Prolonged circulation of recombinant human granulocyte-colony stimulating factor by covalent linkage to albumin through a heterobifunctional polyethylene glycol.
OBJECTIVE
Recombinant human granulocyte-colony stimulating factor (rhG-CSF) was covalently conjugated to both rat and human serum albumin (RSA and HSA respectively) to increases the circulating half life (t1/2) of rhG-CSF.


METHODS
Conjugates of RSA (MW 67,000) and HSA (MW 66,000) were prepared by linking the two proteins through a heterobifunctional maleimido-carboxyl polyethylene glycol (PEG) and were tested in the rat. The conjugates were injected intravenously (IV) at the equivalent dose of 50 micrograms/kg of rhG-CSF, and white blood cell (WBC) counts and plasma concentrations of drug were determined. A comparison of pharmacokinetic parameters was made between rhG-CSF, the conjugates RSA-PEG-rhG-CSF and HSA-PEG-rhG-CSF, and a non-covalent mixture of rhG-CSF and HSA.


RESULTS
The albumin-rhG-CSF conjugates are eliminated more slowly from the circulation. The clearance values are reduced from 0.839 +/- 0.121 ml/min/kg for rhG-CSF to 0.172 +/- 0.013 ml/min/kg for RSA-PEG-rhG-CSF and 0.141 +/- 0.005 ml/min/kg for HSA-PEG-rhG-CSF. WBC counts increased in both absolute number and duration as compared to rhG-CSF alone. The albumin rhG-CSF conjugates had enhanced serum stability relative to free rhG-CSF. The rate of degradation of the albumin conjugates incubated in rat serum at 37 degrees C decreased five fold.


CONCLUSIONS
The results from the study show that specific conjugation of rhG-CSF to albumin decreases plasma clearance in vivo, causes increased WBC response, and increases serum stability as compared to free rhG-CSF.
Paige
A G
AG
Department of Pharmaceutics and Drug Delivery, Amgen Inc., Thousand Oaks, California 91320, USA.
Whitcomb
K L
KL
Liu
J
J
Kinstler
O
O
D000418:Albumins / Q000378:metabolism*; D000818:Animals; D016179:Granulocyte Colony-Stimulating Factor / Q000493:pharmacokinetics*; D008297:Male; D011092:Polyethylene Glycols / Q000378:metabolism*; D051381:Rats; D017207:Rats, Sprague-Dawley; D011994:Recombinant Proteins / Q000493:pharmacokinetics; D013997:Time Factors
D000418:Albumins; D011994:Recombinant Proteins; D016179:Granulocyte Colony-Stimulating Factor; D011092:Polyethylene Glycols