Фармакологическая модуляция CXCL12/CXCR4/ACKR3 для нейродисфункций — обзор.

Background

G protein-coupled receptors (GPCRs) represent the largest class of cell membrane receptors in human, counting over 800 gene members. Their location at the plasma membrane allows the transduction of extracellular signals and their transformation into physiological outputs. Main endogenous ligands include hormones, odors, neurotransmitters, or chemokines. Coupling between ligands and GPCRs is crucial for physiological processes related to sensory, neurological and immune functions. Consequently, defective or abnormal GPCR signaling is observed in various pathological conditions, such as cardiac deficits, type 2 diabetes, obesity, depression, Alzheimer’s disease (AD) chronic inflammation and cancer [ 1 ]. These receptors therefore constitute attractive targets for drug development and GPCR-targeting compounds represent over a third of all current FDA-approved drugs [ 2 ]. Moreover, central nervous system (CNS) diseases are the most prominent disorders implicating GPCR pharmacological targeting [ 3 ].

Among the large GPCR family, chemokines and their receptor(s) form a complex network that orchestrates immune responses by guiding the migration of immune cells to inflammation sites. Chemokine receptors are part of the Rhodopsin-like (or class A) family of GPCRs [ 1 ], and are mostly activated by chemokines. Chemokines are small secreted peptides (8–10 kDa) that belong the functional superfamily of cytokines. Upon binding to their receptor(s), they induce an oriented cell migration process called chemotaxis, which is essential to embryogenesis, adult tissue homeostasis and wound healing [ 4 ].

Most chemokine receptors are promiscuous, i.e., can bind and respond to more than one ligand. However, their different interactors belong to one chemokine structural group, defined by the position of two cysteine residues (C, CC, CXC or CX3C). Chemokine receptors are consequently coded by their ligand group specificity [ 5 ].

Chemokine receptors can be divided into two major functional groups, based on their downstream cellular effectors: (i) “classical” chemokine receptors, which are G protein-coupled receptors that primarily signal through Gi-type G proteins to induce intracellular cascades and cell migration, and (ii) “atypical” chemokine receptors (ACKRs) that generally do not activate canonical G protein signalling but rather regulate chemokine availability and distribution through high-affinity ligand binding, ligand internalization and trafficking. These mechanisms, often involving β-arrestin-dependant pathways, shape chemokine gradients and thereby modulate leukocyte migration and inflammatory responses [ 5 ].

Besides their well-described role in the immune system, chemokines play an important role in the central nervous system (CNS). In the adult CNS, three chemokine signaling pathway have mostly been studied: CCL2/CCR2, CXCL12/CXCR4/ACKR3 and CX3CL1/CX3CR1. Changes in their expression and function have been associated with various CNS disorders such as Alzheimer’s and Parkinson’s (PD) diseases, HIV-associated encephalopathy, stroke, multiple sclerosis (MS), and also with brain tumor development [ 6 ]. Among these, the CXCL12/CXCR4/ACKR3 triad stands out with its essential role in CNS development.

In this review, we summarize the broad implication of CXCL12/CXCR4/ACKR3 chemokine-receptor axis in the CNS, and we especially focus on recent approaches for modulating CXCL12/CXCR4/ACKR3 in CNS disorders.

CXCL12/CXCR4/ACKR3 signalisation

The CXCL12/CXCR4/ACKR3 signalling axis plays a critical role in various tissues, in both developmental and adult physiopathology (Fig. 1 ). The CXCL12/CXCR4 duo has first been described in tissue organization during embryogenesis, hematopoietic cell trafficking and immune surveillance. Shortly later, this axis was rapidly associated with disease, such as cancer (e.g., various solid tumors and non-Hodgkin lymphoma) or acquired (e.g., AIDS) or innate defects in the immune system (e.g., WHIM syndrome and multiple myeloma) [ 7 ].

ACKR3 and CXCR4 are the two most conserved chemokine receptors among vertebrates, indicating their essential function. Indeed, CXCR4 deletion in mice has lethal consequences related to disrupted development of the immune, circulatory and central nervous system [ 8 – 11 ]. This phenotype is very similar to what was observed in mice lacking CXCL12 (i.e., reduced haematopoiesis and cardiac defects) [ 12 ]. In the same line, mice deficient in ACKR3 exhibit severe abnormalities in cardiovascular and lymphatic systems, also leading to perinatal lethality [ 13 , 14 ]. The three components of this signalling pathway show strong homology between human and mouse, at the level of both gene and protein. Mice models therefore allow an appropriate preclinical investigation for various pathologies [ 15 ].

CXCL12

The chemokine CXCL12, previously known as stromal cell-derived factor-1 (SDF-1) or pre-B cell growth-stimulating factor (PBSF), is probably the most studied member of the chemokine family. Although classified as a homeostatic chemokine, CXCL12 also plays an important role during inflammation, cell proliferation and chemotaxis [ 16 ]. It is the major chemokine produced in the bone marrow, where it regulates the homing, quiescence and differentiation of hematopoietic progenitor cells [ 17 ].

In human, the Cxcl12 gene is located on chromosome 10q11 and initiates the production of seven isoforms resulting from alternative splicing (α, β, γ, δ, ε, θ and the predicted isoform iso7), CXCL12α being the most prevalent and ubiquitously expressed protein [ 18 ]. The splice variants differ by their fourth exon and display tissue-dependent expression and functions [ 7 ]. It is to be noted that the splice variant CXCL12 γ is located in very active, less vascularized organs such as the brain and the heart [ 18 ]. The homologous sequence in Mus musculus genome is located on chromosome 6 and gives rise to only three protein isoforms (α, β, γ).

The mature protein has a typical chemokine fold, characterized by three parallel β-strands, an overlapping C-terminal ⍺-helix and disordered N- and C-terminal ends that play crucial role in receptor activation [ 19 ]. As part of the CXC chemokine subfamily, characterized by the presence of two cysteines separated by one other amino acid at the amino-terminal part, CXCL12 three-dimensional structure is defined by two disulphide bonds, Cys9-Cys34 and Cys11-Cys50, essential for its conformation and binding to CXCR4.

Besides its well established interactions with CXCR4 and ACKR3, CXCL12 has recently been described for binding the atypical chemokine receptors ACKR1 (binding the dimeric form of CXCL12) and the newly described member ACKR5 (formerly known as GPR182) [ 20 ]. CXCL12 binding to those receptors leads to different molecular and biological consequences.

CXCR4

CXCR4, also known as cluster of differentiation 184 (CD184), fusin or leukocyte-derived seven-transmembrane domain receptor (LESTR), was originally discovered for its role as co-factor for human immunodeficiency virus (HIV) cell entry, via gp120 binding, and then identified as receptor for the CXCL12 chemokine [ 21 , 22 ].

CXCR4 is highly expressed in the thymus, particularly in immature double positive CD4+/CD8 + thymocytes [ 9 ]. It is found at the surface of all leukocytes, especially hematopoietic stem cells and progenitors.

In the human genome, Cxcr4 is located on chromosome 2q22. Transcription forms two splice variants, namely CXCR4-A and -B. It is thought that CXCR4-B is the most active isoform, while CXCR4-A is more of a back-up receptor with reduced efficiency. Like its chemokine ligand CXCL12, CXCR4 is an evolutionary conserved protein showing 89% similarity between human and mouse, suggesting the biological importance of the CXCL12/CXCR4 pathway, at least in mammals [ 23 ].

While CXCL12 is the most widely described ligand for CXCR4, the receptor also binds the macrophage migration inhibitory factor MIF, the viral protein vCCL2, β-defensins 2/3 and the extracellular ubiquitin (eUb) [ 9 , 24 – 26 ]. CXCR4 also oligomerizes with other chemokine and non-chemokine receptors, such as CCR5 and ACKR3, the cannabinoid receptor 2 (CB2), or the delta opioid receptor, inducing distinct functional consequences [ 27 , 28 ].

ACKR3

ACKR3 was initially described as the orphan G-protein coupled receptor RDC1 (Receptor-Deficient Chemokine 1) [ 29 ]. Several years later, the RDC1 was renamed as CXCR7 after uncovering the binding of two CXC-chemokine ligands, i.e., CXCL12 and CXCL11 [ 30 – 32 ]. Genomic proximity between Ackr3 and Cxcr4 genes (position 2q22 and 2q37, respectively) as well as their sequence similarity facilitated the deorphanization of the receptor. In 2014, CXCR7 was assigned to the family of atypical chemokine receptors, and finally renamed as ACKR3 [ 5 ].

ACKR3 shares its chemokine ligands CXCL12 and CXCL11 with the chemokine receptors CXCR4 and CXCR3, respectively. Interestingly, CXCL12 binding affinity is approximately 10-fold higher for ACKR3 than CXCR4 [ 31 ]. Besides, ACKR3 also has non-chemokine binding partners: vCCL2, MIF, the 12 C-terminal residues of the proadrenomedullin peptide (PAMP-12) and a broad range of opioid peptides [ 33 – 35 ].

Expression of ACKR3 has been described in vascular endothelial cells, B cells, mesenchymal cells, in diverse regions of the CNS and in the adrenal glands [ 36 ].

ACKR3 and CXCR4 share very similar structural features (i.e., seven transmembrane domains, three intracellular and three extracellular loops), yet are radically different in their ligand-induced response (see Sect. 2.5.). Atypical chemokine receptors are unified by their inability to signal via G proteins and consequent failure to induce Ca 2+ transients and mediate cell migration [ 37 ]. Accordingly, ACKR3 is widely recognized as a β-arrestin-biased receptor [ 38 ], although it has been reported to exceptionally signal through G proteins in primary human astrocytes and human glioma cells [ 39 ]. Interestingly, ACKR3 transmembrane helices adopt a basal conformation that is similar to active canonical receptors. This active-like structure is likely to contribute to the constitutive binding to β-arrestin and might potentially participate in receptor trafficking between cell membrane and intracellular vesicles [ 40 ]. This G protein-independent response characteristic to atypical receptors is explained by a variation in sequence in the second intracellular loop of the receptor (IC2), where the DRYLAIV amino acid motif present in CXCR4 is modified into a DRYLSIT sequence in ACKR3, unable to interact with G protein [ 41 ].

Other CXCL12 receptors (ACKR1 and ACKR5)

The atypical receptors ACKR1 and ACKR5 are two promiscuous receptors, both binding over ten chemokine ligands, including CXCL12.

ACKR1, or DARC (Duffy Antigen/Receptor for Chemokines) has also been reported for CXCL12 binding, but only in its dimeric form [ 42 ]. Unlike with its other receptors, interaction between CXCL12 homodimers and ACKR1 does not lead to G protein coupling, nor β-arrestin recruitment, and consequently does not lead to intracellular signaling [ 20 ].

