The bicyclam AMD3100 story

Identifying new small molecule anti-invasive compounds for glioma treatment

Glioblastoma is a disease with poor survival rates after diagnosis. Treatment of the disease involves debulking of the tumor, which is limited by the degree of invasiveness of the disease. Therefore, a treatment to halt the invasion of glioma is desirable for clinical implementation. There have been several candidate compounds targeting specific aspects of invasion, including cell adhesions, matrix degradation, and cytoskeletal rearrangement, but they have failed clinically for a variety of reasons. New targets against glioma invasion include upstream mediators of these classical targets in an effort to better inhibit invasion with more specificity for cancer. Included in these treatments is a new class of compounds inhibiting the generation of reactive oxygen species by targeting the NADPH oxidases. These compounds stand to inhibit multiple pathways, including nuclear factor kappa B and Akt. By conducting a screen of compounds thought to inhibit these pathways, a new compound to halt invasion was found that may have a beneficial effect against glioma, based on recent publications. Further, there are still limitations to the treatment of glioblastoma regardless of the discovery of new targets and compounds that should be addressed to better the therapies against this deadly cancer.

Chemokines and squamous cancer of the head and neck: targets for therapeutic intervention?

The biological properties of squamous carcinoma cells are intimately regulated by a multitude of cytokines and growth factors; the most well studied of these include epidermal growth factor receptor agonists and members of the transforming growth factor-beta family. The recent explosion of research in the field of chemokine function as a mediator of tumor progression has led to the possibility that these small, immunomodulatory proteins also play key roles in squamous carcinogenesis and may, therefore, be potential targets for novel therapeutic approaches.

Chemokine receptor modeling: an interdisciplinary approach to drug design

Chemokines and their receptors are integral components of the immune response, regulating lymphocyte development, homing and trafficking, and playing a key role in the pathophysiology of many diseases. Chemokine receptors have, therefore, become the target for both small-molecule, peptide and antibody therapeutics. Chemokine receptors belong to the family of seven transmembrane receptor class A G protein-coupled receptors. The publication of the crystal structure of the archetypal class A seven transmembrane receptor protein rhodopsin, and other G protein-coupled receptors, including C-X-C chemokine receptor 4 and C-C chemokine receptor 5, provided the opportunity to create homology models of chemokine receptors. In this review, we describe an interdisciplinary approach to chemokine receptor modeling and the utility of this approach for structure-based drug design of chemokine receptor inhibitors.

Synthesis of pyridine derivatives as potential antagonists of chemokine receptor type 4

A series of pyridine derivatives were synthesized as potential inhibitors of chemokine receptor type 4. This chemokine receptor has been linked to various disease pathways including HIV-1 proliferation, autoimmune disorders, inflammatory diseases, and cancer metastasis. The compounds were tested for activity using an affinity binding assay and an assay that tests the ability to inhibit cell invasion. Two hit compounds (2b and 2j) have been identified for further evaluation that inhibit cell invasion by at least 50% and have an effective concentration of less than 100 nM in the binding affinity assay. The structures of the synthesized compounds were confirmed by spectral data.

Discovery of tetrahydroisoquinoline-based CXCR4 antagonists

A de novo hit-to-lead effort involving the redesign of benzimidazole-containing antagonists of the CXCR4 receptor resulted in the discovery of a novel series of 1,2,3,4-tetrahydroisoquinoline (TIQ) analogues. In general, this series of compounds show good potencies (3-650 nM) in assays involving CXCR4 function, including both inhibition of attachment of X4 HIV-1IIIB virus in MAGI-CCR5/CXCR4 cells and inhibition of calcium release in Chem-1 cells. Series profiling permitted the identification of TIQ-(R)-stereoisomer 15 as a potent and selective CXCR4 antagonist lead candidate with a promising in vitro profile. The drug-like properties of 15 were determined in ADME in vitro studies, revealing low metabolic liability potential. Further in vivo evaluations included pharmacokinetic experiments in rats and mice, where 15 was shown to have oral bioavailability (F = 63%) and resulted in the mobilization of white blood cells (WBCs) in a dose-dependent manner.

The role of metabotropic glutamate receptor 5 on the stromal cell-derived factor-1/CXCR4 system in oral cancer

We have demonstrated that blocking CXCR4 may be a potent anti-metastatic therapy for CXCR4-related oral cancer. However, as CXCR4 antagonists are currently in clinical use to induce the mobilization of hematopoietic stem cells, continuous administration as an inhibitor for the metastasis may lead to persistent leukocytosis. In this study, we investigated the novel therapeutic downstream target(s) of the SDF-1/CXCR4 system, using B88-SDF-1 cells, which have an autocrine SDF-1/CXCR4 system and exhibit distant metastatic potential in vivo. Microarray analysis revealed that 418 genes were upregulated in B88-SDF-1 cells. We identified a gene that is highly upregulated in B88-SDF-1 cells, metabotropic glutamate receptor 5 (mGluR5), which was downregulated following treatment with 1,1’ -[1,4-Phenylenebis(methylene)]bis-1,4,8,11-tetraazacyclotetradecane octahydrochloride (AMD3100), a CXCR4 antagonist. The upregulation of mGluR5 mRNA in the SDF-1/CXCR4 system was predominately regulated by the Ras-extracellular signal-regulated kinase (ERK)1/2 pathway. Additionally, the growth of B88-SDF-1 cells was not affected by the mGluR5 agonist (S)-3,5-DHPG (DHPG) or the mGluR5 antagonists 2-Methyl-6-(phenylethynyl)pyridine (MPEP) and 3-((2-Methyl-1,3-thiazol-4-yl)ethynyl)pyridine (MTEP). However, we observed that DHPG promoted B88-SDF-1 cell migration, whereas both MPEP and MTEP inhibited B88-SDF-1 cell migration. To assess drug toxicity, the antagonists were intraperitoneally injected into immunocompetent mice for 4 weeks. Mice injected with MPEP (5 mg/kg) and MTEP (5 mg/kg) did not exhibit any side effects, such as hematotoxicity, allergic reactions or weight loss. The administration of antagonists significantly inhibited the metastasis of B88-SDF-1 cells to the lungs of nude mice. These results suggest that blocking mGluR5 with antagonists such as MPEP and MTEP could prevent metastasis in CXCR4-related oral cancer without causing side effects.

