Two distinct CXCR4 antagonists mobilize progenitor cells in mice by different mechanisms

Abstract

Pharmacological mobilization of hematopoietic progenitor cells (HPCs) is used clinically to harvest HPCs for bone marrow transplants. It is now widely accepted that the CXCR4:CXCL12 chemokine axis plays a critical role in the retention of HPCs in the bone marrow, and CXCR4 antagonists have been developed for their mobilization. The first of this class of drugs to be US Food and Drug Administration-approved was the bicyclam AMD3100. In addition to mobilizing HPCs and leukocytes in naïve mice, AMD3100 has been shown to mobilize mesenchymal progenitor cells (MPCs) in vascular endothelial growth factor (VEGF-A) pretreated mice. AMD3100 binds to the transmembrane region of CXCR4 and is thought to mobilize HPCs by reversing the gradient of CXCL12 across the bone marrow endothelium. Consistent with this hypothesis, our data show that selective neutralization of CXCL12, with chalcone 4-phosphate (C4P), inhibited AMD3100-stimulated mobilization of HPCs and leukocytes in naïve mice and MPCs in VEGF-A pretreated mice. In contrast it is shown here that the CXCR4 antagonist KRH3955 that binds to the extracellular loop of CXCR4 does not reverse the CXCL12 chemokine gradient. However, this drug efficiently mobilizes HPCs, a response that is not inhibited by C4P. In contrast, KRH3955 does not mobilize MPCs in VEGF-A pretreated mice. These data suggest that CXCR4 antagonists that bind to distinct regions of the receptor mobilize progenitor cells by distinct molecular mechanisms

CXCR4, the master regulator of neutrophil trafficking in homeostasis and disease

“…Our studies revealed that chalcone 4-phosphate, when administered alone, had no effect on circulating numbers of murine neutrophils; however, it significantly suppressed the mobilisation of neutrophils by AMD3100. 23 This is consistent with a model whereby the AMD3100-induced rise in circulating CXCL12 is critical for neutrophil mobilisation (Figure 3). In contrast, KRH3955, a distinct CXCR4 antagonist, does not reverse the CXCL12 gradient across the BME, but still efficiently mobilises neutrophils from the bone marrow, implying that KRH3955 disrupting the CXR4/CXCL12 retention axis directly is sufficient for mobilisation under homeostasis ( Figure 3).…”

“…To test this hypothesis, we made use of chalcone 4‐phosphate, a CXCL12‐neutralising ligand. Our studies revealed that chalcone 4‐phosphate, when administered alone, had no effect on circulating numbers of murine neutrophils; however, it significantly suppressed the mobilisation of neutrophils by AMD3100 . This is consistent with a model whereby the AMD3100‐induced rise in circulating CXCL12 is critical for neutrophil mobilisation (Figure ).…”

“…This is consistent with a model whereby the AMD3100‐induced rise in circulating CXCL12 is critical for neutrophil mobilisation (Figure ). In contrast, KRH3955, a distinct CXCR4 antagonist, does not reverse the CXCL12 gradient across the BME, but still efficiently mobilises neutrophils from the bone marrow, implying that KRH3955 disrupting the CXR4/CXCL12 retention axis directly is sufficient for mobilisation under homeostasis (Figure ) . To understand why these 2 CXCR4 antagonists have different physiological mechanisms of action, we need to consider how they interact with CXCR4 at the molecular level.…”

“…In contrast, KRH3955, a distinct CXCR4 antagonist, does not reverse the CXCL12 gradient across the BME, but still efficiently mobilises neutrophils from the bone marrow, implying that KRH3955 disrupting the CXR4/CXCL12 retention axis directly is sufficient for mobilisation under homeostasis ( Figure 3). 23 To understand why these 2 CXCR4 antagonists have different physiological mechanisms of action, we need to consider how they interact with CXCR4 at the molecular level. CXCL12 normally binds to CXCR4 in a stepwise manner, with the b-sheet and 50-s loop of CXCL12 first interacting with the extracellular region of CXCR4 and secondly the N-terminal domain of CXCL12 interacting with the transmembrane region of CXCR4.…”

Ubiquitous overexpression of CXCL12 confers radiation protection and enhances mobilization of hematopoietic stem and progenitor cells

“…Previous reports showed that the CXCR4-CXCL12 interaction is a key factor in the retention of the HSPCs in the BM. Loss of CXCL12 in the BM or inhibition of the CXCR4-CXCL12 interaction using AMD3100 led to both significantly reduced retention of HSPCs in the BM and facilitated their egress to the blood (Bonig et al, 2009;Dar et al, 2011;Redpath et al, 2017;Rosenkilde et al, 2004;Winkler et al, 2012). In our model where CXCL12 is broadly overexpressed, including in the blood (Figure 1Bii), BM specific CXCR4-CXCL12 interaction is perturbed, likely leading to the increased mobilization ( Figures 5B, and S4C).…”