Pharmacological effects of recombinant human granulocyte colony-stimulating factor modified by polyethylene glycol on anticancer drug-induced neutropenia in mice

Hepatic killing but not clearance of systemically circulating bacteria is dependent upon peripheral leukocytes via Mac-1 (CD11b/CD18)

The hepatic reticuloendothelial system (RES) is the primary mechanism for removing circulating bacteria from the systemic circulation. While Kupffer cells are important for this process, leukocytes appear to play a significant role as well. Hepatic leukocyte accumulation following ischemia/reperfusion or cytokine stimulation is well documented, but its contribution to phagocytic killing by the hepatic RES is not fully understood. We evaluated the role of leukocytes in general, and leukocyte-endothelial adhesion in particular, in hepatic RES function. This was done by inducing confirmed leukopenia with cyclophosphamide or by blocking leukocyte-endothelial adhesion molecules with specific blocking antibodies. Hepatic phagocytic clearance (HPC) and hepatic phagocytic killing (HKE) of systemically intravenously injected E. coli were assayed and quantitated by a validated dual isotope label technique. HPC among the various experimental groups and respective controls varied only slightly, with no statistically significant differences observed. Leukopenia or CD11b blockade each significantly decreased the HKE relative to the controls. Antibody blockade of certain other adhesion molecules had no significant effect on HKE (or HPC). The role of leukocytes in killing systemically circulating bacteria is an integral component of hepatic RES function. This capability of the leukocyte appears to be dependent, in part, on the adhesion molecule, Mac-1.

Pharmacokinetic analysis of pegylated megakaryocyte growth and development factor in humans

Phase I studies with pegylated megakaryocyte growth and development factor (PEG-rHuMGDF), a c-Mpl ligand that stimulates megakaryopoiesis, have demonstrated that PEG-rHuMGDF is biologically active alone and causes a dose-related enhancement of platelet recovery when administered after chemotherapy. Here we report the dose-ranging pharmacokinetics of PEG-rHuMGDF. Pre-injection blood samples were drawn daily for pharmacokinetic studies on 43 patients. An ELISA, established using PEG-rHuMGDF as the standard, was able to quantitate Mpl ligand at concentrations > 0.02 ng/mL. Over the dose range 0.03 to 5.0 microg/kg/day, subcutaneous administration produced linear increases in steady-state serum levels. Maximum levels of PEG-rHuMGDF attained after 5.0 microg/kg/day were 5.88 to 10.9 ng/mL. After discontinuation of PEG-rHuMGDF, concentrations of Mpl ligand returned to baseline within 5 days. The pharmacokinetics were best described by a one-compartment model with first-order absorption, an absorption delay, and non linear clearance over the first 48 hours. The mean terminal half-life was 33.3 + 16.7 hours, and the average apparent at steady state was 27.7 + 14.0 mL/h/kg; both were independent of administered dose. The apparent clearance of PEG-rHuMGDF was not predicted by platelet count. Administration of chemotherapy and Filgrastim did not alter the pharmacokinetics of PEG-rHuMGDF.

In vivo effects of pegylated recombinant human megakaryocyte growth and development factor on hematopoiesis in normal mice

The in vivo effects of pegylated recombinant human megakaryocyte growth and development factor (PEG-rHuMGDF), a truncated molecule of recombinant human thrombopoietin modified with polyethylene glycol, were investigated in normal Balb/c mice. PEG-rHuMGDF was more potent in producing platelets and the dose-response curve was steeper compared with the case of the nonpegylated form of this molecule. Five consecutive injections with PEG-rHuMGDF caused a dose-dependent increase in peripheral platelet counts with a peak on day 8. There was a dose-dependent rise in platelet counts on day 8 at daily doses from 0.333 to 30 micrograms/kg. Intermediate doses of PEG-rHuMGDF (1.111 to 10 micrograms/kg/day) caused a significant decrease in mean platelet volume, and conversely, higher doses of PEG-rHuMGDF (30 to 270 micrograms/kg/day) induced a dose-dependent increase in mean platelet volume. There was a dose-dependent decrease in hemoglobin concentration with a minimum on day 8 but no significant reduction in reticulocyte counts following PEG-rHuMGDF administration. White blood cell counts were unchanged by PEG-rHuMGDF treatment. Marrow megakaryocyte size enlarged to 1.5-fold and the number of marrow megakaryocytes increased to sixfold by consecutive administration of PEG-rHuMGDF at 30 micrograms/kg/day. A twofold increase in the number of marrow megakaryocytic progenitor cells (colony-forming units-megakaryocyte) was also observed. Marrow erythroid progenitor (colony-forming units-erythroid) counts decreased but splenic colony-forming units-erythroid, marrow and splenic erythro/myeloid progenitor cell counts, and splenic granulocyte/macrophage progenitor cell counts increased with PEG-rHuMGDF treatment. Marrow and splenic erythroid burst-forming cells were unchanged. These results indicate that PEG-rHuMGDF, a truncated molecule of thrombopoietin, is a potent stimulator for megakaryopoiesis and thrombopoiesis, and also affects the development of other hematopoietic cells in normal mice.