Erratum: The CXC chemokine SDF-1 is the ligand for LESTR/fusin and prevents infection by T-cell-line-adapted HIV-1

The chemical diversity and structure-based evolution of non-peptide CXCR4 antagonists with diverse therapeutic potential

The CXC chemokine receptor 4 (CXCR4) is a highly reserved G-protein coupled 7-transmembrane (TM) chemokine receptor which consists of 352 amino acids. CXCR4 has only one endogenous chemokine ligand of CXCL12, besides several other natural nonchemokine ligands such as extracellular ubiquitin and noncognate ligand of MIF. CXCR4 strongly binds to CXCL12 and the resulting CXCLl2/CXCR4 axis is the molecular basis of their various biological functions, which include: (1) mediating immune and inflammatory response; (2) regulation of hematopoietic stem cell migration and homing; (3) an essential co-receptor for HIV entry into host cells; (4) participation in the process of embryonic development; (5) malignant tumor invasion and metastasis; (6) myocardial infarction, ischemic stroke and acute kidney injury. Correspondingly, CXCR4 antagonists find potential therapeutic applications in HIV infection, as well as hematopoietic stem cell migration, inflammation, immune-related diseases, tumor and ischemic diseases. Recently, great achievements have been made and a number of non-peptide CXCR4 antagonists with diversity scaffolds have been discovered. In this review, the discovery of small molecule CXCR4 antagonists focused on the structures, activities, evolution and development of representative CXCR4 antagonists is comprehensively described. The central role of CXCR4 in diverse cellular signaling pathways and its involvement in several diseases progressions are discussed as well.

Oroxylin A reverses the drug resistance of chronic myelogenous leukemia cells to imatinib through CXCL12/CXCR7 axis in bone marrow microenvironment

Imatinib (IM), a tyrosine-kinase inhibitor, is used in treatment of multiple cancers, most notably Philadelphia chromosome-positive (Ph⁺ ) chronic myelogenous leukemia (CML). However, the majority of patients continue to present with minimal residual disease occurred in the bone marrow (BM) microenvironment. One of the key factors that contribute to leukemia cell drug resistance is chemokine CXCL12. In the current study, co-culturing CML cell K562 and KU812 with BM stromal cell M2-10B4 attenuated IM-induced apoptosis. CXCL12/CXCR7 pathway was activated in co-culture models, which was further proved to be related to drug resistance by silencing CXCR7. ERK phosphorylation and downstream apoptosis related proteins' activation were also observed in co-culture group after the activation of CXCR7. Moreover, oroxylin A, a bioactive flavonoid isolated from the root of Scutellaria baicalensis Georgi, was found to be effective in reversing BM stroma induced CML resistance to IM. After cells were treated with weakly toxic concentration of oroxylin A, cell apoptosis induced by IM in co-culture model was enhanced. And the activated CXCL12/CXCR7 pathway, the expression of p-ERK and downstream apoptosis related proteins were suppressed. The in vivo study also showed that oroxylin A increased apoptosis of CML cells with low systemic toxicity, and the mechanism was consistent with the in vitro study. In conclusion, oroxylin A improved sensitivity of CML cells to IM treatment in BM microenvironment through regulating CXCL12/CXCR7 pathway. © 2016 Wiley Periodicals, Inc.

Inhibition of signaling between human CXCR4 and zebrafish ligands by the small molecule IT1t impairs the formation of triple-negative breast cancer early metastases in a zebrafish xenograft model

Triple-negative breast cancer (TNBC) is a highly aggressive and recurrent type of breast carcinoma that is associated with poor patient prognosis. Because of the limited efficacy of current treatments, new therapeutic strategies need to be developed. The CXCR4-CXCL12 chemokine signaling axis guides cell migration in physiological and pathological processes, including breast cancer metastasis. Although targeted therapies to inhibit the CXCR4-CXCL12 axis are under clinical experimentation, still no effective therapeutic approaches have been established to block CXCR4 in TNBC. To unravel the role of the CXCR4-CXCL12 axis in the formation of TNBC early metastases, we used the zebrafish xenograft model. Importantly, we demonstrate that cross-communication between the zebrafish and human ligands and receptors takes place and human tumor cells expressing CXCR4 initiate early metastatic events by sensing zebrafish cognate ligands at the metastatic site. Taking advantage of the conserved intercommunication between human tumor cells and the zebrafish host, we blocked TNBC early metastatic events by chemical and genetic inhibition of CXCR4 signaling. We used IT1t, a potent CXCR4 antagonist, and show for the first time its promising anti-tumor effects. In conclusion, we confirm the validity of the zebrafish as a xenotransplantation model and propose a pharmacological approach to target CXCR4 in TNBC.

Summary: CXCR4-expressing human tumor cells respond to zebrafish cognate ligands and initiate metastatic events in a zebrafish xenograft model. The CXCR4 antagonist IT1t has promising tumor inhibitory effects.

CXCR4 chemokine receptors, histone deacetylase inhibitors and acute lymphoblastic leukemia

Acute lymphoblastic leukemia (ALL) is a malignancy with the potential to infiltrate the liver, spleen, lymph nodes and brain. The mechanism for selective homing of ALL cells to preferential sites has long been unclear. Recent reports indicate that the chemokine receptor CXCR4 is found on ALL cells and its ligand is highly expressed at sites associated with ALL-induced organ infiltration. This results in chemotaxis, or directed migration of leukemic cells from the bone marrow via the circulation to preferential sites of extramedullary organ infiltration. Because overexpression of CXCR4 on ALL cells is associated with high extramedullary organ infiltration and shorter disease-free survival, numerous pharmacological agents affecting CXCR4 have currently been investigated. The most promising data are available for histone deacetylase inhibitors (HDAIs), which have been shown to be safe and well tolerated in phase I clinical trials. In vitro, HDAIs extensively down-regulate CXCR4 protein and mRNA levels. As a result, the ability of CXCR4 ligand to induce cellular migration is impaired. Wider recognition of the role of CXCR4 in ALL and manipulation of this important mechanism may lead to novel approaches in the treatment and outcome of this disease.