Inhibition of the CXCL12/CXCR4-axis as preventive therapy for radiation-induced pulmonary fibrosis

Background

A devastating late injury caused by radiation is pulmonary fibrosis. This risk may limit the volume of irradiation and compromise potentially curative therapy. Therefore, development of a therapy to prevent this toxicity can be of great benefit for this patient population. Activation of the chemokine receptor CXCR4 by its ligand stromal cell-derived factor 1 (SDF-1/CXCL12) may be important in the development of radiation-induced pulmonary fibrosis. Here, we tested whether MSX-122, a novel small molecule and partial CXCR4 antagonist, can block development of this fibrotic process.

Methodology/Principal Findings

The radiation-induced lung fibrosis model used was C57BL/6 mice irradiated to the entire thorax or right hemithorax to 20 Gy. Our parabiotic model involved joining a transgenic C57BL/6 mouse expressing GFP with a wild-type mouse that was subsequently irradiated to assess for migration of GFP+ bone marrow-derived progenitor cells to the irradiated lung. CXCL12 levels in the bronchoalveolar lavage fluid (BALF) and serum after irradiation were determined by ELISA. CXCR4 and CXCL12 mRNA in the irradiated lung was determined by RNase protection assay. Irradiated mice were treated daily with AMD3100, an established CXCR4 antagonist; MSX-122; and their corresponding vehicles to determine impact of drug treatment on fibrosis development. Fibrosis was assessed by serial CTs and histology. After irradiation, CXCL12 levels increased in BALF and serum with a corresponding rise in CXCR4 mRNA within irradiated lungs consistent with recruitment of a CXCR4+ cell population. Using our parabiotic model, we demonstrated recruitment of CXCR4+ bone marrow-derived mesenchymal stem cells, identified based on marker expression, to irradiated lungs. Finally, irradiated mice that received MSX-122 had significant reductions in development of pulmonary fibrosis while AMD3100 did not significantly suppress this fibrotic process.

Conclusions/Significance

CXCR4 inhibition by drugs such as MSX-122 may alleviate potential radiation-induced lung injury, presenting future therapeutic opportunities for patients requiring chest irradiation.

Emerging targets in cancer management: role of the CXCL12/CXCR4 axis

The chemokine CXCL12 (SDF-1) and its cell surface receptor CXCR4 were first identified as regulators of lymphocyte trafficking to the bone marrow. Soon after, the CXCL12/CXCR4 axis was proposed to regulate the trafficking of breast cancer cells to sites of metastasis. More recently, it was established that CXCR4 plays a central role in cancer cell proliferation, invasion, and dissemination in the majority of malignant diseases. The stem cell concept of cancer has revolutionized the understanding of tumorigenesis and cancer treatment. A growing body of evidence indicates that a subset of cancer cells, referred to as cancer stem cells (CSCs), plays a critical role in tumor initiation, metastatic colonization, and resistance to therapy. Although the signals generated by the metastatic niche that regulate CSCs are not yet fully understood, accumulating evidence suggests a key role of the CXCL12/CXCR4 axis. In this review we focus on physiological functions of the CXCL12/CXCR4 signaling pathway and its role in cancer and CSCs, and we discuss the potential for targeting this pathway in cancer management.

CXC chemokine receptor 4 expression, CXC chemokine receptor 4 activation, and wild-type nucleophosmin are independently associated with unfavorable prognosis in patients with acute myeloid leukemia

BACKGROUND

CXC chemokine receptor 4 (CXCR4) is activated by phosphorylation and essential for migration of hematopoietic precursors to bone marrow. CXCR4 overexpression predicts unfavorable prognosis in patients with acute myeloid leukemia (AML). Nucleophosmin (NPM1) mutation is the most frequent genetic abnormality in patients with AML and predicts a favorable prognosis. In vitro studies have suggested that mutant nucleophosmin (NPM) decreases CXCR4-mediated chemotaxis by downregulating CXCR4, thereby linking the NPM and CXCR4 pathways.

PATIENTS AND METHODS

In a group of 117 untreated adults with AML, we used immunohistochemistry to assess bone marrow specimens for CXCR4 and phosphorylated CXCR4 (pCXCR4) expression. All cases also were analyzed for NPM1 mutations using polymerase chain reaction-based methods.

RESULTS

CXCR4 expression was detected in 75 patients (64%), and pCXCR4 expression was detected in 31 patients (26%). NPM1 mutations were detected in 63 patients (54%). NPM1 mutations did not correlate with CXCR4 (P = .212) or pCXCR4 (P = .355) expression. The median 5-year overall survival was 27% (95% confidence interval, 19-36), with a median follow-up of 8 months (95% confidence interval, 6-15). In a multivariate Cox proportional hazards model, reduced overall and progression-free survival rates were associated with a history of antecedent hematologic disorder, failure to achieve complete remission, thrombocytopenia, unfavorable cytogenetics, CXCR4 expression, and wild-type NPM1. pCXCR4 expression was independently associated with shorter progression-free survival.

CONCLUSIONS

There is no correlation between NPM1 mutations and CXCR4 or pCXCR4 expression, suggesting that the CXCR4 and NPM pathways act independently in adult AML.