ACKR5, also known as GPR182, is the newest member of the ACKR family [ 43 ]. As part of the atypical chemokine receptors, ACKR5 does not induce G protein-mediated signaling but shows strong constitutive interaction with β-arrestins 1 and 2. In the amino acid sequence, the DRYLAIV motif located in the IC2 of CXCR4 is modified into DRYVTLT, supporting the lack of G protein coupling [ 43 ]. ACKR3 is the closest paralogue of ACKR5, and both receptors have overlapping ligand binding for CXCL11 and CXCL12. However, unlike CXCL12 binding to CXCR4 or ACKR3, CXCL12-ACKR5 interaction hardly influences β-arrestin recruitment [ 44 ].

As ACKR5 was very recently added in the ACKR family and ACKR1 does not directly impact CXCL12/CXCR4/ACKR3 signaling, their contribution in this axis remains to be determined and will not be further discussed in the following sections.

CXCL12-mediated signalling pathways

CXCL12 is a ligand for CXCR4 and ACKR3 and induces different molecular and biological consequences when binding to one or the other receptor (Fig. 2 ).

CXCL12 binding to CXCR4 triggers the conformational change of the receptor, promoting both the GDP/GTP exchange at the G αi and the consecutive G αi/ G βγ dissociation. The GTP-loaded G αi inhibits the adenylyl cyclase-mediated cyclic adenosine monophosphate (cAMP) production and thereby reduces the activation of the downstream effector protein kinase A (PKA). Upon receptor activation, both G αi subunit and G βƔ heterodimer can activate phosphoinositide-3 kinase (PI3K), followed by protein kinase B (also known as Akt) and mTOR, leading to cell migration, proliferation and survival. The dissociated G βƔ dimer is involved in the activation of Ras/Raf/ERK cascade, inducing cellular consequences related to gene expression and cell cycle progression. G βƔ dimer also triggers phospholipase C (PLC) activation, which in turn catalyzes the hydrolysis of PIP2 (phosphatidylinositol 4,5-bisphosphate) into DAG (diacylglycerol) and IP3 (inositol 1,4,5-triphosphate). DAG promotes the activation of protein kinase C (PKC) and mitogen associated protein kinase (MAPK), eventually leading to chemotaxis. IP3 triggers the release of Ca 2+ from the endoplasmic reticulum into the cytoplasm (Fig. 2 a) [ 45 – 47 ].

Following CXCL12 binding, CXCR4 is rapidly phosphorylated by G protein-coupled receptor kinases (GRKs) on serine residues located on the intracellular carboxy-terminal extremity. The phosphorylated residues recruit β-arrestin, promoting the uncoupling of G proteins and inducing clathrin-mediated receptor endocytosis, thereby inducing receptor desensitization (Fig. 2 b) [ 48 ].

Unlike CXCR4, ACKR3 functions as G protein-independent receptor by directly recruiting β-arrestin2 upon binding of CXCL11 or CXCL12 (Fig. 2 b) [ 38 ]. While β-arrestin-dependant receptor internalization is by far the most described signalling function for ACKR3, recent work identified BMP2K (bone morphology protein 2-inducible kinase) as a novel ACKR3-interactor capable of inducing receptor endocytosis in a β-arrestin-independent manner [ 49 ]. Internalization of the receptor-ligand complex in turn leads to their lysosomal degradation and recycling. ACKR3 continuously cycles between the plasma membrane and endosomal compartment. However, receptor internalization increases upon ligand binding [ 50 ]. As a result, ACKR3 acts as a scavenger for CXCL12, thereby regulating extracellular concentration of the chemokine and indirectly influencing CXCL12-induced CXCR4 signalisation.

The two chemokine receptors for CXCL12, CXCR4 and ACKR3 can form homo- and heterodimers, leading to different signaling pathways. CXCR4-CXCR4 homodimers lead to G protein-independent JAK/STAT activation [ 51 ], while CXCR4-ACKR3 heterodimers influence CXCL12-induced signals, thereby inhibiting G αi -mediated signalization [ 52 ]. It is to be noted that CXCR4 also can heterodimerize with other GPCRs (e.g., CCR2, CCR5, CXCR3, beta-2 adrenergic receptor and opioid receptors), leading to various complex cellular responses [ 27 , 53 – 55 ].

Physiopathology: focus on the CNS

The CXCL12/CXCR4/ACKR3 chemokine axis plays a critical role in the CNS, both during development and in adult brain homeostasis.

Similarly to its function in other organs, CXCL12 guides neuronal precursor migration during embryogenesis, contributing to hippocampal and cortical organization [ 56 ]. CXCR4 null mice have defects in neural precursor survival and oligodendrocyte progenitor cell (OPCs) migration during embryonic and postnatal CNS development [ 57 ].

In postnatal and adult stages, CXCL12 also participate in axonal guidance, synaptic functions and stemness maintenance. High levels of CXCR4 and CXCL12 are observed in the subventricular zone (SVZ) adjacent to the lateral ventricles and the subgranular zone (SGZ) located in the dentate gyrus, which are both neural stem cell niches in the adult brain [ 58 , 59 ]. Numerous studies have underscored the regulatory role of CXCL12 through both CXCR4 and ACKR3 for the proper functioning of neural progenitor cells (NPC), favouring their survival, promoting quiescence and guiding NPC migration towards CNS damaged sites [ 60 – 62 ].

Among ACKRs, ACKR3 is considered as endowed with the most prominent functions [ 63 ] and is broadly expressed across various brain regions, such as the cortex, hippocampus (including the dentate gyrus), hypothalamus, cerebellum, olfactory bulbs, subventricular zone and spinal cord [ 64 ]. In ACKR3-Venus knock-in mice, strong expression of the receptor has been shown in brain endothelial vascular cells, hippocampal GABAergic interneurons and neuroblast neighbouring cells [ 65 ]. In addition to its role in chemokine scavenging and gradient regulation, ACKR3 has been shown to exert non-canonical functions in the CNS through its interaction with Connexin 43 (Cx43), the most abundant gap junction protein. In astrocytes, ACKR3 can interact with Cx43, promoting its internalization, thereby reducing astrocytic gap junctions and intracellular communication [ 66 ]. Such relationship between ACKR3 and gap junctions might be relevant in CNS physiopathology, such as demonstrated in the context of subarachnoid hemorrhage [ 67 ].

In adults, the CXCL12/CXCR4 pathway has been shown to exert neuroprotective effects, favouring neural repair after cerebral ischemia [ 68 ]. Although CXCL12 is constitutively expressed in the CNS, its expression increases under pathological conditions such as brain ischemia, brain tumor or multiple sclerosis [ 69 ].

Given its multifaced roles in neurodevelopment, neural stem cell regulation and neuroprotection, dysregulation of the CXCL12/CXCR4/ACKR3 axis contributes to CNS pathogenesis, making CXCL12 and its receptors attractive targets for pharmacological intervention [ 6 ].

An overview of the modulators of the CXCL12/CXCR4/ACKR3 axis

Like other GPCRs, CXCR4 and ACKR3, as well as their shared ligand CXCL12, have been in the center of recent drug development endeavors. After a brief description of these compounds in this section, we will thoroughly review ongoing research in the context of various CNS-diseases (Table 1 ).

GPCR targeting compounds can be from different classes, ranging from synthetic small molecules, metabolites, peptides or antibodies [ 1 ]. The principal modulators of the CXCL12/CXCR4/ACKR3 axis that have been tested in CNS-related pathological conditions are listed in Table 1 . Clinical trials are indicated when applicable.

From all pharmacological modulators of the axis, the bicyclam AMD3100, also known as Plerixaforor or Mozobil®, is by far the most widely described. From 1990’s until early 2000’s, AMD3100 was initially named JM3100 and tested to block HIV-1 virus entry into CD4 + T cells for the treatment of AIDS [ 71 ]. While its application was discontinued due to cardiac toxicity and insufficient efficiency, researchers unexpectedly highlighted the upregulated level of hematopoietic cells in blood circulation following Plerixafor administration. This effect was then further investigated for different diseases and the use of Plerixafor was approved in 2008 by the FDA for non-Hodgkin lymphoma and multiple myeloma patients [ 84 ]. The increase in CD34 + hematopoietic cells also showed promising therapeutic effects for the treatment of WHIM syndrome (Warts, Hypogammaglobulinemia, Infections, and Myelokathexis), a rare hereditary immunodeficiency caused by a gain-of-function mutations in the Cxcr4 gene where young mature leucocytes are retained in the bone marrow. In a phase 3 clinical trial, Plerixafor administration significantly improved WHIM patients’ quality of life ( NCT02231879 ) [ 85 ]. Besides its positive contribution in immunological pathologies, the use of Plerixafor for cancer treatment also is highly investigated. While overall well tolerated, mild adverse events associated with Plerixafor include diarrhea, nausea, fatigue, injection site reactions, headache, dizziness and arthralgia [ 86 ]. To cope with Plerixafor-induced toxicity and its lack of oral bioavailability due to its lipophilic nature, numerous other small CXCR4 antagonists have been developed and tested in various pathological conditions. The second FDA-approved CXCR4 antagonist is Mavorixafor, also known as AMD070, AMD11070 or XOLREMDI®. Initially, AMD070 was described as an anti-HIV drug, just as AMD3100 [ 72 ]. This compound was then tested for its immunomodulatory properties, particularly for the treatment of WHIM syndrome. In a phase 3 trial ( NCT03995108 ), Mavorixafor administration was well tolerated and demonstrated a clinically relevant increase of circulating lymphocytes and neutrophils in WHIM patients [ 87 ]. This led to Mavorixafor approval by the US FDA in April 2024 [ 88 ].

While Plerixafor has a lower antagonism efficacy in vitro compared to Movarixafor (IC 50 values are 44 nM and 13 nM, respectively), it has a superior effect in hematopoietic stem cells mobilization in vivo. This biological difference was attributed to pharmacological properties of the two modulators, with Movarixafor acting as a full antagonist (inhibiting both G protein and β-arrestin recruitment) and Plerixafor acting as a biased antagonist, stimulating β-arrestin recruitment while fully antagonizing G protein activation [ 89 ].

