The synergistic effects of CXCR4 and EGFR on promoting EGF-mediated metastasis in ovarian cancer cells

CXC chemokine receptor 4 (CXCR4) is a cell surface receptor that has been reported to mediate the metastasis of many solid tumors including ovarian, breast, lung and prostate. The over-expression of the epidermal growth factor receptor (EGFR) is associated with the majority of ovarian cancer and has been implicated in the process of malignant transformation by promoting cell proliferation, survival, and motility. In this research, the result first showed that epidermis growth factor (EGF) enhanced the expression of CXCR4 and the migration of ovarian cancer cells, moreover, both stromal cell derived factor-1alpha (SDF-1alpha) and EGF-induced high matrix metallopeptidase 9 (MMP9) expressions. Molecular analysis indicated that augmented CXCR4 and MMP9 expression was regulated by phosphatidylinositol-3-kinase(PI3K)/Akt signal transduction pathway. These results suggested a possible important "cross-talk" between CXCR4 and EGFR intracellular pathways that might link signals of tumor deteriorated and provided a plausible explanation for the poor overall survival rate of patients whose co-expression of CXCR4 and EGFR was detected in their tissue sections. It enlightened that, compared to the respective inhibition of the EGFR or CXCR4 signaling, the simultaneous inhibition of them might be a more useful therapeutic strategy of cancer.     

Imaging agents for the chemokine receptor 4 (CXCR4)

The interaction between the chemokine receptor 4 (CXCR4) and stromal cell-derived factor-1 (SDF-1, also known as CXCL12) is a natural regulatory process in the human body. However, CXCR4 over-expression is also found in diseases such as cancer, where it plays a role in, among others, the metastatic spread. For this reason it is an interesting biomarker for the field of diagnostic oncology, and therefore, it is gaining increasing interest for applications in molecular imaging. Especially "small-molecule" imaging agents based on T140, FC131 and AMD3100 have been extensively studied. SDF-1, antibodies, pepducins and bioluminescence have also been used to visualize CXCR4. In this critical review reported CXCR4 targeting imaging agents are described based on their affinity, specificity and biodistribution. The level wherein CXCR4 is up-regulated in cancer patients and its relation to the different cell lines and animal models used to evaluate the efficacy of the imaging agents is also discussed (221 references).     

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

Giving a one-two punch: A bicyclam-based biodegradable polycation with CXCR4 antagonistic activity shows potential for combining cancer chemotherapy with gene therapy or siRNA therapy. This dual-function polycation prevents cancer cell invasion by inhibiting CXCL12-stimulated CXCR4 activation, while at the same time efficiently and safely delivering therapeutic DNA into cancer cells.     

A synthetic heparan sulfate-mimetic peptide conjugated to a mini CD4 displays very high anti- HIV-1 activity independently of coreceptor usage

The HIV-1 envelope gp120, which features both the virus receptor (CD4) and coreceptor (CCR5/CXCR4) binding sites, offers multiple sites for therapeutic intervention. However, the latter becomes exposed, thus vulnerable to inhibition, only transiently when the virus has already bound cellular CD4. To pierce this defense mechanism, we engineered a series of heparan sulfate mimicking tridecapeptides and showed that one of them target the gp120 coreceptor binding site with μM affinity. Covalently linked to a CD4-mimetic that binds to gp120 and renders the coreceptor binding domain available to be targeted, the conjugated tridecapeptide now displays nanomolar affinity for its target. Using solubilized coreceptors captured on top of sensorchip we show that it inhibits gp120 binding to both CCR5 and CXCR4 and in peripheral blood mononuclear cells broadly inhibits HIV-1 replication with an IC(50) of 1 nM.     

Selective addition of CXCR3+CCR4-CD4+ Th1 cells enhances generation of cytotoxic T cells by dendritic cells in vitro