Expression of the chemokine receptor CXCR7 in CXCR4-expressing human 143B osteosarcoma cells enhances lung metastasis of intratibial xenografts in SCID mice

More effective treatment of metastasizing osteosarcoma with a current mean 5-year survival rate of less than 20% requires more detailed knowledge on mechanisms and key regulatory molecules of the complex metastatic process. CXCR4, the receptor of the chemokine CXCL12, has been reported to promote tumor progression and metastasis in osteosarcoma. CXCR7 is a recently deorphanized CXCL12-scavenging receptor with so far not well-defined functions in tumor biology. The present study focused on a potential malignancy enhancing function of CXCR7 in interaction with CXCR4 in osteosarcoma, which was investigated in an intratibial osteosarcoma model in SCID mice, making use of the human 143B osteosarcoma cell line that spontaneously metastasizes to the lung and expresses endogenous CXCR4. 143B osteosarcoma cells stably expressing LacZ (143B-LacZ cells) were retrovirally transduced with a gene encoding HA-tagged CXCR7 (143B-LacZ-X7-HA cells). 143B-LacZ-X7-HA cells co-expressing CXCR7 and CXCR4 exhibited CXCL12 scavenging and enhanced adhesion to IL-1β-activated HUVEC cells compared to 143B-LacZ cells expressing CXCR4 alone. SCID mice intratibially injected with 143B-LacZ-X7-HA cells had significantly (p<0.05) smaller primary tumors, but significantly (p<0.05) higher numbers of lung metastases than mice injected with 143B-LacZ cells. Unexpectedly, 143B-LacZ-X7-HA cells, unlike 143B-LacZ cells, also metastasized with high incidence to the auriculum cordis. In conclusion, expression of the CXCL12 scavenging receptor CXCR7 in the CXCR4-expressing human 143B osteosarcoma cell line enhances its metastatic activity in intratibial primary tumors in SCID mice that predominantly metastasize to the lung and thereby closely mimic the human disease. These findings point to CXCR7 as a target, complementary to previously proposed CXCR4, for more effective metastasis-suppressive treatment in osteosarcoma.

Fragment-based optimization of small molecule CXCL12 inhibitors for antagonizing the CXCL12/CXCR4 interaction

The chemokine CXCL12 and its G protein-coupled receptor (GPCR) CXCR4 are high-priority clinical targets because of their involvement in metastatic cancers (also implicated in autoimmune disease and cardiovascular disease). Because chemokines interact with two distinct sites to bind and activate their receptors, both the GPCRs and chemokines are potential targets for small molecule inhibition. A number of chemokines have been validated as targets for drug development, but virtually all drug discovery efforts focus on the GPCRs. However, all CXCR4 receptor antagonists with the exception of MSX-122 have failed in clinical trials due to unmanageable toxicities, emphasizing the need for alternative strategies to interfere with CXCL12/CXCR4-guided metastatic homing. Although targeting the relatively featureless surface of CXCL12 was presumed to be challenging, focusing efforts at the sulfotyrosine (sY) binding pockets proved successful for procuring initial hits. Using a hybrid structure-based in silico/NMR screening strategy, we recently identified a ligand that occludes the receptor recognition site. From this initial hit, we designed a small fragment library containing only nine tetrazole derivatives using a fragment-based and bioisostere approach to target the sY binding sites of CXCL12. Compound binding modes and affinities were studied by 2D NMR spectroscopy, X-ray crystallography, molecular docking and cell-based functional assays. Our results demonstrate that the sY binding sites are conducive to the development of high affinity inhibitors with better ligand efficiency (LE) than typical protein-protein interaction inhibitors (LE ≤ 0.24). Our novel tetrazole-based fragment 18 was identified to bind the sY21 site with a K(d) of 24 μM (LE = 0.30). Optimization of 18 yielded compound 25 which specifically inhibits CXCL12-induced migration with an improvement in potency over the initial hit 9. The fragment from this library that exhibited the highest affinity and ligand efficiency (11: K(d) = 13 μM, LE = 0.33) may serve as a starting point for development of inhibitors targeting the sY12 site.

Remote ischaemic preconditioning involves signalling through the SDF-1α/CXCR4 signalling axis

Ischaemic preconditioning is one of the most potent experimental modalities known to decrease infarct size after ischaemia and reperfusion. Much interest has been stimulated by the phenomenon of remote ischaemic conditioning (RIC), in which the preconditioning stimulus is applied to a limb remote from the heart to stimulate cardioprotection via an unidentified humoral factor, believed to be a protein between 3.5 and 15 kDa. Stromal cell-derived factor-1 (SDF-1α or CXCL12) is a chemokine of 10 kDa that is induced by hypoxia and recruits stem cells, but also exerts direct, acute, cardioprotection via its receptor, CXCR4. The serum dipeptidase DPPIV cleaves and inactivates SDF-1α. We measured SDF-1α in rat plasma and found it was significantly increased by RIC. DPPIV activity was unchanged after RIC, suggesting that increased synthesis or release or SDF-1α caused the increase in plasma levels. AMD3100, a highly specific inhibitor of CXCR4, was used to investigate the hypothesis that SDF-1α is involved in RIC. RIC in rats, which decreased infarct size from 53 ± 3 % to 27 ± 3 % (n = 6, P < 0.05), was blocked in rats treated with AMD3100 (40 ± 4 %). RIC also improved functional recovery of cardiac papillary muscle, and this, too, was blocked by AMD3100. Direct application of SDF-1α was confirmed to be protective in this model and was blocked by AMD3100. RIC stimulates SDF-1α release, and this 10-kDa peptide appears to be required for the mechanism of RIC.