In contrast to CXCR4, fewer studies describe molecules that target ACKR3. In 2009, the CXCR4 inhibitor AMD3100 was also demonstrated as ACKR3 agonist at high concentration (> 10 μm) [ 81 ]. Besides, ACKR3-specific modulators have also been described. Among the most common small molecules, one can cite CCX771, VUF11207 , and ACT-1004-1239 [ 79 , 80 , 82 ]. VUF11207 and ACT-1004-1239 are respectively specific agonist and antagonist of the receptor, while CCX771 has controversial pharmacological properties. This molecule was initially described by Zabel et al. as a selective ACKR3 agonist, inducing β-arrestin recruitment and reducing CXCL12-induced tumor cell migration [ 80 ]. However, Cruz-Ortengo et al. rather described CCX771 as an ACKR3 antagonist in the context of multiple sclerosis [ 90 ]. In 2018, Salazar et al. generated X7Ab, an anti-ACKR3 single chain antibody for the treatment of glioblastoma [ 83 ]. Regarding their clinical application, ACT-1004-1239 is the first-in-class ACKR3 modulator that has undergone phase 1 clinical trials for assessing its safety, tolerability and pharmacokinetics ( NCT03869320 and NCT04286750 ). Its oral administration was well tolerated in healthy humans and induced a dose-dependent increase of CXCL12 concentration [ 91 ].

Regarding the targeting of the ligand, NOX-A12 stands out in literature as RNA aptamer anti-CXCL12 [ 70 ]. In preclinical and clinical studies, NOX-A12 is safe and mobilizes leucocytes and hematopoietic stem cells into peripheral blood in a dose-dependent manner [ 92 ]. This CXCL12-inhibitor has already undergone clinical trials for stem cell transplantation ( NCT00976378 and NCT01194934 ), multiple myeloma ( NCT01521533 ), chronic lymphocytic leukemia ( NCT01486797 ), metastatic colorectal and pancreatic cancer ( NCT03168139 ) and glioblastoma ( NCT04121455 ).

Targeting the CXCL12/CXCR4/ACKR3 axis in CNS pathologies

As previously said, while CXCL12 and its receptors have been described in neurological development, they also participate the pathogenesis of different CNS disorders. This section summarizes both the possible role of the CXCL12/CXCR4/ACKR3 axis in various CNS diseases and the applications for CXCL12/CXCR4/ACKR3 modulators in those disorders, divided between the fields of neuroinflammation and neuro-oncology.

Neuroinflammation

The understanding of brain immunity has drastically evolved in the last decades. Originally, it was widely thought that the brain was isolated from peripheral immune system because of the existence of a specialized barrier, later designated the blood–brain barrier (BBB). In this first model, the brain was considered as an “immune privileged” organ, where microglial cells are the only CNS resident immune component, and peripheral immune cell infiltration is restricted to disease states and inflammation. Between 1990 and 2010, studies showed immune cell infiltration in healthy contexts, including CNS plasticity and repair. This belief was called the “protective immunity” paradigm, in which the CNS is subjected to immune surveillance in homeostasis. More recent work identified specialized immunological compartments in the brain, containing immune cells and preventing excessive neuroinflammation. These so-called “brain immunological niches” include the meninges, the choroid plexuses and the perivascular spaces [ 93 ].

While neuroinflammation can be protective in some contexts, it can also be deleterious and lead to various pathologies. The contribution of the CXCL12/CXCR4/ACKR3 axis has been extensively investigated in multiple conditions involving inflammation ranging from multiple sclerosis (MS), neurodegenerative disorders (e.g., AD, PD or amyotrophic lateral sclerosis (ALS)), or stroke-induced acute CNS inflammation (Fig. 3 ).

Recent literature review supports and describes the potential of targeting CXCL12/CXCR4/ACKR3 chemokine/receptor axis in those various pathological conditions, aiming for neuroprotection and cognitive improvement [ 94 ].

Multiple sclerosis (MS)

The relation between the CXCL12/CXCR4/ACKR3 axis and multiple sclerosis (MS), the most common autoimmune disease affecting the CNS, has been extensively reviewed in 2017 by Chu et al. [ 69 ].

Several studies investigated the function of CXCL12 and its receptors in MS, using preclinical experimental murine autoimmune encephalomyelitis models (EAE). This experimental model for human MS recapitulates the key pathological features of the disease, including chronic inflammation, demyelination and neurodegeneration [ 95 ].

In EAE models, CXCL12 has been reported to exert anti-inflammatory effects by restricting CXCR4 + leukocytes to perivascular spaces [ 96 ]. In contrast, elevated CXCL12 levels within the corpus callosum (a major myelinated fiber tract between the two cerebral hemispheres) promote the migration of CXCR4-expressing OPCs, facilitating their recruitment to demyelinated lesions and supporting remyelination. These effects were demonstrated by CXCR4 antagonism using AMD3100 [ 97 ].

These apparently opposing effects on cell migration in the context of MS might be explained by the spatial distribution of CXCL12 within the CNS. High CXCL12 expression at the abluminal side of the BBB retains CXCR4 + leukocytes, confining them to perivascular niches and thereby limiting excessive immune cell infiltration into the CNS. Conversely, under pathological conditions such as demyelinating lesions where CXCL12 levels increase within the brain parenchyma, including the corpus callosum , CXCR4 + OPCs exhibit enhanced migratory capacities, promoting their recruitment and maturation at sites of damage and ultimately contributing to remyelination.

Besides the CXCR4-mediated function described hereabove, Cruz-Orengo et al. identified ACKR3 as key factor facilitating leukocyte entry into the CNS parenchyma, suggesting that this receptor blockade could be beneficial for the treatment of multiple sclerosis [ 98 ]. In a follow-up study, they showed that ACKR3 blocking using CCX771 as potent antagonist improves EAE mice clinical outcome, both by preventing excessive inflammation and preserving axonal integrity [ 90 ]. The benefits of ACKR3 antagonism in MS could most likely be attributed to a subsequent increase of abluminal CXCL12 levels, preventing excessive leukocyte abundance in the CNS parenchyma.

The use of CCX771 in EAE preclinical models was further supported by Williams et al., showing that CCX771 promotes maturation of OPCs towards pro-myelinating oligodendrocytes [ 99 ]. More recently, Pouzol et al. also validated ACKR3 as a valuable target for multiple sclerosis using another promising potent antagonist, ACT-1004-1239, capable penetrating into the CNS and improving mice clinical score [ 100 , 101 ]. Taken together, these data suggest that the CXCL12/CXCR4/ACKR3 is a promising therapeutic candidate to improve remyelination in MS. While no evidence in human has yet been described, ACT-1004-1239 was shown safe in early phase trials and might be further tested in conditions where ACKR3 blocking is a promising approach in preclinical studies, such as MS [ 91 ].

Besides the function of CXCL12 and its receptors in the context of MS, ໿Andrés-Benito et al. showed in increased CXCL12 level in the cerebrospinal fluid (CSF) of MS patients, which can be useful for diagnosis [ 102 ].

Neurodegeneration

Studies indicated that CXCL12, CXCR4 and ACKR3 play important roles in brain plasticity, resulting in different outcomes in neurodegenerative disorders.

AD is the most common form of dementia, characterized by extracellular amyloid beta (Aβ) accumulation and hyperphosphorylated tau protein neurofibrillary tangles. In AD patients, the expression of CXCL12 and its receptors is inversely correlated, CXCL12 being downregulated while CXCR4 and ACKR3 levels are elevated in comparison with healthy tissue. While CXCL12 gene expression decreases and CXCR4 gene expression significantly increases in all brain regions [ 103 ], ACKR3 increased protein level stands out in astrocytes from AD patients’ hippocampus [ 104 ].

In this context, CXCL12 has been indicated as pro-inflammatory and neuroprotective, increasing microglial phagocytosis of Aβ deposits [ 7 , 105 ]. The function of CXCR4 is however controversial in this context. Administration of the CXCR4 antagonist AMD3100 in acute Aβ-injected mice and chronic 3xTg AD mice led to neuroprotective effects, reduced neuroinflammation and improved cognitive abilities [ 106 ]. However, it induced memory deficits according to other studies performed in young adult wild-type mice [ 62 , 107 ]. Of note, cell targets of AMD3100 were not systematically addressed, and treatment schemes (i.e. administration routes, dose, timing, etc.) were variable across studies. However, we may hypothesize that AMD3100 treatment impacts neuronal physiology and cognition in a context-dependent manner. On the other hand, ACKR3 has also been investigated in AD pathology using different experimental models. ACKR3 knockdown in mice is accompanied by a reduction of CXCL12 and CXCR4 expression in hippocampal homogenates, a decreased number of doublecortin-positive cells in the hippocampus, and learning and memory deficits [ 62 ]. The neuroprotective function of ACKR3 was also described in a study led by Das et al. using siRNA and different pharmacological modulators of the receptor: AMD3100, VUF11207 (agonists) and CCX771 (antagonist). ACKR3 agonists reduced neurodegeneration by increasing microglial inflammatory functions, while ACKR3 siRNA worsens memory impairments [ 108 ].

In PD, the main neuropathological hallmarks are the formation of abnormal ⍺-synuclein aggregates called Lewy bodies and the degeneration of dopaminergic neurons, mainly of the pars compacta of the locus niger , leading to motor disabilities and other non-motor symptoms [ 109 ]. Studies reported that PD patients exhibit higher levels of inflammatory markers in blood and cerebrospinal fluid that differ from healthy subjects. Among these, CXCL12 is upregulated and stands out as a putative diagnostic marker [ 110 ]. Besides, Li et al. shown that CXCL12 is upregulated in postmortem brain tissue of PD patients, and that CXCL12/CXCR4 axis is associated with ⍺-synuclein-mediated neuroinflammation through microglial accumulation, a response significantly reduced upon AMD3100 treatment in vitro [ 111 ]. While microglia is described as a key player in PD neurodegeneration, CXCR4-guided migration of CD4 + T cells also participate in this process, further supporting the therapeutic inhibition of the CXCL12/CXCR4 axis for slowing down PD physiopathology [ 112 ]. In addition to the pharmacological effects of the compounds listed here above, AMD3100 also might improve the efficacy of neural stem cell transplantation in a rat model of Parkinson’s disease [ 113 ]. This therapeutic approach represents a promising strategy for neurodegenerative diseases for replacing damaged neurons, as well as promoting neural network regeneration via the modulation of neurotrophic and inflammatory factors [ 114 ].

CXCR4 downregulation therefore appears as a promising therapeutic approach for neuroprotection and/or slowing down disease progression in AD and PD [ 115 ]. Recently, Tripathi and Kumar discovered about fifty molecules structurally similar to the FDA-approved CXCR4 antagonist Mavorixafor by molecular docking and simulation. Among them, ZINC49067615 and ZINC103242147 appeared as the most interesting candidates by their ability to cross the BBB, their higher affinity towards CXCR4 as well as a stable interaction with the receptor [ 73 ]. Thus, authors suggest that these molecules could show higher inhibitory activity toward CXCR4 as compared to Mavorixafor and should be biologically validated in the context of neurodegenerative disorders.