Increasing importance is being given to the stimulation of Th1 response in cancer immunotherapy because its presence can shift the direction of adaptive immune responses toward protective immunity. Based on chemokine receptor expression, CXCR3⁺CCR4^-CD4⁺ T cells as Th1-type cells were investigated its capacity in monocyte-derived dendritic cell (DC) maturation and polarization, and induction of antigen specific cytotoxic T lymphocytes (CTL) in vitro. The levels of IL-4, IL-5 and IL-10 were decreased to the basal level compared with high production of IFN-γ, TNF-α, and IL-2 in CXCR3⁺CCR4^-CD4⁺ T cells stimulated with anti-CD3 and anti-CD28 antibodies. Co-incubation of activated CD4⁺ or CXCR3⁺CCR4^-CD4⁺ T cells with DC (CD4⁺/DC or CXCR3⁺CD4⁺/DC, respectively) particularly up-regulated IL-12 and CD80 expression compared with DC matured with TNF-α and LPS (mDC). Although there was no significant difference between the effects of the CXCR3⁺CCR4^-CD4⁺ and CD4⁺ T cells on DC phenotype expression, CXCR3⁺CD4⁺/DC in CTL culture were able to expand number of CD8⁺ T cells and increased frequencies of IFN-γ secreting cells and overall cytolytic activity against tumor antigen WT-1. These results demonstrated that the selective addition of CXCR3⁺CCR4^-CD4⁺ T cells to CTL cultures could enhance the induction of CTLs by DC in vitro, and implicated on a novel strategy for adoptive T cell therapy.     

Application of affinity selection-mass spectrometry assays to purification and affinity-based screening of the chemokine receptor CXCR4

Affinity selection-mass spectrometry (AS-MS) is a sensitive technology for identifying small molecules that bind to target proteins, and assays enabled by AS-MS can be used to delineate relative binding affinities of ligands for proteins. 'Indirect' AS-MS assays employ size-exclusion techniques to separate target-ligand complexes from unbound ligands, and target-associated ligands are then specifically detected by liquid chromatography mass spectrometry. We report how indirect AS-MS binding assays with known reference control compounds were used as guideposts for development of an optimized purification method for CXCR4, a G-protein coupled chemokine receptor, for which we sought novel antagonists. The CXCR4 purification method that was developed was amenable to scale-up and enabled the screening of purified recombinant human CXCR4 against a large combinatorial library of small molecules by high throughput indirect AS-MS. The screen resulted in the discovery of new ligands that competed off binding of reference compounds to CXCR4 in AS-MS binding assays and that antagonized SDF1α-triggered responses and CXCR4-mediated HIV1 viral uptake in cell-based assays. This report provides a methodological paradigm whereby indirect AS-MS-based ligand binding assays may be used to guide optimal integral membrane protein purification methods that enable downstream affinity selection-based applications such as high throughput AS-MS screens.     

A CXCR4‐Targeted Site‐Specific Antibody–Drug Conjugate

A chemically defined anti‐CXCR4–auristatin antibody–drug conjugate (ADC) was synthesized that selectively eliminates tumor cells overexpressing the CXCR4 receptor. The unnatural amino acid p‐acetylphenylalanine (pAcF) was site‐specifically incorporated into an anti‐CXCR4 immunoglobulin G (IgG) and conjugated to an auristatin through a stable, non‐cleavable oxime linkage to afford a chemically homogeneous ADC. The full‐length anti‐CXCR4 ADC was selectively cytotoxic to CXCR4⁺ cancer cells in vitro (half maximal effective concentration (EC₅₀)≈80–100 pM ). Moreover, the anti‐CXCR4 ADC eliminated pulmonary lesions from human osteosarcoma cells in a lung‐seeding tumor model in mice. No significant overt toxicity was observed but there was a modest decrease in the bone‐marrow‐derived CXCR4⁺ cell population. Because CXCR4 is highly expressed in a majority of metastatic cancers, a CXCR4–auristatin ADC may be useful for the treatment of a variety of metastatic malignancies.     

Inhibitory effect of CXC chemokine receptor 4 antagonist AMD3100 on bleomycin induced murine pulmonary fibrosis

CXC chemokine receptor 4 (CXCR4), which binds the stromal cell-derived factor-1 (SDF-1), has been shown to play a critical role in mobilizing the bone marrow (BM)-derived stem cells and inflammatory cells. We studied the effects of AMD3100, CXCR4 antagonist, on a murine bleomycin-induced pulmonary fibrosis model. Treatment of mice with AMD3100 in bleomycin-treated mice resulted in the decrease of SDF-1 in bronchoalveolar lavage (BAL) fluids at an early stage and was followed by the decrease of fibrocytes in the lung. AMD3100 treatment decreased the SDF-1 mRNA expression, fibrocyte numbers in the lung at an early stage (day 3) and CXCR4 expression at the later stage (day 7 and 21) after bleomycin injury. The collagen content and pulmonary fibrosis were significantly attenuated by AMD3100 treatment in later stage of bleomycin injury. AMD3100 treatment also decreased the murine mesenchymal and hematopoietic stem cell chemotaxis when either in the stimulation with bleomycin treated lung lysates or SDF-1 in vitro. In BM stem cell experiments, the phosphorylation of p38 MAPK which was induced by SDF-1 was significantly blocked by addition of AMD3100. Our data suggest that AMD3100 might be effective in preventing the pulmonary fibrosis by inhibiting the fibrocyte mobilization to the injured lung via blocking the SDF-1/CXCR4 axis.     