Upregulated expression of C-X-C chemokine receptor 4 is an independent prognostic predictor for patients with gastric cancer

Aberrant chemokine (C-X-C motif) receptor CXCR4 expressions in malignant tissues have been reported, but its role in gastric cancer prognosis remains unknown. Our studies were designed to investigate the expression and prognostic significance of CXCR4 in patients with gastric cancer. CXCR4 expression was retrospectively analyzed by immunohistochemistry in 97 patients with gastric adenocarcinoma from China. Results were assessed for association with clinical features and overall survival by using Kaplan-Meier analysis. Prognostic values of CXCR4 expression and clinical outcomes were evaluated by Cox regression analysis. A molecular prognostic stratification scheme incorporating CXCR4 expression was determined by using receiver operating characteristic (ROC) analysis. The results show that CXCR4 predominantly localized in the cell membranes and cytoplasm. The protein level of CXCR4 was upregulation in gastric cancer tissues and upregulated expression of CXCR4 was only significantly associated with Lauren classification (P<0.001). Increased CXCR4 expression in gastric cancer tissues was positively correlated with poor overall survival of gastric cancer patients (P<0.001). Further multivariate Cox regression analysis suggested that intratumoral CXCR4 expression was an independent prognostic indicator for the disease. Applying the prognostic value of intratumoral CXCR4 density to TNM stage system showed a better prognostic value in patients with gastric cancer. In conclusion, intratumoral CXCR4 expression was recognized as an independent prognostic marker for the overall survival of patients with gastric cancer. On the basis of TNM stage, detection of CXCR4 expression will be helpful for predicting prognosis for patients with gastric cancer.

Physiology and pharmacology of plerixafor

Autologous hematopoietic stem cell (HSC) transplantation is an important therapeutic option for patients with non-Hodgkin's lymphoma and multiple myeloma. The primary source of HSC is from the peripheral blood which requires mobilization from the bone marrow. Current mobilization regimens include cytokines such as G-CSF and/or chemotherapy. However not all patients mobilize enough HSC to proceed to transplant. The chemokine receptor CXCR4 and its ligand CXCL12 are an integral part of the mechanism of HSC retention in the bone marrow niche. The discovery of plerixafor, a selective inhibitor of CXCR4, has provided a new additional means of mobilizing HSC for autologous transplantation. Plerixafor consists of two cyclam rings with a phenylenebis(methylene) linker. It inhibits CXCL12 binding to CXCR4 and subsequent downstream events including chemotaxis. The molecular interactions of plerixafor have been defined indicating a unique binding mode to CXCR4. Plerixafor rapidly mobilizes HSC within hours compared with the multi-day treatment required by G-CSF in mouse, dog and non-human primate. The mobilized cells once transplanted are capable of timely and endurable engraftment. Additionally CXCR4 has been implicated in the pathology of HIV, inflammatory disease and cancer and the pharmacology of plerixafor in various disease models is described.

Dancing with chemical formulae of antivirals: a personal account

A chemical structure is a joy forever, and this is how I perceived the chemical structures of a number of antiviral compounds with which I have been personally acquainted over the past 3 decades: (1) amino acid esters of acyclovir (i.e. valaciclovir); (2) 5-substituted 2'-deoxyuridines (i.e. brivudin); (3) 2',3'-dideoxynucleoside analogues (i.e. stavudine); (4) acyclic nucleoside phosphonates (ANPs) (i.e. cidofovir, adefovir); (5) tenofovir disoproxil fumarate (TDF) and drug combinations therewith; (6) tenofovir alafenamide (TAF, GS-7340), a new phosphonoamidate prodrug of tenofovir; (7) pro-prodrugs of PMEG (i.e. GS-9191 and GS-9219); (8) new ANPs: O-DAPy and 5-aza-C phosphonates; (9) non-nucleoside reverse transcriptase inhibitors (NNRTIs): HEPT and TIBO derivatives; and (10) bicyclam derivatives (i.e. AMD3100).

Mobilization of endogenous stem cell populations enhances fracture healing in a murine femoral fracture model

BACKGROUND AIMS

Delivery of bone marrow-derived stem and progenitor cells to the site of injury is an effective strategy to enhance bone healing. An alternate approach is to mobilize endogenous, heterogeneous stem cells that will home to the site of injury. AMD3100 is an antagonist of the chemokine receptor 4 (CXCR4) that rapidly mobilizes stem cell populations into peripheral blood. Our hypothesis was that increasing circulating numbers of stem and progenitor cells using AMD3100 will improve bone fracture healing.

METHODS

A transverse femoral fracture was induced in C57BL/6 mice, after which they were subcutaneously injected for 3 d with AMD3100 or saline control. Mesenchymal stromal cells, hematopoietic stem and progenitor cells and endothelial progenitor cells in the peripheral blood and bone marrow were evaluated by means of flow cytometry, automated hematology analysis and cell culture 24 h after injection and/or fracture. Healing was assessed up to 84 d after fracture by histomorphometry and micro-computed tomography.

RESULTS

AMD3100 injection resulted in higher numbers of circulating mesenchymal stromal cells, hematopoietic stem cells and endothelial progenitor cells. Micro-computed tomography data demonstrated that the fracture callus was significantly larger compared with the saline controls at day 21 and significantly smaller (remodeled) at day 84. AMD3100-treated mice have a significantly higher bone mineral density than do saline-treated counterparts at day 84.

CONCLUSIONS

Our data demonstrate that early cell mobilization had significant positive effects on healing throughout the regenerative process. Rapid mobilization of endogenous stem cells could provide an effective alternative strategy to cell transplantation for enhancing tissue regeneration.

Design of cell-permeable stapled peptides as HIV-1 integrase inhibitors

HIV-1 integrase (IN) catalyzes the integration of viral DNA into the host genome, involving several interactions with the viral and cellular proteins. We have previously identified peptide IN inhibitors derived from the α-helical regions along the dimeric interface of HIV-1 IN. Herein, we show that appropriate hydrocarbon stapling of these peptides to stabilize their helical structure remarkably improves the cell permeability, thus allowing inhibition of the HIV-1 replication in cell culture. Furthermore, the stabilized peptides inhibit the interaction of IN with the cellular cofactor LEDGF/p75. Cellular uptake of the stapled peptide was confirmed in four different cell lines using a fluorescein-labeled analogue. Given their enhanced potency and cell permeability, these stapled peptides can serve as not only lead IN inhibitors but also prototypical biochemical probes or "nanoneedles" for the elucidation of HIV-1 IN dimerization and host cofactor interactions within their native cellular environment.

