CXCR4 as a novel target in immunology: moving away from typical antagonists

Decoding the function of cancer-associated fibroblasts in osteosarcoma: Molecular pathways, therapeutic approaches and prognostic significance

Herein, we summarize the latest insights into osteosarcoma, the most prevalent primary malignant bone tumor, known for its aggressive nature, poor outcome, and especially poor prognosis when metastasis develops. Given recent research implicating the crucial role of the tumor microenvironment (TME) in osteosarcoma progression, cancer-associated fibroblasts (CAFs) emerged as key players. Through the secretion of cytokines, remodeling of the extracellular matrix (ECM), and cross-talk with osteosarcoma cells, CAFs collectively promote tumor growth, metastasis, and immune evasion. Exosomes derived from CAFs, which could also serve as important mediators of osteosarcoma progression, have been found to transport oncogenic lncRNAs like SNHG17 and linc00881. Moreover, some subtypes of CAFs, such as TOP2A + CAFs, have shown significant prognostic value for tumor aggressiveness. Thus, targeted CAFs was identified as a promising therapeutic modality, with strategies such as fibroblast activation protein (FAP) inhibition, TGF-β blockade, and CXCL12/CXCR4 axis inhibition demonstrating positive outcomes in preclinical models. The combination of CAF-targeted therapies with immunotherapies or chemotherapy has shown additional potential to reverse this CAF-induced resistance. Autophagy regulation in CAFs can be therapeutic opportunities for novel Interevent strategies.

Sorafenib-Drug Delivery Strategies in Primary Liver Cancer

Current primary liver cancer therapies, including sorafenib and transarterial chemoembolization, face significant limitations due to chemoresistance caused by impaired drug uptake, altered metabolism, and other genetic modulations. These challenges contribute to relapse rates of 50-80% within five years. The need for improved treatment strategies (adjuvant therapy, unsatisfactory enhanced permeability and retention (EPR) effect) has driven research into advanced drug delivery systems, including targeted nanoparticles, biomaterials, and combinatory approaches. Therefore, this review evaluates recent advancements in primary liver cancer pharmacotherapy, focusing on the potential of drug delivery systems for sorafenib and its derivatives. Approaches such as leveraging Kupffer cells for tumor migration or utilizing smaller NPs for inter-/intracellular delivery, address EPR limitations. Biomaterials and targeted therapies focusing on targeting have demonstrated effectiveness in increasing tumor-specific delivery, but clinical evidence remains limited. Combination therapies have emerged as an interesting solution to overcoming chemoresistance or to broadening therapeutic functionality. Biomimetic delivery systems, employing blood cells or exosomes, provide methods for targeting tumors, preventing metastasis, and strengthening immune responses. However, significant differences between preclinical models and human physiology remain a barrier to translating these findings into clinical success. Future research must focus on the development of adjuvant therapy and refining drug delivery systems to overcome the limitations of tumor heterogeneity and low drug accumulation.

Dual targeting of CXCR4 and EZH2 in endometriosis

We recently showed that endometriotic peritoneal fluid (PF) altered the regulation of enhancer of zeste homolog 2 (EZH2) and H3K27me3. This study aimed to determine if PF by regulating EZH2/H3K27me3 modulated C-X-C chemokine receptor type 4 (CXCR4), a major chemokine involved in the proliferation and migration processes in endometriosis. Endometriotic PF induced the mRNA expression of CXCR4 and EZH2 and protein expression of H3K27me3 in human endometrial stromal cells (hESCs) and eutopic endometrium (Eu). CXCR4 inhibitor, AMD3100, decreased the PF-induced expression of these factors and reduced migration, but increased the proliferation of hESCs. In contrast, the EZH2 inhibitor, GSK126, decreased the expression of EZH2 and H3K27me3 and reduced proliferation, but increased the expression of CXCR4 and migration of hESCs. A combination of both inhibitors decreased the expression of CXCR4, EZH2, and H3K27me3, as well as reduced cell proliferation and migration. Our study suggests that targeting both CXCR4 (inflammation) and EZH2 (epigenetics) may be a better alternative for women with endometriosis.

