improved up to 1,000-fold compared to the corresponding peptide monomers. The dimers were constructed using peptide monomers which have only one reactive amine per molecule, allowing us to conclude that the increase in potency can be attributed to a structure in which two peptides are linked through their respective amino termini to the difunctional PEG molecule. In addition, an inactive peptide was converted into a weak agonist by PEG-induced dimerization.


CONCLUSIONS
The potency of previously isolated peptides that are modest agonists of the EPO receptor was dramatically increased by PEG-induced dimerization. The EPO receptor is thought to be dimerized during activation, so our results are consistent with the proposed 2:2 receptor : peptide stoichiometry. The conversion of an inactive peptide into an agonist further supports the idea that dimerization can mediate receptor activation.
Johnson
D L
DL
Drug Discovery Research, R.W. Johnson Pharmaceutical Research Institute, Route 202, Box 300, Raritan, NJ 08869, USA. djohnson@prius.jnj. com
Farrell
F X
FX
Barbone
F P
FP
McMahon
F J
FJ
Tullai
J
J
Kroon
D
D
Freedy
J
J
Zivin
R A
RA
Mulcahy
L S
LS
Jolliffe
L K
LK
D000818:Animals; D001667:Binding, Competitive / Q000187:drug effects; D002455:Cell Division / Q000502:physiology; D002851:Chromatography, High Pressure Liquid; D003432:Cross-Linking Reagents; D004910:Erythrocyte Membrane / Q000378:metabolism; D004912:Erythrocytes / Q000378:metabolism*; D004920:Erythropoiesis / Q000502:physiology*; D004921:Erythropoietin / Q000302:isolation & purification / Q000378:metabolism*; D005110:Extracellular Space / Q000378:metabolism; D006801:Humans; D066298:In Vitro Techniques; D007504:Iron Radioisotopes; D013058:Mass Spectrometry; D051379:Mice; D008970:Molecular Weight; D011086:Polycythemia / Q000097:blood; D011092:Polyethylene Glycols / Q000378:metabolism; D017467:Receptors, Erythropoietin / Q000819:agonists / Q000096:biosynthesis; D011994:Recombinant Proteins
D003432:Cross-Linking Reagents; D007504:Iron Radioisotopes; D017467:Receptors, Erythropoietin; D011994:Recombinant Proteins; D004921:Erythropoietin; D011092:Polyethylene Glycols