APB-F1, a long-acting feline granulocyte colony-stimulating factor fusion protein, created by exploiting FL335, a chimeric Fab specific for feline serum albumin

• Published in: Veterinary immunology and immunopathology Vol. 240; p. 110322
• Main Authors: Chi, Hyun-jin, Park, Mihyun, Han, Jae-kyu, Kim, Sun-mi, Kang, SeungGoo, Yang, Jin-hyuk, Cha, Sang-hoon
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01.10.2021
• Subjects: Animals; Antibodies; Antigen-binding fragment (fab); Cat; Cat Diseases - therapy; Cats; CHO Cells; Cricetinae; Cricetulus; Dogs; Granulocyte Colony-Stimulating Factor - pharmacology; Granulocyte-colony stimulating factor (G-CSF); Immunoglobulin Fab Fragments - pharmacology; Neutropenia; Neutropenia - therapy; Pegfilgrastim; Recombinant Proteins - pharmacology; Serum albumin; Serum Albumin - immunology; Granulocyte-colony stimulating factor (G-CSF); Pegfilgrastim; Serum albumin; Antigen-binding fragment (fab); Cat; Neutropenia
• ISSN: 0165-2427; 1873-2534
• DOI: 10.1016/j.vetimm.2021.110322

•FL335 is a human/cat chimeric Fab antibody specific for feline serum albumin (FSA).•APB-F1 is a recombinant fusion protein composed of FL335 + flexible peptide linker + feline G-CSF (fG-CSF).•APB-F1 is a bifunctional molecule possessing high affinity binding to FSA as well as intact fG-CSF bioactivity.•APB-F1 has an extended serum half-life and exhibits superb G-CSF bioactivity in cats.•Anti-serum albumin Fab-associated (SAFA) technology is applicable in creating valuable biologics for veterinary medicine. Off-label use of a human granulocyte colony stimulating factor (hG-CSF) has been allowed to treat dogs and cats with neutropenia. However, repeated administration of hG-CSF induces undesirable anti-drug antibody (ADA) responses, implying the necessity of animal-derived G-CSF as a therapeutic reagent, preferably with a long-acting capability. Herein, we generated a recombinant fusion protein by genetically combining FL335, a chimeric Fab specific for feline serum albumin (FSA), and feline G-CSF (fG-CSF), with the ultimate goal of developing a long-acting therapeutic fG-CSF for cats. The resulting FL335-fG-CSF fusion protein, referred to as APB-F1, was produced well as a functional form in a Chinese hamster ovary (CHO) expression system. In in vitro analyses, APB-F1 bound to FSA at high affinity (KD = 400 pM) and possessed 0.78 × 107 U/mg G-CSF biological activity, clearly proving its biological functionality. Pharmacokinetic (PK) and pharmacodynamic (PD) studies using healthy cats revealed that the serum half-life (t1/2) of APB-F1 was increased five times compared with that of fG-CSF (t1/2 = 13.3 h vs. 2.7 h) in subcutaneous (SC) injections. Additionally, APB-F1 induced a profound and sustained increase in white blood cell (WBC) and actual neutrophil count (ANC) up to 10 days, which was far superior to other G-CSF preparations, including filgrastim (Neupogen™) and even pegfilgrastim (Neulasta™). Conclusively, a long-acting fG-CSF with potent in vivo bioactivity was successfully created by using FL335; thus, we provided evidence that our “anti-serum albumin Fab-associated” (SAFA) technology can be applied reliably in developing valuable long-acting biologics in veterinary medicine.