Identification and catalog of viral transcriptional regulators in human diseases

Viral genomes encode viral transcriptional regulators (vTRs) that manipulate host gene expression to facilitate replication and evade immune detection. Nevertheless, their role in non-cancerous diseases remains largely underexplored. Here, we unveiled 268 new candidate vTRs from 14 of the 20 viral families we investigated. We mapped vTRs' genome-wide binding profiles and identified their potential human targets, which were enriched in immune-mediated pathways, neurodegenerative disorders, and cancers. Through vTR DNA-binding preference analysis, 283 virus-specific and human-like motifs were identified. Prioritized Epstein-Barr virus (EBV) vTR target genes were associated with multiple sclerosis (MS), rheumatoid arthritis, and systemic lupus erythematosus. The partitioned heritability study among 19 diseases indicated significant enrichment of these diseases in EBV vTR-binding sites, implicating EBV vTRs' roles in immune-mediated disorders. Finally, drug repurposing analysis pinpointed candidate drugs for MS, asthma, and Alzheimer disease. This study enhances our understanding of vTRs in diverse human diseases and identifies potential therapeutic targets for future investigation.

Structural insights into CXCR4 modulation and oligomerization

Activation of the chemokine receptor CXCR4 by its chemokine ligand CXCL12 regulates diverse cellular processes. Previously reported crystal structures of CXCR4 revealed the architecture of an inactive, homodimeric receptor. However, many structural aspects of CXCR4 remain poorly understood. Here, we use cryo-electron microscopy to investigate various modes of human CXCR4 regulation. CXCL12 activates CXCR4 by inserting its N terminus deep into the CXCR4 orthosteric pocket. The binding of US Food and Drug Administration-approved antagonist AMD3100 is stabilized by electrostatic interactions with acidic residues in the seven-transmembrane-helix bundle. A potent antibody blocker, REGN7663, binds across the extracellular face of CXCR4 and inserts its complementarity-determining region H3 loop into the orthosteric pocket. Trimeric and tetrameric structures of CXCR4 reveal modes of G-protein-coupled receptor oligomerization. We show that CXCR4 adopts distinct subunit conformations in trimeric and tetrameric assemblies, highlighting how oligomerization could allosterically regulate chemokine receptor function.

Repeated CXCR4 Blockade by Plerixafor Attenuates Transplant Vasculopathy in Murine Aortic Allografts

Plerixafor, a hematopoietic stem cell mobilization agent, increases the peripheral blood content of effector and regulatory T cells and may have beneficial effects on cardiac allograft vasculopathy. The aim of the current study was to evaluate its effects in a murine aortic allograft model using different application procedures. Allogeneic donor aorta grafts (n = 8/group) from C57BL/6 mice(H2b) were abdominally transplanted into CBA mice (H2k). Plerixafor application was performed either continuously for 14 d using abdominally implanted osmotic pumps (1 mg/kg/d) or i.p. with a single dose (1 and 5 mg/kg) on day 0 or pulsed injections of 1 mg/kg on days 0, 7, 14, and 21. Cell distribution was monitored by FACS. Aortic grafts were evaluated for neointima development by Elastica-van-Gieson on day 30. Immunofluorescence and intragraft gene expression analysis were performed. On day 14, significantly fewer hematopoietic stem cells were found in the bone marrow of all plerixafor-treated mice. In the pulsed application group, significantly more hematopoietic stem cells were found in the peripheral blood on day 14 (0.045 ± 0.002%; p < 0.01 [pulsed]; versus 0.0068 ± 0.002% [control]) and also more regulatory T cells. PCR revealed lower inflammatory cytokines. The luminal occlusion was significantly reduced in the pulsed treated group (33.65 ± 8.84 versus 53.13 ± 12.41) going along with decreased neointimal CD4+ T cell and plasmacytoid dendritic cell infiltration, as well as less smooth muscle cell proliferation. The application of plerixafor attenuates chronic rejection in aortic allografts via immunomodulatory effects. Injection of repeated low-dose plerixafor is the most effective application form in the aortic transplant model.