Antiviral drug development--success and failure: a personal perspective with a Japanese connection

At the 25th International Conference on Antiviral Research, I received a special recognition for my contribution to the International Society of Antiviral Research over a period of 25 years (from 1987 until 2012). This review follows the theme of my presentation at that event, which comprised 10 reminiscences, all with a Japanese connection concerning the success, or otherwise, in the clinical development of: double- and single-stranded polynucleotides; suramin, a polysulfonate; dextran sulfate, a polysulfate; brivudin; BVaraU; 2',3'-dideoxynucleoside analogues; HEPT; adefovir and tenofovir; CXCR4 antagonists; and elvitegravir.

Benzenesulfonamides: a unique class of chemokine receptor type 4 inhibitors

The interaction of CXCR4 with CXCL12 (SDF-1) plays a critical role in cancer metastasis by facilitating the homing of tumor cells to metastatic sites. Based on our previously published work on CXCR4 antagonists, we have synthesized a series of aryl sulfonamides that inhibit the CXCR4/CXCL12 interaction. Analogue bioactivities were assessed with binding affinity and Matrigel invasion assays. Computer modeling was employed to evaluate a selection of the new analogues docked into the CXCR4 X-ray structure and to rationalize discrepancies between the affinity and Matrigel in vitro assays. A lead compound displays nanomolar potency in the binding affinity assay (IC(50)=8.0 nM) and the Matrigel invasion assay (100 % blockade of invasion at 10 nM). These data demonstrate that benzenesulfonamides are a unique class of CXCR4 inhibitors with high potency.

When human immunodeficiency virus meets chemokines and microglia: neuroprotection or neurodegeneration?

Chemokines are chemotactic cytokines that were originally discovered as promoters of leukocyte proliferation and mobility. In recent years, however, evidence has demonstrated constitutive expression of chemokines and chemokine receptors in a variety of cells in the central and peripheral nervous system and has proposed a role for chemokines in neurodegenerative diseases characterized by inflammation and microglia proliferation. In addition, chemokine receptors, and in particular CXCR4 and CCR5, mediate human immunodeficiency virus type 1 (HIV) infection of immunocompetent cells as well as microglia. Subsequently, HIV, through a variety of mechanisms, promotes synapto-dendritic alterations and neuronal loss that ultimately lead to motor and cognitive impairments. These events are accompanied by microglia activation. Nevertheless, a microglia-mediated mechanism of neuronal degeneration alone cannot fully explain some of the pathological features of HIV infected brain such as synaptic simplification. In this article, we present evidence that some of the microglia responses to HIV are beneficial and neuroprotective. These include the ability of microglia to release anti-inflammatory cytokines, to remove dying cells and to promote axonal sprouting.

An algorithm for utilizing peripheral blood CD34 count as a predictor of the need for plerixafor in autologous stem cell mobilization--cost-effectiveness analysis

Certain patients who receive granulocyte colony-stimulating factor (GCSF) for autologous hematopoietic stem cell (AHSC) collection fail to mobilize well enough to proceed with transplant. When plerixafor is used with GCSF, the likelihood of achieving the CD34⁺ stem cell target in fewer collections is higher; plerixafor use in all patients is unlikely to be cost-effective. This study retrospectively evaluated the effectiveness of utilizing a peripheral blood CD34⁺ stem cell count (PBCD34) ≤8/µL on day 4 of GCSF-based AHSC mobilization as a threshold for plerixafor administration, and compared the efficacy of collection and cost analysis using historical controls. All patients in the study cohort reached their CD34⁺ targets in ≤3 collections. Significantly more patients who received plerixafor + GCSF versus GCSF alone reached their CD34⁺ target in one collection (P = 0.045); however, there were no significant differences in the number of collections or in cumulative product yields. The historical cohort had 10.3% mobilization failures; the number of collections per patient needed to reach the target was significantly higher in the historical cohort versus study cohort (P = 0.001) as was the number of patients requiring more than one collection to reach their target (P = 0.023). However, the average cost per patient was also significantly higher in the study cohort (P = 0.025). Further refinement of the algorithm may reduce the difference in cost between the two mobilization strategies.

Real-time detection of the chemokine CXCL12 in urine samples by surface plasmon resonance

Surface plasmon resonance (SPR)-based biosensors are established tools for measuring biomolecular interactions between unlabeled analytes in real time, and are thus an ideal method to evaluate G protein-coupled receptor (GPCR) binding interactions. Using as a vehicle lentiviral particles bearing the chemokine receptor CXCR4 in its native plasma membrane context, SPR analysis can be performed using the particles as specific receptors to monitor the CXCR4 interaction with its ligand, CXCL12. The method shows linear correlation in the 5-40 nM range, with low intra- and inter-assay variation, a relative standard deviation <10%, chip-to-chip variation <12%, with stability of the sensor response for more than 150 measurements in the same chip over a four-week period. Our objective was to develop a method for rapid detection and quantification of analytes such as CXCL12 in biological samples, with no need for pretreatment. As a proof of concept, we tested for CXCL12 in urine samples from rheumatoid arthritis patients, who have elevated levels of this chemokine in plasma and synovial fluid. The biosensor method allowed sensitive, reproducible CXCL12 detection in the physiological range, suggesting its value for the diagnosis of autoimmune disorders.

