Filgrastim(granulocytecolony)

Properties

Mr. of human G-CSF is 18,671 (calculated polypeptide backbone) and 18–19 kDa on SDS-PAGE (O-glycosylated form secreted from tumor cell lines). The pI varies from 5 to 6 depending on O-glycosylation. The nonglycosylated form produced by E. coli retains biological activity.

Synthesis and release

The expression of the G-CSF gene is regulated by pathogen-mediated transcriptional and posttranscriptional pathways. Inflammatory factors such as bacterial lipopolysaccharide, interleukin-1β, tumor necrosis factor α, IL-1, and IL-17 from Th17 cells induce G-CSF expression via intracellular signaling though NF-κB, C/EBPα, and C/EBPβ. The increase in the number of circulating neutrophils reduces the production of G-CSF in the bone marrow.

Agonists and Antagonists

Filgrastim produced by E. coli attached an additional N-terminal methionine, and lenograstim produced by CHO cells attached a single O-glycan; these were developed as therapeutic biologicals. Other molecules, including pegylated filgrastim, follow as next-generation therapeutic reagents. The fusion proteins of G-CSF with IgG1-Fc and IgG4-Fc are reported. 
An antagonistic compound specific to G-CSF-G-CSFR signaling has not been reported yet.

Biological functions

G-CSF stimulates the proliferation, differentiation, and survival of neutrophil precursors in the bone marrow to promote their maturation process. G-CSF exerts minimal direct effects on the production of hematopoietic cell types other than the neutrophil lineage, as obtained in white blood cell differentials during clinical trials. The G-CSF-G-CSFR signaling in mature neutrophils activates multiple effector functions in response to bacterial infections, such as superoxide anion generation, the release of arachidonic acid, and the production of leukocyte alkaline phosphatase and myeloperoxidase. Neurons of the CNS express both G-CSF and G-CSF-R, suggesting an autocrine neuroprotection system, as a nonhematopoietic function

Description

Granulocyte colony-stimulating factor is the primary regulator of proliferation and differentiation, maturation, survival, and functions of neutrophils/ granulocytes to exert biological defense mechanisms via neutrophil progenitors in the bone marrow. The bone marrow colony-forming activity of maturing granulocytes was recognized in various cell and tissue cultures. Murine G-CSF was first purified from a lungconditioned medium from mice injected with bacterial endotoxin. The human G-CSF was purified from the conditioned media of tumor cell lines, and the cDNA was independently cloned in 1986 by two groups.

Clinical Use

Recombinant G-CSF therapies by filgrastim and lenograstim have been established in several indications. Primarily, G-CSF is administered to patients with severe congenital or chronic neutropenia caused by a myeloid maturation arrest in the bone marrow. G-CSF is also applicable to therapy-induced neutropenia developed in cancer patients receiving myelosuppressive chemotherapy and bone marrow transplant and in patients with acute myeloid leukemia receiving induction or consolidation chemotherapy. In addition, G-CSF induces the release of hematopoietic stem and progenitor cells from the bone marrow into the peripheral blood. Therefore, G-CSF is used in transplantation therapy for the mobilization and isolation of peripheral hematopoietic stem cells. The stem cell mobilization by G-CSF is supported by multiple mechanisms, including proteolytic enzyme release, the modulation of adhesion molecules, and the activation of CXCR4 chemokine receptors. Recently, the nonhemopoietic role of G-CSF has been evaluated in clinical trials including spinal cord injury by the ability of G-CSF for neuroprotective and neuroregenerative actions.

Structure and conformation

The human G-CSF and its receptor (G-CSFR) form a 2:2 complex with a crossover interaction between the Ig-like domains of the G-CSFR and GCSF. The predominant form of mature human G-CSF consists of 174 aa reduces, internally two disulfide bridges (C36dC42 and C64dC74), and one O-glycan at T133. In the splicing variant, consisting of 177 aa residues with the insertion of V-S-E between L35 and C36, the biological activity decreases 10-fold due to the modification of the ligand-receptor conformation. The reason for the difference in the biological roles of the two forms has not yet been elucidated.