Targeting immune cell recruitment in atherosclerosis

Atherosclerosis is the primary underlying cause of myocardial infarction and stroke. Atherosclerotic cardiovascular disease is characterized by a chronic inflammatory reaction in medium-to-large-sized arteries, with its onset and perpetuation driven by leukocytes infiltrating the subendothelial space. Activation of endothelial cells triggered by hyperlipidaemia and lipoprotein retention in the arterial intima initiates the accumulation of pro-inflammatory leukocytes in the arterial wall, fostering the progression of atherosclerosis. This inflammatory response is coordinated by an array of soluble mediators, namely cytokines and chemokines, that amplify inflammation both locally and systemically and are complemented by tissue-specific molecules that regulate the homing, adhesion and transmigration of leukocytes. Despite abundant evidence from mouse models, only a few therapies targeting leukocytes in atherosclerosis have been assessed in humans. The major challenges for the clinical translation of these therapies include the lack of tissue specificity and insufficient selectivity of inhibition strategies. In this Review, we discuss the latest research on receptor-ligand pairs and interactors that regulate leukocyte influx into the inflamed artery wall, primarily focusing on studies that used pharmacological interventions. We also discuss mechanisms that promote the resolution of inflammation and highlight how major findings from these research areas hold promise as potential therapeutic strategies for atherosclerotic cardiovascular disease.

IS4-FAM, a fluorescent tool to study CXCR4 affinity and competitive antagonism in native cancer cells

The ability to accurately measure drug-target interaction is critical for the discovery of new therapeutics. Classical pharmacological bioassays such as radioligand or fluorescent ligand binding assays can define the affinity or Kd of a ligand for a receptor with the lower the Kd, the stronger the binding and the higher the affinity. However, in many drug discovery laboratories today, the target of interest if often artificially upregulated by means of transfection to modify the host cell's genetic makeup. This then potentially invalidates the assumptions of classical pharmacology affinity calculations as the receptor of interest is no longer at normal physiological densities. The CXCR4 receptor is expressed on many different cancer cell types and is associated with metastasis and poor prognosis. Therefore, the CXCR4 receptor is a desirable target for novel therapeutics. In this study, we explore the applicability of the newly developed fluorescently tagged CXCR4 antagonists, IS4-FAM as an investigative tool to study CXCR4 affinity and competitive antagonism in native, non-transfected cancer cells using confocal microscopy and flow cytometry. IS4-FAM directly labels CXCR4 in several cell lines including high CXCR4 expressing SK-MEL-28 (malignant melanoma) and PC3 (metastatic prostate cancer) and lower CXCR4 expressing THP-1 (acute monocytic leukemia) and was competitive with the established CXCR4 antagonist, AMD3100. This highlights the potential of IS4-FAM as a pharmacological tool for drug discovery in native cells lines and tissues.

Novel Anti-Enterovirus A71 Compounds Discovered by Repositioning Antivirals from the Open-Source MMV Pandemic Response Box

The open-source drug library, namely, MMV Pandemic Response Box, contains 153 antiviral agents, a chemically and pharmacologically diverse mixture of early-stage, emerging anti-infective scaffolds, and mature compounds currently undergoing clinical development. Hence, the Pandemic Response Box might contain compounds that bind and interfere with target molecules or cellular pathways that are conserved or shared among the closely related viruses with enterovirus A71 (EV-A71). This study aimed to screen antiviral agents included in the Pandemic Response Box for repurposing to anti-EV-A71 activity and investigate the inhibitory effects of the compounds on viral replication. The compounds' cytotoxicity and ability to rescue infected cells were determined by % cell survival using an SRB assay. The hit compounds were verified for anti-EV-A71 activity by virus reduction assays for viral RNA copy numbers, viral protein synthesis, and mature particle production using qRT-PCR, Western blot analysis, and CCID50 assay, respectively. It was found that some of the hit compounds could reduce EV-A71 genome replication and protein synthesis. D-D7 (2-pyridone-containing human rhinovirus 3C protease inhibitor) exhibited the highest anti-EV-A71 activity. Even though D-D7 has been originally indicated as a polyprotein processing inhibitor of human rhinovirus 3C protease, it could be repurposed as an anti-EV-A71 agent.

CXCR4: from B-cell development to B cell-mediated diseases

Chemokine receptors are members of the G protein-coupled receptor superfamily. The C-X-C chemokine receptor type 4 (CXCR4), one of the most studied chemokine receptors, is widely expressed in hematopoietic and immune cell populations. It is involved in leukocyte trafficking in lymphoid organs and inflammatory sites through its interaction with its natural ligand CXCL12. CXCR4 assumes a pivotal role in B-cell development, ranging from early progenitors to the differentiation of antibody-secreting cells. This review emphasizes the significance of CXCR4 across the various stages of B-cell development, including central tolerance, and delves into the association between CXCR4 and B cell-mediated disorders, from immunodeficiencies such as WHIM (warts, hypogammaglobulinemia, infections, and myelokathexis) syndrome to autoimmune diseases such as systemic lupus erythematosus. The potential of CXCR4 as a therapeutic target is discussed, especially through the identification of novel molecules capable of modulating specific pockets of the CXCR4 molecule. These insights provide a basis for innovative therapeutic approaches in the field.