Imaging CXCL12-CXCR4 signaling in ovarian cancer therapy

Chemokine CXCL12 and receptor CXCR4 have emerged as promising therapeutic targets for ovarian cancer, a disease that continues to have a dismal prognosis. CXCL12-CXCR4 signaling drives proliferation, survival, and invasion of ovarian cancer cells, leading to tumor growth and metastasis. Pleiotropic effects of CXCR4 in multiple key steps in ovarian cancer suggest that blocking this pathway will improve outcomes for patients with this disease. To quantify CXCL12-CXCR4 signaling in cell-based assays and living mouse models of ovarian cancer, we developed a click beetle red luciferase complementation reporter that detects activation of CXCR4 based on recruitment of the cytosolic adapter protein β-arrestin 2. Both in two-dimensional and three-dimensional cell cultures, we established that bioluminescence from this reporter measures CXCL12-dependent activation of CXCR4 and inhibition of this pathway with AMD3100, a clinically-approved small molecule that blocks CXCL12-CXCR4 binding. We used this imaging system to quantify CXCL12-CXCR4 signaling in a mouse model of metastatic ovarian cancer and showed that treatment with AMD3100 interrupted this pathway in vivo. Combination therapy with AMD3100 and cisplatin significantly decreased tumor burden in mice, although differences in overall survival were not significantly greater than treatment with either agent as monotherapy. These studies establish a molecular imaging reporter system for analyzing CXCL12-CXCR4 signaling in ovarian cancer, which can be used to investigate biology and therapeutic targeting of this pathway in cell-based assays and living mice.

The puzzling role of CXCR4 in human immunodeficiency virus infection

The human immunodeficiency virus type-1 (HIV-1) is the etiological agent of the acquired immunodeficiency syndrome (AIDS), a disease highly lethal in the absence of combination antiretroviral therapy. HIV infects CD4(+) cells of the immune system (T cells, monocyte-macrophages and dendritic cells) via interaction with a universal primary receptor, the CD4 molecule, followed by a mandatory interaction with a second receptor (co-receptor) belonging to the chemokine receptor family. Apart from some rare cases, two chemokine receptors have been evolutionarily selected to accomplish this need for HIV-1: CCR5 and CXCR4. Yet, usage of these two receptors appears to be neither casual nor simply explained by their levels of cell surface expression. While CCR5 use is the universal rule at the start of every infection regardless of the transmission route (blood-related, sexual or mother to child), CXCR4 utilization emerges later in disease coinciding with the immunological deficient phase of infection. Moreover, in most instances CXCR4 use as viral entry co-receptor is associated with maintenance of CCR5 use. Since antiviral agents preventing CCR5 utilization by the virus are already in use, while others targeting either CCR5 or CXCR4 (or both) are under investigation, understanding the biological correlates of this "asymmetrical" utilization of HIV entry co-receptors bears relevance for the clinical choice of which therapeutics should be administered to infected individuals. We will here summarize the basic knowledge and the hypotheses underlying the puzzling and yet unequivocal role of CXCR4 in HIV-1 infection.

CXCR4(+) dendritic cells promote angiogenesis during embryo implantation in mice

Early pregnancy is characterized by decidual adaption to the developing embryo involving angiogenesis and vascular growth. Failure of decidual vascular expansion is linked to diseases of pregnancy. Dendritic cells (DC) have been associated with vascular growth during early gestation, though it is unknown whether their capacity to modulate angiogenesis is ubiquitous to all DC subsets. Here, we show that DC normally found associated with the decidual vasculature co-express the C-X-C chemokine receptor type 4 (CXCR4). In addition, we demonstrate that impaired homing of CXCR4(+)DC during early gestation provoked a disorganized decidual vasculature with impaired spiral artery remodeling later in gestation. In contrast, adoptive transfer experiments provided evidence that CXCR4(+)DC are able to rescue early pregnancy by normalizing decidual vascular growth and delivery of pro-angiogenic factors, which results in adequate remodeling of the spiral arteries during placental development. Taken together, our results indicate an important role of CXCR4(+)DC in the regulation of decidual angiogenesis and highlight the importance of the CXCL12/CXCR4 pathway during this process, suggesting that this may represent a key pathway to evaluate during pregnancy pathologies associated with impaired vascular expansion.

Advances in stem cell mobilization

The use of mobilized peripheral blood stem cells (PBSCs) has largely replaced the use of bone marrow as a source of stem cells for both allogeneic and autologous stem cell transplantation. G-CSF with or without chemotherapy is the most commonly used regimen for stem cell mobilization. Some donors or patients, especially the heavily pretreated patients, fail to mobilize the targeted number of stem cells with this regimen. A better understanding of the mechanisms involved in hematopoietic stem cell (HSC) trafficking could lead to the development of newer mobilizing agents and therapeutic approaches. This review will cover the current methods for stem cell mobilization and recent developments in the understanding of the biology of stem cells and the bone marrow microenvironment.

Chemokine receptor trio: CXCR3, CXCR4 and CXCR7 crosstalk via CXCL11 and CXCL12

Although chemokines are well established to function in immunity and endothelial cell activation and proliferation, a rapidly growing literature suggests that CXC Chemokine receptors CXCR3, CXCR4 and CXCR7 are critical in the development and progression of solid tumors. The effect of these chemokine receptors in tumorigenesis is mediated via interactions with shared ligands I-TAC (CXCL11) and SDF-1 (CXCL12). Over the last decade, CXCR4 has been extensively reported to be overexpressed in most human solid tumors and has earned considerable attention toward elucidating its role in cancer metastasis. To enrich the existing armamentarium of anti-cancerous agents, many inhibitors of CXCL12-CXCR4 axis have emerged as additional or alternative agents for neo-adjuvant treatments and even many of them are in preclinical and clinical stages of their development. However, the discovery of CXCR7 as another receptor for CXCL12 with rather high binding affinity and recent reports about its involvement in cancer progression, has questioned the potential of "selective blockade" of CXCR4 as cancer chemotherapeutics. Interestingly, CXCR7 can also bind another chemokine CXCL11, which is an established ligand for CXCR3. Recent reports have documented that CXCR3 and their ligands are overexpressed in different solid tumors and regulate tumor growth and metastasis. Therefore, it is important to consider the interactions and crosstalk between these three chemokine receptors and their ligand mediated signaling cascades for the development of effective anti-cancer therapies. Emerging evidence also indicates that these receptors are differentially expressed in tumor endothelial cells as well as in cancer stem cells, suggesting their direct role in regulating tumor angiogenesis and metastasis. In this review, we will focus on the signals mediated by this receptor trio via their shared ligands and their role in tumor growth and progression.