Amyotrophic lateral sclerosis (ALS) is a neurodegenerative pathology defined by the loss of motor neurons in the motor cortex and spinal cord, leading to progressive muscle weakness and paralysis [ 116 ].

Studies led by Andrés-Benito et al. highlighted increased CXCL12 levels in ALS patient CSF, suggesting its potential as complementary diagnostic biomarker, together with NF-L and YKL40 proteins [ 102 ]. In their study, they demonstrated that both CXCL12, CXCR4 and ACKR3 are localized in motor neurons in both control and ALS tissue. Under pathological conditions, CXCL12 is also present in a few glial cells, CXCR4 in degenerating motor neurons and in a subset of oligodendroglia-like cells, and ACKR3 in reactive astrocytes from pyramidal tracts in ALS.

Finally, ACKR3 is found in motor neurons of both control and ALS samples, as well as in reactive astrocytes in the pyramidal tracts in ALS [ 102 ]. The clinical implication of CXCR4 was addressed in a transgenic mouse model of ALS, using chronic AMD3100 administration. CXCR4 antagonism alleviates symptoms of the disease by attenuating the breakdown of the blood-spinal cord barrier (BSCB), decreasing microglial inflammatory response and preventing motor neuron destruction [ 117 ]. Therefore, approaches targeting CXCR4 might be clinically relevant in ALS patients and should further be addressed.

Neurooncology

Over the last years, literature has recognized the role of the tissue ecosytem in tumor progression, for both primary tumor development and metastasis establishment. The tumor microenvironment (TME) is a complex system that comprises all the non-cancerous host cells in the tumor, as well as non-cellular components, including the extracellular matrix and soluble molecules such as growth factors, extracellular vesicles, cytokines and chemokines [ 118 ]. While chemokines are critical in directing the spatial organization of immune cells within tumors to deliver an effective anti-tumor response, they also participate in the recruitment of pro-tumorigenic immune cells that favor tumor development [ 119 , 120 ]. Chemokine circuits were shown to shape TME in solid tumors, including brain tumors [ 121 , 122 ]. Targeting of key chemokine players in such context is a strategy that has raised interest for improving responses to cancer therapies.

Compared to normal tissue, the expression of CXCR4 receptor is upregulated in many cancers, including kidney, breast, lung, ovarian, pancreas, prostate, melanoma and brain [ 123 ]. Overall, the CXCL12/CXCR4/ACKR3 axis is considered as an active participant in the formation of primary CNS tumors and brain metastases. The expression of these three genes correlates with tumor grade, recurrence, treatment resistance and poor prognosis [ 83 , 84 , 124 , 125 ]. Considering the relevance of this chemokine axis in cancer, different chemical modulators have been tested in the field of neuro-oncology, and some compounds have entered clinical trials (Table 1 ).

Primary brain tumors (with a focus on glioblastoma)

Primary tumors affecting the CNS cause significant mortality worldwide, in spite of their low incidence. The wide histo-molecular diversity of such tumors renders the development of treatments extremely challenging [ 126 ]. From all brain tumors, glioblastomas are the most prevalent (accounting for about 50%), as well as the deadliest [ 127 ].

CXCR4 antagonists in glioblastoma

The contribution of the CXCL12/CXCR4/ACKR3 chemokine axis in glioblastoma has been extensively studied in the last years, notably using pharmacological modulators, showing promising outcomes in (pre)clinical studies (Fig. 4 ). In the field, the CXCR4 antagonist AMD3100, or Plerixafor, is the most used compound. Overall, literature has shown that AMD3100 exerts its antitumoral effect through different mechanisms, leading to reduced tumor growth in vitro and in preclinical models. At the molecular scale, studies led on different cell types (e.g., breast and prostate cancer) showed that AMD3100 is associated with reduced activation of downstream CXCR4 effectors, ERK1/2 and Akt, involved in tumor cell migration, proliferation and survival [ 84 ]. Kioi et al. demonstrated that AMD3100 administration blocks vasculogenesis, thereby preventing glioblastoma recurrence in orthotopic xenografts [ 128 ]. CXCR4 antagonism also contributes to the modulation of glioblastoma TME by reducing the infiltration of pro-tumoral myeloid-derived suppressor cells [ 129 ]. The use of Plerixafor has also been tested in combination with the immunotherapeutic agent anti-PD-1 (pembrolizumab) in preclinical models, leading to an improved survival [ 130 ]. Additionally, preclinical studies showed that the CXCL12/CXCR4 axis promotes radio- and chemoresistance, and AMD3100 treatment significantly reverses this phenotype [ 131 , 132 ].

Considering its promising effects as new therapeutics in preclinical models, Plerixafor has entered phase 1/2 clinical trials testing for brain tumors (Table 1 ). Overall, a low toxicity was reported, alone or in combination with radio/chemotherapy or with the anti-angiogenic agent bevacizumab [ 133 , 134 ]. To date, no phase 3 trial has proven the efficiency of Plerixafor treatment in glioblastoma patients.

In an in vitro study, Luo et al. shown that CPZ1344, a compound structurally similar to AMD3100, was efficient on the U87 glioblastoma cells [ 135 ]. In this study, CPZ1344 inhibited U87 proliferation and migration, as well as angiogenesis in HUVEC cells, suggesting that CPZ1344 might serve as new anti-tumor therapeutics [ 74 ].

In the same line, another CXCR4-specific antagonist named peptide R has shown promising effects in inhibiting CXCL12-mediated glioblastoma growth and migration in vitro [ 77 ]. In U87 cells orthotopic xenograft models, peptide R also impaired tumor vasculature and favored the polarization of tumor associated macrophages towards a “M1-like” anti-tumoral phenotype [ 136 ]. In 2019, a peptide R derivative (Pep R54) showing a higher affinity towards CXCR4 was efficient in combination with anti-PD-1 for melanoma treatment [ 137 ]. This approach might also be relevant and could be considered for glioblastoma.

PRX177561 was also described as novel CXCR4 antagonist, showing promising effects both in vitro and in preclinical models. This compound was tested alone or in combination with bevacizumab and sunitinib [ 75 , 76 ].

A mutated form of CXCL12 called P2G, where a proline is switched by a glycine at position 2 in the amino acid sequence of the chemokine [ 78 ], demonstrated encouraging antagonistic effects towards CXCR4 in glioblastoma [ 138 ]. In this article, the modified chemokine delivered by an oncolytic herpes simplex virus impairs glioblastoma cells properties (e.g., stemness, proliferation, migration) and significantly reduces tumor growth in vivo.

ACKR3 modulators in glioblastoma

ACKR3, the other receptor for CXCL12, has also gained interest in the field of neuro-oncology.

In 2014, ACKR3 antagonist CCX771 was administered after irradiation in glioblastoma-bearing mice, preventing tumor recurrence and leading to a prolonged survival [ 139 ]. Salazar et al. later demonstrated that combining the chemotherapeutic agent temozolomide and the chimeric antibody X7Ab anti-ACKR3 was efficient for improving overall survival in glioblastoma preclinical models [ 83 ]. Their study also suggested that this combinational treatment was efficient in engaging an anti-tumoral immune response, as shown with the enhanced M1-like macrophage polarization.

More recently, the impact of ACKR3 modulation on glioblastoma immune microenvironment was described using VUF11207 , a potent ACKR3 agonist [ 140 ]. In this study, they showed that ACKR3 activation elicits anti-tumor immunity by promoting T cell activation. Moreover, VUF11207 potentiated an anti-PD-L1 response, indicating a promising effect for favoring immune checkpoint blocker (ICB) response in glioblastoma.

CXCL12 inhibition in glioblastoma

Besides investigating the receptors, other studies also focused on CXCL12. Liu et al. showed that CXCL12 inhibition using the CXCL12-specific RNA aptamer NOXA-12 inhibits tumor recurrence in rats [ 141 ]. In 2024, the phase 1/2 GLORIA trial ( NCT04121455 ) combining radiotherapy and NOX-A12 administration validated treatment safety in newly diagnosed glioblastoma patients and suggested its positive impact on progression-free survival [ 142 ].

Brain metastases

The CXCL12/CXCR4/ACKR3 chemokine axis has also been demonstrated to guide the migration of CXCR4-positive metastatic tumor cells in CXCL12-rich organs such as the brain, the liver, the lungs and the bone marrow [ 18 , 123 ]. The establishment of brain metastases has been widely studied in breast and lung cancers, or in acute lymphoblastic leukemia. Unlike CXCR4, while ACKR3 promotes primary tumor growth in both breast and non-small-cell lung cancer (NSCLC), no evidence suggests a function in brain metastasis [ 143 ].

In breast cancer metastasis, CXCL12 expression in the brain attracts CXCR4 positive tumor cells from primary site. In this context, AMD3100 administration was shown efficient in diminishing breast tumor cells brain invasion [ 144 ].

In NSCLC, CXCL12/CXCR4 signalling has been associated with the spread of lung cancer cells to the brain [ 145 ]. Multiple studies have shown that blocking the CXCL12/CXCR4 axis efficiently reduced lung cancer cell migration. Depletion of CXCL12 using a monoclonal anti-CXCL12 antibody in vivo impaired tumor establishment at secondary sites, including in the brain [ 146 ]. In another study, Li et al. described AMD3100 as a candidate to decrease brain-specific metastasis in lung cancer, by strengthening tight junctions of the BBB and limiting the penetration of tumor cells [ 147 ].

Inhibiting CXCR4 with AMD3100 has also shown promising effects in B and T precursor acute lymphoblastic leukemia (B-ALL and T-ALL, respectively) by preventing CNS colonisation of tumor cells [ 148 , 149 ]. Similarly, a blockade of the CXCL12/CXCR4 axis with AMD11070 (Mavorixafor), inhibits the leukemia-meningeal cell adhesion, thereby attenuating chemoresistance [ 150 ].

Conclusions

Chemokines and their receptors, in particular the CXCL12/CXCR4/ACKR3 axis, play a crucial role in tissue development and homeostasis, including in the CNS. Dysregulation of this axis lays the foundation for several neurological disorders, both during development and in adulthood. This observation led to intense research efforts harnessing pharmacological modulators in neuropathological contexts. Although several compounds targeting CXCL12, CXCR4 or ACKR3 have been developed in the latest years, only few of them have been addressed in CNS conditions. The CXCL12-targeting aptamer NOX-A12 stands out as the lead modulator, showing promising antitumor effects in patients with newly diagnosed glioblastoma. Concerning CXCR4, Plerixafor and Mavorixafor remain the reference compounds for a large number of CNS diseases, including glioblastoma and brain metastasis, neurodegenerative diseases (AD, PD, ALS) and multiple sclerosis. More recently, ACKR3 pharmacological modulation also shown promising effects in reducing neuroinflammation and favoring anti-tumoral immunity. Agonists and antagonists of the receptor have been tested in these contexts, notably ACT-1004-1239, CCX771 and VUF11207 . Although numerous other modulators targeting CXCL12, CXCR4 or ACKR3 have been developed, their application remains limited to in vitro testing or preclinical models, and several of them have not yet been explored for CNS disorders.