Enhancement of the T140-based pharmacophores leads to the development of more potent and bio-stable CXCR4 antagonists

A CXCR4 antagonistic peptide, T140, and its bio-stable analogs, such as Ac-TE14011, were previously developed. These peptides inhibit the entry of T cell line-tropic strains of HIV-1 (X4-HIV-1) into T cells. Herein, a series of TE14011 analogs having modifications in the N-terminal region were synthesized to develop effective compounds with increased biostability. Among these analogs, 4F-benzoyl-TE14011 (TF14013) showed the strongest anti-HIV activity derived from CXCR4-antagonism, suggesting that a 4-fluorobenzoyl moiety at the N-terminus of T140 analogs constitutes a novel T140-based pharmacophore for CXCR4 antagonists. Structure-activity relationship (SAR) studies on TE14011 analogs with N(alpha)-acylation by several benzoic acid derivatives have disclosed a significant relationship between the anti-HIV activity and the Hammett constant (sigma) of substituted benzoic acids. TF14013 was found to be stable in mouse serum, but not completely stable in rat liver homogenate due to deletion of the C-terminal Arg14-NH2 from the parent peptide. This biodegradation was completely suppressed by N-alkyl-amidation at the C-terminus. Taken together, the enhancement of the T140-based pharmacophores led to development of a novel CXCR4 antagonist, 4F-benzoyl-TE14011-Me (TF14013-Me), which has very high anti-HIV activity and increased biostability.     

Direct interaction between an allosteric agonist pepducin and the chemokine receptor CXCR4

Cell surface heptahelical G protein-coupled receptors (GPCRs) mediate critical cellular signaling pathways and are important pharmaceutical drug targets. (1) In addition to traditional small-molecule approaches, lipopeptide-based GPCR-derived pepducins have emerged as a new class of pharmaceutical agents. (2, 3) To better understand how pepducins interact with targeted receptors, we developed a cell-based photo-cross-linking approach to study the interaction between the pepducin agonist ATI-2341 and its target receptor, chemokine C-X-C-type receptor 4 (CXCR4). A pepducin analogue, ATI-2766, formed a specific UV-light-dependent cross-link to CXCR4 and to mutants with truncations of the N-terminus, the known chemokine docking site. These results demonstrate that CXCR4 is the direct binding target of ATI-2341 and suggest a new mechanism for allosteric modulation of GPCR activity. Adaptation and application of our findings should prove useful in further understanding pepducin modulation of GPCRs as well as enable new experimental approaches to better understand GPCR signal transduction.     

An Ultra‐High Fluorescence Enhancement and High Throughput Assay for Revealing Expression and Internalization of Chemokine Receptor CXCR4

Revealing chemokine receptor CXCR4 expression, distribution, and internalization levels in different cancers helps to evaluate cancer progression or prognosis and to set personalized treatment strategy. We here describe a sensitive and high‐throughput immunoassay for determining CXCR4 expression and distribution in cancer cells. The assay is accessible to a wide range of users in an ordinary lab only by dip‐coating poly(styrene‐co‐N‐isopropylacrylamide) spheres on the glass substrate. The self‐ assembled spheres form three‐dimensional photonic colloidal crystals which enhance the fluorescence of CF647 and Alexa Fluor 647 by a factor of up to 1000. CXCR4 in cells is detected by using the sandwich immunoassay, where the primary antibody recognizes CXCR4 and the secondary antibody is labeled with CF647. With the newly established assay, we quantified the total expression of CXCR4, its distribution on the cell membrane and cytoplasm, and revealed their internalization level upon SDF‐1α activation in various cancer cells, even for those with extremely low expression level.     

Development of a linear type of low molecular weight CXCR4 antagonists based on T140 analogs

A linear type of several low molecular weight CXCR4 antagonists were developed based on T140 analogs, which were previously found to be strong CXCR4 antagonists that block X4-HIV-1 entry and have inhibitory activities against cancer metastasis/progression and rheumatoid arthritis.     