CXCR4 expression predicts early liver recurrence and poor survival after resection of pancreatic adenocarcinoma

OBJECTIVES

Liver metastasis develops in 60% of patients after resection of pancreatic adenocarcinoma (PAC) and carries a dismal prognosis, but factors predictive of liver recurrence are poorly understood. Experimental evidence suggests that liver metastasis of PAC is mediated by CXCL12/CXCR4 signaling and can be inhibited by CXCR4 antagonist. We aimed to verify whether CXCR4 expression predicts early liver recurrence and poor survival after resection, and to explore the usefulness of CXCR4 status for prognosis prediction.

METHODS

Ninety-seven consecutive PAC patients undergoing R0 resection were analyzed. CXCR4 expression was analyzed by immunohistochemistry, and its associations with liver recurrence-free survival and overall survival were analyzed by Kaplan-Meier estimates and multivariable Cox and accelerated failure time regression models.

RESULTS

CXCR4-positive patients had a worse prognosis than CXCR4-negative patients, with a shorter liver recurrence-free survival (median: 8.7 vs. 39.7 months; P=0.004) and overall survival (median: 10.2 vs. 22.3 months; P<0.001). Overall survival for CXCR4-positive stage IIa patients was similar to that for stage IIb patients and significantly shorter than that for CXCR4-negative stage IIa patients (median: 9.7 vs. 27.4 months; P=0.002). CXCR4 positivity was significantly associated with liver recurrence (adjusted hazard ratio 2.22, 95% confidence interval (CI) 1.15-4.30; P=0.018) and predicted a 46% (95% CI 9-68%) and 35% (95% CI 7-54%) reduction in liver recurrence-free survival and overall survival, respectively.

CONCLUSIONS

Tumor CXCR4 expression independently predicts early liver recurrence and poor overall survival after resection of PAC. CXCR4 status stratifies stage IIa patients into two groups with a striking difference in prognosis.

The lymphotactin receptor is expressed in epithelial ovarian carcinoma and contributes to cell migration and proliferation

Chemokine receptor-ligand interactions are important to support functioning of both normal and pathologic cells. The expression and function of chemokine receptors in epithelial ovarian carcinoma (EOC) is largely unknown. Here, we report that the lymphotactin receptor (XCR1) was expressed in primary and metastatic human epithelial ovarian carcinoma (EOC) specimens and cell lines. In contrast, expression of XCR1 was not detected in the normal ovary or in human normal ovarian surface epithelial cells. Our data indicate that XCL1 and XCL2 are either present in the malignant ascites or expressed by the ovarian carcinoma cells. The addition of lymphotactin (XCL1 and XCL2) stimulated migration and proliferation of XCR1-positive cells. Reduction of XCR1 expression in ovarian carcinoma cell line SKOV-3 resulted in abrogated diaphragm and peritoneal wall tumor formation and in reduced frequency of colonic, splenetic, and liver nodules in an in vivo xenograft mouse model. Taken together, our data suggest that XCR1 is expressed early during the course of tumorigenic transformation and contributes towards increased cell migration and proliferation, which can facilitate the prometastatic behavior of EOC cells.

Dual-function CXCR4 antagonist polyplexes to deliver gene therapy and inhibit cancer cell invasion

A bicyclam-based biodegradable polycation with CXCR4 antagonistic activity was developed with potential for combined drug/gene cancer therapies. The dual-function polycation prevents cancer cell invasion by inhibiting CXCL12 stimulated CXCR4 activation, while at the same time efficiently and safely delivers plasmid DNA into cancer cells.

Pharmacological modulation of chemokine receptor function

G protein-coupled chemokine receptors and their peptidergic ligands are interesting therapeutic targets due to their involvement in various immune-related diseases, including rheumatoid arthritis, multiple sclerosis, inflammatory bowel disease, chronic obstructive pulmonary disease, HIV-1 infection and cancer. To tackle these diseases, a lot of effort has been focused on discovery and development of small-molecule chemokine receptor antagonists. This has been rewarded by the market approval of two novel chemokine receptor inhibitors, AMD3100 (CXCR4) and Maraviroc (CCR5) for stem cell mobilization and treatment of HIV-1 infection respectively. The recent GPCR crystal structures together with mutagenesis and pharmacological studies have aided in understanding how small-molecule ligands interact with chemokine receptors. Many of these ligands display behaviour deviating from simple competition and do not interact with the chemokine binding site, providing evidence for an allosteric mode of action. This review aims to give an overview of the evidence supporting modulation of this intriguing receptor family by a range of ligands, including small molecules, peptides and antibodies. Moreover, the computer-assisted modelling of chemokine receptor-ligand interactions is discussed in view of GPCR crystal structures. Finally, the implications of concepts such as functional selectivity and chemokine receptor dimerization are considered.