One of the greatest challenges for translating drug candidates into clinical applications for such pathologies is the presence of the blood brain barrier, which significantly limits the number of compounds that can penetrate the brain.

When considering the development of new modulators (or the improvement of existing molecules), it is essential to question their biophysical properties. Alternatively, delivery methods such as nanoparticles also might facilitate drug delivery into the CNS (such as demonstrated by Alghamri et al. for glioblastoma treatment) [ 129 ]. However, BBB crossing might not be strictly necessary for treatment efficacy in CNS pathologies. Some compounds can indeed act through systemic mechanisms that indirectly influence the CNS microenvironment, for instance by modulating peripheral immune responses, circulating cytokines or chemokine gradients, despite limited direct brain exposure. This concept is illustrated by the GLORIA trial in glioblastoma patients using the NOX-A12 aptamer, which exhibits low BBB penetration but appears to act primarily through systemic disruption of CXCL12 signaling and subsequent modulation of immune cell recruitment in the CNS [ 142 ].

Overall, the CXCL12/CXCR4/ACKR3 axis represents a valuable, yet context-dependent therapeutic target in CNS disorders. As an example, the use of AMD3100 (Plerixafor) might be beneficial in Parkinson’s disease by promoting Lewy bodies clearance, while it is suggested deleterious in multiple sclerosis. Targeting one or another component of this axis also leads to drastically different outcomes, such as CXCR4 inhibition being detrimental in multiple sclerosis, while ACKR3 antagonism shows beneficial effects.

In summary, the CXCL12/CXCR4/ACKR3 axis emerges as a central regulator of CNS physiology and pathology, with significant therapeutic promise. Addressing the current limitations in drug delivery and target selectivity, and most especially contextual signalling will be pivotal for future success. Continued exploration of CXCL12/CXCR4/ACKR3 pathway will help to yield novel insights and therapeutic opportunities across a broad spectrum of CNS disorders.

Abbreviations

Adenylyl cyclase

Atypical chemokine receptor 1

Atypical chemokine receptor 3

Atypical chemokine receptor 5

Alzheimers’ disease

Acquired immunodeficiency syndrome

Protein kinase B

Amyotrophic lateral sclerosis

Amyloid beta

B precursor acute lymphoblastic leukemia

Blood-brain barrier

Blood-spinal cord barrier

Cyclic adenosine monophosphate

Cannabinoid receptor 2

Cluster of differentiation 184

Central nervous system

Cerebrospinal fluid

CXC-Ligand 11

CXC-Ligand 12

CXC-Receptor 3

CXC-Receptor 4

CXC-Receptor 7

Diacylglycerol

Duffy Antigen/Receptor for Chemokines

Experimental autoimmune encephalomyelitis

Extracellular ubiquitin

Food and drug administration

Guanosine diphosphate

Glycoprotein 120

G protein-coupled receptor

G protein-coupled receptor 182

G protein-coupled receptor kinase

Guanosine triphosphate

Human immunodeficiency virus

Intracellular loop 2

Immune checkpoint blocker

Inositol 1,4,5-triphosphate

Ionizing radiation

Leukocyte-derived seven-transmembrane domain receptor

Mitogen associated protein kinase

Macrophage migration inhibitory factor

Multiple sclerosis

Neural progenitor cell

Non-small-cell lung cancer

Oligodendrocyte progenitor cell

Proadrenomedullin peptide

Pre-B cell growth-stimulating factor

Parkinsons’disease

Phosphoinositide-3 kinase

Phosphatidylinositol 4,5-bisphosphate

Protein kinase A

Phospholipase C

Receptor-Deficient Chemokine 1

Stromal cell-derived factor-1

Subgranular zone

Subventricular zone

T precursor acute lymphoblastic leukemia

Tumor microenvironment

Temozolomide

United States

Warts, Hypogammaglobulinemia, Infections, and Myelokathexis syndrome

Authors’ contributions

AK: conception and design, data analysis and interpretation, manuscript drafting and revision. BR: Data interpretation, manuscript revision, project funding. VN: Conception and design, data interpretation, manuscript revision, project funding. All authors approve the submitted version of the manuscript.

Funding

This work was supported by the University of Liège, the Fondation Hospitalo-Universitaire Léon Frédéricq, and the F.R.S.-FNRS research fund in Belgium. AK is a F.R.S.-FNRS-Télévie PhD fellow (grant 7.6518.24).

Data availability

No datasets were generated or analysed during the current study.

Declarations

Competing interests

The authors declare no competing interests.

Footnotes

Publisher’s note

Springer Nature remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.

References

1. Yang D, et al. G protein-coupled receptors: structure- and function-based drug discovery. Signal Transduct Target Ther. 2021;6(1):7. 10.1038/s41392-020-00435-w.

2. Hauser AS, Attwood MM, Rask-Andersen M, Schiöth HB, Gloriam DE. Trends in GPCR drug discovery: new agents, targets and indications. Nat Rev Drug Discov. 2017;16(12):829–42. 10.1038/nrd.2017.178.

3. Azam S, et al. G-Protein-Coupled Receptors in CNS: A Potential Neurodegenerative Disorders and Associated. Cells. 2020;9:506.

4. Rossi D, Zlotnik A. The biology of chemokines and their receptors. Annu Rev Immunol. 2000;18:217–42. 10.1146/annurev.immunol.18.1.217.

5. Bachelerie F, et al. International Union of Basic and Clinical Pharmacology. [corrected]. LXXXIX. Update on the extended family of chemokine receptors and introducing a new nomenclature for atypical chemokine receptors. Pharmacol Rev. 2014;66(1):1–79. 10.1124/pr.113.007724.

6. Réaux-Le Goazigo A, Van Steenwinckel J, Rostène W, Mélik Parsadaniantz S. Current status of chemokines in the adult CNS. Prog Neurobiol. 2013;104:67–92. 10.1016/j.pneurobio.2013.02.001.

7. Janssens R, Struyf S, Proost P. Pathological roles of the homeostatic chemokine CXCL12., Cytokine Growth Factor Rev. 2018;44:51–68 10.1016/j.cytogfr.2018.10.004.

8. Tachibana K et al. Jun., The chemokine receptor CXCR4 is essential for vascularization of the gastrointestinal tract., Nature. 1998;393(6685):591–594 10.1038/31261.

9. Zou YR, Kottmann AH, Kuroda M, Taniuchi I, Littman DR. Function of the chemokine receptor CXCR4 in haematopoiesis and in cerebellar development., Nature. 1998;393(6685):595–599. 10.1038/31269.

10. Ma Q et al. Aug., Impaired B-lymphopoiesis, myelopoiesis, and derailed cerebellar neuron migration in CXCR4- and SDF-1-deficient mice., Proc. Natl. Acad. Sci. U. S. A.1998;95(16):9448–9453. 10.1073/pnas.95.16.9448.

11. Ödemis V, et al. Mice deficient in the chemokine receptor CXCR4 exhibit impaired limb innervation and myogenesis. Mol Cell Neurosci. 2005;30(4):494–505. 10.1016/j.mcn.2005.07.019.

12. Nagasawa T et al. Aug., Defects of B-cell lymphopoiesis and bone-marrow myelopoiesis in mice lacking the CXC chemokine PBSF/SDF-1., Nature. 1996;382(6592):635–638 10.1038/382635a0.

13. Sierro F et al. Sep., Disrupted cardiac development but normal hematopoiesis in mice deficient in the second CXCL12/SDF-1 receptor, CXCR7. Proc. Natl. Acad. Sci. U. S. A. 2007;104(37):14759–14764. 10.1073/pnas.0702229104.

14. Gerrits H, et al. Early postnatal lethality and cardiovascular defects in CXCR7-deficient mice. Genesis. 2008;46(5):235–45. 10.1002/dvg.20387.

15. Shirozu M, et al. Structure and chromosomal localization of the human stromal cell-derived factor 1 (SDF1) gene. Genomics. 1995;28(3):495–500. 10.1006/geno.1995.1180.

16. Chen K, Bao Z, Tang P, Gong W, Yoshimura T, Wang JM. Chemokines in homeostasis and diseases. Cell. Mol. Immunol. 2018;15(4)324–334. 10.1038/cmi.2017.134.

17. Sugiyama T, Kohara H, Noda M, Nagasawa T. Maintenance of the hematopoietic stem cell pool by CXCL12-CXCR4 chemokine signaling in bone marrow stromal cell niches., Immunity. 2006;25(6):977–988. 10.1016/j.immuni.2006.10.016.

18. Janowski M. Functional diversity of SDF-1 splicing variants. Cell Adh Migr. 2009;3(3):243–9. 10.4161/cam.3.3.8260.

19. Righetti A, Giulietti M, Šabanović B, Occhipinti G, Principato G, Piva F. CXCL12 and Its Isoforms: Different Roles in Pancreatic Cancer? J. Oncol. 2019;2019:1-13. 10.1155/2019/9681698.

20. Szpakowska M, et al. New pairings and deorphanization among the atypical chemokine receptor family - physiological and clinical relevance. Front Immunol. 2023;14:1133394. 10.3389/fimmu.2023.1133394.

21. Loetscher M, Geiser T, O’Reilly T, Zwahlen R, Baggiolini M, Moser B. Cloning of a human seven-transmembrane domain receptor, LESTR, that is highly expressed in leukocytes. J Biol Chem. 1994;269(1):232–7.

22. Feng Y, Broder CC, Kennedy PE, Berger EA. HIV-1 entry cofactor: functional cDNA cloning of a seven-transmembrane, G protein-coupled receptor. Science. 1996;272(5263):872–7. 10.1126/science.272.5263.872.

23. Pawig L, Klasen C, Weber C, Bernhagen J, Noels H. Diversity and Inter-Connections in the CXCR4 Chemokine Receptor/Ligand Family: Molecular Perspectives. Front Immunol. 2015;6:429. 10.3389/fimmu.2015.00429.

24. Feng Z, Dubyak GR, Lederman MM, Weinberg A. Cutting edge: human beta defensin 3–a novel antagonist of the HIV-1 coreceptor CXCR4. J. Immunol. 2006;177(2)782–786. 10.4049/jimmunol.177.2.782.

25. Bernhagen J, et al. MIF is a noncognate ligand of CXC chemokine receptors in inflammatory and atherogenic cell recruitment. Nat Med. 2007;13(5):587–96. 10.1038/nm1567.

