Recombinant granulocyte colony-stimulating factor-transferrin fusion protein as an oral myelopoietic agent.

An expression construct harboring granulocyte colony-stimulating factor (G-CSF)-transferrin (Tf) fusion protein (G-CSF-Tf) was engineered by fusing human cDNAs encoding G-CSF and Tf to explore the feasibility of using Tf as a carrier moiety for oral delivery of therapeutic proteins. The recombinant protein, G-CSF-Tf, was harvested from protein-free, conditioned medium of transfected HEK293 cells. The in vitro studies demonstrated that the purified G-CSF-Tf fusion protein possesses the activity of both Tf receptor (TfR) binding in Caco-2 cells and G-CSF-dependent stimulation of NFS-60 cell proliferation. Subcutaneous administration of G-CSF-Tf fusion protein to BDF1 mice demonstrated a pharmacological effect comparable to the commercial G-CSF on the increase of absolute neutrophil counts (ANC). However, the fusion protein elicited a significant increase in ANC upon oral administration to BDF1 mice, whereas G-CSF had no effect. This study also showed that orally administered G-CSF-Tf elicits a sustained myelopoietic effect up to 3 days, whereas the s.c. administered G-CSF or G-CSF-Tf lasts only 1 day. Furthermore, coadministration of free Tf abolished the increase of ANC by orally delivered G-CSF-Tf, suggesting that the recombinant protein is absorbed via a TfR-mediated process in the gastrointestinal tract. Taken together, we conclude that the Tf-based recombinant fusion protein technology represents a promising approach for future development of orally effective peptide and protein drugs.