Noninvasive imaging reveals inhibition of ovarian cancer by targeting CXCL12-CXCR4

Patients with metastatic ovarian cancer continue to have a dismal prognosis, emphasizing the need for new strategies to identify and develop new molecular targets for therapy. Chemokine CXCL12 and its receptor CXCR4 are upregulated in metastatic ovarian cancer cells and the intraperitoneal tumor microenvironment. CXCL12-CXCR4 signaling promotes multiple steps in proliferation and dissemination of ovarian cancer cells, suggesting that targeted inhibition of this pathway will limit tumor progression. To investigate CXCL12-CXCR4 signaling in ovarian cancer and establish effects of inhibiting this pathway on tumor progression and survival, we designed a Gaussia luciferase complementation imaging reporter system to detect CXCL12 binding to CXCR4 in ovarian cancer cells. In cell-based assays, we established that the complementation imaging reporter could detect CXCL12 binding to CXCR4 and quantify specific inhibition of ligand-receptor interaction. We monitored CXCL12-CXCR4 binding and inhibition in a mouse xenograft model of metastatic human ovarian cancer by imaging Gaussia luciferase complementation and assessed tumor progression with firefly luciferase. Bioluminescence imaging studies in living mice showed that treatment with AMD3100, a clinically approved inhibitor of CXCL12-CXCR4, blocked ligand-receptor binding and reduced growth of ovarian cancer cells. Treatment with AMD3100 also modestly improved overall survival of mice with metastatic ovarian cancer. The Gaussia luciferase complementation imaging reporter system will facilitate further preclinical development and optimization of CXCL12-CXCR4 targeted compounds for treatment of ovarian cancer. Our research supports clinical translation of existing CXCR4 inhibitors for molecular therapy for ovarian cancer.

Development of a unique small molecule modulator of CXCR4

Background

Metastasis, the spread and growth of tumor cells to distant organ sites, represents the most devastating attribute and plays a major role in the morbidity and mortality of cancer. Inflammation is crucial for malignant tumor transformation and survival. Thus, blocking inflammation is expected to serve as an effective cancer treatment. Among anti-inflammation therapies, chemokine modulation is now beginning to emerge from the pipeline. CXC chemokine receptor-4 (CXCR4) and its ligand stromal cell-derived factor-1 (CXCL12) interaction and the resulting cell signaling cascade have emerged as highly relevant targets since they play pleiotropic roles in metastatic progression. The unique function of CXCR4 is to promote the homing of tumor cells to their microenvironment at the distant organ sites.

Methodology/Principal Findings

We describe the actions of N,N′-(1,4-phenylenebis(methylene))dipyrimidin-2-amine (designated MSX-122), a novel small molecule and partial CXCR4 antagonist with properties quite unlike that of any other reported CXCR4 antagonists, which was prepared in a single chemical step using a reductive amination reaction. Its specificity toward CXCR4 was tested in a binding affinity assay and a ligand competition assay using ¹⁸F-labeled MSX-122. The potency of the compound was determined in two functional assays, Matrigel invasion assay and cAMP modulation. The therapeutic potential of MSX-122 was evaluated in three different murine models for inflammation including an experimental colitis, carrageenan induced paw edema, and bleomycin induced lung fibrosis and three different animal models for metastasis including breast cancer micrometastasis in lung, head and neck cancer metastasis in lung, and uveal melanoma micrometastasis in liver in which CXCR4 was reported to play crucial roles.

Conclusions/Significance

We developed a novel small molecule, MSX-122, that is a partial CXCR4 antagonist without mobilizing stem cells, which can be safer for long-term blockade of metastasis than other reported CXCR4 antagonists.

Plerixafor plus granulocyte-colony stimulating factor for autologous hematopoietic stem cell mobilization in patients with metastatic neuroblastoma

Current therapies for high-risk neuroblastoma (NB) necessitate the availability of several aliquots of autologous peripheral blood stem cells to reverse-associated myelosuppression. Priming with the CXCR4 inhibitor plerixafor plus G-CSF was associated with successful stem cell harvest in 5/7 heavily prior-treated patients with stage 4 NB who had previously failed G-CSF priming. Minimal residual disease was not detected in harvested cells from any patient despite the presence of disease in bone/bone marrow in 6/7. Hematopoietic reconstitution was achieved in all three patients receiving plerixafor-primed stem cells after myeloablative therapy. Plerixafor is an effective and safe agent for stem cell collection in patients with NB.

Development of novel CXCR4-based therapeutics

INTRODUCTION

During embryogenesis, CXCR4, a chemokine receptor, and its ligand, stromal cell-derived factor-1 (SDF-1/CXCL12), are critically involved in the development of the hematopoietic, nerve and endothelial tissues by regulating tissue progenitor cell migration, homing and survival. In adult life, the CXCR4 axis serves as the key factor for stem and immune cell trafficking. More importantly, CXCR4-CXCL12 axis plays a critical role in HIV, stem cell mobilization, autoimmune diseases, cancer and tissue regeneration. Targeting the CXCR4-CXCL12 axis, therefore, is an attractive therapeutic approach in various diseases.

AREAS COVERED

In this review, we update current knowledge about CXCR4-CXCL12 biology, therapeutic approaches and therapeutic agents. The data presented was collected from http://www.ncbi.nlm.nih.gov/pubmed , http://clinicaltrials.gov/ , http://bloodjournal.hematologylibrary.org/ .

EXPERT OPINION

Development of CXCR4 antagonists with increased affinity, extended pharmacokinetics and/or pharmacodynamics and with the capacity to differentially target CXCR4 may lead to a development of novel therapeutics for HIV, cancer, tissue regeneration and stem cell collection.

Cellular therapies supplement: strategies for improving transplant efficiency in the context of cellular therapeutics

The field of hematopoietic stem cell transplantation (HSCT) has overcome many obstacles that have led to our current clinical ability to utilize cells collected from marrow, mobilized peripheral blood, or umbilical cord blood for the treatment of malignant and nonmalignant hematologic diseases. It is in this context that it becomes evident that future progress will lie in our development of an understanding of the biology by which the process of HSCT is regulated. By understanding the cellular components and the mechanisms by which HSCT is either enhanced or suppressed it will then be possible to design therapeutic strategies to improve rates of engraftment that will have a positive impact on immune reconstitution post-HSCT. In this review we focus primarily on allogeneic hematopoietic stem cell transplantation (allo-HSCT), the current challenges associated with allo-HSCT, and some developing strategies to improve engraftment in this setting.