26. Saini V et al. Sep., The CXC chemokine receptor 4 ligands ubiquitin and stromal cell-derived factor-1α function through distinct receptor interactions. J. Biol. Chem. 2011;286(38):33466–33477. 10.1074/jbc.M111.233742.

27. Pello OM et al. Feb., Ligand stabilization of CXCR4/delta-opioid receptor heterodimers reveals a mechanism for immune response regulation. Eur. J. Immunol. 2008;38(2):537–549. 10.1002/eji.200737630.

28. Coke CJ, et al. Simultaneous Activation of Induced Heterodimerization between CXCR4 Chemokine Receptor and Cannabinoid Receptor 2 (CB2) Reveals a Mechanism for Regulation of Tumor Progression. J Biol Chem. 2016;291:9991–10005. 10.1074/jbc.M115.712661.

29. Libert F, Parmentier M, Lefort A, Dumont JE, Vassart G. Complete nucleotide sequence of a putative G protein coupled receptor: RDC1. Nucleic Acids Res. 1990;18(7):1917. 10.1093/nar/18.7.1917.

30. Heesen M, Berman MA, Charest A, Housman D, Gerard C, Dorf ME. Cloning and chromosomal mapping of an orphan chemokine receptor: mouse RDC1., Immunogenetics. 1998;47(5):364–370. 10.1007/s002510050371.

31. Balabanian K et al. Oct., The chemokine SDF-1/CXCL12 binds to and signals through the orphan receptor RDC1 in T lymphocytes. J. Biol. Chem. 2005;280(42):35760–35766. 10.1074/jbc.M508234200.

32. Burns JM et al. Sep., A novel chemokine receptor for SDF-1 and I-TAC involved in cell survival, cell adhesion, and tumor development. J. Exp. Med. 2006;203(9):2201–2213. 10.1084/jem.20052144.

33. Szpakowska M, et al. Human herpesvirus 8-encoded chemokine vCCL2/vMIP-II is an agonist of the atypical chemokine receptor ACKR3/CXCR7. Biochem Pharmacol. 2016;114:14–21. 10.1016/j.bcp.2016.05.012.

34. Meyrath M, et al. The atypical chemokine receptor ACKR3/CXCR7 is a broad-spectrum scavenger for opioid peptides. Nat Commun. 2020;11(1):3033. 10.1038/s41467-020-16664-0.

35. Meyrath M, et al. Proadrenomedullin N-Terminal 20 Peptides (PAMPs) Are Agonists of the Chemokine Scavenger Receptor ACKR3/CXCR7. ACS Pharmacol Transl Sci. 2021;4(2):813–23. 10.1021/acsptsci.1c00006.

36. Szpakowska M et al. Mar., Inclusion of ACKR5 in the systematic nomenclature of atypical chemokine receptors. Nature reviews. Immunology. 2025;25(3):225–226. 10.1038/s41577-025-01135-8.

37. Samus M, Rot A. Atypical chemokine receptors in cancer. Cytokine. 2024;176(2023):156504. 10.1016/j.cyto.2024.156504

38. Rajagopal S et al. β-Arrestin- But not G protein-mediated signaling by the ‘decoy’ receptor CXCR7, Proc. Natl. Acad. Sci. U. S. A. 2010;107(2):628–632. 10.1073/pnas.0912852107.

39. Ödemis V, et al. The presumed atypical chemokine receptor CXCR7 signals through Gi/o proteins in primary rodent astrocytes and human glioma cells. Glia. 2012;60(3):372–81. 10.1002/glia.22271.

40. Yen Y-C, et al. Structures of atypical chemokine receptor 3 reveal the basis for its promiscuity and signaling bias. Sci Adv. 2022;8(28):eabn8063. 10.1126/sciadv.abn8063.

41. Graham GJ, Locati M, Mantovani A, Rot A, Thelen M. The biochemistry and biology of the atypical chemokine receptors. Immunol Lett. 2012;145:1–2. 10.1016/j.imlet.2012.04.004.

42. Gutjahr JC, et al. The dimeric form of CXCL12 binds to atypical chemokine receptor 1. Sci Signal. 2021;14(696). 10.1126/scisignal.abc9012.

43. Chevigné A, Legler DF, Rot A, Sozzani S, Szpakowska M, Thelen M. International Union of Basic and Clinical Pharmacology. CXVIII. Update on the nomenclature for atypical chemokine receptors, including ACKR5. Pharmacol Rev. 2025;77(1):100012. 10.1124/pharmrev.124.001361.

44. Le Mercier A et al. Apr., GPR182 is an endothelium-specific atypical chemokine receptor that maintains hematopoietic stem cell homeostasis. Proc. Natl. Acad. Sci. U. S. A. 2021;118(17). 10.1073/pnas.2021596118.

45. Bao S, et al. CXC chemokine receptor 4 (CXCR4) blockade in cancer treatment. J Cancer Res Clin Oncol. 2023;149(10):7945–68. 10.1007/s00432-022-04444-w.

46. Pozzobon T, Goldoni G, Viola A, Molon B. CXCR4 signaling in health and disease. Immunol Lett. 2016;177:6–15. 10.1016/j.imlet.2016.06.006.

47. García-Cuesta EM, Santiago CA, Vallejo-Díaz J, Juarranz Y, Rodríguez-Frade JM, Mellado M. The Role of the CXCL12/CXCR4/ACKR3 Axis in Autoimmune Diseases, Front. Endocrinol. (Lausanne). 2019;10:1–16. 10.3389/fendo.2019.00585.

48. Shi Y, Riese DJ 2, Shen J. The Role of the CXCL12/CXCR4/CXCR7 Chemokine Axis in Cancer. Front Pharmacol. 2020;11:574667. 10.3389/fphar.2020.574667.

49. Hicks C, et al. ACKR3 Proximity Labeling Identifies Novel G protein- and β-arrestin-independent GPCR Interacting Proteins. bioRxiv Prepr Serv Biol. 2024. 10.1101/2024.01.27.577545.

50. Luker KE, Steele JM, Mihalko LA, Ray P, Luker GD. Constitutive and chemokine-dependent internalization and recycling of CXCR7 in breast cancer cells to degrade chemokine ligands. Oncogene. 2010;29(32):4599–4610. 10.1038/onc.2010.212.

51. Vila-Coro AJ, Rodríguez-Frade JM, Martín A, De Ana MC, Moreno-Ortíz C, Martínez-A, Mellado M. The chemokine SDF-1alpha triggers CXCR4 receptor dimerization and activates the JAK/STAT pathway. FASEB J Off Publ Fed Am Soc Exp Biol. 1999;13(13):1699–710.

52. Levoye A, Balabanian K, Baleux F, Bachelerie F, Lagane B. CXCR7 heterodimerizes with CXCR4 and regulates CXCL12-mediated G protein signaling. Blood. 2009;113(24):6085–6093. 10.1182/blood-2008-12-196618.

53. Sohy D et al. Nov., Hetero-oligomerization of CCR2, CCR5, and CXCR4 and the protean effects of ‘selective’ antagonists. J. Biol. Chem. 2009;284(45):31270–31279. 10.1074/jbc.M109.054809.

54. Watts AO et al. Apr., Identification and profiling of CXCR3-CXCR4 chemokine receptor heteromer complexes. Br. J. Pharmacol. 2013;168(7):1662–1674. 10.1111/bph.12064.

55. Liang J et al. Apr., The β2-adrenergic receptor associates with CXCR4 multimers in human cancer cells. Proc. Natl. Acad. Sci. U. S. A. 2024;121(14):e2304897121. 10.1073/pnas.2304897121.

56. Stumm R, Kolodziej A, Schulz S, Kohtz JD, Höllt V. Patterns of SDF-1alpha and SDF-1gamma mRNAs, migration pathways, and phenotypes of CXCR4-expressing neurons in the developing rat telencephalon. J Comp Neurol. 2007;502(3):382–99. 10.1002/cne.21336.

57. Dziembowska M, Tham TN, Lau P, Vitry S, Lazarini F, Dubois-Dalcq M. A role for CXCR4 signaling in survival and migration of neural and oligodendrocyte precursors. Glia. 2005;50(3):258–69. 10.1002/glia.20170.

58. Berger O, Li G, Han S-M, Paredes M, Pleasure SJ. Expression of SDF-1 and CXCR4 during reorganization of the postnatal dentate gyrus. Dev Neurosci. 2007;29:1–2. 10.1159/000096210.

59. Klein RS, Rubin JB. Immune and nervous system CXCL12 and CXCR4: parallel roles in patterning and plasticity. Trends Immunol. 2004;25(6):306–14. 10.1016/j.it.2004.04.002.

60. Li M, Ransohoff RM. Multiple roles of chemokine CXCL12 in the central nervous system: a migration from immunology to neurobiology. Prog Neurobiol. 2008;84(2):116–31. 10.1016/j.pneurobio.2007.11.003.

61. Zhu B et al. Nov., CXCL12 enhances human neural progenitor cell survival through a CXCR7- and CXCR4-mediated endocytotic signaling pathway. Stem Cells. 2012;30(11):2571–2583. 10.1002/stem.1239.

62. Trousse F, et al. Knockdown of the CXCL12/CXCR7 chemokine pathway results in learning deficits and neural progenitor maturation impairment in mice. Brain Behav Immun. 2019;80:697–710. 10.1016/j.bbi.2019.05.019.

63. Lindsay HG, Hendrix CJ, Gonzalez Murcia JD, Haynie C, Weber KS. The Role of Atypical Chemokine Receptors in Neuroinflammation and Neurodegenerative Disorders. Int J Mol Sci. 2023;24(22). 10.3390/ijms242216493.

64. Banisadr G, Podojil JR, Miller SD, Miller RJ. Pattern of CXCR7 Gene Expression in Mouse Brain Under Normal and Inflammatory Conditions., J. neuroimmune Pharmacol. Off. J. Soc. NeuroImmune Pharmacol. 2016;11(1):26–35. 10.1007/s11481-015-9616-y.

65. Ehrlich AT, et al. Ackr3-Venus knock-in mouse lights up brain vasculature. Mol Brain. 2021;14(1):151. 10.1186/s13041-021-00862-y.

66. Fumagalli A, et al. The atypical chemokine receptor 3 interacts with Connexin 43 inhibiting astrocytic gap junctional intercellular communication. Nat Commun. 2020;11(1):4855. 10.1038/s41467-020-18634-y.

67. Yan J et al. Role of Cx43 and ACKR3 in Modulating Astrocytic Response and Neuronal Survival Post-Subarachnoid Hemorrhage, Glia. 2025;73(8):1565–1588. 10.1002/glia.70008.