Lipidation of a bioactive cyclotide-based CXCR4 antagonist greatly improves its pharmacokinetic profile in vivo

The CXCR4 chemokine is a key molecular regulator of many biological functions controlling leukocyte functions during inflammation and immunity, and during embryonic development. Overexpression of CXCR4 is also associated with many types of cancer where its activation promotes angiogenesis, tumor growth/survival, and metastasis. In addition, CXCR4 is involved in HIV replication, working as a co-receptor for viral entry, making CXCR4 a very attractive target for developing novel therapeutic agents. Here we report the pharmacokinetic profile in rats of a potent CXCR4 antagonist cyclotide, MCo-CVX-5c, previously developed in our group that displayed a remarkable in vivo resistance to biological degradation in serum. This bioactive cyclotide, however, was rapidly eliminated through renal clearance. Several lipidated versions of cyclotide MCo-CVX-5c showed a significant increase in the half-life when compared to the unlipidated form. The palmitoylated version of cyclotide MCo-CVX-5c displayed similar CXCR4 antagonistic activity as the unlipidated cyclotide, while the cyclotide modified with octadecanedioic (18-oxo-octadecanoic) acid exhibited a remarkable decrease in its ability to antagonize CXCR4. Similar results were also obtained when tested for its ability to inhibit growth in two cancer cell lines and HIV infection in cells. These results show that the half-life of cyclotides can be improved by lipidation although it can also affect their biological activity depending on the lipid employed.

Toll-like Receptor Response to Human Immunodeficiency Virus Type 1 or Co-Infection with Hepatitis B or C Virus: An Overview

Toll-like receptors (TLRs) are evolutionarily conserved pattern recognition receptors that play important roles in the early detection of pathogen-associated molecular patterns and shaping innate and adaptive immune responses, which may influence the consequences of infection. Similarly to other viral infections, human immunodeficiency virus type 1 (HIV-1) also modulates the host TLR response; therefore, a proper understanding of the response induced by human HIV-1 or co-infection with hepatitis B virus (HBV) or hepatitis C virus (HCV), due to the common mode of transmission of these viruses, is essential for understanding HIV-1 pathogenesis during mono- or co-infection with HBV or HCV, as well as for HIV-1 cure strategies. In this review, we discuss the host TLR response during HIV-1 infection and the innate immune evasion mechanisms adopted by HIV-1 for infection establishment. We also examine changes in the host TLR response during HIV-1 co-infection with HBV or HCV; however, this type of study is extremely scarce. Moreover, we discuss studies investigating TLR agonists as latency-reverting agents and immune stimulators towards new strategies for curing HIV. This understanding will help develop a new strategy for curing HIV-1 mono-infection or co-infection with HBV or HCV.

Discovery of Bis-Imidazoline Derivatives as New CXCR4 Ligands

The chemokine receptor CXCR4 and its ligand CXCL12 regulate leukocyte trafficking, homeostasis and functions and are potential therapeutic targets in many diseases such as HIV-1 infection and cancers. Here, we identified new CXCR4 ligands in the CERMN chemical library using a FRET-based high-throughput screening assay. These are bis-imidazoline compounds comprising two imidazole rings linked by an alkyl chain. The molecules displace CXCL12 binding with submicromolar potencies, similarly to AMD3100, the only marketed CXCR4 ligand. They also inhibit anti-CXCR4 mAb 12G5 binding, CXCL12-mediated chemotaxis and HIV-1 infection. Further studies with newly synthesized derivatives pointed out to a role of alkyl chain length on the bis-imidazoline properties, with molecules with an even number of carbons equal to 8, 10 or 12 being the most potent. Interestingly, these differ in the functions of CXCR4 that they influence. Site-directed mutagenesis and molecular docking predict that the alkyl chain folds in such a way that the two imidazole groups become lodged in the transmembrane binding cavity of CXCR4. Results also suggest that the alkyl chain length influences how the imidazole rings positions in the cavity. These results may provide a basis for the design of new CXCR4 antagonists targeting specific functions of the receptor.