Abstract 353: Pharmacokinetic studies on a novel recombinant human granulocyte colony stimulating factor in rats

Abstract

Abstract Background: Recombinant human granulocyte colony stimulating factor (G-CSF) has been used as a therapeutic drug for leukopenia of cancer patients who receive myelo-suppressive radio- or chemotherapy. Due to its intrinsic instability, G-CSF has to be administered to patients frequently to maintain high plasma concentrations for therapeutic effects. We report here that a recombinant G-CSF derivative (rhG-CSFa), which was previously found to exhibit a greater biological activity than wild-type G-CSF does, displays enhanced stability in vitro, and superior bioavailability in vivo. Methods: The pharmacokinetics of rhG-CSFa and G-CSF was investigated in rats; various groups of the rats received either intravenous (i.v.) or subcutaneous (s.c.) injection of rhG-CSFa, at one of three different doses (20, 50 or 100 µg/kg). The serum samples were collected at multiple time points after the drug administration (from 0.08 to 12 h). The concentrations of rhG-CSFa and wild-type G-CSF in various serum samples were determined by a sandwich ELISA. Pharmacokinetic parameters were analyzed by fitting the serum drug concentration-time data to a one- or two-compartment model, with use of the Winnonlin 5.2 software. For proteolytic studies in vitro, the concentrations of rhG-CSFa or G-CSF were determined at 3-min intervals after addition of the respective drug to rat serum or plasma. Results: Pharmacokinetic analysis of serum rhG-CSFa or G-CSF levels indicated that, at each dose tested, for either routes of drug administration, the area under concentration-time curve (AUC) values were higher for rhG-CSFa than for G-CSF. For example, at the dose of 20 µg/kg, s.c., the AUC value was 850 ± 80 ng*hr/ml for rhG-CSFa and 430 ± 50 for ng*hr/ml for G-CSF (n=5). At the dose of 20 µg/kg, i.v., the AUC value was 1150 ± 480 ng*hr/ml for rhG-CSFa and 810 ± 150 for ng*hr/ml for G-CSF (n=5). Differences in other pharmacokinetics parameters, including serum half-life (t1/2) and maximum serum concentration (Cmax), were also observed, further indicating greater serum bioavailability of the rhG-CSFa, as compared to G-CSF. Results from subsequent in vitro serum and plasma stability studies showed that the rates of drug disappearance were slower for rhG-CSFa than for G-CSF, when the respective drug was added to either serum (by 1.5 fold) or plasma (by 1.8 fold). This finding suggested that the rates of proteolysis of the rhG-CSFa were much slower, as compared to the rates of proteolysis of the wild-type G-CSF, either in serum or in plasma. Conclusions: The novel rhG-CSFa has a much better serum and plasma stability in vitro and a much higher bioavailability in vivo, as compared to the conventional G-CSF. The increased stability and bioavailability of the rhG-CSF may explain, at least partly, the greater therapeutic efficacy of rhG-CSFa than that of G-CSF in rats, and suggests that rhG-CSFa will also have enhanced therapeutic efficacy in human patients. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 353.