68. Shyu W-C et al. Feb., Stromal cell-derived factor-1 alpha promotes neuroprotection, angiogenesis, and mobilization/homing of bone marrow-derived cells in stroke rats. J. Pharmacol. Exp. Ther. 2008;324(2):834–849. 10.1124/jpet.107.127746.

69. Chu T, Shields LBE, Zhang YP, Feng S-Q, Shields CB, Cai J. CXCL12/CXCR4/CXCR7 Chemokine Axis in the Central Nervous System: Therapeutic Targets for Remyelination in Demyelinating Diseases., Neurosci. a Rev. J. bringing Neurobiol. Neurol. psychiatry. 2017;23(6):627–648. 10.1177/1073858416685690.

70. Sayyed SG, et al. Podocytes produce homeostatic chemokine stromal cell-derived factor-1/CXCL12, which contributes to glomerulosclerosis, podocyte loss and albuminuria in a mouse model of type 2 diabetes. Diabetologia. 2009;52(11):2445–54. 10.1007/s00125-009-1493-6.

71. D. C. E, et al. Highly potent and selective inhibition of human immunodeficiency virus by the bicyclam derivative JM3100. Antimicrob Agents Chemother. 1994;38(3):668–74. 10.1128/aac.38.4.668.

72. Skerlj RT, et al. Discovery of novel small molecule orally bioavailable C-X-C chemokine receptor 4 antagonists that are potent inhibitors of T-tropic (X4) HIV-1 replication. J Med Chem. 2010;53(8):3376–88. 10.1021/jm100073m.

73. Tripathi R, Kumar P. Preliminary study to identify CXCR4 inhibitors as potential therapeutic agents for Alzheimer’s and Parkinson’s diseases. Integr Biol (Camb). 2023;15. 10.1093/intbio/zyad012.

74. Luo Z, Wang B, Chen Y, Liu H, Shi L. Novel CXCR4 Inhibitor CPZ1344 inhibits the proliferation, migration and angiogenesis of glioblastoma. Pathol Oncol Res. 2020;26(4):2597–604. 10.1007/s12253-020-00827-x.

75. Gravina GL, et al. The novel CXCR4 antagonist, PRX177561, reduces tumor cell proliferation and accelerates cancer stem cell differentiation in glioblastoma preclinical models. Tumour Biol J Int Soc Oncodevelopmental Biol Med. 2017;39(6):1010428317695528. 10.1177/1010428317695528.

76. Gravina GL, et al. The brain-penetrating CXCR4 antagonist, PRX177561, increases the antitumor effects of bevacizumab and sunitinib in preclinical models of human glioblastoma. J Hematol Oncol. 2017;10(1). 10.1186/s13045-016-0377-8.

77. Portella L, et al. Preclinical development of a novel class of CXCR4 antagonist impairing solid tumors growth and metastases. PLoS ONE. 2013;8(9):e74548. 10.1371/journal.pone.0074548.

78. Crump MP, et al. Solution structure and basis for functional activity of stromal cell-derived factor‐1; dissociation of CXCR4 activation from binding and inhibition of HIV‐1. EMBO J. 1997;16(23):6996–7007. 10.1093/emboj/16.23.6996.

79. Richard-Bildstein S, et al. Discovery of the potent, selective, orally available CXCR7 antagonist ACT-1004-1239. J Med Chem. 2020;63(24):15864–82. 10.1021/acs.jmedchem.0c01588.

80. Zabel BA, et al. Elucidation of CXCR7-mediated signaling events and inhibition of CXCR4-mediated tumor cell transendothelial migration by CXCR7 ligands. J Immunol. 2009;183(5):3204–11. 10.4049/jimmunol.0900269.

81. Kalatskaya I, Berchiche YA, Gravel S, Limberg BJ, Rosenbaum JS, Heveker N. AMD3100 is a CXCR7 ligand with allosteric agonist properties. Mol Pharmacol. 2009;75(5):1240–7. 10.1124/mol.108.053389.

82. Wijtmans M, et al. Synthesis, modeling and functional activity of substituted styrene-amides as small-molecule CXCR7 agonists. Eur J Med Chem. 2012;51:184–92. 10.1016/j.ejmech.2012.02.041.

83. Salazar N, et al. A Chimeric Antibody against ACKR3/CXCR7 in Combination with TMZ Activates Immune Responses and Extends Survival in Mouse GBM Models. Mol Ther. 2018;26(5):1354–65. 10.1016/j.ymthe.2018.02.030.

84. Wang J, Tannous BA, Poznansky MC, Chen H. CXCR4 antagonist AMD3100 (plerixafor): From an impurity to a therapeutic agent. Pharmacol Res. 2020;159:105010. 10.1016/j.phrs.2020.105010.

85. McDermott DH et al. Jan., Plerixafor for the Treatment of WHIM Syndrome. N. Engl. J. Med. 2019;380(2):163–170. 10.1056/NEJMoa1808575.

86. Pantin J, et al. Effect of high-dose plerixafor on CD34(+) cell mobilization in healthy stem cell donors: results of a randomized crossover trial. Haematologica. 2017;102(3):600–9. 10.3324/haematol.2016.147132.

87. Badolato R et al. Jul., A phase 3 randomized trial of mavorixafor, a CXCR4 antagonist, for WHIM syndrome. Blood. 2024;144(1):35–45. 10.1182/blood.2023022658.

88. Hoy SM. Mavorixafor: First Approval. Drugs. 2024;84(8):969–75. 10.1007/s40265-024-02063-y.

89. Jørgensen AS, et al. Biased action of the CXCR4-targeting drug plerixafor is essential for its superior hematopoietic stem cell mobilization. Commun Biol. 2021;4(1):569. 10.1038/s42003-021-02070-9.

90. Cruz-Orengo L, Chen Y-J, Kim JH, Dorsey D, Song S-K, Klein RS. CXCR7 antagonism prevents axonal injury during experimental autoimmune encephalomyelitis as revealed by in vivo axial diffusivity. J Neuroinflammation. 2011;8:170. 10.1186/1742-2094-8-170.

91. Huynh C, et al. Target engagement of the first-in-class CXCR7 antagonist ACT-1004-1239 following multiple-dose administration in mice and humans. Biomed Pharmacother. 2021;144:112363. 10.1016/j.biopha.2021.112363. October.

92. Vater A et al. Jul., Hematopoietic stem and progenitor cell mobilization in mice and humans by a first-in-class mirror-image oligonucleotide inhibitor of CXCL12. Clin. Pharmacol. Ther. 2013;94(1):150–157. 10.1038/clpt.2013.58.

93. Castellani G, Croese T, Ramos JMP, Schwartz M. Transforming the understanding of brain immunity. Sci (80-). 2023;380(6640):eabo7649. 10.1126/science.abo7649.

94. Sarallah R, Jahani S, Soltani Khaboushan A, Moaveni AK, Amiri M, Majidi Zolbin M. The role of CXCL12/CXCR4/CXCR7 axis in cognitive impairment associated with neurodegenerative diseases. Brain Behav Immun - Heal. 2025;43:100932. 10.1016/j.bbih.2024.100932.

95. Constantinescu CS, Farooqi N, O’Brien K, Gran B. Experimental autoimmune encephalomyelitis (EAE) as a model for multiple sclerosis (MS). Br J Pharmacol. 2011;164(4):1079–106. 10.1111/j.1476-5381.2011.01302.x.

96. McCandless EE, Wang Q, Woerner BM, Harper JM, Klein RS. CXCL12 limits inflammation by localizing mononuclear infiltrates to the perivascular space during experimental autoimmune encephalomyelitis. J. Immunol. 2006;177(11):8053–8064. 10.4049/jimmunol.177.11.8053.

97. Patel JR, McCandless EE, Dorsey D, Klein RS. CXCR4 promotes differentiation of oligodendrocyte progenitors and remyelination. Proc. Natl. Acad. Sci. U. S. A. 2010;107(24):11062–11067. 10.1073/pnas.1006301107.

98. Cruz-Orengo L et al. Feb., CXCR7 influences leukocyte entry into the CNS parenchyma by controlling abluminal CXCL12 abundance during autoimmunity., J. Exp. Med. 2011;208(2):327–339. 10.1084/jem.20102010.

99. Williams JL, Patel JR, Daniels BP, Klein RS. Targeting CXCR7/ACKR3 as a therapeutic strategy to promote remyelination in the adult central nervous system. J Exp Med. 2014;211(5):791–9. 10.1084/jem.20131224.

100. Pouzol L, et al. ACT-1004-1239, a first-in-class CXCR7 antagonist with both immunomodulatory and promyelinating effects for the treatment of inflammatory demyelinating diseases. FASEB J Off Publ Fed Am Soc Exp Biol. 2021;35(3):e21431. 10.1096/fj.202002465R.

101. Pouzol L et al. ACKR3 Antagonism Enhances the Repair of Demyelinated Lesions Through Both Immunomodulatory and Remyelinating Effects, Neurochem. Res. 2024;49(8):2087–2104. 10.1007/s11064-024-04173-1.

102. Andrés-Benito P, et al. Increased C-X-C Motif Chemokine Ligand 12 Levels in Cerebrospinal Fluid as a Candidate Biomarker in Sporadic Amyotrophic Lateral Sclerosis. Int J Mol Sci. 2020;21(22). 10.3390/ijms21228680.

103. Sanfilippo C, Castrogiovanni P, Imbesi R, Nunnari G, Rosa MD. Postsynaptic damage and microglial activation in AD patients could be linked CXCR4/CXCL12 expression levels. Brain Res. 2020;1749:147127. 10.1016/j.brainres.2020.147127.

104. Puchert M, et al. Astrocytic expression of the CXCL12 receptor, CXCR7/ACKR3 is a hallmark of the diseased, but not developing CNS. Mol Cell Neurosci. 2017;85:105–18. 10.1016/j.mcn.2017.09.001.

105. Wang Q, et al. Stromal cell-derived factor 1α decreases β-amyloid deposition in Alzheimer’s disease mouse model. Brain Res. 2012;1459:15–26. 10.1016/j.brainres.2012.04.011.

106. Gavriel Y, Rabinovich-Nikitin I, Ezra A, Barbiro B, Solomon B. Subcutaneous Administration of AMD3100 into Mice Models of Alzheimer’s Disease Ameliorated Cognitive Impairment, Reduced Neuroinflammation, and Improved Pathophysiological Markers, J. Alzheimer’s Dis. 2020;78(2):653–671. 10.3233/JAD-200506.

107. Parachikova A, Cotman CW. Reduced CXCL12/CXCR4 results in impaired learning and is downregulated in a mouse model of Alzheimer disease., Neurobiol. Dis. 2007;28(2):143–153. 10.1016/j.nbd.2007.07.001.

