The CXCR4 agonist peptide, CTCE-0021, rapidly mobilizes polymorphonuclear neutrophils and hematopoietic progenitor cells into peripheral blood and synergizes with granulocyte colony-stimulating factor

Objective. Mobilization of hematopoietic stem and progenitor cells (HSPC) by stromal cell-derived factor-1 (SDF-1) has been described; however, sustained adenoviral delivery or N-terminal modification was required for effect and could not be demonstrated with native protein. The aim of this study was to further investigate the SDF-1 alpha/CXCR4 axis in HSPC mobilization using CTCE-0021, a cyclized CXCR4 agonist peptide, with comparable bioactivity and improved stability relative to SDF-1 alpha. Methods. Peripheral blood cells and hematopoietic progenitor cells (HPC) were quantitated in mice administered single or multiple doses of CTCE-0021 or SDF-1 alpha, or mobilized by granulocyte colony-stimulating factor (G-CSF) in combination with CTCE-0021. Proteases, cytokines, and receptors implicated in HSPC mobilization were evaluated to determine mechanism of action. Results. CTCE-0021 dose-dependently elevated blood nentrophils polymorphonuclear neutrophil [PMN] within 5 minutes that peaked after I hour and persisted for 24 hours. PMN mobilization could be maintained by daily dosing. CTCE-0021 mobilized colony-forming unit granulocyte macrophage (CFU-GM), burst-forming unit erythroid (BFU-E), and CFU-granulocyte-erythrocyte-monocyte-megakaryocyte (CFU-GEMM) that peaked within 1 hour after administration, and synergistically enhanced both PMN and HSPC mobilization when combined with G-CSF. Mobilization induced by CTCE-0021 was associated with rapid downregulation of CXCR4 expression on HPC. No appreciable changes in proteases implicated in HPC mobilization were observed. Significantly elevated plasma SDF-1 was detected in mobilized mice, which likely represents CTCE-0021. Conclusion. These studies indicate that CTCE-0021 is an efficient and rapid mobilizer of PMN and HPC when used alone and shows synergistic activity when used in combination with G-CSF. The mobilizing effect of this peptide appears to be mediated by downregulation of the CXCR4 receptor on HPC and altered chemokine gradient. (c) 2005 International Society for Experimental Hematology. Published by Elsevier Inc.