title: Prolonged circulation of recombinant human granulocyte-colony stimulating factor by covalent linkage to albumin through a heterobifunctional polyethylene glycol.
abstract: 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.
authors.affiliation: Department of Pharmaceutics and Drug Delivery, Amgen Inc., Thousand Oaks, California 91320, USA.
authors.forename: A G
authors.initials: AG
authors.lastname: Paige
authors.forename: K L
authors.initials: KL
authors.lastname: Whitcomb
authors.forename: J
authors.initials: J
authors.lastname: Liu
authors.forename: O
authors.initials: O
authors.lastname: Kinstler
mesh_terms: 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
chemical_list: D000418:Albumins; D011994:Recombinant Proteins; D016179:Granulocyte Colony-Stimulating Factor; D011092:Polyethylene Glycols