108. Das S, Mishra KP, Chanda S, Ganju L, Singh SB. CXCR7: A key neuroprotective molecule against alarmin HMGB1 mediated CNS pathophysiology and subsequent memory impairment. Brain Behav Immun. 2019;82:319–37. 10.1016/j.bbi.2019.09.003.

109. Cattaneo C, Jost WH. Pain in Parkinson’s Disease: Pathophysiology, Classification and Treatment. JIN. 2023;22(5):132–null.

110. Qu Y, et al. A systematic review and meta-analysis of inflammatory biomarkers in Parkinson’s disease. NPJ Park Dis. 2023;9(1). 10.1038/s41531-023-00449-5.

111. Li Y, et al. CXCL12 is involved in α-synuclein-triggered neuroinflammation of Parkinson’s disease. J Neuroinflammation. 2019;16(1):263. 10.1186/s12974-019-1646-6.

112. Gate D et al. Nov., CD4(+) T cells contribute to neurodegeneration in Lewy body dementia., Science. 2021;374(6569):868–874. 10.1126/science.abf7266.

113. Xu J-T, et al. Effect of stromal cell-derived factor-1/CXCR4 axis in neural stem cell transplantation for Parkinson’s disease. Neural Regen Res. 2020;15(1):112–9. 10.4103/1673-5374.264470.

114. De Gioia R, et al. Neural Stem Cell Transplantation for Neurodegenerative Diseases. Int J Mol Sci. 2020;21(9). 10.3390/ijms21093103.

115. Zhang J et al. Resveratrol Protects PC12 Cell against 6-OHDA Damage via CXCR4 Signaling Pathway., Evid. Based. Complement. Alternat. Med. 2015;2015:730121. 10.1155/2015/730121.

116. La Cognata V, Morello G, Guarnaccia M, Cavallaro S. The multifaceted role of the CXC chemokines and receptors signaling axes in ALS pathophysiology. Prog Neurobiol. 2024;235:102587. 10.1016/j.pneurobio.2024.102587.

117. Rabinovich-Nikitin I, Ezra A, Barbiro B, Rabinovich-Toidman P, Solomon B. Chronic administration of AMD3100 increases survival and alleviates pathology in SOD1G93A mice model of ALS. J Neuroinflammation. 2016;13(1):123. 10.1186/s12974-016-0587-6.

118. Dapash M, Hou D, Castro B, Lee-Chang C, Lesniak MS. The Interplay between Glioblastoma and Its Microenvironment., Cells. 2021;10(9) 10.3390/cells10092257.

119. Kohli K, Pillarisetty VG, Kim TS. Key chemokines direct migration of immune cells in solid tumors. Cancer Gene Ther. 2022;29(1):10–21. 10.1038/s41417-021-00303-x.

120. Ozga AJ, Chow MT, Luster AD. Chemokines and the immune response to cancer. Immunity. 2021;54(5):859–74. 10.1016/j.immuni.2021.01.012.

121. Isci D, et al. Patient-Oriented Perspective on Chemokine Receptor Expression and Function in Glioma. Cancers (Basel). 2021;14(1). 10.3390/cancers14010130.

122. D’Uonnolo G, et al. Patient-based multilevel transcriptome exploration highlights relevant chemokines and chemokine receptor axes in glioblastoma. Comput Biol Med. 2024;182:109197. 10.1016/j.compbiomed.2024.109197.

123. Smaldone G, et al. Targeting the CXCR4/CXCL12 Axis in Cancer Therapy: Analysis of Recent Advances in the Development of Potential Anticancer Agents. Molecules. 2025;30(6). 10.3390/molecules30061380.

124. Stevenson CB et al. Sep., CXCR4 expression is elevated in glioblastoma multiforme and correlates with an increase in intensity and extent of peritumoral T2-weighted magnetic resonance imaging signal abnormalities., Neurosurgery. 2008;63(3):560–570. 10.1227/01.NEU.0000324896.26088.EF.

125. Würth R, Bajetto A, Harrison JK, Barbieri F, Florio T. CXCL12 modulation of CXCR4 and CXCR7 activity in human glioblastoma stem-like cells and regulation of the tumor microenvironment. Front Cell Neurosci. 2014;8:144. 10.3389/fncel.2014.00144.

126. Louis DN et al. Aug., The 2021 WHO Classification of Tumors of the Central Nervous System: a summary., Neuro. Oncol. 2021;23(8):1231–1251. 10.1093/neuonc/noab106.

127. Schaff LR, Mellinghoff IK. Glioblastoma and Other Primary Brain Malignancies in Adults: A Review. JAMA. 2023;329(7):574–87. 10.1001/jama.2023.0023.

128. Kioi M, Vogel H, Schultz G, Hoffman RM, Harsh GR, Brown JM. Inhibition of vasculogenesis, but not angiogenesis, prevents the recurrence of glioblastoma after irradiation in mice., J. Clin. Invest. 2010;120(3):694–705. 10.1172/JCI40283.

129. Alghamri MS et al. Jun., Systemic Delivery of an Adjuvant CXCR4–CXCL12 Signaling Inhibitor Encapsulated in Synthetic Protein Nanoparticles for Glioma Immunotherapy, ACS Nano. 2022;16(6):8729–8750. 10.1021/acsnano.1c07492.

130. Wu A et al. Jun., Combination anti-CXCR4 and anti-PD-1 immunotherapy provides survival benefit in glioblastoma through immune cell modulation of tumor microenvironment., J. Neurooncol. 2019;143(2):241–249. 10.1007/s11060-019-03172-5.

131. Goffart N, et al. CXCL12 mediates glioblastoma resistance to radiotherapy in the subventricular zone. Neuro Oncol. 2017;19(1):66–77. 10.1093/neuonc/now136.

132. Wang S, Chen C, Li J, Xu X, Chen W, Li F. The CXCL12/CXCR4 axis confers temozolomide resistance to human glioblastoma cells via up-regulation of FOXM1. J Neurol Sci. 2020;414:116837. 10.1016/j.jns.2020.116837.

133. Lee EQ, et al. Phase I and Biomarker Study of Plerixafor and Bevacizumab in Recurrent High-Grade Glioma. Clin cancer Res Off J Am Assoc Cancer Res. 2018;24:4643–9. 10.1158/1078-0432.CCR-18-1025.

134. Thomas RP et al. Dec., Macrophage Exclusion after Radiation Therapy (MERT): A First in Human Phase I/II Trial using a CXCR4 Inhibitor in Glioblastoma., Clin. cancer Res. an Off. J. Am. Assoc. Cancer Res. 2019;25(23):6948–6957. 10.1158/1078-0432.CCR-19-1421.

135. Allen M, Bjerke M, Edlund H, Nelander S, Westermark B. Origin of the U87MG glioma cell line: Good news and bad news. Sci Transl Med. 2016;8(354):354re3. 10.1126/scitranslmed.aaf6853.

136. Mercurio L, et al. Targeting CXCR4 by a selective peptide antagonist modulates tumor microenvironment and microglia reactivity in a human glioblastoma model. J Exp Clin Cancer Res. 2016;35:55. 10.1186/s13046-016-0326-y.

137. D’Alterio C, et al. Targeting CXCR4 potentiates anti-PD-1 efficacy modifying the tumor microenvironment and inhibiting neoplastic PD-1. J Exp Clin Cancer Res. 2019;38(1):432. 10.1186/s13046-019-1420-8.

138. Paolo D, et al. An oncolytic herpesvirus expressing a CXCR4 antagonist interferes with glioblastoma cells’ stemness features and migration. Mol Ther Oncol. 2025;33(4):201083. 10.1016/j.omton.2025.201083.

139. Walters MJ, et al. Inhibition of CXCR7 extends survival following irradiation of brain tumours in mice and rats. Br J Cancer. 2014;110(5):1179–88. 10.1038/bjc.2013.830.

140. Liu C-C, et al. CXCR7 activation evokes the anti-PD-L1 antibody against glioblastoma by remodeling CXCL12-mediated immunity. Cell Death Dis. 2024;15(6):434. 10.1038/s41419-024-06784-6.

141. Liu S-C et al. Jan., Blockade of SDF-1 after irradiation inhibits tumor recurrences of autochthonous brain tumors in rats., Neuro. Oncol. 2014;16(1):21-28. 10.1093/neuonc/not149.

142. Giordano FA, et al. L-RNA aptamer-based CXCL12 inhibition combined with radiotherapy in newly-diagnosed glioblastoma: dose escalation of the phase I/II GLORIA trial. Nat Commun. 2024;15(1):4210. 10.1038/s41467-024-48416-9.

143. Miao Z et al. Oct., CXCR7 (RDC1) promotes breast and lung tumor growth in vivo and is expressed on tumor-associated vasculature., Proc. Natl. Acad. Sci. U. S. A. 2007;104(40):15735–15740. 10.1073/pnas.0610444104.

144. Chung B, et al. Human brain metastatic stroma attracts breast cancer cells via chemokines CXCL16 and CXCL12. NPJ breast cancer. 2017;3(6). 10.1038/s41523-017-0008-8.

145. Cavallaro S. CXCR4/CXCL12 in non-small-cell lung cancer metastasis to the brain., Int. J. Mol. Sci. 2013;14(1):1713–1727. 10.3390/ijms14011713.

146. Phillips RJ, Burdick MD, Lutz M, Belperio JA, Keane MP, Strieter RM. The stromal derived factor-1/CXCL12-CXC chemokine receptor 4 biological axis in non-small cell lung cancer metastases., Am. J. Respir. Crit. Care Med. 2003;197(12):1676–1686. 10.1164/rccm.200301-071OC

147. Li H, et al. AMD3100 inhibits brain-specific metastasis in lung cancer via suppressing the SDF-1/CXCR4 axis and protecting blood-brain barrier. Am J Transl Res. 2017;9(12):5259–74.

148. Rajakumar SA, Grandal I, Minden MD, Hitzler JK, Guidos CJ, Danska JS. Targeted blockade of immune mechanisms inhibit B precursor acute lymphoblastic leukemia cell invasion of the central nervous system. Cell Rep Med. 2021;2(12):100470. 10.1016/j.xcrm.2021.100470.

149. Jost TR, et al. Role of CXCR4-mediated bone marrow colonization in CNS infiltration by T cell acute lymphoblastic leukemia. J Leukoc Biol. 2016;99:1077–87. 10.1189/jlb.5MA0915-394R.

150. Jonart LM, Ostergaard J, Brooks A, Fitzpatrick G, Chen L, Gordon PM. CXCR4 antagonists disrupt leukaemia-meningeal cell adhesion and attenuate chemoresistance. Br J Haematol. 2023;201(3):459–69. 10.1111/bjh.18607.

Associated Data

Data Availability Statement

No datasets were generated or analysed during the current study.