Ligand-guided optimization of CXCR4 homology models for virtual screening using a multiple chemotype approach

CXCR4 is a G-protein coupled receptor for CXCL12 that plays an important role in human immunodeficiency virus infection, cancer growth and metastasization, immune cell trafficking and WHIM syndrome. In the absence of an X-ray crystal structure, theoretical modeling of the CXCR4 receptor remains an important tool for structure–function analysis and to guide the discovery of new antagonists with potential clinical use. In this study, the combination of experimental data and molecular modeling approaches allowed the development of optimized ligand-receptor models useful for elucidation of the molecular determinants of small molecule binding and functional antagonism. The ligand-guided homology modeling approach used in this study explicitly re-shaped the CXCR4 binding pocket in order to improve discrimination between known CXCR4 antagonists and random decoys. Refinement based on multiple test-sets with small compounds from single chemotypes provided the best early enrichment performance. These results provide an important tool for structure-based drug design and virtual ligand screening of new CXCR4 antagonists.     

Disulfide Bond Replacement with 1,4- and 1,5-Disubstituted [1,2,3]-Triazole on C-X-C Chemokine Receptor Type 4 (CXCR4) Peptide Ligands: Small Changes that Make Big Differences

Here we investigated the structural and biological effects ensuing from the disulfide bond replacement of a potent and selective C-X-C chemokine receptor type 4 (CXCR4) peptide antagonist, with 1,4- and 1,5- disubstituted 1,2,3-triazole moieties. Both strategies produced candidates that showed high affinity and selectivity against CXCR4. Notably, when assessed for their ability to modulate the CXCL12-mediated cell migration, the 1,4-triazole variant conserved the antagonistic effect in the low-mid nanomolar range, while the 1,5-triazole one displayed the ability to activate the migration, becoming the first in class low-molecular-weight CXCR4 peptide agonist. By combining NMR and computational studies, we provided a valuable model that highlighted differences in the interactions of the two peptidomimetics with the receptor that could account for their different functional profile. Finally, we envisage that our findings could be translated to different GPCR-interacting peptides for the pursuit of novel chemical probes that could assist in dissecting the complex puzzle of this fundamental class of transmembrane receptors.     

CXCR4 Stimulates Macropinocytosis: Implications for Cellular Uptake of Arginine-Rich Cell-Penetrating Peptides and HIV

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Highlights? CXCR4 was identified as a receptor to stimulate cellular uptake of R12 peptide ? Interaction with R12 stimulates internalization of CXCR4 via macropinocytosis ? SDF-1α and HIV-1 gp120 protein also induce macropinocytosis ? Macropinocytic uptake of HIV-1 diminished the infection of host cells     

Bivalent ligands of CXCR4 with rigid linkers for elucidation of the dimerization state in cells

To date, challenges in the design of bivalent ligands for G protein-coupled receptors (GPCRs) have revealed difficulties stemming from lack of knowledge of the state of oligomerization of the GPCR. The synthetic bivalent ligands with rigid linkers that are presented here can predict the dimer form of CXCR4 and be applied to molecular probes in cancerous cells. This "molecular ruler" approach would be useful in elucidating the details of CXCR4 oligomer formation.     

In vitro migration capacity of human adipose tissue-derived mesenchymal stem cells reflects their expression of receptors for chemokines and growth factors

The homing properties of adipose tissue-derived mesenchymal stem cells (AdMSCs) have stimulated intravenous applications for their use in stem cell therapy. However, the soluble factors and corresponding cellular receptors responsible for inducing chemotaxis of AdMSCs have not yet been reported. In the present study, the migration capacity of human AdMSCs (hAdMSCs) toward various cytokines or growth factors (GFs) and the expression of their receptors were determined. In a conventional migration assay, PDGF-AB, TGF-β1, and TNF-α showed the most effective chemoattractant activity. When AdMSCs were preincubated with various chemokines or GF, and then allowed to migrate toward medium containing 10% FBS, those preincubated with TNF-α showed the highest migratory activity. Next, hAdMSCs were either preincubated or not with TNF-α, and allowed to migrate in response to various GFs or chemokines. Prestimulation with TNF-α increased the migration activity of hAdMSCs compared to unstimulated hAdMSCs. When analyzed by FACS and RT-PCR methods, hAdMSCs were found to express C-C chemokine receptor type 1 (CCR1), CCR7, C-X-C chemokine receptor type 4 (CXCR4), CXCR5, CXCR6, EGF receptor, fibroblast growth factor receptor 1, TGF-β receptor 2, TNF receptor superfamily member 1A, PDGF receptor A and PDGF receptor B at both the protein and the mRNA levels. These results indicate that the migration capacity of hAdMSCs is controlled by various GFs and chemokines. Prior in vitro modulation of the homing capacity of hAdMSCs could stimulate their movement into injured sites in vivo when administered intravenously, thereby improving their therapeutic potential.     

