Receptor-mediated clearance of G-CSF derivative nartograstim in bone marrow of rats

Pharmacokinetic and pharmacodynamic modelling of the novel human granulocyte colony-stimulating factor derivative Maxy-G34 and pegfilgrastim in rats

OBJECTIVES

This study aims to compare pharmacokinetics and pharmacodynamics of pegfilgrastim, a pharmaceutical recombinant human granulocyte colony-stimulating factor (rhG-CSF), with that of a newly developed reagent, Maxy-G34. This comparison was performed using rat experiments and biomathematical modelling of granulopoiesis.

METHODS

Healthy rats and those with cyclophosphamide-induced neutropenia were treated with either pegfilgrastim or Maxy-G34 under various schedules. Time courses of absolute neutrophil count (ANC) and G-CSF serum level were measured and we constructed a combined pharmacokinetic/pharmacodynamic model of both drugs. Neutropenic episodes were assessed by experimental data and model simulations.

RESULTS

Both Pegfilgrastim and Maxy-G34 showed strong dose-dependent efficacy in reducing neutropenic episodes. However, time courses of ANC and G-CSF serum levels were markedly different. The biomathematical model showed good agreement with these data. We estimated that differences between the two drugs could be explained by lower bioavailability and reduced elimination of Maxy-G34. Based on the data and model interpolations, we estimated that Maxy-G34 is superior in reducing neutropenic episodes. Also, we predicted that G-CSF administration 48 h after cyclophosphamide would be superior to its administration after 2 or 24 h, for both derivatives.

CONCLUSION

Maxy-G34 is a highly potent drug for stimulation of neutrophil production in rats. By our modelling approach, we quantified differences between Maxy-G34 and pegfilgrastim, related to pharmacokinetic parameters. Model simulations can be used to estimate optimal dosing and timing options in the present preclinical rat model.

Increasing systemic exposure of methotrexate by active efflux mediated by multidrug resistance-associated protein 3 (mrp3/abcc3)

The aim of this study was to investigate the functional importance of multidrug resistance-associated protein (Mrp)3/Abcc3 and Mrp4/Abcc4 in the pharmacokinetics of methotrexate. Compared with the corresponding wild-type mice, the plasma concentrations of methotrexate given orally were similar in Abcc4(-/-) mice and were significantly lower in Abcc3(-/-) mice. Pharmacokinetic parameters related to hepatobiliary transport were determined under steady-state conditions in wild-type and Abcc3(-/-) mice that were given a constant intravenous infusion of methotrexate. The biliary clearance, based on the plasma concentration, was 1.6-fold greater in Abcc3(-/-) mice than in wild-type mice (23 and 15 ml/min/kg, respectively, P < 0.05). Because the basolateral uptake and canalicular efflux clearances of methotrexate were similar in wild-type and Abcc3(-/-) mice, this result suggests that the basolateral efflux clearance of methotrexate is decreased in the liver of Abcc3(-/-) mice. Furthermore, a lower fraction of absorption of methotrexate (F(a) F(g)) was suggested in Abcc3(-/-) mice (0.49 and 0.29 in wild-type and Abcc3(-/-) mice, respectively). The mucosal-to-serosal transport rate of methotrexate, determined in vitro using everted sacs, was highest in the duodenum and was significantly decreased in Abcc3(-/-) mice compared with wild-type mice. This is ascribed to the reduced intrinsic efflux clearance of methotrexate across the serosal membrane (22 and 5.3 mul/min/sac in wild-type and Abcc3(-/-) mice, respectively, P < 0.05). These results suggest that Mrp3 mediates basolateral efflux of methotrexate in the liver and duodenum, thereby serving to increase systemic exposure, whereas Mrp4 is likely to play only a limited role in the systemic methotrexate exposure.

GlycoPEGylation of recombinant therapeutic proteins produced in Escherichia coli

Covalent attachment of polyethylene glycol, PEGylation, has been shown to prolong the half-life and enhance the pharmacodynamics of therapeutic proteins. Current methods for PEGylation, which rely on chemical conjugation through reactive groups on amino acids, often generate isoforms in which PEG is attached at sites that interfere with bioactivity. Here, we present a novel strategy for site-directed PEGylation using glycosyltransferases to attach PEG to O-glycans. The process involves enzymatic GalNAc glycosylation at specific serine and threonine residues in proteins expressed without glycosylation in Escherichia coli, followed by enzymatic transfer of sialic acid conjugated with PEG to the introduced GalNAc residues. The strategy was applied to three therapeutic polypeptides, granulocyte colony stimulating factor (G-CSF), interferon-alpha2b (IFN-alpha2b), and granulocyte/macrophage colony stimulating factor (GM-CSF), which are currently in clinical use.

Kinetic analysis of the disposition of insulin-like growth factor 1 in healthy volunteers

PURPOSE

Insulin-like growth factor 1 (IGF-1) is predominantly bound to its specific binding proteins (IGFBPs) in circulating plasma. In the present study, pharmacokinetic analysis of IGF-1 was performed in healthy volunteers to characterize the effect of interactions with IGFBPs on IGF-1 disposition.

METHODS

Plasma concentration profiles of both free and bound IGF-1 were examined at several doses. An in vitro plasma protein binding was also analyzed.

RESULTS

The total body clearance (CLtotal) for the free IGF-1 was much higher than the creatinine clearance, suggesting that the major elimination pathway is by a route other than renal glomerular filtration. The CLtotal for the free IGF-1 exhibited a dose-dependent reduction whereas that for the sum of unbound and bound IGF-1 increased on increasing the dose. The data obtained fitted closely a one-compartment model that involved the binding and dissociation of IGF-1, as well as its biosynthesis and elimination. The estimated parameters suggest that IGF-1 exhibits high affinity binding to IGFBPs. the rate-limiting step in the overall elimination being the dissociation from IGFBPs.

CONCLUSIONS

The saturation of both the plasma protein binding and elimination accounts for the nonlinear pharmacokinetic profile. The binding to IGFBPs markedly limits both the distribution and elimination of IGF-1.

Renal clearance of a recombinant granulocyte colony-stimulating factor, nartograstim, in rats

PURPOSE

To clarify the role of the kidney in the elimination of a recombinant human granulocyte colony-stimulating factor, nartograstim, we have investigated its pharmacokinetics in rats with renal failure.

METHODS

The steady-state clearance (CLss) were determined by the intravenous infusion for 4 hr to unilateral renally-ligated and cisplatin-treated rats, whose renal functions were about 50 and 10% of controls, respectively.

RESULTS

CLss of nartograstim (27 ml/hr/kg) in the renally-ligated rats at a high infusion rate was significantly lower (25%) than in control rats (p < 0.05). CLss in these rats, at a low infusion rate was 95 ml/hr/kg, 14% lower than in control rats. The saturable CLss in these rats, 68 ml/hr/kg, was not significantly different from control rats (75 ml/hr/kg, p > 0.05). Also, CLss in cisplatin-treated rats with extensive renal failure, at a high infusion rate, decreased to 57% of controls. Furthermore, the total body clearances (CLtot) of nartograstim after bolus intravenous administration to renally-ligated and cisplatin-treated rats were reduced to 33-49% of controls.

CONCLUSIONS

These results suggest that the kidney may be responsible for 40-50% of the nonsaturable clearance of nartograstim. Thus, the kidney should make a major contribution to the elimination of nartograstim when rats are given a high dose of nartograstim, which saturates the receptor-mediated clearance.