CXCR4 inhibition suppresses Cd-induced renal oxidative stress,apoptosis, and fibrosis by inhibiting the TGF-β1/Smad pathway

This study aimed to investigate the role and mechanism of CXC chemokine receptor 4 (CXCR4) in cadmium (Cd)-induced renal injury. CXCR4 and TGF-β1/Smad pathway protein levels were detected by western blotting. Indicators related to renal function and oxidative stress factors were assessed and reactive oxygen species (ROS) level was evaluated by staining. TUNEL was used to measure apoptosis rate. PAS and Masson's trichrome staining were used to detect the level of renal fibrosis. The expression of Bcl-2, Bax, Cleaved-caspase 3, fibronectin, and collagen I proteins were detected by western blotting, immunohistochemistry, or immunofluorescence. The expression of CXCR4 was increased in a Cd-induced chronic renal injury model in rats. Si-CXCR4 decreased levels of TGF-β1, TGF-βR1, p-Smad2/Smad2, p-Smad3/Smad3, the renal weight index, urine protein, blood urea nitrogen, blood creatinine, and levels of MDA but raised the levels of SOD and GSH-Px. In addition, si-CXCR4 inhibited apoptosis in Cd-treated rats. CXCR4 inhibition alleviated fibrosis levels in Cd-treated rats. In Cd-treated cells, TGF-β attenuated the suppressive effect of CXCR4 inhibition on the TGF-β1/Smad pathway. TGF-β intervention increased MDA and ROS, and downregulated SOD and GSH-Px. TGF-β attenuated the inhibitory effect of CXCR4 on apoptosis and fibrosis. CXCR4 inhibition decreased levels of Cd-induced renal oxidative stress, apoptosis, and fibrosis by inhibiting the TGF-β1/Smad pathway.     

Synthesis and Anti-HIV Activity of a Novel Series of Isoquinoline-Based CXCR4 Antagonists

An expansion of the structure–activity relationship study of CXCR4 antagonists led to the synthesis of a series of isoquinolines, bearing a tetrahydroquinoline or a 3-methylpyridinyl moiety as head group. All compounds were investigated for CXCR4 affinity and antagonism in competition binding and calcium mobilization assays, respectively. In addition, the anti-HIV activity of all analogues was determined. All compounds showed excellent activity, with compound 24c being the most promising one, since it displayed consistently low nanomolar activity in the various assays.     

Comparison of ligand-based and receptor-based virtual screening of HIV entry inhibitors for the CXCR4 and CCR5 receptors using 3D ligand shape matching and ligand-receptor docking

HIV infection is initiated by fusion of the virus with the target cell through binding of the viral gp120 protein with the CD4 cell surface receptor protein and the CXCR4 or CCR5 co-receptors. There is currently considerable interest in developing novel ligands that can modulate the conformations of these co-receptors and, hence, ultimately block virus-cell fusion. This article describes a detailed comparison of the performance of receptor-based and ligand-based virtual screening approaches to find CXCR4 and CCR5 antagonists that could potentially serve as HIV entry inhibitors. Because no crystal structures for these proteins are available, homology models of CXCR4 and CCR5 have been built, using bovine rhodopsin as the template. For ligand-based virtual screening, several shape-based and property-based molecular comparison approaches have been compared, using high-affinity ligands as query molecules. These methods were compared by virtually screening a library assembled by us, consisting of 602 known CXCR4 and CCR5 inhibitors and some 4700 similar presumed inactive molecules. For each receptor, the library was queried using known binders, and the enrichment factors and diversity of the resulting virtual hit lists were analyzed. Overall, ligand-based shape-matching searches yielded higher enrichments than receptor-based docking, especially for CXCR4. The results obtained for CCR5 suggest the possibility that different active scaffolds bind in different ways within the CCR5 pocket.